Residual temperature bias effects in stratospheric species distributions from LIMS

Abstract

pThe 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 ( classCombining double low line"inline-formula"iA/i) minus descending ( classCombining double low line"inline-formula"iD/i) orbital temperature-pressure or classCombining double low line"inline-formula"iT/i(ip/i) profiles (their classCombining double low line"inline-formula"iA/i-iD/i values) that affect ( classCombining double low line"inline-formula"iA/i-iD/i) species values. Systematic classCombining double low line"inline-formula"iA/i-iD/i biases in classCombining double low line"inline-formula"iT/i(ip/i) can arise from small radiance biases and/or from viewing anomalies along orbits. There can also be ( classCombining double low line"inline-formula"iA/i-iD/i) differences in classCombining double low line"inline-formula"iT/i(ip/i) due to not resolving and correcting for all of the atmospheric temperature gradient along LIMS tangent view-paths. An error in classCombining double low line"inline-formula"iT/i(ip/i) 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 classCombining double low line"inline-formula"iA/i-iD/i differences for ozone, H classCombining double low line"inline-formula"2O, and HNO classCombining double low line"inline-formula"3 but not for NO classCombining double low line"inline-formula"2. Percentage differences are larger in the lower stratosphere for ozone and H classCombining double low line"inline-formula"2O 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 classCombining double low line"inline-formula"2O, and potential vorticity for the middle stratosphere to show that their average ( classCombining double low line"inline-formula"iA/i+iD/i) 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 classCombining double low line"inline-formula"2O, while keeping in mind that there are uncorrected nonlocal thermodynamic equilibrium effects in daytime ozone in the lower mesosphere and in daytime H classCombining double low line"inline-formula"2O 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./p.