deltap = ta - tsf + gamma_blk*ht
flwupa=ocean_emissivity*stefan*tsf**4
dflwupdT=4. _d 0*ocean_emissivity*stefan*tsf**3
flwupa=snow_emissivity*stefan*tsf**4
dflwupdT=4. _d 0*snow_emissivity*stefan*tsf**3
flwupa=ice_emissivity*stefan*tsf**4
dflwupdT=4. _d 0*ice_emissivity*stefan*tsf**3
_RL tsf ! surface temperature [K]