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1.
Boundary-Layer Wind Structure in a Landfalling Tropical Cyclone   总被引：1，自引：0，他引：1  
In this study, a slab boundary layer model with a constant depth is used to analyze the boundary-layer wind structure in a landfalling tropical cyclone. Asymmetry is found in both the tangential and radial components of horizontal wind in the tropical cyclone boundary layer at landfall. For a steady tropical cyclone on a straight coastline at landfall, the magnitude of the radial component is greater in the offshoreflow side and the tangential component is greater over the sea, slightly offshore, therefore the greater total wind speed occurs in the offshore-flow side over the sea. The budget analysis suggests that： （1） a greater surface friction over land produces a greater inflow and the nonlinear effect advects the maximum inflow downstream, and （2） a smaller surface friction over the sea makes the decrease of the tangential wind component less than that over land. Moreover, the boundary layer wind structures in a tropical cyclone are related to the locations of the tropical cyclone relative to the coastline due to the different surface frictions. During tropical cyclone landfall, the impact of rough terrain on the cyclone increases, so the magnitude of the radial component of wind speed increases in the offshore-flow side and the tangential component outside the radius of maximum wind speed decreases gradually.  相似文献   

2.
A statistical comparative analysis of tropical cyclone activity over the Arabian Sea and Bay of Bengal (BoB) has been conducted using best-track data and wind radii information from 1977 to 2018 issued by the Joint Typhoon Warning Center. Results have shown that the annual variation in the frequency and duration of tropical cyclones has a significant increasing trend over the Arabian Sea and an insignificant decreasing trend over the BoB. The monthly frequency of tropical cyclones in both the Arabian Sea and the BoB shows a notable bimodal character, with peaks occurring in May and October–November, respectively. The maximum frequency of tropical cyclones occurs in the second peak as a result of the higher moisture content at mid-levels in the autumn. However, the largest proportion of strong cyclones (H1–H5 grades) occurs in the first peak as a result of the higher sea surface temperatures in early summer. Tropical cyclones in the Arabian Sea break out later during the first peak and activity ends earlier during the second peak, in contrast with those in the over BoB. This is related to the onset and drawback times of the southwest monsoon in the two basins. Tropical cyclones in the Arabian Sea are mainly generated in the eastern basin, whereas in the BoB the genesis locations have a meridional (zonal) distribution in May–June (October–November) as a result of the seasonal movement of the low-level positive vorticity belt. The Arabian Sea is dominated by western and northwestern tropical cyclones by that track west and NW, accounting for about 74.6%, whereas the tropical cyclones with a NE track account for only 25.4%. The proportions of the three types of tracks are similar in the BoB, with each accounting for about 33% of the tropical cyclones. The mean intensity and size of tropical cyclones over the Arabian Sea are stronger and larger, respectively, than those over the BoB and the size of tropical cyclones over the North Indian Ocean in early summer is larger than that in autumn. The asymmetrical structure of tropical cyclones over North Indian Ocean is affected by the topography and the longest radius of the 34 kt surface wind often lies in the eastern quadrant of the tropical cyclone circulation in both sea areas. FAN Xiao-ting (樊晓婷), LI Ying (李 英), et al.  相似文献   

3.
An objective prediction approach to the 6 h-144 h track and intensity of tropical cyclones over the northwestern Pacific is proposed. On the basis of both analog deviation technique and completed historical sample curve library, the track or intensity prediction for each forecast period are determined respectively through the optimum weighted superposition of displacement or intensity change of the cases, with different number and weighted coefficient corresponding to minimal analog deviation, from different tropical cyclone or different stage of the same cyclone. so that the prediction results for both forecast period and entire process are optimal. The verification suggests that the approach exhibits better forecast performance than other previous forecast methods by having remarkable decreasing forecast errors in short-and medium-range forecast of both track and intensity,and that the approach can also be used to predict effectively the decay process of tropical cyclone and is able to predict anomalous track and tropical depression.  相似文献   

