The Relationship Between Indian Ocean SST and Tropical Cyclone Genesis Frequency over North Indian Ocean in May

Tropical cyclone(TC)activities in the North Indian Ocean(NIO)peak in May during the pre-monsoon period,but the TC frequency shows obvious inter-annual variations.By conducting statistical analysis and dynamic diagnosis of long-term data from 1948 to 2016,the relationship between the inter-annual variations of Indian Ocean SST and NIO TC genesis frequency in May is analyzed in this paper.Furthermore,the potential mechanism concerning the effect of SST anomaly on TC frequency is also investigated.The findings are as follows:1)there is a broadly consistent negative correlation between NIO TC frequency in May and SST in the Indian Ocean from March to May,with the key influencing area located in the southwestern Indian Ocean(SWIO);2)the anomalies of SST in SWIO(SWIO-SST)are closely related to a teleconnection pattern surrounding the Indian Ocean,which can significantly modulate the high-level divergence,mid-level vertical motion and other related environmental factors and ultimately influence the formation of TCs over the NIO;3)the increasing trend of SWIO-SST may play an essential role in the downward trend of NIO TC frequency over the past 69 years.

Statistical characteristics and mechanisms of mesoscale eddies in the North Indian Ocean

The statistical characteristics and mechanisms of mesoscale eddies in the North Indian Ocean are investigated by adopting multi-sensor satellite data from 1993 to 2019.In the Arabian Sea(AS),seasonal variation of eddy characteristics is remarkable,while the intraseasonal variability caused by planetary waves is crucial in the Bay of Bengal(BOB).Seasonal variation of the eddy kinetic energy(EKE)is distinct along the west boundary of AS,especially in the Somali Current region.In the BOB,larger EKE occurs at the northwest basin from March to May,to the east of Sri Lanka from June to September,and along the east coast of India from November to December.The wind stress work(WW)is further studied to figure out the direct influence of wind forcing on EKE.The WW exerts positive effects on EKE along the west boundary of AS and in the south of India/Sri Lanka during the two monsoon seasons.Besides,the WW also has impact on EKE along the east coast of India in November and December.Eventually,we investigate the characteristics and the driving mechanisms of long lifespan eddies.In the AS,long lifespan anti-cyclonic eddies(AEs)mainly generate in the Socotra,the West Indian Coastal Current and the East Arabian Current regions,while cyclonic eddies(CEs)are concentrated in the northwest region.In the BOB,long lifespan AEs mostly form near the west of Myanmar,while CEs are accumulated at the north and northwest basin.The instabilities caused by Rossby waves,coastal Kelvin waves,seasonal currents,together with wind stress forcing exert enormous efforts on the generation and evolution of these eddies.

Seasonal Behaviour of Mesoscale Eddy Trajectories in the North Indian Ocean Based on Satellite Altimetry

In the north Indian Ocean (NIO), maps of sea level anomaly from satellite altimetry were analysed from January-1995 to December-2000. The study attempted to trace the trajectories of the individual mesoscale anomalies manually and to understand seasonal changes in terms of phase speed. Mesoscale anomalies are detected as concentric circular shapes and diameters of ~90 km to 600 km and the minimum 30 days life cycle. Relatively higher eddy kinetic energy was noticed in the northwestern region of the NIO. Individual mesoscale anomalies, namely positive (warm, anticyclonic eddies) and negative (cold, cyclonic eddies) showing travelling direction westward in the NIO basins. In autumn, the number of negative anomalies detected is more than positive anomalies and vice versa during summer. The westward propagating positive (negative) anomalies in the Arabian Sea start appearing in winter (spring) along (away from) the west coast of India and west of 65°E;individual anomalies move to the west in spring/summer/autumn and collide along Somalia’s & Arabian coast. A group of positive (negative) anomalies trajectories appears as a tail at the southern tip of India are located west of the Laccadive ridge in winter (summer to autumn) associated with LH (LL). The Bay of Bengal (BB) trajectories show southwestward in northern BB, westward in central BB and northwestward in southern BB;individual anomalies are appearing along the west coast of Andaman & Nicobar ridge. The zonal phase speed decreases away from the equator, and the magnitude varies longitudinally in each season in the form of a wave-like pattern propagating westward from autumn to summer;the life cycle of the wave is almost 365 days (a year). The theoretical phase speed of the first mode of the baroclinic Rossby waves is quite similar to that of averaged zonal speed. Therefore mesoscale anomalies (eddies) are embedded into the large waves like phenomenon (Rossby waves), responsible for creating high variability and EKE in the region of NIO along the western boundaries.

