Meteorology PDF - Clouds, Air Masses, and Pressure

Meteorology Loreta Lope Apaya 44  Table of Contents Module 4: Clouds Introduction 47 Learning Objectives 47 Lesson 1. What are Clouds 48 Lesson 1.1 Types of Clouds...

Meteorology Loreta Lope Apaya 44  Table of Contents Module 4: Clouds Introduction 47 Learning Objectives 47 Lesson 1. What are Clouds 48 Lesson 1.1 Types of Clouds 49 Lesson 1.2 Characteristics of Clouds 50 Lesson 1.3 Cloud Formation 53 Lesson 2. Weather and Clouds 54 Lesson 2.1 The Water Cycle 57 Lesson 3. Precipitation 60 Lesson 3.1 Types of Precipitation 61 Assessment Task 63 Summary 65 References 66 Module 5: AIR MASSES AND DISTURBANCES Introduction 68 Learning Objectives 68 Lesson 1. What are Air Masses? 69 Lesson 1.1 Characteristics of Air Masses 70 Lesson 1.2 Air Mass Classification 71 Lesson 1.3 Weather Fronts 72 Lesson 1.4 Fronts Formation and Effect 74 Lesson 2. Weather Disturbances 78 Lesson 2.1: What are Typhoons 78 Lesson 2.2: Cyclone Classification 80 Lesson 2.3: Formation of Cyclones 83 Assessment Task 85 Summary 86 References 86 Module 6: Air Pressure 88 Introduction 88 Learning Objectives Lesson 1. Atmospheric Pressure 89 45 Lesson 1.1 Measurement of Atmospheric Pressure 93 Lesson 2. Air Pressure and Height Elevation 94 Lesson 2.1 Types of Air Pressure 95 Lesson 2.2 Atmospheric Temperature and Density 97 Lesson 2.3 Air Pressure and Density 98 Lesson 2.4. Pressure-Temperature-Density Relationship 98 Lesson 3. Air Pressure Maps 100 Lesson 3.1 Weather Maps 101 Lesson 3.2 The Isobars 102 Lesson 3.3 Applications of Pressure 106 Lesson 4. Sample Problems and Solutions 108 Assessment Task 110 Summary 111 References 112 Module 7: Weather Forecasting and Control Introduction 113 Learning Objectives 113 Lesson 1. Weather Forecasting 114 Lesson 1.1 Tools in Weather Forecasting 114 Lesson 1.2 Where the forecasts are sent? 119 Lesson 1.3 Types of Weather Forecasting 120 Lesson 1.4 Forecasting Methods 121 Lesson 2 Weather Terms Used in PAGASA 122 Lesson 3 How do forecasters work? 124 Lesson 3.1 Forecasting Methods 124 Lesson 3.2 Forecasting Techniques 125 Lesson 3.3 Forecasting Rules 126 Lesson 4: Measuring Moisture in the Atmosphere 128 Assessment Task 131 Summary 132 References 133 46  MODULE 4 CLOUDS Introduction A cloud is a large collection of very tiny droplets of water or ice crystals. The droplets are so small and light that they can float in the air. All air contains water, but near the ground it is usually in the form of an invisible gas called water vapor. When warm air rises, it expands and cools. Cool air can't hold as much water vapor as warm air, so some of the vapor condenses onto tiny pieces of dust that are floating in the air and forms a tiny droplet around each dust particle. When billions of these droplets come together they become a visible cloud (Weather Wiz Kids, 2015). This module focuses on different types and characteristics of clouds. Learning Outcomes At the end of the lesson, the students will be able to: 1. Analyze how clouds are formed; 2. Distinguish different processes involved in Water cycle that contribute in the formation of precipitations; 3. Compare and contrasts the three basic types of cloud; and 4. Distinguish one type of cloud as to their characteristics and altitude. 46 Lesson 1: What are Clouds? Figure 4.1 Clouds Source: Earth Science for Kids (2020) Interesting Facts about Clouds: (TSI, 2020) A cloud that forms on the ground is called fog. Some clouds you see in the sky might be from airplanes. These are called contrails. High level cirrus clouds may travel at speeds up to 100 mph. Even though clouds float in the air, a single cumulus cloud can weigh hundreds of tons. Other planets with atmospheres have clouds including Venus, Jupiter, and Saturn. 48 Lesson 1.1: Types of Clouds (Earth Science for Kids, 2020) Figure 4.2 Types of Clouds Source: Earth Science for Kids (2020) 1. Cirrus - Cirrus clouds are high level clouds that are thin and wispy. They appear during good weather. 2. Cirrocumulus - These are high clouds that look like tiny cotton balls bunched together. 3. Cirrostratus - High, flat clouds that might cover the sky making it appear overcast. These clouds signal that it may rain in the next day or so. 4. Altostratus - Medium level clouds that form a dark gray covering. Usually they are a sign of rain. 5. Altocumulus - Middle level clouds that are small, white, and puffy. 6. Nimbostratus - These are thick, dark gray middle level to low level clouds. They usually bring rain or snow. 49  7. Stratus - Stratus clouds are low level clouds that are flat and tend to cover much of the sky. They are gray in color and may produce light rain or drizzle. 8. Stratocumulus - These are low, puffy, and gray clouds. They may produce a little rain and can turn into nimbostratus clouds. 9. Cumulus - Cumulus clouds are low to mid-level clouds. They are big, white, puffy, and beautiful clouds. They usually mean good weather unless they grow really tall and turn into cumulonimbus clouds. 10. Cumulonimbus - Cumulonimbus clouds are very tall clouds that span all the way from low level to high level. They can cause violent thunderstorms with heavy rain, hail, and even tornadoes. Lesson 1.2. Characteristics of Clouds (Funk, n.d.) Clouds are classified according to their height above and appearance (texture) from the ground. The following cloud roots and translations summarize the components of this classification system: 1) Cirro-: curl of hair, high; 2) Alto-: mid; 3) Strato-: layer; 4) Nimbo-: rain, precipitation; and 5) Cumulo-: heap. High-level clouds High-level clouds occur above about 20,000 feet and are given the prefix “cirro.” Due to cold tropospheric temperatures at these levels, the clouds primarily are composed of ice crystals, and often appear thin, streaky, and white (although a low sun angle, e.g., near sunset, can create an array of color on the clouds). The three main types of high clouds are cirrus, cirrostratus, and cirrocumulus (Funk, n.d.). 50 Mid-level clouds The bases of clouds in the middle level of the troposphere, given the prefix “alto,” appear between 6,500 and 20,000 feet. Depending on the altitude, time of year, and vertical temperature structure of the troposphere, these clouds may be composed of liquid water droplets, ice crystals, or a combination of the two, including supercooled droplets (i.e., liquid droplets whose temperatures are below freezing). The two main type of mid-level clouds are altostratus and altocumulus. (Funk, n.d.). Low-level clouds: Low-level clouds are not given a prefix, although their names are derived from “strato” or “cumulo,” depending on their characteristics. Low clouds occur below 6500 feet, and normally consist of liquid water droplets or even supercooled droplets, except during cold winter storms when ice crystals (and snow) comprise much of the clouds (Funk, n.d.). Table 4.1 Cloud Chart (Weather Wiz Kids, 2015) 51 Figure 4.3 Stratocumulus Clouds Source: Kirkham (2009) Figure 4.4 Altocumulus Clouds Source: Kirkham (2009) 52 Lesson 1.3: Cloud Formation (Pidwirny & Jones, 2009) Condensation or deposition of water above the Earth's surface creates clouds. In general, clouds develop in any air mass that becomes saturated (relative humidity becomes 100%). Saturation can occur by way of atmospheric mechanisms that cause the temperature of an air mass to be cooled to its dew point or frost point (Pidwirny & Jones, 2009). The following mechanisms or processes can achieve this outcome causing clouds to develop: 1. Orographic uplift occurs when air is forced to rise because of the physical presence of elevated land. As the parcel rises it cools as a result of adiabatic expansion at a rate of approximately 10° Celsius per 1000 meters until saturation. a. The development of clouds and resulting heavy quantities of precipitation along the west coast of Canada are mainly due to this process. 2. Convectional lifting is associated with surface heating of the air at the ground surface. If enough heating occurs, the mass of air becomes warmer and lighter than the air in the surrounding environment, and just like a hot air balloon it begins to rise, expand, and cool. When sufficient cooling has taken place, saturation occurs forming clouds. This process is active in the interior of continents and near the equator forming cumulus clouds and or cumulonimbus clouds (thunderstorms). a. The rain that is associated with the development of thunderstorm clouds is delivered in large amounts over short periods of time in extremely localized areas. 