Simulations of precipitation using NRCM and comparisons with satellite observations and CAM: annual cycle

The accurate representation of rainfall in models of global climate has been a challenging task for climate modelers owing to its small space and time scales. Quantifying this variability is important for comparing simulations of atmospheric behavior with real time observations. In this regard, this paper compares both the statistical and dynamically forced aspects of precipitation variability simulated by the high-resolution (36?km) Nested Regional Climate Model (NRCM), with satellite observations from the Tropical Rainfall Measuring Mission (TRMM) 3B42 dataset and simulations from the Community Atmosphere Model (CAM) at T85 spatial resolution. Six years of rainfall rate data (2000?C2005) from within the Tropics (30°S?C30°N) have been used in the analysis and results are presented in terms of long-term mean rain rates, amplitude and phase of the annual cycle and seasonal mean maps of precipitation. Our primary focus is on characterizing the annual cycle of rainfall over four land regions of the Tropics namely, the Indian Monsoon, the Amazon, Tropical Africa and the North American monsoon. The lower tropospheric circulation patterns are analyzed in both the observations and the models to identify possible causes for biases in the simulated precipitation. The 6-year mean precipitation simulated by both models show substantial biases throughout the global Tropics with NRCM/CAM systematically underestimating/overestimating rainfall almost everywhere. The seasonal march of rainfall across the equator, following the motion of the sun, is clearly seen in the harmonic vector maps. The timing of peak rainfall (phase) produced by NRCM is in closer agreement with the observations compared to CAM. However like the long-time mean, the magnitude of seasonal mean rainfall is greatly underestimated by NRCM throughout the Tropical land mass. Some of these regional biases can be attributed to erroneous circulation and moisture surpluses/deficits in the lower troposphere in both models. Overall, the results seem to indicate that employing a higher spatial resolution (36?km) does not significantly improve simulation of precipitation. We speculate that a combination of several physics parameterizations and lack of model tuning gives rise to the observed differences between NRCM and the observations.     

短时强降水临近预报的思路与方法

利用高密度地面自动站逐小时降水观测资料,分析了河南省2010-2015年雨季（5-9月）短时强降水（flash heavyrain,FHR）的时空分布特征。主要结果如下：河南省FHR集中发生在7、8月,其中7月最多,8月次之;河南雨季FHR量、降水贡献和发生频率的局地差异明显,主要存在4个大值区,即豫北黄河以北地区、豫东商丘地区、豫西南伏牛山以南以东地区、豫南沿淮及其以南地区;地形对降水的增幅作用显著,且主要是通过增加FHR发生频次实现的;FHR频次日变化呈明显的双峰结构,傍晚至凌晨的前半夜为FHR频发时段;4个大值区内FHR频次日变化差异明显,如黄河以北地区其日变化幅度较大、呈单峰型,而沿淮及其以南地区其日变化幅度较小、呈持续活跃型;大部分FHR前后都伴随着连续降水,降水过程的持续时间主要在1~8 h之间,持续时间大于等于3 h的过程主要位于两个与地形密切相关的高频集中区,即伏牛山以东支脉的喇叭口地形区和沿淮及其以南地区。

     

Decadal long convection-permitting regional climate simulations over eastern China: evaluation of diurnal cycle of precipitation

With a decadal long period (1998–2010) climate simulation using the Weather Research and Forecasting model at convection-permitting resolution (4 km) (WRF_CPM), the diurnal cycles of precipitation amount (PA), frequency (PF) and intensity (PI) and their related large-scale atmospheric circulations over eastern China are analyzed. The simulations are further compared against the CN05.1, CMORPH v1.0 and the ECMWF Re-Analysis Interim (ERAIN). Results show that WRF_CPM can reasonably represent the observed seasonal rainfall and the atmospheric circulations. As for the features at a sub-daily scale, WRF_CPM is superior at reproducing the diurnal amplitude of PF that is similar to PA in terms of the spatial distribution. Moreover, the diurnal peak timing of summer PF and PA over the three sub-regions, i.e., North China (NC), Yangtze-Huaihe River basin (YHR) and South China (SC), can be properly reproduced by WRF_CPM. The observed precipitation systems exhibit obvious eastward propagation from the Plateau to its downstream, which may be due to the solenoid circulations associated with the low-level anomalous wind and moisture convergence. However, they are almost overestimated by WRF_CPM and in turn causing overestimated precipitation along YHR. The early morning precipitation in WRF_CPM has a larger fraction than CMORPH, which is related to the overestimated nocturnal low-level jet. Whereas, due to the solar heating and the land-sea breezes, the late-afternoon precipitation peak is mainly located along the coasts of eastern China, which matches well with the vertical motion in WRF_CPM.     

