777 GROUNDSCHOOL Temperature, Stability, Fronts, & Thunderstorms

Transcription

1 777 GROUNDSCHOOL 2018 Temperature, Stability, Fronts, & Thunderstorms

2 The Atmosphere Heating Transfer of heat occurs thru Radiation Advection Convection Matter changes states due to the amount of heat it holds Heating of the atmosphere occurs from the ground up As sun warms the ground, heat radiates from the ground into the surrounding air

3 The Atmosphere Cooling As the atmosphere is heated from the ground up, temperature usually decrease as altitude decreases Lapse rate is a measure of the decrease in temperature as altitude increases If temperature does increase as altitude increases an inversion is said to have occurred Eg at seal level the temperature is 13degrees, at 1000 the temperature is 20degrees An Isothermal layer is one where the temperature of the air remains constant for some depth Eg air temperature is 12degrees

4 Lapse Rate The rate at which temperature decreases in the atmosphere ICAO 1.98/1000 Dry 3/1000 Saturated 1.5/1000

5 The Atmosphere Heating Type Radiation Advection Convection Heat transfers from Solid to Gas / Liquid Gas to Gas Liquid to Liquid

6 STABILITY Normal flow of air is in the horizontal direction Disturbances of air may cause air to move in the vertical direction Stable air is when air resists upward and downward motion and will return to its original horizontal position if displaced Cold air tends to be stable A shallow lapse rate often means stable air Unstable air is when air tends to move further up or down if displaced Warm air tends to be unstable A steep lapse rate often means unstable air

7 STABILITY AND LAPSE RATE Stable air flight characteristics include Poor visibility Stratus type cloud Light precipitation Steady winds change rapidly with height Smooth flight conditions Unstable air flight characteristics include Good visibility Cumulus clouds Showery precipitation Gusty winds Turbulence

8 AIR MASSES An Air Mass is a large section of the troposphere with uniform properties of temperature and moisture in the horizontal Takes on properties over the land which it formed over An air mass which formed over water is referred to as maritime air An air mass which formed over land is referred to as continental air The 3 air regions in North America are Arctic, Polar, Tropical

9 AIR MASS CONTINENTAL Continental Arctic (ca) and Continental Polar (cp) are air masses which originate over cold ice and snow covered surfaces Consists of cold dry air Brings a cold wave once they move south

10 AIR MASS MARITIME Maritime Arctic (ma) and Maritime Polar (mp) are cold moist air masses that form over water Consist of moist cold air

11 AIR MASS TROPICAL Maritime Tropical (mt) consists of warm moist air formed over oceans on the tropics Due to the fact that North America is narrow down south Unstable Extensive fog

12 QUESTION

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14 FRONTS The troposphere is made up of air masses, the transition point between said air masses are called Fronts Interaction amongst fontal zones is responsible for weather changes A front is defined by which air mass is more dominant Eg cold air mass moving onto warm air mass is called a cold front Fronts we will cover: Warm Cold Stationary Occluded

15 FRONTS COLD Occurs when a mass of Cold air overtakes a mass of Warm air Cold air being more dense forces warm air up violently Cold fronts form steep slopes Results in narrow cuculiform clouds Precipitation Thunder Most violent front

16 COLD FRONT

17 FRONTS - WARM Warm Fronts occur when a mass of warm air advances onto a retreating mass of cold air Warm air is less dense and climbs on top of the cold air Warm fronts form long gentle slopes (500NM) May form stratoform clouds if stable Cirrus Cirrostratus Altostratus Nimbus Stratus May form thunderstorms within stratoform clouds if unstable

18 WARM FRONT

19 FRONTS STATIONARY Stationary Fronts are the result when neither air mass (cold and warm) is advancing or retreating Winds will blow parallel to the front Weather will be similar (but less intense) than a warm front Usually dissipates, sometimes becomes warm or cold front

20 STATIONARY FRONT

21 FRONTS OCCLUDED Occluded Fronts occur when a cold front over takes a warm front completely and lifts it off the ground Often the cold air will become cool air in the process via advection and surface friction May be referred to as occluded warm front or occluded cold front Generally carries characteristics of a warm front

22 OCCLUDED FRONT

23 FRONTS

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25 THUNDERSTORM REQUIRMENTS 3 requirements for a thunderstorm are Unstable air High moisture content Lifting agent The difference in intensity between these 3 factors is the difference between a cloud and thunderstorm

26 STAGES OF A THUNDERSTORM

27 CUMULUS STAGE Starting point of a thunderstorm Strong updrafts (from unstable air) and lifting agents lead to cumulus clouds turning into towering cumulus and eventually cumulonimbus clouds Often no precipitation

28 MATURE STAGE Cumulus clouds grows very large often up to in height Top spreads into an anvil shape Updrafts of 6000 /min and downdrafts of 2000 /min Downdrafts spread up to 5nm in front of the storms Precipitation, thunder, and violent turbulence are expected

29 DISSIPATING Precipitation often falls and cools the lower region of the cloud causing it to dissipate Downdrafts continue to occur throughout entire cell except for one portion Updraft occurs in single position Precipitation ceases and the cell spreads out into an anvil shape

30 QUESTION

31 EXPECTED WEATHER Severe turbulence Up/ downdrafts Heavy precipitation hail Icing Lighting String gusts

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