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Weather Notes 1.0
A) Atmospheric variables (4):
1) Temperature as it relates to:
a) duration of insolation...............................longer day = higher temperaturers
b) time of day...............................................afternoon (2-3 PM) = highest temperature
c) season of year...........................................late summer = highest temperatures
d) altitude (in troposphere)...........................higher altitudes = lower temperatures
e) latitude......................................................equator (0 degrees latitude) = highest temperatures
f) cloud cover................................................more clouds = lower temperatures
g) aerosols and particulates (smoke).............more ‘stuff’ in the air = lower temperatures
h) absorptive qualities of land/water..............land gets hotter faster and land cools off faster.
2) Pressure as it relates to:
a) altitude..........................................higher = lower pressure
b) temperature...................................higher temp = lower pressure
c) moisture in air (humidity).............more moisture = lower pressure
d) highest pressure............................cold/dry air @ lower altitudes = high pressure
e) lowest pressure.............................warm/moist air @ higher altitudes = low pressure
f) pressure measurement - pressure measured with a barometer. Measured in:
1) millibars 2) inches of Hg(mercury) 3) atm (atmospheres) - pressure at sea level = 1 atm
3) Humidity (moisture content of air)
a) Absolute humidity - amount of water vapor in the air
b) Relative humidity - amount of water vapor in the air as compared to the maximum capacity of the air
at a given temp.
Affected by: a) temperature - warmer air can hold more water vapor
b) actual water content of air
4) Dew point - The temperature at which:
a) air is saturated (filled)
b) relative humidity is 100%
c) evaporation effectively stops
d) wet bulb temperature = dry bulb temperature
e) water vapor will condense*
* If the dew point is < freezing point then water vapor sublimates into ice/snow
B) Cloud formation
1) Air rises, cools to dew point, condensation occurs
2) Releases heat into air (540 cal/g)
3) Water must condense onto nuclei (condensation nuclei - pollen, dust, etc.)
4) If dewpoint <0⁰C, then ice crystals sublimate.
5) Clouds are aerosols (droplets or ice)
6) Droplets remain suspended until heavy enough to fall
a) Rain & Hail - frozen rain (both begin as liquids)
b) Snow - (vapor to solid, sublimation) - only form of precipitation that begins as solid
7) The cloud base is the altitude at which the air temperature is at the dew point.
C) Convection in the atmosphere
1) Depends on density differences
a) Least dense air (warm and moist) rises
b) As the air rises it expands and cools* becoming more dense.
* if the air is cooled to the dew point, condensation occurs. This removes moisture from the air which is
now not only cooler but also dryer. Cool, dry air is the most dense air.
c) Now this more dense air sinks completing the convection current
2) Convection currents are caused by unequal heating of Earth's surface
a) Land = low specific heat = it heats & cools quickly
b) Water = high specific heat = it heats & cools slowly
c) Different surface characteristics: Rough/dark or smooth/light
d) Different cloud cover: Clouds reflect light keeping the surface beneath them cool.
f)Different latitudes: Poles are cold, Equator is warm.
D) How does air move?
1) From high pressure to low pressure
2) From cool and dry to warm and moist
3) Coriolis effect
a) air flows counterclockwise INTO a low = “cyclone”
b) air flows clockwise OUT OF a high = “anticyclone”
4 Wind speed is dependent on the pressure gradient*
*The greater the difference (gradient, slope) between the high and the low pressure systems, the faster the winds
blow.
E) Air mass characteristics: A large body of air with similar temperature and moisture
1) Depends on the surface over which they formed:
a over ocean = moist (maritime) - m
b over land = dry (continental) - c
c warm region = tropical - T
d cold region = polar - P = cold, arctic - A = coldest
2) Air masses are described by their temperature and moisture content:
a cP or cA = cold and dry = high pressure
b)mT = warm and moist = low pressure
F) Fronts: interface between two or more air masses
1) cold front - A cold air mass is replacing a warmer air mass.
2) warm front - Warm air mass replacing a cooler air mass
3) stationary front - A front that stops moving or is moving very slowly
4) occluded front (cold overtakes warm) - When a warm front is trapped by 2 cold fronts
Important stuff to remember:
> Whether you are looking at numbers, reading a graph, or looking at a picture of a sling psychrometer, always
remember that the closer together the wet and dry bulb temperatures are, the higher the relative humidity and
therefore, the greater the chance or precipitation.
If wet bulb temp. = dry bulb temp. then RH = 100%
> Heat is distributed around the planet by winds in the atmosphere AND by currents in the ocean