scholarly journals Change in the variability in the Western Pacific pattern during boreal winter: roles of tropical Pacific sea surface temperature anomalies and North Pacific storm track activity

2021 ◽  
Author(s):  
Hasi Aru ◽  
Shangfeng Chen ◽  
Wen Chen
Keyword(s):  
Surface Temperature ◽  
North Pacific ◽  
Storm Track ◽  
Sea Surface ◽  
Boreal Winter ◽  
Sea Surface Temperature Anomalies ◽  
Storm Track Activity ◽  
The Western Pacific ◽  
Western Pacific Pattern ◽  
North Pacific Storm Track

scholarly journals Change In The Variability In The Western Pacific Pattern During Boreal Winter: Roles of Tropical Pacific Sea Surface Temperature Anomalies And North Pacific Storm Track Activity

2021 ◽  
Author(s):  
Hasi Aru ◽  
Shangfeng Chen ◽  
Wen Chen
Keyword(s):  
Surface Temperature ◽  
North Pacific ◽  
Storm Track ◽  
High Variability ◽  
Sea Surface ◽  
Boreal Winter ◽  
The North ◽  
The Western Pacific ◽  
The North Pacific ◽  
North Pacific Storm Track

Abstract Using multiple reanalysis datasets, this study reveals that the variability in the Western Pacific pattern (WP) in boreal winter has shown notable changes during recent decades. The variability in the winter WP exhibited a marked weakening trend before the early 2000s and increased slightly thereafter. Two epochs with the highest and lowest WP variabilities are selected for a comparative analysis. Winter WP-related meridional dipole atmospheric anomalies over the North Pacific were stronger and had a broader range during the high-variability epoch than during the low-variability epoch. Correspondingly, the winter WP had larger impacts on surface temperature variations over Eurasia and North America during the high-variability epoch than during the low-variability epoch. We find that the shift in the winter WP variability is closely related to changes in the connection between the winter WP and the El Niño-Southern Oscillation (ENSO) and to changes in the amplitude of the North Pacific storm track. Specifically, ENSO had a closer connection with the WP during the high-variability epoch, at which time the amplitude of the North Pacific storm track was also stronger. During the high-variability epoch, the extratropical atmospheric anomalies generated by the tropical ENSO shifted westward and projected more on the WP-related atmospheric anomalies, thus contributing to an increase in WP variability. In addition, the larger amplitude of the North Pacific storm track that occurred during the high-variability epoch led to the stronger feedback of synoptic-scale eddies to the mean flow and contributed to stronger WP variability. Further analysis indicates that the change in the connection of ENSO with the WP may be partly related to the zonal shift of the sea surface temperature anomaly in the tropical Pacific associated with ENSO.

The Forcing of the Pacific Decadal Oscillation*

2005 ◽  
Vol 18 (21) ◽  
pp. 4355-4373 ◽  
Author(s):  
Niklas Schneider ◽  
Bruce D. Cornuelle
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Pacific Decadal Oscillation ◽  
North Pacific ◽  
Sea Surface ◽  
Aleutian Low ◽  
The Pacific ◽  
Sea Surface Temperature Anomalies ◽  
Zonal Advection ◽  
The Kuroshio

Abstract The Pacific decadal oscillation (PDO), defined as the leading empirical orthogonal function of North Pacific sea surface temperature anomalies, is a widely used index for decadal variability. It is shown that the PDO can be recovered from a reconstruction of North Pacific sea surface temperature anomalies based on a first-order autoregressive model and forcing by variability of the Aleutian low, El Niño–Southern Oscillation (ENSO), and oceanic zonal advection anomalies in the Kuroshio–Oyashio Extension. The latter results from oceanic Rossby waves that are forced by North Pacific Ekman pumping. The SST response patterns to these processes are not orthogonal, and they determine the spatial characteristics of the PDO. The importance of the different forcing processes is frequency dependent. At interannual time scales, forcing from ENSO and the Aleutian low determines the response in equal parts. At decadal time scales, zonal advection in the Kuroshio–Oyashio Extension, ENSO, and anomalies of the Aleutian low each account for similar amounts of the PDO variance. These results support the hypothesis that the PDO is not a dynamical mode, but arises from the superposition of sea surface temperature fluctuations with different dynamical origins.

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