北美-东亚冬季极端低温空间复合事件及其与高空急流的联系

Wintertime concurrent cold extremes between North America and East Asia:dynamics and linkage with jet streams variability

摘要:

随着全球气候变化的加剧,极端低温事件在发生频率、降温速率等方面都有显著变化,对人类健康、社会经济和生态环境造成了重大影响。研究指出,许多不同地区会同步发生极端低温事件,此类事件被称为极端低温空间复合事件,往往与高空急流异常相联系。本研究基于1979—2022年美国气候预测中心的高分辨率网格化逐日最低地表气温数据集以及NCEP/NCAR再分析数据,针对冬季极端低温空间复合事件进行统计分析,寻找该复合事件下的高空急流分布特征及可能的影响机制。结果表明,东亚与北美在候尺度上存在发生极端低温空间复合事件的空间同步性。通过对环流场的对比分析发现,纬向环流上,高空急流整体增强,两地位势高度易出现负异常,正负分布的位势高度异常呈现出类Rossby-4波的特征;经向环流上,受高空急流影响,则易于造成冷空气从高纬向低纬输送。进一步从热力学方程的角度分析影响的相对贡献,指出经向温度平流和非绝热冷却是造成东亚和北美地区极端低温空间复合事件的重要原因。

Abstract:

In recent decades,the Northern Hemisphere has experienced frequent temperature extremes that have significantly influenced human well-being,socioeconomic stability,and ecological systems.Among these,concurrent cold extremes have concurrently occurred across multiple regions and have drawn increasing attention,often linked to variations in jet stream dynamics.Despite growing interest,most studies have focused on individual events,leaving a limited understanding of the mechanisms driving concurrent temperature extremes across regions.This study focused on the characteristics and possible mechanisms of concurrent cold extremes in East Asia and North America during winter from 1979 to 2021,using the Climate Prediction Center minimum surface air temperature dataset and the NCEP/NCAR reanalysis dataset.Cold extremes were defined as daily minimum temperatures falling below the 10th percentile at each grid point,and their frequencies were analyzed across different time scales.The East Asia (73°—145°E,4°—53°N)and North America (160°—12°W,25°—75°N)were selected as the dominant study regions.The results show that concurrent cold extremes between East Asia and North America predominantly occurred on a pentad time scale.While the frequency of such events has shown a decreasing trend since 2000,significant concurrent cold extremes continue to occur on smaller time scales.Synchronicity between the two regions was confirmed through lead-lag correlation coefficients analysis,highlighting a robust connection.Further analysis of the atmospheric circulations and thermodynamic conditions during concurrent cold extremes identified key mechanisms.Zonal circulation patterns showed enhanced jet streams over the western Pacific Ocean and the West Atlantic Ocean,accompanied by negative geopotential height anomalies.These anomalies formed a Rossby wave-4 pattern,facilitating cold air advection from high latitudes to low latitudes.Meridional circulation analysis supported this,demonstrating the role of jet stream variations in transporting cold air masses.From a thermodynamic perspective,meridional temperature advection and non-adiabatic cooling emerged as the two most significant contributors to concurrent cold extremes in East Asia and North America.These findings provide new insights into the dynamics of concurrent cold extremes in the Northern Hemisphere and highlight the critical role of jet stream variability.Regional differences in temperature impacts between East Asia and North America were noted and need further investigation.Additionally,the resemblance of geopotential height anomalies to a Rossby wave-4 pattern suggests a need for further exploration of the underlying wave dynamics.This study advances the understanding of concurrent temperature extremes and their linkage to atmospheric circulation,offering a foundation for future research and prediction efforts.