8. The accompanying diagram shows air flowing from the ocean over a coastal moun

Question

8. The accompanying diagram shows air flowing from the ocean over a coastal mountain range. Assume that the dew-point temperature remains constant in dry air (that is, relative humidity less than 100 percent). If the air parcel becomes saturated, the dew-point temperature will cool at the wet adiabatic rate as it ascends, but it will not change as the air parcel descends. Use this information to complete the following: a. Determine the air temperature and dew-point temperature for the air parcel at each location (B-G) shown on the diagram. b. At what elevation will clouds begin to form (with relative humidity = 100 percent)? c. Compare the air temperatures at points A and G. Why are they different? d. How did the water vapor content of the air change as the parcel of air e. On which side of the mountain might you expect lush vegetation, and on f. Where in the United States might you find a situation like what is traversed the mountain? (Hint: Compare dew-point temperatures.) which side would you expect desert-like conditions? pictured here? 4 km 3 km C. 2 km Windward FLeeward A. Sea level Temperature at point A-27C Dew point temperature at Point A Dry adiabatic rate·IOC/n Wet odiobatic rate 5°C/km G. 17C

Explanation / Answer

Dewpoint temperature(Td) = Temperature-(100-RH)/5

=> Relative Humidity(RH)= 100-5(T-Td)

Now,

Ans a)

Temperature at A= 27 degrees Celcius

Dewpoint temp = 17  degrees Celcius

Relative humidity at point A = 50 %

Relative humidity at point C = 100%

Relative humidity on the leeward side = 0%

On the windward side the parcel experiences wet adiabatic lapse rate and on the leeward side, it experiences dry adiabatic lapse rate.

Ans b)

Clouds will start to form at a height of 2 km.

Ans c)

Air temperature at G is far greater than that at A. This is because the air is moist at A and experiences moist adiabatic lapse rate while cooling but when the parcel descends on the leeward side, it experiences dry adiabatic lapse rate and therefore rises in temperature at a higher rate.

Ans d)

The water vapour content decreased at a fast rate as the parcel of air moved from point C to E. The loss of water was in the form of precipitation.

Ans e) We would expect lush vegetation on the windward side because it receives heavy rainfall. On the leeward side, desert-like conditions prevail because of hot dry prevailing air.

Ans f) We find such winds on the west coast of the United States. Chinook winds are a typical example.

Point Temperature in degree celsius Dew point temperature in degree celsius B 22 12 C 17 17 D 12 12 E 22 2 F 32 12 G 42 22

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