Multiseason evaluation of the MM5, COAMPS and WRF over southeast United States

Three models, MM5, COAMPS, and WRF, have been applied for the warm season in 2003 and the cool season in 2003?C2004 to evaluate their performances. All models run over the same domain area covering the north Gulf Mexico and southeastern United States (US) region with the same spatial resolution of 27?km. It was found that the temporal variations of the mean error distribution and strength at 24 and 36?h were rather weak for surface temperature, sea level pressure, and surface wind speed for all models. A warm bias in surface temperature forecasts dominated over land during the warm season, whereas a cool bias existed during the cool season. The MM5 and WRF produced negative biases of sea level pressure during the warm season and positive biases during the cool season while the COAMPS yielded a similar distribution of sea level pressure biases during both seasons. During both seasons, similar surface wind speed biases produced by each model included a high wind speed forecast over most areas by MM5 while the COAMPS and WRF yielded weak surface winds over the western Plains and stronger surface winds over the eastern Plains. Root-mean-squared errors revealed that the forecast of surface temperature, sea level pressure, and surface wind speed were degraded with the increase of forecast time. For rainfall evaluation, it was found that the MM5 underpredicted seasonal precipitation while the COAMPS and WRF overpredicted. The bias scores revealed that the MM5 yielded an underprediction of the coverage of precipitation areas, especially for heavier rainfall events. The MM5 presented the lower threat score at lighter rainfall events compared to the COAMPS and WRF. For moderate and heavier thresholds, all models lacked forecast accuracy. The WRF accuracy in predicting precipitation was heavily dependent upon the performance of the selected cumulus parameterization scheme. Use of the Grell?CDevenyi and Bette?CMiller?CJanjic schemes helps suppress precipitation overprediction.     

1975—2016年秦巴山区极端气温事件的空间差异性分析

利用秦巴山区88个气象站1975—2016年的逐日气温数据,结合16个极端气温指数分析了秦巴山区极端气温阈值的空间分布及极端气温事件变化趋势的海拔依赖性。结果表明：极端气温阈值存在明显的空间分布差异,表现为极端低温阈值与极端高温阈值由西北向东南均有增温趋势;总体来看,极端气温暖事件（SU25、TR20、TX90P、TN90P、WSDI）增加幅度大于冷事件（FD0、ID0、TX10P、TN10P、CSDI）减少幅度,且变化趋势较冷事件更显著;全区霜冻日数、夏日日数、冷夜日数、暖昼日数及高温极值（TXx、TXn）变化均比较显著;区域作物生长期西部增长趋势较东部显著,多数站点变化幅度在3~6 d/10a之间;海拔越高发生极端低温事件的气温越低,极端低温阈值变化趋势为-0.36℃/100m;海拔越低发生极端高温事件的气温越高,极端高温变化趋势达0.5℃/100m,且均通过99%的信度检验;区域极端气温极值指数的变化趋势与海拔呈显著正相关,具有明显的海拔依赖性,表现为海拔越高,极值指数增加趋势越明显。     

2010-2019年浙江暖季短时强降水特征分析

利用2010-2019年浙江省暖季(5-9月)1426个国家站和区域站小时雨量数据和NCEP 1° X 1°逐日4次再分析资料,分析了浙江省暖季短时强降水、极端短时强降水时空分布特征及区域性短时强降水事件,结果表明:①近10年暖季短时强降水频次呈增多趋势,降水强度变化平稳;8月(上旬)降水频次最多,9月(中旬)强度最强...     

