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1.
The present study revealed that a climate regime shift occurred during the 1988–1991 period involving changes in tropical cyclone (TC) intensity (central pressure, maximum sustained wind speed) during the summer near 30°N in East Asia. Climatologically, TC intensity at 110°–125°E near 30°N (over Mainland China) is the weakest at that latitude while the strongest is found at 125°–130°E (over Korea). The TC intensity during the 1991–2015 (91–15) period had strengthened significantly compared to that of the 1965–1988 (65–88) period. The strengthening was due to a significantly lower frequency of TCs that passed through Mainland China during the 91–15 period. This lower frequency of was due to anomalous northeasterlies blown from the anomalous anticyclonic circulation located over continental East Asia and that had strengthened along the coast. Instead, TCs mainly followed a path from eastern regions in the subtropical western North Pacific to Korea and Japan via the East China Sea due to anomalous cyclonic circulations that had strengthened in the western North Pacific. In addition, low vertical wind shear had formed along the mid-latitude region in East Asia and along the main TC track in the 91–15 period, and most regions in the western North Pacific experienced a higher sea surface temperature state during the 91–15 period than in the previous period, indicating that a favorable environment had formed to maintain strong intensities of TCs at the mid–latitudes. The characteristics of TCs at the lower latitudes caused a strong TC intensity at the time of landfall in Korea and a gradual shifting trend of landing location from the western to southern coast in recent years. 相似文献
2.
利用夏季东亚地区500 h Pa高度场和菲律宾附近的降水场进行SVD分析,将东亚500 h Pa高度场对应的时间序列定义为PJ指数,该指数不仅清楚地反映PJ型的年际变化,而且反应出PJ型的年代际变化,即500 h Pa高度场型态在20世纪70年代末由"气旋、反气旋、气旋"型突变为"反气旋、气旋、反气旋"型。本文研究表明PJ指数的年际变化与ENSO事件有密切的联系:El Ni1o事件通过电容器充电效应使印度洋海温增暖,而增暖的印度洋海温在菲律宾海附近强迫出异常反气旋,并沿东亚沿岸激发出PJ遥相关型。而PJ型态的年代际变化与热带印度洋SST的持续增暖有关。虽然许多学者认为是菲律宾附近海温异常引起对流异常,并沿东亚沿岸激发出PJ遥相关型,但我们认为该区域的海温变化并不是造成PJ型年际和年代际变化的原因,而是由于该区域有反气旋(或者气旋)异常,从而辐射增加(减少),蒸发减弱(增加),温跃层下降(上升),SST变暖(变冷),该区域的海温变暖意味着对流是减弱的。本文进一步利用大气环流模式ECHAM5.4进行数值试验,结果表明:当热带印度洋增暖时,在菲律宾海附近强迫出反气旋,并沿东亚激发出"反气旋、气旋、反气旋"PJ遥相关型。 相似文献
3.
Hydrography and Circulation in the Eastern Tropical Indian Ocean during April-May 2011 总被引：2，自引：0，他引：2 
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下载免费PDF全文 The distribution of hydrography and circulation in the eastern tropical Indian Ocean(ETIO) during April-May 2011 were analyzed using cruise observations,satellite observations,and historic hydrographic data.It was observed that warm water(28℃) occupies the upper 50-m layer in the ETIO.Low-salinity surface water was observed at the mouth of the Bay of Bengal(BOB),which further extends to the Arabian Sea and off Sumatra via the Sri Lanka coast and the eastern bay mouth.Arabian Sea high-salinity water(ASHSW) is carried eastward along the equator to around 90°E by the equatorial undercurrent(EUC).It also runs south of Sri Lanka(north to 3°N) and in the western bay mouth(west to 87°E) but is much shallower than its counterpart at the equator.It is suggested to be the residual of the ASHSW,which intrudes into the BOB during the preceding southwest monsoon.Our results also show that,in the south of Sri Lanka,just below this subsurface high-salinity water,very-low-salinity water(about 34.8) occurs at depths of 100-200 m.Further analysis suggests that this low-salinity water comes from the BOB. 相似文献
4.
