“11•26”阿勒泰地区特强寒潮天气过程分析

Analysis of “11•26” Strong Cold Wave Weather Process in the Altay Region

本文利用实况观测资料以及NCEP提供的分辨率为1˚ × 1˚的FNL再分析资料,对新疆阿勒泰地区2022年11月25日至28日的特强寒潮天气过程成因进行了诊断分析,结果表明,此次寒潮天气过程极端性强,爆发性剧烈、最低气温低、影响范围广、降雪量大、大风强度强。全地区共计6成气象站点达特强寒潮标准,最低气温普遍降至−30℃以下,低温中心达−48.6℃。阿尔泰山沿线出现暴雪,阿勒泰市积雪深度突破11月历史同期极值。26日偏东大风急转偏西大风,5站风力达11级以上。前期阿勒泰受暖脊控制,暖平流旺盛,地面气温持续上升至0℃。强冷空气在西伯利亚地区堆积,低涡冷中心强度达−48℃,700 hPa、850 hPa冷中心强度达−36℃、−32℃。随着欧洲脊发展东扩,西伯利亚低涡中的横槽转竖东移,地面1062.5 hPa冷高压中心沿着北方路径南下,在阿勒泰北部边境东移,−50 × 10−5℃•s−1冷平流中心进入阿勒泰,产生剧烈降温,地面超过20厘米雪面的辐射降温作用进一步加大了降温幅度。地面冷高压与新疆南部的低压中心压差达到50 hPa,气压梯度力大。冷空气进入阿勒泰后24小时内变压幅度达到20 hPa以上,产生地面西北大风。冷空气下沉加速以及地形作用都对大风强度有增幅效果。高空西风急流中心最大风速超过60 m/s,抽吸辐散作用强烈。500 hPa西伯利亚低涡受到欧洲脊前北风带引导的冷空气南下补充,同时与咸海低涡合并,强度持续增强。高低空低涡前部西南急流强盛,配合低空东风急流,水汽在阿勒泰地区上空辐合。加之锋面抬升以及阿尔泰山地形强迫抬升作用,阿尔泰山迎风坡沿线出现暴雪。

This paper uses real-time observational data and 1˚ × 1˚ resolution FNL reanalysis data provided by NCEP to diagnose and analyze the causes of the strong cold wave weather process in the Altay region of Xinjiang from November 25th to 28th, 2022. The results show that this cold wave weather pro-cess is extremely intense, with explosive and severe characteristics, low minimum temperatures, wide range of impacts, heavy snowfall, and strong winds. A total of 60% of the meteorological sta-tions in the entire region reached the criteria for a strong cold wave, with minimum temperatures generally dropping below −30˚C and the temperature center reaching −48.6˚C. Blizzard conditions occurred along the Altai Mountains, and the snow depth in Altay City surpassed the historical ex-treme value for November. On the 26th, the winds shifted rapidly from the east to the west, with wind speeds reaching above 11 on the Beaufort scale at 5 stations. Initially, Altay was under the control of a warm ridge, with strong warm advection, and surface temperatures continued to rise to 0˚C. Cold air accumulated in the Siberian region, with the intensity of the cold vortex center reach-ing −48˚C and the intensities of the 700 hPa and 850 hPa cold centers reaching −36˚C and −32˚C, respectively. As the European ridge expanded eastward, the transverse trough in the Siberian trough shifted vertically eastward. The cold high-pressure center of 1062.5 hPa along the north-ward path descended southward into the northern border of Altay, where the −50 × 10−5˚C•s−1 cold advection center entered, resulting in a severe temperature drop. The radiative cooling effect of the snow surface exceeding 20 centimeters further enhanced the cooling magnitude. The pressure gra-dient between the surface cold high-pressure system and the weak low-pressure center in southern Xinjiang reached 50 hPa, resulting in a strong pressure gradient force. Within 24 hours of the arri-val of the cold air, the pressure change at Altay exceeded 20 hPa, resulting in a northwest wind at the surface. The acceleration of the sinking of the cold air and the effect of the terrain both amplified the intensity of the strong winds. The maximum wind speed in the mid-level westerly jet exceeded 60 m/s, and the effect of advection and divergence was strong. The Siberian trough at 500 hPa was replenished by the cold air guided by the north wind belt ahead of the European ridge, and it merged with the Caspian Sea trough, continuously increasing in intensity. The southwest jet in the front of the upper and lower-level trough was strong, and it converged with the eastward jet in the lower levels, causing moisture convergence in the Altay region. Additionally, the uplift of the front and the significant forced uplift of the Altai Mountain terrain led to blizzard conditions along the windward slope of the Altai Mountains.