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Impact of the combined assimilation of GPM/IMGER precipitation and Himawari-8/AHI water vapor radiance on snowfall forecasts using WRF model and 4Dvar system 利用 WRF 模式和 4Dvar 系统合并同化 GPM/IMGER 降水和 Himawari-8/AHI 水汽辐射对降雪预报的影响
IF 4.5 2区 地球科学 Q1 METEOROLOGY & ATMOSPHERIC SCIENCES Pub Date : 2024-10-13 DOI: 10.1016/j.atmosres.2024.107726
In this study, the investigation is made to reveal the impact of multi-strategically assimilating Global Precipitation Measurement (GPM) precipitation and Himawari-8/Advanced Himawari Imager (AHI) water vapor radiances (WVR) on forecasting a heavy snowfall event in the Eastern Qinghai-Tibet Plateau (EQTP) employing the Weather Research and Forecast model (WRF) and the Four-Dimensional Variational (4DVar) assimilation system (WRF-4DVar). The multiple data assimilation (DA) strategies include control tests (CON), the individual assimilation of AHI and GPM tests (DA_AHI and DA_GPM) and the joint assimilation of GPM and AHI (DA_G&A), with different initial times. The results indicate that GPM precipitation effectively captures mesoscale atmospheric details, but its scope is confined to a limited area. AHI WVR is sensitive to upper-middle atmospheric humidity and furnishes extensive-scale environmental parameters such as water vapor transport characteristics. The joint assimilation of the two not only yields multi-dimensional atmospheric insights but also addresses the limitations of individual assimilation. Assimilation GPM and AHI are respective sensitivity to the lower layers (about 800hpa) and upper layers (about 400hpa) of model. The individual assimilation GPM has the greatest effect on near-surface humidity field, and AHI plays a dominant role in the joint assimilation. By assimilating different remote sensing products at different initial times of NWPs, the thermodynamic and dynamic structures are variously reconstructed, leading to the different snowfall scenes. In addition, we further compare the 12-hourly cumulative snowfall with in-situ meteorological station observations. The predictions of snowfall from DA_G&A perform much better with the correlation coefficient (CC) and root-mean-square error (RMSE) 0.36 and 3.14 mm, respectively. As for different initial times of NWPs, the best snowfall forecast is 0600 UTC on October 28, 2022, and the CC is 0.4. Nevertheless, accurately predicting precipitation areas, intensity, and temporal variations remains challenging, particularly for solid precipitation like snowfall. Thus, meticulous consideration of weather process characteristics, observation attributes, and relevant parameter configurations during DA are imperative to enhance the efficiency of observation data utilization.
本研究利用天气研究与预报模式(WRF)和四维变分同化系统(WRF-4DVar),多策略同化全球降水测量(GPM)降水量和向日葵8号/高级向日葵成像仪(AHI)水汽辐射量(WVR)对青藏高原东部强降雪事件预报的影响。多种数据同化(DA)策略包括控制测试(CON)、AHI 和 GPM 的单独同化测试(DA_AHI 和 DA_GPM)以及 GPM 和 AHI 的联合同化(DA_G&A),初始时间各不相同。结果表明,GPM 降水能有效捕捉中尺度大气细节,但其范围仅限于有限区域。AHI WVR 对中高层大气湿度敏感,并能提供大尺度环境参数,如水汽输送特征。二者的联合同化不仅能产生多维大气洞察力,还能解决单独同化的局限性。同化 GPM 和 AHI 分别对模式的下层(约 800hpa )和上层(约 400hpa )具有敏感性。单个同化 GPM 对近地面湿度场的影响最大,而 AHI 在联合同化中起主导作用。通过在 NWPs 的不同初始时间同化不同的遥感产品,重建了不同的热力学和动力学结构,从而形成了不同的降雪场景。此外,我们还进一步将 12 小时累积降雪量与现场气象站观测数据进行了比较。结果表明,DA_G&A 对降雪量的预测效果更好,相关系数(CC)和均方根误差(RMSE)分别为 0.36 和 3.14 毫米。至于不同初始时间的 NWPs,2022 年 10 月 28 日 0600 UTC 的降雪预报最佳,CC 为 0.4。尽管如此,准确预测降水区域、强度和时间变化仍具有挑战性,尤其是降雪等固体降水。因此,要提高观测数据的利用效率,就必须在数据分析过程中对天气过程特征、观测属性和相关参数配置进行细致的考虑。
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引用次数: 0
Quantitative analysis of the contribution of moisture recycling to precipitation in the cold region 水汽循环对寒冷地区降水贡献的定量分析
IF 4.5 2区 地球科学 Q1 METEOROLOGY & ATMOSPHERIC SCIENCES Pub Date : 2024-10-13 DOI: 10.1016/j.atmosres.2024.107729
This study quantitatively analyzed the contribution rate of recycled moisture to precipitation in the basin based on the Craig-Gordon model and the three-end-member mixing model through selecting 456 precipitation sample data collected from six sampling points in the source region of the Yellow River from September 2019 to August 2021. The results showed that: the contribution rate of moisture recycling to precipitation during the growing season is 40 %, and the total contribution to local moisture recycling is equivalent to 41 mm of precipitation. The contribution rate of evaporation and transpiration has obvious seasonal variation characteristics, showing a trend of decreasing first and then increasing in the source region of the Yellow River. Spatially, the contribution rate of evaporation and transpiration showed an increasing trend from south to north. It is assumed that all the precipitation generated by moisture recycling produces runoff, and the water yield is about 51 × 108 m3, which is 25 % of the total annual average runoff. In addition, the proportion of local moisture recirculation is mainly related to altitude, topography, vegetation coverage, and meteorological factors. Moisture recirculation is one of the important sources of precipitation in the source region of the Yellow River.