Interannual variability of landfalling tropical cyclones(TCs) in China during 1960-2010 is investigated.By using the method of partial least squares regression(PLS-regression),canonical ENSO and ENSO Modoki are identified to be the factors that contribute to the interannual variability of landfalling TCs.El Ni o Modoki years are associated with a greater-than-average frequency of landfalling TCs in China,but reversed in canonical El Ni o years.Significant difference in genesis locations of landfalling TCs in China for the two kinds of El Ni o phases occurs dominantly in the northern tropical western North Pacific(WNP).The patterns of low-level circulation anomalies and outgoing longwave radiation(OLR) anomalies associated with landfalling TC genesis with different types of El Ni o phases are examined.During canonical El Ni o years,a broad zonal band of positive OLR anomalies dominates the tropical WNP,while the circulation anomalies exhibit a meridionally symmetrical dipole pattern with an anticyclonic anomaly in the subtropics and a cyclonic anomaly near the tropics.In El Ni o Modoki years,a vast region of negative OLR anomalies,roughly to the south of 25°N with a strong large-scale cyclonic anomaly over the tropical WNP,provides a more favorable condition for landfalling TC genesis compared to its counterpart during canonical El Ni o years.For more landfalling TCs formed in the northern tropical WNP in El Ni o Modoki years,there are more TCs making landfall on the northern coast of China in El Ni o Modoki years than in canonical El Ni o years.The number of landfalling TCs is slightly above normal in canonical La Ni a years.Enhanced convection is found in the South China Sea(SCS) and the west of the tropical WNP,which results in landfalling TCs forming more westward in canonical La Ni a years.During La Ni a Modoki years,the landfalling TC frequency are below normal,owing to an unfavorable condition for TC genesis persisting in a broad zonal band from 5°N to 25°N.Since the western North Pacific subtropical high(WNPSH) in La Ni a Modoki years is located in the westernmost region,TCs mainly make landfall on the south coast of China. 相似文献
5.
Summary The seasonal and diurnal variations in the vertical component of the atmospheric electric field, air temperature, relative humidity and horizontal wind speed were studied using the surface data for the two periods (1936–40) and (1962–66) recorded at the tropical urban station, Colaba, Bombay (18°51N, 72°49E, 11 m ASL), located on the west coast of India.The atmospheric electric field during the latter period (1962–66) is significantly higher (up to 42.3%) than the earlier period (1936–40). This has been attributed to the enhanced particulate concentrations in the atmosphere. The increase noticed in the atmospheric electric field is a maximum during winter and minimum during the monsoon. The atmospheric electric field exhibited a marked semi-diurnal oscillation with peaks at 0900 LST and 2200 LST during winter, premonsoon and post-monsoon seasons of both the periods. During the monsoon season the double oscillation is not marked.The variations noticed in the surface air temperature and the relative humidity are in agreement with those observed in the atmospheric electric field. The horizontal wind speed showed a decrease which has been attributed to the surface roughness resulting from urbanization.With 7 Figures 相似文献
6.
During the late summer of 1979, massive changes occurred in the distribution of temperature over Eur asia north of 15oN. At 300 hPa, zonal mean temperature averaged over Eurasia along 20o－25oN de-creased sharply around 23 August. An abrupt decrease in 300 hPa zonal mean temperature also occurred over extensive mid-latitude zones (40o－55oN) around 18 August, i. e., about 5 days prior to the monsoon withdrawal over South Asia.The intensity and location of N－S oriented, vertical overturning underwent significant changes over Eurasia during the transition from summer to fall. Near 20o－25oN, zonal mean updrafts weakened con-siderably during the transition period (18－27 August). Around 45oN, zonal mean downdrafts and the asso-ciated cooling (radiative) rate increased considerably during the transition period.Near 15oN, 300 hPa zonal mean temperature fluctuated nearly periodically with an approximate 40-day period. These fluctuations appear to be associated with a small imbalance between 40-day filtered adiabatic cooling (heating) and diabatic heating (cooling). 相似文献
7.
基于三维时域有限差分数值算法（3D-FDTD）建立了雷击高建筑物电磁场传播模型,研究了负地闪击中不同高度建筑物时回击垂直电场、角向磁场以及水平电场沿地表的传播规律。模拟结果表明:建筑物的高度对雷电电场峰值的影响显著,如当建筑物高度从100 m增加至600 m时,在距离d=100 m位置的垂直电场峰值减小了63%,水平电场正极性峰值的增加比例为84%、负极性峰值的绝对值增加比例高达130%;观测位置不变时,角向磁场峰值和水平电场正极性峰值均会随着建筑物高度的增加而增大;对于距离d=100 m,300 m时,垂直电场的峰值随着建筑物高度的增加而减小,而d=500 m时,垂直电场峰值随着建筑物高度的增加呈现出先增大后减小的趋势;此外,建筑物高度会影响垂直电场峰值对距离的敏感程度,建筑物越低（高）,相应的垂直电场峰值随着观测距离增大衰减越快（慢）。该文研究结果能够为现代化城市中高建筑物附近线缆、室外设备等的雷电防护方案设计提供参考。 相似文献
8.
