add xlat fix in radiation_gases.f from Dustin

Author: grantfirl

physics/Radiation/radiation_gases.f

@@ -896,7 +896,7 @@ subroutine getgases( plvl, xlon, xlat, IMAX, LMAX, ico2flg,       &
         do i = 1, IMAX
           xlon1 = xlon(i)
           if ( xlon1 < 0.0 ) xlon1 = xlon1 + con_pi  ! if xlon in -pi->pi, convert to 0->2pi
-          xlat1 = hfpi - xlat(i)                     ! if xlat in pi/2 -> -pi/2 range
+          xlat1 = max(0._kind_phys, hfpi - xlat(i))  ! if xlat in pi/2 -> -pi/2 range
 !note     xlat1 = xlat(i)                            ! if xlat in 0 -> pi range
 
           ilon = min( IMXCO2, int( xlon1*tmp + 1 ))