VERY NARROW-BAND MODEL-CALCULATIONS OF ATMOSPHERIC FLUXES AND COOLINGRATES

A new very narrow band model (VNBM) approach has been developed and in corporated into the MODTRAN atmospheric transmittance-radiance code. T he VNBM includes a computational spectral resolution of 1 cm(-1), a si ngle-line Voigt equivalent width formalism that is based on the Rodger s-Williams approximation and accounts for the finite spectral width of the interval, explicit consideration of line tails, a statistical lin e overlap correction, a new sublayer integration approach that treats the effect of the sublayer temperature gradient on the path radiance. and the Curtis-Godson (CG) approximation for inhomogeneous paths. A mo dified procedure for determining the line density parameter 1/d is int roduced, which reduces its magnitude. This results in a partial correc tion of the VNBM tendency to overestimate the interval equivalent widt hs. The standard two parameter CG approximation is used for H2O and CO 2 while the Goody three parameter CG approximation is used for O-3. At mospheric flux and cooling rate predictions using a research version o f MODTRAN, MODR, are presented for H2O (with and without the continuum ), CO2, and O-3 for several model atmospheres. The effect of doubling the CO2 concentration is also considered. These calculations are compa red to line-by-line (LBL) model calculations using the AER, GLA, GFDL, and GISS codes. The MODR predictions fall within the spread of the LB L results. The effects of decreasing the band model spectral resolutio n are illustrated using CO2 cooling rate and flux calculations.