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1.
Seasonal forecasting of tropical cyclogenesis over the North Indian Ocean   总被引:1,自引:0,他引:1  
Over the North Indian Ocean (NIO) and particularly over the Bay of Bengal (BoB), the post-monsoon season from October to December (OND) are known to produce tropical cyclones, which cause damage to life and property over India and many neighbouring countries. The variability of frequency of cyclonic disturbances (CDs) during OND season is found to be associated with variability of previous large-scale features during monsoon season from June to September, which is used to develop seasonal forecast model of CDs frequency over the BoB and NIO based on principal component regression (PCR). Six dynamical/thermodynamical parameters during previous June–August, viz., (i) sea surface temperature (SST) over the equatorial central Pacific, (ii) sea level pressure (SLP) over the southeastern equatorial Indian Ocean, (iii) meridional wind over the eastern equatorial Indian Ocean at 850 hPa, (iv) strength of upper level easterly, (v) strength of monsoon westerly over North Indian Ocean at 850 hPa, and (vi) SST over the northwest Pacific having significant and stable relationship with CDs over BoB in subsequent OND season are used in PCR model for a training period of 40 years (1971–2010) and the latest four years (2011–2014) are used for validation. The PCR model indicates highly significant correlation coefficient of 0.77 (0.76) between forecast and observed frequency of CD over the BoB (NIO) for the whole period of 44 years and is associated with the root mean square error and mean absolute error ≤ 1 CD. With respect to the category forecast of CD frequency over BoB and NIO, the Hit score is found to be about 63% and the Relative Operating Curves (ROC) for above and below normal forecast is found to be having much better forecast skill than the climatology. The PCR model performs very well, particularly for the above and below normal CD year over the BoB and the NIO, during the test period from 2011 to 2014.  相似文献   

2.
Variability of precipitation and temperature was examined on multiple time scales using data from five surface observing stations in the center of Guanajuato state, Mexico, as well as gridded data from the North American Regional Reanalysis (NARR). Frequency of days with total precipitation exceeding the 90th percentile was not found to have increased from 1979-2011. However, frequency of days with maximum temperature above the 90th percentile more than doubled from 1979-2011, and frequency of days with maximum temperature below the 10th percentile decreased by almost half over the same period, an important result given the scarcity of water resources for the agriculture-based economy. Precipitation within the growing season was found to vary by phase of the Madden-Julian oscillation (MJO), with MJO phases 1-3 associated with above-normal rainfall and MJO phases 4-7 with normal or below normal rainfall. Composite anomalies of precipitation, surface pressure, surface wind, surface temperature, and 700 mbar height showed that days with rainfall in Guanajuato were associated with on-shore, upslope flow, reduced surface temperatures, and reduced potential evaporation. Composites for MJO phases 1-3 and 8 agreed well with these anomalies. Similarly, composite anomalies for days without rainfall in Guanajuato showed warm surface temperatures, broad anticyclonic flow over much of northern Mexico, and enhanced potential evaporation. Composites for MJO phases 4-7 agreed well with these anomalies.  相似文献   

3.
4.
欧亚和我国东北冬春季积雪对东北夏季气温的影响   总被引:5,自引:0,他引:5  
张茜  李栋梁 《冰川冻土》2012,34(2):284-295
根据我国东北及邻近地区123个气象站的逐日气温和积雪深度资料,欧亚大陆积雪面积以及NCEP/NCAR全球再分析月平均500hPa高度场资料,通过相关、合成分析等方法,研究了东北夏季气温异常对欧亚和我国东北冬春季积雪的响应,并从大气环流的角度出发分析了欧亚和我国东北冬春季积雪对东北夏季气温异常形成的影响机制.结果表明:东北地区夏季气温与欧亚大陆春季积雪面积以及东北冬季累积雪深的异常存在明显的关系.欧亚春季积雪面积的扩大与维持有利于8月我国东北上空500hPa位势高度的偏低,环流上表现出西欧与我国东北地区槽加深,泰梅尔阻塞高压加强的特征.由于欧亚中高纬上空的环流经向度加大,槽后脊前的西北气流加强,诱导冷空气南下,从而造成东北全区8月气温一致偏低;东北冬季累积雪深减少则有利于6月东北全区、7月东北西南部上空的位势高度偏低(负距平),造成相关区域气温偏低.研究结果对于提高东北夏季气温的短期气候预测水平具有重要意义.  相似文献   