中国大陆降水日变化研究进展

文章概述了中国大陆降水日变化的最新研究成果,给出了中国大陆降水日变化的整体图像,指出目前数值模式模拟降水日变化的局限性,为及时了解和掌握降水日变化研究进展、开展相关科学研究和进行降水预报服务提供了有价值的科学依据和参考。现有研究表明：（1）中国大陆夏季降水日变化的区域特征明显。在夏季,东南和东北地区的降水日峰值主要集中在下午;西南地区多在午夜达到降水峰值;长江中上游地区的降水多出现在清晨;中东部地区清晨、午后双峰并存;青藏高原大部分地区是下午和午夜峰值并存。（2）降水日变化存在季节差异和季节内演变。冷季降水日峰值时刻的区域差异较暖季明显减小,在冷季南方大部分地区都表现为清晨峰值;中东部地区暖季降水日变化随季风雨带的南北进退表现出清晰的季节内演变,季风活跃（间断）期的日降水峰值多发生在清晨（下午）。（3）持续性降水和局地短时降水的云结构特性以及降水日峰值出现时间存在显著差异。持续性降水以层状云特性为主,地表降水和降水廓线的峰值大多位于午夜后至清晨;短时降水以对流降水为主,峰值时间则多出现在下午至午夜前。（4）降水日变化涉及不同尺度的山-谷风、海-陆风和大气环流的综合影响,涉及复杂的云雨形成和演变过程,对流层低层环流日变化对降水日变化的区域差异亦有重要影响。（5）目前数值模式对中国降水日变化的模拟能力有限,且模拟结果具有很强的模式依赖性,仅仅提高模式水平分辨率并不能总是达到改善模拟结果的目的,关键是要减少存在于降水相关的物理过程参数化方案中的不确定性问题。     

近20年中国气象灾害损失的初步分析

采用全国气象部门收集的县（区）域行政单元灾情普查资料,结合全国气象站点降水观测资料,分析了1984—2008年中国暴雨及其引发的洪涝灾害的时空演变特点及灾害损失情况,揭示了气候变化及人类活动双重作用下中国暴雨洪涝灾害变化趋势和演变特点,以及暴雨洪涝灾害影响的时空差异性。结果表明：近25 a来中国暴雨日数总体上稍有增加,暴雨强度和暴雨天数的空间分布均表现为南方高于北方,东部高于西部的特点,20世纪90年代中后期为中国暴雨高发期。研究时段内,中国暴雨洪涝灾害造成的直接经济损失呈增加趋势,但直接经济损失占当年GDP的比例则呈下降趋势,平均每年经济损失约为573亿元人民币,损失较高的地区主要集中在中国南方地区,县域年平均损失超过2 000万元的县约占15%,其中有34个县超过亿元。受灾人口呈增加趋势,但因灾死亡人口呈下降趋势;暴雨洪涝灾害对农作物受灾面积和绝收面积的影响均呈微弱上升趋势,年平均作物受灾面积近9.00×10⁶ hm²,作物绝收面积为1.27×10⁶ hm²。

     