Observed Relationship between Surface Freshwater Flux and Salinity in The North Indian Ocean

Using 10-year (2001 10) monthly evaporation, precipitation, and sea surface salinity (SSS) datasets, the relationship between local freshwater flux and SSS in the north Indian Ocean (NIO) is evaluated quantitatively. The results suggest a highly positive linear correlation between freshwater flux and SSS in the Arabian Sea (correlation coefficient, R=0.74) and the western equatorial Indian Ocean (R=0.73), whereas the linear relationships are relatively weaker in the Bay of Bengal (R=0.50) and the eastern equatorial Indian Ocean (R=0.40). Additionally, the interannual variations of freshwater flux and SSS and their mutual relationship are investigated in four sub- regions for pre-monsoon, monsoon, and post-monsoon seasons separately. The satellite retrievals of SSS from the Soil Moisture and Ocean Salinity (SMOS) and Aquarius missions can provide continuous and consistent SSS fields for a better understanding of its variability and the differences between the freshwater flux and SSS signals, which are commonly thought to be linearly related.

Local intraseasonal air-sea relationship over the North Indian Ocean and western North Pacific during the spring-to-summer transition

该工作研究了1998-2013年春夏转换期间的两种主要模态的局地季节内海气相互作用。大气要素场和海表热通量在高频尺度上(10-20天)显示出更大的变率。在北印度洋,南海和菲律宾海,30-60天的海温和海表热通量的显著相关区域更大,并且相关系数更高。结果表明在两个时间尺度上在北印度洋,南海和西北太平洋存在强烈的局地海气相互作用,然而海气相互作用的强度取决于区域和要素的选取方式。

Impact of Tropical Cyclones over the North Indian Ocean on Weather in China and Related Forecasting Techniques:A Review of Progress

Tropical cyclones(TCs)over the North Indian Ocean(NIO)are closely related to Asian summer monsoon activities and have a great impact on the precipitation in the Tibetan Plateau,southwestern China,and even the middle and lower reaches of the Yangtze River.In this paper,the research progress on the impacting mechanisms of NIO TCs on the weather in China and associated forecasting techniques is synthesized and reviewed,including characteristics of the NIO TC activity,its variability under climate change,related precipitation mechanism,and associated forecasting techniques.On this basis,the limitations and deficiencies in previous research on the physical mechanisms and forecasting techniques of NIO TCs affecting the weather in China are elucidated and the directions for future investigations are discussed.

North Indian Ocean tropical cyclone activities influenced by the Indian Ocean Dipole mode

Using Joint Typhoon Warning Center tropical cyclone(TC)track data over the North Indian Ocean(NIO),National Centers for Environmental Prediction monthly reanalysis wind and outgoing long-wave radiation data,and National Oceanic and Atmospheric Administration sea surface temperature data from 1981 to 2010,spatiotemporal distributions of NIO TC activity and relationships with local sea surface temperature(SST)were studied with statistical diagnosis methods.Results of empirical orthogonal function(EOF)analysis of NIO TC occurrence frequency show that the EOF1 mode,which accounts for 16%of total variance,consistently represents variations of TC occurrence frequency over the whole NIO basin.However,spatial dis- tributions of EOF1 mode are not uniform,mainly indicating variations of westward-moving TCs in the Bay of Bengal.The prevailing TC activity variation mode oscillates significantly on a quasi-5 year interannual time scale.NIO TC activity is notably influenced by the Indian Ocean dipole(IOD)mode.When the Indian Ocean is in a positive(negative)phase of the IOD, NIO SST anomalies are warm in the west(east)and cold in the east(west),which can weaken(strengthen)convection over the Bay of Bengal and eastern Arabian Sea,and cause anticyclonic(cyclonic)atmospheric circulation anomalies at low levels. This results in less(more)TC genesis and reduced(increased)opportunities for TC occurrence in the NIO.In addition,positive(negative)IOD events may strengthen(weaken)westerly steering flow over the Bay of Bengal,which further leads to fewer(more)westward-moving TCs which appear in regions west of 90°E in that bay.