5.
焦洋  游庆龙  林厚博  闵锦忠 《冰川冻土》2014,36(6):1385-1393
基于青藏高原地区1960-2010年高分辨率(0.5°×0.5°)的逐日地面气温格点资料以及 1960-2010年NCEP/NCAR全球月平均海平面气压场、高度场、风场的再分析格点资料(2.5°×2.5°), 通过计算青藏高原(74.75°~104.25° E, 26.75°~40.25° N)冬季地面温度平均值经标准化处理后得到的区域冬季气温强度指数, 分析了冬季北极涛动(AO)、西伯利亚高压与同期青藏高原地面气温的特征和关系. 结果表明: AO为负(正)相位时, 中高纬西风气流偏弱(强), 有(不)利于极地冷空气向南输送, 西伯利亚地区源地冬季风偏强(弱), 青藏高原冬季气温指数减小(增大), 地面气温偏低(高). 对AO作M-K突变分析, 发现其突变年份为1975年, 通过对突变年份前后高度场和风场作差值场分析, 结果显示: 冬季AO处于高指数时期, 500 hPa上, 欧洲东部槽变浅, 青藏高原北部的高压脊减弱, 环流呈纬向发展, 青藏高原上盛行偏南风, 气温偏高, 青藏高原地区为暖冬期; 200 hPa 上, 青藏高原东部的槽明显加深, 使得青藏高原地区对流层顶至平流层底的环流趋势以经向发展为主, 该区域主要受到偏北的急流控制, 易导致降温.  相似文献   

6.
Extremely cold weather has an important influence on winter production and life in the Greater Khingan Mountains region. This paper uses the daily minimum temperature data of ground observation stations during extreme cold weather from 1974 to 2021 in the Greater Khingan Mountains region, monthly circulation index data, the spatial distribution and temporal variation characteristics of extreme cold days and extreme minimum temperature were analyzed by climate statistical method; The abrupt changes and periods of extreme cold days and extreme minimum temperature were tested by Mann-Kendall method and Morlet wavelet analysis; calculating the recurrence period of extreme minimum temperature by empirical frequency method; correlation method was used to analyze the circulation factors which had significant influence on the number of extremely cold days. The results are followed: (1) The spatial distribution of extreme cold days in the Greater Khingan Mountains region was not uniform, and gradually decreasing from northwest to south. The extreme cold days was at most 717 d in Huzhong, and at least 29 d in Gagadaki, the extreme cold days in the whole region mutated in 1979, and the average annual extreme cold days decreased 14.2 d after the mutation compared with that before the mutation, and the annual extremely cold days have a significant cycle of 2 to 4 years. (2) The extreme minimum temperature in the whole region mutated in 1990, before the mutation the extreme minimum temperature was low and after the mutation began to rise, the significant cycle of annual extreme minimum temperature was 4 to 5 years, the extreme lowest temperature was -49.6 ℃ in Mohe, followed by -49.2 ℃ in Huzhong; the extreme lowest temperature occurs once every 2 years, once every 5 years and once every 10 years in Huzhong, while the extreme lowest temperature occurs once in 20 years, once in 50 years and once in 100 years in Mohe. (3) SCAND teleconnection patterm has a good correlation with extreme cold days in winter(January, February and December)in the Greater Khingan Mountains region. Positive growth of the circulation mode, it has great influence on the extreme cold weather in winter in the Greater Khingan Mountains region. © 2022 Science Press (China).  相似文献   

7.
青海高原冬季持续低温集中程度的气候特征及其成因   总被引:3,自引:1,他引:2  
采用青海高原37个台站1961-2010年逐日气温数据, 着重讨论了持续3 d及以上低温过程集中程度的变化特征及其发生机制.结果表明: 低温集中度(LTCD)和集中期(LTCP)具有表征低温在时空场上非均匀性的较好分辨力; 近50 a青海高原冬季低温事件及其集中度均呈逐年明显减少趋势, 集中期明显提前; 利用REOF结合CAST方法分区并探讨了影响青海不同区域低温集中度的主要环流系统及因子, 发现影响柴达木盆地的主要系统为极涡和北大西洋涛动, 而青南牧区主要是由于局地气候反馈机制影响; 唐古拉地区的主要影响系统位于极区、 乌拉尔山地区及东部鄂霍次克海附近; 与东部农业区的相关体现为自西向东呈"+ - +"波列型分布, 反映冷空气不断东移过程中受东部高压阻塞, 在东部农业区堆积, 形成冷空气过程从而造成该地区集中度偏高.  相似文献   

