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1.
The evolution of the tropospheric temperature fields over Indian and South China Sea monsoon areas and their thermal mechanisms are compared and analyzed during the period from March to June, 1996. The results show that the onsets of the Indian and South China Sea summer monsoons are closely associated with the seasonal warming in the troposphere over the zonal belt of 10°N~30°N in these areas, which leads to the inversion of meridional temperature gradient. During the pre-onset period, the warming over the South China Sea monsoon region is mainly due to the warm horizontal advection and diabatic (latent) heating processes. Meanwhile, the warming is suppressed by the vertical adiabatic process (cooling). In spring over the Indian monsoon region, the significant adiabatic heating due to the subsidence motion, which compensates the cooling due to the strong cold advection and diabatic cooling processes, results in a larger warming rate than over the South China Sea monsoon region. However, the meridional temperature gradient over the Indian monsoon region is so large during the late winter and early spring that it takes longer time to warm the troposphere to have the reversion of meridional temperature gradient than it does over the South China Sea monsoon region. It results in the phenomenon that the South China Sea summer monsoon generally breaks out earlier than the Indian summer monsoon.  相似文献   

2.
The evaporation rate over South China is estimated based on the Climate Prediction Center Merged Analysis of Precipitation(CMAP)data and the NCEP/DOE reanalysis II data from 1979 to 2007. The temporal variation of evaporation over South China and its relationship to precipitation are discussed. Climatologically,the evaporation rate over South China is the largest in July and smallest in March.In spring and summer,the evaporation rate is approximately one half of the precipitation rate.However,the evaporation rate is approximately equal to the precipitation rate in fall and winter.The year-to-year variation of the evaporation rate over South China is quite in phase with that of the precipitation rate in the period from February to May but out of phase with that of the precipitation rate in early winter.Over South China there is a pronounced decreasing trend in the evaporation in colder seasons and a positive correlation between the evaporation variation and the rainfall variation in spring.In summer,the abnormality of rainfall over South China is closely related to the anomalous evaporation over the northeastern part of the South China Sea and its eastern vicinity.In winter,the rainfall variation in South China has a close linkage with the evaporation variation in a belt area covering the eastern Arabian Sea,the Bay of Bengal,the southeastern periphery of the Plateau,the southern part of South China Sea and the central part of Indonesia.  相似文献   

3.
Based on TBB data from Meteorological Institute Research of Japan, study is carried out of the features of seasonal transition of Asian-Australian monsoons and Asian summer monsoon establishment,indicating that the transition begins as early as in April, followed by abrupt change in May-June; the Asian summer monsoon situation is fully established in June. The winter convective center in Sumatra moved steadily northwestward across the "land bridge" of the maritime continent and the Indo-China Peninsula as time goes from winter to summer, thus giving rise to the change in large scale circulations that is responsible for the summer monsoon establishment over SE Asia and India; the South China Sea to the western Pacific summer monsoon onset bears a close relation to the active convection in the Indo China Peninsula and steady eastward retreat of the subtropical TBB high-value band,corresponding to the western Pacific subtropical high.  相似文献   

4.
The onset of South China Sea summer monsoon in 1998 occurred on May 21st. Using the U.S. National Centers for Environmental Prediction reanalysis data, this paper examines the physical process of the weakening of a subtropical anticyclone in West Pacific during the onset period using the Zwack-Okossi vorticity equation. Results show that during the pre-onset period, the positive vorticity advection in front of an upper tropospheric trough was the most dominant physical mechanism for the increase of the cyclonic vorticity on the 850-hPa layer over the South China Sea and its nearby region. The secondary contribution to the increase of the cyclonic vorticity was the warm-air advection. After the onset, the magnitude of the latent-heat warming term rapidly increased and its effect on the increase of the cyclonic vorticity was about the same as the positive-vorticity advection. The adiabatic term and divergence term contributed negatively to the increase of the cyclonic vorticity most of the time. Thus, the positive vorticity advection is the most important physical mechanism for the weakening of the West Pacific subtropical anticyclone over the South China Sea during the onset period.  相似文献   

