Weather (you like it or not!) Regent’s Earth Science - Topics #7

Weather Short term condition of atmosphere. Due to unequal heating of Earth’s surface. Happens in the troposphere (lowest atmosphere layer), because this is the only layer with water. See pg #13 E.S.R.T.

All of these change when insolation changes. Atmosphere Variables Temperature Dew Point Air Pressure Precipitation Clouds Wind All of these change when insolation changes.

Heating of the Atmosphere Conduction Direct Absorption of EM insolation. Absorption of Infrared from re-radiation by CO2 & H2O vapor. Latent Heat released during condensation that makes clouds. Frictional Drag as air rubs across Earth’s surface.

Heat Transfer in the Atmosphere Transfer is by Convection. Vertical - Warm Rises/Cool Sinks. Horizontal - Pressure differences cause wind (the bottom ½ of convection cycle). Air Cooling Because it is far above Earth’s surface Cool Air Sinking Wind Warm Air Rising

Adiabatic Heating & Cooling (Orographic Effect) Warm air forced up mtn. rises, expands & cools. So… windward side of mtn. ranges have precipitation. Air dried before passing over mtn. range Cool dry air forced to sink, compress & warm even more than it cooled due to lack of moisture. So… leeward side of mtn. ranges have deserts. Vegetation thrives on windward side. ie. Redwood Nat. Park Mohave & Moab Deserts are examples Rain Shadow Desert

Density & Atmospheric Pressure Barometric Pressure IS Air Pressure! Denser (cooler air) is HIGH pressure. The weight of the stack of air atoms above your head = air pressure. Usually 950 -1050mb range @ sea-level. Mercury Barometer Aneroid Barometer

Temperature & Pressure As temperature increases Air EXPANDS & becomes less dense Lower Pressure

Moisture & Pressure H (hydrogen) is the lightest of all elements. Increase H2O vapor Air is mostly N (nitrogen) & gets replaced by lighter hydrogen atoms SO… Air gets lighter w/ water vapor & Lower Pressure Remember: HIGH DRY LOW WET

As altitude increases Less air over your head Lower Pressure Altitude & Pressure As altitude increases Less air over your head Lower Pressure

Wind Wind is a vector quantity. Wind is named by the direction it comes from and measured w/ weather vane or wind sock. Moves from high pressure to low pressure. Wind is deflected to right in northern hemisphere by coriolis effect. Clockwise & out from High pressure center Counter-clockwise & in to a low pressure center

Wind Speed Fast Wind Slow Wind The greater the pressure gradient the faster the wind. Isobars closer means faster wind. Measured w/ Anemometer. Fast Wind Slow Wind

Wind belts cause prevailing winds Planetary Wind Belts Wind belts cause prevailing winds You are HERE! SW Winds move NE So our weather moves to the Northeast!

Surface Ocean Currents They are pushed by prevailing winds. So... Oceans circulate clockwise in the northern hemisphere & counter-clockwise in the southern hemisphere. 30° N Equator See ESRT Pg #4

Atmosphere Moisture (Humidity) Can be SOLID, LIQUID or GAS Precipitation removes particles from air. Aerosols become condensation nuclei & then part of raindrops or snowflakes. So precipitation cleans pollution from air.

Evapotranspiration Evaporation + Transpiration = Evapotranspiration Evaporation is liquid to gas phase change. Transpiration is water from plants

Evaporation Increases If… surface area increases. wind increases. temperature increases. relative humidity decreases.

Relative Humidity Compares the amount of moisture in the air to what the air could hold if saturated at that temperature. 0% = None 50% = ½ full 100% = Saturated (Full) Warmer air atoms are farther apart so there is more space for H2O.

Dew Point Temperature is the Temperature Where… air becomes saturated. air reaches 100% relative humidity. water vapor condenses into liquid water. clouds form.

Dew Point Temperature & Relative Humidity ESRT References Top of both tables is the difference between wet & dry bulb temps. Use that column. Dry bulb IS the current air temperature. Use that row. Sling psychrometer measures wet & dry bulb temps..

Dew Point Temperature & Relative Humidity ESRT References 10°C – 6°C = 4°C Dry Bulb = 10°C Wet Bulb = 6°C

Cloud Formation H2O in the air. Cool air to dew point temperature. Condensation nuclei (dust particles) in air. Warm air rises to the altitude of the DPT where the vapor condenses into billions of small cloud droplets. Water vapor condenses Altitude of Dew Pt. Temp.

Precipitation Tiny cloud droplets collide and stick together. When droplets get large enough they fall through the rising warm air.

c = continental (dry) m = maritime (moist) P = Polar (cool) T = Tropical (warm) A = Arctic Air Masses mP cP mP mT mT mT cT maritime tropical

Hail particles circulate, freeze and grow in layers to get bigger. Cold Front Cold air push warm air Cumulonimbus clouds Thunderstorms Lightning Heavy Rain Hail Tornadoes . . 3 0°C . 1 2 Cold Air (High Pressure) Sinking Hail particles circulate, freeze and grow in layers to get bigger. Warm Air Rising Earth Surface

Warm Front (The Blue Line) Stratus clouds Overcast All-day rain Warm Air Rising Cold Air (High Pressure) Earth Surface

Low Pressure System W/ Cold & Warm Fronts on Maps Cool w/ Clear Skies Overcast Skies All-Day Rain H H Cold Cold Air Air Warm Air L Possible Thunderstorms Partly Cloudy Nice All of this will move to the NORTHEAST!

. Occluded Front Cold front catches up to warm front. Stratus & cumulonimbus All-day rain w/ thunderstorm at end (Blue Lines) . Warm Air (Forced Up) Cold Air (High Pressure) Cold Air (High Pressure) Earth Surface

Occluded Front on Maps Cold dense air can move faster than the warm air. So cold fronts catch up to warm fronts while rotating counter-clockwise.

Station Models NO UNITS on station model data. See ESRT for data placement Air Pressure Code Drop Decimal Pt. 975.2 9752 Drop the 9 or 10 9752 752 Un-coding Pressure Put in Decimal Pt. 752 75.2 Put 9 or 10 back so that # is between 950 &1050mb __75.2 975.2