8.
A statistical model for predicting the intensity of tropical cyclones in the Bay of Bengal has been proposed. The model is developed applying multiple linear regression technique. The model parameters are determined from the database of 62 cyclones that developed over the Bay of Bengal during the period 1981–2000. The parameters selected as predictors are: initial storm intensity, intensity changes during past 12 hours, storm motion speed, initial storm latitude position, vertical wind shear averaged along the storm track, vorticity at 850 hPa, Divergence at 200 hPa and sea surface temperature (SST). When the model is tested with the dependent samples of 62 cyclones, the forecast skill of the model for forecasts up to 72 hours is found to be reasonably good. The average absolute errors (AAE) are less than 10 knots for forecasts up to 36 hours and maximum forecast error of order 14 knots occurs at 60 hours and 72 hours. When the model is tested with the independent samples of 15 cyclones (during 2000 to 2007), the AAE is found to be less than 13 knots (ranging from 5.1 to 12.5 knots) for forecast up to 72 hours. The model is found to be superior to the empirical model proposed by Roy Bhowmik et al (2007) for the Bay of Bengal.  相似文献   

9.
The output from Global Forecasting System (GFS) T574L64 operational at India Meteorological Department (IMD), New Delhi is used for obtaining location specific quantitative forecast of maximum and minimum temperatures over India in the medium range time scale. In this study, a statistical bias correction algorithm has been introduced to reduce the systematic bias in the 24–120 hour GFS model location specific forecast of maximum and minimum temperatures for 98 selected synoptic stations, representing different geographical regions of India. The statistical bias correction algorithm used for minimizing the bias of the next forecast is Decaying Weighted Mean (DWM), as it is suitable for small samples. The main objective of this study is to evaluate the skill of Direct Model Output (DMO) and Bias Corrected (BC) GFS for location specific forecast of maximum and minimum temperatures over India. The performance skill of 24–120 hour DMO and BC forecast of GFS model is evaluated for all the 98 synoptic stations during summer (May-August 2012) and winter (November 2012–February 2013) seasons using different statistical evaluation skill measures. The magnitude of Mean Absolute Error (MAE) and Root Mean Squared Error (RMSE) for BC GFS forecast is lower than DMO during both summer and winter seasons. The BC GFS forecasts have higher skill score as compared to GFS DMO over most of the stations in all day-1 to day-5 forecasts during both summer and winter seasons. It is concluded from the study that the skill of GFS statistical BC forecast improves over the GFS DMO remarkably and hence can be used as an operational weather forecasting system for location specific forecast over India.  相似文献   

10.
《Atmósfera》2014,27(3):287-303
Given the growing interest of the general public in accessing commercial weather forecasts through various media outlets and the available impetuses for promoting tourism in Saudi Arabia (SA), a first attempt is made to present a forecast skill comparison for surface temperature in four cities (Wejh, Yenbo, Jeddah, and Gizan) along the west coast of SA, for the 61-day transitional period (from January 16 to March 16) between the December-January-February (DJF) and the March-April-May (MAM) seasons. A simple skill score comparison method is used to assess the next-day city forecasts for surface temperature from six commercial weather forecast providers based on the operational numerical weather prediction (NWP) model outputs. All the NWP model forecast providers performed better than the respective daily climatology (Clm) for each station. Depending upon the station and the provider, the absolute average maximum daily surface temperature difference between the forecasts and the observations was less than 2 °C. Daily surface temperature forecasts from two versions of an atmospheric-ocean general circulation model are also compared to assess their performance for these coastal locations.  相似文献   

