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Home , Adiabatic process, Evapotranspiration

GEO 101, Feb. 27, 2014 Relative varies with 1. Availability of moisture

Relative humidity = ratio of amount of vapor in air to 2. changes for a given amount of amount of water vapor air can hold at that temperature

Relative humidity = content / capacity x 100%

Evaporation requires Processes that put water into the air Source: 1. to change water from liquid to vapor 2. by plants Usually comes from the sun Vapor gradient: Evapotranspiration Air not saturated Relative low humidity

Transpiration requires plants ACTUAL EVAPOTRANSPIRATION (AE) affected by… 1. Availability of water Plants lose 2. Temperature of air water through their leaves 3. Relative Humidity 4. Speed 5. Vegetative cover

Potential evapotranspiration … PET the amount of water that would be added to the Plants take in atmosphere if there were NO LIMITS on the water through availability of water. Function of 2, 3, 4, and 5 their roots Stomates allow CO in, O and H O out 2 2 2 above…mostly related to latitude (insolation).

6 CO2 + 6 H20 + sunlight = C6H12O8 +6 O2

1 Average Monthly Water Budget: Jackson, MS PET If cool saturated air, decrease capacity, air becomes over saturated, water vapor has to get out of air, AE occurs. Moisture deficit Temperature at which condensation occurs = DEWPOINT

Moisture CONDENSATION affected by… surplus 1) Relative humidity moisture utilization 2) Degree of cooling 3) Availability of nuclei recharge

CONDENSATION DEW AND FROST Water vapor condenses or sublimates on a surface

CONDENSATION AND Water vapor condenses on nuclei

Clouds form when air cools below its dewpoint Types of fog

meters feet

Radiation

Upslope Evaporation

2 Temperature structure of atmosphere = normal

Adiabatic processes: internal to a parcel of air “Normally” gets colder as you go up at ≈ 6.5°C per 1000 m

PROCESS that cools air below dewpoint  clouds Occurs when parcel of air is LIFTED up into atmosphere.

Remember...

meters

°C

Temperature inversion: it gets warmer as you go up The normal lapse rate instead of getting colder like it is supposed to do. would be like having thermometers tied to a tall tower that reached to the top of the Surface inversion Inversion aloft and (starts at surface) starts above taking a temperature surface reading at each thermometer at the same time. Altitude in meters in Altitude Altitude in meters in Altitude

Degrees Celsius Degrees Celsius

Atmospheric pressure decreases with increasing altitude 500 312 mi Adiabatic processes: internal to a parcel of air

400 Air molecules

300

200 Altitude (km) Altitude Air density

100 62 mi

Air 90% in first pressure 10 mi 10 mi

3 Dry adiabatic rate ≈ 10°C per 1000 m -20 0 Vertically moving air parcels that are NOT SATURATED follow the dry adiabatic rate of temperature change when ascending or descending.

-10 10 Subtropical Highs air descends warms adiabatically capacity to hold water vapor increases 0 20 relative humidity decreases Horse latitudes

meters 10 30 °C

Dry adiabatic rate vs. Reminder: water vapor contains normal lapse rate

If air parcel is cooler than surrounding air, it will not rise = stable.

If air parcel is warmer than surrounding air, it will rise = unstable.

20 24 25

25 27 30 meters

°C

Dry adiabatic rate As air cools, it can hold less water vapor. If ≈ 10°C/1000m cooled below saturation point, condensation occurs at dewpoint temperature. The altitude Wet (moist, where this occurs is called the lifting satuated) condensation level. Clouds start here. adiabatic rate ≈ 5-6°C/1000m (Varies with Condensation releases energy to the moisture content, surrounding environment. temperature, and pressure)

Dewpoint Dewpoint = 20°C

LCL = 1000 m meters

°C

4 If parcel stays warmer than surrounding air, it will continue to rise

Dewpoint

meters

°C

WHAT YOU MUST KNOW ABOUT THE ADIABATIC PROCESS

Normal or environmental lapse rate ≈ 6.5°C/1000m Adiabatic rate is not the same as the normal (environmental) lapse rate. Can be inversions or variations Normal (environmental) lapse rate = temperature structure of the atmosphere Dry adiabatic rate = DAR ≈ 10°C/1000m Adiabatic rates = temperature changes in a rising (cooling) or Wet or saturated adiabatic rate = SAR ≈ 5-6°C/1000m falling (warming) parcel of air.

Parcel will only rise if it is warmer than the surrounding air!

When rising parcel cools to dewpoint temperature Adiabatic cooling  Condensation condensation starts and clouds form Condensation  Clouds lifting condensation level Clouds  Precipitation latent heat is released into the parcel Sleet continued cooling is at the slower wet adiabatic rate

Descending parcels warm at the dry adiabatic rate.

5 Hail Glaze

Snow Snowflakes For adiabatic cooling to occur, air must rise via atmospheric lifting!

Types of atmospheric lifting Reminder: Precipitable water vapor by latitude

cm

Frontal = warm goes up over cold air Convective = bubbles of warm wet air

Capacity of air to hold moisture directly related to temperature

Orographic = up a mountainside Convergent = air meets in a LOW

6 Latitudinal variation in precipitation Wind and pressure belt review Only every other person gets a worksheet WITH a partner to fill it out Put both of your names on the worksheet Try to reason your way through it without your notes Use your notes as a last resort Turn it in

Know the lifting mechanisms, or lack thereof, that explain this latitudinal pattern

7