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1.
CHEN Lianshou 《大气科学进展》2004,21(3):505-514
There has been much progress in the study of tropical cyclones and tropical meteorology in China in the past few years. A new atmospheric field experiment of tropical cyclone landfall with the acronym of CLATEX (China Landfalling Typhoon Experiment) was implemented in July-August 2002. The boundary layer characteristics of the target typhoon Vongfong and the mesoscale structural features of other landfalling typhoons were studied. In addition, typhoon track operational forecasting errors in the last decade have been reduced because the operational monitoring equipment and forecast techniques were improved.Some results from the research program on tropical cyclone landfall, structure and intensity change, intensification near coastal waters, interaction between tropical cyclone and mid-latitude circulation, and the interaction among different scales of motion are described in this paper. Four major meteorological scientific experiments in China with international cooperation were implemented in 1998: the South China Sea monsoon field experiment (SCSMEX), the Tibetan Plateau field experiment (TIPEX), the Huaihe River basin energy and water cycle experiment (HUBEX), and the South China heavy rain scientific experiment(HUAMEX). Although these field experiments have different scientific objectives, they commonly relate to monsoon activities and they interact with each other. The valuable intensive observation data that were obtained have already been shared internationally. Some new findings have been published recently.Other research work in China, such as the tropical air-sea interaction, tropical atmospheric circulation,and weather systems, axe reviewed in this paper as well. Some research results have shown that the rainfall anomalies for different regions in China were closely related to the stages of E1 Nifio events. 相似文献
2.
Contrasting the tropical responses to zonally asymmetric extratropical and tropical thermal forcing 总被引：1，自引：1，他引：0
The mechanism is investigated by which extratropical thermal forcing with a finite zonal extent produces global impact. The goal is to understand the near-global response to a weakened Atlantic meridional overturning circulation suggested by paleoclimate data and modeling studies. An atmospheric model coupled to an aquaplanet slab mixed layer ocean, in which the unperturbed climate is zonally symmetric, is perturbed by prescribing cooling of the mixed layer in the Northern Hemisphere and heating of equal magnitude in the Southern Hemisphere, over some finite range of longitudes. In the case of heating/cooling confined to the extratropics, the zonally asymmetric forcing is homogenized by midlatitude westerlies and extratropical eddies before passing on to the tropics, inducing a zonally symmetric tropical response. In addition, the zonal mean responses vary little as the zonal extent of the forced region is changed, holding the zonal mean heating fixed, implying little impact of stationary eddies on the zonal mean. In contrast, when the heating/cooling is confined to the tropics, the zonally asymmetric forcing produces a highly localized response with slight westward extension, due to advection by mean easterly trade winds. Regardless of the forcing location, neither the spatial structure nor the zonal mean responses are strongly affected by wind–evaporation–sea surface temperature feedback. 相似文献
3.
利用1979—2012年西北太平洋热带气旋最佳路径资料,Hadley中心的海温资料和NCEP/NCAR再分析资料等,研究了夏季(6—10月)热带北大西洋海温异常与西北太平洋热带气旋(Tropical Cyclone,TC)生成的关系及其可能机制。结果表明,夏季热带北大西洋海温异常与同期西北太平洋TC生成频次之间存在显著的负相关关系。热带北大西洋海温的异常增暖可产生一对东—西向分布的偶极型低层异常环流,其中气旋性异常环流位于北大西洋/东太平洋地区,反气旋异常环流位于西北太平洋地区。该反气旋环流异常使得TC主要生成区的对流活动受到抑制、低层涡度正异常、中低层相对湿度负异常、中层下沉气流异常,这些动力/热力条件均不利于TC生成。此外,西北太平洋地区低层涡旋动能负异常,同时来自大尺度环流的涡旋动能的正压转换也受到抑制,不能为TC的生成和发展提供额外能量源。反之亦然。 相似文献
4.
