The 2020/21 Extremely Cold Winter in China Influenced by the Synergistic Effect of La Niña and Warm Arctic

In the first half of winter 2020/21,China has experienced an extremely cold period across both northern and southern regions,with record-breaking low temperatures set in many stations of China.Meanwhile,a moderate La Ni?a event which exceeded both oceanic and atmospheric thresholds began in August 2020 and in a few months developed into its mature phase,just prior to the 2020/21 winter.In this report,the mid?high-latitude large-scale atmospheric circulation anomalies in the Northern Hemisphere,which were forced by the negative phase of Arctic Oscillation,a strengthened Siberian High,an intensified Ural High and a deepened East Asian Trough,are considered to be the direct reason for the frequent cold surges in winter 2020/21.At the same time,the synergistic effect of the warm Arctic and the cold tropical Pacific(La Ni?a)provided an indispensable background,at a hemispheric scale,to intensify the atmospheric circulation anomalies in middle-to-high latitudes.In the end,a most recent La Ni?a prediction is provided and the on-coming evolution of climate is discussed for the remaining part of the 2020/21 winter for the purpose of future decision-making and early warning.     

2009/2010年冬季云南严重干旱的原因分析

2009/2010年冬季我国云南省出现严重干旱,这次大范围严重干旱是较长时期降水稀少所造成的。首先讨论云南省冬季降水偏多和偏少时大气环流和海温的统计特征,基于它们的统计关系,再对2009/2010年冬季我国云南省的严重干旱进行个例对比分析。研究表明西风带环流系统异常是造成这次干旱灾害的主要成因。贝加尔湖为高度负距平,东亚沿海为高度正距平,从贝加尔湖以西到东亚中高纬度西风带较平直,冬季冷空气偏弱,很难影响西南地区。尤其是副热带中东急流减弱,从欧洲东部到里海为高压脊控制,西风带的扰动系统不易东移到东亚上空;青藏高原上空为稳定的高压脊,孟加拉湾南支槽减弱,云南省受异常西北气流控制。对太平洋和印度洋海温的分析表明,虽然海温异常可以影响冬季的云南降水,但海温异常并不是2009/2010年冬季云南省降水偏少的最重要原因。     

WINTERTIME MIDDLE EAST SUBTROPICAL WESTERLY JET STREAM INTERANNUAL VARIATION CHARACTERISTICS AND ITS POSSIBLE PHYSICAL FACTORS

Using National Centers for Environmental Prediction/Department of Energy (NCEP/DOE) monthly reanalysis data and an extended reconstruction of the sea surface temperature data provided by National Oceanic and Atmospheric Administration, the basic characteristics of the interannual variation in the wintertime Middle East subtropical westerly jet stream (MEJ) and its possible physical factors are studied. The results show that the climatological mean MEJ axis extends southwestward-northeastward and that its center lies in the northwest part of the Arabian Peninsula. The south-north shift of the MEJ axis and its intensity show obvious interannual variations that are closely related to the El Ni?o-Southern Oscillation (ENSO) and the mid-high latitude atmospheric circulation. The zonal symmetric response of the Asian jet to the ENSO-related tropical convective forcing causes the MEJ axis shift, and the Arctic Oscillation (AO) causes the middle-western MEJ axis shift. Due to the influences of both the zonal symmetric response of the Asian jet to the ENSO-related tropical convective forcing and the dynamical role of the AO, an east-west out-of-phase MEJ axis shift is observed. Furthermore, the zonal asymmetric response to the ENSO-related tropical convective forcing can lead to an anomalous Mediterranean convergence (MC) in the high troposphere. The MC anomaly excites a zonal wave train along the Afro-Asian jet, which causes the middle-western MEJ axis shift. Under the effects of both the zonal symmetric response to the ENSO-related tropical convective forcing and the wave train along the Afro-Asian jet excited by the MC anomaly, an east-west in-phase MEJ axis shift pattern is expressed. Finally, the AO affects the MEJ intensity, whereas the East Atlantic (EA) teleconnection influences the middle-western MEJ intensity. Under the dynamical roles of the AO and EA, the change in the MEJ intensity is demonstrated.     

