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1.
Typhoons can cause substantial sea surface cooling (typically 2–4 °C), which is usually biased to the right side of the storm track. Under influence of the complex bathymetry of the southern Taiwan Strait (TS), two types of sea surface temperature (SST) response, cooling and warming, each associated with a different type of typhoon track were identified using satellite and mooring observations. When a typhoon moved westward (or northwestward) and passed through the TS (track A), the SST cooling in the TS was biased toward the left of the storm track. Numerical model results indicated that in track A, strong wind stress accelerates the flow east of the Taiwan Banks and drove the bottom flow to uplift due to the topography. Moreover, both wind stress and wind stress curl enhanced the Luzon loop. After the typhoon passed, the mean circulation was modified around strong cooling in the southern TS, causing more South China Sea surface water to be distributed to the Kuroshio region. However, when a typhoon moved westward (or northwestward) and passed south of the TS, SST warming was induced in the southern TS (track B). The model results indicated that when the typhoon passed to the south of the TS, the typhoon-induced horizontal divergent flow travelled to the north, where it encountered the shallower shelf of the TS that was confined to the water, causing warm water transported into this area to accumulate and downwelling to occur. This can be regarded as redistributing the heat content in the shelf area. After the typhoon, the thickened mixed layer resulting from downwelling prevented the formation of near-inertial waves and reduced the vertical mixing.  相似文献   

2.
The Luzon Strait (LS) is a wide channel between Taiwan and the Luzon islands. Eastward of the LS, the Kuroshio Current (KC) flows northward along the eastern coasts of Luzon and Taiwan. A typhoon is a strong and localized low-pressure weather system that occurs frequently in the vicinity of the Taiwan area. One typical typhoon track, passing through the seas surrounding Taiwan, is a zonal path across the LS. The satellite measured SST, corresponding to typhoons Pabuk (5 Aug. 2007–12 Aug. 2007) and Dujuan (29 Aug. 2003–5 Sep. 2003), which both moved along this path, demonstrated that a classic right bias cooling occurs to the north of the storm track, during the typhoon forced period. However, some cold anomaly water also present toward left (south) of the storm track east of the LS in the relaxation period. This paper adopted a three-dimensional hydrostatic primitive equation model to study the possible causes of this southward transport of cold waters. Both model results and the observed SST anomaly revealed that the strength of the upper ocean cooling depends on whether a resonant regime between the typhoon winds and the near-inertial currents can be excited. To the east of the LS, the convergence between the warm Kuroshio water and the cold wakes in the poststorm period will enhance the southward spreading of cold anomaly water. The enhanced vertical mixing, induced by the southward propagation of nearly inertial waves associated with the cold wakes, can also produce some cold anomaly to the south of a storm track in the poststorm period. Both mechanisms can contribute to the occurrence of some cold anomaly water to the south of the storm track east of the KC. To the west of the LS, the convergence between the warm Kuroshio water and the cold upwelling water from the northern South China Sea can further strengthen the Kuroshio front in the LS.  相似文献   

3.
How would typhoon activity over the western North Pacific change for various scenarios of future global warming?Using the model projections of the Coupled Model Intercomparison Project phase 3(CMIP 3)under the SRES A1B scenario,we generated summer(September)ice-free Arctic conditions,also referred to as Blue Arctic conditions,and then used the corresponding monthly sea surface temperature(SST)and a set of CO2concentrations to drive an AGCM model to simulate the resulting changes in background conditions affecting typhoon activity over the western North Pacific.Our results show that,during typhoon season(June to October),atmospheric and ocean circulations over the western North Pacific would be significantly different from the present circulations.Changes in the vertical shear of zonal wind and outgoing longwave radiation(OLR)in the western North Pacific are favorable for westward and northward shift,respectively,of the location of typhoon genesis.Moreover,changes in the above fields over the key area may be conducive to less frequent typhoons.In addition,the tropical cyclone genesis potential index(GPI)over the western North Pacific would decrease(increase)east(west)of 150°E(140°E).  相似文献   

