Dependency of typhoon intensity and genesis locations on El Ni?o phase and SST shift over the western North Pacific     

Kyung-Ja Ha  Soon-Jo Yoon  Kyung-Sook Yun  Jong-Seong Kug  Yeon-Soo Jang  Johnny C. L. Chan 《Theoretical and Applied Climatology》2012,109(3-4):383-395

The effects of the El Ni?o-Southern Oscillation (ENSO) phase and the shifting of the ENSO sea surface temperature (SST) on the intensity of tropical cyclones (TC) have been extensively investigated in terms of TC genesis locations in the western North Pacific (WNP). To advance the hypothesis for a relation of genesis location–intensity that the TC formation location hints its intensity, two cases have been compared, which include the phase of the decaying El Ni?o turning over to La Ni?a (type I) and the phase that recovers to a neutral condition (type II). In addition, the shift of ENSO SST to the central Pacific warming (CPW) from the East Pacific warming (EPW) has been examined. The genesis potential index (GPI) and the accumulated cyclone energy have been applied to compare the differences between the ENSO phase and the TC formation location. It was apparent that ENSO influences the WNP typhoon formation location depending on the cycle of the ENSO phase. In addition, the typhoon activity was affected by the zonal shift of the El Ni?o SST. The CPW, which has maximum SST over the central Pacific, tends to have a persistently high GPI over the WNP in September–November and June–August, demonstrating that the formation locations of strong TCs significantly shift southeastward compared with the EPW having SST maximum over the eastern Pacific. CPW years revealed a distinguishable relationship between the TC formation location and the TC between the tropical depression (TD) + tropical storm (TS) and the intense typhoon of category 4?+?5.  相似文献   

Potential use of a regional climate model in seasonal tropical cyclone activity predictions in the western North Pacific     

Andie Y. M. Au-Yeung  Johnny C. L. Chan 《Climate Dynamics》2012,39(3-4):783-794

This study investigates the potential use of a regional climate model in forecasting seasonal tropical cyclone (TC) activity. A modified version of Regional Climate Model Version 3 (RegCM3) is used to examine the ability of the model to simulate TC genesis and landfalling TC tracks for the active TC season in the western North Pacific. In the model, a TC is identified as a vortex satisfying several conditions, including local maximum relative vorticity at 850?hPa with a value?≥450?×?10^?6?s^?1, and the temperature at 300?hPa being 1°C higher than the average temperature within 15° latitude radius from the TC center. Tracks are traced by following these found vortices. Six-month ensemble (8 members each) simulations are performed for each year from 1982 to 2001 so that the climatology of the model can be compared to the Joint Typhoon Warning Center (JTWC) observed best-track dataset. The 20-year ensemble experiments show that the RegCM3 can be used to simulate vortices with a wind structure and temperature profile similar to those of real TCs. The model also reproduces tracks very similar to those observed with features like genesis in the tropics, recurvature at higher latitudes and landfall/decay. The similarity of the 500-hPa geopotential height patterns between RegCM3 and the European Centre for Medium-Range Weather Forecasts 40 Year Re-analysis (ERA-40) shows that the model can simulate the subtropical high to a large extent. The simulated climatological monthly spatial distributions as well as the interannual variability of TC occurrence are also similar to the JTWC data. These results imply the possibility of producing seasonal forecasts of tropical cyclones using real-time global climate model predictions as boundary conditions for the RegCM3.  相似文献   

A high resolution palaeoclimatic record for the last 27,500 years in tropical West Africa from the carbon and nitrogen isotopic composition of lacustrine organic matter     

Michael R. Talbot  Truls Johannessen 《Earth and Planetary Science Letters》1992,110(1-4):23-37

