Agricultural Engineering 1 Fundamentals Of Agriculture PDF

AGRICULTURAL ENGINEERING 1 FUNDAMENTALS OF AGRICULTURAL ENGINEERING 1 INTRODUCTION Lecture Outline: Soil and Water Management 1. Sources and qualities of irrigation water 2. Conveyance and distribution of irrigation water 3. Methods of irrigation 4. Estimation of irrigation and...

AGRICULTURAL ENGINEERING 1 FUNDAMENTALS OF AGRICULTURAL ENGINEERING 1 INTRODUCTION Lecture Outline: Soil and Water Management 1. Sources and qualities of irrigation water 2. Conveyance and distribution of irrigation water 3. Methods of irrigation 4. Estimation of irrigation and diversion requirements 5. Flow measurements: irrigated farm practices 6. Fundamental concepts of drainage 7. Drainage of agricultural land INTRODUCTION Lecture Outline: Soil and Water Conservation 1. Soil erosion and sedimentation 2. Conservation practices 3. Conservation structures INTRODUCTION Lecture Outline: Legal and Administrative Aspects of Water Use 1. Water Laws (General) 2. Philippine water laws INTRODUCTION FUNDAMENTALS OF AGRICULTURAL ENG’G Atmospheric Science Soil and Water Plant Science Management Animal Science Effects of weather and Soil and Water Soil Science climate Conservation THE BIG PICTURE: WORLD PROBLEM 1. Increasing population "The power of population is so superior to the power of the earth to produce subsistence for man, that premature death must in some shape or other visit the human race” —Malthus T.R. 1798. An essay on the principle of population. Chapter VII, p61  THE BIG PICTURE 2. Land conversion  THE BIG PICTURE 3. Water shortage Agriculture vs. Domestic Production vs. Consumption Annual losses (‘000 Mg) in Philippine rice production due to typhoons/floods, droughts and pests from 1970 – 1990 (PhilRice-BAS, 1994) With all the problems where do we fit in? ✓ food security ✓ intensify land usage – by applying what we learned in school and outside school ✓ efficient usage of available resources  INTRODUCTION It seems incredible that so many aspects of our daily lives are actually impacted by climate… Are we changing our eating patterns because food prices are escalating due to droughts or floods or fires? Do our water sources still supply sufficient water to meet our needs? Can we continue to live where we currently live or has our livelihood already impacted by changes? INTRODUCTION TO WEATHER AND CLIMATE OUR EXPERIENCE OF WEATHER AND CLIMATE… WEATHER AND CLIMATE ARE PART OF OUR DAILY LIVES… From early civilization (population patterns) to migration A region’s climate controls the types of plants and crops that can grow there, and the type of animals that the plant life can support INTRODUCTION TO WEATHER AND CLIMATE OUR EXPERIENCE WITH WEATHER IS OFTEN CONFUSED WITH CLIMATE… Weather is the observable state of the atmosphere at any given time and place Climate, unlike weather, is a concept rather than an observable phenomenon. To make a complete description of your current climate, you need to consult historical weather records.  INTRODUCTION TO WEATHER AND CLIMATE According to Robert Heinlein: “ Climate is WHAT YOU EXPECT, like a very hot summer, and weather is WHAT YOU GET, like a hot day with an occasional rain and thunderstorms.” INTRODUCTION TO WEATHER AND CLIMATE WEATHER and CLIMATE The difference between weather and climate is a MEASURE OF TIME WEATHER - is what the condition of the atmosphere are over a short period of time. - in most places, weather can change from minute-to-minute, hour-to-hour, day-to-day, and season-to-season. CLIMATE - is the description of the long-term pattern of weather in a particular area. - Is the average weather for a particular region and time period, usually taken over 30 years. WHAT ARE THE INGREDIENTS THAT MAKE UP OUR WEATHER AND CLIMATE INTRODUCTION THE EARTH Surface area: 510,072,000 km² 148,940,000 km² land (29.2 %) 361,132,000 km² water (70.8 %) Shape: Oblique Spheroid Average distance from the sun: 149,597,887.5 km Rotation: 23 hours 56 minutes 4.1 seconds Famous "Blue Marble" photograph of Earth, taken from Apollo 17 Revolution: 365.256366 days INTRODUCTION THE EARTH TROPIC OF CANCER TROPIC OF CAPRICORN INTRODUCTION Atmospheric phenomena are represented in terms of a spherical coordinate system, rotating with the earth. The coordinates are: = latitude = longitude = distance from the center of the earth Wallace and Hobbs. 