南海至西太平洋一带夏季低空越赤道气流和季风的初步研究 总被引：4，自引：3，他引：4
本文对南海至西太平洋一带夏季低空越赤道气流的情况和西南季风的来源,进行了初步研究。发现:(1)就气候平均而言,东非低空急流的影响范围,包括印度南部、孟加拉湾南部直到中南半岛南部和南海南部。在这一范围内,夏季月平均西南季风强度的年际变化十分一致;(2)夏季在中南半岛南部、南海南部,西南季风的主要来源是上游印度、孟加拉湾地区,直接来自南半球的气流比重不大。而热带西北太平洋的西南季风,则主要来自南半球;(3)在110-140°E 的赤道地区,并不存在一支主要的越赤道气流;(4)在150°E 附近的新几内亚东岸,有一条越赤道气流的通道。热带西北太平洋的西南季风,主要就是这支越赤道气流转向而成(但似乎要求这支气流的南风分量强度超过某一下限,即存在一阈值,才能对西北太平洋的西南季风变化有影响)。新几内亚岛上的山脉,对南半球东南信风的阻挡,是形成这支越赤道气流的重要原因之一;(5)大致在15°N 以南的南亚至西北太平洋地区,其西南季风主要由二支气流构成:一支在非洲东岸附近越过赤道,成为东非低空急流,经印度南部,往下游一直影响到南海南部;另一支在新几内亚东岸附近越过赤道,转向成西南气流影响西北太平洋。 相似文献
9.
选取１９８２／１９８３年夏季（６～８月）欧洲中期预报中心８５０ｈＰａ、３００ｈＰａ两层纬向风场的网格点资料，采用复经验正交函数（ＣＥＯＦ）讨论了准双周振荡的位相传播及振荡的地理特征。结果表明：①２０°Ｎ以南对流层高层（３００ｈＰａ）１９８２年振荡显著区域是印度半岛至菲律宾东部一个西西北－东东南走向的带状区域４低层（８５０ｈＰａ）１９８２年５°～１５°Ｎ之间以及中国东南部及其沿海地区都是振荡的显著区域；而１９８３年３０°Ｎ以南振荡明显比１９８２年弱，只有中国东南沿海部分地区及孟加拉湾东南、马来西亚北部是振荡的显著区域。②对流层高层（３００ｈＰａ）１９８２年８５°～９０°Ｅ，３０°～４０°Ｎ的青藏高原是振荡的源区，其南传支波列可传到盂加拉湾北部的２０°Ｎ附近；而１９８３年青藏高原上８０°～９０°Ｅ，３５°～４０°Ｎ区域是振荡的汇区。 相似文献
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11.
Birgitta Källstrand Hans Bergström Jørgen Højstrup Ann-Sofi Smedman 《Boundary-Layer Meteorology》2000,95(2):161-188
For two consecutive days during spring 1997, the windfield over the Baltic Sea has been studied. Thestrength of the geostrophic wind speed is the majordifference in synoptic conditions between these twodays. During both days, the mesoscale wind field overmost of the Baltic Sea is quite heterogeneous; themodifications primarily being caused by the land-seacontrasts. On the day with the weaker wind speed,sea-breeze circulations develop. As a consequence, thewind direction at lower levels is more or lessopposite to the geostrophic over large areas of theBaltic Sea and the surface wind speed decreases withoffshore distance. Wind speed maxima caused by the seabreezes are found along the east coasts in the studiedarea. For the other day, the slow growth of a stableinternal boundary layer over the sea also gives asurface wind speed decrease with offshore distancefrom the coast. 相似文献
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Summer Monsoon Impacts on Chlorophyll-a Concentration in the Middle of the South China Sea: Climatological Mean and Annual Variability 下载免费PDF全文
下载免费PDF全文 Climatological mean and annual variations of Chlorophyll-a(Chl-a) distribution,sea surface wind(SSW),and sea surface temperature(SST) from 1998 to 2008 were analyzed in the middle of the South China Sea(SCS),focusing on the typical region off the east coast of Vietnam(8.5-14°N,109.5-114°E).Based on remote sensing data and SCS summer monsoon index(SCSSMI) data,high Chl-a concentrations in the middle of the SCS in the southwest summer monsoon season(June-September) may be related to strong Ekman pumping and strong wind stress.The maximum of the monthly averaged climatological Chl-a in the summer appeared in August.According to the annual variation,there was a significant negative correlation(r =-0.42) between the SCSSMI and SST,a strongly positive correlation(r=0.61) between the SCSSMI and Chl-a,and a strongly negative correlation(r =-0.74) between the SST and Chl-a in the typical region off the east coast of Vietnam during 1998-2008.Due to the El Ni?o event specifically,the phenomena of a low Chl-a concentration,high SST and weak SCSSMI were extremely predominant in the summer of 1998.These relationships imply that the SCSSMI associated with the SST could be used to predict the annual variability of summer Chl-a in the SCS. 相似文献
13.