4.
This study proposed three algorithms that can potentially be used to provide sea surface temperature (SST) conditions for typhoon prediction models. Different from traditional data assimilation approaches, which provide prescribed initial/boundary conditions, our proposed algorithms aim to resolve a flow-dependent SST feedback between growing typhoons and oceans in the future time. Two of these algorithms are based on linear temperature equations (TE-based), and the other is based on an innovative technique involving machine learning (ML-based). The algorithms are then implemented into a Weather Research and Forecasting model for the simulation of typhoon to assess their effectiveness, and the results show significant improvement in simulated storm intensities by including ocean cooling feedback. The TE-based algorithm I considers wind-induced ocean vertical mixing and upwelling processes only, and thus obtained a synoptic and relatively smooth sea surface temperature cooling. The TE-based algorithm II incorporates not only typhoon winds but also ocean information, and thus resolves more cooling features. The ML-based algorithm is based on a neural network, consisting of multiple layers of input variables and neurons, and produces the best estimate of the cooling structure, in terms of its amplitude and position. Sensitivity analysis indicated that the typhoon-induced ocean cooling is a nonlinear process involving interactions of multiple atmospheric and oceanic variables. Therefore, with an appropriate selection of input variables and neuron sizes, the ML-based algorithm appears to be more efficient in prognosing the typhoon-induced ocean cooling and in predicting typhoon intensity than those algorithms based on linear regression methods.  相似文献   

5.
赤道MJO活动对南海夏季风爆发的影响   总被引:6,自引:0,他引:6       下载免费PDF全文
利用1979—2013年NCEP/DOE再分析资料的大气多要素日平均资料、美国NOAA日平均向外长波辐射资料和ERSST月平均海温资料,分析赤道大气季节内振荡(简称MJO)活动对南海夏季风爆发的影响及其与热带海温信号等的协同作用.结果表明,赤道MJO活动与南海夏季风爆发密切联系,MJO的湿位相(即对流活跃位相)处于西太平洋位相时,有利于南海夏季风爆发,而MJO湿位相处于印度洋位相时,则不利于南海夏季风爆发.赤道MJO活动影响南海夏季风爆发的物理过程主要是大气对热源响应的结果,当MJO湿位相处于西太平洋位相时,一方面热带西太平洋对流加强使潜热释放增加,导致处于热源西北侧的南海—西北太平洋地区对流层低层由于Rossby响应产生气旋性环流异常,气旋性环流异常则有利于西太平洋副热带高压的东退,另一方面菲律宾附近热源促进对流层高层南亚高压在中南半岛和南海北部的建立,使南海地区高层为偏东风,从而有利于南海夏季风建立;当湿位相MJO处于印度洋位相时,热带西太平洋对流减弱转为大气冷源,情况基本相反,不利于南海夏季风建立.MJO活动、孟加拉湾气旋性环流与年际尺度海温变化协同作用,共同对南海夏季风爆发迟早产生影响,近35年南海夏季风爆发时间与海温信号不一致的年份,基本上是由于季节转换期间的MJO活动特征及孟加拉湾气旋性环流是否形成而造成,因此三者综合考虑对于提高季风爆发时间预测水平具有重要意义.  相似文献   

6.
Rationalized by the observational circulation pattern in the upper ocean of the North Pacific, meridional friction term is first incorporated in a barotropic theoretical model of the wind-driven circulation. The governing potential vorticity equation thence has β term and wind stress curl term (the two of the Sverdrup balance), zonal friction term and meridional friction term. The analytical solution satisfactorily captures many important features of the wind-driven circulation in the North Pacific: Kuroshio, Oyashio, Kuroshio extension, North Equatorial Current, and especially the eastern boundary currents in the North Pacific, i.e. California current and Alaska current.  相似文献   

7.
Barotropic responses of the East China Sea to typhoon KOMPASU are investigated using a high-resolution, three-dimensional, primitive equation, and finite volume coastal ocean model. Even the fact that the typhoon KOMPASU only brushed across the brink of China mainland without landing, it still imposed great influence across China's east coastal area, where storm surges ranging from 35 to 70 cm were intrigued during this event and a large wake of water setdown due to the outward radial transport driven by the cyclonic wind stress was generated after the KOMPASU traveled across the Yellow Sea. Analysis of the numerical results reveals that the barotropic waves propagating along the coast after the typhoon's landing can be identified as Kelvin wave and the currents associated with the storm are geostrophic currents. A series of model runs are initiated to diagnose the effects of wind stress, atmospheric pressure, and storm track variation on the surge's spatial distribution in the East China Sea. The barotropic waves affected by the atmospheric disturbance due to the typhoon in deep Pacific Ocean travel far more rapidly, arriving at the coastal regions at least 60 h ahead of the typhoon. The wave amplitudes are merely 0.2–0.4 cm and damp gradually due to friction. The model experiments also confirm that the surge levels in nearshore regions are highly dominated by winds, whereas the water level variations in deeper areas are controlled by the atmospheric pressure forcing during typhoon events in the East China Sea.  相似文献   

