Cause analysis of flood-drought alternation event in July 2022 in arid and semi-arid region of Inner Mongolia

doi:10.11755/j.issn.1006-7639(2024)-01-0011

Abstract

Abstract:

The rainfall in July of 2022 in the central and western regions of Inner Mongolia was obviously less and showed a phased characteristic of more in the early stage and less in the late stage. The analysis of circulation distribution and configuration in different stages is of great significance for further improving precipitation forecast ability in flood season in this region. Daily precipitation of 116 national meteorological stations in Inner Mongolia, 130 climate indexes from the National Climate Center, daily reanalysis data from National Center for Environmental Prediction/National Center for Atmospheric Science (NCEP/NCAR) and monthly sea surface temperature (SST) data from the National Oceanic and Atmospheric Administration (NOAA) were used to analyze the causes of the flood-drought transition event in the central and western regions of Inner Mongolia in July 2022. The results are as follows: (1) In July 2022, the rainfall in the central and western regions of Inner Mongolia was seriously less, which was the least in the same period since 1991 in this region, and the meteorological drought was relatively serious. (2) From July 1 to 11, the precipitation was relatively more, the cold air path was northward and the intensity was weak, the Western Pacific Subtropical high was weak and its location was northward and westward, and the warm and cold air intermingled in the central and western regions of Inner Mongolia. In addition, the position of upper westerly jet was northward during this period, and the central and western regions of Inner Mongolia were located in the south of the jet axis, which was conducive to upper level divergence and the development of upward movement. While from July 12 to 31, the precipitation was obviously less, the meridian of circulation increased, the cold air activity path was more southerly and the intensity increased, the Western Pacific subtropical high was obviously stronger and the location was southward, which was not conducive to water vapor transport. In addition, the location of upper westerly jet was southward, and the central and western part of Inner Mongolia was located in the north of the jet axis, which was not conducive to upper level divergence and the development of upward movement. The stronger disturbance of the upper westerly jet in mid and late July was conducive to stimulating the meridional teleconnection wave train from East Asia to the Northwest Pacific, which led to the position of the Western Pacific subtropical high southward and less precipitation. (3) The abnormal SST from the Sea of Japan to the northwest of the North Pacific was one of the important external forcing signals that affect the amount of precipitation in central and western regions of Inner Mongolia. In July 2022, the SST in the region was abnormally high, and the cyclonic circulation triggered by the abnormal SST over the region weakened the meridional transport of warm and humid water vapor in the south, which was one of the reasons for the change of precipitation from flood to drought in central and western regions of Inner Mongolia.

Key words: the central and western part of Inner Mongolia, July of 2022, flood-drought alternation, meteorological drought, abnormal sea surface temperature

摘要：

2022年7月内蒙古中西部地区降水明显偏少，且呈前期偏多、后期偏少的涝—旱转折性分布特征，分析不同阶段环流分布差异和影响系统间的配置对进一步做好内蒙古汛期降水预测具有重要作用。利用内蒙古116站逐日降水量、国家气候中心130项气候指数、美国国家环境预报中心/国家大气科学研究中心（National Center for Enviromental Prediction/National Center for Atmospheric Research，NCEP/NCAR）逐日再分析资料和美国国家海洋和大气管理局（National Oceanic and Atmospheric Administration，NOAA）逐月海表温度资料，分析2022年7月内蒙古中西部地区涝-旱转折事件的成因。结果表明：（1）2022年7月内蒙古中西部地区降水量严重偏少，为该地区1991年以来同期降水最少、气象干旱最为严重。（2）7月1—11日降水相对偏多，冷空气路径偏北且强度较弱，西太平洋副热带高压强度偏弱，位置偏北、偏西，冷暖空气在内蒙古中西部地区交绥，加之这一时段高空西风急流位置偏北，内蒙古中西部位于急流轴以南，有利于高层辐散和上升运动发展。7月12—31日降水明显偏少，环流经向度加大，冷空气活动路径偏南且强度增强，西太平洋副热带高压强度偏强且位置明显偏南，不利于水汽输送，加之高空西风急流位置偏南，内蒙古中西部位于急流轴以北，不利于高层辐散和上升运动发展；7月中旬后期至下旬高空西风急流南北向扰动偏强有利于激发东亚—西北太平洋经向遥相关波列，使得西太平洋副热带高压位置偏南从而导致降水偏少。（3）日本海至北太平洋西北部地区的海温异常是影响内蒙古中西部地区降水多寡的重要外强迫信号之一。2022年7月该海区海温异常偏高，其上空激发的气旋式环流减弱了南方暖湿水汽的经向输送，是导致内蒙古中西部降水由涝转旱的原因之一。

