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Impacts of the Thermal Effects of Sub-grid Orography on the heavy rainfall events Along the Yangtze River Valley in 1991

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Advances in Atmospheric Sciences 2007年第5期24卷 881-892页

作者：冯蕾张耀存 Department of Atmospheric Sciences Nanjing University Nanjing 210093

A P - σ regional climate model using a parameterization scheme to account for the thermal effects of the sub-grid scale orography was used to simulate the three heavy rainfall events that occurred within the Yangtze River Valley during the mei-yu period of 1991. The simulation results showed that by considering the sub-grid scale topography scheme, one can significantly improve the performance of the model for simulating the rainfall distribution and intensity during these three heavy rainfall events, most especially the second and third. It was also discovered that the rainfall was mainly due to convective precipitation. The comparison between experiments, either with and without the sub-grid scale topography scheme, showed that the model using the scheme reproduced the convergence intensity and distribution at the 850 hPa level and the ascending motion and moisture convergence center located at 500 hPa over the Yangtze River valley. However, some deviations still exist in the simulation of the atmospheric moisture content, the convergence distribution and the moisture transportation route, which mainly result in lower simulated precipitation levels. Further analysis of the simulation results demonstrated that the sub-grid topography scheme modified the distribution of the surface energy budget components, especially at the south and southwest edges of the Tibetan Plateau, leading to the development and eastward propagation of the negative geopotential height difference and positive temperature-lapse rate difference at 700 hPa, which possibly led to an improved precipitation simulation over eastern China.

关键词： sub-grid scale orographic parameterization heavy rainfall events numerical simulation

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Decadal Features of heavy rainfall events in Eastern China

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Acta meteorologica Sinica 2012年第3期26卷 289-303页

作者：陈活泼孙建奇范可 Nansen-Zhu International Research Centre Institute of Atmospheric Physics Chinese Academy of Sciences Climate Change Research Center Chinese Academy of Sciences Graduate University of Chinese Academy of Sciences

Based on daily precipitation data, the spatial-temporal features of heavy rainfall events （HREs） during 1960-2009 are investigated. The results indicate that the HREs experienced strong decadal variability in the past 50 years, and the decadal features varied across regions. More HRE days are observed in the 1960s, 1980s, and 1999s over Northeast China （NEC）; in the 1960s, 1970s, and 1990s over North China （NC）; in the early 1960s, 1980s, and 2000s over the Huaihe River basin （HR）; in the 1970s 1990s over the mid-lower reaches of the Yangtze River valley （YR）; and in the 1970s and 1990s over South China （SC）. These decadal changes of HRE days in eastern China are closely associated with the decadal variations of water content and stratification stability of the local atmosphere. The intensity of HREs in each sub-region is also characterized by strong decadal variability. The HRE intensity and frequency co-vary on the long-term trend, and show consistent variability over NEC, NC, and YR, but inconsistent variability over SC and HR. Further analysis of the relationships between the annual rainfall and HRE frequency as well as intensity indicates that the HRE frequency is the major contributor to the total rainfall variability in eastern China, while the HRE intensity shows only relative weak contribution.

关键词： heavy rainfall events decadal variability eastern China atmosphere water content stratifica-tion stability

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Moist Potential Vorticity Vector for Diagnosis of heavy rainfall events in Tanzania

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Journal of Geoscience and Environment Protection 2016年第9期4卷 128-145页

作者： Philbert Modest Luhunga George Djolov Edmund Mutayoba Department of Geography Geo-Informatics and Meteorology University of Pretoria Pretoria South Africa Research Section Tanzania Meteorological Agency Dar es Salaam Tanzania Department of Built Environmental Engineering Mbeya University of Science and Technology Mbeya Tanzania

In this paper, we modify the convective vorticity vector (CVV) defined as a cross product of absolute vorticity and gradient of equivalent potential temperature to moist potential vorticity vector (MPVV) defined as a cross product of absolute vorticity () and the gradient of the moist-air entropy potential temperature (). The patterns of (MPVV) are compared with the patterns of heavy rainfall events that occurred over different regions in Tanzania on 20th to 22nd December, 2011 and on 5th to 8th May, 2015. Moreover, the article aimed at assessing the relative contributions of the magnitude, horizontal and vertical components of (MPVV) detecting on the observed patterns of rainfall events. Dynamic and thermodynamic variables: wind speed, temperature, atmospheric pressure and relative humidity from numerical output generated by the Weather Research and Forecasting (WRF) model running at Tanzania Meteorological Agency (TMA) were used to compute MPVV. It is found that MPVV provide accurate tracking of locations received heavy rainfall, suggesting its potential use as a dynamic tracer for heavy rainfall events in Tanzania. Finally it is found that the first and second components of MPVV contribute almost equally in tracing locations received heavy rainfall events. The magnitude of MPVV described the locations received heavy rainfall events better than the components.

关键词： Moist Potential Vorticity Vector Moist-Air Entropic Potential Temperature heavy rainfall events

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Assessing the Variability of heavy rainfall during October to December rainfall Season in Tanzania

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Atmospheric and Climate Sciences 2021年第2期11卷 267-283页

作者： Lovina Peter Japheth Guirong Tan Ladislaus Benedict Chang’a Agnes Lawrence Kijazi Kantamla Biseke Mafuru Isack Yonah Tanzania Meteorological Authority Dar es Salaam Tanzania Nanjing University of Science and Technology Nanjing China

heavy rainfall is one of the primary causes of flood during rainy season in Tanzania leading to severe socio-economic impacts. The study aimed at assessing and characterizing the variability of heavy rainfall events (HREs) using Empirical Orthogonal Function (EOF), Mann-Kendal (MK) trend test, Correlation and Composite analysis methods. Based on the daily-observed precipitation and reanalysis data sets for the October to December (OND) rainfall season of 35 years (1981-2015), the spatial and temporal characteristics of HREs in Tanzania are studied. The relationship between heavy rainfall (HR) and large-scale circulation anomalies including the Indian Ocean dipole (IOD) and El Ni?o southern oscillation (ENSO) indices was assessed. The study found that, approximately 590 HREs were concentrated over northern sector and coastal belt of Tanzania. The monthly variability indicates that HREs are more pronounced in December followed by November while October being the least affected. The occurrence of HREs over the Lake Victoria, Kigoma and Tabora is largely attributed to low-level convergence of westerlies and enhanced moisture from Congo basin accompanied by a pronounced rising limb of Indian Walker circulation cell. A time-series analysis of HRE exhibits an inter-annual variation characterized by a slightly increasing trend, though the computed trends were not statistically significant at 95% confidence level. In most part of Tanzania HREs were positively correlated with both ENSO and IOD indices, underscoring the critical role of ENSO and Indian Ocean dynamic in modulating rainfall variability over the region. In general, it has been found that most of the HREs are generally triggered or amplified by large-scale circulation patterns such as ENSO and IOD.

关键词： rainfall Variability heavy rainfall events OND Tanzania

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