本研究通过选取2019年9月至2021年8月黄河源区6个采样点采集的456个降水样资料,基于Craig-Gordon模型和三端成员混合模型,定量分析了流域内循环水汽对降水的贡献率。结果表明:生长季水汽循环对降水的贡献率为 40%,对当地水汽循环的总贡献相当于 41 mm 降水量。蒸发蒸腾贡献率具有明显的季节变化特征,在黄河源区呈先减后增的趋势。从空间上看,蒸发蒸腾贡献率由南向北呈上升趋势。假设墒情循环产生的降水全部产生径流,产水量约为 51 × 108 m3,占年均径流总量的 25%。此外,当地水汽再循环的比例主要与海拔、地形、植被覆盖率和气象因素有关。水汽再循环是黄河源区降水的重要来源之一。
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引用次数: 0
Comparison of 2-m surface temperature data between reanalysis and observations over the Arabian Peninsula 阿拉伯半岛上空再分析与观测数据之间的 2 米地表温度数据比较
IF 4.5 2区 地球科学 Q1 METEOROLOGY & ATMOSPHERIC SCIENCES Pub Date : 2024-10-11 DOI: 10.1016/j.atmosres.2024.107725
The 2-m temperature data is a significant indicator for studying the weather extremes and the exchange of water and energy fluxes between the surface and atmosphere. This study compared three reanalysis datasets, i.e., ERA5, ERA5-Land, and MERRA-2, with observations from in-situ sources from 1990 to 2022 using various statistical error metrics and extreme temperature indices over the Arabian Peninsula (AP) region. We selected these reanalysis datasets due to the continuous improvements and higher spatiotemporal output better capturing the temperature variability. The spatiotemporal climatology shows lower temperatures in winter (<15 °C) and maximum in summer (>35 °C); however, the reanalysis data show more deviations in temperature during the cold season than in the warm season. The reanalysis data underestimated the frequency of the cold (<10 °C) and hot (>30 °C) days across the four regions, except ERA5-Land, which closely followed observed data. The strength of the correlation shows better performance (>0.90) in the cold extremes (cold nights and cold days) frequency than the hot extremes. On an interannual scale, reanalysis products exhibit strong correlations (>0.90) with in-situ data across most regions, particularly in winter and autumn, moderate in spring, and weaker in summer. The reanalysis data shows negative biases in the inland regions and positive biases in the coastal areas with consistent root mean square differences (RMSD) spatiotemporally. The differences in performance are due to the topography and poor representation of the energy fluxes, especially in MERRA-2 as well as missing data in observations. This study recommends ERA5-Land as the first choice for extreme weather simulations in the region, followed by MERRA-2 and ERA5 on the same scale, but proper attention is needed when using reanalysis data for cold and hot extremes.
