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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/amt-2019-504
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2019-504
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  31 Jan 2020

31 Jan 2020

Review status
A revised version of this preprint was accepted for the journal AMT and is expected to appear here in due course.

Establishment of AIRS Climate-Level Radiometric Stability using Radiance Anomaly Retrievals of Minor Gases and SST

L. Larrabee Strow and Sergio DeSouza-Machado L. Larrabee Strow and Sergio DeSouza-Machado
  • Dept of Physics and JCET, University of Maryland Baltimore County, Baltimore, Maryland

Abstract. Temperature, H2O, and O3 profiles, as well as CO2, N2O, CH4, CFC12, and SST scalar anomalies are computed using a clear subset of AIRS observations over ocean for the first 16-years of NASA's EOS-AQUA AIRS operation. The AIRS Level 1c radiances are averaged over 16 days and 40 equal-area zonal bins and then converted to brightness temperature anomalies. Geophysical anomalies are retrieved from the brightness temperature anomalies using a relatively standard optimal estimation approach. The CO2, N2O, CH4, and CFC12 anomalies are derived by applying a vertically uniform multiplicative shift to each gas in order to obtain an estimate for the ngas mixing ratio. The minor gas anomalies are compared to the NOAA ESRL in-situ values and used to estimate the radiometric stability of the AIRS radiances. Similarly the retrieved SST anomalies are compared to the SST values used in the ERA-Interim reanalysis and to NOAA's OISST SST product. These inter-comparisons strongly suggest that many AIRS channels are stable to better than 0.02 to 0.03 K/Decade, well below climate trend levels, indicating that the AIRS blackbody is not drifting. However, detailed examination of the anomaly retrieval residuals (observed minus computed) show various small unphysical shifts that correspond to AIRS hardware events (shutdowns, etc.). Some examples are given highlighting how the AIRS radiances stability could be improved, especially for channels sensitive to N2O and CH4. The AIRS short wave channels exhibit larger drifts that make them unsuitable for climate trending, and they are avoided in this work. The AIRS Level 2 surface temperature retrievals only use short wave channels. We summarize how these short wave drifts impacts recently published comparisons of AIRS surface temperature trends to other surface climatologies.

L. Larrabee Strow and Sergio DeSouza-Machado

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L. Larrabee Strow and Sergio DeSouza-Machado

L. Larrabee Strow and Sergio DeSouza-Machado

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Latest update: 04 Aug 2020
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Short summary
The NASA AIRS satellite instrument has measured the infrared emission of the Earth continuously since 2002. If AIRS measurements are stable, these radiances can provide globally consistent multi-decade trends of important climate variables, including the Earth's surface temperature, and the atmospheric temperature and humidity versus height. Using the sensitivity of the AIRS radiances to well-known carbon dioxide trends, we show that AIRS is stable to 0.02K/decade, well below climate trends.
The NASA AIRS satellite instrument has measured the infrared emission of the Earth continuously...
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