POSSIBLE IMPACTS OF MADDEN–JULIAN OSCILLATION ON THE SEVERE RAIN-SNOW WEATHER IN CHINA DURING NOVEMBER 2009

Possible relationships between MJO and the severe rain-snow weather in Eastern China during November of 2009 are analyzed and results show that a strong MJO process is one of the strong impact factors.MJO is very active over the Indian Ocean in November 2009.Especially,it maintains 9 days in MJO phase 3,just corresponding to the two strongest rain-snow processes.Composites of MJO events show that when the MJO convective center is located over the Indian Ocean,the probability of rainfall is significantly increased and the temperature is lower than normal in eastern China,which is consistent with the situation in November of 2009.Atmospheric circulation anomalies of mid-and higher-latitudes can be influenced by the tropical MJO convection forcing and this influence could be realized by teleconnection.When the MJO is over the Indian Ocean,it is favorable for the maintenance of a circulation pattern of two ridges versus one trough at mid-and higher-latitudes.Meanwhile,the western Pacific subtropical high is stronger and more westward than normal,and a significant convective belt appears over eastern East Asia.All these circulation anomalies shown in the composite result also appeared in the observations in November 2009,which indicates the general features of relationships between the MJO and the circulation anomalies over the extratropics.Besides the zonal circulation anomalies,the MJO convection can also lead to meridional circulation anomalies.When the MJO convection is located over the Indian Ocean,the western Pacific is dominated by anomalous descending motion,and the eastern East Asia is controlled by strong convergence and ascending motion.Therefore,an anomalous meridional circulation is formed between the tropics and middle latitudes,enhancing the northward transportation of low-level moisture.It is potentially helpful to understanding and even forecasting such kind of rain-snow weather anomalies as that in November 2009 using MJO.

Analysis on the Heavy Snow Weather Process in Benxi Area

[Objective] The aim was to study the formation and development of a heavy snow in Benxi area. [Method] Based on conventional meteorological data, the formation and development of a heavy snow in Benxi area from December 4th to 5th in 2009 were analyzed from the aspects of weather situation evolution and physical quantity field feature. [Result] The heavy snow was caused by upper trough and North China cyclone. In this process, there was upper level divergence and lower level convergence over Benxi area, and it was warm at low attitude and cold at high attitude; southwest jet at low attitude transported water vapor from Bohai Sea to eastern Liaoning, which provided good water vapor condition for snow, but it didn’t reach heavy snow due to inadequate ascending force. The development of Ural Mountains high ridge played an important role in the snow process and the strengthened high ridge moving northward was beneficial to the southward movement of cold air and deepening of upper trough. Analysis on physical quantity field could provide reference for predicting beginning and ending time and strength of heavy snow. [Conclusion] The study could provide basis for the forecast of heavy snow.

Study on Diagnosis Weather Process and Flight Impact of Heavy Snowfall in Northeast China “11/2021”

Based on ERA5 reanalysis data, the characteristics of weather situation, water vapor condition, dynamic uplift condition, energy condition, ice accumulation environment and flight effect of aircraft in the heavy snowfall process in northeast China from November 5 to 12, 2021 are analyzed. The results show that the heavy snowfall process in Northeast China is caused by the combination of Northeast China Cold Vortex, trough, low level frontal cyclone and cold front. Through the analysis of the physical field, it is found that the sufficient water vapor transport is from the south and the southeast, the convergence rising in the lower layer, divergence “pumping” in the upper layer, air flow rising in the vertical plane and a large amount of convection effective potential energy are all contributing to the heavy snowfall. The impact of heavy snowfall on flight mainly includes low visibility and ice accumulation. Water vapor flux, water vapor flux divergence, vertical velocity, potential temperature and convective effective potential energy can all be used as the judging indexes of heavy snowfall forecast.