2 米气温数据是研究极端天气以及地表与大气之间水和能量通量交换的重要指标。本研究利用各种统计误差指标和阿拉伯半岛(AP)地区的极端温度指数,比较了三个再分析数据集(即ERA5、ERA5-Land 和 MERRA-2)与 1990 年至 2022 年的原地观测数据。我们之所以选择这些再分析数据集,是因为这些数据集不断改进,时空输出更高,能更好地捕捉温度变化。时空气候学显示冬季气温较低(15 °C),夏季气温最高(35 °C);然而,再分析数据显示冷季气温偏差大于暖季。再分析数据低估了四个地区的低温日(10 °C)和高温日(30 °C)的频率,只有ERA5-陆地数据与观测数据密切相关。从相关性的强度来看,极端寒冷天气(寒冷夜晚和寒冷白天)频率的相关性(>0.90)优于极端炎热天气。在年际尺度上,再分析产品与大部分地区的实地数据表现出很强的相关性(0.90),尤其是在冬季和秋季,春季的相关性一般,夏季的相关性较弱。再分析数据在内陆地区呈现负偏差,在沿海地区呈现正偏差,时空均方根差(RMSD)一致。性能差异是由于地形和能量通量表示不佳造成的,特别是在 MERRA-2 中,以及观测数据的缺失。本研究建议将ERA5-Land作为该地区极端天气模拟的首选,其次是相同尺度的MERRA-2和ERA5,但在使用再分析数据进行冷热极端天气模拟时需要适当注意。
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引用次数: 0
Response of urban heat island effects within the planetary boundary layer to heat waves and impact of horizontal advection over Shanghai 行星边界层内的城市热岛效应对热浪的响应以及上海上空水平对流的影响
IF 4.5 2区 地球科学 Q1 METEOROLOGY & ATMOSPHERIC SCIENCES Pub Date : 2024-10-10 DOI: 10.1016/j.atmosres.2024.107721
This study characterizes the variation of the urban heat island (UHI) within the planetary boundary layer (PBL) and investigates the horizontal advection effects on the UHI variation throughout a heat wave (HW) event over Shanghai municipality in August 2019 based on numerical model simulations. It is found that the UHI intensifies under HW conditions with the UHI intensity gradually weakening from the surface upwards. The daytime UHIs during the HW are 3.68 K (29.27 %), 1.41 K (33.52 %) and 1.04 K (36.97 %) higher than those during the pre-HW at the surface, near-surface and in the PBL, respectively, while the nighttime UHIs have no significant response to the HW at least for this case. The mean UHIs during the HW period at the surface, near-surface (2 m) and in the PBL are 6.83 K (2.68 K), 2.45 K (1.34 K), and 1.73 K (0.04 K) in the daytime (nighttime), respectively. The PBL UHI generally exists only in the daytime potentially caused by the thermal convective diffusion. The near-surface and PBL UHIs are significantly affected by the horizontal advection, resulting in different UHI intensities and variations against rural regions in different orientations. Cold advection from the Yangtze River (the ocean) in the riverside (coastal) rural region corresponds to the great UHI intensification, while the strong cold advection in the urban region well explains the fast UHI weakening. This study highlights that, besides local thermal factors, synoptic circulation also play an important role in the interaction between the UHI effect and HW events.
本研究描述了行星边界层(PBL)内城市热岛(UHI)的变化特征,并基于数值模式模拟研究了2019年8月上海市上空热浪(HW)事件中水平对流对UHI变化的影响。研究发现,在热浪条件下,UHI 加剧,UHI 强度从地表向上逐渐减弱。HW期间,地表、近地面和PBL的昼间UHI分别比HW前高3.68 K(29.27%)、1.41 K(33.52%)和1.04 K(36.97%),而夜间UHI至少在此情况下对HW无明显响应。降温期间,地表、近地表(2 米)和后海湾的平均 UHI 分别为白天 6.83 K(2.68 K)、2.45 K(1.34 K)和 1.73 K(0.04 K)。一般来说,PBL UHI 只存在于白天,可能是由热对流扩散引起的。近地面和后海平面超高气温影响受水平对流的影响较大,导致不同方向的农村地区超高气温强度和变化不同。在沿江(沿海)农村地区,来自长江(海洋)的冷平流导致了巨大的 UHI 增强,而城市地区的强冷平流则很好地解释了 UHI 的快速减弱。这项研究强调,除了局地热力因素外,同步环流也在超高温影响和高湿度事件之间的相互作用中发挥了重要作用。
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引用次数: 0
Role of the subtropical southern Indian Ocean in the interannual variability of Antarctic summer sea ice 亚热带南印度洋在南极夏季海冰年际变化中的作用
IF 4.5 2区 地球科学 Q1 METEOROLOGY & ATMOSPHERIC SCIENCES Pub Date : 2024-10-10 DOI: 10.1016/j.atmosres.2024.107723
Through data diagnosis and dynamic analysis, this study aims to reveal the potential influence of the Subtropical Dipole Pattern (SDP) in the southern Indian Ocean on the interannual variation of south polar sea ice. The results indicate that a robust teleconnection exists between the SDP and south polar sea ice. At least two months in advance, the SDP significantly affects the Antarctic summer sea-ice anomalies. Specifically, during the positive (negative) phase of the SDP, the Amundsen–Ross Sea and the western Indian Ocean sectors exhibit significant positive (negative) sea-ice anomalies, accompanied by negative (positive) sea-ice anomalies in the Bellingshausen Sea and the Weddell Sea. Planetary wave trains, stimulated over the SDP by anomalous rainfall and latent heat release, establish this teleconnection. These planetary wave trains, guided by westerly jets, then spread eastward and poleward, causing atmospheric circulation anomalies that affect Antarctic sea ice. The Antarctic sea-ice anomalies connected to the SDP are mostly consistent with abnormalities in the surface air temperature and wind fields.
