Variability of North Pacific Jet Anomalies and their link to tropical convection in Winter

This study examines the contribution of tropical convection to the intraseasonal variability of North Pacific jet stream, using NOAA Interpolated Outgoing Longwave Radiation (OLR) and ERA-Interim reanalysis daily data from ECMWF for 1979-2011 boreal winters. On intraseasonal time scales, the North Pacific jet stream exhibits two forms of variability: the oscillation dominated by Pacific/ North American teleconnection (PNA), and eastward shift of jet anomalies from early winter (November – December) to late winter (February - March). The later form is rarely noted before. The focus of this study is on the key dynamic link between tropical convection and the eastward shift.

The empirical orthogonal function (EOF) analysis is performed on the zonal wind anomalies over the North Pacific domain. Regression analysis shows that enhanced tropical convection over the Eastern Pacific precedes the first EOF mode, which is highly correlated with PNA. The second EOF mode shifts eastward from early winter to late winter. A series of composite analysis reveals that intensified tropical convection over the Maritime Continent leads the eastward shift of North Pacific jet anomalies. A 3-dimentional wave activity flux analysis suggests the following processes: during late winter, enhanced tropical convection over the Maritime Continent induces upward wave activity to its north. Then in the upper troposphere of midlatitude, waves propagate northward and eastward, converge over the eastern Pacific and accelerate the jet stream. The composite analysis of transient eddies shows that storm track weakens and shifts southeastward from early winter to late winter, in correspondence to the jet anomalies. This indicates the predictability of local weather from the signal of tropical convection is possible on intraseasonal time scales.