3. Convergence or frontal lifting takes place when two masses of air come together. In most cases, the two air masses have different temperature and moisture characteristics. One of the air masses is usually warm and moist, while the other is cold and dry. The leading edge of the latter air mass acts as an inclined wall or front causing the moist warm air to be lifted. Of course, the lifting causes the warm moist air mass to cool due to expansion resulting in saturation (Pidwirny & Jones, 2009). a. This cloud formation mechanism is common at the mid-latitudes where cyclones form along the polar front and near the equator where the trade winds meet at the intertropical convergence zone. 53  4. Radiative cooling occurs when the Sun is no longer supplying the ground and overlying air with energy derived from solar insolation (e.g., night). Instead, the surface of the Earth now begins to lose energy in the form of longwave radiation which causes the ground and air above it to cool (Pidwirny & Jones, 2009). a. The clouds that result from this type of cooling take the form of surface fog. Lesson 2: Weather and Clouds (Pidwirny & Jones, 2009) 1. Cirrus clouds are usually white and predict fair to pleasant weather. By watching the movement of cirrus clouds, you can tell from which direction weather is approaching. When you see cirrus clouds, it usually indicates that a change in the weather will occur within 24 hours (Pidwirny & Jones, 2009). Figure 4.5 Cirrus Clouds Source: Kirkham (2009) 2. Cirrostratus clouds are thin, sheet like high clouds that often cover the entire sky. They are so thin that the sun and moon can be seen through them. Cirrostratus clouds usually come 12-24 hours before a rain or snow storm 3. Cirrocumulus clouds appear as small, rounded white puffs that appear in long rows. The small ripples in the cirrocumulus clouds sometime resemble the scales of a fish. 54  Cirrocumulus clouds are usually seen in the winter and indicate fair, but cold weather. In tropical regions, they may indicate an approaching hurricane 4. Altostratus clouds are gray or blue-gray mid-level clouds composed of ice crystals and water droplets. The clouds usually cover the entire sky. In the thinner areas of the clouds, the sun may be dimly visible as a round disk. Altostratus clouds often form ahead of storms with continuous rain or snow. 5. Altocumulus clouds are mid-level clouds that are made of water droplets and appear as gray puffy masses. They usually form in groups. If you see altocumulus clouds on a warm, sticky morning, be prepared to see thunderstorms late in the afternoon. 6. Stratus clouds are uniform grayish clouds that often cover the entire sky. They resemble fog that doesn't reach the ground. Light mist or drizzle sometimes falls out of these clouds. 7. Stratocumulus clouds are low, puffy and gray. Most form in rows with blue sky visible in between them. Rain rarely occurs with stratocumulus clouds, however, they can turn into nimbostratus clouds. 8. Nimbostratus clouds form a dark gray, wet looking cloudy layer associated with continuously falling rain or snow. They often produce precipitation that is usually light to moderate. 9. Cumulonimbus clouds are thunderstorm clouds. High winds can flatten the top of the cloud into an anvil-like shape. Cumulonimbus clouds are associated with heavy rain, snow, hail, lightning and even tornadoes. The anvil usually points in the direction the storm is moving. 10. Cumulus clouds are white, puffy clouds that look like pieces of floating cotton. Cumulus clouds are often called "fair-weather clouds". The base of each cloud is flat and the top of each cloud has rounded towers. When the top of the cumulus clouds resemble the head of a cauliflower, it is called cumulus congestus or towering cumulus. These clouds grow upward and they can develop into giant cumulonimbus clouds, which are thunderstorm clouds. 55  Figure 4.6 Cumulus Clouds Source: Kirkham (2009) Figure 4.7 Cumulonimbus Clouds Source: Kirkham (2009) 56 Lesson 2.1: The Water Cycle Hydrologic cycle is also called Water. It deals with the origin and distribution of water on the globe. It is a complex pathways that include passage of water from gaseous stage in the atmosphere to oceans, lakes, rivers etc. (Palit, 2014). Hydrological cycle includes the following processes: Evaporation Condensation Precipitation Interception Infiltration Percolation Transportation Runoff Storage Figure 4.8 The Water Cycle Source: Bytes (2008-2020) 57  Figure 4.9 The Hydrologic Cycle Source: Palit (2014) Evaporation: (Bytes, n.d.) Evaporation is the technique of a liquid’s surface changing to a gas. In the water cycle, liquid water (in the ocean, lakes or streams) disperses and becomes water vapor. Water vapour includes us, as a noteworthy bit of the air we expend. Water rage is moreover noteworthy ozone hurting substance. Ozone exhausting substances, for instance, water smoke and carbon dioxide, secure the Earth and keep the planet adequately warm to keep up life as we are likely mindful of it. The water cycle’s dissipation method is driven by the sun. As the sun interfaces with liquid water outwardly of the ocean, the water transforms into an imperceptible gas (water seethe). Dissipation is moreover influenced by wind, temperature and the thickness of the waterway. 58  Figure 4.10 Evaporation in Water Cycle Source: Bytes,(n.d.) Water Cycle Condensation Condensation is the methodology of a gas changing to a liquid. In the water cycle, water seethe in nature accumulates and gets liquid (Bytes, n.d.). Condensation can happen high in the climate or at ground level. Fogs structure as water rage consolidates or ends up being progressively centered (thick). Water seethe around little particles called cloud condensation cores (CCN). CCN can be spots of buildup, salt or toxic substances. Fogs at ground level are called dimness or mist (Bytes, n.d.). Like dissipation, condensation is similarly influenced by the sun. As water seethe cools, it lands at its drenching most extreme or dew point. Pneumatic power is similarly a critical effect on the dew motivation behind a region (Bytes, n.d.). 59  Figure 4.11 Condensation in Water Cycle Source: Bytes (n.d.) Lesson 3 Precipitation Figure 4.12 Precipitation in Water Cycle Source: Bytes (n.d.) 60  As opposed to dissipation and buildup, precipitation is not a methodology. Precipitation depicts any liquid or solid water that tumbles to Earth in light of buildup noticeable all around. Precipitation consolidates storm, a day away from work hail (Bytes, n.d.). Fog is not precipitation. The water in the fog does not accumulate sufficiently to quicken, or consolidate, and tumble to Earth. Fog and haze are a bit of the water cycle called environment: they are liquid water suspended noticeable all around. Precipitation is one of the various ways water is cycled from nature to the Earth or ocean (Bytes, n.d.). Lesson 3.1: Types of Precipitation (Ali, 2011) Figure 4.13 Forms of Precipitation Source: Ali, (2011) 61  Ali, (2011) stated that In meteorology, the various types of precipitation often include the character or phase of the precipitation which is falling to ground level. Precipitation falls in many forms, or phases. They can be subdivided into: 1. Liquid precipitation: a. Drizzle b. Rain c. Cloudburst 2. Freezing precipitation: a. Freezing drizzle b. Freezing rain c. Rain and snow mixed / Slush d. Drizzle and snow mixed / Slush 3. Frozen precipitation: a. Snow b. Snow grains c. Ice crystals d. Ice pellets / Sleet e. Snow pellets / Graupel f. Hail g. Megacryometeor Please watch this YouTube video: The Water Cycle o https://www.youtube.com/watch?v=al-do-HGuIk 62 Assessment Task 4-1 A. Fill-in the blank with correct word/s. 1. – condensation of water vapor onto the ground or objects on the ground 2. – deposition of water vapor onto the ground or objects on the ground 3. – condensation that freezes 4. – condensation of water vapor onto airborne aerosols, forming a cloud in contact with the ground 5. – condensation of water vapor onto airborne aerosols aloft 6. are high, thin, wispy, and feathery. Cirrus means curl or wisp of hair. 7. are large, rounded, fluffy, cottony- looking clouds. Cumulus means heap or pile. 8. are low, flat sheets of clouds that look like one huge cloud covering the whole sky. 9. (cumulus, stratus, stratocumulus) that lie below 6,500 feet (1,981 m) 10. (altocumulus, nimbostratus, altostratus) that form between 6,500 and 20,000 feet (1981–6,096 m) 11. (cirrus, cirrocumulus, cirrostratus) that form above 20,000 feet (6,096 m) 12. The word means rain. 63  Assessment Task 4-2 B. Hydrologic Processes: 1. – The transition of liquid molecules into the gaseous phase (water in a bowl disappears) 2. – The transition of gaseous molecules into the liquid phase (beads of water on a cold pipe) 3. – The transition of solid molecules into the gaseous phase (an ice museum vanishes) 4. – The transition of gaseous molecules into the solid phase (frost on a cold morning) 5. – air that contains as much water vapor as possible (at a given temperature) such that additional water vapor would result in condensation 6. – air that contains less water vapor (at a given temperature) than possible 7. – air that contains more water vapor than possible (at a given temperature) 8. – The portion of total pressure exerted by water vapor 64  Summary Clouds are created when water vapor, an invisible gas, turns into liquid water droplets. These water droplets form on tiny particles, like dust, that are floating in the air. You hang up a wet towel and, when you come back, it's dry Clouds form when moist, warm rising air cools and expands in the atmosphere. he water vapor in the air condenses to form tiny water droplets which are the basis of cloud. Clouds are made up of droplets of liquid water or particles of ice that are so tiny that they remain floating in air. While it's true that clouds contain water, they actually aren't made of water vapor. If they were, you wouldn't be able to see them. The water that makes up clouds is in liquid or ice form. The air around us is partially made up of invisible water vapor. Three types of clouds Clouds form in three basic patterns: Cirrus, from cirro, meaning curly or fibrous. Stratus, from strato, suggesting sheets or layers. Cumulus, from cumulo, indicating heaped or piled (Weather Wiz Kids, 2015). 65  References Ali, H. (2011, Dec.23) Precipitation presentation. https://www.slideshare.net/hamza07/precipitation-presentation Bytes, C. (n.d.).Geography Revision - Water Cycle.https://geography-revision.co.uk/a- level/physical/water-cycle/ Earth Science. (n.d). University of Mysore, Mysore.https://www.slideshare.net/bala1957/elements-of-climate-and-weather Jdlowe78.