Name:_______________________________________________________             Section:________________

part 1:  Lapse Rates and Stability

1.   Table 6.1 below gives some information about parcels of air at five weather stations.  Use the saturation curve in Figure 6.1 and your knowledge of adiabatic processes to fill in the rest of the table, assuming that the parcels of air are forced to rise.

TABLE 6.1    Rising Air Parcels at Five Weather Stations

Air temperature at ground level (°C)         13               33               23               32               30

Water vapor content of the air (g/kg)          5               10               11              13                       17

Dew point temperature (°C)                      3              14                       15               18               22

 

 

Figure 6.1  Saturation Curve

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2.   Table 6.2 provides information on the environmental lapse rate (ELR) from a weather balloon.  Table 6.2 also provides information on the air temperature and dew point for two air parcels at ground level (0 m).

a.   Draw a graph of the environmental lapse rate (ELR) data presented in Table 6.2 on the graph provided (Figure 6.2) and connect the points with straight line segments.

b.   Draw a graph that represents the adiabatic temperature change that results when Parcel A is forced to rise from the surface to an elevation of 1200m.  Do this on the same graph (Figure 6.2) as the ELR for part (a).

c.   Draw a graph that represents the adiabatic temperature change that results when Parcel B is forced to rise from the surface to an elevation of 1200m.  This should be done on the same graph (Figure 6.2) as the ELR for part (a).

d.   Label the portion of the graphs for Parcels A and B (Figure 6.2) where the air is cooling at the dry and saturated adiabatic rates.

e.   Label the level at which condensation occurs and clouds develop.

f.    Decide at what elevations the parcels of air are stable or unstable and label the graph (Figure 6.2) clearly.

 

TABLE 6.2  Environmental Lapse Rate Data and Rising Parcels of Air

          0                   16.0                   0                      18.0                   0                     18.0

       100                   15.0                                            17.0                                             17.0

       200                   15.0                                            16.0                     SATURATED     16.0

       300                   14.0                                             15.0                                           15.4

       400                   13.0                       SATURATED  14.0                                              14.8

       500                   12.0                                            13.4                                             14.2

       600                   14.0                       NOT RISING 12.8                      NOT RISING      13.6

       700                   13.5                                            12.2                                                         13.0

       800                   13.0                                            11.6                                             12.4

       900                   12.0                                            11.0                                             11.8

     1000                   12.0                                            10.4                                             11.2

     1100                                                                       9.8                                             10.6

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.   a.   Between what altitudes does a temperature inversion occur? 500-600; ISOTHERMAL 50-150

 

b.   Label the graph (Figure 6.2) where the inversion occurs.

4.   a.   Is the density of parcel A greater at the earth's surface or at 1200 meters?  SURFACE

 

b.   Why? THE AIR PARCEL EXPANDS AS IT RISES, SO THE SAME NUMBER OF AIR MOLECULES OCCUPY GREATER VOLUME; THUS LESSER DENSITY ALOFT DESPITE LOWER TEMPERATURE

5.   a.   At 1200 m, is the air surrounding parcel B be more, less, or the same density as the air inside parcel B? SAME

 

b.   Why? THE SURROUNDING AIR HAS THE SAME TEMPERATURE AS PARCEL B

6.   a.   Which parcel produced the cloud with the lowest (nearest to the surface) cloud base? B

 

b.   Why? IT REACHED SATURATION (DRY BULB TEMP = DEW POINT) AT 200 M

 

 

7.   a.   Which parcel produced the cloud with the most vertical development? B

 

b.   Why? PARCEL B RISES 400 MORE METERS AFTER REACHING SATURATION, WHILE PARCEL A RISES ONLY 200 MORE METERS AFTER REACHING SATURATION.

 

 

8.   Which parcel is more likely to produce precipitation? B

Name:_______________________________________________________             Section:________________

part 2:  Adiabatic Processes and Orographic Precipitation

            Orographic precipitation results when air is forced to rise over mountains.  The rising air cools adiabatically as it rises over the windward side of the mountains, and then warms adiabatically as it sinks down the leeward side.  Figure 6.3 below shows a parcel of air starting at point A, which is at sea level (0 meters).  The temperature of the air at point A is 25°C and the water vapor content is 15g/kg.  Refer to Figure 6.1 (in Part 1) for information on the saturation mixing ratio.  The parcel is forced to rise over the mountain, eventually ending at point D, which is also at sea level (0 meters).

