c$Author: fredfox $
c$Date: 2001-07-03 19:00:00 $
c$Revision: 1.1.2.1 $
c$Source: /weru/cvs/weps/weps.src/hydro/airtempsin.for,v $
      real*4 function airtempsin(tsec, tmax, tmin)

c     + + + PURPOSE + + +
c     Returns the value of air temperature as a function of time of day
c     using a sinusoidal approximation of temperature through the daily
c     maximum and daily minimum, which are assumed to occur at 6pm and
c     6am respectively.

c     + + + ARGUMENT DECLARATIONS + + +
      real*4  tsec, tmax, tmin

c     + + + ARGUMENT DEFINITIONS + + +
c     tsec  - time of day with 0 at midnight (seconds)
c     tmax  - daily maximum temperature (C)
c     tmin  - daily minimum temperature (C)

C*** LOCAL DECLARATIONS ***
      real*4 pi, halfperiod
      parameter( pi = 3.1415927 )
      parameter( halfperiod = 43200 )

      airtempsin = 0.5*(tmax + tmin
     &           + (tmax-tmin)*sin(pi*(tsec/halfperiod +1.0)))

      return
      end