Weather and Climate PPT

TOPIC 1 WEATHER AND CLIMATE By the end of the unit ,you should be able to ► Define weather and climate ► Distinguish between weather and climate ► List elements of weather ► Describe instruments used to measure weather elements ► Read and record weather data ► Outline elements of weather and climat...

TOPIC 1 WEATHER AND CLIMATE By the end of the unit ,you should be able to ► Define weather and climate ► Distinguish between weather and climate ► List elements of weather ► Describe instruments used to measure weather elements ► Read and record weather data ► Outline elements of weather and climate ► Discuss some factors affecting weather and climate WEATHER ELEMENTS AND INSTRUMENTS ► WHAT IS WEATHER AND CLIMATE?  New word ► Weather is the state of the atmosphere over a short period of time. ► Simply put, it is the daily conditions of the atmosphere ► When discussing weather ,we consider elements such as temperature,humidity,pressure,rainfall etc. ► E.g.on a particular day we may say that the weather tat the weather is hot or cold,rainy or sunny etc ► Weather conditions are observed over short periods of time and have daily influence on our lives Weather conditions CLIMATE ► It is the pattern of weather of a place over a long period of time ► To determine the climate of a particular place,weather conditions are recorded on a daiy basis over a certain period of time(usually 30 years and above) ► From this data, patterns begin to form where the weather experienced is roughly the same over certain periods of the year. ► E.g you may notice that it is colder in June than other months of the year or it rains from November to March. ► Whilst weather is a short term occurrence ,climate takes a longer consideration of the average weather conditions of a geographical area. ► An area can be hot on specific days but on average ,the climate of that area may not necessarily be hot. ► The difference between weather and climate is based on time considerations  DIFFERENCES BETWEEN WEATHER AND CLIMATE ► Weather refers to the short-term ► Climate refers to the long-term average of atmospheric conditions in a specific weather patterns observed over a specific location or region, typically over hours, region, typically over decades or centuries. days, or weeks. ► 2. It involves variables such as ► 2. It encompasses the statistical analysis of temperature, humidity, precipitation, wind weather variables such as temperature, speed and direction, cloud cover, and precipitation, and wind patterns over an atmospheric pressure.. extended period. ►. Climate change refers to significant ► 3. Weather forecasts are predictions of alterations in average weather conditions and future weather conditions based on patterns over an extended period, often current atmospheric data and computer resulting from natural processes or human models. activities. ELEMENTS OF WEATHER ► To determine weather conditions ,we need to understand weather elements ► These weather elements are ► Temperature sunshine ► Pressure cloud cover ► Humidity wind speed and direction ► Rainfall ► We will discuss how these are measured using various weather instruments 1.TEMPERATURE ► It describes how hot or cold a place is at a given time. ► It is the degree of hotness or coldness of the air. ► The main factor that influences temperature is the angle of the sun. ► This element is measured the maximum and minimum thermometer or a Six's thermometer and is measured in degrees Celsius(⁰C) ► When we cannot go outside to play because it is too hot or when we put on our jerseys because it is too cold,that’s temperature. ► On a map ,lines that join places of the same temperature are called ISOTHERMS  Isotherms are lines joining places of the same temperature ► The lowest temperature recorded is called the minimum temperature ► The highest recorded temperature is called maximum temperature ► The temperature range is calculated by subtracting the daily minimum temperature from the maximum temperature e.g if the highest recorded temperature was 30 and the lowest was 19 the daily range will be 11 Page 6 there is a table with temperature readings  ► Mean temperature is the average temperature of the atmosphere as indicated CALCULATIN by a properly exposed thermometer during a given period,usually a day,month,or year G ► Daily average temperature/mean TEMPERATU temperature is calculated by adding the maximum and minimum temperature and RE then divide by two. ► The weekly average is calculated by summing up the daily averages and dividing by seven ► The