In recent decades,with global warming,the Arctic region has exhibited a particularly significant warming trend.As a critical component of the high-latitude climate system,Arctic cyclones are closely linked to various weather phenomena in the Arctic,such as extreme winds and heavy precipitation events.Different from extratropical cyclones in midlatitude,the development and maintenance of some Arctic cyclones are influenced by the tropopause polar vortex (TPV).And the strengthening,maintenance,and vertical structure of these cyclones show significant differences due to effects of the TPV.The climate system in the Arctic region is complex and diverse.Therefore,to further explore the influence mechanism of Arctic cyclones while considering their unique physical mechanism,we aim to study the impact of stratospheric temperature anomalies on the development and maintenance of Arctic cyclones in summer.
At three characteristic phases of cyclone lifecycle-initial formation,peak intensity,and maximum intensification rate-the distances between cyclone centers and TPV centers were systematically calculated.If the distance is less than 1000 km,it is considered that there is a connection between the cyclone and TPV,and it is a TPV cyclone.Conversely,it is determined to be a cyclone unrelated to TPV,that is,a non-TPV cyclone.Two representative intense cyclone cases were selected from the top 100 cyclones in the northern marginal of Eurasia region (NMER):one exhibiting strong dynamical coupling with the TPV and the other unrelated to TPV.Through the weather research and forecasting (WRF) numerical model,control and sensitivity experiments were designed and executed to conduct a comparative investigation into how stratospheric temperature anomalies modulate cyclones of contrasting structural types and their regionally correlated precipitation responses.
The analysis reveals that cyclone cases closely associated with the TPV are influenced by the downward intrusion of high potential vorticity from the stratosphere into the troposphere,exhibiting a distinct quasi-barotropic structure with a warm-over-cold pattern.In the sensitivity experiments,after reducing the horizontal thermal differences in the upper troposphere and above,the folding characteristics of the tropopause are significantly weakened.Correspondingly,the stratospheric potential vorticity intrusion and absolute vorticity around the cyclone center are notably reduced,leading to a significant decrease in both the intensity of the cyclone center and the associated precipitation.In contrast,for another Arctic cyclone process unrelated to TPV activity,the formation and development are primarily driven by baroclinic instability.The horizontal thermal differences in the stratosphere would not show significant changes in the cyclone intensity or precipitation.The study primarily investigates the impacts of stratospheric temperature anomalies on Arctic cyclones,while there are relatively few discussions on other important factors that may affect Arctic cyclone activities and precipitation,such as ocean circulation,the feedback mechanism of the interaction between sea ice changes and the atmosphere.Future research requires expansion of cyclone case samples to enable more comprehensive investigations.Meanwhile,in order to refine the impact on precipitation more precisely,in the subsequent further study of the precipitation accompanying different types of Arctic cyclones,a higher resolution can be selected for WRF simulation to compare and analyze the possible precipitation differences caused by the resolution.