Diagnosis of seasonal variations of tropical cyclogenesis over the South China Sea using a genesis potential index

This study examines the seasonal variations of tropical cyclogenesis over the South China Sea (SCS) using a genesis potential (GP) index developed by Emanuel and Nolan. How different environmental factors (including low-level vorticity, mid-level relative humidity, vertical wind shear, and potential intensity) contribute to these variations is investigated. Composite anomalies of the GP index are produced for the summer and winter monsoons separately. These composites replicate the observed seasonal variations of the observed frequency and location of tropical cyclogenesis over the SCS. The degree of contribution by each factor in different regions is determined quantitatively by producing composites of modified indices in which only one of the contributing factors varies, with the others set to climatology. Over the northern SCS, potential intensity makes the largest contributions to the seasonal variations in tropical cyclogenesis. Over the southern SCS, the low-level relative vorticity plays the primary role in the seasonal modulation of tropical cyclone (TC) genesis frequency, and the vertical wind shear plays the secondary role. Thermodynamic factors play more important roles for the seasonal variations in tropical cyclogenesis over the northern SCS, while dynamic factors are more important in the seasonal modulation of TC genesis frequency over the southern SCS.     

Modulation of tropical cyclogenesis over the South China Sea by ENSO Modoki during boreal summer

This study examines the modulation of tropical cyclogenesis over the South China Sea(SCS) by the El Nio-Southern Oscillation(ENSO) Modoki during the boreal summer. Results reveal that there were more tropical cyclones(TCs) formed over the SCS during central Pacific warming years and less TC frequency during central Pacific cooling years. How different environmental factors(including low-level relative vorticity, mid-level relative humidity, vertical wind shear, and potential intensity) contribute to this influence is investigated, using a genesis potential(GP) index developed by Emanuel and Nolan. Composite anomalies of the GP index are produced for central Pacific warming and cooling years separately, which could account for the changes of TC frequency over the SCS in different ENSO Modoki phases. The degree of contribution by each factor is determined quantitatively by producing composites of modified indices in which only one of the contributing factors varies, with the others set to climatology. The results suggest that the vertical wind shear and low-level relative vorticity, which are associated with the ENSO Modoki-induced anomalous circulations in Matsuno-Gill patterns, make the largest contributions to the ENSO Modoki modulation of tropical cyclogenesis over the SCS as implied by the GP index. These results highlight the important roles of dynamic factors in the modulation of TC frequency over the SCS by the ENSO Modoki during the boreal summer.     

Oscillation in frequency of tropical cyclones passing Taiwan and Hainan Islands and the relationship with summer monsoon

The temporal variations in the frequency of tropical cyclones (TCs) traversing the Taiwan and Hainan Islands (TH islands), were analyzed using a best-track TC dataset from the Joint Typhoon Warning Center for the period 1945-2007. Results show that the oscillations were interannual and interdecadal on the timescales of 2-8 and 8-12 years, respectively. It is also shown that the number of TCs formed in the western North Pacific basin (WNP) and of those traversing the TH islands varied intraseasonally. These results also held for typhoons traversing the TH islands, although the oscillations were less apparent. This study identified interrelationships between the frequency of TCs making landfall on the TH islands and the East Asia summer monsoon (EASM), the South Asia summer monsoon (SASM), and the South China Sea summer monsoon (SCSSM). The SCSSM significantly influenced the number of TCs traversing Hainan Island, but had little influence on the number of TCs traversing Taiwan Island. By contrast, the SASM influenced the numbers of TCs traversing both of the TH islands, shown by correlation coefficients of 0.41 for Taiwan Island and -0.25 for Hainan Island. In addition, the frequency of TC landfall on Taiwan Island increased during years of enhanced EASM, as indicated by a correlation coefficient of 0.4.     

Features of ocean surface winds observed by the QuikSCAT satellite before tropical cyclogenesis over the South China Sea

Ocean surface winds observed by the Quick Scatterometer (QuikSCAT) satellite prior to the geneses of 36 tropical cy- clones (TCs) in the South China Sea (SCS) are investigated in this paper. The results show that there are areas with negative mean horizontal divergence around the TC genesis locations three days prior to TC formation. The divergence term [-(f ζ)( u/ x v/ y)] in the vorticity equation is calculated based upon the QuikSCAT ocean surface wind data. The calculated mean divergence term is about 10.3 times the mean relative vorticity increase rate around the TC genesis position one day prior to TC genesis, which shows the important contributions of the divergence term to the vorticity increase prior to TC formation. It is suggested that criteria related with the divergence and divergence term be applied in early detections of tropical cyclogenesis using the QuikSCAT satellite data.     