本研究旨在通过数据诊断和动态分析,揭示南印度洋副热带偶极模式(SDP)对南极海冰年际变化的潜在影响。研究结果表明,副热带偶极模式与南极海冰之间存在着强有力的远程联系。至少提前两个月,SDP 就会对南极夏季海冰异常产生重大影响。具体来说,在 SDP 的正值(负值)阶段,阿蒙森-罗斯海和西印度洋海区表现出明显的正值(负值)海冰异常,同时贝林斯豪森海和威德尔海也出现负值(正值)海冰异常。行星波列受异常降雨和潜热释放的刺激,在 SDP 上建立了这种远距离联系。这些行星波列在西风喷流的引导下,向东和向极地扩散,造成大气环流异常,从而影响南极海冰。与 SDP 有关的南极海冰异常大多与地表气温和风场的异常一致。
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引用次数: 0
Analysis of gradient wind balance during the rapid intensification of Hurricane Wilma (2005) 威尔玛飓风(2005 年)迅速增强期间的梯度风平衡分析
IF 4.5 2区 地球科学 Q1 METEOROLOGY & ATMOSPHERIC SCIENCES Pub Date : 2024-10-10 DOI: 10.1016/j.atmosres.2024.107722
Understanding the rapid intensification (RI) of Hurricane Wilma (2005) in terms of the maximum wind has been carried out in a series of papers, this study examines the gradient wind balance and imbalance during RI, based on a 72-h Wilma prediction conducted using the Weather Research Forecast Model (WRF) with the 1-km grid resolution. Results show that the pressure gradient force (PGF) near the eyewall increases rapidly during the RI period. The maximum PGF associated with the gradient wind balance is determined by the strong radial gradient of the thermal field near the eyewall, resulting from the warming in the eye and adiabatic cooling near the eyewall. The maximum PGF occurs inside the radius of the maximum wind, causing a convergence region and intense updrafts, which favors RI. In a balanced symmetric framework, the hydrostatic PGF accounts for a major fraction (70 %–90 %) of the predicted PGF, and the secondary circulation is underestimated by the Sawyer-Eliassen equation within the boundary layer, at upper levels and through the intense eyewall updrafts where gradient wind imbalance occurs. The unbalanced force accelerates the boundary-layer radial inflow that contributes to the inward contraction of the eyewall and then enhances the radially inward advection of high absolute angular momentum. The eyewall convection strengthens where the boundary-layer inflows, convergence, and heat and moisture flux are collocated. With the high inertial stability, a sufficient conversion efficiency from energy to kinematic energy favors the RI of Wilma.
已有一系列论文从最大风力的角度对飓风威尔玛(2005 年)的快速增强(RI)进行了研究,本研究基于使用 1 千米网格分辨率的气象研究预测模式(WRF)进行的 72 小时威尔玛预测,对 RI 期间的梯度风力平衡和不平衡进行了研究。结果表明,在 RI 期间,眼球附近的压力梯度力(PGF)迅速增加。与梯度风平衡相关的最大压力梯度力是由眼球附近热场的强烈径向梯度决定的,这种梯度是由眼球内的增温和眼球附近的绝热冷却造成的。最大 PGF 出现在最大风半径内,造成一个辐合区和强烈的上升气流,有利于 RI。在平衡对称框架中,静压 PGF 占预测 PGF 的主要部分(70%-90%),Sawyer-Eliassen 方程低估了边界层内、高层和发生梯度风不平衡的强烈眼球上升气流中的次级环流。不平衡力加速了边界层的径向流入,导致眼墙向内收缩,然后加强了高绝对角动量的径向向内对流。在边界层流入、辐合以及热量和水汽通量共同作用的地方,眼墙对流会加强。由于惯性稳定性高,能量到运动能量的转换效率足够高,有利于威尔玛的 RI。
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引用次数: 0
An extreme precipitation event over Dronning Maud Land, East Antarctica - A case study of an atmospheric river event using the Polar WRF Model 南极洲东部德龙宁毛德地极端降水事件--利用极地 WRF 模式进行的大气河流事件案例研究
IF 4.5 2区 地球科学 Q1 METEOROLOGY & ATMOSPHERIC SCIENCES Pub Date : 2024-10-10 DOI: 10.1016/j.atmosres.2024.107724