5.
The characteristics and possible causes of changes in persistent precipitation(PP) and non-persistent precipitation(NPP) over South China during flood season are investigated using daily precipitation data from 63 stations in South China and NCEP/NCAR reanalysis data from 1961 to 2010. This investigation is performed using the Kendall's tau linear trend analysis, correlation analysis, abrupt climate change analysis, wavelet analysis, and composite analysis techniques. The results indicate that PP dominates total precipitation over South China throughout the year. The amounts of PP and NPP during flood season vary primarily on a 2–5-yr oscillation. This oscillation is more prominent during the early flood season(EFS; April–June). NPP has increased significantly over the past 50 years while PP has increased slightly during the whole flood season. These trends are mainly due to a significant increase in NPP during the EFS and a weak increase in PP during the late flood season(LFS; July–September). The contribution of EFS NPP to total flood season precipitation has increased significantly while the contribution of EFS PP has declined. The relative contributions of both types of precipitation during LFS have not changed significantly. The increase in EFS NPP over South China is likely related to the combined efects of a stronger supply of cold air from the north and a weaker supply of warm, moist air from the south. The increase in NPP amount may also be partially attributable to a reduction in the stability of the atmosphere over South China.  相似文献   

6.
The Earliest Onset Areas and Mechanism of the Tropical Asian Summer Monsoon   总被引:1,自引:0,他引:1  
The multi-yearly averaged pentad meteorological fields at 850 hPa of the NCEP/NCAR reanalysis dada and the TBB fields of the Japan Meteorological Agency during 1980-1994 are analyzed. It is found that if the pentad is taken as the time unit of the monsoon onset, then the tropical Asian summer monsoon (TASM) onsets earliest, simultaneously and abruptly over the whole area in the Bay of Bengal (BOB), the Indo-China Peninsula (ICP), and the South China Sea (SCS), east of 90°E, in the 27th to 28th pentads of a year (Pentads 3 to 4 in May), while it onsets later in the India Peninsula (IP) and the Arabian Sea (AS), west of 90°E. The TASM bursts first at the south end of the IP in the 30th to 31st pentads near 10°N, and advances gradually northward to the whole area, by the end of June. Analysis of the possible mechanism depicts that the rapid changes of the surface sensible heat flux, air temperature, and pressure in spring and early summer in the middle to high latitudes of the East Asian continent between 100°E and 120癊are crucially responsible for the earliest onset of the TASM in the BOB to the SCS areas. It is their rapid changes that induce a continental depression to form and break through the high system of pressure originally located in the above continental areas. The low depression in turn introduces the southwesterly to come into the BOB to the SCS areas, east of 90°E, and thus makes the SCS summer monsoon (SCSSM) burst out earliest in Asia. In the IP to the AS areas, west of 90°E, the surface sensible heat flux almost does not experience obvious change during April and May, which makes the tropical Indian summer monsoon (TISM) onset later than the SCSSM by about a month. Therefore, it is concluded that the meridian of 90°E is the demarcation line between the South Asian summer monsoon (SASM, i.e., the TISM) and the East Asian summer monsoon (EASM, including the SCSSM). Besides, the temporal relations between the TASM onset and the seasonal variation of the South Asian high (SAH) are discussed, too, and it is found that there are good relations between the monsoon onset time and the SAH center positions. When the SAH center advances to north of 20°N, the SCSSM onsets, and to north of 25°N, the TISM onsets at its south end. Comparison between the onset time such determined and that with other methodologies shows fair consistency in the SCS area and some differences in the IP area.  相似文献   

7.
By using 40-year NCEP reanalysis daily data (1958-1997), we have analyzed the climatic characteristics of summer monsoon onset in the South China Sea (105°E ~ 120°E, 5°N ~ 20°N, to be simplified as SCS in the text followed) pentad by pentad (5 days). According to our new definition, in the monsoon area of the SCS two of the following conditions should be satisfied: 1) At 850hPa, the southwest winds should be greater than 2m/s. 2) At 850 hPa, θse should be greater than 335°K. The new definition means that the summer monsoon is the southwest winds with high temperature and high moisture. The onset of the SCS summer monsoon is defined to start when one half of the SCS area (105°E ~ 120°E,5°N ~ 20°N) is controlled by the summer monsoon. The analyzed results revealed the following: 1) The summer monsoon in the SCS starts to build up abruptly in the 4th pentad in May. 2) The summer monsoon onset in the SCS is resulted from the development and intensification of southwesterly monsoon in the Bay of Bengal. 3) The onset of the summer monsoon and establishment of the summer monsoon rainfall season in the SCS occur simultaneously. 4) During the summer monsoon onset in the SCS, troughs deepen and widen quickly in the lower troposphere of the India; the subtropical high in the Western Pacific moves eastward off the SCS in the middle troposphere; the easterly advances northward over the SCS in the upper troposphere.  相似文献   