北京地区夏季极端降水变化特征及城市化影响

利用1981-2016年京津冀地区174个国家站逐日降水资料,采用百分位方法和线性倾向估计方法对京津冀地区极端降水的时空分布特征及演变趋势进行了分析。结果表明：（1）对于京津冀地区极端降水空间分布,不同百分位降水阈值表现为一致的分布特征,年平均极端降水量、平均极端降水强度与百分位极端降水阈值分布大体一致,而年平均极端降水日数的分布则与其相反。（2）年平均极端降水量在103.6~259.1 mm之间,年平均极端降水日数在3.0~4.0 d之间,平均极端降水强度在大雨到暴雨之间,极端降水量对总降水量贡献达28%以上。（3）极端降水总站次和极端降水日数年变化趋势一致,7月、8月和10月是极端降水较活跃月份。（4）在36 a期间,年平均极端降水量、年平均极端降水日数、平均极端降水强度以及极端降水量对总降水量贡献的变化趋势分布情况基本一致,呈减少趋势的站点均相对较多,年平均极端降水量增减幅度较大,年平均极端降水日数变化在1 d·（10 a）^-1以内,平均极端降水强度和极端降水量对总降水量贡献减少趋势相对明显。

     

Evaluation of precipitation trends from high-resolution satellite precipitation products over Mainland China

Climate Dynamics - Many studies have reported the excellent ability of high-resolution satellite precipitation products (0.25° or finer) to capture the spatial distribution of precipitation....     

Characteristics of diurnal variations of warm-season precipitation over Xinjiang Province in China

降水日变化受大气热力,动力过程以及复杂地形影响,演变特征复杂且区域差异显著.本文采用中国气象局发布的中国地面与CMORPH融合逐小时降水产品(2008-2019年),分析了新疆省暖季降水日变化特征.研究结果表明:(1)新疆大部分地区降水主峰值发生在清晨;(2)持续时间超过三小时的降水事件是新疆地区主要降水事件,贡献了南...     

中国大陆日降水峰值时间位相的区域特征分析

利用高密度的中国国家级地面气象站逐时降水数据,系统分析和比较了中国大陆地区暖季降水量、降水频次和降水强度的日变化峰值位相的整体特征、空间分布差异及典型区域平均的日变化演变特征。研究指出,中国大陆暖季降水日变化峰值时间主要表现为下午、清晨、夜间3类典型位相,且整体而言降水频次的清晨峰值更凸出,降水强度以下午峰值为主。综合考虑降水量和降水频次的日变化峰值位相,发现中国大陆地区降水日变化峰值位相在空间分布上存在7个典型区域:下午峰值区(东北至华北山区、东南内陆地区)、夜间峰值区(四川盆地西部至云贵高原东部、华北平原西部贴近山地的区域)和清晨峰值区(华北平原东部、秦巴山区至华中西南部)各两个,以及傍晚至夜间峰值位相的青藏高原区。各典型区域内部具有较一致的降水量和频次的日峰值时间位相,而区域边缘或交界处降水量和频次的峰值位相则相反,主要是降水量的下午主峰值时段与降水频次的清晨主峰值时段的错位。从降水量、降水频次和降水强度的日变化的演变特征来看,午后峰值区、夜间峰值区和青藏高原的傍晚至夜间峰值区的多数台站,都存在降水量位相滞后于降水强度而超前于降水频次的特征,这应是降水演变过程中时间演变不对称性和对流云系发展演变的具体表现。     

Areal differences in diurnal variations in summer precipitation over Beijing metropolitan region