8.
An operational storm surge forecasting system aimed at providing warning information for storm surges has been developed and evaluated using four typhoon events. The warning system triggered by typhoon forecasts from Taiwan Cooperative Precipitation Ensemble Forecast Experiment (TAPEX) has been executed with two storm surge forecasting scenarios with and without tides. Three numerical experiments applying different meteorological inputs have been designed to assess the impact of typhoon forcing on storm surges. One uses synthetic wind fields, and the others use realistic wind fields with and without adjustments to the initial wind fields for the background circulation. Local observations from Central Weather Bureau (CWB) weather stations and tide gauge stations are used to evaluate the wind fields and storm surges from our numerical experiments. The comparison results show that the accuracy of the storm surge forecast is dominated by the track, the intensity, and the driving flow of a typhoon. When the structure of a typhoon is disturbed by Taiwan’s topography, using meteorological inputs from real wind fields can result in a better typhoon simulation than using inputs from synthetic wind fields. The driving flow also determines the impact of topography on typhoon movement. For quickly moving typhoons, storm forcing from TAPEX is reliable when a typhoon is strong enough to be relatively unaffected by environmental flows; otherwise, storm forcing from a sophisticated typhoon initialization scheme that better simulates the typhoon and environmental flows results in a more accurate prediction of storm surges. Therefore, when a typhoon moves slowly and interacts more with the topography and environmental flows, incorporating realistic wind fields with adjustments to the initial wind fields for the background circulation in the warning system will obtain better predictions for a typhoon and its resultant storm surges.  相似文献   

9.
As large-scale ocean circulation is a key regulator in the redistribution of oceanic energy, evaluating the multi-decadal trends in the western Pacific Ocean circulation under global warming is essential for not only understanding the basic physical processes but also predicting future climate change in the western Pacific. Employing the hydrological observations of World Ocean Atlas 2018(WOA18) from 1955 to 2017, this study calculated the geostrophic currents, volume transport and multidecadal trends for the North Equatorial Current(NEC), the North Equatorial Countercurrent(NECC), the Mindanao Current(MC), the Kuroshio Current(KC) in the origin and the New Guinea Coastal Undercurrent(NGCUC) within tropical western Pacific Ocean over multi-decades. Furthermore, this study examined the contributions of temperature and salinity variations. The results showed significant strengthening trends in NEC, MC and NGCUC over the past six decades, which is mainly contributed by temperature variations and consistent with the tendency in the dynamic height pattern. Zonal wind stress averaged over the western Pacific Ocean in the same latitude of each current represents the decadal variation and multi-decadal trends in corresponding ocean currents, indicating that the trade wind forcing plays an important role in the decadal trend in the tropical western Pacific circulation. Uncertainties in the observed hydrological data and trends in the currents over the tropical western Pacific are also discussed. Given that the WOA18 dataset covers most of the historical hydrological sampling data for the tropical western Pacific, this paper provides important observational information on the multi-decadal trend of the large-scale ocean circulation in the western Pacific.  相似文献   

10.
The relationship between the sea ice cover in the North Pacific and the typhoon frequency has been studied in this paper. It follows that the index for the sea ice cover in the North Pacific (ISA) both in December-January-February (DJF) and in March-April-May (MAM) is negatively correlated with annual typhoon number over the western North Pacific (TNWNP) during 1965―2004, with correlation coeffi-cients of -0.42 and -0.49 respectively (above 99% significant level). Large sea ice cover in the North Pacific tends to decrease TNWNP. Positive ISA (MAM) is associated with the tropical circulation and SST anomalies in the North Pacific, which may lead to unfavorable dynamic and thermal conditions for typhoon genesis over WNP from June to October (JJASO). The variability of the atmospheric circula-tion over the North Pacific, associated with the ISA anomaly in MAM is connected to the tropical at-mospheric circulation variability in MAM via the teleconnection wave train. Besides, as the tropical circulation has strong seasonal persistency from the MAM to JJASO, thus, the ISA in MAM-related variability of the tropical atmospheric circulation as well as the SST can affect the typhoon activity over the western North Pacific.  相似文献   

