Changes between Version 25 and Version 26 of doc/tec/radiation

Timestamp:

Apr 5, 2016 10:19:38 AM (9 years ago)

Author:

maronga

Comment:

--

doc/tec/radiation

@@ -114 +114 @@
 
 === Basics ===
+
+The RRTMG scheme is used as a "black box" in PALM. The main advantage is that radiative effects of clouds are explicitly treated in RRTMG. RRTMG is used as a vertical column model called for each horizontal grid point. Effects of cloud shadows that depend on the declination of the sun and horizontal radiative transfer are neglected at the moment. Moreover, ice clouds are not considered. In principle, the coupling to PALM is realized by performing the following steps each time RRTMG is called:
+1. Provide vertical profiles of actual temperature and water vapor mixing ratio for the LES column at full and half levels of the RRTMG grid
+2. Provide vertical profiles of the in-cloud liquid water path and the effective droplet radius for each grid volume for each LES column in case of clouds
+3. Call RRTMG longwave radiation routine using the above profiles
+4. (is sun is up) call RRTMG longwave radiation routine using the above profiles
+5. RRTMG provides radiative surface fluxes (longwave incoming, longwave outgoing, shortwave incoming, shortwave outgoing) as well as shortwave and longwave heating rates for each grid volume in the LES column. Moreover a tendency for the change in outgoing longwave radiation for a change in surface temperature is provided.
+6. Calculate net radiation
+
+The calculated heating rates are later used as tendency terms in the prognostic equations for temperature. The radiative fluxes are used in the solver for the energy budget of the Earth's surface.
+
+As the radiative transfer is done from the surface to the top of the atmosphere, the LES profiles need to be extended in the vertical direction. Moreover, RRTMG requires profiles of pressure and trace gases in the atmosphere. During initialization, vertical sounding data and trace gas sounding are read from two netCDF files (such sounding data is delivered as two netCDF files with RRTMG and is used by default in PALM. The user can replace these files to adjust the sounding profiles). 
+
+The following profiles must be provided to RRTMG:
+* hydrostatic pressure at full and half levels
+* temperature at full and half levels
+* H20 mixing ratio
+* O3 mixing ratio
+* O2 mixing ratio
+* CO2 mixing ratio
+* CH4 mixing ratio
+* N20 mixing ratio
+* CFC11 mixing ratio
+* CFC 12 mixing ratio
+* CFC 22 mixing ratio
+* CCL4 mixing ratio
+In order to avoid large gradients at the interface between PALM's upper boundary and the upper atmospheric profiles, temperature and H20 mixing ratio profiles are gradually blended over 5 grid points above the LES domain.
+
+Note that additionally, several flag parameters required by RRTMG are automatically set in PALM.
+
+
+==== Calculation of surface albedos