4.
The effect of climate change on tropical cyclone intensity has been an important scientific issue for a few decades.Although theory and modeling suggest the intensification of tropical cyclones in a warming climate,there are uncertainties in the assessed and projected responses of tropical cyclone intensity to climate change.While a few comprehensive reviews have already provided an assessment of the effect of climate change on tropical cyclone activity including tropical cyclone intensity,this review focuses mainly on the understanding of the effect of climate change on basin-wide tropical cyclone intensity,including indices for basin-wide tropical cyclone intensity,historical datasets used for intensity trend detection,environmental control of tropical cyclone intensity,detection and simulation of tropical cyclone intensity change,and some issues on the assessment of the effect of climate change on tropical cyclone intensity.In addition to the uncertainty in the historical datasets,intertwined natural variabilities,the considerable model bias in the projected large-scale environment,and poorly simulated inner-core structures of tropical cyclones,it is suggested that factors controlling the basin-wide intensity can be different from individual tropical cyclones since the assessment of the effect of climate change treats tropical cyclones in a basin as a whole.  相似文献   

5.
As shown in a statistical analysis of the relationship between environmental fields at varied timeand tropical cyclone motion, the forecasting ability of the initisl environmental field predictors for tropical cyclone motion decreases with the increase of valid time period of forecast;it is higher with these predictors at a fUture time than at an initial time. The work also indicates that for the tropical cyclone motion over a given period of valid forecast, better predictors appear at times mostly differing from thevalid periods; for periods at 48-120 h the environmental predictors at 48-72 h are more capable of forecasting. With statistical interpretation of NWP products, a predictive model for tropical cyclone motionis superior in performance over a statistical forecasting model that employes predictors of the initial field in the basic framework. The concluding remarks can be used as reference in the construction of an objective prediction model for tropical cyclone motion.  相似文献   

6.
The characteristics of temporal and spatial distribution of tropical cyclone frequencies over the South China Sea areas and its affecting factors in the past 50yrs are analyzed based on typhoon data that provided by CMA and Simple Ocean Data Assimilation (SODA). The results show that the tropical cyclone frequencies from June to October show concentrated geographic distribution, for they mainly distribute over the SCS area from 15 - 20 °N. The characteristics present significant interdecadal changes. The impact of oceanic factors on the tropical cyclone frequencies in the SCS area is mainly realized by La Ni(n)a and La Ni(n)a-like events before 1975 but mainly by El Ni(n)o and El Nifo-like events after 1975.  相似文献   

7.
Accurate simulation of tropical cyclone tracks is a prerequisite for tropical cyclone risk assessment. Against the spatial characteristics of tropical cyclone tracks in the Northwest Pacific region, stochastic simulation method based on classification model is used to simulate tropical cyclone tracks in this region. Such simulation includes the classification method, the genesis model, the traveling model, and the lysis model. Tropical cyclone tracks in the Northwest Pacific region are classified into five categories on the basis of its movement characteristics and steering positions. In the genesis model, Gaussian kernel probability density functions with the biased cross validation method are used to simulate the annual occurrence number and genesis positions. The traveling model is established on the basis of the mean and mean square error of the historical 6 h latitude and longitude displacements. The termination probability is used as the discrimination standard in the lysis model. Then, this stochastic simulation method of tropical cyclone tracks is applied and qualitatively evaluated with different diagnostics. Results show that the tropical cyclone tracks in Northwest Pacific can be satisfactorily simulated with this classification model.  相似文献   

8.
Previous studies showed that 4 D-Var technique used for data assimilation could be modified for weather control. This study demonstrates the ability of 4 D-Var to influence the future path of a tropical cyclone by calculating perturbations in WRF simulation. Given the background error covariance matrix, the initial field is improved by the vortex dynamic initialization technique. Our results show that 4 D-Var can be applied to control the trajectory of simulated tropical cyclones by producing "optimal" perturbations. In the numerical simulation experiment of Typhoon Mitag in 2019, after this kind of weather control similar to data assimilation, the tropical cyclone moved obviously,and the damaging wind over the coastline weakened. The prediction results after the initial field modified by 4 D-Var have a great change, and the position of the tropical cyclone moved about 0.5° southeastward after assimilation,which misses the southeast coast of China. Moreover, the damaging wind is also weakened. Since the 4 D-Var is premised on the assumption that the model is perfect and does not consider the model error, then the research plan to consider model error and introduce new methods is discussed in the paper.  相似文献   