2006. Atmospheric Science: 2nd ed. INTRODUCTION THE EARTH’S SURFACE REALMS INTRODUCTION THE EARTH’S SURFACE REALMS Atmosphere An envelope of gases surrounding Earth that extends up to approximately 10,000 km above Earth's surface (the extreme edges of the atmosphere lie about 35,000 km above the surface). Composition of the Atmosphere Near the Earth’s Surface (Donald, 1998) Percent Gas (and Particles) Symbol (by Volume) Dry Air Nitrogen N2 78.08 Oxygen O2 20.95 Argon Ar 0.93 Permanent Gases Neon Ne 0.0018 Helium He 0.0005 Hydrogen H2 0.00006 Xenon Xe 0.000009 Water vapor H2O 0 to 4 Carbon dioxide CO2 0.036 Methane CH4 0.00017 Variable Nitrous oxide N2O 0.00003 Gases Ozone O3 0.000004 Aerosols (dust, soot, etc.) 0.000001 Chloroflourocarbons(CFCs) 0.00000002 Composition of the Atmosphere Near the Earth’s Surface (Barry and Chorley, 2003) 1. Primary gases Nitrogen 99 % Oxygen 2. Greenhouse gases CO2 O3 H 2O CH4 CFCs N 2O Hydrogenated halocarbons (HCFCs or HFCs) 3. Aerosols - particles that are 5µm in radius Properties of the Atmosphere ✓ made up of MOLECULES; has WEIGHT ; and occupies SPACE ✓ exerts pressure approximately 760 mmHg; 14.7 psi; 1013.25 mbar ✓ mobile  VERTICAL STRUCTURE OF THE ATMOSPHERE Atmospheric pressure and density http://rst.gsfc.nasa.gov/Sect14/Sect14_1a.html VERTICAL STRUCTURE OF THE ATMOSPHERE Atmospheric pressure and density AIR DENSITY It is the mass of the air molecules in a given volume of space the molecules are being pulled down by a strong, invisible force called gravity. gravity squeezes (compresses) air molecules closer together which causes their number in a given volume to increase. VERTICAL STRUCTURE OF THE ATMOSPHERE Atmospheric pressure and density Because of this, most (99%) of the atmosphere's mass lies within 30 km of Earth's surface.  VERTICAL STRUCTURE OF THE ATMOSPHERE Based on atmospheric pressure and density http://rst.gsfc.nasa.gov/Sect14/Sect14_1a.html VERTICAL STRUCTURE OF THE ATMOSPHERE Based on atmospheric pressure and density AIR PRESSURE As we increase our elevation, the air molecules decreases; hence, atmospheric pressure always decreases with increasing height. VERTICAL STRUCTURE OF THE ATMOSPHERE Based on atmospheric pressure and density If more molecules are packed together, it becomes more dense, the air weighs more, and the surface pressure goes up. (Ahrens, 1998) VERTICAL STRUCTURE OF THE ATMOSPHERE Based on atmospheric pressure and density It also obeys few simple gas laws in response to changes in pressure and temperature: Boyle’s Law Charles’ Law VERTICAL STRUCTURE OF THE ATMOSPHERE Based on atmospheric pressure and density Boyle’s Law - at a constant temperature, the volume (V) of a mass of gas varies inversely as its pressure (P) constant VERTICAL STRUCTURE OF THE ATMOSPHERE Based on atmospheric pressure and density Charles’ Law - at a constant pressure, the volume (V) of a mass of gas varies directly with absolute temperature (T) in degree Kelvin constant These laws imply that the 3 properties (pressure, temperature and volume) are completely interdependent. VERTICAL STRUCTURE OF THE ATMOSPHERE Based on atmospheric pressure and density When the 2 gas laws are combined they will give the following relationship: where m = mass of air R = gas constant It is convenient to use density, ρ (mass/volume), rather than volume when studying atmosphere: VERTICAL STRUCTURE OF THE ATMOSPHERE Based on atmospheric pressure and density Thus, at a given air pressure, an increase in air temperature causes a decrease in air density, and vice versa.  