The influences of the multi-scale sea surface temperature anomalies in
the North Pacific on the jet stream in winter: Application of
Liang-Kleeman information flow method and CAM5.3
Abstract
Using Climate Forecast System Reanalysis (CFSR) data and numerical
simulations, the impacts of the multi-scale sea surface temperature
(SST) anomalies in the North Pacific on the boreal winter atmospheric
circulations are investigated. The basin-scale SST anomaly as the
Pacific Decadal Oscillation (PDO) pattern, a narrow meridional band of
frontal-scale smoothed SST anomaly in the subtropical front zone (STFZ)
and the spatial dispersed eddy-scale SST anomalies within the STFZ are
the three types of forcings. The results of Liang-Kleeman information
flow method find that all three oceanic forcings may correspond to the
winter North Pacific jet changing with the similar pattern. Furthermore,
several simulations are used to reveal the differences and detail
processes of the three forcings. The basin-scale cold PDO-pattern SST
anomaly first causes negative turbulent heat flux anomalies, atmospheric
cooling, and wind deceleration in the lower atmosphere. Subsequently,
the cooling temperature with an amplified southern lower temperature
gradient and baroclinity brings a lagging middle warming because of the
enhanced atmospheric eddy heat transport. The poleward and upward
development of baroclinic fluctuations eventually causes the
acceleration of the upper jet. The smoothed frontal- and eddy-scale SST
anomalies in the STFZ cause comparable anomalous jet as the basin-scale
by changing the upward baroclinic energy and E-P fluxes. The forcing
effects of multi-scale SST anomalies coexist simultaneously in the
mid-latitude North Pacific, which can cause similar anomalous upper
atmospheric circulations. This is probably why it is tricky to define
the certain oceanic forcing that leads to specific atmospheric
circulation variation in observations