function hydrostatic,p1,p2,t1,t2

;--------------------------------------------------------------
; purpose:
;
;  calculate the geometric height, dz (km), between 2 levels
;
; input:
;   p1.....pressure at level 1 (mbar)
;   p2.....pressure at level 2 (mbar)
;   t1.....temperature at level 1 (K)
;   t2.....temperature at level 2 (K)
;
; output:
;   dz.....gemetric height between p1 and p2 (km)
;
; source: Mark Hervig
;   
;--------------------------------------------------------------

   dz = 0.001 * 0.5*(t1+t2)*alog(p2/p1)*287.05/9.80616

   return,dz
   end