Dynamical and Chemical Features of a Cutoff Low over Northeast China in July 2007:Results from Satellite Measurements and Reanalysis

The European Centre for Medium-Range Weather Forecasts Re-Analysis Interim(ERA-Interim) meteorology and measurements from the Microwave Limb Sounder,High Resolution Dynamics Limb Sounder,and Ozone Monitoring Instrument onboard the Earth Observing System Aura satellite were applied to analyze the dynamical and chemical features of a cutoff low(COL) event over northeast China in early July 2007.The results showed the polar stratospheric origin of an upper-level warm-core cyclone at 100-300 hPa,associated with a funnel-shaped tropopause intruding into the mid-troposphere just above the COL center.The impacts of the stratospheric intrusion on both column ozone and ozone profiles were investigated using satellite measurements.When the intensity of the COL peaked on 10 July 2007,the total column ozone(TCO) increase reached a maximum(40-70 DU).This could be dynamically attributed to both the descent of the tropopause(～75%) and the downward transport of stratospheric ozone across the tropopause(～25%).Analysis of the tropospheric ozone profiles provided evidence for irreversible transport/mixing of ozone-rich stratospheric air across the tropopause near the upper-level front region ahead of the COL center.This ozone intrusion underwent downstream transport by the upper tropospheric winds,leading to further increase in TCO by 12-16 DU over broad regions extending from east China toward the northern Japan Sea via South Korea.Meteorological analysis also showed the precedence of the stratospheric intrusion ahead of the development of cyclones in the middle and lower troposphere.