Extreme precipitation events (EPEs) are crucial in Antarctica, impacting the Antarctic ice sheet's surface mass balance and stability. Comprehensive case studies are essential for better understanding these events and the underlying processes driving them. Here, we investigate an extreme snowfall event in Dronning Maud Land (DML), East Antarctica on November 8 and 9, 2015. This event contributed approximately 22 % of the annual accumulation in less than two days and exhibited high spatial variability in precipitation distribution. We employed a high-resolution atmospheric model specifically optimized for the polar regions (Polar WRF) and ERA5 reanalysis data to analyze the event in detail. Our findings highlight the importance of a blocking high-pressure ridge of record strength that effectively blocked and diverted a strong extratropical cyclone into DML, ultimately leading to the heavy snowfall event. The sudden deepening of the cyclone was initiated by a ‘jet streak’ in the upper atmosphere that steered the system southeastwards towards the Antarctic coast. Notably, we observed an anomalously high poleward moisture transport in the form of a strong atmospheric river on November 7, 2015. This atmospheric river originated in the South Atlantic Ocean and tracked poleward from the 30°S-40°S latitude band. Vertical cross-sections of the model outputs indicate that most of the precipitation was concentrated in regions with steep orography along the path of the atmospheric river. This interaction between the atmospheric river and the steep terrain led to the uplift of maritime air, resulting in heavy snowfall. This study highlights the significance of extreme upper and lower atmospheric conditions in driving intense moisture transport towards coastal DML. The interaction between the atmospheric river and the steep orography contributed to heavy snowfall, underscoring the importance of considering orographic influences in understanding EPEs in Antarctica.
极端降水事件(EPEs)对南极洲至关重要,会影响南极冰盖的表面质量平衡和稳定性。全面的案例研究对于更好地了解这些事件及其背后的驱动过程至关重要。在此,我们研究了 2015 年 11 月 8 日和 9 日在南极洲东部德龙宁毛德地(DML)发生的极端降雪事件。这次降雪事件在不到两天的时间里造成了约 22% 的年积雪量,降水分布的空间变异性很大。我们采用了专为极地地区优化的高分辨率大气模型(极地 WRF)和ERA5 再分析数据,对该事件进行了详细分析。我们的研究结果突显了创纪录强度的阻挡高压脊的重要性,它有效地阻挡了强热带外气旋并使其转向 DML,最终导致了这次强降雪事件。气旋的突然加深是由高层大气中的 "喷流条纹 "引发的,它将该系统引向东南方的南极海岸。值得注意的是,我们在 2015 年 11 月 7 日观测到了异常高的极地水汽输送,其形式为一条强大的大气河流。这条大气河发源于南大西洋,从南纬 30 度-40 度纬度带向极地移动。模式输出的垂直剖面图显示,大部分降水都集中在大气河流路径沿线地形陡峭的地区。大气河流与陡峭地形之间的相互作用导致海洋性空气抬升,造成大雪。这项研究突出表明,极端的上下大气条件在推动水汽向 DML 沿海地区强烈输送方面具有重要意义。大气河流与陡峭地形之间的相互作用导致了大量降雪,突出表明了在理解南极洲极端气候事件时考虑地形影响的重要性。
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引用次数: 0
Model sensitivity in predicting extreme precipitation events in urban areas: A case study over Beijing 预测城市地区极端降水事件的模型敏感性:北京上空的案例研究
IF 4.5 2区 地球科学 Q1 METEOROLOGY & ATMOSPHERIC SCIENCES Pub Date : 2024-10-09 DOI: 10.1016/j.atmosres.2024.107719
Understanding and forecasting the spatial and temporal distributions of extreme precipitation over urban areas is crucial for effective planning and mitigation efforts. However, this task remains challenging as accurate forecasting depends on properly representing urban surfacees and their interactions with the planetary boundary layer (PBL). We examined the hindcast of an extreme precipitation event over Beijing on 21–22 July 2012. The primary focus was assessing its sensitivity to two widely used PBL parameterizations (MYJ and YSU), two urban parameterizations (SLUCM and BEP_BEM), and two different land-use and land-cover (LULC) datasets.
