Atmosphere-Ocean Interactions in the Mid-Latitude North Atlantic and the Impact on River Runoff Over Siberia

The atmospheric fluctuations associated with sea surface temperature (SST) anomalies in the northern North Atlantic and their subsequent effects on river runoff variations over Siberia are studied in this thesis. A data analysis is performed in Part I of the thesis using 50 years (1930 -79) of records of SST sea level pressure, precipitation and runoff. It is found from this analysis that the winter SST anomalies in the northern North Atlantic are significantly correlated with the winter and the following summer runoff fluctuations of the Ob and Yenisey rivers in western Siberia. A modelling study is conducted in Part II of the thesis to investigate the variability of winter atmospheric responses to the SST anomalies in the northwest Atlantic. Experiments are performed with an atmospheric global spectral model using both November and January conditions. The atmospheric responses to the prescribed positive SST anomalies obtained are found to be completely different in the November and January simulations. Over the Atlantic, a positive (negative) geopotential height anomaly center is observed downstream of the warm SST area in the November (January) case. A comprehensive diagnostic analysis of the heat advection in the experiments is carried out to obtain a deeper understanding of the physical maintenance of the two responses.