Imprints of the North Atlantic Oscillation on four unusual atmospheric parameters

Abstract

Using data for 41 yr (1958–1998) from the National Center for Environmental Prediction–National Center for Atmospheric Research reanalysis the authors study the impact of the North Atlantic Oscillation (NAO) on four atmospheric parameters. These four parameters have three common characteristics: their previous limited use as climate diagnosis tools, their high dependence on changes in atmospheric circulation and their relationship with variables associated with the development of synoptic perturbances. They are: (1) relative angular momentum from 500 hPa to 200 hPa and from 55°N to 90°N, (2) advection of temperature at 500 hPa, (3) equivalent temperature at 850 hPa and (4) distribution of upper level low systems (ULL). The most significant results are: (1) a significant positive correlation between the relative angular momentum from 500 hPa to 200 hPa and from 55°N to 90 °N with the NAO index computed as the normalized pressure difference between Ponta Delgada (Azores) and Reykjavik (Iceland), (2) the NAO affects 500 hPa temperature advection from 45°N to 70°N and a positive NAO index is alternatively related to positive or negative anomalies of advection. The relationship is positive over the Atlantic, Asia and Western America and negative over Europe, the Pacific and Eastern America. (3) The correlation pattern between NAO index and the equivalent temperature at 850 hPa shows a semiannular structure with negative correlations over the Arctic and positive correlations over midlatitudes with the exception of the Pacific area, and (4) the distribution of ULL systems is only influenced by NAO over both sides of the Atlantic Ocean and for the latitude belt from 20°N to 50°N.