New discovery of seafloor hydrothermal activity on the Indian Ocean Carlsberg Ridge and Southern North Atlantic Ridge-progress during the 26th Chinese COMRA cruise

The 26th Chinese COMRA （China Ocean Mineral Resources Research ＆ Development Association） cruise was an important cruise. The Carlsberg Ridge （CR） of the Northwest Indian Ocean and the North Atlantic Ridge （NAR）, in which less investigation has been carried out for hydrothermal activities, were investigated and studied during the first two legs of the 26th COMRA cruise. During the first leg, we found one hydrother- mal activity field located in the CR at 3.5^-3.8~ N on the Northwest Indian Ocean Ridge （NWIR）, and sampled seafloor polymetallic sulfide deposits where only abnormalities were found before. During the second leg, we found a new hydrothermal anomaly field located in the NAR at 4^-7~N. The discovery of two hydrother- real and anomaly fields filled in the gap of hydrothermal investigation and study in the corresponding re- ~ions for China.

The Oscillation between Tropical Indian Ocean and North Pacific:Evidence and Possible Impact on Winter Climate in China

This paper provides evidence that the variation of boreal winter sea level pressure (SLP) over the North Pacific is out-of-phase with SLP fluctuation over the tropical Indian Ocean on both the interdecadal and interannual time scales.Subsequently,a SLP between tropical Indian Ocean and North Pacific (TIO-NP) oscillation index is defined to indicate the variation of such out-of-phase fluctuation.Moreover,the simultaneous surface air temperature and precipitation anomalies in China are closely related to TIO-NP oscillations.Below-normal surface air temperature anomalies in the northern and the eastern part of China,and less rainfall in southern China,correspond to positive TIO-NP oscillation phase with negative SLP anomalies in tropical Indian Ocean and positive anomalies in North Pacific.The TIO-NP oscillation affects China's winter climate anomalies,possibly through modulating the northeast East Asia winter monsoon.

APPLICATION OF FUZZY CLUSTERING TECHNIQUE FOR ANALYSIS OF NORTH INDIAN OCEAN TROPICAL CYCLONE TRACKS

A fuzzy, c-means(FCM) clustering technique is explored to investigate the track of tropical cyclones over the North Indian Ocean(NIO) for the period(1976-2014). A total of fi ve clusters is objectively identifi ed based on partition index,partition coeffi cient, Dunn Index and separation index. The results obtained during analysis emphasized that each cluster has the unique features in terms of their genesis location, landfall, travel duration, trajectory, seasonality, accumulated cyclone energy and Intensity. Analysis of large scale environmental parameters, constructed preceding day of genesis show some of these parameters to be potential precursors to TC formation for almost all the clusters, most prominently, mid-tropospheric humidity, zonal wind,vorticity and outgoing long wave radiation of the main developing regions. The individual clusters have the several distinct features in their seasonal cycles.The cluster C5 shows distinct bimodal distributions where as other clusters are formed throughout the year. ENSO infl uenced the cyclone frequency in two of the fi ve clusters. The MJO is found to play an important role in the genesis of the cyclone. The post monsoon season cyclone frequency is more in MJO phase 2, 3 and 4. The technique(FCM) can be used as a guideline in terms of the probable affected zone of TC Tracks by the operational forecasters.

Prediction and mechanistic analysis of May precipitation in North China based on April Indian Ocean SST and the Northwest Pacific Dipole

尽管华北区域五月降水(NCMP)占华北区域年总降水量的比率较少,但是其气候变率较大,对华北区域气候和农业生产等具有重要影响.基于观测和再分析资料,发现NCMP与前期四月的印度洋海温(IOSST)和西北太平洋偶极子(NWPD)具有显著关系,NCMP可能受到IOSST和NWPD的协同影响.进一步分析表明,前期四月暖(冷)的IOSST和正(负)位相的NWPD能够分别通过调节印度洋和西北太平洋区域的局地环流增强(减弱)从印度洋和西北太平洋向华北区域输送的水汽,进而增强(减弱)NCMP.最后基于四月IOSST和NWPD构建了NCMP异常的预测模型,后报检验显示该模型对NCMP异常具有较好的预测能力.

