Copyright 1999 American Association for the Advancement of Science. Further electronic distribution is not allowed. Gallery of Figures and Tables Figure 1.
Positive winds are westerly, negative winds are easterly.
OLR values below about 235 W m indicate an increased likelihood of deep cumulus cloudiness and heavy convective precipitation. OLR data are from the National Centers for Environmental Prediction. Monthly average SST anomaly for December 1997 is also shown. The anomaly is relative to the SST climatology referred to in Fig. 2 . The normal seasonal cycle is shown by magenta lines.