# Environmental lapse rate

Topics: Dew point, Atmospheric thermodynamics, Thermodynamic diagrams Pages: 10 (2405 words) Published: February 16, 2014
The Environmental Lapse Rate
Exercise A (Total = 12 marks)
The heights of the temperature °c measurements are given in meters (m) Convert each of these to the appropriate height in Hectopascals (hPa):

Height (m)Temperature°cHectopacals (hPa)
0221000
150018850
300013700
40007600
5000-15500
6000-22400
7000-36300
8000-41200
8500-49150
9000-58100

a) Plot a simple graph to display these data (3 marks): see attached b) what does the graph tell you about the temperature profile? (1 mark). I can infer that as the height in meters increases along with pressure (Pascal’s) the temperature decreases.

Calculate the environmental lapse rate (ELR) on the basis of the data given (show all stages of your working and the units involved) (4 marks). The environmental lapse rate (ELR) on the data given is

8.8 (recurring)…

I have calculated this by taking away the highest temperature from the lower: 22°c -(-58°c)= 80°c∴ there is a 80°c overall change in temperature over 9000m 9000÷9= 1000
And… 80÷9= 8.88888….

Suggest one cause of error in using only the temperatures at the lowest and highest heights to calculate the ELR (2 marks). One error in only taking the highest and lowest temperatures only into account when calculating ELR is that there may be fluctuations within the altitudes e.g. a rise at 3500m from 3000m then a fall at 4000m as it is most likely that there isn’t a direct decrease in temperature

Calculating ‘parcel’ lapse rates and cooling
Exercise B (Total = 12 marks)
A parcel of unsaturated air moves upwards from the ground. The temperature measured at the ground is 15. Assuming that the air parcel moves adiabatically through the atmosphere, what will be its temperature at each pressure level up to and including 500 hPa? (Assume ground level is equivalent to 1000 hPa) (4 marks). Height (hPa)Temperature°c

500-35
600-25
700-15
800-5
9005
100015

If the parcel is then forced down to a height of 3000 m, what will its temperature be? (2 marks).

If a parcel is then forced down a height of 3000m, its temperature will be -15°c as 3000m is 700hPa. This is due to the fact that the atmospheric pressure at 3000m is 700hPa. Temperature decreases along the DALR because the air parcel expands. This is due to fact that pressure decreases within the atmosphere.

Re-calculate parts (1) and (2) but this time assume that air parcel is saturated (6 marks). Height (hPa)Temperature°c
500-15
600-9
700-3
8003
9009
100015

If the saturated air parcel is now forced down a height of 3000m, its temperature will be -3°c as 3000m is equal to 700hPa

Environmental Stability
Exercise C (Total = 10 marks)
The following temperature soundings are obtained:

Height (hPa)Temperature°cSaturated air parcel (°c/1000m/100hpa)Unsaturated air parcel (°c/1000m/100hPa) 1000343434
800122214
7002164
600-210-6
500-124-16
300-25-8-36
200-30-14-46

The stability of the atmosphere with the saturated air mass is unstable as the air mass is warmer than the environment. However if the parcel of air were to be saturated from ground level, it would rise in the atmosphere and decrease in temperature at the SALR. But this parcel of air would carry on ascending in the atmosphere, making it stable.

The unsaturated air mass is conditionally unstable, as it will rise to about at 600hPa/4000m the parcel of air becomes saturated as it has become cooler than the environmental temperature surrounding it. It will then continue to decreasing in temperature at the saturated adiabatic lapse rate (SALR) of around 6°c /1000m, as it descends making it unstable

Dew points, relative humidity and cloud formation
Exercise D (Total = 22 marks)

Plot a graph of mixing ratio vs. temperature and use this to help answer the questions in this section (6 marks). The graph may be plotted either in Excel or...

References: John W. James. (2011). Sierra Nevada. Available: http://www.britannica.com/EBchecked/topic/543431/Sierra-Nevada. Last accessed 11th Nov 2013
Bruce Walters. (2009). lee wave. Available: http://www.britannica.com/EBchecked/topic/334629/lee-wave. Last accessed 11 Nov 2013.
N/A. (2010). Topographic lifting. Available: http://apollo.lsc.vsc.edu/classes/met130/notes/chapter6/lift_topo_wave.html. Last accessed 11 Nov 2013.
Brian J. Billings. (2007). SIERRA ROTORS. A COMPARATIVE STUDY OF THREE MOUNTAIN WAVE AND ROTOR EVENTS. n/a (N/A), p1-18.
Brian J. Billings. (2007). SIERRA NEVADA. CLIMATOLOGY OF WESTERLY WIND EVENTS IN THE LEE OF. n/a (N/A), p1-5.