VERTICAL STRUCTURE OF THE ATMOSPHERE Based on atmospheric pressure and density Representation of the state of a working substance in a cylinder on a p–V diagram. The work done by the working substance in passing from P to Q is p dV, which is equal to the blue-shaded area. [Reprinted from Atmospheric Science: An Introductory Survey, 1st Edition, J. M. Wallace and P. V. Hobbs, p. 62, Copyright 1977, with permission from Elsevier.] VERTICAL STRUCTURE OF THE ATMOSPHERE Based on temperature profile  VERTICAL STRUCTURE OF THE ATMOSPHERE http://www.kowoma.de/en/gps/additional/atmosphere.htm  VERTICAL STRUCTURE OF THE ATMOSPHERE http://www.kowoma.de/en/gps/additional/atmosphere.htm VERTICAL STRUCTURE OF THE ATMOSPHERE TROPOSPHERE (turning or changing sphere) lowest region of the atmosphere. marked by generally decreasing temperature with height VERTICAL STRUCTURE OF THE ATMOSPHERE The rate at which the temperature decreases with height is called, temperature lapse rate (Ahrens, 1998) VERTICAL STRUCTURE OF THE ATMOSPHERE Occasionally, the air temperature may actually increase with height, producing a condition known as temperature inversion. VERTICAL STRUCTURE OF THE ATMOSPHERE TROPOSPHERE (turning or changing sphere) lowest region of the atmosphere. marked by generally decreasing temperature with height contains the greater part (approximately 75%) of the mass of the atmosphere. characterized by vertical air motions, clouds and weather  VERTICAL STRUCTURE OF THE ATMOSPHERE http://www.kowoma.de/en/gps/additional/atmosphere.htm VERTICAL STRUCTURE OF THE ATMOSPHERE TROPOPAUSE the elevation varies, higher during summer and lower in winter in all latitudes. TROPICS (low latitudes) and on the equator it is approximately 18 km above mean sea level. POLES (high latitudes) it is approximately 8 km above mean sea level. VERTICAL STRUCTURE OF THE ATMOSPHERE Isothermal layers VERTICAL STRUCTURE OF THE ATMOSPHERE VERTICAL STRUCTURE OF THE ATMOSPHERE STRATOSPHERE (stratified sphere) extends up to about 50-55 km and accounts for about 10% of the atmospheric mass. cloudless and calm air; ideal for jets and aircrafts. offers greater visibility and smooth flying conditions contains the ozone layer VERTICAL STRUCTURE OF THE ATMOSPHERE VERTICAL STRUCTURE OF THE ATMOSPHERE MESOSPHERE (middle sphere) air contains fewer oxygen molecules, even though the percentage of nitrogen and oxygen is the same as it was at the earth’s surface VERTICAL STRUCTURE OF THE ATMOSPHERE  VERTICAL STRUCTURE OF THE ATMOSPHERE THERMOSPHERE “hot layer” energetic solar radiation are used to break oxygen molecules apart into oxygen atoms (photodissociation), warming the air Image from: http://www.pollutiononline.com/article.mvc/Climate-Change-Affecting-Earths-Outermost-Atm-0001  photodissociation Depth of penetration of solar ultraviolet radiation in the Earth’s atmosphere for overhead sun and an average ozone profile. [Adapted from K. N. Liou, An Introduction to Atmospheric Radiation, Academic Press, p. 78, Copyright (2002), with permission from Elsevier.]  VERTICAL STRUCTURE OF THE ATMOSPHERE EXOSPHERE about or approximately 500 km (300 mi) above the earth’s surface. atoms and molecules shoot off into space upper limit of the atmosphere Image from: http://www.pollutiononline.com/article.mvc/Climate-Change-Affecting-Earths-Outermost-Atm-0001 VERTICAL STRUCTURE OF THE ATMOSPHERE Composition (Ahrens, 1998) IONOSPHERE not a layer but rather an electrified region. high solar radiation entering the thermosphere strips electrons from oxygen and nitrogen atoms creating free electrons (photoionization). high concentration of IONS these free electrons are capable of reflecting radio or sound waves.  