The Trend of Changes in Surface Wind in the Indian Ocean, in the Period from 1981 to 2015, Using Reanalysis Data, NCEP/NCAR

Knowing the pattern of surface winds on the seas and oceans and how it changes over time is of great importance. In this research, the monthly surface wind fields on the Indian Ocean have been studied and analyzed for a 35-year period (1981-2015), using NCEP/NCAR data reanalysis. The results show that transition from cold to warm pattern happens in May and that the summer monsoon pattern begins in June and continues until August. The wind speed pattern tends to the winter monsoon from November on. The maximum average wind speed in June is 13 m/s and its minimum is 2 m/s in October. Direction of prevailing winds is the southwest in the summer. The highest wind speed happens in the latitude of 10 - 15 degrees. Analysis of the wind distribution shows that the wind speed of 2 - 5 m/s happens in about 60% of the cases. There is probability of blowing 0.5 - 4 m/s wind for all months;but this probability is higher in the autumn (October and November) than that in the summer (July and August). Probability of the monthly over 5 m/s winds shows a definitely opposite distribution;that is, wind speed in July and August is higher than that in October. A long-term survey on the speed of surface water wind and sea surface temperature shows an opposite changing trend in wind speed and sea surface temperature during a 55-year statistical period. Wind speed reduced, while the sea surface temperature was increasing. The wind speed gradient in the upper levels of atmosphere graph has been increasing;this phenomenon confirms the effects of global warming and ocean warming on the monsoon system patterns in the Indian Ocean. Keywords

东亚夏季风与热带海气相互作用研究进展

在东亚夏季风变异的众多影响因子中,热带海温是影响夏季风系统变化的主要原因。近年来,国内外学者在热带海温异常对东亚夏季风影响的研究方面取得了很大进展。本文从季节内、年际到年代际时间尺度,简要回顾了近年来关于热带海气相互作用影响东亚夏季风变异及其机理的研究进展,特别综述了关于ENSO(El Ni?o-Southern Oscillation)、热带印度洋和大西洋海温异常对东亚夏季风系统的影响和机理方面的主要研究进展。此外,本文还系统回顾了热带海温对东亚夏季风与冬季风关联的影响及过程。最后,提出了在热带海温异常影响东亚夏季风季节内尺度变化、全球变暖下热带海温的变化及其对东亚夏季风的影响等方面值得深入探讨的科学问题。

Climatological and Seasonal Variations of the Tropical Cyclone Genesis Potential Index Based on Oceanic Parameters in the Global Ocean

This study investigates the global performance of the tropical cyclone(TC)genesis potential index based on oceanic parameters(GPI_(ocean))proposed by Zhang et al.(2016).In six major TC formation basins,GPI_(ocean)can represent the seasonal variations of TC genesis over most basins,except for the North Indian Ocean(NIO).The monthly climatological GPI_(ocean)shows only a single peak in the NIO,which cannot describe the bimodal pattern of the annual cycle of TC genesis.To determine the cause of the poor performance of GPI_(ocean)in the NIO,the relative contributions of different parameters related to GPI_(ocean)are calculated and compared with those related to the genesis potential index developed by Emanuel and Nolan(2004)(GPI04).Results show that the net longwave radiation on the sea surface is responsible for the single peak of TC genesis in the NIO in boreal summer.Compared with GPI04,vertical wind shear is not involved in GPI_(ocean).Vertical wind shear is the dominant factor inhibiting TC genesis in the NIO in boreal summer.Therefore,the absence of vertical wind shear in GPI_(ocean)results in the failure of the annual cycle of TC genesis in the NIO.

Importance of Aerosol Optical Depth in the Atmospheric Correction of Ocean Colour Remote Sensing Data

Atmospheric aerosols being an important component of the atmosphere play an important role in global and regional climate change. Aerosols can affect air quality, climate change and human health and have a significant effect on the solar energy budget. To study their quantitative effect is a challenging task due to their high spatial and temporal variability. This parameter represents one of the extinction coefficients of solar radiation and rate of suspended particles in the atmosphere. Ocean Colour Remote Sensing provides information about the four major geophysical parameters like chlorophyll and total suspended sediment concentration, vertical diffuse attenuation co-efficient and the aerosol optical thickness measured at 865 nm. Aerosol optical depth can be expressed as function of wavelength through Angstrom’s equation ?, where “α” and “β” are known as Angstrom parameters. The Angstrom exponent, “α” is related to the size distribution of the aerosol particles and “β” represents the amount of aerosols present in the atmosphere. In this present study, an attempt is made to study the impact of these two parameters by changing values from 0 to 0.05 for “α” and from 0.0 to 0.6 for “β” in SeaDAS processing for estimating the aerosol optical depth. From this study, it is clear that for most of the applications either in the coastal or open ocean waters, alpha value varies from 0.0 to 0.3 over the north Indian Ocean. However, this has been further evaluated by various combinations for retrieving the AOD using OCM-2 data.