Using hourly rain-gauge measurements for the period 2004?C2007, differences in diurnal variation in summer (June?CAugust) precipitation are investigated in four distinct areas of Beijing: the urban area (UA), suburban area (SA), north mountainous area (NMA), and south mountainous area (SMA), which are distinguished empirically based on underlying surface conditions and verified with a statistical rotated empirical orthogonal function. The diurnal cycles and spatial patterns in seasonal mean precipitation amount, intensity, and frequency in the four areas are compared. Results show that the four areas have distinct diurnal variation patterns in precipitation amounts, with a single peak observed in UA and NMA in the late afternoon, which are 80?% and 121?% higher than their daily average, respectively, and two peaks in SA during the late afternoon and early morning with magnitudes exceeding the daily mean by 76?% and 29?%, respectively. There are also two peaks in SMA: a weaker nocturnal diurnal peak and an afternoon peak. The minimum amounts of rainfall observed in the forenoon in UA, SA, and SMA are 53?%, 47?%, and 57?% lower than the daily mean in each area, respectively, and that observed in the early morning in NMA is 50?% lower than the daily mean. The diurnal variations in precipitation intensities resemble those for precipitation amount in all four areas, but more intense precipitation is observed in SA (2.4?mm/h) than in UA (2.2?mm/h). The lowest frequency for the whole day is observed in UA, whereas the highest frequency occurs in the mountainous areas in the daytime, especially in the late afternoon in SMA. Diurnal variations in surface air temperature and divergence fields in the four areas are further investigated to interpret the physical mechanisms that underlie the spatial and temporal differences in summer diurnal precipitation, and the results indicate the possible dominance of the local circulation arising from mountain?Cvalley wind and the differences in underlying surface heating between the urban, suburban, and mountainous areas of Beijing.     

The diurnal cycle of surface air temperature in simulated present and doubled CO2 climates

 The diurnal range of surface air temperature (rT _a ) simulated for present and doubled CO₂ climates by the CSIRO9 GCM is analysed. Based on mean diurnal cycles of temperature and surface heat fluxes, a theory for understanding the results is developed. The cycles are described as the response to a diurnal forcing which is represented well by the diurnal mean flux of net shortwave radiation at the surface (SW) minus the evaporative (E) and sensible (H) fluxes. The response is modified by heat absorbed by the ground, and by the cycle in downward longwave (LW) radiation, but these effects are nearly proportional to the range in surface temperature. Thus in seasonal means, rT _a is approximately given by SW–E–H divided by 6 W m^-2/^°C. A multiple regression model for (rT _a ) is developed, based on quantities known to influence SW, E and H, and applied to both spatial variation in seasonal means, and day-to-day variation at a range of locations. In both cases, rT _a is shown to be influenced by cloud cover, snow extent and wind speed. It is influenced by soil moisture, although this effect is closely tied to that of cloud. In seasonal means rT _a is also well correlated with precipitable water, apparently because of the latter’s influence on E+H. The regression model describes well the spatial variation in the doubled CO₂ change in rT _a . The annual mean change in rT _a over land on doubling CO₂ was −0.36 ^°C, partly because of a decrease in the mean diurnal forcing (as defined in the theory), but also apparently because of the effect of nonlinearity in T _s of the upward longwave emission. A diagnostic radiation calculation indicates that the CO₂ and water vapour provide a small increase in rT _a through the downward LW response, which partially counters a decrease due to a reduction of SW by the gases. Received: 8 November 1995 / Accepted: 3 January 1997     

青藏高原那曲地区夏季对流云结构及雨滴谱分布日变化特征

利用青藏高原东侧甘孜站Ka波段云雷达2019年6—8月观测资料,对该地区非降水云垂直结构特征进行了分析。结果表明：（1）甘孜非降水云中单层云的出现率为78.3%,高于两层云的出现率18.3%和多层云的出现率3.4%。分不同高度云来看,低云的出现率为46%,中云和高云各占27%,当云层数增加时,中云和高云的出现率增加。（2）云的出现率具有白天小、夜间大的日变化特征,云层数增多后,上层云出现率的日变化特征减弱;地形对云出现率的日变化有一定影响。（3）云底高和云顶高的垂直分布结构多为双峰形态,当出现三层云时,下层云的垂直结构为单峰形态。（4）甘孜云厚呈现出云压缩现象：单层云的平均云厚约为3.8 km;两层云的下层云平均云厚约为2.5 km,上层云平均云厚约为1.5 km;三层云的下层云平均云厚减小至约1.8 km,上层云平均云厚减小至约1.2 km,中层云平均云厚最小,约为1 km;云压缩现象随云层数增加而愈发明显。地基云雷达展示了局地云探测的优势,有益于高原云探测和研究。

     

Spatiotemporal variability of methane over the Amazon from satellite observations

