OLD Water vapor-Non precipitating conditions products

A Saphir/Madras retrieval scheme has been developed to retrieve the integrated and vertical distribution of atmospheric water vapour. The algorithm deals with clear and cloudy but non-precipitating scenes, over land and ocean. The retrieval is performed in the Madras Level 1B resolution of the 89 GHz chanbel, at a 10 km horizontal resolution.

The inversion algorithm is based on a neural network scheme that follows the approach described in (Aires et al., 2001, 2012, Bernardo et al., 2012, Karbou et al. 2005). A preliminary calibration procedure (Aires et al., 2010) is used to ensure Radiative Transfer Model (RTM) coherency with the chosen reference RTM: RTTOV. The retrievals over land surfaces are made possible by the use of a priori information on the microwave surface emissivities (Prigent et al. 2006).

The retrieval of relative humidity (%) is performed over 6 atmospheric layers + 1 surface layer:

-85.180 to 122.040 hPa

-122.040 to 253.710 hPa

-253.710 to 436.950hPa

-436.950 to 702.730 hPa

-702.730 to 882.800 hPa

-882.800 to 985.880 hPa

-985.880 to 1013.25 hPa (corresponding to the surface layer)

The integrated water vapour is given in kg.m^-2.

In addition a Saphir-only scheme has been developed in order to derive the upper tropospheric humidity (UTHs) from the 3 upper channels (+/- 0.2 GHz, +/- 1.1 GHz and +/-2.8 GHz). This retrieval follows the method developed initially for IR measurements (6.3 microns) of the HIRS (e.g. Soden & Bretherton, 1993) and METEOSAT-MVIRI (e.g. Schmetz and Turpeinen, 1988) radiometers and recently applied to microwave observations (Spencer & Braswell, 1997; Buehler & John, 2005)

Figure 1: UTH derived from the 3 upper channels of SAPHIR for the 9 dec 2011; precipitating pixels (detected by the BRAIN algorithm applied to the MADRAS L1 data) appear as black.

For more information, contact Hélène Brogniez (helene.brogniez@latmos.ipsl.fr).

References:

Aires F., C. Prigent, W.B. Rossow, and M. Rothstein, 2001: A new neural network approach including first-guess for retrieval of atmospheric water vapor, cloud liquid water path, surface temperature and emissivities over land from satellite microwave observations, Journal of Geophysical Research, vol. 106, No. D14, pp. 14,887-14,907.

Aires F., F. Bernardo, H. Brogniez, and C. Prigent, 2010: An innovative calibration method for the inversion of satellite observations, J. of Applied Meteorol. Climatol., vol. 49, p2458-2473.

Aires F., F. Bernardo, and C. Prigent, 2012: Atmospheric water-vapour profiling from passive microwave sounders over ocean and land. Part I: Methodology for the Megha-Tropiques mission, Q. J. R. Meteorol. Soc., DOI: 10.1002/qj.1888

Bernardo F., F. Aires , and C. Prigent, 2012: Atmospheric water-vapour profiling from passive microwave sounders over ocean and land. Part II: Validation using existing instruments, Q. J. R. Meteorol. Soc., DOI: 10.1002/qj.1946

Prigent C., F. Aires, and W.B. Rossow, Land Surface Microwave Emissivities over the Globe for a Decade, 2006: Bulletin of the American Meteorological Society, DOI:10.1175/BAMS-87-11-1573, pp. 1572-1584.

Karbou F., Aires, F., Prigent, C. Retrieval of temperature and water vapor atmospheric profiles over Africa using AMSU microwave observations, 2005: Journal of Geophysical Research, Vol. 110, No. D7, D07109 10.1029/2004JD005318.

Buehler and John, 2005: A simple method to relatve microwave radiances to upper tropospheric humidity, J. Geophys. Res, 110, doi:10.1029/2004JD005111.

Schmetz and Turpeinen, 1988: Estimation of the Upper Tropospheric Relative Humidity field from METEOSAT water vapor image data, J. App. Meteor., 27, 889-899.

Soden and Bretherton, 1993: Upper Tropospheric Relative HUmidity from the GOES 6.7 microns channel: Method and climatology for July 1987, J. Geophys Res., 98, 16,669-16,688.

Spencer and Braswell, 1997: How dry is the tropical free troposphere ? Implications for a global warming theory. BAMS, 78, 1097-1106.