Interannual Variability of Thermal Characteristics in the Indian Ocean under the Conditions of Global Warming

Purpose. The purpose of this work is to clarify the tendencies and regional features of interannual changes in the surface air temperature (T-a), the sea surface temperature (SST), and the water temperature (T-w) in the upper 950-m layer in the Indian Ocean basin including the adjacent area of the Southern Ocean - up to 65 degrees S over the past four decades, which are manifested as a result of planetary changes and a shift in the climate regime at the turn of the XX-XXI centuries. Methods and Results. Based on the data of the Global meteorological network, reanalysis, optimal interpolation and the Global oceanographic data assimilation system GODAS (NOAA), the regional features and trends of interannual fluctuations in the water and air temperature, and their relationship with the variations in climatic indices and pressure fields in the centers of the atmosphere and wind action have been determined for the last 4 decades. The methods of a cluster, correlation, and regression analysis, and the apparatus of empirical orthogonal functions were used. The results obtained made it possible to characterize the degree of inhomogeneity of the responses of the atmosphere surface layer, SST, and vertical distribution of T-w to the ongoing global changes, to identify the isolated regions, and to quantify the rate of warming in these water areas. Conclusions. Climatic changes in the atmosphere near-water layer and on the sea surface are expressed in positive trends (b) of changes in the SST fields and air temperature in most of the Indian Ocean basin. The values of the air temperature trends on land in the coastal areas are higher than those in the adjacent sea areas. The maximum values of the T-a trends (similar to 0.5 degrees C/10 years) over the water area of the region are noted in the area located to the north of the Madagascar Island, and those of the SST trends (similar to 0.3-0.4 degrees C/10 years) - in the central part of the ocean. In the T-a field, the individual areas with the minimal and negative values of T-a trends are observed in the northeastern, southwestern, and southern parts of the water area, and in the SST field - over a large area in the southern part of the ocean, namely, in the zone of influence of the cold Antarctic Circumpolar Current waters. The process of warming or cooling is significantly heterogeneous not only in space but also in time. In the upper 100-m layer of the water column, the spatial structure of the water temperature trends is rearranged. Below this layer, the maximum positive trends (on average 0.2-0.5 degrees C per a decade for a region) are observed in the southern and southwestern parts of the water area, and the negative ones (-0.1... -0.2 degrees C) - in the northwestern and southeastern parts. In course of the past 15 years, the largest relative increase of heat content in various layers occurred in the south of the ocean - it was by an order of magnitude higher than those in the other regions despite the insignificant SST trends.