Tsuneaki Suzuki

Effects of band division on radiative calculations

Band division is an important basis in radiative calculations, and the configuration of band divisions for various research purposes directly influences the accuracy and speed of radiative transfer compu- tations. We explore four band-division schemes and their impacts on computed radiative fluxes and cooling rates. We explain that discrepan- cies in solar radiation at the surface that exist between radiation models and observations under clear-sky conditions arise partly from ignoring minor gases and weak absorption bands for major gases.

Multiple‐Scaling Method for Anisotropic Scattering And Its Applications to Radiance Calculations

Radiative transfer (RT) equation for anisotropic light scattering due to large particles is often solved using so‐called truncation approximation, which accelerates computation by approximating the phase function by a finite series truncated at a limited number of terms or by a geometrically‐truncated function. The approximation produces bias in computed radiance. This study devoted to reduce the bias. It is shown that different truncation approximations can be used for each order of scattering and that accurate radiance can be obtained by using exact phase function for the first‐order scattering and truncated, approximated function for multiple scattering. If the degree of approximation is small for the first three or four scattering events, highly accurate radiance can be calculated even if higher‐order scattering is treated with scaled properties with a smooth phase function. The multiple‐scaling method has been implemented in a new linearized radiative transfer model, which has been developed for the ...

AGCM experiment of the effect of cumulus suppression on convection center formation over the Bay of Bengal

[1] We examined the effect of cumulus triggering on the distribution of precipitation during the Indian summer monsoon using the CCSR/NIES/FRCGC atmospheric general circulation model (AGCM) with different cumulus parameterizations. To investigate the effect, we carried out two kinds of simulation. The no-cumulus-suppression (NOCS) run used the original AGCM in which we implemented the prognostic Arakawa-Schubert (AS) scheme. In the other run, we introduced cumulus suppression (CS) as an additional condition of the AS scheme; the CS permitted cumulus convection only when the environmental relative humidity averaged in the modeled cumulus cloud region of the AS scheme exceeded 80%. Special attention was given to the formation of the convection center over the Bay of Bengal (CCBB). The NOCS run could not reproduce the CCBB because the original AS scheme was controlled solely by the convective available potential energy (CAPE). In the CS run, the CS suppressed the unrealistic precipitation simulated in the NOCS run east of the Indian subcontinent (around Sri Lanka) through large-scale topographical effects and well reproduced the westward propagating disturbances coming from the South China Sea and Indochina Peninsula. The westward propagating disturbances created heavy rain in the Bay of Bengal. As a result, the CS run reproduced the realistic distribution of precipitation during the Indian summer monsoon. The AGCM experiment showed that the triggering of cumulus convection played a key role in the distribution of precipitation in the Indian summer monsoon. For instance, the CS suppressed the unrealistic precipitation east of the Indian subcontinent. In addition, in the CS run, ascending motion orographically produced by the large-scale horizontal flow triggered cumulus convection around the northeast coast of the Bay of Bengal, and the propagating disturbances brought heavy rainfall to the Bay of Bengal.