! File %M% from Library %Q% ! Version %I% from %G% extracted: %H% !------------------------------------------------------------------------------ REAL (KIND = ireals) FUNCTION SfcFlx_lwradatm (T_a, e_a, cl_tot, cl_low) !------------------------------------------------------------------------------ ! ! Description: ! ! Computes the long-wave radiation flux from the atmosphere ! as function of air temperature, water vapour pressure and cloud fraction. ! ! ! Current Code Owner: DWD, Dmitrii Mironov ! Phone: +49-69-8062 2705 ! Fax: +49-69-8062 3721 ! E-mail: dmitrii.mironov@dwd.de ! ! History: ! Version Date Name ! ---------- ---------- ---- ! 1.00 2005/11/17 Dmitrii Mironov ! Initial release ! !VERSION! !DATE! ! ! ! Code Description: ! Language: Fortran 90. ! Software Standards: "European Standards for Writing and ! Documenting Exchangeable Fortran 90 Code". !============================================================================== ! ! Declarations: ! ! Modules used: !_dm Parameters are USEd in module "SfcFlx". !_nu USE data_parameters , ONLY : & !_nu ireals, & ! KIND-type parameter for real variables !_nu iintegers ! KIND-type parameter for "normal" integer variables !============================================================================== IMPLICIT NONE !============================================================================== ! ! Declarations ! Input (function argument) REAL (KIND = ireals), INTENT(IN) :: & T_a , & ! Air temperature [K] e_a , & ! Water vapour pressure [N m^{-2} = kg m^{-1} s^{-2}] cl_tot , & ! Total cloud cover [0,1] cl_low ! Lowe-level cloud cover [0,1] ! Local parameters ! Coefficients in the empirical formulation ! developed at the Main Geophysical Observatory (MGO), St. Petersburg, Russia. REAL (KIND = ireals), PARAMETER :: & c_lmMGO_1 = 43.057924_ireals , & ! Empirical coefficient c_lmMGO_2 = 540.795_ireals ! Empirical coefficient ! Temperature-dependent cloud-correction coefficients in the MGO formula INTEGER (KIND = iintegers), PARAMETER :: & nband_coef = 6_iintegers ! Number of temperature bands REAL (KIND = ireals), PARAMETER, DIMENSION (nband_coef) :: & corr_cl_tot = (/0.70_ireals, 0.45_ireals, 0.32_ireals, & 0.23_ireals, 0.18_ireals, 0.13_ireals/) , & ! Total clouds corr_cl_low = (/0.76_ireals, 0.49_ireals, 0.35_ireals, & 0.26_ireals, 0.20_ireals, 0.15_ireals/) , & ! Low-level clouds corr_cl_midhigh = (/0.46_ireals, 0.30_ireals, 0.21_ireals, & 0.15_ireals, 0.12_ireals, 0.09_ireals/) ! Mid- and high-level clouds REAL (KIND = ireals), PARAMETER :: & T_low = 253.15_ireals , & ! Low-limit temperature in the interpolation formula [K] del_T = 10.0_ireals ! Temperature step in the interpolation formula [K] ! Coefficients in the empirical water-vapour correction function ! (see Fung et al. 1984, Zapadka and Wozniak 2000, Zapadka et al. 2001). REAL (KIND = ireals), PARAMETER :: & c_watvap_corr_min = 0.6100_ireals , & ! Empirical coefficient (minimum value of the correction function) c_watvap_corr_max = 0.7320_ireals , & ! Empirical coefficient (maximum value of the correction function) c_watvap_corr_e = 0.0050_ireals ! Empirical coefficient [(N m^{-2})^{-1/2}] ! Local variables of type INTEGER INTEGER (KIND = iintegers) :: & i ! Loop index ! Local variables of type REAL REAL (KIND = ireals) :: & c_cl_tot_corr , & ! The MGO cloud correction coefficient, total clouds c_cl_low_corr , & ! The MGO cloud correction coefficient, low-level clouds c_cl_midhigh_corr , & ! The MGO cloud correction coefficient, mid- and high-level clouds T_corr , & ! Temperature used to compute the MGO cloud correction [K] f_wvpres_corr , & ! Correction function with respect to water vapour f_cloud_corr ! Correction function with respect to cloudiness !============================================================================== ! Start calculations !------------------------------------------------------------------------------ ! Water-vapour correction function f_wvpres_corr = c_watvap_corr_min + c_watvap_corr_e*SQRT(e_a) f_wvpres_corr = MIN(f_wvpres_corr, c_watvap_corr_max) ! Cloud-correction coefficients using the MGO formulation with linear interpolation IF(T_a.LT.T_low) THEN c_cl_tot_corr = corr_cl_tot(1) c_cl_low_corr = corr_cl_low(1) c_cl_midhigh_corr = corr_cl_midhigh(1) ELSE IF(T_a.GE.T_low+(nband_coef-1_iintegers)*del_T) THEN c_cl_tot_corr = corr_cl_tot(nband_coef) c_cl_low_corr = corr_cl_low(nband_coef) c_cl_midhigh_corr = corr_cl_midhigh(nband_coef) ELSE T_corr = T_low DO i=1, nband_coef-1 IF(T_a.GE.T_corr.AND.T_a.LT.T_corr+del_T) THEN c_cl_tot_corr = (T_a-T_corr)/del_T c_cl_low_corr = corr_cl_low(i) + (corr_cl_low(i+1)-corr_cl_low(i))*c_cl_tot_corr c_cl_midhigh_corr = corr_cl_midhigh(i) + (corr_cl_midhigh(i+1)-corr_cl_midhigh(i))*c_cl_tot_corr c_cl_tot_corr = corr_cl_tot(i) + (corr_cl_tot(i+1)-corr_cl_tot(i))*c_cl_tot_corr END IF T_corr = T_corr + del_T END DO END IF ! Cloud correction function IF(cl_low.LT.0._ireals) THEN ! Total cloud cover only f_cloud_corr = 1._ireals + c_cl_tot_corr*cl_tot*cl_tot ELSE ! Total and low-level cloud cover f_cloud_corr = (1._ireals + c_cl_low_corr*cl_low*cl_low) & * (1._ireals + c_cl_midhigh_corr*(cl_tot*cl_tot-cl_low*cl_low)) END IF ! Long-wave radiation flux [W m^{-2}] ! The MGO formulation !_nu The MGO formulation !_nu SfcFlx_lwradatm = -SfcFlx_lwradatm*c_lwrad_emis & !_nu * (c_lmMGO_1*SQRT(tpsf_C_StefBoltz*T_a**4_iintegers)-c_lmMGO_2) !_nu ! "Conventional" formulation ! (see Fung et al. 1984, Zapadka and Wozniak 2000, Zapadka et al. 2001) SfcFlx_lwradatm = -c_lwrad_emis*tpsf_C_StefBoltz*T_a**4_iintegers & * f_wvpres_corr*f_cloud_corr !------------------------------------------------------------------------------ ! End calculations !============================================================================== END FUNCTION SfcFlx_lwradatm