An Alternative Index for the Onset of the Summer Monsoon over the South China Sea

1　Introduction　TheindicesfortheAsianmonsoonhavebeenstud iedinmanyworks .Recently ,thechoiceofpropermonsoonindiceshasreceivedexceptionalattentionandraisedcontroversy (WebsterandYang ,1 992 ;Goswa mietal.,1 999;Goswami,2 0 0 0 ;Wang ,2 0 0 0 ) .Us ingzona…     

Circulation patterns of summer monsoon corresponding to two kinds of indices over the South China Sea

The characteristics of circulation corresponding to two kinds of indices of summer monsoon onset over the South China Sea (SCS) have been discussed using the reanalysis data of the National Centers for Environmental Prediction-National Center for Atmospheric Research. It is found that there are two patterns of deep convection that occur at different locations and influence the summer monsoon onset over the SCS. One is over the Asia continent and the western Pacific corresponding to the southwesterly of summer monsoon prevailing over the northern and central part of the SCS, while the other is near the Philippines that affects the westerly summer monsoon as prevailing over the central and southern southern part of the SCS. Since these two kinds of convection affecting the summer monsoon onset do not always occur together, thus the summer monsoon onset time is different when determined by various indices.     

Anomalies of asian summer monsoon related to ssta in the south China Sea and the tropical pacific

ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅＳｏｕｔｈＣｈｉｎａＳｅａ(ＳＣＳ)ｉｓａｐａｒｔｌｙ ｅｎｃｌｏｓｅｄｏｃｅａｎｂａｓｉｎｏｖｅｒｌａｉｄｂｙａｐｒｏｎｏｕｎｃｅｄｍｏｎｓｏｏｎｓｕｒｆａｃｅｗｉｎｄ .Ｐａｓｔｓｔｕｄｉｅｓ (Ｃｈｅｎｅｔａｌ.,1 991 ;ＤｉｎｇａｎｄＭｕｒａｋａｍｉ,1 994 ;Ｙａｎ ,1 997;ＬｉａｎｇＢｉｑｉ,1 991 ;ＬｉａｎｇＪｉａｎｙｉｎ ,1 991 )ｉｎｄｉｃａｔｅｔｈａｔａｈｕｇｅｗａｒｍｗａｔｅｒｐｏｏｌｊｏｉｎｔｌｙｃｏｎｔｒｉｂｕｔｅｄｂｙｔｈｅｗｅｓｔｅｒｎＰａｃｉｆｉｃ ,ｅａ…     

太阳磁场磁性指数的变化对南亚夏季风环流强度的影响

利用太阳黑子相对数资料,根据太阳磁场磁性特征建立了太阳磁场磁性指数时间序列,并利用NCEP/NCAR再分析资料建立了1948-2006年的南亚夏季风环流强度指数,对两者之间存在的可能相关关系作了分析。结果表明：太阳磁场磁性变化是激发南亚夏季风环流强度年代际变化的重要原因,当太阳北（南）半球磁场磁极为N（S）极为前导时,南亚夏季风环流强度较强,当太阳北（南）半球磁场磁极为S（N）极为前导时,南亚夏季风环流强度较弱,太阳磁场磁性强度的变化超前于南亚夏季风环流强度变化5年左右。两者之间的这种相关关系,为南亚夏季风环流强度年代际变化方面的预测提供了理论依据。     

Effects of spectral nudging on the 2010 East Asia summer monsoon using WRF model

The performance of spectral nudging in an investigation of the 2010 East Asia summer monsoon was assessed using the Weather Research and Forecasting (WRF) model, forced by 1-degree NCEP Global Final Analysis (FNL). Two pairs of experiments were made, spectral nudging (SP) and non-spectral nudging (NOSP), with five members in each group. The members were distinguished by different initial times, and the analysis was based on the ensemble mean of the two simulation pairs. The SP was able to constrain error growth in large-scale circulation in upper-level, during simulation, and generate realistic regional scale patterns. The main focus was the model ability to simulate precipitation. The Tropical Rainfall Measuring Mission (TRMM) 3B42 product was used for precipitation verification. Mean precipitation magnitude was generally overestimated by WRF. Nevertheless, SP simulations suppressed overestimation relative to the NOSP experiments. Compared to TRMM, SP also improved model simulation of precipitation in spatial and temporal distributions, with the ability to reproduce movement of rainbands. However, extreme precipitation events were suppressed in the SP simulations.     

