Upper Tropospheric Humidity with respect to Ice

We use brightness temperature data from the High-Resolution Infrared Radiation Sounder (HIRS) onboard the NOAA series of satellites, to produce a 40-year data set of Upper Tropospheric Humidity with respect to Ice (UTHi). The UTHi values are derived from brightness temperatures in channels 6 and 12 (upper tropospheric temperature channel and upper tropospheric water vapor channel correspondingly) using a retrieval method developed by Gierens and Eleftheratos (2019) in conjunction with the application of intercalibration coefficients from Shi and Bates (2011). As channel 6 is in the CO2 absorption band and CO2 concentrations have increased since 1980, channel 6 brightness temperature records have been influenced negatively by approximately 2oK in the 40-year period (Shi et al., 2016).  We correct the T6 data, by applying a correction formula based on the global CO2-related brightness temperature false decrease in the 40-year period and the month-to-month change of CO2 with a reference CO2 value of 370 ppm. Due to the switch of the HIRS instrument in 2000 which was accompanied by a change in the central wavelength of channel 12 there was a break in the time series of the respective brightness temperature data and subsequently to the UTHi data. We perform a bias correction and eliminate this break during the application of the retrieval equation. After the application of the previous bias corrections, we calculate the UTHi in a 2.5° x 2.5° data grid for 70°S-70°N on a monthly temporal scale.

The file contains the fraction of UTHi threshold exceedances above 70, 80, 90 and 100%, together with their respective deseasonalized anomalies. The temporal and spatial resolution is the same as in the file , which contains the monthly mean UTHi data.

Gierens, K. & Eleftheratos, K. On the interpretation of upper-tropospheric humidity based on a second-order retrieval from infrared radiances. Atmos Chem Phys 19, 3733–3746 (2019).

Shi, L. & Bates, J. J. Three decades of intersatellite-calibrated high-resolution infrared radiation sounder upper tropospheric water vapor. Journal of Geophysical Research Atmospheres 116, (2011).

Shi, L., Matthews, J. L., Ho, S. P., Yang, Q. & Bates, J. J. Algorithm development of temperature and humidity profile retrievals for long-term HIRS observations. Remote Sens (Basel) 8, (2016).Users who are interested in using this UTHi dataset are strongly recommended to contact first Dr. Kostas Eleftheratos ([e-mail]).