5.1.2  Adjusted Average Temperature

Temperatures obtained from the LCD are adjusted for the elevation difference that may exist between the LCD station and the actual site.  In general, air temperatures decrease about 0.5 to 0.9^oC per 100 m (3 to 5^oF per 1000 ft) rise in altitude (Mockus 1971).  Using the ideal gas law with the assumption of dry adiabatic conditions, Eagleson (1970) derived an approximate lapse rate (i.e., rate of change of temperature with height in the free atmosphere) of   1^oC decrease per 100 m (5.5^oF decrease per 1000 ft).  This dry adiabatic lapse rate is a maximum rate (excluding superadiabatic conditions).  A mean lapse rate as suggested by Linsley et al. (1975) is a decrease of about 0.7^oC per 100 m (3.8^oF per 1000 ft) of vertical rise.  By using the mean lapse rate suggested by Linsley et al. (1975), the adjusted average monthly temperature is computed as follows:



where

T_aj   is the adjusted average monthly temperature at the actual site for the j-th month (C)
 T_uj   is the unadjusted average monthly temperature at the LCD station for the j-th month ( C)
  h₀  is the elevation of LCD station (m)
  h₁   is the elevation of actual site (m).