photoionization Depth of penetration of solar ultraviolet radiation in the Earth’s atmosphere for overhead sun and an average ozone profile. [Adapted from K. N. Liou, An Introduction to Atmospheric Radiation, Academic Press, p. 78, Copyright (2002), with permission from Elsevier.] IONOSPHERE (Ahrens, 1998)  In summary, the earth and its atmosphere are dynamic systems that are constantly changing. While major transformations of the earth’s surface are completed after a long period of time, the state of the atmosphere can change in a matter of minutes. METEOROLOGY the study of the atmosphere and its phenomena (weather and climate) INTRODUCTION TO WEATHER AND CLIMATE WEATHER - which is always changing – is comprised of the elements of: Air temperature Visibility Humidity Wind Precipitation Atmospheric pressure Clouds WEATHER OR CLIMATIC CONTROLS OR FACTORS - acting at various intensities and combinations to produce the observed changes in the weather and climate elements: Latitude Wind and Air masses Altitude Low and high pressure cells Land and Water distribution INTRODUCTION THE EARTH Other facts: PARALLELISM - consistent inclination of the earth’s axis of spin with respect to the plane of its orbit PARALLELISM + SHAPE OF THE EARTH + EARTH’S MOTION TO ITS AXIS ✓ Distribution of solar energy ✓ Seasonal changes ✓ Day and night length variation INTRODUCTION THE EARTH Other facts: Schematic of the Earth’s orbital variations. The precession cycle in the tilt of the Earth’s axis is represented by a single cone; the cycle in the obliquity of the axis is represented by the presence of two concentric cones, and the extrema in the ellipticity of the orbit are represented by the pair of ellipses. The figure is not drawn to scale. [Adapted from J. T. Houghton, Global Warming: The Complete Briefing, 2nd Edition, Cambridge University Press, p. 55 (1997).] INTRODUCTION THE EARTH Other facts: 100,000-year cycle in eccentricity (the degree of ellipticity, defined as the distance from the center to either focus of the ellipse divided by the length of the major axis), which ranges from 0 to 0.06 and is currently 0.017, 41,000-year cycle in the obliquity (i.e., the tilt of the Earth’s axis of rotation relative to the plane of the Earth’s orbit) which ranges from 22.0° to 24.5° and is currently 23.5°, and 23,000- and 19,000-year cycles in the precession of the Earth’s orbit. As a result of the precession cycle, the day of the year on which the Earth is closest to the sun (currently January 3) progresses through the year at a rate of 1.7 calendar day per century Wallace and Hobbs. 2006. Atmospheric Science: 2nd ed. INTRODUCTION THE EARTH INTRODUCTION THE EARTH Autumnal Equinox Summer Solstice Winter Solstice Vernal Equinox INTRODUCTION THE EARTH SOLSTICE The name is derived from the Latin sol (sun) and sistere (to stand still), because at the solstices, the Sun stands still in declination; that is, the apparent movement of the Sun's path north or south comes to a stop before reversing direction. INTRODUCTION THE EARTH EQUINOX The name "equinox" is derived from the Latin aequus (equal) and nox (night), because around the equinox, the night and day are approximately equally long. INTRODUCTION THE EARTH This is a file from the Wikimedia Commons. INTRODUCTION THE EARTH This is a file from the Wikimedia Commons. INTRODUCTION THE EARTH This is a file from the Wikimedia Commons. INTRODUCTION THE EARTH The Summer Solstice: (around June 21st) It is the longest day of the year in the Northern Hemisphere It is the shortest day of the year in the Southern Hemisphere The sun rises north of east and sets north of west Summer begins in the Northern Hemisphere Winter begins in the Southern Hemisphere INTRODUCTION THE EARTH W S N E INTRODUCTION THE EARTH http://rst.gsfc.nasa.gov/Sect14/Sect14_1a.html INTRODUCTION THE EARTH The Autumn Equinox (around September 23rd) Twelve hours of darkness and twelve hours of light all over the earth The sun rises due east and sets due west Autumn begins in the Northern Hemisphere Spring begins in the Southern Hemisphere INTRODUCTION THE EARTH The Winter Solstice: (around December 21st) It is the shortest day in the Northern Hemisphere It is the longest day in the Southern Hemisphere The sun rises south of east and sets south of west Winter begins in the Northern Hemisphere Summer begins in the