8.
ON THE PROCESS OF SUMMER MONSOON ONSET OVER EAST ASIA   总被引:6,自引:0,他引:6  
Using daily observational rainfall data covered 194 stations of China from 1961 to 1995 andNCEP model analyzed pentad precipitation data of global grid point from 1979 to 1997,thedistribution of onset date of rainy season over Asian area from spring to summer is studied in thispaper.The analyzed results show that there exist two stages of rainy season onset over East Asianregion from spring to summer rainy season onset accompanying subtropical monsoon and tropicalmonsoon respectively.The former rain belt is mainly formed by the convergence of cold air and therecurred southwesterly flow from western part of subtropical high and westerly flow from the so-called western trough of subtropical region occurring during winter to spring over South Asia.Thelatter is formed in the process of subtropical monsoon rain belt over inshore regions of South ChinaSea originally coming from south of Changjiang (Yangtze) River Basin advancing with northwardshift of subtropical high after the onset of tropical monsoon over South China Sea.The pre-floodrainy season over South China region then came into mature period and the second peak of rainfallappeared.Meiyu,the rainy season over Changjiang-Huaihe River Basin and North China thenformed consequently.The process of summer tropical monsoon onset over South China Sea in 1998is also discussed in this paper.It indicated that the monsoon during summer tropical monsoononset over South China Sea is the result of the westerly flow over middle part of South China Sea,which is from the new generated cyclone formed in north subtropical high entering into SouthChina Sea,converged with the tropical southwesterly flow recurred by the intensified cross-equatorial flow.  相似文献   

9.
By using monthly NCEP/NCAR meridional gridpoint wind data at the levels of 1000, 850, 700,600, 500, 400, 300, 200, 150 and 100 hPa from 1948 to 2004, the intensity of global cross-equatorial flows is calculated. The spatial and temporal variation of global cross-equatorial flows at the 850-hPa level are shown and discussed. The results show that the strength of the 850-hPa global cross-equatorial flows represent obvious long-term variation and interdecadal change during the period. Evidence suggests that the cross-equatorial flow of the passages at 45 - 50 °E in June to August, 105 - 115 °E in May to September,130 - 140 °E in May to September and May to November and 20 - 25 °E in February to April intensified and that the cross-equatorial flow of the passages at 50 - 35 °W in June to August weaken in the past 57 years, with an increase of 0.25m/s/10a for summer Somali Jet and increase of 0.32 m/s/10a for crossequatorial flow at 130 - 140 °E in May to September The results of Singular Spectrum Analysis (SSA) for the time series indicate that for the cross-equatorial flow at 850 hPa, the interdecadal and long-term trend changes are 35% - 45%, and the interannual variation is no more than 30%, in variance contribution. The results also reveal that the interannual variation of intensity of the summer cross-equatorial flows in the Pacific is significantly correlated with Southern Oscillation. With weak Southern Oscillation, strong crossequatorial flows in Pacific will happen, though the summer Somali Jet is only a little positively correlated with North Atlantic Oscillation (NAD).  相似文献   

10.
The climatological features and interannual variation of winter-to-spring transition over southern China and its surrounding areas, and its possible mechanisms are examined in this study. The climatological mean winter-to-spring transition is approximately in mid-March over southern China and the northern South China Sea. During the transition stage, anomalous southwest winds prevail at low-level over southern China and its nearby regions with enhanced convergence center over southern China, bringing more moisture from the Bay of Bengal (BOB) and the South China Sea (SCS) to southern China; meanwhile, the upper level is characterized by an obvious divergence wind pattern over southern China to the southwest part of Japan and enhanced upward motion. All the change of circulation is favorable to an increase of precipitation over southern China after seasonal transition. The winter-to-spring transition is predominantly on the interannual variation over southern China and the northern SCS. Early winter-to-spring transitions may induce more precipitation over southern China in spring, especially in March, while late cases will result in less precipitation. The interannual variability of the winter-to-spring transition and the related large-scale circulation are closely associated with the decaying phase of ENSO events. The warm ENSO events contribute to early winter-to-spring transitions and more precipitation over southern China.  相似文献   