Sensitivity experiments were initialized at different times to explore the model dependence on initial conditions. The analyses were conducted over three selected regions: the entire model domain covering the Beijing metropolitan area, an upwind region of Beijing, and the entire urban area of Beijing. The results show that the MYJ PBL scheme performs better than the YSU PBL scheme in capturing near-surface air temperature as well as the location and timing of the heaviest precipitation. The variability in simulated precipitation among the chosen PBL schemes is lower compared to that among different time of initializations. The LULC impacted the spatial distribution of precipitation but its effect on the amount of precipitation was minimal. Overall, using a combination of the MYJ PBL scheme, SLUCM urban parameterization, and locally-enhanced Beijing LULC, and initializing the model simulations at 0000 UTC July 20, 2012, demonstrated superior performance in capturing precipitation levels, despite some spatial discrepancies in the precipitation distribution. The performance of BEP_BEM urban parameterization is similar to SLUCM across various factors such as average rain rate, maximum rain rate, and rain volume. These findings offer valuable insights towards better simulations of extreme precipitation and flooding in rapidly urbanizing areas such as Beijing.
了解和预报城市地区极端降水的时空分布对有效规划和减灾工作至关重要。然而,这项任务仍然具有挑战性,因为准确的预报取决于对城市表面及其与行星边界层(PBL)之间相互作用的正确描述。我们研究了 2012 年 7 月 21-22 日北京极端降水事件的后预报。主要重点是评估其对两种广泛使用的 PBL 参数化(MYJ 和 YSU)、两种城市参数化(SLUCM 和 BEP_BEM)以及两种不同的土地利用和土地覆盖(LULC)数据集的敏感性。对三个选定区域进行了分析:覆盖北京大都市区的整个模型域、北京的一个上风区域和整个北京城区。结果表明,MYJ PBL 方案在捕捉近地面气温以及最强降水的位置和时间方面优于 YSU PBL 方案。与不同初始化时间的降水量相比,所选 PBL 方案的模拟降水量变化较小。LULC 对降水的空间分布有影响,但对降水量的影响很小。总的来说,使用 MYJ PBL 方案、SLUCM 城市参数化和本地增强的北京 LULC,并在 2012 年 7 月 20 日 0000 UTC 时初始化模式模拟,尽管降水量分布在空间上存在一些差异,但在捕捉降水量方面表现优异。在平均降雨率、最大降雨率和雨量等各种因素上,BEP_BEM 城市参数化的性能与 SLUCM 相似。这些发现为更好地模拟北京等快速城市化地区的极端降水和洪水提供了宝贵的见解。
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引用次数: 0
Rainfall characteristics over the Congo Air Boundary Region in southern Africa: A comparison of station and gridded rainfall products 南部非洲刚果空气边界地区的降雨特征:站点和网格降雨产品比较
IF 4.5 2区 地球科学 Q1 METEOROLOGY & ATMOSPHERIC SCIENCES Pub Date : 2024-10-06 DOI: 10.1016/j.atmosres.2024.107718
Strong meridional rainfall gradients exist between the tropics and subtropics in southwestern Africa, bounded to the north by the moist Congo basin and to the south by the Kalahari Desert. This domain received relatively little scientific attention compared to the rest of southern Africa. In this study, the limited available station data are assessed against six gridded rainfall products (CHIRPS, PERSIANN-CDR, ERA5, GPCC and CPC) for various rainfall characteristics. The nearest neighbour approach was used to match the closest rainfall dataset pixel to each station location, with the assumption that each rain gauge represents observation of various pixels of products, irrespective of product resolution. Results reveal that ERA5, CHIRPS and PERSIANN-CDR tend to represent the monthly rainfall totals and number of rainy days well for most stations although magnitudes and monthly peaks differ. CPC and GPCC tend to perform poorly for magnitudes of rainfall, rainy days and monthly cycles especially for Angolan stations. These products also fail to adequately capture spatial distributions of rainfall, with poor representation of the strong gradients found in the region.
Correlations between various gridded rainfall products mostly show good agreement in rainfall totals and rainy days. For early summer (October–November-December) moderate rainy days, ERA5 and CHIRPS products tend to have more days than the stations while CPC and GPCC products perform poorly over Angola and in the south. ERA5 generally overestimates rainfall in mountainous regions, while other products tend to underestimate it. Based on the Simple Daily Intensity Index, it was found that for most of the gridded rainfall products tend to overestimate rainfall during rainy days in the northern and wetter part of the domain. Furthermore, for heavy rainfall, CPC and GPCC tend to compare fairly well with stations in the southern and eastern parts of the domain but poorly with those in the western parts. PERSIANN-CDR tends to underestimate heavy rainy days for most stations in early and late summer (January–February-March-April). However, CHIRPS compares well at several stations, while ERA5 performs well for stations located in the south. This study helps provide useful guidance in choosing suitable rainfall gridded datasets for assessing long term rainfall cycles, daily rainfall characteristics as well as extremes over southwestern Africa.