Southern Hemisphere INTRODUCTION THE EARTH The Vernal Equinox (around March 21st) Twelve hours of daylight and twelve hours of darkness all over the earth The sun rises due east and sets due west Spring begins in the Northern Hemisphere Autumn begins in the Southern Hemisphere http://www.windows.ucar.edu/tour/link=/earth/Atmosphere/earth_atmosph_radiation_budget.html GENERAL ATMOSPHERIC CIRCULATION - general picture of the atmospheric motion. - the average flow of air over the entire globe. - determined by averaging wind observations over a long period of time – 20 years or more. - responsible for the development and displacement of most small-scale weather systems; complex wind patterns and pressure belts. GENERAL ATMOSPHERIC CIRCULATION What causes air to move? GENERAL ATMOSPHERIC CIRCULATION Unequal distribution of heat energy in the atmosphere GENERAL ATMOSPHERIC CIRCULATION Unequal distribution of heat energy.. SOLSTICES GENERAL ATMOSPHERIC CIRCULATION Solar heat energy is concentrated most strongly at the equator and decreases polarward. GENERAL ATMOSPHERIC CIRCULATION Overall the system is in radiative balance, various geographic areas and surface types are heated differentially. That is, some areas absorb and emit more or less heat than other areas, giving rise to localized energy surpluses and deficits. GENERAL ATMOSPHERIC CIRCULATION On a broad global view, at latitudes higher than 37 degrees, more radiant energy is lost to space each year than is received, while at lower latitudes, more energy is gained from the sun than is returned to space as heat Annualized energy balance by latitude GENERAL ATMOSPHERIC CIRCULATION If this is true, what will happen? GENERAL ATMOSPHERIC CIRCULATION If there were no heat transferred between the tropics and the polar regions, the tropics would get hotter and hotter, while the poles would get colder and colder. GENERAL ATMOSPHERIC CIRCULATION 3 MECHANISMS OF HEAT TRANSFER WITHIN THE EARTH- ATMOSPHERE SYSTEM: Radiation Electromagnetic waves transfer energy (both heat and light) between two bodies, without the necessary aid of an intervening material medium, at a speed of 300x106 m s–1 (i.e. the speed of light). GENERAL ATMOSPHERIC CIRCULATION 3 MECHANISMS OF HEAT TRANSFER WITHIN THE EARTH- ATMOSPHERE SYSTEM: Radiation Wavelength, frequency, and wave number are used alternatively in characterizing radiation.  SHORTWAVE RADIATION < 4 µm LONGWAVE RADIATION > 4 µm http://www.windows.ucar.edu/tour/link=/earth/Atmosphere/earth_atmosph_radiation_budget.html  GENERAL ATMOSPHERIC CIRCULATION 3 MECHANISMS OF HEAT TRANSFER WITHIN THE EARTH- ATMOSPHERE SYSTEM: Radiation The electromagnetic spectrum Wallace and Hobbs. 2006. Atmospheric Science: 2nd ed. GENERAL ATMOSPHERIC CIRCULATION 3 MECHANISMS OF HEAT TRANSFER WITHIN THE EARTH- ATMOSPHERE SYSTEM: Conduction heat passes through a substance from a warmer to a colder part through the transfer of adjacent molecular vibrations. Convection occurs in fluids (including gases) that are able to circulate internally and distribute heated parts of the mass. GENERAL ATMOSPHERIC CIRCULATION 3 MECHANISMS OF HEAT TRANSFER WITHIN THE EARTH- ATMOSPHERE SYSTEM: Convection transfer energy in 2 forms: Sensible heat Latent heat GENERAL ATMOSPHERIC CIRCULATION This latitudinal heat imbalance is what drives the circulation of the atmosphere and oceans: the heat energy is redistributed from warmer to colder areas by means of atmospheric air circulation (60%) and ocean currents (40%). GENERAL ATMOSPHERIC CIRCULATION Highly simplified schematic of the thermohaline circulation. Shading denotes regions of downwelling, blue arrows denote transport of bottom water, and red arrows denote the return flow of surface water. [Adapted from W. J. Schmitz, Jr., “On the interbasin-scale thermohaline circulation,” Rev. Geophys.,33, p. 166, Copyright 1995 American Geophysical Union.] GENERAL ATMOSPHERIC CIRCULATION In the process of heat redistribution, the winds of the globe and the storms