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AVIATION 120

. WACN31 CWLW 311534 AIRMET D1 CANCELLED AT 1533Z CWLW- AMEND GFACN31 CWUL 311145 ISSUE AIRMET D1 ISSUED IN ERROR. REFER TO WACN35 CWLW AIRMET M2. END/AM/CMAC-W WACN35 CWLW 311447 AIRMET M2 ISSUED AT 1447Z CWLW- AMEND GFACN35 CWUL 311145 ISSUE WTN 45 NM OF LN /6045N12546W/110N MUNCHO LAKE - /6043N14041W/165W WHITEHORSE. AIRMET M1 ISSUED IN ERROR. REFER TO AIRMET M2. ADD..VC LRG LKS LCL ST CIGS 5-10 AGL WITH 3SM BR. NIL CHG EXPD. END/AM/CMAC-W .

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AVIATION 120

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    1. AVIATION 120 Meteorology

    2. WACN31 CWLW 311534 AIRMET D1 CANCELLED AT 1533Z CWLW- AMEND GFACN31 CWUL 311145 ISSUE AIRMET D1 ISSUED IN ERROR. REFER TO WACN35 CWLW AIRMET M2. END/AM/CMAC-W WACN35 CWLW 311447 AIRMET M2 ISSUED AT 1447Z CWLW- AMEND GFACN35 CWUL 311145 ISSUE WTN 45 NM OF LN /6045N12546W/110N MUNCHO LAKE - /6043N14041W/165W WHITEHORSE. AIRMET M1 ISSUED IN ERROR. REFER TO AIRMET M2. ADD..VC LRG LKS LCL ST CIGS 5-10 AGL WITH 3SM BR. NIL CHG EXPD. END/AM/CMAC-W

    3. Todays Agenda NOTICE: There will be a quiz next week. Chapters 1,2,3,4 in meteorology today, chapters 1,2,3 in air command weather manual, and all associated slides. Atmospheric Heating (continued) Daily Temperatures Solar and Earth radiation, Wind, Cloud, Terrain Temperature Controls Measuring the temperature Impact on aviation Atmospheric Cooling Radiational cooling Nocturnal inversions Impact of wind, cloud, terrain, large bodies of water Evaporative cooling Advective cooling Adiabatic processes Expansion/compression Adiabatic lapse rates Expansion cooling processes Temperature and human comfort

    4. Daily Temperatures Recall from previous class: Incoming shortwave radiation energy from the sun reaches a maximum about noon each day Outgoing longwave radiation energy from the earths surface is emitted 24 hours a day Daily maximum and minimum temperatures occur about 16:00 and 06:00 respectively due to the interaction between the incoming and outgoing radiation curves as shown here Note the daily temperature tends to follow the outgoing energy curve the atmosphere is primarily heated from below by the outgoing longwave radiation

    5. Daily Temperatures (cont.) The timing of daily maximum temperature can vary due to cloud cover, proximity to large bodies of water and even storms The magnitude of daily maximum temperature depends on the above factors as well as many other conditions such as ground vegetation, exposed soil type, ground moisture, local winds, altitude, latitude, season etc.

    6. Temperature Controls The main controls of temperature are: Latitude Land and water distrubution Ocean currents Elevation Latitude is the main control of temperature since the amount of incoming solar energy is distributed by latitude Note also how temperature is impacted by land versus ocean Ocean currents can increase the temperature of a high latitude more than would otherwise be expected: e.g. The Gulf Stream warms the UK more than other places of similar latitude with maritime climates Increased elevation tends to cause the temperature to be lower than would otherwise occur The following diagram depicts the average global temperature (in F) distribution in January:

    7. Measuring Temperature Temperature is measured by a thermometer which can be one of many types: Liquid in glass Maximum and Minimum thermometers Electrical Electrical resistance thermometers are used in AUTO stations Thermistors are used in radiosondes Thermocouple Radiometers Measure emitted IR radiation to determine temperature. Used in satellites Bimetallic Dissimilar metals are welded together and will cause a bending movement as each metal expands/contracts at a different rate with temperature change Thermograph Bimetallic thermometer attached to a pen and rotating drum to record temperature over time. Being replaced with data loggers

    8. Measuring Temperature (cont.) Temperature must be measured in the shade! Why? Shading the thermometer is an important function for the Stevenson Screen Why is the Stevenson Screen located so high above the ground? Why is it painted white? Local variations in location of the weather instruments can impact temperature readings

    9. Temperatures Impact on Aviation High Temperatures: Reduce aircraft performance due to high Density Altitude: Increase takeoff distances Reduce climb rates Reduce the altitudes available to turbine engines Increase fuel burn Reduce operational efficiency Have a significant impact on weather creation: May cause instability/thunderstorms/tornados etc. May cause tropical storms/hurricanes/mid latitude cyclones etc. Heat is the fuel that drives the weather

    10. Atmospheric Cooling Reference and Study Material: Chapter 3 in Meteorology Today Chapter 3 in the Air Command Weather Manual

    11. Radiational Cooling Recall that all objects above 0K radiate energy All other things being equal, if outgoing energy exceeds incoming energy, an object will cool by radiational cooling After the daytime max temperature, both the atmosphere and Earths surface cool by radiating IR energy away The surface is much better at radiating energy away than the air above, so cools more quickly than the air above shortly after sunset As night progresses, the surface and air in contact with it cool more quickly than air a few meters above and sets up what is known as a radiation inversion A radiation inversion occurs when the air near the ground is colder than the air above. It is most likely to occur when: Wind is calm Nights are long Skies are clear; and The air is dry The ground is snow covered Radiation inversions can be topped anywhere from few meters to as high as 10000 during the long, cold polar night. More commonly, in the mid latitudes, they are topped around 1000 AGL Radiational cooling is usually responsible for creating the coldest temperatures overnight

    12. Nocturnal Temperature Profiles

    13. Radiational Cooling (cont.) The radiation inversion is affected by: Wind Due to turbulent mixing, the cool air near the surface is raised to higher altitudes Wind tends to weaken or impede radiation inversions Cloud Cloud re-radiates IR radiation toward the ground and tends to reduce the amount of radiational cooling that occurs overnight Terrain Cold, dense air will tend to flow downhill (katabatic wind) into low lying areas overnight Cold air pooling in valleys can create very strong inversions In areas where cold air can flow away, the radiation is weak or doesnt occur Warm air may occur on valley sides well above the valley bottom

    14. Thermal Belt

    15. Radiational Cooling (cont.) The radiation inversion is affected by (cont): Large bodies of water Since water has a much higher specific heat than dry land, water takes much longer to cool than land does nocturnal inversions tend to be much weaker or non-existent near large bodies of water as a result Greatest daily temperature range is found near the earths surface

    19. Evaporative Cooling As rain falls through the air, some, and occasionally, all of it evaporates Water changing state from a liquid to a gas requires heat energy from the atmosphere which causes the air to cool What do you think is going to happen when rain is evaporating (adding moisture to the air) and the air is cooling? Beware of strong downdrafts associated with rain showers due to this cooling effect

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