Hiroaki Ueda Yuusuke Amagai Masamitsu Hayasaki 《Asia-Pacific Journal of Atmospheric Sciences》2017,53(2):287-293
La Niña conditions during boreal winter sometimes brings excessive snowfall in Japan, especially on the East Sea/Sea of Japan coastal and mountain areas through intensified northwesterly cold winds caused by La-Niña related atmospheric teleconnection. Meanwhile, snowfall events also increase in the Pacific coast area of Japan during the El Niño state due to extratropical cyclones passing along the south coast of Japan (hereafter referred to as South-coast cyclone). In the present study, we investigated year-to-year snowfall/rainfall variations based on meteorological station data and cyclone tracks identified by using the Japanese 55-year Reanalysis. The result clearly indicates increase of the South-coast cyclone during El Niño-developing winters, which is consistent with excessive snow-fall in the northern part of the Pacific coast. Strong subtropical jet hampers cyclogenesis due to less vertical interaction through the trapping of upper-level eddies. During El Niño-developing winters, the subtropical jet is weakened over East Asia, indicating dynamic linkage to increased cyclone frequency. In addition to this, both the deepening of the upper-tropospheric trough over East Asia and anomalous low-tropospheric northwest anticyclones extending from the Philippines toward Japan are also consistent with the enhancement of cyclogenesis over the East China Sea as well as warm winter in Japan. 相似文献
14.
A climatology of extratropical cyclones (ECs) over East Asia (20 -75 N, 60 -160 E) is analyzed by applying an improved objective detection and tracking algorithm to the 4-time daily sea level pressure fields from the European Centre for Medium-range Weather Forecasts (ECMWF) reanalysis data. A total of 12914 EC processes for the period of 1958-2001 are identified, with an EC database integrated and EC activities reanalyzed using the objective algorithm. The results reveal that there are three major cyclogenesis regions: West Siberian Plain, Mongolia (to the south of Lake Baikal), and the coastal region of East China; whereas significant cyclolysis regions are observed in Siberia north of 60 N, Northeast China, and Okhotsk Sea-Northwest Pacific. It is found that the EC lifetime is largely 1-7 days while winter ECs have the shortest lifespan. The ECs are the weakest in summer among the four seasons. Strong ECs often appear in West Siberia, Northeast China, and Okhotsk Sea-Northwest Pacific. Statistical analysis based on k-means clustering has identified 6 dominating trajectories in the area south of 55 N and east of 80 E, among which 4 tracks have important impacts on weather/climate in China. ECs occurring in spring (summer) tend to travel the longest (shortest). They move the fastest in winter, and the slowest in summer. In winter, cyclones move fast in Northeast China, some areas of the Yangtze-Huaihe River region, and the south of Japan, with speed greater than 15 m s 1 . Explosively-deepening cyclones are found to occur frequently along the east coast of China, Japan, and Northwest Pacific, but very few storms occur over the inland area. Bombs prefer to occur in winter, spring, and autumn. Their annual number and intensity in 1990 and 1992 in East Asia (EA) are smaller and weaker than their counterparts in North America. 相似文献
15.
Soon-Chang Yoon Sang-Woo Kim Suk-Jin Choi In-Jin Choi 《Asia-Pacific Journal of Atmospheric Sciences》2010,46(3):279-286
We investigated the regional-scale relationships between columnar aerosol loads and summer monsoon circulation, and also the precipitation over northeast Asia using aerosol optical depth (AOD) data obtained from the 8-year MODIS, AERONET Sun/sky radiometer, and precipitation data acquired under the Global Precipitation Climatology Project (GPCP). These high-quality data revealed the regional-scale link between AOD and summer monsoon circulation, precipitation in July over northeast Asian countries, and their distinct spatial and annual variabilities. Compared to the mean AOD for the entire period of 2001–2008, the increase of almost 40–50% in the AOD value in July 2005 and July 2007 was found over the downwind regions of China (Yellow Sea, Korean peninsula, and East Sea), with negative precipitation anomalies. This can be attributable to the strong westerly confluent flows, between cyclone flows by continental thermal low centered over the northern China and anticyclonic flows by the western North Pacific High, which transport anthropogenic pollution aerosols emitted from east China to aforementioned downwind high AOD regions along the rim of the Pacific marine airmass. In July 2002, however, the easterly flows transported anthropogenic aerosols from east China to the southwestern part of China in July 2002. As a result, the AOD off the coast of China was dramatically reduced in spite of decreasing rainfall. From the calculation of the cross-correlation coefficient between MODIS-derived AOD anomalies and GPCP precipitation anomalies in July over the period 2001–2008, we found negative correlations over the areas encompassed by 105–115°E and 30–35°N and by 120–140°E and 35–40°N (Yellow Sea, Korean peninsula, and East Sea). This suggests that aerosol loads over these regions are easily influenced by the Asian monsoon flow system and associated precipitation. 相似文献
16.