新旧气候态的差异及其对江西气候业务的影响

利用1961—2022年江西74个气象站平均气温、最高气温、最低气温、降水量、相对湿度、平均风速和日照时数资料,对比分析了1991—2020年和1981—2010年新、旧气候态下气象要素差异,探讨气候平均值改变对气候影响评价和预测业务的影响。结果表明：新气候态下,江西省三类气温的年和季节平均值均上升,年降水量总体增加将弱化气温偏高、降水偏多的变化特征。年和季节平均风速距平山区减小而平原地区增大;年日照时数距平总体增加。极端高温年份减少,极端低温年份增多,其中平均气温和最低气温的极端高（低）温年发生概率的降幅（增幅）比最高气温更大。极端强降水年发生概率在赣西北、赣中大部、赣南西北部等地区夏季减少,赣南中南部地区冬季增大。全省历年极端日高温、低温和强降水事件发生站次总体减少。新、旧气候态的更替会对气候业务产生影响,如冬季气温偏冷的年份增加,偏暖的年份减少,需对冷、暖冬事件进行重新评估,夏季降水增多的变化特征减弱,将导致夏季降水预测量级和趋势发生改变。     

Spatial patterns and temporal trends of daily precipitation indices in Iran

Spatial patterns of daily precipitation indices and their temporal trends over Iran are investigated using the APHRODITE gridded daily precipitation dataset for the period 1961–2004. The performance and limitations of the gridded dataset are checked against observations at ten rain-gauge stations that are representative of different climates in Iran. Results suggest that the spatial patterns of the indices reflect the role of orography and sea neighborhoods in differentiating central-southern arid and semi-arid regions from northern and western mountainous humid areas. It is also found that western Iran is impacted by the most extreme daily precipitation events occurring in the country, though the number of rainy days has its maximum in the Caspian Sea region. The time series of precipitation indices is checked for long-term trends using the least squares method and Mann-Kendall test. The maximum daily precipitation per year shows upward trends in most of Iran, though being statistically significant only in western regions. In the same regions, upward trends are also observed in the number of wet days and in the accumulated precipitation and intensity during wet days. Conversely, the contribution of precipitation events below the 75th percentile to the annual total precipitation is decreasing with time, suggesting that extreme events are responsible for the upward trend observed in the total annual precipitation and in the other indices. This tendency towards more severe/extreme precipitation events, if confirmed by other datasets and further analyses with longer records, would require the implementation of adequate water resources management plans in western Iran aimed at mitigating the increasing risk of intense precipitation and associated flash floods and soil erosion.     

概率调整法在气候模式模拟降水量订正中的应用

应用概率调整法订正区域气候模式系统PRECIS在SRES A1B情景下模拟的各季节全国日降水量。以第95百分位降水量为阈值,利用Γ分布分段拟合1962年12月—1972年11月的模拟值,构建传递函数,得到1991年12月—2001年11月的订正值。结果表明:全国平均日降水量空间分布的模拟改善明显,偏差百分率高于100%的格点比例从23.5%降低到1.0%;对各地区平均降水月循环的模拟结果改善,冷季降水较暖季更接近观测,提高拟合优度是改进订正方法的关键;多数地区连续干日数、连续5 d最大降水量及极端降水贡献率的空间强度、概率分布与空间相关性的订正效果显著。总体来说,该方法对模拟中国区域降水的平均态与极端降水均有明显改善,有助于气候评估工作的展开。     

呼和浩特近59年降水极端事件分析

利用呼和浩特气象站1951—2009年逐日降水量资料,以年序列的第90个百分位,建立了日降水量极端气候事件的阈值,检测了近59年来呼和浩特逐日降水量极端事件的出现频率,分析了极端事件阈值和日数及降水量的年际、年代际和季节变化,结果显示：①呼和浩特日降水极端事件的阈值小,为10.6mm;全年极端事件出现的频次11d。②降水极端事件主要出现在4-10月,且8月最多。③近59年来呼和浩特全年降水极端事件及其降水量没有显著的增减变化趋势,但而进入21世纪后,极端降水事件及其降水量的变率加大,降水强度明显减小。     

