The horizontal and vertical structure of east Asian winter monsoon pressure surges

Abstract

East Asian cold‐air outbreaks, accompanied by increasing surface pressure (‘pressure surges’), are shown to be an important aspect of the subseasonal variability of the winter monsoon system. In this study the statistical linear relationship between pressure surges, tropical convection, and tropospheric circulation is assessed using a ten‐year data set (1985/86‐1994/95) of the European Centre for Medium‐Range Weather Forecasts gridded operational analyses. From spectral analysis the pressure, wind, and temperature fluctuations indicative of strong pressure surges are found to have statistically‐significant spectral peaks at submonthly periods (6 to 30 days). Linear regression analysis is used to detail the time evolution of the dominant horizontal and vertical structure of east Asian pressure surges. Surges are shown to relate significantly to circulation anomalies in both the meridional and zonal components of the lower‐tropospheric wind. Relationships between east Asian pressure surges in the submonthly band and tropical circulation anomalies are found over the Bay of Bengal, the eastern Indian Ocean, Indonesia, and the western Pacific regions. Submonthly surges over the South China Sea are related to strong surges and convective activity south of Indonesia, over the South China Sea, the eastern Indian Ocean, and the Philippine regions. Surge‐enhanced convective activity is found to precede an enhancement of the local east Asian Hadley cell. Submonthly surges over the Philippine Sea are related to periods of westerly‐wind anomalies and convective activity in the western Pacific. Upper‐level wave activity over western Asia precedes submonthly surges. the wave activity amplifies in the region of the Pacific jet stream, and can be traced dispersing equatoward through the region of upper‐level westerlies over the eastern tropical Pacific.