An Intercomparison of Radiation Codes for Retrieving Upper–Tropospheric Humidity in the 6.3–<i>m</i>m Band: A Report from the First GVaP Workshop

Soden, Brian J.; Tjemkes, Stephen; Schmetz, Johannes; Saunders, Roger; Bates, John J.; Ellingson, Bryon; Engelen, Richard; Garand, Louis; Jackson, Daniel; Jedlovec, Gary J.; Kleespies, Thomas J.; Randel, David L.; Rayer, Peter; Salathé, Eric P.; Schwarzkopf, D.; Scott, N. A.; Sohn, Byung-Ju; Souza-Machado, S. De; Strow, L. Larrabee; Tobin, David C.; Turner, Duncan L.; Delst, Paul van; Wehr, T.

doi:10.1175/1520-0477(2000)081<0797:aiorcf>2.3.co;2

Cited by 44 publications

(33 citation statements)

References 18 publications

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“…Studying three-hourly weather data from 15 000 worldwide stations, Dai (2001) found that the most frequent (morning) hour of showery precipitation over water is out of phase with those over land and the latter exhibited large seasonal variability. Similar large variability was also reported in wind measurements (Dai and Deser, 1999) and cloud and water vapor data (Soden, 2000;Tian et al, 2004). However, such strong zonal variations of the diurnal amplitude would require very dense RO soundings to suppress aliasing effects.…”

Section: Discussionsupporting

confidence: 78%

Atmospheric diurnal variations observed with GPS radio occultation soundings

Xie

et al. 2010

Atmos. Chem. Phys.

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Abstract. The diurnal variation, driven by solar forcing, is a fundamental mode in the Earth's weather and climate system. Radio occultation (RO) measurements from the six COSMIC satellites (Constellation Observing System for Meteorology, Ionosphere and Climate) provide nearly uniform global coverage with high vertical resolution, all-weather and diurnal sampling capability. This paper analyzes the diurnal variations of temperature and refractivity from three-year (2007)(2008)(2009)) COSMIC RO measurements in the troposphere and stratosphere between 30 • S and 30 • N. The RO observations reveal both propagating and trapped vertical structures of diurnal variations, including transition regions near the tropopause where data with high vertical resolution are critical. In the tropics the diurnal amplitude in refractivity shows the minimum around 14 km and increases to a local maximum around 32 km in the stratosphere. The upward propagating component of the migrating diurnal tides in the tropics is clearly captured by the GPS RO measurements, which show a downward progression in phase from stratopause to the upper troposphere with a vertical wavelength of about 25 km. At ∼32 km the seasonal variation of the tidal amplitude maximizes at the opposite side of the equator relative to the solar forcing. The vertical structure of tidal amplitude shows strong seasonal variations and becomes asymmetric along the equator and tilted toward the summer hemisphere in the solstice months. Such asymmetry becomes less prominent in equinox months.

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Section: Discussionsupporting

confidence: 78%

Atmospheric diurnal variations observed with GPS radio occultation soundings

Xie

et al. 2010

Atmos. Chem. Phys.

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“…RTTOV uses HITRAN-2000 (Rothman et al, 2003) as spectroscopic data base. For the specific case of the 6.3 µm strong vibration-rotation absorption band by water vapor, the RTTOV model takes into account the water vapor continuum (foreign-broadening and self-broadening, model CKD-2.4; Clough et al, 1989) that has a non-negligible contribution in the water vapor band (e.g., Stephens et al, 1996, andSoden et al, 2000). Based on the work of Brunel and Turner (2003) referenced in the RTTOV v9 user guide, the bias uncertainty of RTTOV with respect to the Meteosat water vapor channel is < 0.1 K, with a standard deviation of > 0.3 K.…”