(18 November 2013).Cloud Formation.https://www.slideshare.net/jdlowe78/cloud- formation-28383426 Kirkham, S. (13 September 2009).Atmospheric Moisture ppt.https://www.slideshare.net/wskirkham/atmospheric-moisture Lopes, C. C., Cantero, C. N.T., Pulido, M.J.N., & Flores, R. G. (2017), Earth Science For Senior High (Core Subject K to 12 based, LORIMAR Publishing, Cubao, Quezon City, Metro Manila Palit, N. (27 April 2014). Hydrologic Cycle ppt.https://www.slideshare.net/nandapalit/hydrologic- cycle-33994221 Pidwirny, M. & Jones, S. (2009).PhysicalGeography.net. http://www.physicalgeography.net/fundamentals/8e.html Rabago ,L. M. , Flores, A. C., Mingoa, T.R., Ferrer, D.L., Obille Jr., E. C. & Cano, M. C. (2007). Dynamic Science: An Integration of Physical and Biological Science Modular Approach. Vibal Publishing House, Inc., Metro Manila, Cebu, Davao Randolf, Keila. (5 November 2014). Cloud Classification and Characteristics ppt. https://www.slideshare.net/ Salandanan , G.G., Faltado III, R.E. & Lopez, M.B. (2016), Earth and Life Sciences For Senior High Sch ool(Core Subject).LORIMAR Publishing, Cubao, Quezon City, Metro Manila TSI (Technological Solutions, Inc.). (2020). Earth Science for Kids.https://www.ducksters.com/science/earth_science/clouds.php Ted Funk. (n.d).The Science Corner. https://www.weather.gov/media/lmk/soo/cloudchart.pdf 66 Weather Wiz Kids.(2015).Clouds.https://www.weatherwizkids.com/weather-clouds.htm Wingate, V.M. (n.d). Clouds https://www.slideshare.net/casaue2/cloud-types-presentation 67  MODULE 5 AIR MASSES AND DISTURBANCES Introduction An air mass is a large volume of air in the atmosphere that is mostly uniform in temperature and moisture. Air masses can extend thousands of kilometers in any direction, and can reach from ground level to the stratosphere—16 kilometers (10 miles) into the atmosphere. Meteorologists identify air masses according to where they form over the Earth. There are four categories for air masses: arctic, tropical, polar and equatorial. Arctic air masses form in the Arctic region and are very cold. Tropical air masses form in low-latitude areas and are moderately warm. Polar air masses take shape in high-latitude regions and are cold. Equatorial air masses develop near the Equator and are warm (Rutledge, Ramroop, Boudreau, McDaniel, Teng, Sprout, Hall, & Hunt, 2011). Learning Outcomes At the end of the lesson, the students will be able to: 1. Define an air mass and fronts; 2. Determine an air mass using air mass classification system; 3. Distinguish each of the four basic types of air masses; and 4. Differentiate each of the types of fronts classified according to their temperatures. 68 Lesson 1: What are Air Masses? Air masses are relatively large bodies of air that are horizontally uniform in characteristics. They may extend across an entire continent and are relatively uniform in temperature and moisture content. The boundary separating two different air masses is called a front, and it is along these fronts that a substantial amount of our weather occurs (OK-FIRST Project, Oklahoma Climatological Survey,1996-2004). Air masses are weather patterns resulting from movements of large bodies of air called air masses. It is a huge body of air that has similar temperatures and amounts of moisture at any given altitude. Due to its size, it may take several days for an air mass to move an area. This causes us to experience fairly constant weather, often called air-mass weather. When an air mass moves out of a region carries temperature and moisture conditions with it. As it moves ,the characteristics of an airmass change and so does the weather in the area over which the air mass moves (Eudalddiaz, 2013). Figure 5.1 Air Mass Source: Oklahoma Climatological Survey (1996-2004) 69 Lesson 1.1: Characteristics of Air Masses (Sherwood, 2019) Type 1: The Coldest of All Air masses at the Polar Regions form between 60 degrees latitude and the North or South Pole. Northern Canada and Siberia are common sources of these cold, dry masses, although they can also form over water. Because they are extremely dry, polar masses have few clouds. Meteorologists use a capital P to refer to these masses. Some resources differentiate between polar air masses and extremely cold ones that form very close to the poles. Arctic masses are abbreviated with an “A,” while Antarctic masses use “AA.” Type 2: Warming Up Tropical air masses form within 25 degrees latitude of the equator. This means that the temperature will be warm or even hot. These masses, abbreviated with a “T,” can develop over land or water. Source regions include the Gulf of Mexico, southwestern United States and northern Mexico. As the air from these air masses moves over the land of the US, they will rapidly cool and usually result in precipitation and storms. Type 3: Land Ho! Continental air masses develop between 25- and 60-degrees latitude, either north or south of the equator. As indicated by their name, they form over large land areas, so they're dry. Since meteorologists consider this a secondary classification, it’s represented by a lower case “c.” When describing an air mass, meteorologists indicate both the humidity and temperature, in that order. For example, an air mass that originates over northern land is labeled “cP” for continental and polar regions. This air is dry and cold. A very dry and hot air mass that forms around the U.S. and Mexican border is labeled “cT” -- continental and tropical. This usually does not include air masses that form over mountainous regions. 70 Type 4: Water, Water Everywhere (Sherwood, 2019) Air masses with high humidity form over oceans. This “maritime” classification corresponds to the same latitudes as continental masses. It is also considered a secondary category and is abbreviated “m.” Therefore, a humid, cold mass that develops over polar oceans is categorized as “mP.” This type of air mass impacts the U.S. west coast in winter. Humid and warm air masses often come from the Gulf of Mexico and southern Atlantic Ocean and are labeled “mT.” These have a strong effect on weather in the American southwest (Sherwood, 2019). Lesson 1.2: Air Mass Classification (Sherwood, 2019) c - continental (land) m - maritime (water) P - polar (cold) A - arctic (extremely cold) T - tropic (warm) cP - cold, dry, stable cT - hot, dry, stable air aloft, unstable at surface mP - cool, moist, unstable mT - warm, moist, unstable 71 Table 5.1 Air Mass Characteristics (Sherwood, 2019) Lesson 1.3: Weather Fronts (Sherwood, 2019) There are 4 main types of fronts. These are: Cold front Warm front Stationary front Ocluded front 72 Figure 5.2 Main Types of Fronts Source: Burcu & Stefan (2015) 73 Table 5.2 Air Comparison of Fronts (Sherwood, 2019) Lesson 1.4: Fronts Formation and Effect (Burcu & Stefan, 2015) Warm fronts A warm front indicates that warm air is advancing and rising up over the colder air. This is because the warm air is ‘lighter’ or less dense, than the cold air. Therefore warm fronts occur where warmer air is replacing cooler air at the surface. As the warm front approaches there is a gradual deterioration in the weather. Clouds gradually lower from higher cirrus, through altostratus, to stratus and nimbostratus at the front. There is often a prolonged spell of rainfall which is often heavy. Behind the warm front the rain becomes lighter, turns to drizzle or ceases, but it remains cloudy. Temperatures rise behind the warm front and winds turn clockwise, also known as a wind ‘veer’. Pressure falls steadily ahead of and during the passage of the warm front, but then rises slowly after its passage (Burcu & Stefan, 2015). 74  Figure 5.3: Formation and Cross- Section of a Warm Front Source: Burcu & Stefan (2015) Cold fronts (Burcu & Stefan, 2015) A cold front indicates that cold air is advancing and pushing underneath warmer air at the surface. This occurs because the cold air is ‘heavier’ or denser than the warm air. Therefore cold fronts occur where cooler air is replacing warmer air at the surface. The passage of weather associated with a cold front is much shorter lived than that with a warm front. As there is often a lot of cloud in the warmer air ahead of the cold front, there is often little indication of the approaching cold front. As the front passes temperatures fall and there is often a short spell of very heavy rain, sometimes with embedded thunderstorms and cumulonimbus clouds. Behind the front the weather is much brighter with broken clouds but occasional showers. Winds veer with 75 the passage of the cold front and are often strong and gusty, especially near showers. Pressure rises throughout the approach and passage of the cold front (Burcu & Stefan, 2015). Figure 5.4 Formation of Cold Front in diagrammatic form Source: Burcu & Stefan, 2015 Figure 5.5 Cross section through a cold Front in diagrammatic form Source: Burcu & Stefan, 2015 76 Occlusions (Burcu & Stefan, 2015) In a mature depression the warm front normally precedes the cold front. Cold fronts generally travel much quicker than warm fronts, and eventually it will catch up with the warm front. Where the two fronts meet, warm air is lifted from the surface and an occlusion is formed. An occlusion can be thought of as having similar characteristics to both warm and cold fronts. The weather ahead of an occlusion is similar to that ahead of a warm front, whilst the weather behind is similar to that behind a cold front (Burcu & Stefan, 2015). Figure 5.6 Formation of Occlusion Source: Burcu & Stefan, 2015 Figure 5.7 Occlusion in cross section Source: Metlink ( 2017) 77 Lesson 2: Weather Disturbances (Susita, 2013) Weather disturbance is a general term that describes any pulse