3.1.2 Variation of Pressure with Elevation With the variation of temperature in the troposphere as found above, it is now rather straightforward to find the variation in pressure with (geopotential) elevation. Once again, beginning with the expression for a small change in pressure, dp-pg dz and assuming air to be an ideal gas: dp = dz RT The Standard Atmosphere go To + z ln In XR To And finally, p(z) = po (1+ % (1 + 1/2) T go XR (3.2) Elev (m) T (K) p (kPa) 0 288.2 101.33 500 284.9 95.46 1,000 281.7 89.88 2,000 275.7 79.50 5,000 255.7 54.05 8,850 230.7 31.50 11,000 216.8 22.70 See Appendix E for more details. Exercise 3.1(i) Using a constant specific heat ratio for air of cp/c = k = 1.4 and the fact that - = R for an ideal gas, estimate the DALR in the troposphere and express. your answer in C/km.