11.
The South China Sea is a hotspot for regional climate research. Over the past 40 years, considerable im provement has been made in the development and utilization of the islands in the South China Sea, leading to a substantialchange in the land-use of the islands. However, research on the impact of human development on the local climate of theseislands is lacking. This study analyzed the characteristics of local climate changes on the islands in the South China Seabased on data from the Yongxing Island Observation Station and ERA5 re-analysis. Furthermore, the influence of urba nization on the local climate of the South China Sea islands was explored in this study. The findings revealed that the 10-year average temperature in Yongxing Island increased by approximately 1.11 °C from 1961 to 2020, and the contributionof island development and urbanization to the local warming rate over 60 years was approximately 36.2%. The linearincreasing trend of the annual hot days from 1961–2020 was approximately 14.84 days per decade. The diurnal tem perature range exhibited an increasing trend of 0.05 °C per decade, whereas the number of cold days decreased by 1.06days per decade. The rapid increase in construction on Yongxing Island from 2005 to 2021 led to a decrease in observedsurface wind speed by 0.32 m s –1 per decade. Consequently, the number of days with strong winds decreased, whereas thenumber of days with weak winds increased. Additionally, relative humidity exhibited a rapid decline from 2001 to 2016and then rebounded. The study also found substantial differences between the ERA5 re-analysis and observation data,particularly in wind speed and relative humidity, indicating that the use of re-analysis data for climate resource assessmentand climate change evaluation on island areas may not be feasible.  相似文献   

12.
The interannual variations of summer surface air temperature over Northeast China (NEC) were investigated through a month-to-month analysis from May to August. The results suggested that the warmer temperature over NEC is related to a local positive 500-hPa geopotential height anomaly for all four months. However, the teleconnection patterns of atmospheric circulation anomalies associated with the monthly surface air temperature over NEC behave as a distinguished subseasonal variation, although the local positive height anomaly is common from month to month. In May and June, the teleconnection pattern is characterized by a wave train in the upper and middle troposphere from the Indian Peninsula to NEC. This wave train is stronger in June than in May, possibly due to the positive feedback between the wave train and the South Asian rainfall anomaly in June, when the South Asian summer monsoon has been established. In July and August, however, the teleconnection pattern associated with the NEC temperature anomalies is characterized by an East Asia/Pacific (EAP) or Pacific/Japan (PJ) pattern, with the existence of precipitation anomalies over the Philippine Sea and the South China Sea. This pattern is much clearer in July corresponding to the stronger convection over the Philippine Sea compared to that in August.  相似文献   

13.
This study investigates the relationship between subseasonal variations of the circulation and sea surface temperature(SST) over the South China–East Asian coastal region(EACR) in association with the persistent heavy rainfall(PHR) events over South China during May–August through statistical analysis. Based on the intensity threshold and duration criterion of the daily rainfall, a total of 63 May–June(MJ) and 59July–August(JA) PHR events are selected over South China from 1979 to 2011. The lower-level circulation anomalies on subseasonal timescale exhibit an anomalous cyclone over South China and an anomalous anticyclone shaped like a tongue over the South China Sea(SCS) during the PHR events for MJ group.The anomalous cyclone over South China in MJ originates from low-value systems in the mid-high latitudes before the rainfall. The anomalous anticyclone over the SCS is due to the westward extension of the western Pacific subtropical high(WPSH) and the southeastward propagation of the anomalous anticyclone from South China before the rainfall. For JA group, the lower-level anomalous circulation pattern is similar to that for MJ over the South China–EACR, but with di?erent features of propagation. The subseasonal anomalous anticyclone is also related to the westward stretch of the WPSH, while the anomalous cyclone is traced back to the weak anomalous cyclone over the Philippine Sea several days before the rainfall events.Positive SST anomaly(SSTA) is observed over the SCS and the Philippine Sea during the MJ PHR events on the subseasonal timescale. It is closely linked with the variation of local anomalous anticyclone. In contrast, negative SSTA occupies the South China coastal region for the JA PHR events, and it is driven by the anomalous cyclone which propagates northwestward from the Philippine Sea. The subseasonal positive(negative) SSTAs are generated via the local processes of above(below)-normal incident solar radiation and below(above)-normal latent heat fluxes. The possible role of the subseasonal SSTA in the local convective instability is also analyzed in this study.  相似文献   