2024年2月17—23日中国大范围强寒潮雨雪冰冻强对流过程涉及的若干问题

2024年2月中下旬我国出现一次多灾种高影响天气过程。这是一次几十年一遇的过程,出现了大范围强寒潮雨雪冰冻天气并伴随强对流发生,涉及到强寒潮、沙尘、降雨、降雪、冻雨,以及强对流和伴随的大冰雹和雷暴大风,多种高影响天气在一次过程中都有所呈现,其过程之复杂异常罕见。本文针对此次过程中值得深入探讨的问题、高影响天气发生发展可能机理、相应的预报挑战等进行简要梳理,为后续对此次过程的细致和深入分析研究做一个引子。

The Utility of 1000 - 500 mb Thickness and Weather Type as a Rain-Snow Divide: A 30-Year Study at Albany, NY

Winter synoptic conditions that produce snowfall with bitterly cold temperatures create both social and economic hazards in the capital city of Albany, NY. Sometimes these systems are forecasted in error to produce rain or mixed precipitation. It is beneficial for meteorologists to better understand the commonly used 5400 and 1300 GPM line to better forecast rain versus snow events. Other studies have looked into the use of the 5400 GPM (540 dm) line but none have assessed the validity of this boundary with respect to weather type characterization at Albany. This study aims to determine the reliability of the widely referenced guides for depicting the rain-snow line, and improve forecast aids for the vertical atmosphere during winter precipitation events. The mean daily 500, 850, 925 and 1000 mb heights and weather type frequency of the Spatial Synoptic Classification between November and March of 1980 - 2012 are analyzed. Results indicate that the standard vertical boundaries are inaccurate indicators of a rain versus snow event in Albany. More reasonable rain-snow cut offs for the 1000 - 500 and 1000 - 850 mb thicknesses are 5222 and 1262 GPM. For the 1000 - 925 mb level, 606 GPM is a helpful aid of identifying the rain-snow boundary. Further scrutinizing by weather type indicates that the rain-snow boundary also varies depending on what air mass/weather type is present on a given day. For instance, when the most prominent weather type is observed over Albany (Dry Polar), at the 1000 - 850 mb and 1000 - 500 mb layers, a boundary of 1242 GPM and 5152 GPM is found to be most representative. Results indicate only for the rarest of winter weather types observed over Albany, Moist Tropical, are the standard cut offs useful. Determining the reliability of this precipitation indicator at a specific station, like Albany, could enable meteorologists in other regions of the country to draw parallels between weather type, precipitation, and thickness in their forecast zones.

2023年3月29日贵南地区暴雪天气过程分析

文章利用MICAPS常规观测资料、卫星云图资料及C波段雷达资料对青海省海南州贵南地区2023年3月29日暴雪天气过程进行分析,结果表明:500 hPa高空短波槽及切变线是此次暴雪天气过程高空的主要影响系统;低空及地面较好的水汽条件、不稳定层结和触发机制相互配合,构成了贵南地区出现极端性降雪天气有利的气象因子;十分充沛的局地水汽条件是此次极端降雪天气发生的主要原因之一;贵南地区中小尺度的气旋式辐合系统提供了较好的辐合抬升条件,这是此次暴雪天气过程局地性强和降水强度大的另一个原因。分析结果可为今后类似暴雪天气过程预报提供参考依据。

2013—2023年铜鼓雨雪天气回波特征分析

为了研究铜鼓县冬季雨雪天气背景和雷达回波特征,文章使用铜鼓地面资料、天气图和雷达回波等资料,对铜鼓雨雪天气过程进行分析。结果表明:1957—2023年,铜鼓国家基本气象站观测到雪深≥0.1 cm的频次有62次,≥1.0 cm的有18次,其中2022-02-22T20:00/2022-02-23T08:00降雪深度最大,为24 cm;铜鼓降雪天气系统有500 hPa槽前,200 hPa出流区,700 hPa或850 hPa有切变线,850 hPa有西南急流和东风气流;铜鼓雨雪天气雷达拼图典型特征是回波强度最大为35 dBZ,一般在25 dBZ左右;回波结构均匀,呈东北—西南走向条带状结构;铜鼓降雪的回波顶高都在3 km~5 km,回波强度在15~30 dBZ。研究结果为铜鼓雨雪天气的预报预警提供了分析依据。