11.
本文使用欧洲ECMWF(ERA40)再分析资料,通过经验正交函数(Empirical Orthogonal Function,EOF)分解探讨了冬季北太平洋风暴轴的变异特征,使用回归分析得到了与风暴轴空间异常型相关的冬季大气平均流异常、表层海温(Sea Surface Temperature,SST)异常的空间耦合型.研究结果表明,冬季北太平洋风暴轴主要有两种空间异常型,第一种是风暴轴中东部明显北抬(南压),使得整个风暴轴向东北(东南)倾斜,与此同时,在中纬度北太平洋海区,冬季暖(冷)异常的洋面上是异常高压(低压),海气系统在垂直向表现为一种暖脊(冷槽)配置,在对流层中高层是太平洋-北美(Pacific North American,PNA)型负(正)位相.第二种是风暴轴整体性加强(减弱)并偏北(南),此时,黑潮区海温异常偏暖(冷),低层阿留申低压和高空的西风急流略偏北(南),对流层中高层表现为西太平洋(Western Pacific,WP)型负(正)位相.风暴轴EOF分解的时间系数与阿留申低压指数、PNA指数、WP指数,以及与尼诺3区(NINO3)指数、黑潮海温指数间显著的相关性再次证实了在北太平洋中纬度地区存在着SST异常、风暴轴异常和大气平均流异常三者间的空间耦合型.  相似文献   

12.
A coupled ocean and boundary layer flux numerical modeling system is used to study the upper ocean response to surface heat and momentum fluxes associated with a major hurricane, namely, Hurricane Dennis (July 2005) in the Gulf of Mexico. A suite of experiments is run using this modeling system, constructed by coupling a Navy Coastal Ocean Model simulation of the Gulf of Mexico to an atmospheric flux model. The modeling system is forced by wind fields produced from satellite scatterometer and atmospheric model wind data, and by numerical weather prediction air temperature data. The experiments are initialized from a data assimilative hindcast model run and then forced by surface fluxes with no assimilation for the time during which Hurricane Dennis impacted the region. Four experiments are run to aid in the analysis: one is forced by heat and momentum fluxes, one by only momentum fluxes, one by only heat fluxes, and one with no surface forcing. An equation describing the change in the upper ocean hurricane heat potential due to the storm is developed. Analysis of the model results show that surface heat fluxes are primarily responsible for widespread reduction (0.5°–1.5°C) of sea surface temperature over the inner West Florida Shelf 100–300 km away from the storm center. Momentum fluxes are responsible for stronger surface cooling (2°C) near the center of the storm. The upper ocean heat loss near the storm center of more than 200 MJ/m2 is primarily due to the vertical flux of thermal energy between the surface layer and deep ocean. Heat loss to the atmosphere during the storm’s passage is approximately 100–150 MJ/m2. The upper ocean cooling is enhanced where the preexisting mixed layer is shallow, e.g., within a cyclonic circulation feature, although the heat flux to the atmosphere in these locations is markedly reduced.  相似文献   

13.
In the austral summer of 1992–1993 the passage of a storm system drove a strong upper ocean response at 45°S in the mid-South Atlantic. Good in situ observations were obtained. CTD casts revealed that the mixed layer deepened by \sim40 m over 4 days. Wind stirring dominated over buoyancy flux-driven mixing during the onset of high winds. Doppler shear currents further reveal this to be intimately related to inertial dynamics. The penetration depth of inertial currents, which are confined to the mixed layer, increases with time after a wind event, matched by a downward propagation of low values of the Richardson number. This suggests that inertial current shear is instrumental in producing turbulence at the base of the mixed layer. Evolution of inertial transport is simulated using a time series of ship-observed wind stress. Simulated transport is only 30-50% of the observed transport, suggesting that much of the observed inertial motion was forced by an earlier (possibly remote) storm. Close proximity of the subtropical front further complicates the upper ocean response to the storm. A simple heat balance for the upper 100 m reveals that surface cooling and mixing (during the storm) can account for only a small fraction of an apparent \sim1 °C mixed layer cooling.  相似文献   