广东“18.8”季风槽极端降水事件对流尺度集合预报分析

受季风槽影响,2018年8月30—31日华南地区出现一次极端暴雨过程,单日站点累计降水量达1?056.7 mm,刷新了广东有历史纪录以来新的极值。对于此次极端降水事件,常用的业务模式包括欧洲中期天气预报中心全球模式（ECMWF）、日本气象厅谱模式（JMA）和中国气象局广东快速更新同化数值预报系统（CMA-GD）,都低估了降水强度。利用深圳市气象局业务对流尺度集合预报系统分析了此次特大暴雨过程,结果表明：对流尺度集合预报系统对本次特大暴雨过程具有比较好的预报能力,概率匹配平均最大雨量达348.7 mm·(24 h)-1,集合平均的强降水中心和观测基本一致,观测极值附近区域发生大暴雨（≥150 mm）概率最大值达到80%。选取了较“好”和较“差”集合成员预报进行对比分析,发现较“好”成员预报的强降水中心位置和观测基本一致,而较“差”成员预报的降水中心位置则偏向福建地区。较 “好”成员预报出莲花山南侧地面中尺度辐合线较长时间的维持和缓慢移动,导致强降水雨团在莲花山脉附近不断地触发和维持,同时地形的阻挡作用使得对流系统在地形附近区域持续维持,造成了罕见的特大暴雨;而较“差”成员辐合区位于莲花山以北,对流形成后向东、向北移动,最终导致强降水预报位置偏向福建地区。     

近46a重庆汛期极端降水量异常特征

利用重庆33站1961-2006年汛期(5-9月)逐日降水资料,定义了不同台站的极端降水阈值,统计出了不同台站近46a逐年汛期极端降水量,并进行时空分布特征分析。结果表明:重庆地区汛期极端降水量空间分布差异明显,一致性异常分布特征是最主要空间模态,空间分布可分为5个主要区域;各区代表站汛期极端降水量占总降水量的比重相当大;从长期变化趋势来看,整个重庆地区近46a来汛期极端降水变化趋势不显著;各区汛期极端降水主要存在着2~3a、5a左右的年际变化和11a左右的年代际振荡。     

湖南极端干旱气候时段人影作业潜力分析

利用湖南97个气象观测站逐日综合气象干旱指数、逐日降水量和湖南天气气候分区,研究湖南极端干旱特征和极端干旱时段内人工影响天气增雨潜力,结果表明:①湖南极端干旱期有相当的增雨潜力,各个分区的极端干旱频次和大气可降水量年代际变化除70年代外均呈现为北少南多的特点。②极端干旱时段内各分区年均可增雨日数主要表现为月际差异,可增雨日数主要集中在8—10月,各分区区域差异较小,各分区在伏旱期的可增雨日数大约占伏旱期的16%～20%。③湖南极端干旱按照出现的季节分类有11种,频次最高的是夏秋连旱,同时夏秋连旱的可增雨日数最多。     

Historic variation of warm-season rainfall,Southern Colorado Plateau,Southwestern U.S.A.

Rainfall during the warm season (June 15–October 15) is the most important of the year in terms of flood generation and erosion in rivers of the southern Colorado Plateau. Fluvial erosion of the plateau decreased substantially in the 1930s to early 1940s, although the cause of this change has not been linked to variation of warm-season rainfall. This study shows that a decrease of warmseason rainfall frequency was coincident with and probably caused the decreased erosion by reducing the probability of large floods. Warm-season rainfall results from isolated thunderstorms associated with the Southwestern monsoon and from dissipating tropical cyclones and (or) cutoff low-pressure systems that produce widespread, general rainfall. Warm-season rainfall is typically normal to above normal during warm El Niño-Southern Oscillation (ENSO) conditions. A network of 24 long-term precipitation gages was used to develop an index of standardized rainfall anomalies for the southern Colorado Plateau for the period 1900–85. The index shows that the occurrence of anomalously dry years increased and the occurrence of anomalously wet years decreased after the early 1930s, although 1939–41, 1972, and 1980–84 were anomalously wet. The decrease in warm-season rainfall after the early 1930s is related to a decrease in rainfall from dissipating tropical cyclones, shifts in the incidence of meridional circulation in the upper atmosphere, and variability of ENSO conditions.     