人工增雪技术对降低雾霾天气污染物浓度的可行性研究

雾霾天气是影响城镇居民生活健康的主要原因之一,冬季降雪量不足会导致城市内空气污染物浓度加重。为此使用人工增雪技术提高冬季降雪量,并探究人工增雪技术对降低雾霾天气污染物浓度的可行性。分析人工增雪技术的效果和潜力,计算城市内雾霾天气污染物浓度和降雪量间的变化,以此分析该技术的可行性。分析结果表明,人工增雪能降低雾霾天气污染物浓度,有效改善城市内的酸雨情况,优化空气污染质量综合指数,提高空气质量优良率。证明了人工增雪技术对降低雾霾天气污染物浓度的可行性较强。

Comparison and analysis of snow cover data based on dif-ferent definitions of snow cover days

In order to analyze the differences between the two snow cover data, the snow cover data of 884 meteorological stations in China from 1951 to 2005 are counted. The data include days of visual snow observation, snow depth, and snow cover durations, which vary according to different definitions of snow cover days. Two series of data, as defined by ＂snow depth＂ and by ＂weather obser- vation,＂ are investigated here. Our results show that there is no apparent difference between them in east China and the Xinjiang region, but in northeast China and the Tibetan Plateau the ＂weather observation＂ data vary by more than 10 days and the ＂snow depth＂ data vary by 0.4 cm. Especially in the Tibetan Plateau, there are at least 15 more days of＂weather observation＂ snow in most areas （sometimes more than 30 days）. There is an obvious difference in the snow cover data due to bimodal snowfall data in the Tibetan Plateau, which has peak snowfalls from September to October and from .April to May. At those times the temperature is too high for snow cover fol：mation mad only a few days have trace snow cover. Also, the characteristics and changing trends of snow cover are analyzed here based on the snow cover data of nine weather stations iri the northeast region of the Tibetan Plateau, by the Mann-KendaU test. The results show significantly fewer days of snow cover and shorter snow dtwations as defined by ＂snow depth＂ compared to that as defined by ＂weather observation.＂ Mann-Kendall tests of both series of snow cover durations show an abrupt change in 1987.

Early Warning of Snow Disaster in Pasturing Areas of Inner Mongolia

Using ground and remote sensing monitoring, and national standards of snow disaster monitoring evaluation standards, quantitative evaluation of snow disaster was realized. Threshold of animal husbandry weather forecast indexes were applied to establish snow disaster early warning for different grasslands in pasturing areas of Inner Mongolia, and make the grade distribution map of snow disaster early warning. The forecast results basically met the real conditions, it proved that this forecast method was capable of evaluating scale and influence degree of snow disaster. However, the snow disaster grade forecast deviated from the real conditions for the influence of weather forecast accuracy rate.

积雪和沙尘对冰封期青海湖辐射和温度的影响

青藏高原广泛而密集地分布着大量湖泊,受高海拔影响,湖泊多季节性冻结且冰封期较长。湖冰可显著改变湖面和水下辐射、能量传输过程,进而影响局地、区域气候及冰下水生生态系统;然而目前对高原湖泊冰封期湖面特征及湖下热力过程的认识尚不明确。因此,本研究于2022年2月6-28日在青藏高原最大湖泊青海湖进行了冰封期多层湖水-湖冰-大气的系统野外观测;利用获取的野外观测数据及视频影像,结合台站降水资料,研究了冰封期青海湖不同冰面覆盖条件对湖水-湖冰-大气辐射和温度的影响。结果表明,降雪、沙尘、大风等不同天气过程可显著改变冰面物质的分布情况,导致青海湖冰面覆盖物和冰层的厚度发生变化。冰面覆盖物的反照率差异及其对太阳辐射的吸收差异使入射到湖表覆盖物上界面、湖冰上界面的短波辐射和湖冰温度日变化存在显著差别。裸冰时反照率较小且上层少有可吸收太阳辐射的覆盖物,冰面温度的日变化较大。积雪的高反射特性和沙尘的强吸收特性均削弱了入射湖冰表面的短波辐射,使得湖冰温度日变化较小。

