2. The study of weather = METEROLOGY The study of weather = METEROLOGY Weather is the condition of the atmosphere at any given time or place Weather is the condition of the atmosphere at any given time or place Much of weather forecasting and prediction can be accomplished by direct observation – LOOK OUT THE WINDOW!! Much of weather forecasting and prediction can be accomplished by direct observation – LOOK OUT THE WINDOW!! To predict weather, you must make observations of the clouds, wind, temperature, humidity, air pressure and precipitation To predict weather, you must make observations of the clouds, wind, temperature, humidity, air pressure and precipitation

4. Atmospheric Composition The Earth’s atmosphere is made up of many gases, but it is mostly nitrogen and oxygen (Reference Tables) The Earth’s atmosphere is made up of many gases, but it is mostly nitrogen and oxygen (Reference Tables) It also contains water vapor, dust, and ozone – O 3 (a form of oxygen which absorbs UV rays from the sun) It also contains water vapor, dust, and ozone – O 3 (a form of oxygen which absorbs UV rays from the sun) As you go higher in the atmosphere, the amount of air and air pressure (weight of air) decreases As you go higher in the atmosphere, the amount of air and air pressure (weight of air) decreases

6. Structure of the Atmosphere made up of four layers, each with different characteristics (Reference Tables) made up of four layers, each with different characteristics (Reference Tables) Troposphere- lowest layer (we live in this layer). All of Earth’s weather occurs in the troposphere. Temperature decreases as you go higher. Troposphere- lowest layer (we live in this layer). All of Earth’s weather occurs in the troposphere. Temperature decreases as you go higher. Stratosphere- above the troposphere, has strong winds. Temperature increases as you go higher because of the absorption of UV rays by ozone. Stratosphere- above the troposphere, has strong winds. Temperature increases as you go higher because of the absorption of UV rays by ozone. Mesosphere- above the stratosphere. Temperature decreases as you go higher. Mesosphere- above the stratosphere. Temperature decreases as you go higher. Thermosphere- above the mesosphere. Temperature increases as you go higher due to oxygen and nitrogen absorbing solar energy Thermosphere- above the mesosphere. Temperature increases as you go higher due to oxygen and nitrogen absorbing solar energy

7. ESRT PAGE 14

8. ATMOSPHERIC VARIABLES things that can be measured and change from moment to moment things that can be measured and change from moment to moment – Temperature – Air Pressure – Wind Speed and Direction – Water Content & Humidity – Cloud Cover – Precipitation – Others (dust, transparency, pollen, etc)

9. TEMPERATURE Measures the average kinetic energy of molecules. Measures the average kinetic energy of molecules. Heat enters the atmosphere from the sun as solar radiation (Insolation) Heat enters the atmosphere from the sun as solar radiation (Insolation) Average Kinetic Energy- kinetic energy is the energy of motion Average Kinetic Energy- kinetic energy is the energy of motion The temperature of any material is an average of all of the kinetic energies- hence Average Kinetic Energy

10. 3 ways to Measure temperature: Fahrenheit – Water freezes at 32° – Water boils at 212° Celsius – AKA Centigrade (100 levels) – Water freezes at 0° – Water boils at 100° – Makes more sense and is easier to make a thermometer Kelvin – Same scale as Celsius but 0 means zero energy – No degrees mark for Kelvin – 0K means that all atomic vibrations stop.

12. Air Pressure the weight of the air in a certain area the weight of the air in a certain area Sinking air pushes down more- cold air is usually high pressure Sinking air pushes down more- cold air is usually high pressure Rising air pushes down less- hot air is usually low pressure Rising air pushes down less- hot air is usually low pressure Air pressure is measured using an instrument called a barometer Air pressure is measured using an instrument called a barometer It is measured in inches (height of the mercury column in the barometer), or with the metric units called millibars It is measured in inches (height of the mercury column in the barometer), or with the metric units called millibars Use your reference tables for converting inches to millibars Use your reference tables for converting inches to millibars

14. Air pressure drops with increasing altitude (less air) Air pressure drops with increasing altitude (less air) Weather maps show sea level air pressure Weather maps show sea level air pressure It ranges from 960mb – 1050mb It ranges from 960mb – 1050mb Isobars are lines on the weather maps which connect areas of equal air pressure Isobars are lines on the weather maps which connect areas of equal air pressure