are generated ( Donn, 1975) GENERAL ATMOSPHERIC CIRCULATION In during 1680s, according to Edmund Halley; GENERAL ATMOSPHERIC CIRCULATION Which means that the air is warm near the earth’s surface, and warm air rises… http://rst.gsfc.nasa.gov/Sect14/Sect14_1a.html GENERAL ATMOSPHERIC CIRCULATION http://www.kidsgeo.com/geography-for-kids/0045-why-is-the-sky-blue.php but the temperature decreases with altitude, so… GENERAL ATMOSPHERIC CIRCULATION Pressure = temperature x density x constant (Ahrens, 1998. Essentials of Meteorology:2nd ed.) GENERAL ATMOSPHERIC CIRCULATION A simplified description of atmospheric circulation is as follows: (1) the atmosphere is heated more around the equator, (2) the warming air is less dense and rises, and (3) the rising tropical air gets replaced by cooler, denser air moving down GENERAL ATMOSPHERIC CIRCULATION What are the forces that cause the air to move? GENERAL ATMOSPHERIC CIRCULATION NEWTON’S LAW OFMOTION 1st Law A body (air) moves when acted upon by an unbalanced force GENERAL ATMOSPHERIC CIRCULATION NEWTON’S LAW OFMOTION 2nd Law The acceleration of such body (air) is proportional to the magnitude of the unbalanced force acting on it F = ma a = F/m GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES ACTING ON A BODY (AIR) (Barry and Chorley, 2003) ✓ Force due to PRESSURE GRADIENTS ✓ Deflective force due to earth’s rotation – CORIOLI’S FORCE ✓ Force due to FRICTION ✓ Force due to CENTRIPETAL ACCELERATION UNBALANCED FORCES PRESSURE GRADIENTS PRESSURE - force exerted by a mass of air on a unit of area. GRADIENT - a change in a certain property (pressure) with distance. Air pressure gradient exists whenever air pressure changes from one place to another. GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES PRESSURE GRADIENTS What causes air pressure gradients? GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES PRESSURE GRADIENTS air temperature variations (differential heating) = warm to cold water vapor concentration variations = humid to dry air combination = warm + humid air to cold + dry air GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES PRESSURE GRADIENTS The atmosphere obeys the gas law… Pressure = temperature x density x constant If we apply this concept to the atmosphere, then assume the temperature is constant… The air above a region of surface high pressure is more dense than air above a region of surface low pressure. GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES PRESSURE GRADIENTS The atmosphere obeys the gas law… Pressure = temperature x density x constant If we apply this concept to the atmosphere, then assume the pressure is constant… Air that is cold is more dense (heavier) than warm air (lighter) GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES PRESSURE GRADIENTS TYPES OF PRESSURE GRADIENTS VERTICAL PRESSURE GRADIENT - permanent feature of the atmosphere because air pressure is greatest on earth’s surface and decreases with altitude. - in balance with the force of gravity. - convective circulation GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES PRESSURE GRADIENTS TYPES OF PRESSURE GRADIENTS HORIZONTAL PRESSURE GRADIENT - differences in pressure arise from thermal heating contrasts or mechanical causes such as mountain barriers and these differences control the horizontal movement of an air mass. - it is expressed mathematically as: GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES PRESSURE GRADIENTS TYPES OF PRESSURE GRADIENTS HORIZONTAL PRESSURE GRADIENT Fick’s Law where, = density of air dp = change in pressure n = distance GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES PRESSURE GRADIENTS TYPES OF PRESSURE GRADIENTS HORIZONTAL PRESSURE GRADIENT Analysis of the horizontal pressure gradient is done in two ways: 1) Sea-level condition 2) Upper-air condition GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES PRESSURE GRADIENTS HORIZONTAL PRESSURE GRADIENT 1) Sea-level condition - isobars, or lines of equal surface