An upper tropospheric humidity data set from operational satellite microwave data

Abstract

[1] 183.31 GHz observations from the Advanced Microwave Sounding Unit B (AMSU-B) instruments onboard the NOAA 15, 16, and 17 satellites were used to derive a new data set of Upper Tropospheric Humidity (UTH). The data set consist of monthly median and mean data on a 1.5°latitude-longitude grid between 60°S and 60°N, and covers the time period of January 2000 to February 2007. The data from all three instruments are very consistent, with relative difference biases of less than 4% and relative difference standard deviations of 7%. Radiometric contributions by high ice clouds and by the Earth's surface affect the measurements in certain areas. The uncertainty due to clouds is estimated to be up to approximately 10%RH in areas with deep convection. The uncertainty associated with contamination from surface emission can exceed 10%RH in midlatitude winter, where the data therefore should be regarded with caution. Otherwise the surface influence appears negligible. The paper also discusses the UTH median climatology and seasonal cycle, which are found to be broadly consistent with UTH climatologies from other sensors. Finally, the paper presents an initial validation of the new data set against IR satellite data and radiosonde data. The observed biases of up to 9%RH (wet bias relative to HIRS) were found to be broadly consistent with expectations based on earlier studies. The observed standard deviations against all other data sets were below 6%RH. The UTH data are available to the scientific community on http://www.sat.ltu.se.

Technical Note: 30 years of HIRS data of upper tropospheric humidity

“…Although classically ice-supersaturated regions have been defined as cloudfree regions, they are clearly related to cirrus cloud formation and contrail persistence. Thus, infrared-sounder measurements, which are necessarily cloud-cleared, should be combined with microwave-sounder data (183.1 GHz, Buehler et al, 2008), which can be used in cloudy scenes as well. Furthermore, satellite data with stated higher vertical resolution as AIRS (Atmospheric Infrared Sounder) and IASI (Infrared Atmospheric Sounding Interferometer) will be profitable for a study of ice-supersaturated regions since the latter are only a few 100 m shallow on average.…”

Observational evidence for aerosols increasing upper tropospheric humidity

“…UTH data can be accessed at http://www.sat.ltu.se/ projects/uth-clim/ (see Buehler et al, 2008). The dataset used in this study by request from Viju O. John.…”

“…the relative humidity with respect to water, in a layer between approximately 200 and 500 hPa, was obtained from the microwave humidity sounder (MHS; Bonsignori, 2007) on board the MetOp-A satellite for 60 • S to 60 • N. The ascending node was used, crossing the Equator northward at 21:30 local solar time. A microwave method developed by Buehler et al (2008) enabled us to detect relative humidities also in the areas of anvil clouds.…”

Estimating Confidence Intervals around Relative Humidity Profiles from Satellite Observations: Application to the SAPHIR Sounder

“…In fact, observations in the 183.31-GHz rotational transition line of the water molecule allow for the study of RH even in the presence of low-level clouds (Isaacs and Deblonde 1987). High-level clouds combine increased absorption by water vapor within the saturated clouds and scattering by precipitating particles (icy or water droplets; Burns et al 1997;Houshangpour et al 2005;Hong et al 2005;Buehler et al 2008). Such features of the microwave radiation allows for the study of mechanisms at play around the convective cores (Bretherton et al 2004;Hong et al 2008;Zelinka and Hartmann 2009;Chae et al 2011).…”