非洲西南部的热带和亚热带之间存在着强烈的经向降雨梯度,北面是潮湿的刚果盆地,南面是卡拉哈里沙漠。与南部非洲其他地区相比,这一地区受到的科学关注相对较少。本研究根据六种网格降雨产品(CHIRPS、PERSIANN-CDR、ERA5、GPCC 和 CPC)的各种降雨特征,对有限的可用站点数据进行了评估。使用最近邻方法将最接近的降雨数据集像素与每个站点位置相匹配,假设每个雨量计都代表了对不同产品像素的观测,而与产品分辨率无关。结果显示,ERA5、CHIRPS 和 PERSIANN-CDR 能够很好地反映大多数站点的月降雨总量和降雨日数,尽管降雨量和月峰值有所不同。而 CPC 和 GPCC 在降雨量、降雨日数和月降雨周期方面表现不佳,尤其是安哥拉站点。这些产品也未能充分捕捉降雨的空间分布,对该地区发现的强烈梯度表现不佳。各种网格降雨产品之间的相关性大多表明,在降雨总量和降雨日数方面存在良好的一致性。对于初夏(10 月-11 月-12 月)的中雨日,ERA5 和 CHIRPS 产品的雨日往往多于观测站的雨日,而 CPC 和 GPCC 产品在安哥拉上空和南部表现不佳。ERA5通常高估了山区的降雨量,而其他产品往往低估了山区的降雨量。根据简单日强度指数发现,大多数网格降雨产品都倾向于高估北部和湿润地区雨天的降雨量。此外,就暴雨而言,CPC 和 GPCC 与区域南部和东部站点的比较结果相当好,但与西部站点的比较结果较差。在夏初和夏末(1 月-2 月-3 月-4 月),PERSIANN-CDR 往往低估了大多数站点的暴雨日数。不过,CHIRPS 在几个站点的表现不错,而 ERA5 在南部站点的表现也很好。这项研究有助于为评估非洲西南部的长期降雨周期、日降雨特征和极端天气选择合适的降雨网格数据集提供有用的指导。
{"title":"Rainfall characteristics over the Congo Air Boundary Region in southern Africa: A comparison of station and gridded rainfall products","authors":"","doi":"10.1016/j.atmosres.2024.107718","DOIUrl":"10.1016/j.atmosres.2024.107718","url":null,"abstract":"<div><div>Strong meridional rainfall gradients exist between the tropics and subtropics in southwestern Africa, bounded to the north by the moist Congo basin and to the south by the Kalahari Desert. This domain received relatively little scientific attention compared to the rest of southern Africa. In this study, the limited available station data are assessed against six gridded rainfall products (CHIRPS, PERSIANN-CDR, ERA5, GPCC and CPC) for various rainfall characteristics. The nearest neighbour approach was used to match the closest rainfall dataset pixel to each station location, with the assumption that each rain gauge represents observation of various pixels of products, irrespective of product resolution. Results reveal that ERA5, CHIRPS and PERSIANN-CDR tend to represent the monthly rainfall totals and number of rainy days well for most stations although magnitudes and monthly peaks differ. CPC and GPCC tend to perform poorly for magnitudes of rainfall, rainy days and monthly cycles especially for Angolan stations. These products also fail to adequately capture spatial distributions of rainfall, with poor representation of the strong gradients found in the region.</div><div>Correlations between various gridded rainfall products mostly show good agreement in rainfall totals and rainy days. For early summer (October–November-December) moderate rainy days, ERA5 and CHIRPS products tend to have more days than the stations while CPC and GPCC products perform poorly over Angola and in the south. ERA5 generally overestimates rainfall in mountainous regions, while other products tend to underestimate it. Based on the Simple Daily Intensity Index, it was found that for most of the gridded rainfall products tend to overestimate rainfall during rainy days in the northern and wetter part of the domain. Furthermore, for heavy rainfall, CPC and GPCC tend to compare fairly well with stations in the southern and eastern parts of the domain but poorly with those in the western parts. PERSIANN-CDR tends to underestimate heavy rainy days for most stations in early and late summer (January–February-March-April). However, CHIRPS compares well at several stations, while ERA5 performs well for stations located in the south. This study helps provide useful guidance in choosing suitable rainfall gridded datasets for assessing long term rainfall cycles, daily rainfall characteristics as well as extremes over southwestern Africa.</div></div>","PeriodicalId":8600,"journal":{"name":"Atmospheric Research","volume":null,"pages":null},"PeriodicalIF":4.5,"publicationDate":"2024-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142417125","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Microphysical characteristics of torrential predecessor rain events over the Yangtze River Delta Area and the related tropical cyclones 长江三角洲地区暴雨前兆及相关热带气旋的微物理特征
IF 4.5 2区 地球科学 Q1 METEOROLOGY & ATMOSPHERIC SCIENCES Pub Date : 2024-10-05 DOI: 10.1016/j.atmosres.2024.107715