关键词: 内蒙古中西部, 2022年7月, 涝-旱转折, 气象干旱, 海温异常

CLC Number:

P466

LIU Wei, ZHAO Yanli, GAO Jing, LI Linhui, WANG Huimin. Cause analysis of flood-drought alternation event in July 2022 in arid and semi-arid region of Inner Mongolia[J]. Journal of Arid Meteorology, 2024, 42(1): 11-18.

刘炜, 赵艳丽, 高晶, 李林惠, 王慧敏. 2022年7月内蒙古干旱半干旱区涝—旱转折事件的成因分析[J]. 干旱气象, 2024, 42(1): 11-18.

Figures/Tables 10

Fig.1 Spatial distribution of precipitation anomaly percentage in Inner Mongolia in July of 2022（Unit： %）

Fig.2 Spatial distribution of the first REOF mode (a) and its normalized time coefficients (b) of precipitation in July during 1991-2022 (The red rectangle box for the location of midwest Inner Mongolia. the same as below)

Fig.3 Daily precipitation anomaly in the midwest of Inner Mongolia in summer of 2022

Fig.4 The 500 hPa geopotential height field (contours) and its anomalies field (color shaded) (a, Unit: dagpm), 850 hPa wind field anomalies (b, Unit: m·s-1), integral water vapor flux over the whole troposphere (vectors, Unit: kg·m-1·s-1) and its divergence (color shaded, Unit: 10-5 kg·m-2·s-1) anomaly field (c), 200 hPa zonal wind field (contours) and its anomalies (color shaded) in East Asia area (d, Unit: m·s-1) from 1 to 11 July 2022 (the red solid lines for climatological mean line of 586 and 588 dagpm, the green thick dashed line for the location of westerly jet axis. the same as below)

Fig.5 The average meridional circulation（stream lines，Unit： m·s-1） and vertical velocity（color shaded，Unit： 10-2 Pa·s-1） profile over the range of 100.0°E-117.5°E from 1 to 11 July 2022 （The midwest of Inner Mongolia is located between the two red lines. the same as below）

Fig.6 The 500 hPa geopotential height field (contours) and its anomalies field (color shaded) (a, Unit: dagpm), 850 hPa wind field anomalies (b, Unit: m·s-1), integral water vapor flux over the whole troposphere (vectors, Unit: kg·m-1·s-1) and its divergence (color shaded, Unit: 10-5kg·m-2·s-1) anomaly (c), 200 hPa zonal wind field (contours) and its anomalies (color shaded) in East Asia area (d, Unit: m·s-1) from 12 to 31 July 2022

Fig.7 The average meridional circulation（stream lines，Unit： m·s-1） and vertical velocity（color shaded，Unit： 10-2 Pa·s-1） profile over the range of during 100.0°E-117.5°E from 12 to 31 July 2022

Fig.8 Daily variation of averaged 200 hPa zonal wind anomaly over the range of 100.0°E-117.5°E in July 2022（Unit： m·s-1）

Fig.9 The difference field of the averaged geopotential height between 1-11 and 12-31 July 2022 (Unit: gpm) (the dotted areas passing the significant test at α=0.05. the same as below)

Fig.10 Composited sea surface temperature anomaly fields in flood-drought alternation years from 1990 to 2022 (a) and the sea surface temperature anomaly field in July 2022 (b) in middle and western Inner Mongolia（Unit: ℃）

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