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Release of the second CM SAF Upper Tropospheric Humidity data record based on microwave humidity sounders
| This CM SAF climate data record provides a time series of estimates of Upper Tropospheric Humidity (UTH) derived from passive microwave (MW) sounders. UTH contributes significantly to the atmospheric greenhouse effect by having a strong influence on the outgoing longwave radiation, despite the smaller concentration by mass in comparison to lower troposphere. The CM SAF UTH v2.0 data set is based on data from twelve MW sounders operating at 183 GHz in polar orbit that are combined into a single time series covering the period 6 July 1994 to 31 December 2018. These MW sounders include the Special Sensor Microwave - Humidity (SSM/T-2) onboard the DMSP-F[11, 12, 14, 15], the Advanced Microwave Sounding Unit B (AMSU-B) onboard NOAA-[15, 16, 17], the Microwave Humidity Sounder (MHS) onboard NOAA-[18,19] and Metop-[A, B], and the Advanced Technology Microwave Sounder (ATMS) onboard SNPP. Invalid observations affected by deep convective or precipitating clouds, and/or radiation emitted from the surface, together with any spurious observations from individual MW sounders, have been removed from the data set. The UTH provided typically represents a broad atmospheric layer between 500 and 200 hPa. However, the exact height of this layer depends on the atmospheric conditions at the time of the observation. An optional fixed layer approximation adjustment is supplied that users can apply to provide an estimated mean relative humidity (RH) between ±60° latitude for a fixed layer between 500 and 200 hPa (mean_RH). However, users are advised to take care using this correction, especially outside of the tropics where the mean_RH is of lower quality. Users are also advised to take care using UTH observations above ±60° latitude as the retrieval is sometimes less reliable at high latitudes. The CM SAF UTH v2 is a near-global 1°x1° latitude-longitude dataset that is available at both hourly and daily time steps. Users should note that the hourly product does not have observations at every hour for every grid cell and many grid cells in the time series may only have as few as one or two observations in any 24-hour period. However, for periods when multiple satellites are in operation, the majority of hourly time slots may be filled for some grid cells. For both the hourly and daily products, uncertainty components that capture sources of independent (or random), structured (or locally correlated) and common (or systematic) errors in the data are also provided for each grid cell. These uncertainties have been propagated from the input MW top of atmosphere brightness temperatures and through the UTH retrieval; uncertainties due to the retrieval itself are also included in these uncertainty components. In addition, an estimation of the spatial sampling uncertainty is provided. |
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EG / Feb2024