自组织映射神经网络(SOM)降尺度方法对江淮流域逐日降水量的模拟评估

利用1961~2002年ERA-40逐日再分析资料和江淮流域56个台站逐日观测降水量资料,引入基于自组织映射神经网络(Self-Organizing Maps,简称SOM)的统计降尺度方法,对江淮流域夏季(6~8月)逐日降水量进行统计建模与验证,以考察SOM对中国东部季风降水和极端降水的统计降尺度模拟能力。结果表明,SOM通过建立主要天气型与局地降水的条件转换关系,能够再现与观测一致的日降水量概率分布特征,所有台站基于概率分布函数的Brier评分(Brier Score)均近似为0,显著性评分(Significance Score)全部在0.8以上;模拟的多年平均降水日数、中雨日数、夏季总降水量、日降水强度、极端降水阈值和极端降水贡献率区域平均的偏差都低于11%;并且能够在一定程度上模拟出江淮流域夏季降水的时间变率。进一步将SOM降尺度模型应用到BCCCSM1.1(m)模式当前气候情景下,评估其对耦合模式模拟结果的改善能力。发现降尺度显著改善了模式对极端降水模拟偏弱的缺陷,对不同降水指数的模拟较BCC-CSM1.1(m)模式显著提高,降尺度后所有台站6个降水指数的相对误差百分率基本在20%以内,偏差比降尺度前减小了40%~60%;降尺度后6个降水指数气候场的空间相关系数提高到0.9,相对标准差均接近1.0,并且均方根误差在0.5以下。表明SOM降尺度方法显著提高日降水概率分布,特别是概率分布曲线尾部特征的模拟能力,极大改善了模式对极端降水场的模拟能力,为提高未来预估能力提供了基础。     

鄂西北夏季对流云降水微物理过程数值模拟

为了深入研究对流云降水微物理过程特征,为局地对流降水预报和人工增雨提供更多的参考依据,利用三维双参数对流云模式,使用常规单站探空资料,开展湖北两北部山地夏季对流降水实例的批量数值模拟,使用地面降水量和雷达回波资料检验模拟效果,统计分析降水微物理过程特征,归纳总结冰相粒子的形成、增长机制,以及液念水和冰相粒子的相互转化机制。结果表明：（1）对流云模式能够较好地模拟实际对流降水的一些宏观微观特征;（2）当地夏季主要是对流冷云降水,冰相过程是形成降雨的主要物理过程;（3）冰相过程巾过冷水、霰、冰晶之间的相互转化过程是主要的冷云降水形成机制。     

ECMWF极端天气指数在华东台风 降水预报中的应用和检验

选取2015—2018年影响华东地区的13个台风个例,分析降水极端天气指数EFI (Extreme Forecast Index)和SOT (Shift of Tails)与台风降水之间的统计关系。结果表明:EFI和SOT与降水气候百分位之间存在明显的正相关关系。EFI和SOT越大,强降水发生概率越高。随着预报时效的增加,EFI和SOT指数对暴雨和大暴雨的预报效果逐渐变差。对于短期(72 h以内的时效),EFI预报技巧优于SOT,而随着预报时效的延长,SOT的预报技巧逐渐接近并超过EFI。以TS评分最大为标准兼顾合理的预报偏差,得到两种极端天气指数不同预报时效、不同等级暴雨的预报阈值。总体而言,事件越极端,EFI和SOT的预报阈值越大,对于暴雨和大暴雨,EFI指数的预报阈值随着预报时效的延长有减小趋势,而SOT的预报阈值基本保持不变。在台风极端降水预报中,EFI和SOT可以作为EC定量降水预报的补充,有助于减少强降水的漏报,并提早发出预警信息。     

