Abstract
AbstractThe tropospheric water vapor profile record from the Atmospheric Infrared Sounder (AIRS) now spans over a decade, making it a valuable resource for climate studies. To be considered as a Climate Data Record, it is key that the ultimate performance of these observations are understood. The Global Energy and Water cycle Exchanges (GEWEX) water vapor assessment has been tasked with characterizing the current state of the art in water vapor products currently available for climate analysis. Within the scope of this exercise, water vapor profiles from AIRS have been assessed using collocated characterized in situ measurements of tropospheric water vapor between 2007 and 2012. We first show how previously published methods for correcting radiosondes can be applied to global records, which show high correlations to Global Climate Observing System Reference Upper‐Air Network (GRUAN) performance at pressures between the surface and 250 hPa. We go further and show the first comparison of uncertainties from both the newly created Characterized Radiosonde Measurement (CRM) and GRUAN data sets. Global estimates of AIRS water vapor profile (wet/dry) biases relative to GRUAN and CRM are within 6 ± 0.3% ppmv and 15 ± 0.1% ppmv below 300 hPa, respectively. The CRM record allows latitudinal analysis for the first time, which when examined shows sensitivity to changes in absolute concentration due to large‐scale circulation in the International Tropical Convergence Zone. This paper advances the use of state‐of‐the‐art in situ records for characterizing absolute performance, recognizing that long‐term stability needs further research.
Highlights
Water vapor is an important greenhouse gas within the atmosphere that influences the radiative balance of the Earth as well as surface and soil moisture fluxes
For Atmospheric Infrared Sounder (AIRS), a water vapor profile is considered collocated with a Characterized Radiosonde Measurement (CRM) or Global Climate Observing System Reference Upper-Air Network (GRUAN) sounding if the satellite measurement falls within ±3 hr and 100 km of the radiosonde launch
These results indicate that both AIRS and GRUAN agree within 1.5% ppmv for four lowest layers
Summary
Water vapor is an important greenhouse gas within the atmosphere that influences (directly and indirectly) the radiative balance of the Earth as well as surface and soil moisture fluxes. Besides the large amount of available satellite data records such data records are updated frequently and it will be a future element of G-VAP to reassess the change in quality between the different versions Through this effort the selection process of suitable water vapor data products by the general (climate analysis) community and in particular by GEWEX Data and Assessments Panel is supported. These new bias-corrected in situ profiles are referred to as “characterized” rather fiducial as there are a number of assumptions that have to be applied to the operational archive These characterized observations can be thought of as complimentary to GRUAN rather than a direct substitution.
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