9.
The tropical cyclone motion is numerically simulated with a quasi-geostrophic baroclinic model.The flow field of a tropical cyclone is decomposed into its axisymmetric and asymmetric components.The relation between the ventilation flow vector and the motion vector of the tropical cyclone is inves-tigated.The results of numerical experiments indicate:(1) There are both large-scale beta gyres andsmall-scale gyres in the asyrnmetric flow field.(2) The interaction between small-scale gyres andlarge-scale beta gyres leads to the oscillation of translation speed and translation direction for the tropi-cal cyclone.(3) There are the large deviations between the ventilation flow vector calculated bymeans of Fiorino and Elsberry's method and the motion vector of tropical cyclone.(4) The ventila-tion flow vector computed using the improved method closely correlates with the motion vector of thetropical cyclone.  相似文献   

10.
An approach is proposed for predicting turning and acceleration motion trend of the tropicalcyclones over the South China Sea for 72 h in the extrapolated track coordinates.Cross-track(CT)and along-track(AT)components are defined according to the persistently extrapolatedtrack coodinates based on observed positions at the initial and past 24 h times.A kind of straight-forward measure may be provided with CT and AT components for typhoon turning motion and ac-celeration motion.Canonical correlation analysis(CCA)is performed to reveal the correlaotions be-tween tropical cyclone tracks and environmental 500 hPa geopotential height fields.A stepwise dis-criminate analysis technique is adopted to derive the classification functions of the respective threecategories for AT and CT components.Especially,categorical combinations of CT and AT compo-nents are divided into possible 9 regions corresponding with tropical cyclone behaviors.Not onlycan 9 motion trends of a tropical cyclone be predicted,but also the location and its maximum errorat least in certain direction are available.The perfect prediction(PP)verifications indicate that thepercent corrects for the CT and AT categories are 67% and 69% in the independent samples,73%and 53% in the dependent samples,respectively,higher than that of 33.3% for random chance;moreover,the rate for successfully forecasting that in which one of the nine regions the tropical cy-clones will fall at 72 h is about 40%,also higher than the stochastic probability of 11%.Themethod has been proved to be skillful and promising.  相似文献   

11.
The relationship between tropical cyclone activity and ENSO is examined for the major cyclone regions using crosscorrelations,spectral analysis and composite analysis of eastern equatorial Pacific sea surface temperature,thenormalised monthly Southern Oscillation Index(SOI),and tropical cyclone frequencies.The closest relationship betweenthe 3—4 year ENSO period and tropical cyclone activity was found in the western North Pacific west of 160°E and thereseems to be significant potential for seasonal forecasting in this region based on ENSO parameters alone.No significantrelationships were found for the North Indian Ocean,and the remainder of the basins were dominated by oscillationsnear the quasi-biennial period.Physical explanations and forecasting of the seasonal variations in tropical cyclone num-bers in these regions will need to account for the QBO as well as the 3—4 year ENSO connections.  相似文献   

12.
A predictive model for 24-120 h track of the tropical cyclone over the South ChinaSea is set upusing the predictors of CLIPER and with reference to those of EOF and CCA. This EOF-and CCA-basedmodel is compared with dependent and independent samples in veritring forecasts'Analpees appltwg themethods to 500-hPa geopotential heights have shown that the CCA method is able toconcentrate moreoriginal information of variable fleld that has the best global correlation withtropical cyclone track andthus reduces more efficiently error arisen in forecast,despite that can0nicaldistribution of weighted vari-able coefficients derived by it is less well-defined or smoothed of a spacialpattern as is done by eigenvec-tor in the EOF method. The verification indicates a certain degree of skill in both track predictive model,though better results are yielded in the CCA-based one, whose mean vector errorare 159.27, 314.84,524.12, 813.03, and 987.12 km, respectively for periods of 24, 48, 72, 96, and 120 h. The modelmakes an objective approach for prediction of short-and medium-range track of tropical cyclone in theSouth China Sea.  相似文献   