Changes in daily climate extremes in the arid area of northwestern China

There has been a paucity of information on trends in daily climate and climate extremes, especially for the arid region. We analyzed the changes in the indices of climate extremes, on the basis of daily maximum and minimum air temperature and precipitation at 59 meteorological stations in the arid region of northwest China over the period 1960–2003. Twelve indices of extreme temperature and six indices of extreme precipitation are examined. Temperature extremes show a warming trend with a large proportion of stations having statistically significant trends for all temperature indices. The regional occurrence of extreme cool days and nights has decreased by ?0.93 and ?2.36 days/decade, respectively. Over the same period, the occurrence of extreme warm days and nights has increased by 1.25 and 2.10 days/decade, respectively. The number of frost days and ice days shows a statistically significant decrease at the rate of ?3.24 and ?2.75 days/decade, respectively. The extreme temperature indices also show the increasing trend, with larger values for the index describing variations in the lowest minimum temperature. The trends of Min Tmin (Tmax) and Max Tmin (Tmax) are 0.85 (0.61) and 0.32 (0.17)?°C/decade. Most precipitation indices exhibit increasing trends across the region. On average, regional maximum 1-day precipitation, annual total wet-day precipitation, and number of heavy precipitation days and very wet days show insignificant increases. Insignificant decreasing trends are also found for consecutive dry days. The rank-sum statistic value of most temperature indices exhibits consistent or statistically significant trends across the region. The regional medians after 1986 of Min Tmin (Tmax), Max Tmin (Tmax), warm days (nights), and warm spell duration indicator show statistically more larger than medians before 1986, but the frost days, ice days, cool days (nights), and diurnal temperature range reversed. The medians of precipitation indices show insignificant change except for consecutive dry days before and after 1986.     

Does CMIP6 Inspire More Confidence in Simulating Climate Extremes over China?

Based on climate extreme indices calculated from a high-resolution daily observational dataset in China during1961–2005, the performance of 12 climate models from phase 6 of the Coupled Model Intercomparison Project(CMIP6),and 30 models from phase 5 of CMIP(CMIP5), are assessed in terms of spatial distribution and interannual variability. The CMIP6 multi-model ensemble mean(CMIP6-MME) can simulate well the spatial pattern of annual mean temperature,maximum daily maximum temperature, and minimum daily minimum temperature. However, CMIP6-MME has difficulties in reproducing cold nights and warm days, and has large cold biases over the Tibetan Plateau. Its performance in simulating extreme precipitation indices is generally lower than in simulating temperature indices. Compared to CMIP5, CMIP6 models show improvements in the simulation of climate indices over China. This is particularly true for precipitation indices for both the climatological pattern and the interannual variation, except for the consecutive dry days. The arealmean bias for total precipitation has been reduced from 127%(CMIP5-MME) to 79%(CMIP6-MME). The most striking feature is that the dry biases in southern China, very persistent and general in CMIP5-MME, are largely reduced in CMIP6-MME. Stronger ascent together with more abundant moisture can explain this reduction in dry biases. Wet biases for total precipitation, heavy precipitation, and precipitation intensity in the eastern Tibetan Plateau are still present in CMIP6-MME, but smaller, compared to CMIP5-MME.     

1955—2014年杭州极端气温和降水指数变化特征

根据杭州市1955—2014年降水量、气温逐日资料,采用国际通用的极端天气指数和线性倾向估计、M-K检验等方法,分析了杭州市近60 a极端气温和降水的变化特征。结果表明：1）杭州市近60 a的气温呈一致升高趋势,且变化显著,表现为极端高温阈值和极端低温阈值的升高及极端高温日数的增多;极端冷事件显著减少,暖事件显著增多。2）极端降水指数中只有强降水量的增加较明显,主要贡献为夏季和冬季强降水量的增强。3）冬季平均气温、极端低温阈值、霜冻日数等极端冷事件的突变发生于20世纪80年代初中期,夏季平均气温、极端高温阈值、高温日数等极端暖事件的突变发生于20世纪末21世纪初,与全国范围内的气候增暖进程基本一致。另外,降水强度、极端降水阈值等极端降水指数的突变时间在2008年左右,即2008年后气温升高和降水强度的增加突变期叠加,尤其在夏季和冬季表现更突出,可能诱发更多的异常天气。     

