The global circulation of the atmosphere experiences distinct multi-decadal variations. For example, during the mid-1940s through the late 1960s the general circulation functioned differently than it did during the subsequent quarter century between 1970-1994. Prominent differences between these two periods include the strength of the middle latitude westerly circulation patterns, Pacific PNA and Atlantic (NAO), the strength of the Azores high, African Sahel rainfall, frequency of intense (category 3-4-5) hurricanes, frequency and intensity of El Nino events, hemispheric scale north-south SST differences, changes in mean global temperature and numerous related features. Similar but less extreme multi-decadal variations occurred during 1870-1899 versus 1900-1920 versus 1921-1943. Recent ocean SST patterns, salinity in the North Atlantic and many other global circulation features suggest that we are now shifting to a climatic era more typical of the mid-1940s to late 1960s.
It is hypothesized that these multi-decadal circulation differences are due primarily to variations in the strength of the global ocean thermohaline circulation and, in particular, the Atlantic thermohaline portion of this circulation. Taken together, salinity variations in the North Atlantic [such as the Great Salinity Anomaly (GSA) during the late 1960s] and Greeland Ice Core measurements going back thousands of years, indicate that the North Atlantic SST patterns typically fluctuate back and forth on 20-50 year time scales and appear to fit this hypothesis. Warmer than normal North Atlantic SSTs occur with a stronger Atlantic thermohaline circulation and colder SSTs with a weaker circulation.
A step-by-step interpretation of the physical linkages between variations in the Atlantic Ocean thermohaline and associated North Atlantic SST anomalies bring about global circulation multi-decadal changes and lulls and enhancements of Atlantic intense category (3-4-5) hurricanes will be discussed. A return of increased frequency of intense hurricane activity along the U.S.\ East Coast should be anticipated in the next few decades