2023年2月大气环流和天气分析

2023年2月,大气环流的主要特征为,北半球极涡呈偶极型,次中心位于鄂霍次克海,强度较常年偏强;欧亚中高纬地区由多槽型转变为“两槽一脊”型。我国中高纬度大部处于高压脊前锋区内,槽前为正距平,冷空气活动较多但强度偏弱,南支槽位置强度接近常年同期,导致我国北方地区多雨雪天气过程,南方地区出现阶段性阴雨寡照天气。全国平均气温为0.3℃,较常年同期偏高1.6℃,全国平均降水量为15.5 mm,较常年同期偏少5%。

2023年1月大气环流和天气分析

2023年1月大气环流的主要特征是:北半球极涡呈偶极型分布,东北亚低涡偏强。东亚大槽偏东,南支槽偏弱。1月全国平均降水量为8.8 mm,较常年同期(14.3 mm)偏少38%;全国平均气温为-4.4℃,较常年同期(-4.8℃)偏高0.4℃。月内气温冷暖起伏较大,中下旬出现3次冷空气过程,气温由上旬异常偏暖逆转为下旬普遍偏冷的格局,黑龙江出现极寒天气,漠河最低气温达-53℃,刷新我国最低气温纪录。13—16日出现年度首次大范围寒潮天气,具有降温剧烈、风力大、雨雪范围广等特点,新疆、陕西、山西、河南等地出现大雪或暴雪,北方地区出现首次沙尘天气过程。此外,上旬大气扩散和湿清除条件较为不利,出现持续性雾-霾天气。

基于CMA-MESO冰粒子含量的雨雪相态判据应用

利用中国气象局中尺度模式(CMA-MESO)云降水物理直接输出的水凝物混合比,确定基于冰相水凝物占比的雨雪相态判据,并应用于2023年1月14—15日我国大范围降水过程的雨雪相态判别。结果表明:该判据明显改善了基于温度和高度场的厚度判据对我国东部地区雨夹雪范围判别偏大、对分散性雨夹雪漏报的问题,6~18 h时效雨夹雪预报TS评分较厚度判据提升75%~100%,24 h时效降雪预报TS评分较厚度判据提升67%;对全国雨雪范围判别合理,对小范围雨夹雪具有指示作用;对全国3~36 h时效降雨、降雪和雨夹雪预报TS评分为0.76~0.62,0.69~0.63和0.11~0.08;对降雨和降雪存在一定空报和漏报,对24 h时效雨夹雪空报明显;对相态转换过程有较好指示效果,判别代表站相态转换开始时间误差为1~2 h,对我国东部地区代表站的相态转换和雨夹雪持续时间判别优于厚度判据,基于厚度判据雨夹雪预报持续时间偏长。研究结果可为雨雪相态业务预报提供客观预报产品参考。

2022年2月中下旬桂北一次低温雨雪天气过程成因分析

该文利用观测资料、广西中尺度自动站资料及FNL资料,分析了2022年2月中下旬影响桂北的一次低温雨雪冰冻天气。分析表明:(1)过程期间中高纬为两槽一脊型,乌拉尔山高压脊强盛发展,东移缓慢;脊前的强冷空气与南支槽前的西南暖湿气流在华南交汇,为此次低温雨雪天气的产生提供了有利的环流形势。此次过程产生的重要原因是低层强锋区稳定维持。(2)从降雨转为雨夹雪,温度垂直结构,逆温层的高度、厚度及强度、0℃层的高度,近地面融化层的厚度、地面温度都有显著变化。(3)持续的中低层水汽输送和辐合利于冰冻雨雪天气的发生及维持。(4)湿层厚度变化对雨雪相态转化有一定的指示意义。

