The change in temperature as air rises or descends d in the atmosphere. This change is measured by a lapse rate

Transcription

1 Adiabatics The change in temperature as air rises or descends d in the atmosphere. This change is measured by a lapse rate oftenplotted on an adiabatic chart. Such processes are closely connected to precipitation or lack thereof.

2 Lapse Rates Rising air cools at either the Wet Lapse Rate (WLR) or the Dry Lapse Rate (DLR). Usually air cools at the DLR until condensation begins, then it cools at the WLR as it continues to rise. Descending air heats up at the DLR because condensation is impossible in air that is warming.

3 Basic Adiabatic Chart Compares Temperature to Altitude. Altitude IsMeasured in KilometersorPressure or Level

4 The Diagonal Lines Are Called Adiabats. On this version of a Stüve chart, the green diagonal line represents the dry adiabatic lapse rate (DLR) and the dashed blue line represents the wet adiabatic lapse rate (WLR). A parcel starting at the surface with a temperature of 29 C will cool to 9 C at 2 km, the LCL. Condensation begins there and continues to about 5.5 km where the temp will be about 8.5 C. Upon returning to the surface, the parcel temp would be about 42 C Note that at very cold temperatures, the adiabats are effectively parallel to each other. This is due to the fact that very cold air holds almost no moisture so there is basically nothing left to condense or freeze out.

5 Chart for Jackson, MS on Oct 7, 2008 Right Line is the Temperature Profile of the Atmosphere Also Called the Environmental Lapse Rate (ELR), Left Line is the Dew Point Temperature

6 What Kind of Weather Event Is This? Temp and Dew Point Temp Are Almost Equal

7 Basic Adiabatic Chart is a Graph of Temperature on X Axis and Height on Y Axis. Details on Next Slide

8 Details of Previous Slide Another common use of adiabatic charts is to determine how a parcel of air would behave in a given atmosphere. There are two lines on the graph, one represents the change in parcel temp as it moves vertically, the other represents the temp profile (the ELR). The line on the right has to be the parcel because it has only one kink point where condensation begins. The lower part of the line is the parcel rising ii and cooling at the DLR. The upper part of the line is the parcel rising and cooling at the WLR. The line on the left has to be the ELR because it is too complicated to represent the parcel. It has an upper level inversion at about 6km where the air is warmer than the air immediately below it. The bird s foot at the bottom represents the change of temperature from dawn to late afternoon.

9 So, How Will the Parcel Behave in This Particular Atmosphere? The parcel will rise in this particular atmosphere because it is always warmer (to the right) than the surrounding air at a given altitude. (There are two points where the temperatures are nearly the same, but the parcel is still always warmer. This is an unstable atmosphere Thenext slideshowsshows the situation at dawn when the parcelandand the surrounding air have the same temperature. The parcel can not rise because at any altitude it is cooler than the surrounding air. This is a stable atmosphere.

10 An Absolutely Stable Atmosphere, Parcel (line on left) Is Always Cooler Than the Surrounding Atmosphere(line on right) ih)

11 A Conditionally Stable Atmosphere. Initially the Parcel is Cooler than the Surrounding Air, However, at about 5 km, the Parcel Is Warmer. However at km It Is Cooler Because of the Inversion Layer.

12 Adiabatic Chart from the Unisys Site. Temp is Read dfrom the Diagonal Blue Lines

13 Adiabatic Chart for Oakland, CA. This is the standard format for a Stüve diagram. The temperature is read from the blue diagonal line. The temperature at 450 mb (6277 m) is 30 C. The white line on the right is the temperature profile of the atmosphere. The white line on the left is the dew point temperature. Where the lines are close together, there is a lot of moisture. Where they are far apart, the air is very dry.

14 Adiabatic Chart for Oakland, CA. This is the alternate format for a Stüve diagram. The temperature is read like a conventional graph going straight down to the horizontal axis from the point of interest. The temperature at 450 mb (6277 m) is 30 C.

15 Adiabatic Charts Are Also Called a Skew T. The chart below is for Tucson, AZ. The lifted index is The relative humidity is 55.1 %. The amount of precipitable water is 0.72 inches. Where the temp and dew point temp lines touch, the relative humidity is 100%, so there will be clouds at that altitude. There could also be clouds where they almost touch.

16 The Adiabatic Chart Also Gives Wind Speed and Direction. Note How the direction changes slightly and speeds up from 35 knots to 60 knots at about 450 mb (6277 m). This also is the altitude above which the air is much drier. The calculated Lifting Condensation Level (LCL) is 950 mb (532 m). Note the temperature lines touch there.

17 Tucson Sounding, 6 Oct 2011 This is a Stable Atmosphere with Very Little Moisture (LI = 12.5). Surface RH Is 55%. Probably Two Layers of Clouds at 750 and 550 mb.

18 Oakland Sounding, 6 Oct, 2011 Atmosphere Is Unstable (LI = 1.2) 2)and Nearly Saturated with Moisture from Surface to 20,000 ft.

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