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 diagnosi...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.展开更多
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...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.展开更多
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...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.展开更多
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. ...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.展开更多
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 a...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.展开更多
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 Nation...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.展开更多
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...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.展开更多
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 interan...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.展开更多
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 bas...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.展开更多
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...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展开更多
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 ...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.展开更多
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...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.展开更多
基金National Natural Science Foundation of China(41965005,41790471,42075013)Key R&D Plan of Yunnan Province Science and Technology Department(202203AC100006)National Natural Science Foundation of Yunnan Province(202201AS070069)。
文摘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.
基金The National Key Research and Development Program of China under contract No.2019YFC1510000the National Natural Science Foundation of China under contract Nos 41976019 and 41906009.
文摘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.
文摘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.
文摘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.
基金jointly supported by the National Basic Research Program of China[grant numbers 2014CB953902 and2015CB453202]the Strategic Leading Science Projects of the Chinese Academy of Sciences[grant number XDAl 1010402]the National Natural Science Foundation of China[grant numbers 41305065,41305068,and 91337216]
基金Supported by the National Natural Science Foundation of China(41930972 and 52078480)。
文摘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.
基金supported by the National Natural Science Foundation of China (Grant No.U0933603)Special Scientific Research Fund of Meteorological Public Welfare Profession of China(Grant No.GYHY201106005)+1 种基金Natural Science Foundation of Yunnan Province(Grant No.2009CC002)Youth Foundation of Yunnan Province(Grant No.2012FD001)
文摘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.
基金the National Basic Research Program of China under contract No. 2012CB417305China Ocean Mineral Resources Research & Development Association Project under contract No. DY125-11Endowment Fund of International Seabed Authority (the International Cooperative Study on Hydrothermal System at Ultraslow Spreading SWIR)
文摘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.
基金supported by the National Basic Research Program of China (973 Projects) under Grant 2011CB309704the National Special Scientific Research Project for Public Interest under Grant 201006021the National Natural Science Foundation of China under Grants 40890155,U0733002,and 40810059005
文摘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.
文摘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.
文摘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
基金the Strategic Priority Re-search Program of the Chinese Academy of Sciences(No.XDA20060502)the National Key Research and Devel-opment Program of China(No.2019YFA0606701)+2 种基金the National Natural Science Foundation of China(Nos.41925024 and 41731173)the Pioneer Hundred Talents Program of the Chinese Academy of Sciences,the Leading Talents of Guangdong Province Program,Innovation Academy of South China Sea Ecology and Environmental Engineering,Chinese Academy of Sciences(No.ISEE2018PY06)the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Lab-oratory(Guangzhou)(No.GML2019ZD0306).
文摘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.
文摘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.