Residual temperature bias effects in stratospheric species distributions from LIMS

摘要

The Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) instrument operated from 25?October?1978 through 28?May?1979. Its version 6 (V6) profiles were processed and archived in 2002. We present several diagnostic examples of the quality of the V6 stratospheric species distributions based on their level 3 zonal Fourier coefficient products. In particular, we show that there are small differences in the ascending ( A ) minus descending ( D ) orbital temperature–pressure or T ( p ) profiles (their A ? D values) that affect ( A ? D ) species values. Systematic A ? D biases in T ( p ) can arise from small radiance biases and/or from viewing anomalies along orbits. There can also be ( A ? D ) differences in T ( p ) due to not resolving and correcting for all of the atmospheric temperature gradient along LIMS tangent view-paths. An error in T ( p ) affects species retrievals through (1) the Planck blackbody function in forward calculations of limb radiance that are part of the iterative retrieval algorithm of LIMS, and (2) the registration of the measured LIMS species radiance profiles in pressure altitude, mainly for the lower stratosphere. There are clear A ? D differences for ozone, H 2 O, and HNO 3 but not for NO 2 . Percentage differences are larger in the lower stratosphere for ozone and H 2 O because those species are optically thick. We evaluate V6 ozone profile biases in the upper stratosphere with the aid of comparisons against a monthly climatology of UV–ozone soundings from rocketsondes. We also provide results of time series analyses of V6 ozone, H 2 O, and potential vorticity for the middle stratosphere to show that their average ( A + D ) V6 level 3 products provide a clear picture of the evolution of those tracers during Northern Hemisphere winter. We recommend that researchers use the average V6 level 3 product for their science studies of stratospheric ozone and H 2 O, while keeping in mind that there are uncorrected nonlocal thermodynamic equilibrium effects in daytime ozone in the lower mesosphere and in daytime H 2 O in the uppermost stratosphere. We also point out that the present-day Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment provides measurements and retrievals of temperature and ozone that are nearly free of anomalous diurnal variations and of effects from gradients at low and middle latitudes.