Variations in the carbon and nitrogen isotopic composition of bulk organic matter in the sediments of Lake Bosumtwi, Ghana reflect climatically induced changes to the lake and the catchment flora. Cores spanning the last 27.5 kyr of sedimentation in the lake show large oscillations inδ¹³C_org PDB andδ¹⁵N_org Air. The late Pleistocene record is particularly detailed, showing changes of ca. 20‰ in carbon and ca. 10‰ in nitrogen isotopic compositions. These variations are of complex origin. Although different in magnitude, major isotopic excursions in the two records are generally in phase and reveal the occurrence of two major dry intervals at and immediately following the Last Glacial Maximum. The Allerød-Younger Dryas period also seems to have been marked by generally dry conditions in this part of tropical West Africa. Nitrogen isotopic evidence suggests that during the period 9.2–3.2 kyr the lake had an extremely stable water column, probably due to the absence of a windy or cool, dry season, or both. Regular circulation of the water column recommenced during the late Holocene and has persisted until the present day.  相似文献   

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

Meng YAN  Johnny C. L. CHAN  Kun ZHAO 《大气科学进展》2020,37(7):696-706

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.  相似文献   

孟加拉湾季风爆发对南海季风爆发的影响Ⅱ:数值试验   总被引：3，自引：1，他引：3       下载免费PDF全文

刘屹岷  陈仲良  吴国雄 《气象学报》2003,61(1):10-19

通过数值试验研究了孟加拉湾季风爆发期间该地区旺盛的对流凝结加热对南海季风爆发和副热带高压“撤出”南海的影响,结果证明在孟加拉湾地区引入模拟的对流凝结潜热使该地区出现了强烈的上升运动,引起了孟加拉湾季风的爆发。同时由于对凝结加热的非对称Rossby响应,在南海北部导致西风出现和增强及垂直上升运动。因低层水汽平流的共同作用下,在南海北部引起了对流的发展。而正是南海北部的凝结加热促使南海地区温度经向梯度逆转,使副热带高压脊面的倾斜从冬季型转为夏季型,即低层的副热带高压减弱南移。最后当对流在南海地区发展起来时,副热带高压移出南海地区。  相似文献   

Comparison of Remotely Measured and Modelled Currents in Coastal Areas of Norway and Spain     

H. -H. Essen     . Breivik  H. Gü  nther  K. -W. Gurgel  J. Johannessen  H. Klein  T. Schlick  M. Stawarz 《Journal of Atmospheric & Ocean Science》2003,9(1):39-64

Data from two six-week current measurement campaigns at the coasts of Norway and Spain are presented. Spatial coverage of surface currents was obtained by an HF (High Frequency) radar. Subsurface currents were measured by bottom-mounted and ship-borne ADCPs (Acoustic Doppler Current Profiler). The HF data were assimilated by a fine gridded model with the aim of predicting currents for about 6 h. The objective of this article is twofold, to investigate the performance of the instruments and the model, and to show the high temporal and spatial variability of currents in the coastal zones under investigation.

Several strong storms occurred during the experiments with significant waveheights exceeding 11 m (Norway) and 8 m (Spain), respectively. High waves affected both the WEllen RAdar (WERA) (reduced ranges) and the ADCP (unreliable near-surface current velocities). The assimilation algorithm of the model worked well. The comparisons of measured and modelled maps of the surface-current velocity, time series and horizontal gradients reveal good agreement.

The analysis of current data shows similar features for both experimental areas. The dominant M2-tidal currents are weak (amplitudes of about 0.15 ms -1 ). The spatial distribution of the vector correlation between surface current and wind is homogeneous, although single current maps contain strong horizontal variabilities. The portion of current variance linearly forced by wind is about 30%.  相似文献   

建筑物对城市通风自净能力影响的数值试验     

Liu Huizhi  Sang Jianguo  Zhang Boyin  Johnny C.L. Chan  Andrew Y.S.Cheng  Liu Heping 《大气科学进展》2002,19(6):1045-1054

应用城市气候数值模式，分别计算了三栋6层住宅楼和一栋20层住宅楼两类建筑形式影响下的风场，以及在此风场中街道汽车尾气的浓度分布。计算结果表明在总建筑面积基本相同的情况下，高层建筑周围环境的通风自净能力要优于多层建筑。  相似文献   