D. V. Alekseev V. A. Ivanov E. V. Ivancha V. V. Fomin L. V. Cherkesov 《Russian Meteorology and Hydrology》2013,38(4):248-255
An effectiveness of the storm wave attenuation by protective piers in the Sevastopol Bay of the Black Sea is studied on the basis of numerical simulation using the SWAN spectral model. Analyzed are the parameters of waves generated by winds of four main directions as well as by the southern cyclone during the storm on November 11, 2007. It is obtained that waves from the northwest part of the Black Sea penetrate most intensively into the Sevastopol Bay in case of western wind and, to a lesser degree, in case of northern and southern winds. A protective effect of the piers is observed in the west part of the bay only and the wave attenuation near the southern coast is more significant than near the northern one. The area of the southern coast directly behind the southern pier is completely protected from the storm waves and, as moving away from the pier, the danger of intensive wave effect on the coast is kept. 相似文献
17.
0713号台风韦帕路径预报难点分析 总被引：3，自引：0，他引：3
0713号台风韦帕各家都预报在台湾岛北部海上北折,在120°E以东向偏北方向移动,与台风实际在浙闽交界处登陆后在120°E以西转向北上路径存在较大误差.为认识这种预报偏差的原因,应用各种资料对影响台风韦帕北折的可能原因进行探讨.指出:(1)欧洲气象中心天气形势预报误差较大,西风槽底预报比实况偏南,是本次台风路径转折预报失误的主要原因.(2)欧亚500hPa高度场为两脊一槽形势,西风指数从低指数向高指数演变和副热带高压处周期性加强均不利于台风韦帕在台湾东北部海区折向偏北方向移动.(3)地形的影响造成的趋岸左折和港湾"吸引",以及动力场和热力场的分布均有利于台风韦帕在台湾东北部海区折向偏西方向移动. 相似文献
18.
1991年江淮梅雨与副热带高压的低频振荡 总被引：47，自引：4，他引：43
利用NCEP/NCAR再分析资料和观测的台站降水资料研究了1991年梅雨期间江淮洪涝区降水的季节内振荡及其环流特征,着重考察了不同层次副热带高压的低频变化与降水的关系。小波分析表明1991年江淮梅雨期间降水低频振荡的主周期是15~35 d。在低空,15~35 d振荡以异常反气旋(气旋)的形式在中国东南沿海地区交替出现,调控着西太平洋副热带高压进入(退出)南海。低空的这种低频环流型与高空的偶极型涡旋对相耦合,偶极型涡旋对使得南亚高压东伸(西退),形成有利(不利)江淮流域降水的环流形势。江淮流域降水的低频振荡与500hPa北太平洋副热带高压的低频变化及其传播密切相关。当北太平洋西部的位势高度偏高、中部位势高度偏低时,江淮流域降水偏多;反之偏少。这种低频振荡可能起源于北太平洋中部夏威夷群岛附近,然后沿着副热带高压脊线附近向西传播到中国东南沿海。 相似文献
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20.
Fetch Limited Drag Coefficients 总被引：5，自引：1，他引：5
Measurements made at a tower located 2 km off the coast of Denmark inshallow water during the Risø Air Sea Experiment (RASEX) are analyzedto investigate the behaviour of the drag coefficient in the coastal zone.For a given wind speed, the drag coefficient is larger during conditions ofshort fetch (2-5 km) off-shore flow with younger growing waves than it isfor longer fetch (15-25 km) on-shore flow. For the strongest on-shorewinds, wave breaking enhances the drag coefficient. Variation of the neutral drag coefficient in RASEX is dominated byvariation of wave age, frequency bandwidth of the wave spectra and windspeed. The frequency bandwidth is proportional to the broadness of the waveheight spectra and is largest during conditions of light wind speeds. Usingthe RASEX data, simple models of the drag coefficient and roughness length are developed in terms of wind speed, wave age and bandwidth. An off-shoreflow model of the drag coefficient in terms of nondimensional fetch isdeveloped for situations when the wave state is not known. 相似文献