Chapter 5Atmospheric Moisture

hydrologic cycle--movement of water in all forms between earth & atmosphere

Humidity: amount of water vapor in air

● vapor pressure● saturation vapor pressure● absolute humidity● specific humidity● saturation specific humidity● mixing ratio● saturation mixing ratio● relative humidity● dew point temperature

(NOT how much moisture is in the air, but how much moisture the air can hold)

measure of temperature(?!)

Humidity: amount of water vapor in air

● vapor pressure●● absolute humidity● specific humidity●● mixing ratio●● relative humidity● dew point temperature

Humidity: amount of water vapor in air

● vapor pressure●● absolute humidity● specific humidity●● mixing ratio●● relative humidity● dew point temperature

Humidity: amount of water vapor in air

● vapor pressure●● absolute humidity● specific humidity●● mixing ratio● ● relative humidity● dew point temperature

specific humidity: q=mv /(mv+md)mixing ratio: r=mv /md

lets just worry about q or r

Only worry about 4 measures of moistures:

● vapor pressure● mixing ratio● relative humidity● dew point temperature

Relative humidity depends on:

A. moisture content onlyB. temperature onlyC. both moisture content and temperature

Is RH a good choice to compare moisture content at two locations?

What is the dew point temperature?

Now cool the parcel...

If you cool the parcel to 8oC, the dew point temperature A. remains at 10oCB. increases to 12oCC. decreases to 8oC

tutorial on dew point and temperature

● Upper air soundings (weather.uwyo.edu/upperair/sounding)● radar/satellite images(weather.rap.ucar.edu)

factors affecting saturation: 1. curvature

small drops require super-saturation to avoid evaporation

radius and super-saturation tutorial

factors affecting saturation: solution

pure water drops vs solution drops (also includes effects from CCN)

Which of the following is NOT true about condensation nuclei (CN)?

A. CN are more abundant over land than water.

B. there are no natural sources of CN over the open ocean.

C. A large number of CN may inhibit precipitation by creating large numbers of small drops.

D. One possible source of CN is the conversion of gas molecules into aerosols.

E. More than one of the above is false.

First law of thermodynamics

cooling by adiabatic expansion

cooling by adiabatic expansion

cooling by adiabatic expansion

Consider the first law of thermodynamics

Which of the following are not true:A. A diabatic process has while an adiabatic one hasB. Changes in temperature always require heat transfer (either to or from the

system)C. An adiabatic process with no work done will result in a large temperature

change.D. Changes in the internal energy of a (dilute) gas are always related to

changes in temperature.E. More than one of the above is false.

Cumulus congestus clouds expand into the free atmosphere. Which of the following does not apply:

A. The temperature near the cloud top increases as a result of heat transfer via convection from the Earth’s surface.

B. The “sharp” boundaries of the cloud indicate sharp moisture gradients in the atmosphere.

C. There is almost no heat transfer between cloud and the surrounding atmosphere during expansion.

Adiabatic expansion demo

● breathing and blowing● convection over Ft. Craig (from Dr. Sonnenfeld)

Adiabatic Lapse rates

Adiabatic lapse rate: rate a parcel cools with altitude:

● If parcel is moist but not saturated, it cools at the dry adiabatic lapse rate (DALR)

● If parcel is saturated, it cools at the saturated adiabatic lapse rate (SALR)

DALR=1.0oC/100mSALR=0.5oC/100m

Why is DALR > SALR?

Environmental Lapse Rate

Is the rate at which the actual environment cools with altitude.

Chapter 6Cloud development and forms

Air parcels must lift to form clouds: forced lifting

lifting by fronts

lifting by orography;

lifting by convergence

lifting by buoyancy: Is the parcel cooling faster than the environment?

Is parcel cooling faster than the environment?

Is parcel cooling faster than the environment?

1,2,3 are ELRs. Which one isA. absolutely stable?B. absolutely unstable?C. conditionally unstable?

Temperature inversions are examples of

A. extremely stable airB. extremely unstable air

Lapse rates and stability

ELR, SALR, DALR

Clicker questionAn unsaturated parcel cools as it rises adiabatically until it reaches the dew point. A. at this point it is saturatedB. this level is called the lifting condensation level (LCL)C. this level is the level of free convection (LFC)D. A and BE. A and C

clicker questionThe (now saturated) parcel continues to rise.A. The convection is forced until it reaches the level of free

convection (LFC).B. The parcel is still cooler than its surroundings until it

reaches the LFCC. The parcel supersaturates or begins to condense as it

rises.D. Once it reaches the LFC, the parcel becomes more

buoyanct than the surrounding air.E. All of the above.

clicker questionOnce a parcel rises, it rises untilA. it hits a layer of stable airB. it entrains dry airC. it hits the stratosphereD. all of the aboveE. none of the above

why would entraining dry air cause parcel to descend?

Quiz

1. What is the lifting condensation level?2. The environment is cooling faster than the

parcel, is this STABLE or UNSTABLE?3. How does entrainment of dry air stop a

parcel from rising?