14.
Three prominent features of ocean surface turbulent heat fluxes (THF) trends during 1958–2013 are identified based on the Objectively Analyzed air-sea Fluxes (OAFlux) data set. The associated ocean-atmosphere dynamics changes are further investigated based on the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis. First, the THF are enhanced over the mid-latitude expansions of the subtropical western boundary currents (WBCs). An intensified oceanic heat transport, forced by stronger near-surface zonal wind, is likely to be the cause of such THF tendency. Second, the THF are reduced over the tropical eastern Pacific Ocean, which is primarily caused by the decreasing near-surface wind speed and sea surface temperature (SST), associated with a local coupled ocean-atmosphere cooling mode. Finally, the THF are reduced over the northern tropical Atlantic Ocean, which is attributed to the decreasing air-sea humidity and temperature differences as a result of the convergence of near-surface air and the divergence of ocean currents (upwelling).  相似文献   

15.
We investigate the relationship between sea surface temperature (SST) cooling and upwelling along Papua New Guinea’s (PNG) north coast before the onset of El Niño events using a hindcast experiment with a high-resolution ocean general circulation model. Coastal upwelling and related SST cooling appear along PNG north coast during the boreal winter before the onsets of six El Niño events occurring during 1981–2005. Relatively cool SSTs appear along PNG north coast during that time, when anomalous northwesterly surface wind stress, which can cause coastal upwelling by offshore Ekman transport appearing over the region. In addition, anomalous cooling tendencies of SST are observed, accompanying anomalous upward velocities at the base of the mixed layer and shallow anomalies of 27°C isotherm depth. It is also shown that entrainment cooling plays an important role in the cooling of the mixed layer temperature in this region.  相似文献   

16.
Coastal and oceanic SST variability along the western Iberian Peninsula   总被引:1,自引:0,他引:1  
The inter-annual variability of the sea surface temperature (SST) was analyzed along the western Iberian Peninsula in the region ranging from 9.5 °W to 21.5 °W and from 37.5 °N to 42.5 °N with a spatial resolution of 1°×1° from 1900 to 2008. Both coastal and oceanic SST showed an overall increase with warming and cooling cycles similar to those observed in the North Atlantic region and in previous regional studies. In addition, the evolution of coastal and ocean water has been observed to be different. In general, ocean water is more affected by the different warming–cooling cycles than coastal water. In spite of coast and ocean are highly influenced by global changes affecting the whole North Atlantic region, near shore SST has been observed to be correlated with local wind regime, which is itself a manifestation of the Eastern Atlantic (EA) teleconnection pattern.  相似文献   

17.
Kodaira  Tsubasa  Waseda  Takuji 《Ocean Dynamics》2019,69(11):1373-1385

The Kuroshio current is well known for generating cold wakes behind islands over Izu Ridge in Northwestern Pacific. Observational data from the geostationary Himawari-8 satellite for 2015–2017 revealed the occurrence of cold waters during the period when the Kuroshio current flows away from the islands. With a focus on tidal currents, this study presents an investigation of dynamical processes responsible for the formation of areas with low sea surface temperature (SST) through the adoption of a high-resolution numerical ocean model for an event that happened in July 2017. Areas with cold water emerged only when tidal currents are included in the numerical model. The model results indicate the cold surface waters are formed in the vicinity of the islands because of upwelling and vertical mixing. Qualitative features of the cold water formation for each island are found to depend on its size, topography, and ambient currents. Near Kozu Island, the tidal excursion is large enough to cause eddy shedding. These shed eddies are stirred by tidal currents to extend the surface cooling effect to wider areas. Near Hachijo Island, a persistent wake is formed by the ambient northward current. Inclusion of tidal currents destabilizes the wake, and consequently leads to the formation of a low SST area, although no clear eddy shedding is detected. The flow patterns around the islands are classified using an additional non-dimensional parameter, defined as the ratio between tidal excursion and island diameter.