14.
Based on tropical cyclone datasets from Shanghai Typhoon Institute of China Meteorological Administration, the National Centers for Environmental Prediction (NCEP, USA) reanalysis data and the rainfall records from 743 stations in China, the impacts of cyclogenesis number over the South China Sea and the western Pacific are studied on the 30-60-day oscillations in the precipitation of Guangdong during the flooding period. The year with more-than-normal (less-than-normal) tropical cyclogenesis is defined as a ‘high year’ (‘low year’). In light of the irregular periodic oscillations, the method used to construct the composite life cycle is based on nine consecutive phases in each of the cycles. Phases 1, 3, 5, and 7 correspond to, respectively, the time when precipitation anomalies reach the minimum, a positive transition (negative-turning-to-positive) phase, the maximum, and a negative transition phase. The results showed that the precipitation of the 30-60-day oscillations is associated with the interaction between a well-organized eastward propagation system from the Arabian Sea/Bay of Bengal and a westward-propagating system (with cyclonic and anticyclonic anomalies in the northwest-southeast direction) from the South China Sea to western Pacific during the high years, whereas the precipitation is affected during a low year by the circulation over the South China Sea and western Pacific (with cyclonic and anticyclonic anomalies in the northeast-southwest direction). During the high year, the warm and wet air mass from the ocean to the west and south are transported to Guangdong by westerly anomalies and an enclosed latitudinal cell, which ascends in the Northern Hemisphere low latitudes and descends in the Southern Hemisphere low latitudes. During the low year, the warm and wet air mass from the ocean to the south is transported to Guangdong by southwesterly wind anomalies and local ascending movements. Because the kinetic energy, westerly, easterly shift, vertical velocity and vapor transportation averaged over (109–119° E, 10–20° N) is stronger in high years than those in low years, the precipitation of the 30-60-day oscillations in Guangdong is higher in high years than that in low years.  相似文献   

15.
Global gridded daily mean data from the NCEP/NCAR Reanalysis(1948-2012) are used to obtain the onset date,retreat date and duration time series of the South China Sea summer monsoon(SCSSM) for the past 65 years.The summer monsoon onset(retreat) date is defined as the time when the mean zonal wind at 850 hPa shifts steadily from easterly(westerly) to westerly(easterly) and the pseudo-equivalent potential temperature at the same level remains steady at greater than 335 K(less than 335 K) in the South China Sea area[110-120°E(10-20°N)].The clockwise vortex of the equatorial Indian Ocean region,together with the cross-equatorial flow and the subtropical high,plays a decisive role in the burst of the SCSSM.The onset date of the SCSSM is closely related to its intensity.With late(early) onset of the summer monsoon,its intensity is relatively strong(weak),and the zonal wind undergoes an early(late) abrupt change in the upper troposphere.Climate warming significantly affects the onset and retreat dates of the SCSSM and its intensity.With climate warming,the number of early-onset(-retreat) years of the SCSSM is clearly greater(less),and the SCSSM is clearly weakened.  相似文献   

16.
The increase in southern China summer rainfall around 1993 was accompanied by an increase in tropical cyclones that formed in the South China Sea. This study documents the connection of these two features. Our analysis shows that the contribution of tropical cyclones that formed in the South China Sea to southern China summer rainfall experienced a significant increase around 1993, in particular, along the coast and in the heavy rain category. The number of tropical cyclones that formed in the western North Pacific and entered the South China Sea decreased, and their contribution to summer rainfall was reduced in eastern part of southern China (but statistically insignificant). The increase in tropical cyclone-induced rainfall contributed up to ~30% of the total rainfall increase along the coastal regions. The increase of tropical cyclones in the South China Sea appears to be related to an increase in local sea surface temperature.  相似文献   