Effects of the Indo-China Peninsula Heat Fluxes on the 1998 South China Sea Summer Monsoon          下载免费PDF全文

SHI Xueli  Johnny C. L. CHAN  K. C. CHOW  DING Yihui 《Acta Meteorologica Sinica》2005,19(4):457-468

1. IntroductionBecause the South China Sea (SCS) is one of theregions where the Asian summer monsoon onset oc-curs earliest, the SCS summer monsoon (SCSSM) hasalways been a research focus, especially in recent yearswith the implementation of the SCS Monsoon Exper-iment (SCSMEX) (e.g., Tao and Chen, 1987; Changand Chen, 1995; Lau et al., 2000; Ding and Li, 1999;Ding and Liu, 2001; Li and Wu, 2000; Xie et al., 1998;Zhang et al., 2004). Climatologically, the SCSSM on-set is a rem…  相似文献   

Regional and synoptic-scale features associated with inactive periods of the summer monsoon over south china(1)     

C. H. So  Johnny C. L. Chan 《大气科学进展》1997,14(2):223-230

This paper presents an observational study of the physical processes responsible for the inactive period (break) of the summer monsoon over South China (SC). The break of the monsoon is defined by using the rainfall data over Hong Kong Meteorological parameters provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) for the period 1985-1990 are examined. Daily values of each parameter for the six years are then composited each day for the period of 5 days before to 1 day after the break. It is found that several days before the break, changes opposite to those occurred during the onset and active periods begin to take place. This suggests that a feedback mechanism is present which tends to restore the atmosphere to a more stable state. This mechanism may be initiated by the formation of convective clouds during the onset and active periods. These clouds then reduce the solar radiation to the ground, leading to a gradual drop in the temperature. This drop, together with the cooling of the atmosphere due to the large amounts of rainfall, causes the pressure over the SC region to become higher, which in turn induces a westward extension of the subtropical ridge. The decrease in temperature over SC may also shift the location of the heat source to the west, which leads to a concomitant westward shift of the convergence of the southerlies and results in less moisture-laden air reaching the SC region. The atmosphere then becomes unfavourable for heavy convection and therefore a break starts.  相似文献   

Influence of rock mass strength on the erosion rate of alpine cliffs   总被引：1，自引：0，他引：1  

Jeffrey R. Moore  Johnny W. Sanders  William E. Dietrich  Steven D. Glaser 《地球表面变化过程与地形》2009,34(10):1339-1352

Collapse of cliff faces by rockfall is a primary mode of bedrock erosion in alpine environments and exerts a first‐order control on the morphologic development of these landscapes. In this work we investigate the influence of rock mass strength on the retreat rate of alpine cliffs. To quantify rockwall competence we employed the Slope Mass Rating (SMR) geomechanical strength index, a metric that combines numerous factors contributing to the strength of a rock mass. The magnitude of cliff retreat was calculated by estimating the volume of talus at the toe of each rockwall and projecting that material back on to the cliff face, while accounting for the loss of production area as talus buries the base of the wall. Selecting sites within basins swept clean by advancing Last Glacial Maximum (LGM) glaciers allowed us to estimate the time period over which talus accumulation occurred (i.e. the production time). Dividing the magnitude of normal cliff retreat by the production time, we calculated recession rates for each site. Our study area included a portion of the Sierra Nevada between Yosemite National Park and Lake Tahoe. Rockwall recession rates determined for 40 alpine cliffs in this region range from 0·02 to 1·22 mm/year, with an average value of 0·28 mm/year. We found good correlation between rockwall recession rate and SMR which is best characterized by an exponential decrease in erosion rate with increasing rock mass strength. Analysis of the individual components of the SMR reveals that joint orientation (with respect to the cliff face) is the most important parameter affecting the rockwall erosion rate. The complete SMR score, however, best synthesizes the lithologic variables that contribute to the strength and erodibility of these rock slopes. Our data reveal no strong independent correlations between rockwall retreat rate and topographic attributes such as elevation, aspect, or slope angle. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献