Evaluation of MUSICA IASI tropospheric water vapour profiles using theoretical error assessments and comparisons to GRUAN Vaisala RS92 measurements

Abstract

Abstract. Volume mixing ratio water vapour profiles have been retrieved from IASI (Infrared Atmospheric Sounding Interferometer) spectra using the MUSICA (MUlti-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water) processor. The retrievals are done for IASI observations that coincide with Vaisala RS92 radiosonde measurements performed in the framework of the GCOS (Global Climate Observing System) Reference Upper-Air Network (GRUAN) in three different climate zones: the tropics (Manus Island, 2° S), mid-latitudes (Lindenberg, 52° N), and polar regions (Sodankylä, 67° N). The retrievals show good sensitivity with respect to the vertical H2O distribution between 1 km above ground and the upper troposphere. Typical DOFS (degrees of freedom for signal) values are about 5.6 for the tropics, 5.1 for summertime mid-latitudes, 3.8 for wintertime mid-latitudes, and 4.4 for summertime polar regions. The errors of the MUSICA IASI water vapour profiles have been theoretically estimated considering the contribution of many different uncertainty sources. For all three climate regions, unrecognized cirrus clouds and uncertainties in atmospheric temperature have been identified as the most important error sources and they can reach about 25 %. The MUSICA IASI water vapour profiles have been compared to 100 individual coincident GRUAN water vapour profiles. The systematic difference between the data is within 11 % below 12 km altitude; however, at higher altitudes the MUSICA IASI data show a dry bias with respect to the GRUAN data of up to 21 %. The scatter is largest close to the surface (30 %), but never exceeds 21 % above 1 km altitude. The comparison study documents that the MUSICA IASI retrieval processor provides H2O profiles that capture the large variations in H2O volume mixing ratio profiles well from 1 km above ground up to altitudes close to the tropopause. Above 5 km the observed scatter with respect to GRUAN data is in reasonable agreement with the combined MUSICA IASI and GRUAN random errors. The increased scatter at lower altitudes might be explained by surface emissivity uncertainties at the summertime continental sites of Lindenberg and Sodankylä, and the upper tropospheric dry bias might suggest deficits in correctly modelling the spectroscopic line shapes of water vapour.

Intercomparison of Arctic ground-based XH<sub>2</sub>O observations from COCCON, TCCON and NDACC, and application of COCCON XH<sub>2</sub>O for IASI and TROPOMI validation

“…Atmospheric temperature is also fitted but constrained strongly to the EUMETSAT IASI Level 2 temperature product. For more details on the MUSICA IASI retrievals and the validation of the MUSICA IASI H2O product please refer to Schneider et al (2016) and Borger et al (2018). The version presented here is an update as described by Borger et al (2018) using a priori profiles for the gases under consideration, which depend on season and latitude.…”

“…The overall column sensitivities of TCCON increase with increasing altitude, while the column sensitivities of COCCON decrease with increasing altitude. The AVKs for IASI and TROPOMI are not shown here but can be found in Borger et al, 2018 andSchneider et al, 2020, respectively. https://doi.org/10.5194/amt-2020-378 Preprint.…”

“…On the other hand, independent ground-based remote sensing instruments and in situ sensors do not give access to the global scale but can provide very accurate and long-term data, which can be used for satellite validation. Many studies have investigated water vapor comparisons among satellite and ground-based instruments (Schneider and Hase, 2011;Dupuy et al, 2016;Borger et al, 2018;Trieu et al, 2019), but there are only few studies that focus on the Arctic region (Pałm et al, 2010;Buehler et al, 2012;Alraddawi et al, 2018).…”

Reply on RC1

“…The MUSICA IASI data full retrieval product encompasses trace gas profiles of H 2 O, the HDO/H 2 O ratio, N 2 O, CH 4 , and HNO 3 . The data have been validated in several previous studies (Schneider et al, 2016;Borger et al, 2018;García et al, 2018), and it has been shown that the CH 4 product can very well detect the CH 4 signals originating in the upper troposphere/lower stratosphere. MUSICA IASI data using processor versions 3.2.1 and 3.3.0 are currently available for the 2014 to 2020 time period and are presented in Schneider et al (2021).…”

Intercomparison of arctic XH<sub>2</sub>O observations from three ground-based Fourier transform infrared networks and application for satellite validation

“…Conversely, independent ground-based remote sensing instruments and in situ sensors do not give access to the global scale, but they can provide very accurate and long-term data that can be used for satellite validation. Many studies have investigated water vapor comparisons among satellite and ground-based instruments (Schneider and Hase, 2011;Dupuy et al, 2016;Borger et al, 2018;Trieu et al, 2019), but there are only few studies that focus on the Arctic region (Pałm et al, 2010;Buehler et al, 2012;Alraddawi et al, 2018).…”