Abstract
This study used the FLEXPART-WRF trajectory model to perform forward and backward simulations of a cut-off low (COL) event over northeast Asia. The analysis reveals the detailed trajectories and sources of air masses within the COL. Their trajectories illustrate the multi-timescale deep intrusion processes in the upper troposphere and lower stratosphere (UTLS) caused by the COL. The processes of air intrusion from the lower stratosphere to the middle troposphere can be divided into three stages: a slow descent stage, a rapid intrusion stage and a relatively slow intrusion stage. A source analysis of targeted air masses at 300 hPa and 500 hPa shows that the ozone-rich air in the COL primarily originated from an extratropical cyclone over central Siberia and from the extratropical jet stream. The sources of air masses in different parts of the COL show some differences. These results can help explain the ozone distribution characteristics in the main body of a COL at 300 hPa and at 500 hPa that were revealed in a previous study.
Highlights
Stratosphere–troposphere exchange (STE) is an important dynamic process which takes place in the upper troposphere and lower stratosphere (UTLS)
The FLEXPART-WRF model was used for the forward simulation of air parcels, aiming to reveal the air parcel trajectories and transportation characteristics within the cut-off low (COL) in the
This study revealed the multi-timescale transport processes of the deep intrusion in the UTLS associated with a COL, and provided a foundation for the detailed description of the STE process caused by textratropical weather systems
Summary
Stratosphere–troposphere exchange (STE) is an important dynamic process which takes place in the upper troposphere and lower stratosphere (UTLS). In the 1990s, the World Climate Research Program (WCRP) established the Stratospheric Processes and their Role in Climate (SPARC) core plan. Research carried out in recent decades has shown that the atmospheric composition budget and dynamics of the UTLS region play an important role in global radiation balance and climate change [4]. The STACCATO plan [6] and START-05/08 experiments [7,8] launched in Europe and the Tibetan Plateau atmospheric composition program [9,10] conducted in China provided an improved depiction of the STE process related to synoptic and mesoscale systems in extratropical UTLS areas (Ex-UTLS), revealing an active stratosphere–troposphere air-mixing process. In the extratropical STE associated with the synoptic scale weather systems found in the Northern
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