Satellite estimation of humidity of the inner Tiаn Shan in the period 1982–2022: A case study of At-Bashi Ridge (Kyrgyzstan)

Introduction. Western atmospheric jet streams carry moisture over the Northern Tian Shan ridges into the Inner Tian Shan. Long-term weather changes in the Inner Tian Shan diagnose climatic fluctuations in atmospheric moisture transport. This is of considerable interest for understanding the direction of modern climate change in Central Asia. Materials. The area of the At-Bashi Ridge (2700 км2) in Inner Tian Shan, including a large high-altitude Lake Chatyr-Kul (170 km2, 3530 m), were considered. The ridge, with a peak of 4786 m, has a length of 135 km and is characterized by an Alpine type of relief. The initial information related to the period 1982-2022. The list of data used included: FLDASSnowDepth_inst; JRC Monthly Water History, v1.4; ECMWF/ERA5_LAND/MONTHLY (precipitation); NOAA/NCEP_DOE_RE2 (cloud fraction). Also, to diagnose the mountain glaciation state of the At-Bashi Ridge, three satellite images of sub meter resolution dated 09/21/2002, 07/27/2013 and 09/13/2021 were used. The purpose of the work. The aim of the research was to study the humidity regime of the At-Bashi Ridge area during 1982-2022. Research methodology. The change in the average annual snow depth in the test area in the period 1982-2022 was analyzed, as well as the degree of correlation of this parameter with other weather characteristics.Fischer’s criterion acted as a quantitative basis for estimates. Satellite images of sub meter resolution were used to analyze long–term changes in the area of rock outcrops from ice on the slopes of glacial chambers, which diagnoses the glacier state (degradation – stability – growth). Satellite data recorded the process of mountain glaciation growth above the height of 4000 m in the period between 2002–2013. Research results. In order of increasing correlation (F-criterion), with the snowiness of the cold period (October-May) of the At-Bashi Ridge area, the parameters considered were arranged as follows (F=2.11; α=0.01): cloud fraction, F= 3.02; precipitation, F=12.42; the Lake Chatyr-Kul area, F= 12.53; the balance of snow deposits between the windward (north-western) and leeward (south-eastern) At-Bashi Ridge slopes, F= 22.01. According to satellite data, the growth of mountain glaciation in the zone with an altitude above 4000 m in the period 2002-2013 was recorded. Discussion. The At-Bashi Ridge area has three different periods in terms of humidity: dry in 1982-1999 with an average annual snow depth of 0.099± 0.051 m; wet in 2000-2012; 0.192± 0.074 m; and moderately humid in 2013-2022; 0.133± 0.058 m. Ultra-high-resolution satellite images recorded the growth of the mountain glaciation of the At-Bashi Ridge at altitudes of more than 4000 m in the period from 2002 to 2013. This confirms the actual existence of the wet period of 2001-2012. Conclusion. Thus, the current trend of humidity changes of the At-Bashi Ridge does not have an unambiguous direction, but in general, for the period 1982-2022, it is aimed at a certain increase in the snow content in mountains and the area of the Lake Chatyr-Kul. Apparently, the current climate change is accompanied by an increase in the ability of western atmospheric jet fluxes to transfer moisture over the front Northern Tian Shan ranges into the Inner and Central Tian Shan ridges, which may even be accompanied by an increase in the mountain glaciation of these territories in certain periods of time.