Atmospheric circulation difference between warm in early winter and cold in late winter of 2021/2022 over East Asia continent and its causes
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摘要:
2021/2022年冬季东亚大陆地区整体以偏冷为主，气温季节内变化显著，前冬(2021年12月1日—2022年1月26日)气温偏高，后冬(2022年1月28日—2月24日)气温偏低；气温变化的空间差异较大，呈现出显著的北暖南冷特征，尤其在冷时段，南部地区气温偏低幅度比北部地区大1℃左右.本文利用逐日中国观测站点资料和NCEP/NCAR、ERA5等再分析资料分析了2021/2022年冬季东亚大陆前暖后冷的可能原因，发现与冬季气候密切相关的西伯利亚高压、东亚冬季风、平流层极涡、高原高度场、西太平洋副热带高压、东亚高空西风急流、北半球平流层环状模(NAM)等大尺度环流系统均发生了显著的转折性变化，直接导致了东亚大陆冬季前暖后冷的季节变化，但乌拉尔山高压在冷暖时段的变化差异并不明显.另外，赤道中东太平洋冷海温和北大西洋暖海温在后冬的加强变化通过对大气环流的强迫影响，对2022/2021年后冬冷时段冷空气的加强和低温冷事件的发生起到了十分重要的作用.
Abstract:The surface air temperature (SAT) in East Asia continent was lower than normal in winter 2021/2022, but it displayed significantly intraseasonal variability with warmer in early winter (from December 1, 2021 to January 26, 2022) and cooler in late winter (from January 28 to February 24, 2022). Moreover, the spatial distribution of SAT anomalies showed a characteristics of northern warm and southern cold over East Asia continent. Especially, the SAT anomaly in the southern region was approximate 1℃ lower than that in the northern region during in the cold period. In this study, the differences of atmospheric circulation and their possible reasons in winter 2021/2022 are investigated based on the daily station data from CMA and atmospheric reanalysis data from NCEP/NCAR and ERA5. The results show that the SAT variability over East Asia continent is closely related to some key atmospheric circulation systems, including the Siberian high (SH), the East Asian winter monsoon (EAWM), the stratospheric polar vortex, the geopotential height (GHT) in plateau, the Western Pacific subtropical high (WPSH), the westerly jet at upper troposphere in East Asia, and the northern hemisphere annular model (NAM) at stratosphere. The transitional changes of the above atmospheric circulation systems are mainly responsible for the transition from cold to warm in East Asia continent in winter 2021/2022. It should be mentioned that the difference of the Ural Mountain high (UH) between the warm and cold period is no significant. In addition, the cold sea surface temperature (SST) in the tropical central-eastern Pacific and the warm SST in the North Atlantic play a very important role in the strengthening of cold wave and the occurrence of cold events through the forced influence on the atmospheric circulation during cold period in winter 2022/2021.
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图 1
2021/2022年冬季欧亚大陆(a)和中国(b)气温距平分布(单位：℃)，以及东亚不同区域气温逐日变化(c, 单位：℃)
Figure 1.
Distribution of SAT anomalies (unit: ℃) in Eurasia (a) and China (b), with daily SAT variation (c, unit: ℃) in different regions in winter 2021/2022
图 2
2021/2022年冬季暖(左栏)和冷(右栏)时段欧亚大陆(黑色矩形框标注东亚大陆)和中国气温距平分布(单位：℃)
Figure 2.
SAT anomaliesdistribution in Eurasia (rectangular boxes marked East Asia continent) and China during warm (left) and cold (right) period in winter 2021/2022 (unit: ℃)
图 3
2021/2022年冬季暖(左栏)和冷(右栏)时段高低层大气环流平均场(等值线)及距平场(彩色阴影)
Figure 3.
Mean (contours) and anomalies (colored shadings) of atmospheric circulations at different levels during the warm (left) and cold (right) period in winter of 2021/2022
图 4
2021/2022年冬季SHI逐日变化(a，单位：hPa)，以及SHI(b)和UHI(c)分别与东亚大陆不同区域SAT的超前和滞后相关，横坐标正值(负值)表示SHI和UHI滞后(超前)不同区域SAT的天数
Figure 4.
(a) Daily variation of SHI (unit: hPa).The lead-lag correlation between SHI (b)、UHI (c) and the SAT in different regions in winter 2021/2022, with the positive (negative) value on x-axis indicating the days of SHI and UHI lag (lead) SAT
图 5
2021/2022年冬季暖(a)和冷(b)时段500 hPa大气环流异常(高度距平为阴影，单位：gpm；距平风为矢量，单位：m·s-1；垂直速度距平为等值线，单位：10-2Pa·s-1；蓝色和红色矩形框分别为TP-1和TP-2区域)，以及TP-1(c)和TP-2指数(d)的逐日变化(单位：gpm)
Figure 5.