The spatiotemporal variability of the greenhouse gas methane(CH_4) in the atmosphere over the Amazon is studied using data from the space-borne measurements of the Atmospheric Infrared Sounder on board NASA's AQUA satellite for the period 2003–12. The results show a pronounced variability of this gas over the Amazon Basin lowlands region, where wetland areas occur. CH_4 has a well-defined seasonal behavior, with a progressive increase of its concentration during the dry season, followed by a decrease during the wet season. Concerning this variability, the present study indicates the important role of ENSO in modulating the variability of CH_4 emissions over the northern Amazon, where this association seems to be mostly linked to changes in flooded areas in response to ENSO-related precipitation changes. In this region, a CH_4 decrease(increase) is due to the El Nino-related(La Ni ?na-related) dryness(wetness). On the other hand, an increase(decrease) in the biomass burning over the southeastern Amazon during very dry(wet) years explains the increase(decrease) in CH_4 emissions in this region. The present analysis identifies the two main areas of the Amazon, its northern and southeastern sectors, with remarkable interannual variations of CH_4. This result might be useful for future monitoring of the variations in the concentration of CH_4, the second-most important greenhouse gas, in this area.     

中国地区不同强度降水的变化趋势

利用2009—2013年天津地区205个自动气象站的逐时降水资料, 分析了天津地区降水的基本空间分布和日变化特征。结果表明: (1)天津地区降水小时数及小时平均降水强度空间差异明显, 高值区分别位于蓟县北部山区、市区西北侧、滨海新区中南部; (2)天津中北部地区累积降水量峰值主要出现在23—03时, 南部地区则出现在17—19时和04—08时, 降水频次峰值基本都出现在00—09时, 降水强度峰值与累积降水量峰值出现时间类似, 11时为降水强度低谷出现时间; (3)全市傍晚至午夜的降水频次明显较凌晨偏少, 长持续时间(10 h以上)的最大降水易出现在凌晨至清晨, 短时降水(1~4 h)的最大降水易出现在傍晚至午夜; 13—24时多数时次, 无论降水量、频次还是降水强度市区均较其周边地区和沿海地区偏多偏强, 而凌晨多数时次, 市区则以偏少偏弱为主; (4)始于下午至傍晚的降水多为短时降水, 而始于傍晚至凌晨的降水持续时间普遍较长。

     

Recent changes in Phoenix,Arizona summertime diurnal precipitation patterns

Summary Summertime diurnal precipitation patterns for Phoenix, Arizona are analyzed for the period 1954 through 1985. Although the mean precipitation amounts and frequencies for the entire summer monsoon season have not shown any significant effects from the rapidly developing urban heat island, diurnal patterns have displayed substantial changes in the recent period of explosive population growth. During the most recent 16 years, late afternoon and evening storms have become more frequent and produce greater rainfall totals. Sharp declines are noted in the frequency of rain events between midnight and noon; especially large drops occur in the rainfall amounts between 9.00 and 12.00 MST. These findings appear to be consistent with several mechanisms proposed to explain the unusual diurnal character of the summertime rainfall in the Phoenix, Arizona area.

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Zusammenfassung In der vorliegenden Arbeit wird der sommerliche Tagesgang des Niederschlags für Phönix, Arizona, analysiert.Obwohl keine signifikante Beeinflussung der durchschnittlichen Niederschlagsmengen und -häufigkeiten über die gesamte Sommermonsunzeit durch die rasch anwachsende städtische Wärmeinsel zu verzeichnen ist, weisen die Tagesgänge in der jüngsten Zeit explosiven Bevölkerungswachstums substantielle Veränderungen auf. In den vergangenen 16 Jahren sind Unwetter spätnachmittags und abends häufiger geworden und führten zu einer größeren Niederschlagssumme. Eine starke Abnahme der Regenfälle zwischen Mitternacht und Mittag ist zu verzeichnen; bei Regenfällen zwischen 9.00 und 12.00 MST ist der Rückgang besonders deutlich.Wie sich zeigt, stehen diese Beobachtungen im Einklang mit einigen Mechanismen, die zur Erklärung der ungewöhnlichen Tagesverteilung der sommerlichen Regenfälle über Phönix, Arizona, angeführt werden.