Figure 6.3  Orographic Precipitation

 

 

 

 

 

1.   What is the elevation of position B, the base of the cloud?

250 M                         100(25-22.5)=250

2.   What is the temperature of the parcel of air at the top of the mountain, position C, assuming the height of the mountain is 3000 meters? 6^OC

22.5O-[.6((3000M-250M)/100)]=6.0

3.   What is the temperature of the parcel at position D, assuming that all the moisture was lost on the windward side of the mountain and the air stayed below the saturation point as it sank down the leeward side? 36^OC               6OC+(3000M/100)=36

4.   a.   Is the temperature at position D the same, higher than, or lower than the temperature at position A? HIGHER

 

b.   Why? FOR MOST OF THE ASCENT THE AIR COOLED AT THE SLOWER SALR, BUT FOR ALL OF THE DESCENT THE AIR WARMED AT THE FASTER DALR

5.   a.   As the air subsides down the leeward side of the mountain would you expect the relative humidity to increase, decrease, or stay the same? DECREASE

 

b.   Why?  THERE IS NO ADDITION OF MOISTURE, BUT SINCE THE AIR'S CAPACITY FOR MOISTURE INCREASES AS TEMPERATURE IS HIGHER AFTER DESCENT, THE SAME AMOUNT OF MOISTURE REPRESENTS A SMALLER PROPORTION OF WHAT THE AIR COULD HOLD.

6.   What is the name for the locally generated warm, dry wind that descends the leeward slope of mountains? IN INTERIOR NORTH AMERICA IT IS CALLED THE CHINOOK, AFTER THE SALISH INDIAN WORDS FOR "SNOW EATER" (THE CHINOOK OFTEN MELTS SEVERAL INCHES OF SNOWPACK PER HOUR). IN SOUTHERN CALIFORNIA, THESE ARE CALLED THE SANTA ANNA WINDS, BECAUSE THEY OFTEN OCCUR (AND FAN BRUSH FIRES) AT ABOUT THE SEASON OF THE FEAST FOR THIS CATHOLIC SAINT. IN THE FRENCH ALPS THESE WINDS ARE CALLED THE "MISTRAL", WHILE IN AUSTRIA AND GERMANY THEY ARE KNOWN AS "FOEHN".

Name:_______________________________________________________             Section:________________

part 3:  Instability and Convectional Rainfall

            Cloud development may result from convection of warm moist air.  This happens when the earth surface is heated, especially on sunny afternoons.  Energy is transferred from the surface to the air above, causing the air to warm and rise.  Convectional uplift, with subsequent cloud development, is especially important along coasts where moist air masses move onshore from the ocean.  Rapid heating of the ground surface, compared to the ocean, during the summer results in air over the land being much warmer than air over the ocean.  Once heated, the warm air becomes unstable and rises, leading to the formation of cumulus clouds and possible scattered showers (convectional precipitation).  Thermal convection along coasts rarely results in widespread rains.  This scenario of cloud development is represented in Figure 6.4 below.  Think of the air over the surface labeled “Ocean” as the air of the surrounding environment (or still air), which is cooling at an environmental lapse rate (ELR) of 0.52°C/100m.  Over the beach, the land is heating the air causing convectional uplift.  The air rises and cools at the adiabatic lapse rate of temperature (ALR).  Recall that the rate at which the air cools depends on whether the air is saturated or unsaturated.  Use the information provided about the air above the ocean (still air) and the air over the beach (rising air due to convection) shown in Figure 6.4 to answer the following questions.

Figure 6.4  Convectional Precipitation

 

 

 

 

1.   Fill in the pertinent data.

            Environmental lapse rate =         -0.52^oC/100m

            Dry adiabatic lapse rate =          -1.0^OC/100M

            Saturated adiabatic lapse rate =  -0.6^OC/100M

2.   a.   Draw a graph of the ELR from 0 meters up to an elevation of 3000 meters to represent the still air over the ocean on the graph paper provided (Figure 6.5).

b.   Draw a graph of the adiabatic lapse rates of temperature (dry and saturated) from 0 meters up to an elevation of 3000 meters for the rising air over the land on the same graph paper as the ELR (Figure 6.5).

3.   Label the DALR and SALR portions of the adiabatic lapse rate graph.

4.   a.   Label the portion of the atmosphere where the rising air is unstable.

b.   Label the portion of the atmosphere where the rising air is stable.

5.   At what elevation will the base of the convectional cloud form?

AT 1000 m, WHERE DRY AIR TEMPERATURE = DEW POINT

6.   What is the elevation of the top of the cloud? 2600 m

 

7.   What is the air temperature at the top of the cloud? 15.4^OC