An empirical orthogonal functions analysis of the onshore flow of moisture along the west coast of southern Africa using NCEP-DOE AMIP II Re-analyses suggests two dominant modes of variability that are linked to (a) variations in the circulation linked with the South Atlantic anticyclone (b) the intensity of the flow that penetrates from the tropical Atlantic. The second mode, referred as the Equatorial Westerly mode, contributes the most to moisture input from the Atlantic onto the subcontinent at tropical latitudes. Substantial correlations in austral summer between the Atlantic moisture flux in the tropics and rainfall over the upper lands surrounding the Congo basin suggest the potential role played by this zonal mode of water vapour transport. Composites for austral summer months when this Equatorial Westerly mode had a particularly strong expression, show an enhanced moisture input at tropical latitudes that feeds into the deep convection occurring over the Congo basin. Sustained meridional energy fluxes result in above normal rainfall east and south of the Congo belt. During years of reduced equatorial westerly moisture flux, a deficit of available humidity occurs in the southern tropics. A concomitant eastward shift of deep convection to the southwest Indian ocean and southeastern Africa, leads to below normal rainfall over the uplands surrounding the Congo basin. 相似文献
5.
The role of wave energy accumulation in tropical cyclogenesis over the tropical North Atlantic 总被引：1，自引：0，他引：1
A hierarchical modeling approach is used to study the process by which interactions of easterly waves with the background flow can result in a reduction in the longitudinal and vertical scale of the waves. Theory suggests that in flows that possess a negative longitudinal gradient (U x < 0) there is a reduction of longitudinal and vertical group speeds and an increase in regional wave action density (or “wave energy”). Relative vorticity increases locally leading to an increase in the likelihood of tropical cyclogenesis near the wave axis. Opposite impacts on the structure of the waves is expected in a U x > 0 domain. In the simplified framework of a free-surface and divergent shallow water model, Rossby wave properties are tracked through a range of background flow scenarios to determine the important scales of interaction. The importance of wave energy accumulation for tropical cyclogenesis is then studied in a full physics and dynamics model using a nested regional climate model simulation, at 12 km horizontal grid spacing, over the tropical North Atlantic region for the entire 2005 hurricane season. The dynamical environment within which 70% of easterly waves formed tropical cyclones exhibits coherent regions in which easterly winds increase towards the east, consistent with the occurrence of wave energy accumulation. 相似文献
6.
The formation of tropical cyclones 总被引：17，自引：1，他引：16
Prof. Dr. W. M. Gray 《Meteorology and Atmospheric Physics》1998,67(1-4):37-69
Summary This paper attempts a synthesis of new observations and new concepts on how tropical cyclone formation occurs. Despite many worthy observational and numerical modeling studies in recent decades, our understanding of the detailed physical processes associated with the early stages of tropical cyclone formation is still inadequate; operational forecast skill is not very high. Although theoretical ideas cover a wide range of possibilities, results of new observations are helping us to narrow our search into more specific and relevant topic areas.With 33 FiguresPrologueThis paper is dedicated to Professor Herbert Riehl under whom I studied tropical meteorology at the University of Chicago from 1957–1961 and was later associated with at Colorado State University (CSU). Professor Riehl arranged my first aircraft flights into hurricanes in the late 1950s and gave great encouragment to me to explore the secrets of what causes a tropical disturbance to be transformed into a tropical storm.Herbert would persist in asking me nearly every week or so what causes a hurricane to form? I and my graduate students and research colleagues at CSU have been working to uncover the secrets of tropical cyclone formation ever since. The following article gives my current best estimate of the primary physical processes involved with this topic. 相似文献
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Simultaneous observations at up to six levels through a depth of 1100 m from a tethered balloon and instrumented ship's boom of 49 gust fronts associated with convective clouds are used to describe the mean and the detailed characteristics of tropical oceanic cumuli outflow at the surface and in the boundary layer.The changes in temperature and velocity of the maritime tropical gust front are about 50%; of the changes observed in mid-latitude convective outflows. Vertical velocities at the gust front l m s-1 are continuous through the lower 500 m for time periods up to 8 min implying vertical displacements of at least 500 m entirely sufficient at the observed humidities (q >- 15 g kg-1) to initiate new cloud growth. Horizontal and vertical vorticity in the order of 10-3 s-1 to 10-2 s-1 is observed at the gust front. 相似文献
10.
Climate Dynamics - In authors’ previous studies, the role of distinctive mean states in the western North Pacific (WNP) and North Atlantic (NA) in affecting tropical cyclone (TC) size was... 相似文献
11.