冰雪天气下高速公路可变限速控制研究

为保障冰雪天气条件下高速公路的行车安全与通行效率,在建立安全限速模型与交通流预测模型的基础上,提出一种基于粒子群优化算法的可变限速控制策略;首先,通过分析冰雪天气下车辆制动性能和交通流演化规律,提出适用于冰雪天气条件的高速公路安全限速模型以及交通流预测模型;其次,设计了兼顾通行效率与行车安全的优化目标函数,并考虑实际行车需求给出相关约束条件;最后,基于交通流预测模型并结合粒子群优化算法对可变限速值进行求解,并通过搭建的元胞自动机交通流模型将所提出的可变限速策略的控制效果与固定限速方案和分段安全限速方案进行对比仿真实验;仿真结果表明,相比于固定限速方案,可变限速控制减少了总行程时间、总行程延误时间和车辆冲突时间;相比于分段安全限速方案,可变限速控制有效减小了管控路段内的车辆行驶速度标准差,总行程延误时间和车辆冲突暴露时间也有所降低,验证了所提出可变限速控制策略的有效性。

2020年2月13—14日秦皇岛一次大范围降雪天气过程分析

选取高空、地面等气象探测资料,对2020年2月中旬秦皇岛一次降雪天气过程进行分析,结果表明:此过程发生前,亚洲中高纬环流形势为“1槽1脊”型,有1个冷中心为-36.0℃的切断低涡分布于蒙古一带,冷空气南下影响我国华北。在高空槽、中低层切变线、地面倒槽等系统的影响下,产生了降雪天气。降雪期间秦皇岛有明显的湿区,在低空西南风将南方的水汽持续输送,同时东北风将渤海海面的水汽持续输送,提供了丰富的水汽条件。近地层偏东风具有冷垫作用,使得925 hPa以下低空温度急剧下降至-6.0℃,气温下降幅度较大,有利于降水向降雪的现象转换。高空辐散、低空辐合的配置促进垂直运动的产生,提供了有利的动力条件。降雪发生初期,雷达速度产品存在显著的急流特征,急流带来的强水汽输送和强垂直风切变是此次降雪发生发展的关键因素。

许昌近20年初雪天气特征分析

气象上将雨、雪、雹等从天空下降至地面的水汽凝结物,称为“降水”。雪是由大量白色不透明的冰晶(雪晶)和其聚合物(雪团)组成的降水,是水汽遇冷的产物。基于降雪形成的条件,整理近2001—2020年许昌市5个站点的地面资料、探空资料、NCEP再分析资料,分析许昌市初雪出现的时空分布特征,根据影响系统对造成许昌市初雪的环流形势进行分类,结合典型个例给出各种环流形势特点;通过大量个例找出对许昌初雪有影响的天气尺度系统,分析产生初雪的物理量特征,得出初雪天气的具体预报特征。

南方城市降雪概率分析——以绍兴市越城区2022年1—2月降雪天气为例

利用MICAPS 4等分析资料,分析了2022年1—2月发生在绍兴市的5次降雪天气过程,从环流背景、风场、探空、温度场、动力热力等方面总结增大城区降雪天气概率的有利环境特征,结果表明:(1)形势场配置上,北方存在冷高压,东亚槽后冷空气渗透南下,高空位于南支槽前,提供较好的水汽输送条件,700 hPa存在急流,850 hPa低涡切变,低层具有明显的动力强迫作用。(2)温度形势上,冷空气势力偏强,-4℃线压至浙中以南地区。(3)700~850hPa存在较明显逆温层,零度层高度低(<200 m),近地面温度低(2℃左右)。(4)从降雪来看,尤其是积雪情况,高海拔山区降雪概率更大,积雪也一般比城区偏大2~5cm。

冰雪天气下人车碰撞事故严重程度影响因素分析

为降低冰雪天气下行人与机动车碰撞事故的严重程度,保障行人在恶劣天气下的出行安全,文中以美国北卡罗来纳州2010-2020年间发生的1462起冰雪天气下人车碰撞事故为研究对象,按照事故记录从人、车、道路、环境和事故属性5个方面选择22个变量,采用多项逻辑模型建立行人伤害严重程度分析模型,对冰雪天气下的事故受损程度与影响因素关系进行深入分析,并对模型进行检验。结果表明:行人年龄、行人性别、行人是否饮酒、驾驶员年龄、车道数量、光线条件、是否高峰期、发生区、是否有救援这9个变量对冰雪天气下事故严重程度有不同程度的显著性影响。研究结果可为交管部门针对冰雪天气下提出科学有效的事故防治措施提供一定的依据。