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

Abstract

Abstract. The historic Limb Infrared Monitor of the Stratosphere (LIMS) measurements of 1978-1979 from the Nimbus 7 satellite were re-processed with Version 6 (V6) algorithms and archived in 2002. The V6 data set employs updated radiance registration methods, improved spectroscopic line parameters, and a common vertical resolution for all retrieved parameters. Retrieved profiles are spaced about every 1.6 • of latitude along orbits and include the additional parameter of geopotential height. Profiles of O 3 are sensitive to perturbations from emissions of polar stratospheric clouds (PSCs). This work presents results of implementing a firstorder screening for effects of PSCs using simple algorithms based on vertical gradients of the O 3 mixing ratio. Their occurrences are compared with the co-located, retrieved temperatures and related to the temperature thresholds needed for saturation of H 2 O and/or HNO 3 vapor onto PSC particles. Observed daily locations where the major PSC screening criteria are satisfied are validated against PSCs observed with the Stratospheric Aerosol Monitor (SAM) II experiment also on Nimbus 7. Remnants of emissions from PSCs are characterized for O 3 and HNO 3 following the screening. PSCs may also impart a warm bias in the co-located LIMS temperatures, but by no more than 1-2 K at the altitudes of where effects of PSCs are a maximum in the ozone; thus, no PSC screening was applied to the V6 temperatures. Minimum temperatures vary between 187 and 194 K and often occur 1 to 2 km above where PSC effects are first identified in the ozone (most often between about 21 and 28 hPa). Those temperature-pressure values are consistent with conditions for the existence of nitric acid trihydrate (NAT) mixtures and to a lesser extent of super-cooled ternary solution (STS) droplets. A local, temporary uptake of HNO 3 vapor of order 1-3 ppbv is indicated during mid-January for the 550 K surface. Seven-month time series of the distributions of LIMS O 3 and HNO 3 are shown based on their gridded Level 3 data following the PSC screening. Zonal coefficients of both species are essentially free of effects from PSCs on the 550 K surface, based on their average values along PV contours and in terms of equivalent latitude. Remnants of PSCs are still present in O 3 on the 450 K surface during midJanuary. It is judged that the LIMS Level 3 data are of good quality for analyzing the larger-scale, stratospheric chemistry and transport processes during the Arctic winter of 1978-1979.

On the consistency of HNO<sub>3</sub> and NO<sub>2</sub> in the Aleutian High region from the Nimbus 7 LIMS Version 6 data set

“…Holt et al (2012) quantified the exchange of V6 NO 2 from the mesosphere to the middle stratosphere within the polar vortex. Remsberg and Harvey (2016) also found good relationships on the 550 K potential temperature surface (near 30 hPa) for the highest values of V6 HNO 3 , lowest values of ozone, and highest values of potential vorticity (PV) within the Arctic winter vortex. While there are residual effects from polar stratospheric clouds (PSCs) in the ozone and water vapor (H 2 O), those effects are small in the HNO 3 and NO 2 profiles and occur only at temperatures < 194 K and from about 1 to 20 January.…”

“…One exception is the relatively low values of HNO 3 near 80 • N, 0 • E on 17 January in Fig. 2d, which has been interpreted as due to an uptake of gas-phase HNO 3 onto PSC particles just upwind a day or so earlier (Remsberg and Harvey, 2016). However, by 27 January (Fig.…”