| 1. |
- Buehler, Stefan, et al.
(författare)
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Radiative transfer calculations for a passive microwave satellite sensor : comparing a fast model and a line-by-line model
- 2006
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 111:20, s. 20304-
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Tidskriftsartikel (refereegranskat)abstract
- A comparison between the fast radiative transfer model Radiative Transfer for the TIROS Operational Vertical Sounder (RTTOV-7) and the physical radiative transfer model Atmospheric Radiative Transfer Simulator ( ARTS) was carried out. Radiances were simulated for the sounding channels of the Advanced Microwave Sounding Unit B (AMSU-B) for the whole globe for a single time of a single day ( 1 January 2000, 0000 UT). Temperature, pressure, and specific humidity profiles from the reanalysis data set ERA-40 of the European Centre for Medium-Range Weather Forecasts (ECMWF) were used as input for both models; geopotential height profiles were also used but only as input for ARTS. The simulations were made for two different surface emissivities, 0.60 and 0.95. The low surface emissivity case exhibits the larger radiance differences. Although the global values of the mean difference and standard deviation are small ( for example, the global mean difference for channel 18 is 0.014 K and the standard deviation is 0.232 K), the examination of the geographical distribution of the differences shows that large positive or negative values are observed over dry regions of high northern and southern latitudes and over dry elevated regions. The origin of these differences was found to be due to errors introduced by the transmittance parametrization used in RTTOV.
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| 2. |
- Buehler, Stefan, et al.
(författare)
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The impact of temperature errors on perceived humidity supersaturation
- 2003
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 30:14, s. 1759-
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Tidskriftsartikel (refereegranskat)abstract
- A Monte Carlo method is used to study the propagation of temperature uncertainties into relative humidity with respect to ice (RH i ) calculated from specific humidity. For a flat specific humidity distribution and Gaussian temperature uncertainties the resulting RH i distribution drops exponentially at high RH i values—much slower than a Gaussian. This agrees well with the RH i distribution measured by the Microwave Limb Sounder (MLS), which means that such remotely measured RH i distributions can be explained, at least partly, by temperature uncertainties.
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| 3. |
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| 4. |
- John, Viju Oommen, et al.
(författare)
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A cautionary note on the use of Gaussian statistics in satellite-based UTH climatologies
- 2006
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Ingår i: IEEE Geoscience and Remote Sensing Letters. - 1545-598X .- 1558-0571. ; 3:1, s. 130-134
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Tidskriftsartikel (refereegranskat)abstract
- This letter presents a cautionary note on the assumption of Gaussian behavior for upper tropospheric humidity (UTH) derived from satellite data in climatological studies, which can introduce a wet bias in the climatology. An example study using European Centre for Medium-Range Weather Forecasts reanalysis data shows that this wet bias can reach up to 6 %RH, which is significant for climatological applications. A simple Monte Carlo approach demonstrates that these differences and their link to the variability of brightness temperatures are due to a log-normal distribution of the UTH. This problem can be solved by using robust estimators such as the median instead of the arithmetic mean.
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