Summary Since 1995 there has been a resurgence of Atlantic hurricane activity, with 2005 being the most active and destructive hurricane
season on record. The influence of sea surface temperatures (SSTs) upon trends in Atlantic hurricane activity is investigated
by considering SSTs in the southern tropical North Atlantic, an area known as the main development region (MDR). Significant
differences in hurricane activity are observed when comparing the ten coolest and ten warmest years of SSTs in the MDR for
the period spanning from 1941 to 2006, with increasing MDR SSTs linked to the increased duration and frequency of tropical
cyclones. It is concluded that future increases in SSTs, as climate models project, could result in increased Atlantic basin
hurricane activity. Understanding how oceanic processes affecting the MDR may change with climate change could therefore help
increase the predictive capability for hurricane activity.
Authors’ addresses: Paul A. Steenhof, 50 Hendrick, Chelsea, Quebec, J9B 1M1 Canada; William A. Gough, Department of Physical
and Environmental Sciences, University of Toronto at Scarborough, Scarborough, Ontario, Canada 相似文献
12.
Decadal change in relationship between western North Pacific tropical cyclone frequency and the tropical Pacific SST 总被引：1，自引：0，他引：1
Sang-Wook Yeh Sok-Kuh Kang Ben P. Kirtman Joo-Hong Kim Min-Ho Kwon Cheol-Ho Kim 《Meteorology and Atmospheric Physics》2010,106(3-4):179-189
In this study, we examine the relationship between the number of tropical cyclones (TCs) in the western North Pacific and the tropical Pacific sea surface temperature (SST) during the main TC season (July–November) for the period of 1965–2006. Results show that there are periods when TC frequency and the tropical Pacific SST are well correlated and periods when the relationship breaks down. Therefore, decadal variation is readily apparent in the relationship between the TC frequency and the SST variations in the tropical Pacific. We further examine the oceanic and atmospheric states in the two periods (i.e., 1979–1989 vs. 1990–2000) when the marked contrast in the correlation between the TC frequency and the tropical Pacific SST is observed. Before 1990, the analysis indicates that oceanic conditions largely influenced anomalous TC frequency, whereas atmospheric conditions had little impact. After 1990, there the reverse appears to be the case, i.e., atmospheric conditions drive anomalous TC frequency and oceanic conditions are relatively unimportant. A role of atmosphere and ocean in relation to the TC development in the western North Pacific changes, which is consistent with the change of the correlations between the TC frequency and the tropical Pacific SST. 相似文献
13.
Large-scale conversion of tropical forests into pastures or annual crops will likely lead to changes in the local microclimate of those regions. Larger diurnal fluctuations of surface temperature and humidity deficit, increased surface runoff during rainy periods and decreased runoff during the dry season, and decreased soil moistrue are to be expected.It is likely that evapotranspiration will be reduced because of less available radiative energy at the canopy level since grass presents a higher albedo than forests, also because of the reduced availability of soil moisture at the rooting zone primarily during the dry season. Recent results from general circulation model (GCM) simulations of Amazonian deforestation seem to suggest that the equilibrium climate for a grassy vegetation in Amazonia would be one in which regional precipitation would be significantly reduced.Global climate changes probably will occur if there is a marked change in rainfall patterns in tropical forest regions as a result of deforestation. Besides that, biomass burning of tropical forests is likely adding CO2 into the atmosphere, thus contributing to the enhanced greenhouse warming. 相似文献
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Prof. Dr. Stefan Hastenrath 《Theoretical and Applied Climatology》1976,24(1-2):1-24
Summary Surface circulation and climate in the sea areas surrounding the American Continents are discussed on the basis of ship observations for the period 1911–1970 compiled with a one degree latitude-longitude square spatial resolution. Charts depict sub-synoptic scale features in considerable detail, such as the wintertime intrusions of cold dry air from the Atlantic to the Pacific side of the Mexican-Central American land bridge at topographically favoured locations, manifesting themselves in plumes of high wind speed, anticyclonic vorticity, and low sea surface temperature far into the open Pacific. Double peaks in the rainy season are indicated for the Western Caribbean and the easternmost Pacific off the Central American coast, with the September/October maximum most dominant. Among the more significant large-scale features are the near-equatorial trough of low pressure, a kinematic axis, and zonally oriented bands of maximal cloudiness and precipitation frequency, with a seasonal migration of this ensemble from a most equatorward position in Northern winter farther northward during summer. The near-equatorial kinematic axis has the characteristics of a confluence zone over the Western Atlantic, whereas over the Eastern Pacific it is a discontinuity between the Southwesterly flow from the Southern hemisphere and the Northeast Trades. Most intense development is reached during Northern summer. The surface flow discontinuity is broadly embedded in the baric trough. The bands of maximal convergence, cloudiness and precipitation frequency stay well equatorward of the surface flow discontinuity in the Eastern Pacific throughout the year, whereas over the Western Atlantic they switch to the North of the kinematic axis during Northern winter.
