Temperature-related trends in the vertical position of the summer upper tropospheric surface of maximum wind over the Northern Hemisphere

The surface of maximum wind (SMW) is used to examine spatial and temporal variability in the vertical position of jet streams and fast upper tropospheric wind maxima over the Northern Hemisphere (NH) in the NCEP/NCAR Reanalysis for summers 1958-2004. At a given observation time in a gridded data set, the SMW is defined as the surface passing through the fastest analyzed wind above each grid node, with a vertical search domain restricted to the upper troposphere and any tropospheric jet streams extending into the lower stratosphere. The 47-year mean summer SMW generally resides below the tropopause, undulates in the tropics, and descends poleward in middle and high latitudes. Trends in the pressure of the summer SMW are primarily positive, exceed 30 hPa/decade at some locations, and are found over most of the tropics and subtropics for the period 1958-2004. The thermal wind relationship is used to establish links between the SMW pressure trends and temperature gradient changes in the upper troposphere. The changing temperature gradients are consistent with nonuniform tropospheric warming and are correlated with sea surface temperature (SST) variability related to El Nino and the Pacific Decadal Oscillation. Copyright (C) 2006 Royal Meteorological Society.