of energy moving through the atmosphere. They can act as focusing mechanisms for storm formation or even to intensify low pressure system. Types of Weather disturbances: Typhoon/hurricane Tropical cyclones Tornado Figure 5.8: Types of Weather disturbances: Source: Susita( 2013), Weather disturbance ppt Lesson 2.1: What are Typhoons (Susita, 2013) A typhoon is a mature tropical cyclone that develops between 180° and 100°E in the Northern Hemisphere. This region is referred to as the Northwestern Pacific Basin, and is the most active tropical cyclone basin on Earth, accounting for almost one-third of the world's annual tropical cyclones. For organizational purposes, the northern Pacific Ocean is divided into three regions: the eastern (North America to 140°W), central (140°W to 180°), and western (180° to 100°E). The Regional Specialized Meteorological Center (RSMC) for tropical cyclone forecasts is in Japan, with other tropical cyclone warning centers for the northwest Pacific in Hawaii (the Joint Typhoon Warning Center), the Philippines and Hong Kong. While the RSMC names each system, 78 the main name list itself is coordinated among 18 countries that have territories threatened by typhoons each year (Susita, 2013). Typhoon/ Hurricane (Susita, 2013) A large heat engine, where great amounts of heat are being produced from the process of latent heat of condensation. Figure: 5.9 Typhoon/ Hurricane Source: Susita (2013) 79 Table 5.3 Tropical Cyclone Intensity Scale (Justine, 2020) Lesson 2.2: Cyclone Classification (Justine, 2020) In meteorology, a cyclone is a large-scale air mass that rotates around a strong center of low atmospheric pressure. Cyclones are characterized by inward spiraling winds that rotate about a zone of low pressure. The largest low-pressure systems are polar vortices and extratropical cyclones of the largest scale (the synoptic scale). Warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones, tornadoes, and dust devils lie within smaller mesoscale. Upper level cyclones can exist without the presence of a surface low and can pinch off from the base of the tropical upper tropospheric trough during the summer months in the Northern Hemisphere (Justine, 2020). 80 Surface-based types 1. An extratropical cyclone is a synoptic scale low-pressure weather system that does not have tropical characteristics, as it is connected with fronts and horizontal gradients (rather than vertical) in temperature and dew point otherwise known as "baroclinic zones". "Extratropical" is applied to cyclones outside the tropics, in the middle latitudes. These systems may also be described as "mid-latitude cyclones" due to their area of formation, or "post-tropical cyclones" when a tropical cyclone has moved (extratropical transition) beyond the tropics. They are often described as "depressions" or "lows" by weather forecasters and the general public. These are the everyday phenomena that, along with anti-cyclones, drive weather over much of the Earth (Justine, 2020). 2. A polar low is a small-scale, short-lived atmospheric low-pressure system (depression) that is found over the ocean areas poleward of the main polar front in both the Northern and Southern Hemispheres. Polar lows were first identified on the meteorological satellite imagery that became available in the 1960s, which revealed many small-scale cloud vortices at high latitudes (Justine, 2020). 3. A subtropical cyclone is a weather system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. They can form between the equator and the 50th parallel. As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical cyclones or extratropical cyclones, and used terms such as quasi-tropical and semi-tropical to describe the cyclone hybrids (Justine, 2020). 4. A tropical cyclone is a storm system characterized by a low-pressure center and numerous thunderstorms that produce strong winds and flooding rain. A tropical cyclone feeds on heat released when moist air rises, resulting in condensation of water vapour contained in the moist air. They are fueled by a different heat mechanism than other cyclonic windstorms such as nor'easters, European windstorms, and polar lows, leading to their classification as "warm core" storm systems (Justine, 2020). Upper level types 1. A polar, sub-polar, or Arctic cyclone (also known as a polar vortex) is a vast area of low pressure that strengthens in the winter and weakens in the summer. A polar cyclone is a low-pressure weather system, usually spanning 1,000 kilometres (620 mi) to 2,000 kilometres (1,200 mi), in which the air circulates in a counterclockwise direction in the 81  northern hemisphere, and a clockwise direction in the southern hemisphere. The Coriolis acceleration acting on the air masses moving poleward at high altitude, causes a counterclockwise circulation at high altitude. The poleward movement of air originates from the air circulation of the Polar cell. The polar low is not driven by convection as are tropical cyclones, nor the cold and warm air mass interactions as are extratropical cyclones, but is an artifact of the global air movement of the Polar cell (Justine, 2020). 2. Under specific circumstances, upper level cold lows can break off from the base of the Tropical Upper Tropospheric Trough (TUTT), which is located mid-ocean in the Northern Hemisphere during the summer months. These upper tropospheric cyclonic vortices, also known as TUTT cells or TUTT lows, usually move slowly from east-northeast to west- southwest, and their bases generally do not extend below 20,000 feet (6,100 m) in altitude. A weak inverted surface trough within the trade wind is generally found underneath them, and they may also be associated with broad areas of high-level clouds. Downward development results in an increase of cumulus clouds and the appearance of a surface vortex. In rare cases, they become warm-core tropical cyclones. Upper cyclones and the upper troughs that trail tropical cyclones can cause additional outflow channels and aid in their intensification. Developing tropical disturbances can help create or deepen upper troughs or upper lows in their wake due to the outflow jet emanating from the developing tropical disturbance/cyclone (Justine, 2020). Mesoscale (Justine, 2020) 1. A mesocyclone is a vortex of air, 2.0 kilometres (1.2 mi) to 10 kilometres (6.2 mi) in diameter (the mesoscale of meteorology), within a convective storm. Air rises and rotates around a vertical axis, usually in the same direction as low-pressure systems in both northern and southern hemisphere. They are most often cyclonic, that is, associated with a localized low-pressure region within a supercell. Such storms can feature strong surface winds and severe hail. Mesocyclones often occur together with updrafts in supercells, where tornadoes may form. 2. A tornado is a violently rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. Also referred to as twisters, a colloquial term in America, or cyclones, although the word cyclone is used in meteorology, in a wider sense, to name any closed low-pressure circulation. 82  3. A dust devil is a strong, well-formed, and relatively long-lived whirlwind, ranging from small (half a metre wide and a few metres tall) to large (more than 10 metres wide and more than 1000 metres tall). The primary vertical motion is upward. Dust devils are usually harmless, but can on rare occasions grow large e-nough to pose a threat to both people and property. 4. A waterspout is a columnar vortex forming over water that is, in its most common form, a non-supercell tornado over water that is connected to a cumuliform cloud. While it is often weaker than most of its land counterparts, stronger versions spawned by mesocyclones do occur. 5. A gentle vortex over calm water or wet land made visible by rising water vapour. 6. A fire whirl – also colloquially known as a fire devil, fire tornado, firenado, or fire twister – is a whirlwind induced by a fire and often made up of flame or ash(Imipak, 2020). Lesson 2.3: Formation of Cyclones Figure 5.10 Extratropical low-pressure area Source: Imipak (2020) 83  The initial extratropical low-pressure area forms at the location of the red dot on the image. It is usually perpendicular (at a right ange to) the leaf-like cloud formation seen on satellite during the early stage of cyclogenesis. The location of the axis of the upper level jet stream is in light blue (Imipak, 2020). Imipak (2020) said that Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere (a low-pressure area). Cyclogenesis is an umbrella term for at least three different processes, all of which result in the development of some sort of cyclone, and at any size from the microscale to the synoptic scale. Tropical cyclones form due to latent heat driven by significant thunderstorm activity, developing a warm core. Extratropical cyclones form as waves along weather fronts before occluding later in their life cycle as cold core cyclones. Mesocyclones form as warm core cyclones over land and can lead to tornado formation. Waterspouts can also form from mesocyclones, but more often develop from environments of high instability and low vertical wind shear. The process in which an extratropical cyclone undergoes a rapid drop in atmospheric pressure (24 millibars or more) in a 24-hour period is referred to as explosive cyclogenesis and is usually present during the formation of a nor'easter. The anticyclonic equivalent, the process of formation of high-pressure areas, is anticyclogenesis. The opposite of cyclogenesis is cyclolysis (Imipak, 2020). 84  Assessment Task 5-1 Fill-in the blank/s 1. An is an air with distinctive characteristics in terms of temperature and humidity. 