11.
青海省冬季气温变化成因及其预测方法探讨   总被引:1,自引:1,他引:0  
利用青海省1961-2012年冬季气温观测资料、美国环境预报中心(NCEP)和国家大气研究中心(NCAR)月平均高度场再分析资料、国家气候中心和美国国家海洋局和大气管理局提供的126项环流指数, 探讨青海冬季气温变化特征及成因. 结果表明: 1961-2012年青海冬季气温呈显著上升趋势并具明显的年代际变化特征, 于1986年出现由冷向暖的明显转折; 西伯利亚高压、东亚冬季风是影响青海冬季气温的主要系统. 当冬季北半球500 hPa高度场出现欧亚(EU)遥相关型时, 青海冬季易于偏冷, 同时发现大西洋欧洲区极涡强度和赤道太平洋海域海温与东亚冬季风的强弱有密切关系. 采用主成分回归集成方法初步建立青海冬季气温预测模型, 经历史回报检验其距平符号一致率为87%, 具备一定预报技巧和能力.  相似文献   

12.
The Eastern Mediterranean and the Middle East (EMME) is suffering from abnormal cooling of weather conditions and existence of an extreme weather phenomenon known as ice storm Alexa. The present paper investigates the weather conditions over Europe that causes this abnormal weather over the EMME through December of 2013. Daily data sets of several meteorological elements (temperature, precipitation, relative humidity, sea level pressure, and geopotential height at level 500 hPa, etc.) over the northern hemisphere, including Europe and EMME of December of 2013, have been used through the present work. In addition, to that, a time cross section analysis of the daily operational data for meteorological elements (mean surface temperature, temperature and geopotential height at level 500 hPa, relative humidity, precipitation rate, and sea surface pressure) was done over the EMME for December 2013. The methodology of anomaly and correlation coefficient techniques for the data sets has been used. The results uncovered that the EMME has abnormal and very cold weather conditions due to the inference of meridional blocking persisted over Europe and the existence of the extremely negative geopotential height anomaly aloft over Eastern Europe throughout this month.  相似文献   

13.
In this study, the Florida State University Global Spectral Model (FSUGSM), in association with a high-resolution nested regional spectral model (FSUNRSM), is used for short-range weather forecasts over the Indian domain. Three-day forecasts for each day of August 1998 were performed using different versions of the FSUGSM and FSUNRSM and were compared with the observed fields (analysis) obtained from the European Center for Medium Range Weather Forecasts (ECMWF). The impact of physical initialization (a procedure that assimilates observed rain rates into the model atmosphere through a set of reverse algorithms) on rainfall forecasts was examined in detail. A very high nowcasting skill for precipitation is obtained through the use of high-resolution physical initialization applied at the regional model level. Higher skills in wind and precipitation forecasts over the Indian summer monsoon region are achieved using this version of the regional model with physical initialization. A relatively new concept, called the ‘multimodel/multianalysis superensemble’ is described in this paper and is applied for the wind and precipitation forecasts over the Indian subcontinent. Large improvement in forecast skills of wind at 850 hPa level over the Indian subcontinent is shown possible through the use of the multimodel superensemble. The multianalysis superensemble approach that uses the latest satellite data from the Tropical Rainfall Measuring Mission (TRMM) and the Defense Meteorological Satellite Program (DMSP) has shown significant improvement in the skills of precipitation forecasts over the Indian monsoon region.  相似文献   

14.
Extreme-temperature events have a great impact on human society. Thus, knowledge of summer temperatures can be very useful both for the general public and for organizations whose workers operate in the open. An accurate forecasting of summer maximum and minimum temperatures could help to predict heatwave conditions and permit the implementation of strategies aimed at minimizing the negative effects that high temperatures have on human health. The objective of this work is to evaluate the skill of the regional atmospheric and modelling system (RAMS) model in determining daily summer maximum and minimum temperatures in the Valencia Region. For this, we have used the real-time configuration of this model currently running at the Centro de Estudios Ambientales de Mediterráneo Foundation. This operational system is run twice a day, and both runs have a 3-day forecast range. To carry out the verification of the model in this work, the information generated by the system has been broken into individual simulation days for a specific daily run of the model. Moreover, we have analysed the summer forecast period from 1 June to 31 August for 2007, 2008, 2009 and 2010. The results indicate good agreement between observed and simulated maximum temperatures, with RMSE in general near 2 °C both for coastal and inland stations. For this parameter, the model shows a negative bias around ?1.5 °C in the coast, while the opposite trend is observed inland. In addition, RAMS also shows good results in forecasting minimum temperatures for coastal locations, with bias lower than 1 °C and RMSE below 2 °C. However, the model presents some difficulties for this parameter inland, where bias higher than 3 °C and RMSE of about 4 °C have been found. Besides, there is little difference in both temperatures forecasted within the two daily RAMS cycles and that RAMS is very stable in maintaining the forecast performance at least for three forecast days.  相似文献   