17.
The NCEP reanalyzed data, OLR and SST observations are used to study the onset time and the multi-time scales features of the South China Sea (SCS) summer monsoon in 1998 and its interaction with the sea surface temperature and the effect on the precipitation in Guangdong province. It is found that the 1998 SCS summer monsoon set in on May 17 (in the fourth pentad of the month). The year witnesses a weak monsoon with the OLR oscillating at cycles of about 1 month and the Southwest Monsoon of about 1/2 month. The mon-soon over the Bay of Bengal and the cross-equatorial current near 105°are two driving forces for low-frequency variations of the SCS monsoon. The weak activity in the year was resulted from positive anomalies of SST in the equatorial eastern Pacific in early spring and subsequent formation of positive anomalies of SST in the SCS through the Arabian Sea.  相似文献   

18.
The relationship between the variation of precipitation in Guangdong Province is investigated using the correlation analysis and composite comparison methods in conjunction with precipitation data from 36 surface weather stations in the province and reanalyzed 850 hPa data from NCEP, U.S.A. A significant positive correlation is found between the variation of precipitation in summer there and the intensity of the southwesterly over the South China Sea though without being so inconclusive that a strong southwesterly over the sea is accompanied by more rain in Guangdong. For the front-associated flood season in April-June, the former is a carrier of rainwater for Guangdong but with insignificant linkage with the intensity of the southwest monsoon. There is even such a situation in which the precipitation gets stronger though with a weakened southwest monsoon from the tropics in May-June, which is mainly attributable to the increase of monsoon from the subtropics. For the typhoon-associated flood season in July-September, the Guangdong precipitation increases as the southwest monsoon strengthens over the central and northern South China Sea and the subtropical monsoon reduces its effects on the province.  相似文献   

19.
Using the 2006 Global Emissions Data and 2011 NCEP Final Analysis data as the initial and boundary condition, we simulated the three-dimensional distribution of atmospheric chemical pollutants (such as sea salt, PM10, COx, SO2, NOx, O3, etc) during the onset stage of South China Sea (SCS) summer monsoon from 25 April to 25 May in 2011 over the monsoon area of 70°–160°E, 0°–40°N. Simulation results shows that, many changes have taken place in the distribution of atmospheric chemical pollutants near 950 hPa and 400 hPa due to the enhancement of the westerlies and southerlies over the SCS as a result of the monsoon outbreak. Especially, the concentration of pollutants over the SCS is much higher than that over other places because of the strong wind convergence near the surface in situ. Moreover, the vertical distribution of pollutants is also greatly affected by the westerlies and southerlies in the onset process of SCS summer monsoon. Meanwhile, the concentration over land is much greater than that at sea in pre-monsoon period, while the difference between land and sea in the concentration of most pollutants decreases greatly with the onset of SCS summer monsoon.  相似文献   

20.
The South China Sea warm pool interacts vigorously with the summer monsoon which is active in the region. However, there has not been a definition concerning the former warm pool which is as specific as that for the latter. The seasonal and inter-annual variability of the South China Sea warm pool and its relations to the South China Sea monsoon onset were analyzed using Levitus and NCEP/NCAR OISST data. The results show that, the seasonal variability of the South China Sea warm pool is obvious, which is weak in winter, develops rapidly in spring, becomes strong and extensive in summer and early autumn, and quickly decays from mid-autumn. The South China Sea warm pool is 55 m in thickness in the strongest period and its axis is oriented from southwest to northeast with the main section locating along the western offshore steep slope of northern Kalimantan-Palawan Island. For the warm pools in the South China Sea, west Pacific and Indian Ocean, the oscillation, which is within the same large scale air-sea coupling system, is periodic around 5 years. There are additional oscillations of about 2.5 years and simultaneous inter-annual variations for the latter two warm pools. The intensity of the South China Sea warm pool varies by a lag of about 5 months as compared to the west Pacific one. The result also indicates that the inter-annual variation of the intensity index is closely related with the onset time of the South China Sea monsoon. When the former is persistently warmer (colder) in preceding winter and spring, the monsoon in the South China Sea usually sets in on a later (earlier) date in early summer. The relation is associated with the activity of the high pressure over the sea in early summer. An oceanic background is given for the prediction of the South China Sea summer monsoon, though the mechanism through which the warm pool and eventually the monsoon are affected remains unclear.  相似文献   

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