2. Air mass is a body of air with more-or-less physical properties over horizontal distance of hundred of kilometers 3. A weather is a boundary separating two masses of air of different densities 4. Typhoon and hurricanes are both and most of their characteristics are the same. 5. have wind speed of more than 74 mph and are accompanied by hail, strong winds, storm surges and rain. 6. means ”big wind”a term used by the native Americans for storms that originated in the West Atlantic. 7. is derived from the Chinese “Tai Fun” which means “great wind” , winds that developed in the North Pacific. 8. is a storm system characterized by low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. 9. are rotating columns of air usually produced by severe thunderstorms. 10. are Japanese word that means ”harbor wave”, they are ocean waves that can reach a height of 100 ft, and crash onto land. 85  Summary According to Ditan, (2012), storms are the most dangerous and most feared of all phenomena.. There are three types of storms : Tropical cyclones Thunderstorms tornadoes Air masses are Large unit of air in which temperature and moisture conditions are uniform at a given altitude. Moves separately from surroundings temperature and moisture conditions determined by SOURCE REGION of air mass. Front: the boundary between two unlike air masses unlike in temperature, moisture, or both named according to motion of the cold air. Front classification is based primarily on the displacement of fronts and the resultant temperature changes. Four basic types are recognized by this classification: cold front, warm front, occluded front and stationary front.( Air masses and Fronts, ppt ,n.d) References Ditan, C.D. (2014). Earth Sciences. National Book Store, Mandaluyong City Burcu, E. and Stefan V. (2015). Socratic Q&A - What are the main types of fronts?. https://socratic.org/questions/what-are-the-main-types-of-fronts Eudalddiaz (2013 August 28) Air masses and Fronts , https://www.slideshare.net/eudalddiaz/air- masses-and-fronts 86 Fuentes, K.A. (n.d.). Weather Disturbance. https://www.slideserve.com/mandar/weather- disturbance Justine, E. (2020). Typhoon Imipak. (2020).PPT: Air Masses and fronts MetLink.(2017). WEATHER SYSTEMS - Anticyclones, Depressions and Fronts.https://www.metlink.org/secondary/a-level/weather-systems/ Muhaimin, A.K. (2018 September 10). Air masses and fronts. https://www.slideshare.net/2329383/air-masses-and-fronts-113753835 Oklahoma Climatological Survey. (1996-2004). OK-FIRST Project. https://okfirst.mesonet.org/train/meteorology/AirMasses.html Rabago, L. M., Flores, A. C., Mingoa, T.R., Ferrer, D.L., Obille Jr., E. C. & Cano, M. C. (2007). Dynamic Science: An Integration of Physical and Biological Science Modular Approach. Vibal Publishing House, Inc., Metro Manila, Cebu, Davao Rutledge, K., Ramroop, T., Boudreau, D., McDaniel, M., Teng, S., Sprout, E., Hilary Costa, H., Hall, H., & Hunt, J. (2011). National Geographic - Air Mass. https://www.nationalgeographic.org/encyclopedia/air-mass/ Sherwood, S. (2019). Sciencing - What Are the Six Types of Air Masses?.https://sciencing.com/four-types-air-mass-11902.html Uriza, M. (2013 October 27). Weather disturbances. https://www.slideshare.net/Maricris_Usita/weather-disturbance 87  MODULE 6 AIR PRESSURE Introduction The air around you has weight, and it presses against everything it touches. That pressure is called atmospheric pressure, or air pressure. It is the force exerted on a surface by the air above it as gravity pulls it to Earth. Atmospheric pressure is an indicator of weather. When a low-pressure system moves into an area, it usually leads to cloudiness, wind, and precipitation. High-pressure systems usually lead to fair, calm weather (Rutledge et al.2011). Learning Outcomes At the end of the lesson, the students will be able to: 1. Define atmospheric pressure; 2. Distinguish different instruments used to measure atmospheric pressure; 3. Determine the importance of pressure maps; 4. Differentiate between high and low pressure systems; 5. Compare and contrast different types of air pressure; and 6. Solve problems about air Pressure. 88 Lesson 1. Atmospheric Pressure What is atmospheric pressure? Atmospheric pressure is the pressure exerted by the weight of air in the atmosphere of Earth (or that of another planet). In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point (Kaushal,2015). The atmosphere extends to around 1000 km above the ground. The weight of the upper portion of the atmosphere presses down, or compresses, the lower portion and all objects below it. This compression produces air pressure point (Kaushal,2015). How much is normal air pressure at sea level? Imagine a column of air on top of a square (measuring one inch on each side ) on the ground and extending all the way up to the upper limit of the atmosphere. How heavy is that column of air 1000 km high and pushing down on the square inch area below (Rabago, Flores, Mingoa, Ferrer, Obille Jr., & Cano, 2007). Figure.6.1 Pressure Source: Prabodhini (2013) 89  Figure 6.2 Pressure Source: NEVŞEHİR (2020) Figure 6.3 Atmospheric Pressure Source: Prabodhini, (2013) 90  Figure 6.4 Atmospheric Pressure Source: Prabodhini, (2013) Pressure exerted on earth because of atmosphere is called Atmospheric Pressure Figure. 6.5 Effects of Atmospheric Pressure Source: Prabodhini (2013) 91 Try This! Water Glass Trick. and turn it upside down. Fill a cup one-third with water. Cover the entire mouth with an index card.. Holding the card in place, take the cup to the sink and turn it upside down Remove the force of the water pushing down is only about one pound of force your hand from underneath Voila!!! Explain your observation! Because the water inside the cup is lighter than the air outside, the card is held in place by about 15 pounds of force from the air pushing up, while the force of the water pushing down is only about one pound of force ( Kaushal (2015). Figure. 6.6 Water Glass Trick.and turn it upside down Source: Kaushal (2015) 92 Lesson 1.1 Measurement of Atmospheric Pressure (Rabago et.al,2007) An Italian mathematician named Evangelista Toricelli (1608-1647) discovered the weight of that column of air to be 14.69 pounds , often rounded off to14.7. and he used a mercury barometer, an instrument that measures changes in atmospheric pressure, which he himself invented. The value 14.7 lb/in2 at sea level became known as one atmosphere (atm). In the metric system, this is equal to 1013. 25 newtons per square centimeter (1013.25 N/cm2 ). Today, weathermen (also called meteorologists) record atmospheric pressure using another unit of measurement called millibar(mb): 1 atm = 1013.25mb. This value is usually rounded off to 1000 mb or 102 mb (Rabago et.al,2007) Atmospheric pressure, also called barometric pressure, force per unit area exerted by an atmospheric column (that is, the entire body of air above the specified area). 1. A2tmospheric pressure can be measured with a mercury barometer (hence the commonly used synonym barometric pressure), which indicates the height of a column of mercury that exactly balances the weight of the column of atmosphere over the barometer 2. Atmospheric pressure is also measured using an aneroid barometer, in which the sensing element is one or more hollow, partially evacuated, corrugated metal disks supported against collapse by an inside or outside spring; the change in the shape of the disk with changing pressure can be recorded using a pen arm and a clock-driven revolving drum. 2 Figure.6.7 Aneroid Barometer Source: Lough (2003-2020) 93  Figure.6.8 Mercury barometer Source: Rafferty (2020) Lesson 2: Air Pressure and Height Elevation The pressure at any level in the atmosphere may be interpreted as the total weight of the air above a unit area at any elevation. At higher elevations, there are fewer air molecules above a given surface than a similar surface at lower levels. For example, there are fewer molecules above the 50 km surface than are found above the 12 km surface, which is why the pressure is less at 50 km. What this implies is that atmospheric pressure decreases with increasing height. Since most of the atmosphere's molecules are held close to the earth's surface by the force of gravity, air pressure decreases rapidly at first, then more slowly at higher levels. Since more than half of the atmosphere's molecules are located below an altitude of 5.5 km, atmospheric pressure decreases roughly 50% (to around 500 mb) within the lowest 5.5 km. 94 Above 5.5 km, the pressure continues to decrease but at an increasingly slower rate (Rafferty, 2020).. Figure.6.9 Pressure with Height Source: Bramer (2020) Lesson 2.1: Types of Air Pressure (Wiegand, 2020) Next to temperature, pressure is one of the most important physical state variables. The pressure is defined as a force (FN) which acts uniformly over a defined area (A). The different types of pressure are differentiated only by the reference pressure. 95 Absolute pressure (Wiegand, 2020) The clearest reference pressure is the pressure zero, which exists in the air-free space of the universe. A pressure which is related to this reference pressure is known as absolute pressure. For the required differentiation from other types of pressure, it is denoted with the index “abs”, which is derived from the Latin “absolutus”, meaning detached, independent (Wiegand, 2020). Atmospheric pressure (Wiegand, 2020) The probably most important pressure for life on earth is the atmospheric pressure, amb (amb = ambiens = ambient). It is created by the weight of the atmosphere which surrounds the earth up to a height of approx. 