On the quality of the Nimbus 7 LIMS version 6 ozone for studies of the middle atmosphere

Abstract

The Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) radiance profile dataset of 1978/79 was reconditioned and reprocessed to Version 6 (V6) profiles of temperature and species that are improved significantly over those from Version 5 (V5). The LIMS V6 dataset was archived for public use in 2002.Improvements for its ozone include: (1) a more accurate accounting for instrument and spacecraft motion effects in the radiances, (2) the use of better spectroscopic line parameters for its ozone forward model, (3) retrievals of all its scans, (4) more accurate and compatible temperature versus pressure profiles (or T(p)), which are needed for the registration of the ozone radiances and for the removal of temperature effects from them, and (5) a better accounting for interfering species in the lower stratosphere. The retrieved V6 ozone profiles extend from near cloud top altitudes to about 80 km and from 64S to 84N latitude with better sampling along the orbit than for the V5 dataset. Calculated estimates of the single-profile precision and accuracy are provided for the V6 ozone from this study. Precision estimates based on the data themselves are of order 3% or better from 1 to 30 hPa. Estimates of total systematic error for a single profile are hard to generalize because the separate sources of error may not all be of the same sign and they depend somewhat on the atmospheric state. It is estimated that the V6 zonal mean ozone distributions are accurate to within ±9% to ±7% from 50 hPa to 3 hPa, respectively. Effects of a temperature bias can be significant and may be present at 1 to 2 hPa though. There may be ozone biases of order 10% at those levels due to possible biases of up to +2 K, but there is no indication of a similar problem elsewhere in the stratosphere.Simulation studies show that the LIMS retrievals are also underestimating slightly the small amplitudes of the atmospheric temperature tides, which affect its retrieved day/night ozone differences. There are small biases in the middle to lower stratosphere for the ascending versus descending node LIMS ozone, due principally to not accounting for the asymmetric weighting of its radiances across the tangent layer. The estimates of total accuracy were assessed by comparing the daily zonal mean LIMS ozone distributions against those from the Nimbus 7 SBUV Version 8 (V8) dataset for the same period. Generally, the LIMS V6 ozone agrees well with SBUV, except perhaps in the tropical lower stratosphere where the LIMS ozone is less. Still, the accuracy for LIMS V6 ozone in the lower stratosphere is improved over that found for LIMS V5, as indicated by several LIMS comparisons with ECC ozonesonde profiles. The LIMS V6 ozone 2 is considered especially suitable for detailed studies of large-scale stratospheric processes above the 100-hPa level. Comparison of diurnal, photochemical model calculations with the monthly-averaged, upper stratospheric ozone observed from LIMS V6 indicates only a slight ozone deficit for the model at about 2 hPa. However, that ...

A vertically resolved, global, gap-free ozone database for assessing or constraining global climate model simulations

“…Version 6 LIMS data were obtained from the NASA Goddard DAAC (http://daac.gsfc.nasa.gov/). Improvements in the quality of the temperature and geopotential height product over earlier versions are described in Remsberg et al (2004), while more recent improvements to the ozone product are described in Remsberg et al (2007). These LIMS data were available from 25 October 1978 to 28 May 1979 and provide valuable coverage early in the analysis period when few other ozone profile measurements were available.…”

On the quality of the Nimbus 7 LIMS Version 6 water vapor profiles and distributions

“…The H 2 O profiles also have a bias of order 10 to 15% due to estimates of the V6 temperature biases from Remsberg et al (2004, their Remsberg et al (1984b), followed by the zonal mean, V6 minus V5 differences for T(p) in Remsberg et al (2007, their Fig. 3).…”

“…In addition, many of the low altitude portions of the tropical profiles were cutoff due to their low signal levels in the tangent layer. A first-order screening was also conducted for the presence of the interfering emissions from clouds, as evaluated based on the character of the corresponding LIMS ozone profiles that are affected very little by the increasing water vapor of the upper troposphere (Remsberg et al, 2007). Radiance contamination due to clouds is prevalent near the tropical tropopause.…”

Effects of polar stratospheric clouds in the Nimbus 7 LIMS Version 6 data set

“…Then, a further screening for emissions from cirrus clouds was conducted based on instances of abrupt, spurious increases in the ozone mixing ratio in the region of the tropopause. That screening was conducted below the 45 hPa level equatorward of 30 • latitude and below the 100 hPa level poleward of that, as discussed in Remsberg et al (2007).…”