An inter-decadal increase in summer sea level pressure over the Mongolian region around the early 1990s

摘要

The East Asian summer monsoon is affected by processes in the mid-high latitudes in addition to various tropical and subtropical systems. The present study investigates the summer sea level pressure (SLP) variability over northern East Asia (NEA) and emphasizes the closed active center over the Mongolian region. It is found that the seasonal mean Mongolian SLP (MSLP) anomaly is closely connected with the variability of summertime regional synoptic extra-tropical cyclones on longer time scales. A significant inter-decadal increase in the MSLP around the early 1990s has been detected, which is accompanied by a weakening in the activity of regional extra-tropical cyclones. Recent warming over NEA may have a contribution to the inter-decadal change, which features evidently meridional inhomogeneity around 45 degrees N. The inhomogeneous air temperature anomaly distribution results in decreased vertical wind shear, reduced atmospheric baroclinicity over the Mongolian region, and thus inactive regional cyclones and increased MSLP in the latter decade. The associated temperature anomaly distribution may be partly attributed to regional inhomogeneity in cloud and radiation anomalies, and it is further maintained by two positive feedback mechanisms associated with atmospheric internal processes: one via adiabatic heating and the other via horizontal temperature advection.