“黑格比”台风浙沪交界极端降水及物理量特征分析

利用全国综合气象信息共享平台(CIMISS)地面站点降水资料、欧洲中期天气预报中心逐小时再分析资料，分析 “黑格比”台风登陆后在浙江嘉兴、上海金山交界地区(简称“关注区”)产生的极端降水及相关物理量特征，结果表明：(1) 此次降水过程的小时雨强、日降水和过程降水均具有很强的极端性，部分测站达十年一遇甚至是百年一遇标准，杭州湾北岸强降水的极端性比南岸更显著；(2) 关注区对流层低层充足的水汽，以及高低层冷、暖平流的叠加，为极端降水发生发展提供了有利的水汽条件和不稳定条件；(3) 根据物理量的逐小时演变，呈现出低层辐散、高层辐合的环流增强，以及低层强烈的涡旋运动，关注区强降水也随之发生；(4) 此次极端暴雨过程850 hPa第二类热成风螺旋度极值和地面散度经极值排序后呈现较高的百分位置，在相似台风中均具有显著的极端性，对类似路径、小体积台风极端降水的发生具有较好的指示意义。     

Reconstructed Temperature And Precipitation On A Millennial Timescale From Tree-Rings In The Southern Colorado Plateau,U.S.A.

Two independent calibrated and verified climate reconstructions from ecologically contrasting tree-ring sites in the southern Colorado Plateau, U.S.A. reveal decadal-scale climatic trends during the past two millennia. Combining precisely dated annual mean-maximum temperature and October through July precipitation reconstructions yields an unparalleled record of climatic variability. The approach allows for the identification of thirty extreme wet periods and thirty-five extreme dry periods in the 1,425-year precipitation reconstruction and 30 extreme cool periods and 26 extreme warm periods in 2,262-year temperature reconstruction. In addition, the reconstructions were integrated to identify intervals when conditions were extreme in both climatic variables (cool/dry, cool/wet, warm/dry, warm/wet). Noteworthy in the reconstructions are the post-1976 warm/wet period, unprecedented in the 1,425-year record both in amplitude and duration, anomalous and prolonged late 20th century warmth, that while never exceeded, was nearly equaled in magnitude for brief intervals in the past, and substantial decadal-scale variability within the Medieval Warm Period and Little Ice Age intervals.     

Impacts of Urbanization on the Precipitation Characteristics in Guangdong Province,China

With the development of urbanization, whether precipitation characteristics in Guangdong Province, China, from 1981 to 2015 have changed are investigated using rain gauge data from 76 stations. These characteristics include annual precipitation, rainfall frequency, intense rainfall(defined as hourly precipitation ≥ 20 mm), light precipitation(defined as hourly precipitation ≤ 2.5 mm), and extreme rainfall(defined as hourly rainfall exceeding the 99.9 th percentile of the hourly rainfall distribution). During these 35 years, the annual precipitation shows an increasing trend in the urban areas.While rainfall frequency and light precipitation have a decreasing trend, intense rainfall frequency shows an increasing trend. The heavy and extreme rainfall frequency both exhibit an increasing trend in the Pearl River Delta region, where urbanization is the most significant. These trends in both the warm seasons(May-October) and during the pre-flood season(April-June) appear to be more significant. On the contrary, the annual precipitation amount in rural areas has a decreasing trend. Although the heavy and extreme precipitation also show an increasing trend, it is not as strong and significant as that in the urban areas. During periods in which a tropical cyclone makes landfall along the South China Coast, the rainfall in urban areas has been consistently more than that in surrounding areas. The precipitation in the urban areas and to their west is higher after 1995, when the urbanization accelerated. These results suggest that urbanization has a significant impact on the precipitation characteristics of Guangdong Province.