A North Pacific Short-Wave Train during the Extreme Phases of ENSO.

Sea surface temperatures (SSTs) exhibit an interannual seesaw between the eastern and western tropical Pacific in concert with the El Niño-Southern Oscillation (ENSO) cycle. Evidence accumulated from previous studies suggests that a teleconnection link may exist between enhanced rainfall/convection in the western Pacific and precipitation/severe weather over North America. The aforementioned link could possibly be established by a teleconnection wave pattern induced by the anomalously warm/cold SST anomalies in the western tropical Pacific. To demonstrate this possibility, a Fourier scale separation was introduced to divide the ENSO anomalous circulation into two wave regimes: long wave (waves 1-3) and short wave (waves 4-15). The classic PacificNorth American teleconnection pattern is formed by the long-wave regime. In contrast, emerging in the shortwave regime is a well organized wave train that propagates from the western subtropical Pacific along the North Pacific rim into North America. In spite of its vertically uniform structure, the planetary vortex stretching in the vorticity budget is a vital dynamic process to maintain the short-wave train. The contrast of rainfall anomalies with this short-wave train's anomalous divergent circulation indicates that this wave train is induced by the anomalous forcing formed by cold surge vortices over the Philippine Sea. This diagnostic suggestion was substantiated by successful simulations of the short-wave train with January perpetual experiments of the NCAR version 1 of the Community Climate Model (CCM1) using an idealized forcing (with a radius of 10³ km) centered at 0°, 135°E. This newly identified North Pacific short-wave train enables us not only to better understand the formation of the ENSO anomalous circulation over the North Pacific-North America region, but also to establish a link between the climate systems of the western Pacific and North America. [ABSTRACT FROM AUTHOR]