500 km. Up to this altitude, at which the absolute pressure pabs = zero, its magnitude decreases continuously. Furthermore, the atmospheric pressure is subject to weather-dependent fluctuations, as is only too well known from the daily weather report. At sea level, pamb averages 1,013.25 hectopascal (hpa), corresponding to 1,013.25 millibar (mbar). With “cyclones” and “anticyclones”, this pressure varies by about 5 % (Wiegand, 2020). Differential pressure (Wiegand, 2020) The difference between two pressures, p1 and p2, is known as the pressure differential, Δp = p1 - p2. In cases where the difference between two pressures itself represents the measured variable, one refers to the differential pressure, p1,2. Accordingly, in order to measure differential pressure, at first two different pressures are captured in a measuring instrument. Only if the measured values differ from each other, will a differential pressure be indicated. Instances where it is required to measure differential pressure are, for example, level measurement and monitoring applications. 96 Lesson 2.2 Atmospheric Temperature and Density What do scientists tell us about the temperature of air? Temperature is defined as the measure of the average kinetic energy (or energy in motion) of the molecules of an object (in this case, an air mass), indicated by the rise and fall of the column of mercury in a thermometer. A higher temperature of air means that the molecules have greater kinetic energy. They are moving faster, bumping each other with greater force, thereby throwing them farther apart (Rabago, et al., 2007). Figure.6.10 Relationship between Air Pressure and Density Source: Air Pressure (n.d) 97 Lesson 2.3 Air Pressure and Density (Air Pressure, n.d.) The gravitational attraction between Earth and atmospheric gases causes particles of gas to be pulled toward the center of Earth. Air pressure increases as you near the bottom of the atmosphere because of the greater mass of the atmosphere above you. Atmospheric pressure decreases with height because there are fewer and fewer gas particles exerting pressure. The density of air is proportional to the number of particles of air occupying a particular space. Table 6.1. Density Changes with Altitude (Air Pressure, n.d.) Lesson 2.4. Pressure-Temperature-Density Relationship (Air Pressure, n.d.) Temperature, pressure, and density are related. In the atmosphere, temperature is directly proportional to pressure. If an air mass maintains a certain density, as temperature increases or decreases, pressure does, too. 98  In most atmospheric interactions, however, neither density nor pressure remains unchanged Temperature varies with changes in both pressure and density. Temperature is proportional to the ratio of pressure to density, which decreases with increasing altitude Temperature Inversion – A temperature inversion is an increase in temperature with height in an atmospheric layer. – This can happen when the lower layers of the atmosphere lose heat to Earth’s surface and become cooler than the air above them. – A temperature inversion can act like a lid to trap pollution under the inversion layer. – In all cases, the presence or absence of inversions can have a profound effect on weather conditions. Please Watch!!! Check this out: Live Map https://www.ventusky.com/?p=11.3;123.0;5&l=pressure 99 Lesson 3 Air Pressure Maps (Air Pressure, n.d.) Pressure is measured in mb (millibars)—is given by the number to the upper right of the circle. For example, suppose it’s 1019.4 mb. Only the 10s/1s/0.1s are shown –so it is represented as 194. Pressure below 1000 mb would start with high numbers, such as 964 for 996.4mb. Barometric Pressure 138 Add a decimal between the last two digits 13.8 Add a 9 or 10 in front to fit on the scale (ranges from 950.0 to 1050.0) 1013.8 Figure. 6.11 Barometric Pressure Conversion Source: Air Pressure (n.d.) 100 Try This! Remember how to convert Pressure? Show your step by step solution for each. 1) 196………………………….. 2) 423………………………….. 3) 895………………………….. Lesson 3.1 Weather Maps (Air Pressure, n.d.) Meteorologist use weather maps and tools to help them see weather patterns and forecast weather. A weather map is a map where we can find different symbols to help us see how the weather is in different parts of the country. Figure 6.12 Weather Maps and Symbols Source: Cortez (2013) 101 Lesson 3.2 The isobars Those plain lines that curve across the map are called isobars (iso = equal, bar = pressure). They join together places with the same mean sea level air pressure (weight per square area of air above). Some have numbers on them showing this value in hecto Pascals (Air Pressure, n.d.) Isobars and the wind Isobars can tell us about the wind. Christopher Buys-Ballot (1818-90), who was a Dutch meteorologist, made the vital link between isobars and wind in 1857. In the Southern Hemisphere, his rule is as easy to remember as three L's: If you LOOK into the wind, the LOW pressure is on your LEFT (Prabodhini, 2013). Figure.6.13 Isobars and Wind system Source: Prabodhini (2013) The closer the isobars, the stronger the winds. This varies with latitude on a weather map with isobars 4 hectopascals apart, a spacing of about two degrees latitude (with straight isobars) means fresh winds about Auckland but a gale over Fiji (Prabodhini, 2013). 102 THE HIGHS When isobars enclose an area of high pressure this is called a High or anticyclone and its centre is labelled on a weather map by an 'H'. The term 'anticyclone' is a bit of meteorological jargon (Cortez, 2013). The central pressure of a weak High is about 1015hPa, while a strong or intense High has a central pressureabove about 1030hPa. An intensifying High has a rising central pressure, while a weakening High has a falling central pressure. Near a High's centre are light winds and sometimes areas of low cloud called anticyclonic gloom. Round the edge of a High, the winds are sometimes strong. Intense Highs tend to squeeze the isobars together creating areas of strong winds. Winter Highs often bring frost; summer Highs may bring thunderstorms and hail. The bigger Highs are, the slower they tend to move, sometimes 'blocking' the fronts that are trying to follow them (Cortez, 2013). The large “H” means an area of higher pressure. Higher pressure usually means nice, clear weather (Cortez, 2013). Figure.. 6.14 Weather Maps and Symbols Source: Cortez (2013) 103  Figure.6.15 Weather Maps and Symbols Source: Cortez (2013) THE LOWS (Cortez, 2013) Isobars make shapes and patterns. When they enclose an area of low pressure this is called a 'Low' or 'depression' and its centre is labelled on a weather map with an 'L'. The term depression is a bit of meteorological jargon. A low pressure system is like a giant funnel of wind spiralling inwards and upwards forcing warmish air in the centre to rise. As air rises it cools and clouds form (Cortez, 2013). The central pressure of a shallow Low is above 1000 hPa, of a moderate Low 980-1000 hPa, and of a deep or intense Low below 980hPa. If there are two or more centres the Low is said to be complex. If the central pressure is rising the Low is said to be filling or weakening. If the central pressure is falling the Low is said to be intensifying or deepening (Cortez, 2013). 104  The large “L” means an area of lower pressure. Lower pressure usually means clouds, rain, or snow. Figure.6.16 High and Low pressure system Source: Cortez (2013) How many “lows” and “Highs” are on this map? Figure.6.17 High and Low pressure system Source: Cortez (2013) 105 Lesson 3.3 Applications of pressure (Veerendra, 2016) The area of the edge of a knife’s blade is extremely small. This creates a pressure high enough for the blade to cut through a material. Syringes are used to take blood for blood tests. The pressure of the fliuid (blood)forces the liquid to move into the syringe when its plunger is withdrawn. When air is sucked out of a drinking straw , the air pressure inside if decreases and the atmospheric pressure outside forces the liquid to go inside the straw. Skis have a large area to reduce the pressure on the snow. This ensures that the skis do not sink unto the snow too far (Veerendra, 2016). The pressure under the studs on the soles of football shoes is high enough Consequently, as air and dirt particles are sucked into the device.for them to sink into the ground which gives extra grip (Veerendra, 2016). A vacuum cleaner has a fan inside that creates a low pressure inside the device. Consequently, air an dirt particles are sucked into the device (Veerendra, 2016) 106 Figure.6.18 Some applications of pressure Source: Prabodhini (2013) 107 Lesson 4: Sample Problems and Solutions Sample Problem: 1. Determine the mass of Earth's atmosphere using the value of the standard atmosphere. 2. Determine the scale height of Earth's atmosphere — the height the atmosphere would have if its density stayed constant instead of decreasing with altitude. (The scale height is a useful approximation for some calculations in atmospheric sciences.) Since pressure is defined as force divided by area, the force of the atmosphere can be found by multiplying pressure by area. F F = PA ⇐ P= A The force of the atmosphere due to gravity and is called weight (mg). The area it is pressing down on is the surface area of a sphere (4πr2). Substitute these expressions. mg = P(4πr2) Solve for the goal of the problem. P(4πr2) m= g Put numbers in… (101,325 Pa)(4π)(6.37 × 106 m)2 m= 9.8 m/s2 Get answer out… m = 5.27 × 1018 kg Compare this to the mass of the whole Earth. 