16. Changes in Air Pressure Temperature- warm air is lighter than cold air! Temperature- warm air is lighter than cold air! Humidity- humid (moist) air is lighter than dry air!! Water vapor (H 2 O) weighs less than the N and O gases that it pushed out Humidity- humid (moist) air is lighter than dry air!! Water vapor (H 2 O) weighs less than the N and O gases that it pushed out Winds are caused by the unequal heating of the atmosphere (remember that temperature causes changes in air pressure) Winds are caused by the unequal heating of the atmosphere (remember that temperature causes changes in air pressure)

17. Water Vapor in the Air The amount of water vapor in the air depends on the air temperature The amount of water vapor in the air depends on the air temperature The warmer the air, the more water vapor it can hold (think of those hot, humid summer days) The warmer the air, the more water vapor it can hold (think of those hot, humid summer days) The actual amount of water vapor in the air is called specific humidity The actual amount of water vapor in the air is called specific humidity

18. Relative Humidity the amount of water vapor in the air, compared to how much water vapor it could hold at that temperature the amount of water vapor in the air, compared to how much water vapor it could hold at that temperature Relative humidity is a percent measurement Relative humidity is a percent measurement Air with 100% humidity is said to be saturated Air with 100% humidity is said to be saturated – Precipitation will occur

20. Finding Relative Humidity use an instrument called a hygrometer use an instrument called a hygrometer One particular type of hygrometer is called a sling psychrometer One particular type of hygrometer is called a sling psychrometer – This instrument is made of two thermometers attached two a handle – One thermometer has a piece of gauze which is the soaked with water - This is called the WET BULB The other thermometer is called the DRY BULB The other thermometer is called the DRY BULB – These thermometers are swung in the air for a few minutes, and then the temperatures are recorded (take the wet bulb temperature first) The wet bulb thermometer should have a lower temperature, since it removes heat from the thermometer as water evaporates from it The wet bulb thermometer should have a lower temperature, since it removes heat from the thermometer as water evaporates from it The two temperatures are then used to look up the relative humidity on a chart (Reference Tables) The two temperatures are then used to look up the relative humidity on a chart (Reference Tables)

21. Interactive Site - http://www.eram.k12.ny.us/education/sctemp/12345/1269020 014/rhdp.swf

22. Condensation and Dew remember that air’s ability to hold moisture decreases as the temperature decreases remember that air’s ability to hold moisture decreases as the temperature decreases As the air cools, its relative humidity increases As the air cools, its relative humidity increases When the relative humidity reaches 100% (saturated), the water comes out of the air as liquid droplets When the relative humidity reaches 100% (saturated), the water comes out of the air as liquid droplets The temperature at which this will occur is called the dew point The temperature at which this will occur is called the dew point **The dew point can be found using the same method for relative humidity, except use the dew point chart (Reference Tables) **The dew point can be found using the same method for relative humidity, except use the dew point chart (Reference Tables)

23. Condensation can only occur if the water has something to condense on Condensation can only occur if the water has something to condense on Tiny particles in the air on which water condenses is called condensation nuclei Tiny particles in the air on which water condenses is called condensation nuclei This can be dust, salts, chemicals from burning fuel, etc. This can be dust, salts, chemicals from burning fuel, etc. * Water vapor that condenses on the ground is called dew (think of walking across wet grass in the morning) * Water vapor that condenses on the ground is called dew (think of walking across wet grass in the morning) If the dew freezes on the ground, it is called frost If the dew freezes on the ground, it is called frost Water vapor condensing in the air forms clouds Water vapor condensing in the air forms clouds If the cloud forms close to the ground, it is called fog If the cloud forms close to the ground, it is called fog Condensation and Dew

24. Interactive Site - http://www.eram.k12.ny.us/education/sctemp/12345/126902 0469/rhdp.swf

25. Try These… Dry BulbWet BulbR HumidityDPT 26°C20 °C 6 °C5 °C 12 °C8 °C 18 °C17 °C 14 °C 0 °C-3 °C 57% °C 17 °C 86% °C 4 °C 57% °C 4 °C 91% °C 16 °C 100% °C 14 °C 45% °C -9 °C