The Effect of summer tropical heating on the location and intensity of the extratropical westerly jet streams

The role of the summer hemisphere tropical diabatic heating on the location and magnitude of the winter hemisphere subtropical and extratropical westerly jet streams is studied. In particular, the relationships between the extratropical zonal wind, the subtropical meridional wind and the tropical outgoing longwave radiation (OLR) patterns are examined. It is found that the heating field, the cross‐equatorial meridional wind, and the winter zonal wind maxima are closely linked on annual and interannual time scales. These factors indicate that the adjacent hemisphere heating is at least as important as the northern hemisphere orography in determining the location and magnitude of the westerly jet streams. Credence is added to this conclusion by noting the similar associations between the northern hemisphere heating pattern and the location and variations of the southern hemisphere jet streams which are less clearly associated with orography. Furthermore, interannual changes in the location and magnitude of the westerly jet streams are closely related to the El Niño/Southern Oscillation (ENSO) phenomenon. Thus, in addition to the well known relationship between ENSO and the near‐equatorial or symmetric zonal circulation, there is a strong association on the same time scale in the cross‐equatorial flow or asymmetric components about the equator.