Evaluation of Total Precipitable Water Trends From Reprocessed MiRS SNPP ATMS Observations, 2012-2021

Total precipitable water (TPW) is defined as the vertically integrated column water vapor from the earth's surface to the top of the atmosphere. TPW is a key element of the hydrological cycle and is responsive to changes in global climate related to greenhouse-gas-induced warming. In this research, we focus on trend analysis using the TPW retrieval product from the recently reprocessed Microwave Integrated Retrieval System (MiRS) Suomi National Polar-Orbiting Partnership (SNPP) Advanced Technology Microwave Sounder (ATMS) data and compare it with ERA5 reanalysis. The primary results show that the global TPW trend during 2012-2021 from reprocessed SNPP ATMS is 0.46 mm/decade, in relatively good agreement with the trend from ERA5 of 0.39 mm/decade. Trends for tropical and mid-latitude subregions are also in good agreement, with essentially the same trend of 0.43 mm/decade seen in both datasets in the mid-latitudes. Both the datasets show a large positive anomaly associated with the strong El Nino event in 2015-2016, which increased TPW amounts in the tropics. We also found that the TPW trend is not uniformly distributed spatially, with significant regional variations in both sign and amplitude. Nevertheless, the spatial patterns from MiRS SNPP ATMS retrievals and ERA5 analyses are in very good agreement. Both the datasets show that positive TPW trends in terms of relative percentage in the polar regions were on par with those seen in lower latitudes. The results suggest that water vapor observations from a single polar-orbiting microwave instrument with only two local observation times daily may be sufficient to characterize trends in TPW.