Retrieval of nitric oxide in the mesosphere and lower thermosphere from SCIAMACHY limb spectra

TL;DR

This study develops a retrieval method using SCIAMACHY UV spectra to measure nitric oxide densities in the mesosphere and lower thermosphere, providing near-global coverage and validation data for climate models.

Contribution

The paper introduces a novel 3-D retrieval algorithm for NO densities from SCIAMACHY limb spectra, with validation against MIPAS data and detailed resolution analysis.

Findings

Achieved 5-10 km vertical resolution in 70-140 km altitude range.

Obtained approximately global coverage from 60°S to 60°N.

Results agree well with existing MIPAS measurements.

Abstract

We use the ultra-violet (UV) spectra in the range 230--300 nm from the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) to retrieve the nitric oxide (NO) number densities from atmospheric emissions in the gamma-bands in the mesosphere and lower thermosphere. Using 3-D ray tracing, a 2-D retrieval grid, and regularisation with respect to altitude and latitude, we retrieve a whole semi-orbit simultaneously for the altitude range from 60 to 160 km. We present details of the retrieval algorithm, first results, and initial comparisons to data from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). Our results agree on average well with MIPAS data and are in line with previously published measurements from other instruments. For the time of available measurements in 2008--2011, we achieve a vertical resolution of 5--10 km in the altitude range 70--140 km and a horizontal resolution of about 9{\deg} from 60{\deg}S--60{\deg}N. With this we have independent measurements of the NO densities in the mesosphere and lower thermosphere with approximately global coverage. This data can be further used to validate climate models or as input for them.