15.
中国气温变化的两个基本模态的诊断和模拟研究   总被引:11,自引:0,他引:11  
我国地域辽阔,气候复杂多变,在全球变暖的背景下研究中国近百年来的气温变化具有重要的意义。为此我们重建了中国东部71个站1880—2004年四季气温距平序列。通过EOF分析发现了中国气温变化的2种最基本的模态:东部一致变化和关内关外相反变化。这2种模态不随季节变化,而且在不同时期也是稳定的。通过研究这2种模态与变暖趋势的关系发现,20世纪80年代以来的变暖主要是由于第一模态在该时期持续的正位相增强造成的;而20世纪20~40年代的变暖主要是由于第二模态所呈现的正位相所造成的。此外,我们检验了这2种模态在大气环流模式(CAM)中的表现。结果表明:121年(模式中1880—2000年)的集合模拟在一定程度上可以重现第一模态的变化,而第二模态则仅在冬季表现明显。最后,以冬季为例,利用1880—2004年重建及观测的500 hPa高度场资料,通过合成分析进一步研究了这2种模态的环流机制:第一模态正位相对应纬向环流增强,表现在地面气温分布上为东部一致变暖。而负位相则对应东亚大槽加深,东部地区一致变冷。第二模态正位相对应的环流分布则为从东亚北部到阿留申为负距平,东亚到北太平洋中纬度为正距平;对应地面气温分布为关内变暖关外变冷。负位相时环流分布基本相反。这样的环流机制得到了模式研究的支持。  相似文献   

16.
Based on the ERA-Interim atmospheric reanalysis data from the European Medium-Term Weather Forecast Center from 1979 to 2016 and the ERSSTv4 sea surface temperature data from the US National Oceanic and Atmospheric Administration, the regional climate model CWRF was used to simulate the climate characteristics in East Asia. The results show that the CWRF model can well reproduce the average characteristics of the East Asian winter monsoon circulation, including the location and intensity of the low-level continental cold high pressure and variation characteristics of wind field in high and low levels. The occurrence area and frequency of the north wind in the simulation and the reanalysis data were further calculated and compared. It is shown that they are basically consistent. The distribution of air temperature and precipitation over China are well represented by the model. The water vapor transport is also in good agreement with the reanalysis data. The water vapor from the Bay of Bengal plays a vital role in the precipitation over South China. The simulation results of apparent heat source and apparent moisture sink show that the model can well simulate the thermal difference between the East Asian continent and the adjacent sea area. The analysis results indicate that CWRF model has the ability to simulate the main characteristics of the East Asian winter monsoon.  相似文献   

17.
Kinetic energy exchange equations (Saltzman 1957) in wave number domain are partitioned into standing, transient and standing-transient components following Murakami (1978, 1981). These components are computed for the 1991 summer monsoon using dailyu andv grid point data at 2.5° latitude-longitude interval between the equator and 40°N at 200 hPa and 850 hPa levels for the period June through August. The data are obtained from NCMRWF, New Delhi. The study shows that at 200 hPa wave number 1 over Region 3 (30°N to 40°N), wave number 2 over Region 2 (15°N to 30°N) and wave number 3 over Region 1 (equator to 15°N) dominate the spectrum of transport of momentum and wave to zonal mean flow interaction. Wave number 1 over Region 1 and Region 3 and wave number 2 over Region 2 are the major sources of kinetic energy to other waves via wave-to-wave interaction. At 850 hPa wave number 1 over Region 3 has maximum contribution in the spectrum of transport of momentum and kinetic energy and more than 90% of its contribution is from the standing component. This indicates that standing wave number 1 over Region 3 plays a very important role in the dynamics of monsoon circulation of the lower troposphere. The study further shows that although the circulation patterns at 200 hPa and 850 hPa levels are opposite in character, a number of energy processes exhibit a similar character at these levels. For example, (i) transport of momentum by most of the waves is northward, (ii) small scale eddies intensify northward, (iii) eddies are sources of kinetic energy to zonal mean flow over Region 1 and (iv) standing eddies are sources of kinetic energy to transient eddies. Besides the above similarities some contrasting energy processes are also observed. Over Region 2 and Region 3 standing and transient eddies are sources of kinetic energy to zonal mean flow at 200 hPa, while at 850 hPa the direction of exchange of kinetic energy is opposite i.e. zonal mean flow is a source of kinetic energy to standing as well as transient eddies. L(n) interaction indicates that at 200 hPa waves over R2 maintain waves over R1, while at 850 hPa waves over R1 maintain waves over R2. It has been found that the north-south gradient of zonal mean of zonal wind is the deciding factor of wave to zonal mean flow interaction.  相似文献   