pressure, are drawn. SLOW WIND FAST WIND GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES PRESSURE GRADIENTS HORIZONTAL PRESSURE GRADIENT ISOBARIC ANALYSIS is important to locate centers of high and low pressure and as well as determine the magnitude of horizontal air pressure gradients GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES PRESSURE GRADIENTS HORIZONTAL PRESSURE GRADIENT Surface Weather Map (Ahrens, 1998. Essentials of Meteorology:2nd ed.) GENERAL ATMOSPHERIC CIRCULATION  December 1, 2010 8am December 2, 2010 8am Predicted Mean Sea Level Pressure Analysis (Public Weather Forecast, PAGASA) UNBALANCED FORCES If the pressure gradient force were the only force acting upon air, we would always find winds blowing directly from higher toward lower pressure. However, the moment air starts to move, it is deflected in its path by the Coriolis force (Ahrens, 1998). GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES CORIOLIS FORCE The CORIOLIS FORCE arises from the fact that the movement of masses over the earth’s surface is referenced to a moving co-ordinate system (i.e. the latitude and longitude) (Ahrens, 1998. Essentials of Meteorology:2nd ed.) This apparent force is called the Coriolis force after Gaspard Coriolis, a nineteenth-century French scientist who worked it out mathematically. GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES CORIOLIS FORCE With respect to the earth and air movement: Fc = - 2V sin  where; V = wind speed  = angular velocity of spin (15° hr-1 or 2π/24 rad hr-1 for the earth = 7.29 x 10-5 rad/sec  = latitude GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES CORIOLIS FORCE Fc = - 2V sin  The magnitude of the deflection is directly proportional to: (1) the horizontal velocity of the air, and (2) the sine of the latitude (sin 0 = 0; sin 90 = 1). GENERAL ATMOSPHERIC CIRCULATION  UNBALANCED FORCES CORIOLIS FORCE (Ahrens, 1998. Essentials of Meteorology:2nd ed.) GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES CORIOLIS FORCE GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES CORIOLIS FORCE The Coriolis force causes the wind to deflect to the right of its intended path in the Northern Hemisphere and to the left of its intended path in the Southern hemisphere. GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES CORIOLIS FORCE GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES CORIOLIS FORCE GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES FRICTIONAL FORCE - resists wind movement especially those that are close to the ground (up to 1km height). Geostrophic wind (Ahrens, 1998. Essentials of Meteorology:2nd ed.) GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES FRICTIONAL FORCE Geostrophic wind - idealized case - the velocity of the wind at this condition is given by the equation: (Barry and Chorley, 2003) GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES FRICTIONAL FORCE (Ahrens, 1998. Essentials of Meteorology:2nd ed.) GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES FRICTIONAL FORCE GENERAL ATMOSPHERIC CIRCULATION UNBALANCED FORCES CENTRIPETAL ACCELERATION For a body to follow a curved path there must be an inward acceleration (c) towards the centre of rotation. m = moving mass V = velocity r = radius of curvature GENERAL ATMOSPHERIC CIRCULATION  Air, as we have seen, is acted upon by four UNBALANCED FORCES: PRESSURE GRADIENT CORIOLI’S FORCE FRICTION CENTRIPETAL ACCELERATION so as to rise, move laterally, and fall depending on its density GENERAL ATMOSPHERIC CIRCULATION  The air above a region of surface high pressure is more dense than air above a region of surface low pressure… Air that is cold is more dense (heavier) than warm air (lighter)… THERMAL CIRCULATION GENERAL ATMOSPHERIC CIRCULATION  The air above a region of surface high pressure is more dense than air above a region of surface low pressure… Air that is cold is more dense (heavier) than warm air (lighter)… THERMAL CIRCULATION GENERAL ATMOSPHERIC CIRCULATION