5.27 × 1018 kg ≲ 0.0001% 5.97 × 1024 kg The atmosphere is a tiny fraction of the Earth's total mass. Once again, force is pressure times area because pressure is force divided by area. F = PA ⇐ P=F 108  A The force is still the weight of the Earth's atmosphere (mg), but this time don't do anything to the area term. mg = PA Solve for mass… PA m= g and then work on something else. Since density is defined as the ratio of mass to volume, mass is the product of density and volume. (Remember, the symbol for density is the Greek letter rho not the Latin letter p.) m m = ρV ⇐ ρ= V Treat the atmosphere as a very thin shell on top of the surface of the earth. Its volume would then be the surface area of the earth (A) times the thickness of the shell (h). m = ρAh Set the two mass equations equal to one another. PA ρAh = g Solve for thickness and note how nicely area cancels out. P h= ρg We're ready for numbers… (101,325 Pa) h= (1.21 kg/m3)(9.8 m/s2) and an answer. h = 8.5 km Compare this to the radius of the whole Earth. 8.5 km ≳ 0.1% 6371 km Don't think about it as "How thick is the atmosphere" but rather "How thin is the atmosphere". A standard pack of copier or printer paper has 500 sheets. Unwrap two of them and stack one on top of the other. Remove one sheet of paper. That's the thickness of the Earth's atmosphere (Elert, 1998-2020) 109  Assessment Task 6-1 TRUE or FALSE. If False, change the underlined word to make statement true. 1. The force of the atmosphere is due to gravity and is called mass. 2. Pressure is defined operationally as the ratio of mass to volume, 3. Mass is the product of density and volume 4. The atmosphere is a tiny fraction of the Earth's total weight 5. Pressure is defined as force divided by area 6. The closer the isobars as shown in the map, the weaker the winds 7. Air pressure idecreases as you near the bottom of the atmosphere because of the greater mass of the atmosphere above you. 8. Atmospheric pressure increases with height because there are fewer and fewer gas particles exerting pressure 9. The density of air is proportional to the number of particles of air occupying a particular space 10. In the atmosphere, heat is directly proportional to pressure 11. If an air mass maintains a certain pressure as temperature increases or decreases, pressure does, too. 12. When air is sucked out of a drinking straw , the air pressure inside it increases and the atmospheric pressure outside forces the liquid to go inside the straw. 13. Higher pressure usually means clouds, rain, or snow. 14. Meteorologist use weather maps and tools to help them see weather patterns and forecast weather. 15. Atmospheric pressure is the pressure exerted by the weight of air in the atmosphere of Earth (or that of another planet). 110  Summary Air pressure is the pressure exerted by the weight of air above. Exerted in all directions (up, down, and sideways). The air pressure pushing down on an object exactly balances the air pressure pushing up on the object. Average Air Pressure at sea level is: 1 kg/cm2 = 1013.2 mb = 1 atm = 29.92 in. of mercury Barometer: device used for measuring air pressure Unit: millibars (mb) inches of mercury (in. Hg) Atmospheres (atm.) Torricelli: invented the mercury barometer in 1643. The gravitational attraction between Earth and atmospheric gases causes particles of gas to be pulled toward the center of Earth. Temperature, pressure, and density are related (Air Pressure, ppt n.d) Because of Earth’s gravitational pull, there are more molecules of gases, becoming less and less with altitude. Unlike density and pressure, temperature does not follow a simple pattern throughout the thickness of the atmosphere (Rabago, et.al, 2007) 111  References: Agarwal, K. (2015 December 31). Atmospheric Pressure. Published in Education. https://www.slideshare.net/2746226/atmospheric-pressure-56568872?next_slideshow=1 Air Pressure. (n.d). https://www.slideshare.net/atrayeesengupta/air-pressure-presentation Bramer,D. (2010). University of Illinois - Department of Atmospheric Sciences (DAS) - Pressurewith Height. http://www..atmos.uiuc.edu/(Gh)/guides/mtr/prs/hght.rxml Cortez, E. (2013 November 2). Weather Maps and Symbols, https://www.slideshare.net/ckpreciosa/weather-maps-and-symbols Ditan, C.D. (2014). Earth Sciences. National Book Store, Mandaluyong City Elert, G. (1998-2020). The Physics Hypertextbook – Pressure. https://physics.info/pressure/practice.shtml Lough, B. ( 2003-2020), Surf in the Air - Types of Barometer. https://www.stuffintheair.com/barometermakes.html NEVŞEHİR. (2020 June).Daily News - Arts & Life.https://www.hurriyetdailynews.com/hot-air- balloons-return-to-cappadocias-skies-155384 Prabodhini, J. (2013 August 26). Atmospheric pressure ppt. Published in Technology Business https://www.slideshare.net/ERCJPP/lesson3-eng Rabago ,L. M. , Flores, A. C., Mingoa, T.R., Ferrer, D.L., Obille Jr., E. C. & Cano, M. C. (2007). Dynamic Science: An Integration of Physical and Biological Science Modular Approach. Vibal Publishing House, Inc., Metro Manila, Cebu, Davao Rafferty, J.P. (2020). Earth Sciences - Atmospheric pressure. https://www.britannica.com/science/atmospheric-pressure Rutledge, K., Ramroop, T., Boudreau, D., McDaniel, M., Teng, S., Sprout, E., Hilary Costa, H., Hall, H., & Hunt, J. (2011 May 14). National Geographic - Atmospheric Pressure, https://www.nationalgeographic.org/encyclopedia/atmospheric-pressure/ Veerendra. (2016 October). AplusTopper - Applications of Air Pressure in Daily Life, https://www.aplustopper.com/applications-of-pressure-in-daily-life/ Wiegand, A. (2020). Wika - Types of Pressure. https://en.wika.com/landingpage_differential_pressure_en_co.WIKA 112  MODULE 7 Weather Forecasting and Control Introduction Weather forecasting is the application of science and technology to predict the conditions of the atmosphere for a given location and time. There is a vast variety of end uses to weather forecasts. Weather warnings are important forecasts because they are used to protect life and property. Forecasts based on temperature and precipitation are important to agriculture, and therefore to traders within commodity markets. Temperature forecasts are used by utility companies to estimate demand over coming days. On an everyday basis, many use weather forecasts to determine what to wear on a given day. Since outdoor activities are severely curtailed by heavy rain, snow and wind chill, forecasts can be used to plan activities around these events, and to plan ahead and survive them (Bender the Bot, 2020). Learning Outcomes At the end of the lesson, the students will be able to: 1. Define weather forecasting; 2. Familiarize basics of Forecasting and common terms used; 3. Recognize the works of a forecasting and their methods of works; 4. Identify the different types of weather forecasting instruments; and 5. Determine how to measure moisture in atmosphere. 113 Lesson 1: Weather Forecasting (ESSBY, 2015) State Procedures of Weather forecasting. The weather forecasting has now become a science and it is performed by adopting the following procedures (steps): 1. Recording of weather data (temperature, pressure, wind speed and direction, cloud forms, humidity and precipitation, visibility, storms etc.) 2. Collection of weather data from weather recording (observations centers) stations scattered world over including both land and ocean surfaces. 3. Transmission of weather data collected form major weather stations to sub centers. 4. Compilation of weather data. 5. Plotting of weather data on maps and daily weather records, synoptic charts etc. 6. Analysis of weather charts and maps with the help of electronic computers etc, 7. Final forecasting of weather and numerical modeling. Lesson 1.1. Tools in Weather Forecasting (ESSBY, 2015) Radiosonde Is an instrument that is carried aloft by a balloon to send back information on atmospheric temperature, pressure and humidity by means of a small radio transmitter (ESSBY, 2015). Figure 7.1 Radiosonde Source: ESSBY (2015) 114  Figure 7.2 Weather Satellites Source: ESSBY (2015) The most significant device is weather satellite of different kinds attached with different types of sensors for specific purposes and having varying orbital paths around the Earth. The first weather satellite, named TIROS-1 was launched in 1960. The sensors which are attached with satellites send back to the images of clouds to earth’s center. Weather Satellites (on the basis of orbital paths) Same rate of movement around the earth as that the rotational speed of the earth. These are fixed at the altitude of 35 786 km from the sea level. These are called high altitude satellites.Provide scanned pictures of large areas using imaging sensors instruments that provides thermal variations of the atmosphere, moisture etc (ESSBY, 2015). 115 Radar These are useful tools to obtained detailed information about clouds and storms mainly cyclones, tornadoes, hurricanes. Figure 7.3 Weather Satellites Source: ESSBY (2015) Figure 7.4 Supercomputers Source: Yewlett (n.d.) During the last two decades the Met Office has used state-of-the-art supercomputers for numerical weather prediction and more recently, also for predictions of global climate. Collecting 116 data on the weather is very important. Without the data, the computer could not do the calculations that enable it to make weather predictions (ESSBY, 2015). Thermometer (ESSBY, 2015) Measures the air temperature. Most thermometers are closed glass tubes containing liquids such as alcohol or mercury. When air around the tube heats the liquid, the liquid expands and moves up the tube. A scale then shows what the actual temperature is. Figure 7.5 Thermometer Source: Yewlett (n.d.) Sling psychrometer (Yewlett, n.d.) Measures relative humidity, using the cooling effect of evaporation. Two thermometers are used in a sling psychrometer. Wet the cloth of one of the thermometers and swing the psychrometer around a few times. Water evaporates from the cloth, causing the temperatures on that thermometer to be lower than the other. Figure 7.6 Thermometer Source: Yewlett (n.d.) 117 Barometer Measures air pressure. It tells you whether or not the pressure is rising or falling. A rising barometer means sunny and dry conditions, while a falling barometer means stormy and wet conditions. An Italian scientist named Torricelli built the first barometer in 1643 (Yewlett, n.d.) Figure 7.5 Thermometer Source: Yewlett (n.d) YOUR EYES are one of the best ways to help detect the weather. Always keep an eye at the sky and you’ll usually be on top of weather conditions (Weather WizKids, 2020). 