Abstract
This study finds that the winter (December - February) decadal variability of northerly winds in the East Asian Winter Monsoon (EAWM) over the northern part of the East Asia Coast were influenced by forcing from the middle latitudes from the 1950s to 2000s and related to the Pacific Decadal Oscillation (PDO). We propose that the decreased EAWM in recent decades is associated with the change in pressure gradient along the East Asia coast. This mechanism accounts for the change of westward sea-level pressure (SLP) gradient along the Northeast Asia coast, and is affected by the Aleutian Low location, which is associated with the PDO phases. As the Aleutian Low is influenced by the negative PDO phase and moves westward, the SLP gradient between the Siberian High and the Aleutian Low can increase and the northerly wind at 850 hPa will be enhanced. This change is associated with the increased EAWM near Sakhalin Island of Russia to Hokkaido of Japan.
Highlights
East Asia is located in the southeastern region of the Eurasian landmass and influenced by large-scale, low-level anticyclonic circulations in the boreal winter
The correlation coefficient between the zonal pressure gradient at the studied area and the Siberian High center is not significant. This implies that the Siberian High is not the major effecting component of the westward sea-level pressure (SLP) gradient at the study area, but it is correlated with the Aleutian Low in decadal time scales
Using the NCEP Re-analysis data, this study attempted to understand the decadal variability of the East Asian Winter Monsoon (EAWM) since the 1950s over the northeast Asian coast
Summary
East Asia is located in the southeastern region of the Eurasian landmass and influenced by large-scale, low-level anticyclonic circulations in the boreal winter. Used the land-sea SLP difference between the two regions (20 - 50°N, 110°E and 20 - 50°N, 160°E) to calculate the pressure gradient between the Siberian High and Aleutian Low. Sun and Sun (1995) used geopotential height at 500 hPa to display the East Asian trough intensity. We found that the zonal SLP gradient and 850-hPa northerly winds over the middle latitudes between the Siberian High and Aleutian Low are related only to the Aleutian Low location in the decadal time scale. In this time scale, the Siberian High does not play an important role.
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