SYNOPTIC ASPECTS OF FORMATION OF THE EQUATORIAL WESTERLY WINDS OVER THE PACIFIC OCEAN DURING THE EXTREME EL NINO EVENT OF 1997—1998

E. K. Semenov, E. V. Sokolikhina, and N. N. Sokolikhina

The NCEP/NCAR reanalysis data are used to examine a synoptic mechanism of the circulation anomalies in the lower and upper troposphere over the tropical Pacific Ocean observed in the culmination period of the 1997—1998 El Nino. It is shown that among various synoptic situations of the “active” class of the ENSO warm phase three variants of location of the tropical centers of action can be separated, each of which forms its own scenario of the westerly wind anomaly. It is shown for the first time that there is an extended zone of equatorial westerly winds at 500 hPa in periods of the maximum activity of El Nino. This indicates that tropical cyclones arising in the warm phase and producing the westerly wind anomaly are not weak and single tropical depressions, but well-developed pressure—circulation systems that appear in the most active period of the ENSO warm phase in series. A similar vertical structure of the wind field over the equator is not observed anywhere in the tropical zone of the Earth.