13.
The barotropic primitive equations model is used in a numerical study of a tropical cyclone crossing the Subtropical high. It is revealed that apart from its own characteristics, sensitive factors having immediate effects on the motion of the tropical cyclone also include its radial distance from the center of the subtropical high, the variation in latitudinal location and intensity. A complex mechanism for nonlinear interactions among the tropical,subtropical high and β effect is also shown in the experiment, and expected to serve for the diagnosis and prediction of abnormal motion.  相似文献   

14.
The dynamics of tropical cyclone is investigated in a nondivergent barotropic model with nobasic flow. The effect of nonlinear term on the movement and development of tropical cyclone isemphatically demonstrated. The advection of asymmetric vorticity by the symmetric flow (AAVS)produces the small-scale gyres (SSGs). The SSGs counterclockwise rotate around the tropicalcyclone center. The interaction of SSGs with the large-scale beta gyres (LSBGs) leads to theoscillation in translation speed and vacillation in translation direction for tropical cyclone. Theadvection of symmetric vorticity by the asymmetric flow (ASVA) steers the symmetric circulationof tropical cyclone. The ventilation flow vector determined by the asymmetric flow is closecorrelated with the motion vector of tropical cyclone. The nonlinear advection of relative vorticityis an order of magnitude greater than the linear advection of planetary vorticity, However, theasymmetric circulation created by the planetary vorticity advection provides a background conditionfor anomalous motions of the tropical cyclone. The combination of the linear and nonlinear effectsresults in accelerated, decelerated, changing direction and/or counterclockwise looping motions ofthe tropical cyclone.  相似文献   

15.
The characteristics of 200 hPa divergent wind and velocity potential have been analysed for four kinds of tropical cyclone tracks having impact on the SOuth China Sea.It is found that the difference of monsoon circulation in 200 hPa divergence wind field may affect the medium-range movement characteristics of tropical cyclone tracks.Corresponding to the west Pacific subtropical high,the orientation of 200 hPa secondary convergence line and its extension to the west may indicate the variability of track types.The direction of tropical cyclone movement is 2 longitudes west of and parallel to the 200 hPa secondary divergence line.  相似文献   

16.
The influence of the interannual variation of cross-equatorial flow(CEF) on tropical cyclogenesis over the western North Pacific(WNP) is examined in this paper by using the tropical cyclone(TC) best track data from the Joint Typhoon Warning Center and the JRA-25 reanalysis dataset. The results showed that the number of TCs forming to the east of 140°E over the southeastern part of the western North Pacific(WNP) is in highly positive correlation with the variation of the CEF near 125° E and 150° E, i.e., the number of tropical cyclogeneses increases when the cross-equatorial flows are strong. Composite analyses showed that during the years of strong CEF, the variations of OLR, vertical wind shear between 200-850 h Pa, 850 h Pa relative vorticity and 200 h Pa divergence are favorable for tropical cyclogenesis to the east of 140°E over the tropical WNP, and vice versa. Moreover, it is also discussed from the view of barotropic energy conversion that during the years of strong CEF, an eastward-extended monsoon trough leads to the rapid growth of eddy kinetic energy over the eastern part of WNP, which is favorable for tropical cyclogenesis;but during the years of weak CEF, the monsoon trough is located westward in the western part of the WNP, consistent with the growth area of eddy kinetic energy. As a result, there are fewer TC geneses over the eastern part of WNP.Besides, the abrupt strengthening of a close-by CEF 2-4 days before tropical cyclogenesis may be the one of its triggers.  相似文献   

17.
The TOVS data are used to study the structure of a number of tropical cyclones for the year 2000. Differences are found to some extent between what is found and classic conceptual models in that (1) the horizontal structure is asymmetric and variable so that the low-value centers at low levels of the geopotential height field (or the high-value centers at high levels) do not necessarily coincide with the high-value centers of the temperature field; (2) the vertical structure is also variable in the allocation of the anomalies of the geopotential height field between low values at low levels and high values at high levels. It is especially noted that the centers of the anomalies are tilting at both high and low levels or the high level is only at the edge of a high-pressure zone. There is not any significant high-value anomalous center in a corresponding location with the tropical cyclone. The structure of tropical cyclone in the TOVS is also used as reference to modify the structure of typhoon BOGUS in the numerical prediction model system of tropical cyclones. It is found that the modified BOGUS performs better in coordinating with the environment and predicting the track of the tropical cyclone. The demonstration is two-fold — the structure of the typhoon BOGUS is such that it means much in the track prediction and the use of the TOVS-based tropical cyclone structure really helps in improving it. It provides the foundation for modification and evolution of typhoon BOGUS.  相似文献   