Section: Methodsmentioning

confidence: 99%

Climatology of free-tropospheric humidity: extension into the SEVIRI era, evaluation and exemplary analysis

et al. 2014

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Abstract. A new free-tropospheric humidity (FTH) data record is presented. It is based on observations from the Meteosat Visible and Infrared Imager (MVIRI) onboardMeteosat-2-Meteosat-5, as well as Meteosat-7, and the Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard Meteosat-8 and Meteosat-9 at the water absorption band near 6.3 µm. The data set is available under clear-sky and low-level cloud conditions. With the extension to SE-VIRI observations, the data record covers the period 1983-2009 with a spatial resolution of 0.625 • × 0.625 • and a temporal resolution of 3 h.The FTH is the mean relative humidity (RH) in a broad layer in the free troposphere. The relation between the observed brightness temperature (BT) and the FTH is well established. Previous retrievals are refined by taking into account the relative humidity Jacobians in the training process of the statistical retrieval. The temporal coverage is extended into the SEVIRI period, the homogenization of the BT record is improved, and the full archive is reprocessed using updated regression coefficients.The FTH estimated from the Meteosat observations is compared to the FTH computed from the RH profiles of the Analyzed RadioSoundings Archive (ARSA). An average relative bias of −3.2 % and a relative root-mean-square difference (RMSD) of 16.8 % are observed. This relative RMSD agrees with the outcome of an analysis of the total uncertainty of the FTH product. The decadal stability of the FTH data record is 0.5 ± 0.45 % per decade.As exemplary applications, the interannual standard deviation, the differences on decadal scales, and the linear trend in the FTH data record and in the frequency of occurrence of FTH < 10 % (FTHp10) are analyzed per season. Interannual standard deviation maxima and maxima in absolute decadal differences are featured in gradient areas between dry and wet regions, as well as in areas where FTH reaches minima and FTHp10 reaches maxima. An analysis of the FTH linear trends and of the associated uncertainty estimates is achieved to identify possible problems with the data record. Positive trends in FTHp10 are featured in gradient areas between wet and dry regions, in regions where the FTH is minimum, in regions where FTHp10 is maximum, and in regions where differences between FTHp10 averaged over the 2000s and 1990s are negative. However, these positive trends in FTHp10 are associated with maximum standard deviation and are thus hardly significant. This analysis and intercomparisons with other humidity data records are part of the Global Energy and Water Cycle Experiment (GEWEX) Water Vapor Assessment (G-VAP).

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“…A weak point of the UTH algorithm is the fact that retrieval errors of the HIRS/2 channel 12 brightness temperature scale linearly with the relative uncertainty in UTH (Soden et al, 2000). This implies that the largest uncertainties of UTH occur just in the ice supersaturated situations.…”

Section: Influence Of Retrieval Errorsmentioning

confidence: 99%

Ice supersaturation as seen from TOVS

et al. 2004

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Abstract.We have analysed the upper tropospheric humidity with respect to ice (UTHi) data product obtained from the Television Infrared Observation Satellite (TIROS) Operational Vertical Sounder (TOVS) instrument onboard the National Oceanic and Atmospheric Administration NOAA-14 polar orbiting satellite. While in the production of the official UTHi product values in excess of 100% are ignored, we do not so -in view of many recent results obtained from a variety of other in-situ and remote sensing instruments showing that ice supersaturation frequently occurs in the upper troposphere. We show that TOVS is able to detect ice supersaturation at the correct locations (however, only in less than one percent of its soundings, presumably because of TOVS's low vertical resolution), and that the supersaturation follows the well known exponential behaviour. We conclude that values of UTHi in excess of saturation should not be considered a measurement error anymore. The similar re-analysis of TOVS data back to 1979 could give important insights into trends of upper tropospheric humidity.

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An Intercomparison of Radiation Codes for Retrieving Upper–Tropospheric Humidity in the 6.3–mm Band: A Report from the First GVaP Workshop

Cited by 44 publications

References 18 publications

Atmospheric diurnal variations observed with GPS radio occultation soundings

Atmospheric diurnal variations observed with GPS radio occultation soundings

Climatology of free-tropospheric humidity: extension into the SEVIRI era, evaluation and exemplary analysis

Ice supersaturation as seen from TOVS

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