157 Recent Enhancements and Applications of AER's Radiation Models LBLRTM, MonoRTM, OSS, and RRTMG

Monday, 7 July 2014
Karen E. Cady-Pereira, AER, Lexington, MA; and M. J. Alvarado, D. Berthiaume, M. J. Iacono, P. Liang, A. E. Lipton, E. J. Mlawer, J. L. Moncet, V. Payne, and G. Uymin

The radiative transfer models developed at AER are used extensively for a wide range of applications in the atmospheric sciences. In this presentation we will summarize recent enhancements that have been made to these models, present illustrative model applications, and present results of ongoing validation efforts for each model.

AER's line-by-line model LBLRTM is widely regarded as a reference standard within the atmospheric community, with users across a range of disciplines in government agencies, industry, and academia. LBLRTM has been used as the basis of the forward models for the Infrared Atmospheric Sounding Interferometer (IASI) and the NASA Tropospheric Emission Spectrometer (TES). LBLRTM v12.1 calculations in the thermal infrared have been recently validated against a global set of observations from IASI.

MonoRTM is used to train the forward models for microwave channels in the Community Radiative Transfer Model (CRTM) and is widely used in the DOE Atmospheric Systems Research (ASR) program. A major upgrade, called MonoRTM_v5.0, has just been developed and released. The model has been upgraded to utilize line parameters from HITRAN 2012, with the exception of certain water vapor lines (e.g., the 22 and 183 GHz lines) for which carefully validated values are used. MonoRTM_v5.0 has also been enhanced to allow the use of additional broadening information (e.g., broadening of O2 lines by H2O) and to calculate speed dependent Voigt line shapes.

AER's Optimal Spectral Sampling (OSS) method allows the fast and accurate calculation of channel radiances throughout the microwave, visible, and ultraviolet regions. OSS has been implemented in the Joint Center for Satellite Data Assimilation (JCSDA) Community Radiative Transfer Model (CRTM) and in the U. Wisc. UWPHYSRET retrieval package, and is the method selected by EUMETSAT for the operational MTG/IRS L2 processing. Among the advantages of the OSS method is that its numerical accuracy, with respect to LBLRTM and MonoRTM, is selectable, allowing OSS to provide whatever balance of accuracy and computational speed is optimal for a particular application. The number of variable gaseous absorbers available in OSS has been recently increased to 20 to support TES applications. Other recent refinements to OSS include a global training approach (that increases speed by an order of magnitude for hyperspectral sounding sensors), the acceleration of the scattering calculations, and the treatment of Doppler shift.

The accurate and fast radiative transfer models RRTM and RRTMG calculate shortwave fluxes, longwave fluxes, and cooling rates; RRTMG has been implemented in numerous numerical weather prediction (NWP) and climate models. These models use the correlated-k method, and the absorption coefficients used to build the k-distributions were obtained from LBLRTM. RRTM retains the highest accuracy relative to line-by-line results for single column calculations, while RRTMG provides improved efficiency with minimal loss of accuracy for dynamical model applications. RRTMG was recently expanded to take advantage of the time savings offered by graphics processing units (GPUs).

The AER radiative transfer models LBLRTM, MonoRTM, RRTM, and RRTMG and the associated databases (e.g., line parameters, continua, and molecular cross-sections) are publicly available from AER (http://www.rtweb.aer.com).

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