Search

The new single-pixel TROPESS (TRopospheric Ozone and its Precursors from Earth System Sounding) profile retrievals of carbon monoxide (CO) from the Cross-track Infrared Sounder (CrIS) are evaluated using vertical profiles of in situ observations from the National Oceanic and Atmospheric Administration (NOAA) Global Monitoring Laboratory (GML) aircraft program and from the Atmospheric Tomography Mission (ATom) campaigns. The TROPESS optimal estimation retrievals are produced using the MUSES (MUlti-SpEctra, MUlti-SpEcies, MUlti-Sensors) algorithm, which has heritage from retrieval algorithms developed for the EOS/Aura Tropospheric Emission Spectrometer (TES). TROPESS products provide retrieval diagnostics and error covariance matrices that propagate instrument noise as well as the uncertainties from sequential retrievals of parameters such as temperature and water vapor that are required to estimate the carbon monoxide profiles. The validation approach used here evaluates biases in column and profile values as well as the validity of the retrieval error estimates using the mean and variance of the compared satellite and aircraft observations. CrIS–NOAA GML comparisons had biases of 0.6 % for partial column average volume mixing ratios (VMRs) and (2.3, 0.9, −4.5) % for VMRs at (750, 511, 287) hPa vertical levels, respectively, with standard deviations from 9 % to 14 %. CrIS–ATom comparisons had biases of −0.04 % for partial column and (2.2, 0.5, −3.0) % for (750, 511, 287) hPa vertical levels, respectively, with standard deviations from 6 % to 10 %. The reported observational errors for TROPESS/CrIS CO profiles have the expected behavior with respect to the vertical pattern in standard deviation of the comparisons. These comparison results give us confidence in the use of TROPESS/CrIS CO profiles and error characterization for continuing the multi-decadal record of satellite CO observations.

The vertical distribution of ozone plays an important role in atmospheric chemistry, climate change, air pollution, and human health. Over the twenty-first century, spaceborne remote sensing methods and instrumentation have evolved to better characterise this distribution. We quantify the ability of ozone retrievals to characterise this distribution through a combination of thermal infrared (TIR) and Ultra Violet (UV) spectral radiances, harnessing co-located TIR measurements from the Cross Track Infrared Sounder (CrIS), onboard the Suomi National Polar-orbiting Partnership (NPP), and UV measurements from the TROPospheric Monitoring Instrument (TROPOMI), which is on the Sentinel 5-Precursor (S5P) satellite. The combination of TIR and UV measurements improves the ability of satellites to characterise global ozone profiles, over the use of each band individually. The CrIS retrievals enhanced by TROPOMI radiances in the Huggins band (325–335 nm) show good agreement with independent datasets both in the troposphere and in the stratosphere in spite of calibration issues in the TROPOMI UV. Improved performance is characterised in the stratosphere from CrIS-TROPOMI. Comparable performance between CrIS-TROPOMI and CrIS-only is found in the troposphere with degrees of freedom for signal of about 2 globally, but higher in the tropics partitioned equally between the lower and upper troposphere. These results demonstrate that CrIS/TROPOMI retrievals have the potential to substantially improve our understanding of ozone. If spectral accuracy is improved in future TROPOMI calibration, the degrees of freedom of signal in the stratosphere could double when using bands 1 and 2 of TROPOMI (270–330 nm), while tropospheric degrees of freedom of signal could increase by 25 %.