     

Analysis of changes in the magnitude,frequency, and seasonality of heavy precipitation over the contiguous USA

Theoretical and Applied Climatology - Gridded daily precipitation observations over the contiguous USA are used to investigate the past observed changes in the frequency and magnitude of heavy...     

A strategy for merging objective estimates of global daily precipitation from gauge observations,satellite estimates,and numerical predictions

This paper describes a strategy for merging daily precipitation information from gauge observations, satellite estimates(SEs), and numerical predictions at the global scale. The strategy is designed to remove systemic bias and random error from each individual daily precipitation source to produce a better gridded global daily precipitation product through three steps.First, a cumulative distribution function matching procedure is performed to remove systemic bias over gauge-located land areas. Then, the overall biases in SEs and model predictions(MPs) over ocean areas are corrected using a rescaled strategy based on monthly precipitation. Third, an optimal interpolation(OI)–based merging scheme(referred as the HL-OI scheme)is used to combine unbiased gauge observations, SEs, and MPs to reduce random error from each source and to produce a gauge—satellite–model merged daily precipitation analysis, called BMEP-d(Beijing Climate Center Merged Estimation of Precipitation with daily resolution), with complete global coverage. The BMEP-d data from a four-year period(2011–14) demonstrate the ability of the merging strategy to provide global daily precipitation of substantially improved quality.Benefiting from the advantages of the HL-OI scheme for quantitative error estimates, the better source data can obtain more weights during the merging processes. The BMEP-d data exhibit higher consistency with satellite and gauge source data at middle and low latitudes, and with model source data at high latitudes. Overall, independent validations against GPCP-1DD(GPCP one-degree daily) show that the consistencies between BMEP-d and GPCP-1DD are higher than those of each source dataset in terms of spatial pattern, temporal variability, probability distribution, and statistical precipitation events.     

基于多套卫星资料的ERA5全球小时降水频率评估

最近发布的新一代全球再分析资料集ERA5,提供了全球小时降水再分析值,为全球小时降水研究提供又一个数据参考。然而,目前针对ERA5小时降水频率的评估工作还较为有限。本研究采用多套全球卫星观测小时降水对ERA5小时降水的频率进行了评估。对比分析发现:尽管ERA5总降水量与卫星资料出现较好的一致性,但ERA5的小时降水频率约为卫星资料的2～3倍,呈现系统性偏高。进一步分析表明,这主要是由于ERA5大大高估了中、低强度降水事件的数量。其中,ERA5对弱降水频率的高估尤为明显,平均可达卫星降水频率的6倍;此外,ERA5对海洋降水频率的高估程度也大于陆地。ERA5小时降水频率的系统性高估问题对相关研究的潜在影响,尚在进一步评估中。     

双低空急流影响下华南初夏降水日变化的时空分布特征

利用2010—2016年5—6月ERA5逐小时再分析数据集和国家气象信息中心逐小时降水量融合产品,对影响华南地区的低空急流事件进行筛选和分类,并分析天气系统相关的低空急流(Synoptic-system-related Low-Level Jet, SLLJ)和边界层急流(Boundary Layer Jet, BLJ)的日变化及其影响下的华南降水日变化的时空分布特征。结果表明,BLJ和SLLJ在白天减弱、夜间增强,并在凌晨达到峰值,其日变化主要与边界层惯性振荡引起的非地转风的顺时针旋转有关。双急流日华南地区降水量显著增加,且降水日变化有明显的区域差异,这与双急流的演变和配置密切相关。广西中北部主要为SLLJ左前方发生的夜间山区降水,且降水量仅有凌晨的单峰。广西沿海和广东地区存在早晨和午后两个峰值,BLJ出口区辐合和SLLJ入口区辐散的维持有利于降水频率的增大,从而导致午后峰值的出现,而早晨的峰值除了受双急流有利配置的影响外,主要归因于早晨降水强度的增加。