118 Lesson 1.2 Where the forecasts are sent ? Always remember that the forecasters are highly trained people and they use their judgement and expertise to make their forecast based on the information the computer gives them and the information from the radar and the satellite pictures (Yewlet, n.d.). Radiosonde satellites Weather station Radar Supercomputer Aviation National and International Forecaster Forecast Services up to Global forecast services 7 days ahead Figure 7.5 Where the forecasts are sent? Source: Yewlett (n.d.) 119  Figure 7.6 Weather Station Source: Yewlett (n.d) A weather station (ESSBY, 2015) Sends signals back to the Met office computer. The instruments measure pressure, temperature and humidity. Some weather stations are automated. These send their measurements back to the computer directly. Lesson 1.3 Types of Weather forecasting (ESSBY, 2015) On the basis of duration of the validity of forecasts into three types as follows: 1. Short range weather forecasts 2. Medium range weather 3. Long range weather forecasts 120 Short range weather forecasts Most useful predictions of weather wherein forecasts valid from few hours to 48 hours and sometimes 72 hours. It is based on maps weather charts, satellite images. Determines change of atmospheric weather of specific location. It is a persistent method & continuity methods are applied and helps in transportation and fishermen (ESSBY, 2015). Medium range weather It covers the time span from 3 days to 3 weeks. This prediction is done by calculating the average of past and present weather condition (ESSBY, 2015). Long range weather forecasts It covers a time span from a fortnight to season of the year. These are basically statements, exact accuracy is minimum. Not so detailed information (ESSBY, 2015). Lesson 1.4 Forecasting Methods (Weather forecasting, n.d.) Persistent forecast: (short term forecast) when there is no reason for the weather conditions to change. Steady state forecast (trend method). If we know the speed and the direction of the weather system, we can extrapolate to its future location assuming same speed. ♦ Example: a cold front, located 90 km due west from here, is moving eastward at 30 km/hr. Prediction: a cold front will pass through in exactly 3 hours. Analogue forecast (pattern recognition): “I have seen these atmospheric conditions before and based on what happened back then, I can predict tomorrow’s weather”. Statistical forecast: the forecast is made based on ♦ Numerical model’s forecast for weather elements (humidity, cloud cover, wind direction, temperature). ♦ Statistically weighted analogue forecasts based on those 121 “The chance of rain is 60%” It will rain over 60 % of the forecasted area. NO There is a 60% chance that it will rain somewhere within the forecasted area. NO It will rain 60% of the time. NO There is 60% chance that any random location will receive a measurable amount of rain. YES If you stay at one place there is a 60% chance that you will see rain. YES Lesson 2. Weather Terms as Used by PAGASA (PAGASA, n.d.) Table 7.1 Cloud Description (PAGASA, n.d.) Sky condition Definition / description Clear or Sunny State of the sky when it is cloudless, totally clear or with a few Skies small light clouds visible. Has a total cloud cover of less than one okta. Partly Cloudy State of the sky is within 2-5 oktas total cloud cover or has between 30% to 70% cover of the celestial dome. Partly Cloudy to at Mostly partly cloudy but there are times when more than 70% of Times Cloudy the celestial dome is covered with clouds. Mostly or Mainly The sky is mostly covered with clouds but with possible brief Cloudy periods of sunshine. The total cloud cover is between 6 to 8 oktas. Cloudy The sky is covered with clouds between 6 to 8 oktas or has more than 70% cloud cover. Predominantly more clouds than clear sky. 122  Sky condition Definition / description For a longer period during the day, the sun is obscured by clouds. Overcast The sky is totally or completely covered with thick and opaque clouds, 8 oktas or around 100% cloud cover. Precipitation (Rain & Rainshowers) Description (PAGASA, n.d.) Rains Overcast sky with continuous or steady precipitation that may last several hours. Has a water droplets of 0.5 mm or greater in size but if widely scattered the drops may be smaller. Associated with meso-scale (synoptic) system or macro-scale (large scale) system like TC's, Easterly Waves, Monsoons, Fronts and ITCZ. Table 7.2 Precipitation (Rain & Rainshowers (PAGASA, n.d.) Classification Definition / description Very Light Rains Scattered drops that do not completely wet an exposed surface regardless of duration. Light Rains The rate of fall is from trace to 2.5 mm per hour. Individual drops easily identified and puddles(small muddy pools) form slowly. Small streams may flow in gutters. Moderate Rains The rate of fall is between 2.5 mm to 7.5 mm per hour. Puddles rapidly forming and down pipes flowing freely. Heavy Rains The rate of fall is greater than 7.5 mm per hour. The sky is overcast, there is a continuous precipitation. 123  Falls in sheets, misty spray over hard surfaces. May cause roaring noise on roofs. Lesson 3. How Do Forecasters Work? (Bender the Bot, 2020) Weather forecasting is the application of current technology and science to predict the state of the atmosphere for a future time and a given location (Bender the Bot, 2020). Traditional observations made at the surface of atmospheric pressure, temperature, wind speed, wind direction, humidity, precipitation are collected routinely from trained observers, automatic weather stations or buoys. During the data assimilation process, information gained from the observations is used in conjunction with a numerical model's most recent forecast for the time that observations were made to produce the meteorological analysis. Numerical weather prediction models are computer simulations of the atmosphere. They take the analysis as the starting point and evolve the state of the atmosphere forward in time using understanding of physics and fluid dynamics. The complicated equations which govern how the state of a fluid changes with time require supercomputers to solve them. The output from the model provides the basis of the weather forecast. Lesson 3.1 Forecasting Methods (Bender the Bot, 2020) Ancient Forecasting o For millennia, people have tried to forecast the weather. In 650 BCE, the Babylonians predicted the weather from cloud patterns as well as astrology. In about 350 BCE, Aristotle described weather patterns in Meteorologica. Later, Theophrastus compiled a book on weather forecasting, called the Book of Signs. Chinese weather prediction lore extends at least as far back as 300 BCE, which was also around the same time ancient Indian astronomers developed weather- prediction methods. In New Testament times, Jesus himself referred to 124  deciphering and understanding local weather patterns, by saying, "When evening comes, you say, 'It will be fair weather, for the sky is red', and in the morning, 'Today it will be stormy, for the sky is red and overcast.' You know how to interpret the appearance of the sky, but you cannot interpret the signs of the times." (Bender the Bot, 2020). Modern Method o It was not until the invention of the electric telegraph in 1835 that the modern age of weather forecasting began. Before that, the fastest that distant weather reports could travel was around 160 kilometres per day (100 mi/d), but was more typically 60–120 kilometres per day (40–75 mi/day) (whether by land or by sea). By the late 1840s, the telegraph allowed reports of weather conditions from a wide area to be received almost instantaneously, allowing forecasts to be made from knowledge of weather conditions further upwind (Bender the Bot, 2020). Broadcasts o The first ever daily weather forecasts were published in The Times on August 1, 1861, and the first weather maps were produced later in the same year. In 1911, the Met Office began issuing the first marine weather forecasts via radio transmission. These included gale and storm warnings for areas around Great Britain. In the United States, the first public radio forecasts were made in 1925 by Edward B. "E.B." Rideout, on WEEI, the Edison Electric Illuminating station in Boston. Rideout came from the U.S. Weather Bureau, as did WBZ weather forecaster G. Harold Noyes in 1931 (Bender the Bot, 2020). Lesson 3.2 Forecasting Techniques (Bender the Bot, 2020) Persistence o The simplest method of forecasting the weather, persistence, relies upon today's conditions to forecast the conditions tomorrow. This can be a valid way of forecasting the weather when it is in a steady state, such as during the summer season in the tropics. This method of forecasting strongly depends upon the presence of a stagnant we