公元1世纪北印度洋奴隶贸易丛考——以《厄立特里亚海周航志》为中心

在西方古典著作中,广义的厄立特里亚海可以泛指北印度洋,其范围大致包括红海、阿拉伯海、波斯湾以及孟加拉湾等海域。成书于1世纪的《厄立特里亚海周航志》详细记录了当时北印度洋沿岸的海上贸易,奴隶是这片海域贸易往来中颇受青睐的货品。位于非洲之角的马拉欧和奥波内以及波斯地区的阿波罗格斯和奥马纳是奴隶的主要来源地。这些奴隶大多被运往迪奥斯库里德斯岛、婆卢羯车与埃及三地。乐奴是众多奴隶中最为特殊的一种,他们主要供上层尤其是权贵娱乐。奴隶贸易的开展除了受市场调节之外,还与季风、洋流等自然气候息息相关。

印度尼西亚北苏拉威西岛弧岩浆作用及其对板块俯冲起始的制约

板块俯冲起始是板块构造理论的核心内容,但却研究最为薄弱。印度尼西亚北苏拉威西岛弧是始新世期间开始发育的一个印度洋洋内弧,其记录了多期次(包括印度洋、马鲁古海和西里伯斯海)的且处于不同演化阶段的俯冲作用及相应的俯冲起始过程,因此该岛弧是研究板块俯冲起始的天然实验室。本文通过回顾板块俯冲起始研究进展,结合北苏拉威西岛弧内已有的野外调查、锆石U-Pb定年、岩石地球化学特征等,以厘清区域内岛弧岩浆的岩石类型、形成时代、空间分布和岩浆活动节律,制约岛弧岩浆的构造背景和岩浆源区性质等,并着重关注该岛弧内可能与板块俯冲起始相关的地质和岩石记录,如弧前玄武岩、玻安岩、俯冲带(SSZ)型蛇绿岩、变质底板等。在此基础上,综合限定北苏拉威西岛弧记录的印度洋洋壳俯冲历史,探讨其俯冲起始的时间与地球动力学机制。本文仅抛砖引玉,期待更多学者参与到北苏拉威西岛弧板块俯冲起始的研究中来。

我国华南3月份降水异常的可能影响因子分析

利用1951～2005年华南地区3月份的降水资料、NOAA海温资料、Nio3.4指数和NCEP再分析资料,分析了华南3月份降水异常与同期环流场、全球海温场的关系,从环流和海温的角度揭示了华南3月份降水异常的可能原因。结果表明,当华南3月份降水偏多(少)时,在对流层中低层,北太平洋海区存在气旋(反气旋)性环流异常,西太平洋及南海海面上存在反气旋(气旋)性环流异常,这样的环流异常有利(不利)于东南暖湿气流与北方东部异常冷空气在华南地区形成水汽辐合,导致降水显著增多(减少)。进一步的分析表明,ENSO和北印度洋及南海附近海温是影响华南3月份降水异常的重要外强迫因子,ENSO对华南3月降水异常的影响是通过影响春季西太平洋副热带高压和低层风场异常实现的,而北印度洋及南海附近海温对华南3月降水异常的影响则是通过垂直环流场异常和低层风场以及西太平洋副热带高压异常来实现的。

近45年南海-北印度洋波浪能资源评估

利用ERA．40海表101TI风场驱动第三代海浪数值模式（WAVEWATCH-Ⅲ，简称WW3），得到南海-北印度洋1957年9月～2002年8月的海浪资料，计算该海域的波浪能，分析波浪能流密度的四季分布特征、不同能级出现的频率及波浪能流密度的稳定性，为海浪发电、海水淡化等选址提供依据。研究发现，南海-北印度洋海域蕴藏着较为丰富的波浪能：（1）南海-北印度洋大部分海域的年平均波浪能流密度在2kW／m以上，大值区位于南海、孟加拉湾、索马里附近海域。（2）南海=北印度洋海域波浪能流密度大于2kW／m和大于4kW／m出现的频率都较高。（3）南海-北印度洋的波浪能流密度具有较好的稳定性，春季、秋季、冬季的稳定性好于夏季，南海的稳定性好于北印度洋。

北印度洋气候特点分析

根据1950～1995年共46a的北印度洋气象船舶资料,按5°×5°网格统计单元,绘制了历年各月风向频率、平均风速、6级和8级大风、能见度(≥10km和≤4km)、雾和雷暴等气象要素分布图。较为详细地分析了北印度洋风、能见度、雾、雷暴、热带气旋等海洋气象要素的分布特点及其年变化规律。该区是世界著名的季风气候区,夏季的西南季风比冬季东北季风强盛,与我国南海海区的季风特点正好相反。