  相似文献   

18.
Previous investigations have suggested that wind stress curl, the balance of influx- and outflux-induced upwelling, as well as a positive vorticity source fed from the left flank of the Kuroshio are all possible mechanisms that contribute to a persistent cyclonic gyre in the South China Sea (SCS). Studies have also suggested that the loop current that forms from the Kuroshio intrusion in the Luzon Strait, similar to the Loop Current in the Gulf of Mexico (GOM), has rarely been observed in the northern SCS. In this research, an idealized numerical model driven by annual mean wind stress was adopted to investigate the relative importance of dynamic processes that control the mean flow pattern of Kuroshio in the Luzon Strait and regulate circulation in the SCS. An analysis of results drawn from numerical experiments suggests that the three mechanisms are of approximately equal importance in the formation of the persistent cyclonic gyre in the northern SCS. Unlike the Gulf Stream which enters the Gulf of Mexico through the Yucatan Channel, the two topographic ridges that align nearly meridionally in the Luzon Strait keep the Kuroshio flowing roughly northward without distinct intrusion into the SCS. Unsurprisingly, an anticyclonic loop current similar to the Gulf Stream pathway in the GOM was barely observed in the northern SCS.  相似文献   

19.
Coupled assimilation for an intermediated coupled ENSO prediction model   总被引:4,自引:0,他引:4  
Fei Zheng  Jiang Zhu 《Ocean Dynamics》2010,60(5):1061-1073
The value of coupled assimilation is discussed using an intermediate coupled model in which the wind stress is the only atmospheric state which is slavery to model sea surface temperature (SST). In the coupled assimilation analysis, based on the coupled wind–ocean state covariance calculated from the coupled state ensemble, the ocean state is adjusted by assimilating wind data using the ensemble Kalman filter. As revealed by a series of assimilation experiments using simulated observations, the coupled assimilation of wind observations yields better results than the assimilation of SST observations. Specifically, the coupled assimilation of wind observations can help to improve the accuracy of the surface and subsurface currents because the correlation between the wind and ocean currents is stronger than that between SST and ocean currents in the equatorial Pacific. Thus, the coupled assimilation of wind data can decrease the initial condition errors in the surface/subsurface currents that can significantly contribute to SST forecast errors. The value of the coupled assimilation of wind observations is further demonstrated by comparing the prediction skills of three 12-year (1997–2008) hindcast experiments initialized by the ocean-only assimilation scheme that assimilates SST observations, the coupled assimilation scheme that assimilates wind observations, and a nudging scheme that nudges the observed wind stress data, respectively. The prediction skills of two assimilation schemes are significantly better than those of the nudging scheme. The prediction skills of assimilating wind observations are better than assimilating SST observations. Assimilating wind observations for the 2007/2008 La Niña event triggers better predictions, while assimilating SST observations fails to provide an early warning for that event.  相似文献   

20.
A high-resolution, regional coupled atmosphere–ocean model is used to investigate strong air–sea interactions during a rapidly developing extratropical cyclone (ETC) off the east coast of the USA. In this two-way coupled system, surface momentum and heat fluxes derived from the Weather Research and Forecasting model and sea surface temperature (SST) from the Regional Ocean Modeling System are exchanged via the Model Coupling Toolkit. Comparisons are made between the modeled and observed wind velocity, sea level pressure, 10 m air temperature, and sea surface temperature time series, as well as a comparison between the model and one glider transect. Vertical profiles of modeled air temperature and winds in the marine atmospheric boundary layer and temperature variations in the upper ocean during a 3-day storm period are examined at various cross-shelf transects along the eastern seaboard. It is found that the air–sea interactions near the Gulf Stream are important for generating and sustaining the ETC. In particular, locally enhanced winds over a warm sea (relative to the land temperature) induce large surface heat fluxes which cool the upper ocean by up to 2 °C, mainly during the cold air outbreak period after the storm passage. Detailed heat budget analyses show the ocean-to-atmosphere heat flux dominates the upper ocean heat content variations. Results clearly show that dynamic air–sea interactions affecting momentum and buoyancy flux exchanges in ETCs need to be resolved accurately in a coupled atmosphere–ocean modeling framework.  相似文献   

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