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the saturated adiabatic lapse rate

Temperature Changes Inside Clouds. Two processes occur simultaneously inside clouds that affect the temperature.Rising air expands, does work and cools;Condensation releases latent energy which is then stored as internal energy and warms the air inside the cloud.. Temperature Changes Inside Clouds (Cont.).

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the saturated adiabatic lapse rate

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    1. The Saturated Adiabatic Lapse Rate Temperature Changes and Stability Inside Clouds

    3. Temperature Changes Inside Clouds (Cont.) Normally, the cooling due to the work of expansion is greater than the warming associated with the release of latent energy and its conversion to internal energy.

    4. Temperature Changes Inside Clouds (Cont.) Thus, as air rises inside a cloud it still gets colder, but it does so at a slower rate than the Dry Adiabatic Lapse rate. The rate at which rising air inside a cloud cools is called the Saturated Adiabatic Lapse Rate (SALR).

    5. The Saturated Adiabatic Lapse Rate (SALR) The derivation of the equation for the SALR begins with a form of the First Law of Thermodynamics dq = cpdT - adp

    6. The SALR (Cont.) In this case the energy gained, dq, is equal to the latent energy released when water vapor condenses inside the cloud. dq = -Lvdqv where Lv is the latent heat of vaporization, and dqv is the change of specific humidity of the air parcel when water vapor condenses

    7. The SALR (Cont.) Substitute for dq in the First Law of thermodynamics to get -Lvdqv = cpdT adp Add cpdT + Lvdqv to both sides to get

    8. The SALR (Cont.) -cpdT = -adp + Lvdqv Divide by cpdz to get -cpdT = -adp + Lvdqv cpdz cpdz cpdz Since a = 1/? we can write this as

    9. The SALR (Cont.) -dT = - 1 dp + Lvdqv dz cp? dz cpdz From the hydrostatic approximation -1 dp = g ? dz

    10. The SALR (Cont.) Substitution results in -dT = g + LvdqV = Gs dz cp cp dz

    11. The SALR (Cont.) The SALR is always less than the DALR because the cooling caused by adiabatic expansion is partially offest by the release of latent energy during condensation.

    12. The SALR (Cont.) The SALR is a variable. The magnitude of the SALR is determined by the amount of water vapor that condenses.

    13. The SALR (Cont.) When warm moist air rises in a cloud, more water vapor condenses and the SALR is smaller. When cooler, drier air rises inside a cloud, less water vapor condenses and the SALR is larger.

    16. Stability Cases for Clouds (1) When the ELR is greater than the SALR, then the air inside the cloud is unstable. Unstable air moves vertically and we tend to get tall, vertical clouds like cumulus and cumulonimbus.

    17. Stability Cases for Clouds (Cont.)

    18. Stability Cases for Clouds (Cont.) (2) When the ELR is equal to the SALR, then the air inside the cloud is neutral. (3) When the ELR is less than the SALR, then the air inside the cloud is stable.

    19. Stability Cases for Clouds (Cont.) There is much less vertical motion when air is neutral or stable. Thus, when air inside the clouds is neutral or stable, the clouds tend to have a flat, layered appearance. These types of layered clouds are called stratus clouds.

    20. Stability Cases for Clouds (Cont.)

    21. Stability Cases for Clouds (Cont.) There is a special stability case that occurs when the Environmental Lapse Rate is between the Dry Adiabatic Lapse Rate and the Saturated Adiabatic Lapse Rate.

    22. Stability Cases for Clouds (Cont.) For example, what if DALR = 1.00C/100 m ELR = 0.75C/100 m SALR = 0.50C/100 m If the air is unsaturated ELR < DALR and the air is stable, but if the air is saturated, then ELR > SALR and the air is unstable.

    23. Stability Cases for Clouds (Cont.) This special case is called conditionally unstable, because the air must be lifted until it becomes saturated in order for it to become unstable

    25. Stability Cases in Clouds (Cont.) When the atmosphere is conditionally unstable it can lead to the rapid development of thunderstorms when a cold front or other weather feature lifts warm moist air in the spring.

    26. Stability Cases in Clouds (Cont.) The air is stable as long as it isnt lifted high enough, but if it is lifted until the parcel is warmer than the environment, then the air instantaneously becomes unstable and starts rising on its own. Then thunderstorms can form rapidly.

    27. The Effect of Topography on Precipitation Patterns Precipitation patterns in mountainous regions tend to be closely related to the prevailing wind direction. Much higher precipitation amounts fall on the side of the mountains where the air is rising and it is much drier on the side where the air is sinking.

    28. The Effect of Topography on Precipitation Patterns (Cont.) The process where air is forced to rise up the side of a mountain is sometimes called orographic lifting.

    30. The Effect of Topography on Precipitation Patterns (Cont.) Rising motion causes clouds and precipitation on the windward side of the mountain range. Sinking motion causes warm, dry conditions on the leeward side of the mountain. The dry area on the leeward side of the mountain is called the rain shadow.

    31. The Effect of Topography on Precipitation Patterns (Cont.) Since the prevailing wind direction in the middle latitudes is from the west, the western sides of the mountains along the west coast of the U.S. are the rainy sides and the rain shadows occur along the eastern slopes of the mountains.

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