Atmospheric circulation anomalies at 500 hPa during warm (a) and cold (b) period (Shadings are GHT, unit: gpm; vectors are wind, unit: m·s-1; contours are vertical velocity, unit: 10-2Pa·s-1; blue and red boxes indicate the region of TP-1 and TP-2, respectively), daily variations of TP-1 (c) and TP-2 (d, units: gpm) in winter 2021/2022
图 6
2021/2022年冬季暖(a)和冷(b)时段200 hPa波通量(矢量, 单位：m2·s-2)和位势高度距平(阴影，单位：gpm)
Figure 6.
200 hPa wave flux (vector, units: m2·s-2) and GHT anomalies (shading, units: gpm) in warm (a) and cold (b) period in winter 2021/2022
图 7
2021/2022冬季东亚冬季风指数逐日变化(上，单位：m·s-1)以及850 hPa距平风场(下，单位：m·s-1)
Figure 7.
Daily variation of EAWM indices (top, unit: m·s-1) and distribution of 850 hPa wind anomalous (bottom, units: m·s-1) in winter 2021/2022
图 8
2021/2022年冬季(a)暖和(b)冷时段200 hPa西风距平(等值线，红色粗实线为气候平均30 m·s-1等值线)和500 hPa温度梯度(阴影，单位：10-6 k·km-1). 1958—2020年冬季200 hPa西风区域平均(30°N—40°N, 110°E— 150°E)指数分别与(c)850 hPa风场(红色矢量为通过0.05显著性检验)、(d)地面气温场和(e)SLP场的相关分布(相关系数为0.26通过95%显著性检验)
Figure 8.
200 hPa westerly wind anomalies (contours, red thick solid line is the climatological westerlies with the speed of 30 m·s-1) and temperature gradient (shading, units: 10-6k·km1) during (a) warm and (b) cold period in winter 2021/2022. Correlation distribution between westerly wind averaged in the region (30°N—40°N, 110°E—150°E) and (c) 850 hPa wind (red vector passed the 0.05 significance test), (d) SAT, (e) SLP in winter from 1958 to 2020, with the correlation coefficients above 0.26 passed the 95% significance test
图 9
冬季逐日NAM指数的时间-高度剖面图(上，单位：106 m2·s-1)以及1981—2020年冬季NAM指数与中国平均气温的逐日相关(下)，相关系数大于0.26通过95%的显著性检验
Figure 9.
Time-height section of daily NAM index (top, units: 106 m2·s-1) and the correlation between NAM and temperature (bottom) over China in winter from 1981 to 2020, with the correlation coefficients above 0.26 passed the 95% significance test
图 10
2021/2022年冬季逐日副高西伸脊点(a，单位：°E)和脊线位置(b，单位：°N)，阴影为±1个标准差(±1σ)的区域
Figure 10.
Daily variation of west ridge point (a, units: °E) and ridge line position (b, units: °N) of the Western Pacific Subtropical High (WPSH) in winter 2021/2022, with shading for ±1 standard deviation (±1σ)
图 11
冬季(a)东部型La Niña年减去El Niño年的850 hPa风差值场(阴影为通过95%显著性检验的区域，单位：m·s-1)和(b)2021/2022年冬季海温距平分布(单位：℃)
Figure 11.
Difference of 850 hPa wind (unit: m·s-1) between EP La Niña years and El Niño years in winter (shadings indicate the difference exceeding 95% significant test), and (b) distribution of SST anomalous (unit: ℃) in winter 2021/2022
图 12
冬季北大西洋海温暖(左)和冷(右)异常年合成的SAT(上，单位：℃)和SLP(下，单位：hPa)距平场，圆点标注的区域通过95%显著性检验
Figure 12.
Composite fields of SAT (top, units: ℃) and SLP (bottom, units: hPa) anomalies during warm (left) and cold (right) SST years over North Atlantic. Dots indicate the composite exceeding 95% significance test
表 1
不同时段东亚大陆不同区域平均的SAT距平(单位：℃)
Table 1.
SAT anomalies in different regions of East Asia continent in different periods (unit: ℃)
EA_SAT N_SAT SE_SAT SW_SAT 2021-12-01—2022-02-28
(全冬季)-0.06 0.54 -0.20 -0.80 2021-12-01—2022-01-26
(暖时段)1.38 2.10 1.25 0.65 2022-1-28—2022-02-24
(冷时段)-3.22 -2.77 -3.61 -3.93 
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