Westerly winds coming from offshore push air from sea-level (0 m) up and over a

Question

Westerly winds coming from offshore push air from sea-level (0 m) up and over a 3000 m tall coastal mountain. The air then descends down the east side to a valley floor that has an elevation of 0 m. At the base of the west side (starting point) the temperature of the air is 30OC and the dewpoint temperature is 14OC. At some altitude, a cloud base forms around the entire mountain and extends over the peak of the mountain. (2 points each)

Use the saturation vapor pressure chart below as needed to answer the following questions. Use a straightedge and be precise. ?
NOTE! The dewpoint decreases by 2OC per km of altitude increase in unsaturated air.

(a) What is the vapor pressure at the base of the mountain on the west side in mb? ?

(b) What is the saturation vapor pressure at the base of the mountain on the west side in mb? ?

(c) What is the relative humidity at the base of the mountain on the west side in %? ?

(d) What is the altitude of the cloud base in meters? ?

(e) What is the cloud base vapor pressure in mb? ?

(f) What is the cloud base dew point temperature in ?C? ?

(g) What is the temperature on the mountain top?

(h) What is the temperature at the mountain base on the east side in ?C?

Having a hard time determing how to incorporate and the use the graph to get answers.

140 130 120 110 E 100 90 70 60 540 10 20-15-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 2 20 -15 -10 -5 05 10 15 20 25 30 35 40 45 50 55 60 Temperature (C) 2

Explanation / Answer

temperature of the air, T= 30OC

Dew point temperature,Td=14oC

a) vapor pressure at the base of the mountain on the west side in mb

We have T and Td, and Td=T-[(100-RH)/5]. From that we can calculate Relative humidity, RH.

We know RH=(actual vapor pressure/saturated vapor pressure)*100

From this we can calculate actual vapor pressure.

So, Td=T-[(100-RH)/5]

14=30-[(100-RH)/5]

RH=20%

RH=(e/es)*100,

We can find saturated vapor pressure, es from the graph, es at T,30oc=40mb

20=(e/40)*100

There for vapor prssure,e=8mb

b) saturation vapor pressure at the base of the mountain on the west side in mb

"es" at base of the mountain on the west side is es at T, 30oc=40mb

c) Relative humidity at the base of the mountain on the west side in %

We already calculated RH in the first part of the question (a)

RH= 20%

d) Altitude of the cloud base in meters

The rising air cools at the dry adiabatic rate of about 10°C per 1000 m, and the dew point drops at about 2°C per 1000 m, the air temperature and dew point approach each other at the rate of 8°C for every 1000 m of rise. Rising surface air with an air temperature and dew point spread of 8°C would produce saturation and a cloud at an elevation of 1000 m. Put another way, a 1°C difference between the surface air temperature and the dew point produces a cloud base at 125 m. Therefore, by finding the difference between surface air temperature (T) and dew point (TdTd), and multiplying this value by 125, we can estimate the base of the convective cloud forming overhead, as Hmeter=125(TTd)

Hmeter=125(TTd)m

=125(30-14)m=2000m

e) The cloud base vapor pressure in mb

The rising air cools at the dry adiabatic rate of about 10°C per 1000 m, and the dew point drops at about 2°C per 1000 m.

So temperature at cloud base altitude,2000m is 10oc

and Td at cloud bas altitude, 2000m is 10oC

So RH=100%

RH=e/es*100=100

e/es=1

saturated vapor pressure, es at temperature, T(10oC) at cloud base is 10mb

so e=10mb

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