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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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Atmos. Meas. Tech., 9, 4355-4373, 2016
https://doi.org/10.5194/amt-9-4355-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
06 Sep 2016
Evaluation of water vapour assimilation in the tropical upper troposphere and lower stratosphere by a chemical transport model
Swagata Payra1,2,a, Philippe Ricaud1, Rachid Abida1, Laaziz El Amraoui1, Jean-Luc Attié1,2, Emmanuel Rivière3, Fabien Carminati4, and Thomas von Clarmann5 1CNRM, Météo-France, CNRS UMR3589, Toulouse, France
2Laboratoire d'Aérologie, Université de Toulouse, CNRS UMR5560, Toulouse, France
3GSMA, CNRS, Université Champagne Ardennes, Reims, France
4Met Office, Exeter, UK
5KIT, Karlsruhe, Germany
anow at: Birla Institute of Technology Mesra, Jaipur Campus, Rajasthan, India
Abstract. The present analysis deals with one of the most debated aspects of the studies on the upper troposphere/lower stratosphere (UTLS), namely the budget of water vapour (H2O) at the tropical tropopause. Within the French project “Multiscale water budget in the upper troposphere and lower stratosphere in the TROpics” (TRO-pico), a global-scale analysis has been set up based on space-borne observations, models and assimilation techniques. The MOCAGE-VALENTINA assimilation tool has been used to assimilate the Aura Microwave Limb Sounder (MLS) version 3.3 H2O measurements within the 316–5 hPa range from August 2011 to March 2013 with an assimilation window of 1 h. Diagnostics based on observations minus analysis and forecast are developed to assess the quality of the assimilated H2O fields. Comparison with an independent source of H2O measurements in the UTLS based on the space-borne Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) observations and with meteorological ARPEGE analyses is also shown. Sensitivity studies of the analysed fields have been performed by (1) considering periods when no MLS measurements are available and (2) using H2O data from another MLS version (4.2). The studies have been performed within three different spaces in time and space coincidences with MLS (hereafter referred to as MLS space) and MIPAS (MIPAS space) observations and with the model (model space) outputs and at three different levels: 121 hPa (upper troposphere), 100 hPa (tropopause) and 68 hPa (lower stratosphere) in January and February 2012. In the MLS space, the analyses behave consistently with the MLS observations from the upper troposphere to the lower stratosphere. In the model space, the analyses are wetter than the reference atmosphere as represented by ARPEGE and MLS in the upper troposphere (121 hPa) and around the tropopause (100 hPa), but are consistent with MLS and MIPAS in the lower stratosphere (68 hPa). In the MIPAS space, the sensitivity and the vertical resolution of the MIPAS data set at 121 and 100 hPa prevent assessment of the behaviour of the analyses at 121 and 100 hPa, particularly over intense convective areas as the South American, the African and the Maritime continents but, in the lower stratosphere (68 hPa), the analyses are very consistent with MIPAS. Sensitivity studies show the improvement on the H2O analyses in the tropical UTLS when assimilating space-borne measurements of better quality, particularly over the convective areas.

Citation: Payra, S., Ricaud, P., Abida, R., El Amraoui, L., Attié, J.-L., Rivière, E., Carminati, F., and von Clarmann, T.: Evaluation of water vapour assimilation in the tropical upper troposphere and lower stratosphere by a chemical transport model, Atmos. Meas. Tech., 9, 4355-4373, https://doi.org/10.5194/amt-9-4355-2016, 2016.
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Short summary
The study deals with the budget of water vapour (H2O) at the tropical tropopause. The MOCAGE-VALENTINA assimilation tool has been used to assimilate Microwave Limb Sounder H2O space-borne measurements within the 316–5 hPa range from August 2011 to March 2013. Diagnostics are developed to assess the quality of the analyses depending on several parameters. Sensitivity studies show the improvement on the analyses when assimilating measurements of better quality, mainly over the convective areas.
The study deals with the budget of water vapour (H2O) at the tropical tropopause. The...
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