Response of the South China Sea summer monsoon onset to air-sea heat fluxes over the Indian Ocean

We objectively define the onset date of the South China Sea (SCS) summer monsoon, after having evaluated previous studies and considered various factors. Then, interannual and interdecadal characteristics of the SCS summer monsoon onset are analyzed. In addition, we calculate air-sea heat fluxes over the Indian Ocean using the advanced method of CORARE3.0, based on satellite remote sensing data. The onset variation cycle has remarkable interdecadal variability with cycles of 16 a and 28 a. Correlation analysis between air-sea heat fluxes in the Indian Ocean and the SCS summer monsoon indicates that there is a remarkable lag correlation between them. This result has important implications for prediction of the SCS summer monsoon, and provides a scientific basis for further study of the onset process of this monsoon and its prediction. Based on these results, a linear regression equation is obtained to predict the onset date of the monsoon in 2011 and 2012. The forecast is that the onset date of 2011 will be normal or 1 pentad earlier than the normal year, while the onset date in 2012 will be 1-2 pentads later.     

Distribution and generic composition of culturable marine actinomycetes from the sediments of Indian continental slope of Bay of Bengal

Actinomycetes population from continental slope sediment of the Bay of Bengal was studied. Samples were collected during two voyages of FORV Sagar Sampada in 2004 （May-June） and 2005 （July） respectively from 11 transects （each transect had ca. 200 m, 500 m, and 1 000 m depth stations）. The physicochemical parameters of overlying water, and sediment samples were also recorded. The actinomycete population ranged from 5.17 to 51.94 CFU/g dry sediment weight and 9.38 to 45.22 CFU/g dry sediment weight during the two cruises respectively. No actinomycete colony was isolated from stations in 1 000 m depth. Two-way analysis of variance showed significant variation among stations （ANOVA two-way, P〈0.05）, but no significance was found between the two cruises （ANOVA two-way, P〈0.05）. Populations in stations in 500 m depth in both cruises were higher than that of 200 m depth stations with statistically insignificant difference （ANOVA two-way, P〉0.05）. Three actinomycetes genera were identified. Streptomyces was found to be the dominating one in both the cruises, followed by Micromonospora, and Actinomyces. The spore of Streptomyces isolates showed the abundance in spiral spore chain. Spore surface was smooth. Multiple regression analysis revealed that the influencing physico-chemical factors were sediment pH, sediment temperature, TOC, porosity, salinity, and pressure. The media used in the present study was prepared with seawater. Thus, they may represent an autochthonous marine flora and deny the theory of land runoff carriage into the sea for adaptation to the salinity of the seawater and sediments.     

Variability of tropical cyclone in high frequent occurrence regions over the western North Pacific

In this study, three high frequent occurrence regions of tropical cyclones(TCs), i.e., the northern South China Sea(the region S), the south Philippine Sea(the region P) and the region east of Taiwan Island(the region E), are defined with frequency of TC's occurrence at each grid for a 45-year period(1965–2009), where the frequency of occurrence(FO) of TCs is triple the mean value of the whole western North Pacific. Over the region S, there are decreasing trends in the FO of TCs, the number of TCs' tracks going though this region and the number of TCs' genesis in this region. Over the region P, the FO and tracks demonstrate decadal variation with periods of 10–12 year, while over the region E, a significant 4–5 years' oscillation appears in both FO and tracks. It is demonstrated that the differences of TCs' variation in these three different regions are mainly caused by the variation of the Western Pacific Subtropical High(WPSH) at different time scales. The westward shift of WPSH is responsible for the northwesterly anomaly over the region S which inhibits westward TC movement into the region S. On the decadal timescale, the WPSH stretches northwestward because of the anomalous anticyclone over the northwestern part of the region P, and steers more TCs reaching the region P in the greater FO years of the region P. The retreating of the WPSH on the interannual time scale is the main reason for the FO's oscillation over the region E.     

Influence of the Convection over the South China Sea on the Summer Precipitation of Shandong Province

1　Introduction　ShandongProvince ,whichislocatedintheeastofChina ,consistspartlyofpeninsulaandpartlyofinlandwithatotalareaofabout 1 5 0 0 0 0km2 .Lyingfrom34°2 0′Nto 38°2 0′Nandfrom 1 1 4°4 0′Eto 1 2 2°4 0′E ,alltheareabelongstothemoderateregionandtothetypicalAsianmonsoonclimate .SoShandong’ssum merprecipitationaccountsforover 6 0 %oftheannualrainfall,andaccordinglyflood droughtdisastersmain lyoccurinsummer.Moreover,becauseitisgeographi callylocatedinthetransitionalareabetweenthe…