Speaker
Description
Upper tropospheric humidity (UTH) is a crucial diagnostic of the atmospheric water cycle and a significant contributor to climate sensitivity, this highlights the importance of understanding its variability and how it is represented in global climate models.
Initially, using a radiative transfer code, the sensitivity of satellite observations of UTH to temperature and specific humidity is investigated. While these competing changes are minimal enough for the observations to be considered a valid proxy for relative humidity, a spurious increase in UTH of 1% has been identified for a 1K increase in profile temperature when relative humidity remains constant.
Next, we compare the infrared and microwave brightness temperature satellite observations with satellite simulations from the ECMWF Reanalysis v5 (ERA5) reanalysis and the Hadley Centre Global Environment Model version 3 (HadGEM3). These four datasets are utilised to evaluate and characterise UTH climatology and variability from 1979 to the present.
An investigation of the climatology of UTH shows that ERA5 and HadGEM3 produced higher UTH values compared to satellite observations, with mean global UTH being 9.13% and 10.81% higher than the microwave observations, respectively. Further trend evaluations indicate regional increases in UTH over the Indian Ocean while decreases are observed over South America and Indonesia. Variability in UTH has been analysed using Principal Component Analysis (PCA) which shows that the first two main modes of variance in UTH are attributed to the El Niño Southern Oscillation (ENSO).
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