<div><div>The precipitation structures and microphysical characteristics of predecessor rain events (PREs) over the Yangtze River Delta area and related tropical cyclones (TCs) from 2014 to 2019 were investigated using Dual-frequency Precipitation radar data from Global Precipitation Measurement (GPM) for drop size distributions (DSDs). Results showed that the total mean rain rate of PREs was larger than that of TCs, primarily due to higher convective and stratiform rain rates, with enhanced fractional coverage of convective rain in PREs. Examination of microphysical characteristics revealed that a greater quantity of small-sized droplets and a smaller quantity of medium- as well as large-sized droplets contributed towards PREs in comparison with TCs. The conclusion still holds when partitioning DSDs based on different precipitation rate categories. Further investigation of DSDs using gamma functions illustrated that precipitation in PREs had lower average mass-weighted diameters (D<sub>m</sub>) and enhanced normalized number concentration (N<sub>w</sub>) compared with TCs; partitioning precipitation into convective and stratiform components illustrated a larger D<sub>m</sub> and lower N<sub>w</sub> in TCs than PREs. The analysis of microphysical and thermodynamical processes using the reanalysis data indicates that relatively intense convective activity with drier conditions may be favorable to enhancing raindrop growth through collision-coalescence processes, as a result of larger D<sub>m</sub> in TCs than PREs. The empirical relations (Z–R algorithms) applied in different rain regimes (stratiform, convective, and total PREs) revealed significant diversities, relying on weather conditions and geographical locations.</div></div><div><h3>Plain language summary</h3><div>The Yangtze River Delta area is an important economic belt in China. Under climate change, observed frequent occurrences of weather extremes of heavy rainfall and tropical cyclones (TCs) exert adverse effects on economic development in this region. Thus, a deep understanding of the mechanism of TCs torrential rainfall in the Yangtze River Delta area is urgently necessary. In this study, we investigated the precipitation patterns and microphysical characteristics of predecessor rain events (PREs) in the Yangtze River Delta region, and their association with TCs in the South China Sea-Western North Pacific Ocean (SCS-WNPO) area from 2014 to 2019. We found that PREs had a higher total mean precipitation rate than TCs. Further examination using gamma functions demonstrated that PREs exhibited lower average mass-weighted diameters (Dm) and higher normalized intercept parameters (Nw) than TCs. This pattern persisted when distinguishing between convective and stratiform precipitation components. We believe that our study makes a significant contribution to the literature because these results provide valuable insights into the distinct precipitation characteristics of PREs and TCs in the
利用全球降水测量(GPM)的双频降水雷达数据研究了2014-2019年长三角地区前兆雨事件(PREs)和相关热带气旋(TCs)的降水结构和微物理特征。结果表明,PREs 的总平均雨率大于 TCs,主要原因是 PREs 中对流雨和层状雨的雨率更高,对流雨的部分覆盖率也更高。对微观物理特征的研究表明,与 TCs 相比,PREs 有更多的小液滴,而中型和大型液滴的数量较少。根据不同的降水速率类别来划分DSD,这一结论仍然成立。利用伽马函数对DSDs进行的进一步研究表明,与TCs相比,PREs中降水的平均质量加权直径(Dm)更小,归一化数量浓度(Nw)更高;将降水划分为对流和层状成分后,TCs中降水的Dm比PREs大,Nw比PREs小。利用再分析数据对微观物理和热力学过程进行的分析表明,相对强烈的对流活动和较干燥的条件可能有利于通过碰撞-凝聚过程促进雨滴的增长,这也是 TC 比 PRE 的 Dm 大的原因。应用于不同雨态(层状、对流和全 PRE)的经验关系(Z-R 算法)显示出显著的多样性,这取决于天气条件和地理位置。在气候变化的影响下,强降雨和热带气旋等极端天气频发,对该地区的经济发展产生了不利影响。因此,深入了解长三角地区热带气旋暴雨的机理迫在眉睫。在本研究中,我们研究了长三角地区前兆雨事件(PREs)的降水模式和微物理特征,以及它们与2014-2019年南海-西北太平洋(SCS-WNPO)地区TCs的关联。我们发现,PRE 的总平均降水率高于 TC。使用伽马函数进行的进一步研究表明,PREs 的平均质量加权直径(Dm)比 TCs 低,归一化截距参数(Nw)比 TCs 高。在区分对流和层状降水成分时,这种模式依然存在。我们认为我们的研究对文献做出了重要贡献,因为这些结果为研究区域内 PRE 和 TC 的不同降水特征提供了宝贵的见解,有助于更好地理解与热带气旋相关的降水模式,并为减灾提供科学依据。
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Atmospheric Research
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