18.
Systematic and random error and their growth rate and different components of growth rate budget in energy/variance form are investigated at wavenumber domain for medium range tropical (30‡S-30‡N) weather forecast using daily horizontal wind field of 850 hPa up to 5-day forecast for the month of June, 2000 of NCEP (MRF) model. Part I of this paper deals with the study at physical domain. The following are the major findings in this paper:
–  •Tropical systematic error is associated with large scale wave of wavenumber 2, unlike the tropical random error, in which case dominant spectra of random error are observed at higher spectral band of wavenumbers 4–7 in comparison to that of systematic error.
–  •Systematic error growth rate peak is observed at wavenumber 2 up to 4-day forecast then the peak is shifted to wavenumber 1 at 5-day forecast. Random error energy shows maximum growth at wavenumber 4 for 2-day forecast, wavenumber 6 for 3–4 day forecasts and at wavenumber 7 for 1-day and 5-day forecasts.
–  •In the error growth rate budget, flux of systematic error shows the net increase of error energy at wavenumber 1 through the triad interactions with the pairs of waves of other wavenumbers. Flux and pure generation of random error energy are found to be accumulated at wavenumber 4. Resolving the possible triads in wavenumber 4 associated with these terms, it is shown that the wave receives more energy from the pairs of waves of different wavenumbers than it loses, leading to the error energy peak at wavenumber 4. However, the significant triad interaction occurs among the wavenumber 2 and higher wavenumbers in systematic error energy flux.
  相似文献   

19.
Mountain range specific analog weather forecast model is developed utilizing surface weather observations of reference stations in each mountain range in northwest Himalaya (NW-Himalaya). The model searches past similar cases from historical dataset of reference observatory in each mountain range based on current situation. The searched past similar cases of each mountain range are used to draw weather forecast for that mountain range in operational weather forecasting mode, three days in advance. The developed analog weather forecast model is tested with the independent dataset of more than 717 days (542 days for Pir Panjal range in HP) of the past 4 winters (2003–2004 to 2006–2007). Independent test results are reasonably good and suggest that there is some possibility of forecasting weather in operational weather forecasting mode employing analog method over different mountain ranges in NW-Himalaya. Significant difference in overall accuracy of the model is found for prediction of snow day and no-snow day over different mountain ranges, when weather is predicted under snow day and no-snow day weather forecast categories respectively. In the same mountain range, significant difference is also found in overall accuracy of the model for prediction of snow day and no-snow day for different areas. This can be attributed to their geographical position and topographical differences. The analog weather forecast model performs better than persistence and climatological forecast for day-1 predictions for all the mountain ranges except Karakoram range in NW-Himalaya. The developed analog weather forecast model may help as a guidance tool for forecasting weather in operational weather forecasting mode in different mountain ranges in NW-Himalaya.  相似文献   

20.
Analysis of monthly momentum transport of zonal waves at 850 hPa for the period 1979 to 1993, between ‡S and ‡N for January to April, using zonal (u) and meridional (v) components of wind taken from the ECMWF reanalysis field, shows a positive correlation (.1% level of significance) between the Indian summer monsoon rainfall (June through September) and the momentum transport of wave zero TM(0) over latitudinal belt between 25‡S and 5‡N (LB) during March. Northward (Southward) TM(0) observed in March over LB subsequently leads to a good (drought) monsoon season over India which is found to be true even when the year is marked with the El-Nino event. Similarly a strong westerly zone in the Indian Ocean during March, indicates a good monsoon season for the country, even if the year is marked with El-Nino. The study thus suggests two predictors, TM(0) over LB and the strength of westerly zone in the Indian Ocean during March.  相似文献   

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