average temperature of the month is calculated by adding the daily averages for the whole month and then dividing this by the number of days in the month. Measuring temperature ► Temperature is measured in two ways that is using ► Sixs thermometer ► Or using separate maximum and minimum thermometers ► The sixs thermometer combines a maximum and a minimum thermometer in the same device ► It is housed in a Stevenson screen and temperature readings are done on a daily basis ► The sixs thermometr is a single instrument with a U shape ► The right hand side is the maximum side which records the maximum temperature ► The left hand side is the minimum side that measures the lowest temperature reached When the temperature increases alcohol in the left bulb expands and pushes the mercury in the U shaped bend towards the right tube where there is vacuum bulb. The vacuum bulb's purpose is to allow mercury to be pushed towards it when alcohol expands in the right tube. The index (which functions as an indicator) is pushed by the mercury up to the point where the highest recording for that day is taken. When the temperature falls the mercury contracts back in the bulb leaving the index up and that will be highest temperature reading. ► When the temperature drops,the alcohol contracts,drawing the mercury up on the minimum side. ► Alcohol pulls the metal index with its meniscus. On both sides the alcohol measures the temperature whilst the mercury displays it ⮚ As the temperature changes ,the metal indices will remain in their new positions unless the temperature becomes higher or lower than already recorded. ⮚ In sixs thermometer ,the expansion of alcohol indicates the temperature changes ► After the recording is done,the sixs thermometer must be reset with a magnet,which pulls the metal indices back to their original positions. ► The bulb at the top of the minimum scale is full of alcohol ,whilst the bulb at the top of the maximum scale is a vacuum. ► The empty bulb allows the free movement of mercury and alcohol 2. Mean Monthly Temperature This is calculated by adding all mean daily temperatures for the month and dividing by the number of days in the month. 3. Mean Annual Temperature We add mean monthly temperatures and divide by twelve months of the year 4. Daily or Diurnal Temperature Range It is the difference between maximum and minimum temperatures of the day. i.e. maximum - minimum = daily temperature range 5. Monthly Temperature Range It is the highest mean daily temperature minus the lowest mean daily temperature 6. Annual Temperature Range We get by obtaining the month with the highest mean monthly temperature and subtracting the lowest mean monthly temperature. HUMIDITY ∙ Humidity is the amount of water vapour in the atmosphere. ∙ Relative humidity is the amount of moisture in the air compared to the maximum amount that the air can hold at that temperature. ∙ It is, therefore, expressed as a percentage. ∙ The water vapour in the air comes mainly from evaporation. Air is said to be saturated when it holds the maximum amount of water it can at a particular temperature. ► Humidity is measured by an instrument called a hygrometer, also known as a wet and bulb thermometer ► This is kept in a Stevensons screen ∙ When the air is dry the muslin cloth/sleeve will soak water from the container, becomes wet and will cool the bulb. ∙ The other thermometer which has no muslin cloth records the atmospheric temperature as it is without any cooling effect. ∙ The difference between the two temperature readings shows how humid the atmosphere is. ∙ When there is no difference in the temperatures of the two thermometers it means the air is saturated. ∙ Relative humidity will thus be 100%. ∙ A small difference implies that humidity is very high and the air is moist. ∙ A large difference indicates that the air is dry and humidity is very low.  MEASUREMENT OF WIND ∙ Wind is air in motion. ∙ Wind has direction and speed. ► We name a wind after the direction it is blowing from:if a wind is blowing from the north it is a north wind ► We measure wind direction with an instrument called a wind vane and the wind vane uses the points of the compass ► The wind pushes against the tail of the arrow swings parallel to the wind ► The arrow points in the direction that the wind has blown from ► Wind vanes are often placed on top of buildings so that they are fully exposed to the wind. ► We use the eight compass points to record wind direction ► Winds that blow for long periods from one direction are known as prevailing winds  WIND ROSE ∙ The daily wind direction is recorded on a wind rose (see diagrams of wind roses below). ∙ The boxes are marked according to the number of days the wind blew from that direction. ∙ The number of calm days is written on the centre of the wind rose. ► The Wind Rose Above Shows: ∙ The wind rose above has the following data of the month. ∙ There were 4 calm days recorded. ∙ 1 day of South Easterly wind. ∙ 9 days of Southerly wind. ∙ 8 days South westerly wind. ∙ 3 days Westerly wind. ∙ 6 days North Westerly wind. ► 3 days Easterly wind.  