辐射传输模式中地表参数对大气长波辐射的影响

本文利用Liou-Ou一维宽带辐射传输模式，对地表热力参数取值部分作了改进，使用模式大气和青藏高原实测资料对下垫面温度与地表空气温度两者不能合二为一的问题进行了分析，同时还讨论了下垫面温度的日变化对大气长波辐射通量日变化的影响及地表比辐射率的变化对大气长波辐射通量计算结果的修正作用。     

非均一地形近地层风速廓线特点及粗糙度的研究

在中性大气层结条件下,利用35 m铁塔上五层不同高度处的有效风速,分析得到了非均一地形近地面层风速廓线特点及由粗糙元所决定的粗糙度。结果表明:(1)近地面层风速廓线一般符合对数风速廓线模式,其相关系数均大于0.985,标准偏差为0.04左右;(2)粗糙度的值为1.25 m。但由于外界流体运动状态改变可引起粗糙度出现起伏,其变化范围较大,一般在0.038～4.903 m,与风速之间的相关系数为-0.953。     

基于多普勒天气雷达的低空多普勒速度的切变识别算法研究

低空风切变是影响航空器起飞和着陆安全的重要因素,利用多普勒天气雷达径向速度数据,从风的空间和时间变化上对低空风切变的识别进行了研究,并利用一次飑线过程和一次低空急流过程的资料对识别算法进行了验证。识别算法的核心是分别计算二维合成风切变、垂直风切变和时间风切变。在计算二维合成风切变时,先利用风切变强度因子自适应地选择拟合“窗口”的大小,再利用最小二乘线性拟合方法,得到水平风切变。结果表明:自适应多尺度最小二乘法得到的合成风切变,在低空风切变识别效果、切变连续性和边缘数据处理等方面都优于我国多普勒天气雷达的PUP合成风切变;垂直风切变反映了雷达径向速度的高低空配置情况;时间风切变可提供径向速度随时间的变化情况。算法还可应用于民航机场低空风切变的识别和预警。      

Prediction of the Asian-Australian Monsoon Interannual Variations with the Grid-Point Atmospheric Model of IAP LASG （GAMIL）

Seasonal prediction of Asian-Australian monsoon （A-AM） precipitation is one of the most important and challenging tasks in climate prediction. In this paper, we evaluate the performance of Grid Atmospheric Model of IAP LASG （GAMIL） on retrospective prediction of the A-AM interannual variation （IAV）, and determine to what extent GAMIL can capture the two major observed modes of A-AM rainfall IAV for the period 1979-2003. The first mode is associated with the turnabout of warming （cooling） in the Nifio 3.4 region, whereas the second mode leads the warming/cooling by about one year, signaling precursory conditions for ENSO.
We show that the GAMIL one-month lead prediction of the seasonal precipitation anomalies is primarily able to capture major features of the two observed leading modes of the IAV, with the first mode better predicted than the second. It also depicts the relationship between the first mode and ENSO rather well. On the other hand, the GAMIL has deficiencies in capturing the relationship between the second mode and ENSO. We conclude： （1） successful reproduction of the E1 Nifio-excited monsoon-ocean interaction and E1 Nifio forcing may be critical for the seasonal prediction of the A-AM rainfall IAV with the GAMIL; （2） more efforts are needed to improve the simulation not only in the Nifio 3.4 region but also in the joining area of Asia and the Indian-Pacific Ocean; （3） the selection of a one-tier system may improve the ultimate prediction of the A-AM rainfall IAV. These results offer some references for improvement of the GAMIL and associated seasonal prediction skill.     

IAP GCM模式大气背景环流在厄尔尼诺年的异常

本文分析了中国科学院大气物理研究所大气环流模式(IAP GCM)模式大气5～9月平均环流(本文称为背景环流)。结果表明;厄尔尼诺年一系列重要系统(南方涛动、瓦克环流、哈德莱环流、西太平洋副热带高压和热带辐合带)及大范围降水均发生明显异常;北半球西太平洋热带、副热带是环流异常的主要区域。它们与观测资料的分析结果基本一致,从而论证了该模式在低纬环流研究中的应用前景。     

驻马店极端气温分析

利用驻马店10个站气象资料,分析了极端温度的时间变化特征、高温天气与6-8月降水量之间的关系和极端晴热高温、极端湿热高温天气形成的天气背景及影响因子,确定了高温出现的前期预报指标。