18.
Analysis of the climatic characteristics of the tropical cyclones that affect China yields several interesting features. The frequency of these tropical cyclones tended to decrease from 1951 to 2005, with the lowest frequency in the past ten years. The decrease in the frequency of super typhoons is particularly significant. The main season of tropical cyclone activities is from May to November, with an active period from July to September. There are three obvious sources of these tropical cyclones and they vary with seasons and decades. Their movement has also changed with seasons. On average, these tropical cyclones affect China for 5.6 months annually and the period of influence decreases in the past decades. An analysis of daily data indicates that the days of typhoon influence are shorter in winter and spring and longer in summer. The frequency of tropical cyclones is the largest over southeastern China, decreasing northwestward. Taiwan is the region that is affected by tropical cyclones most frequently. The average annual precipitation associated with tropical cyclones has also decreased gradually northwestward from southeastern China.  相似文献   

19.
The relationship between the tropical intra-seasonal oscillation (ISO) and tropical cyclones (TCs) activities over the South China Sea (SCS) is investigated by utilizing the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) global reanalysis data and tropical cyclone best-track data from 1949 to 2009. The main conclusions are: (1) A new ISO index is designed to describe the tropical ISO activity over the SCS, which can simply express ISO for SCS. After examining the applicability of the index constructed by the Climate Prediction Center (CPC), we find that the convection spatial scale reflected by this index is too large to characterize the small-scale SCS and fails to divide the TCs activities over the SCS into active and inactive categories. Consequently, the CPC index can’t replace the function of the new ISO index; (2) The eastward spread process of tropical ISO is divided into eight phases using the new ISO index, the phase variation of which corresponds well with the TCs activities over the SCS. TCs generation and landing are significantly reduced during inactive period (phase 4-6) relative to that during active period (phase 7-3); (3) The composite analyses indicate distinct TCs activities over the SCS, which is consistent with the concomitant propagation of the ISO convective activity. During ISO active period, the weather situations are favorable for TCs development over the SCS, e.g., strong convection, cyclonic shear and weak subtropical high, and vice versa; (4) The condensation heating centers, strong convection and water vapor flux divergence are well collocated with each other during ISO active period. In addition, the vertical profile of condensation heat indicates strong ascending motion and middle-level heating over the SCS during active period, and vice versa. Thus, the eastward propagation of tropical ISO is capable to modulate TCs activities by affecting the heating configuration over the SCS.  相似文献   

20.
To examine effects of sea spray evaporation and dissipative heating on structure and intensity of a real tropical cyclone,the sea spray flux parameterization scheme was incorporated into the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model(MM5).Sensitivity tests were performed with varying the spray source function intensities and with and without dissipation heating.The numerical results indicate that sea spray evaporation increases the interfacial sensible heat flux,which is increased by 16% for the moderate spray and 47% for the heavy spray,but has little effect on the interfacial latent heat flux.The net effect of sea spray evaporation is to decrease the total sensible heat flux and to increase the total latent heat flux.The total enthalpy flux is increased by 1% and 12% with moderate and strong spray amounts,respectively.Consistent with these results,the intensity of the tropical cyclone is increased by 5% and 16% in maximum 10-m wind speed,respectively,due to sea spray evaporation.Sea spray evaporation and dissipative heating modify the tropical cyclone structure in important but complex ways.The effect of sea spray on the near-surface temperature and moisture depends on the spray amounts and its location within the tropical cyclone.Within the high-wind region of a tropical cyclone,the lower atmosphere becomes cooler and moister due to the evaporation of sea spray.However,the dissipative heating offsets the cooling due to sea spray evaporation,which makes the lower atmosphere warmer.  相似文献   

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