Cup anemometer ► Anemometers measure wind speed. ► Wind speed is normally measured in mph or kph, but can also be measured in m/s (metres a second). ► This instrument usually has three or four horizontal arms with little metal cups at the end ,which are fixed to rotating vertical shaft. ► The cups catch the wind and this spins the shaft ,which can be connected to a meter or speedometer ► Digital anemometers are very accurate, but the more basic plastic ones that many schools have aren't very good or accurate at recording light winds. ► Anemometers are normally placed on top of buildings so that they are not protected from the wind and so they don't experience channeling of wind e.g. if an anemometer was placed in a corridor where wind was forced through the readings would be higher than normal.  PRESSURE ► This is the “weight” of the atmosphere on a surface at a particular place and time ► Air has weight and it exerts the weight on Earth and this is what constitutes atmospheric pressure. ► A simple demonstration of atmospheric pressure at work is shown when we drink a liquid with a straw.When air is sucked out of the straw,atmospheric pressure pushes the liquid up ► The height above sea level is called altitude ,it has a great impacton atmospheric pressure ► Pressure decreases as altitude increases because the weight of the atmosphere becomes less dense. ► Pressure is measured in millibars on a barometer ► There are different types of barometers and the two that are commonly used are mercury and aneroid barometers. How the mercury barometer works A graduated glass tube is placed in a jar of mercury.The pressure of the air on the exposed mercury forces it to raise the tube When pressure rises,the mercury rises in the glass tube and when it falls,the mercury drops The reading is taken from the scale of the height reached by the mercury ► HOW THE ANEROID BAROMETER WORKS ► It has a corrugated metal box,which expands when pressure is low and is compressed when the pressure is high. ► The changes in the box are transmitted by a series of lever systems to a pointer that moves on the face of the dial.  SUNSHINE ► Sunshine duration (also referred to as sunlight hours) is simply the length of time that the Earth’s surface is exposed to solar radiation. ► This element of weather is normally measured in hours per day or per year. ► Sunshine duration influences other elements of weather like temperature, humidity, and air pressure as well. ► Sunshine is measured using a sunshine recorder which consists of a spherical glass fixed into a spherical bowel, with a metallic groove that holds a record card. ► The sun’s rays are refracted ,they strike on the record card beneath the glass sphere ► The resulting burnt marks on the card are then used to measure the intensity and duration of sunshine. ► The sunshine recorder should be placed in an area where the sun will not be blocked by buildings or trees. ► It should also be placed to face the sun directly ► The amount of sunlight reaching the surface is called insolation,and is affected by the time of the day,time of the year and cloud cover. ►\ ► RAINFALL ► Rainfall is measured using an instrument called a rain gauge ► The unit measurement for rainfall is millimetres. ∙ The rain gauge is made of copper to prevent corrosion. ∙ The rain gauge should be located far from buildings and trees and it should set up 30cm above the ground to avoid water from splashing in. ► On a map lines joining places of the same rainfall amount are called isohyets  HOW IT WORKS ► During rainfall the funnel of the rain gauge channels the water into the collecting can ► The collected water is then poured into a measuring cylinder ► The amount of collected water is then measured to determine the amount of rainfall received over a specific period of time in millimetres ► Measurement is done every 24 hours ► When there is too much rainwater to fill up the collecting can,the excess is collected in the overflow can and then measured together with what has been collected