With 15 Figures 相似文献
Maritime Klimatologie des tropischen Amerika
Zusammenfassung Klima und Luftzirkulation über den die amerikanischen Kontinente umgebenden Seegebieten werden aufgrund von in Eingradfeldern für den Zeitraum 1911–1970 ausgewerteten Schiffsbeobachtungen besprochen. Großräumige Karten sowie Diagramme und Tabellen des Jahresganges werden für Bodendruck, Wind, Divergenz, relative Wirbelgröße, Wasseroberflächentemperatur (SST), Bewölkung und Niederschlagshäufigkeit dargeboten. Die Karten geben Einzelheiten im subsynoptischen Bereich wieder, wie etwa die winterlichen Kaltlufteinbrüche von der atlantischen zur pazifischen Seite der mexikanischmittelamerikanischen Landbrücke, die sich an orographisch begünstigten Stellen in Zungen von hoher Windgeschwindigkeit, antizyklonaler Wirbelgröße, und niederer SST bis weit in den offenen Pazifik hinein abzeichnen. Eine doppelgipflige Regenzeit ist für das westliche Karibische Meer und den östlichsten Pazifik längs der mittelamerikanischen Küste angezeigt, wobei das Maximum im September/Oktober bei weitem überwiegt.Zu den bezeichnendsten großräumigen Erscheinungen gehören eine Tiefdruckzone in der Nähe des Äquators, eine kinematische Achse, und zonal angeordnete Bänder von maximaler Bewölkung und Niederschlagshäufigkeit; dieses System ist jahreszeitlichen Verlagerungen von einer äquatornächsten Lage im Nordwinter zu weiter nördlichen Breiten im Nordsommer unterworfen. Die kinematische Achse hat über dem westlichen Atlantik die Eigenheiten einer Konfluenzzone, während sie über dem östlichen Pazifik eine Diskontinuität zwischen der von der Südhemisphäre vordringenden Südwestströmung und dem Nordostpassat darstellt. Eine leichte Doppelwelle im Jahresgang ist nur in der Breitenlage der kinematischen Achse über dem Pazifik zu erkennen. Das System ist im Nordsommer am kräftigsten entwickelt. Die Diskontinuität der Bodenströmung ist in die Tiefdruckzone eingebettet. Die Bänder von maximaler Konvergenz, Bewölkung und Niederschlagshäufigkeit bleiben im östlichen Pazifik ganzjährig erheblich äquatorwärts von der Strömungsdiskontinuität während sie über dem westlichen Atlantik im Nordwinter auf die Nordseite der kinematischen Achse überwechseln. Die für das vorliegende Projekt verfügbare räumliche Auflösung dürfte zum Verständnis der sogenannten Intertropischen Konvergenzzone wesentlich sein.
With 15 Figures 相似文献
16.
Procedures have been implemented at the Climate Analysis Center of the National Meteorological Center (CAC/NMC) to provide montly hindcasts of oceanographic conditions in the tropical Pacific. A central component of this system is a primitive equation ocean general circulation model that was developed at the Geophysical Fluid Dynamics Laboratory (GFDL). This is forced with monthly mean fields for wind stress and net heat flux. Until recently the former were derived from ship reports available on the Global Telecommunication System (GTS). The heat fluxes are slightly modified climatological fluxes from Esbensen and Kushnir. To correct for errors in the simulations, thermal data in the upper 450 and surface-temperature data are assimilated montly.Numerical experiments were run to examine the sensitivity of the simulations to small changes in the stress fields. Variations of the drag coefficient by 15% result in differences in sea-surface temperature (SST) and subsurface thermal structure in the eastern Pacific that are comparable with the observed annual and interannual variability. Comparisons with simulations in which the wind stresses were derived from operational atmospheric analyses show sensitivities of the same magnitude. Comparisons of simulations forced either with these of ship-recorded winds to a run with data assimilation show that significant errors are found in both, especially in the off-equatorial regions. Consequently, until forcing fields are improved, accurate simulations will require the use of data assimilation. 相似文献
17.
