Retrieval of nitric oxide in the mesosphere from SCIAMACHY nominal limb spectra

Stefan Bender, Miriam Sinnhuber, Martin Langowski, John P. Burrows
2017 Atmospheric Measurement Techniques  
<p><strong>Abstract.</strong> We present a retrieval algorithm for nitric oxide (NO) number densities from measurements from the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY, on Envisat) nominal limb mode (0–91<span class="thinspace"></span>km). The NO number densities are derived from atmospheric emissions in the gamma bands in the range 230–300<span class="thinspace"></span>nm, measured by the SCIAMACHY ultra-violet (UV) channel 1. The retrieval is adapted
more » ... trieval is adapted from the mesosphere and lower thermosphere mode (MLT, 50–150<span class="thinspace"></span>km) NO retrieval (Bender et al., 2013), including the same 3-D ray tracing, 2-D retrieval grid, and regularisations with respect to altitude and latitude.<br><br>Since the nominal mode limb scans extend only to about 91<span class="thinspace"></span>km, we use NO densities in the lower thermosphere (above 92<span class="thinspace"></span>km), derived from empirical models, as a priori input. The priors are the Nitric Oxide Empirical Model (NOEM; Marsh et al., 2004) and a regression model derived from the MLT NO data comparison (Bender et al., 2015). Our algorithm yields plausible NO number densities from 60 to 85<span class="thinspace"></span>km from the SCIAMACHY nominal limb mode scans. Using a priori input substantially reduces the incorrect attribution of NO from the lower thermosphere, where no direct limb measurements are available. The vertical resolution lies between 5 and 10<span class="thinspace"></span>km in the altitude range 65–80<span class="thinspace"></span>km.<br><br>Analysing all SCIAMACHY nominal limb scans provides almost 10 years (from August 2002 to April 2012) of daily NO measurements in this altitude range. This provides a unique data record of NO in the upper atmosphere and is invaluable for constraining NO in the mesosphere, in particular for testing and validating chemistry climate models during this period.</p>
doi:10.5194/amt-10-209-2017 fatcat:si57ju7lyffhbkp33boil7euuu