Chapter 5. Atmospheric Moisture

Transcription

1 Chapter 5 Atmospheric Moisture

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

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4 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)

5 measure of temperature(?!)

6 Humidity: amount of water vapor in air vapor pressure absolute humidity specific humidity mixing ratio relative humidity dew point temperature

7 Humidity: amount of water vapor in air vapor pressure absolute humidity specific humidity mixing ratio relative humidity dew point temperature

8 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

9 Only worry about 4 measures of moistures: vapor pressure mixing ratio relative humidity dew point temperature

10 Relative humidity depends on: A. moisture content only B. temperature only C. both moisture content and temperature

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

14 What is the dew point temperature?

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16 Now cool the parcel...

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

18 tutorial on dew point and temperature

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

21 factors affecting saturation: 1. curvature

22 radius and super-saturation tutorial small drops require super-saturation to avoid evaporation

23 factors affecting saturation: solution pure water drops vs solution drops (also includes effects from CCN)

24 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.

25 First law of thermodynamics

26 cooling by adiabatic expansion

27 cooling by adiabatic expansion

28 cooling by adiabatic expansion

29 Consider the first law of thermodynamics Which of the following are not true: A. B. C. D. E. A diabatic process has while an adiabatic one has Changes in temperature always require heat transfer (either to or from the system) An adiabatic process with no work done will result in a large temperature change. Changes in the internal energy of a (dilute) gas are always related to changes in temperature. More than one of the above is false.

30 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.

31 Adiabatic expansion demo breathing and blowing convection over Ft. Craig (from Dr. Sonnenfeld)

32 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/100m o SALR=0.5 C/100m Why is DALR > SALR?

33 Environmental Lapse Rate Is the rate at which the actual environment cools with altitude.

34 Chapter 6 Cloud development and forms

35 Air parcels must lift to form clouds: forced lifting lifting by orography; lifting by convergence lifting by fronts

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

37 Is parcel cooling faster than the environment?

38 Is parcel cooling faster than the environment?

39 1,2,3 are ELRs. Which one is A. absolutely stable? B. absolutely unstable? C. conditionally unstable?

40 Temperature inversions are examples of A. extremely stable air B. extremely unstable air

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42 Lapse rates and stability ELR, SALR, DALR

43 Clicker question An unsaturated parcel cools as it rises adiabatically until it reaches the dew point. A. at this point it is saturated B. this level is called the lifting condensation level (LCL) C. this level is the level of free convection (LFC) D. A and B E. A and C

44 clicker question The (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 LFC C. 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.

45 clicker question Once a parcel rises, it rises until A. it hits a layer of stable air B. it entrains dry air C. it hits the stratosphere D. all of the above E. none of the above

46 why would entraining dry air cause parcel to descend?

47 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?