V. A. Sosnin 《Russian Meteorology and Hydrology》2008,33(12):801-808
It is shown that the salinity minimum at subsurface depths of the tropical Pacific is a local phenomenon. Characteristics of the salinity minimum are relative by absolute values and variable in time. It appears and disappears in the intertropical convergence zone according to variability of the freshwater budget sign. The salinity minimum appears during the negative phase of the freshwater budget on the background of the previous freshening of the sea surface. The salinity minimum at intermediate depths in both hemispheres is a single phenomenon of climatic time scale. At present, it exists at intermediate layers in the arid zones of both hemispheres due to the negative phase of the freshwater budget. This minimum is related to the Earth climate system variability at the geological time scale. Differences in its properties in the Northern and Southern hemispheres reflect differences in the freshwater budget values and the duration of their influence at the geological time scale. 相似文献
18.
The forcing efficiency for the first and the second baroclinic modes by the wind stress in tropical oceans has been discussed by calculating equivalent forcing depth from annual mean, seasonal, and pentadal density profiles of the observational data. In the annual mean field, the first mode is forced preferentially in the western Pacific and the Indian Ocean, whereas the second mode is more strongly excited in the Atlantic and the eastern Pacific. This difference is mostly due to the pycnocline depth; the second mode is more dominantly forced where the pycnocline depth is shallower. We also revealed large seasonal variations of the second mode's equivalent forcing depth in the western Indian Ocean. The first mode is more dominantly forced during boreal spring and fall in the western Indian Ocean, while the second mode becomes more dominantly forced during boreal summer and winter. Those are due to seasonal variations of both the zonal wind and the pycnocline depth. Moreover, we show that the excitation of the second mode in the western Pacific increases after the late 1970s, which is associated with the decreasing trend of the zonal pycnocline gradient. Revealing the variation of the equivalent forcing depth will be useful for understanding the oceanic response to winds in tropical oceans and the improvement in the predictability of air-sea coupled climate variability in the tropics. 相似文献
19.
Low-frequency time-space regimes in tropical convection 总被引：2，自引：0，他引：2
Summary The multi-scale time-space regimes of the low-frequency convective activity over the maritime continent and tropical western Pacific are investigated using the monthly infrared radiance black body temperature (IRTBB) over a latitude band of 5S–9S, 80E–160W for the time period of 1980–1993. The complex Morlet wavelet transform and the complex empirical orthogonal function (CEOF) analysis are used. The zonal mean of the monthly IRTBB is dominated by the annual cycle which is influenced by a monsoon regime. An interannual signal around the time scale of 4.8-year and a decadal signal are obvious. In the zonal deviation, each CEOF represents a particular spatial regime; its corresponding principal component exhibits different multi-scale temporal behavior. The first leading component represents the variability due to large scale land-ocean distribution (the maritime continent, the Indian Ocean and the western Pacific) related to monsoon, with a dominant annual time scale. The second leading component represents the fluctuation of Walker circulation, associated with the El Niño-Southern Oscillation (ENSO) events having a main time scale around 4.8-year and the quasi-biennial oscillation (QBO) around 2.4-year. The third leading component represents the variability due to small-scale land-ocean distribution (Java, New Guinea and the surrounding seas), with a dominant annual time scale. The main time scales in all the components seem to be modulated by longer time scales in either amplitude or frequency or both.Different time scales, as well as their in-phase interference, may play different roles in developing an individual ENSO event. The 1982/1983 event is dominated by an enhanced QBO. The 1986/1987 event is dominated by an enhanced 4.8-year oscillation. The 1991 and 1993 events may have resulted from an in-phase interference among several interannual time scales, abnormal annual cycles, and also highfrequency variability.SAIC/General Sciences Corporation.With 6 Figures 相似文献
20.
A detailed analysis is presented of the horizontal wind fluctuations with periods 20 s to 1 hr, and their vertical structure
as measured with light three-cup anemometers in a tropical forest environment. Information collected during the TREND (Tropical Environmental Data) experiment in a monsoon dominated region, was utilized. A special attempt was made to extract information relevant for
dispersion modeling. Variability parameters within and above the forest canopy under different stability conditions were derived.
A similar analysis was performed for a nearby clearing, to facilitate comparison between relatively smooth and rough surfaces,
under identical ambient conditions. A limited sample of data (7 days) was utilized, initially, to develop a methodology to
be later applied on a comprehensive data base, spanning the whole monsoon cycle. 相似文献