The Study Of The Global Mode Of Tropical Cyclones And The Variation Of Tropical Cyclones In High Frequency Of Occurrence Regions In The Western North Pacific

Based on the 44-yr (1965-2008) tropical cyclone (TC) data of the Joint Typhoon Warning Center (JTWC) and the National Hurricane Center (NHC), the data of Atmosphere circulation field from the National Centers Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR), the ERSST from the National Oceanic Atmospheric Administration (NOAA) and the results of GFDL CM2.0 model, some statistic methods, such as Season-reliant Empirical Orthogonal Function (SEOF), Season-reliant Singular Value Decomposition (SSVD), have been used to do the following analysis:the first one is to study the global mode of the TCs and to analyze the relationship between this mode and the SST; the second is to discuss the variation of the TC in the High frequency of occurrence regions (HFOR) in the western north Pacific (WNP) and associated general circulation; the last one is about the climate prediction of TCs using Genesis potential Index defined by Emanuel and Nolan. Some useful results have been got.1. It is the first time to using the SEOF to analysis the global TCs and getting a dominant dependent mode, the global mode of TCs. The analysis also shows that it is influenced by El Nino-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO), the ENSO more important.In this paper, the global mode of TCs is the first dominant mode of the SEOF of global TC based on TC year. Its spatial pattern displays an east-west contrast between enhanced activity in the North Pacific and reduced activity in the North Atlantic and a north-south contrast in the Southern Pacific oceans between active tropics and inactive subtropics, which are coupled with the El Nino and a positive phase of the PDO. The correlation coefficient between the PC1 and the index of ENSO and that between the PC1 and PDO reach 0.83 and 0.56, while the one between the PC1 and North Atlantic Oscillation (NAO) is only 0.06.2. Using the SSVD, the relationship between the global TCs and the SST is discussed. The two leading mode are got, the first one display the relationship between the global mode of TCs and ENSO and PDO, and the second suggests the variation of the global TC with global warming.The second mode reveals regional upward trends over the North Atlantic and the Indo-Pacific warm pool (17.5°S-10°N,70°E-140°E) coupled with the global warming. However, the global total number of frequency of occurrence shows no trend and only an unexpected large amplitude fluctuation driven by ENSO and PDO. The rising temperature of about 0.5～1.0℃in the tropics so far has not yet affected the frequency of occurrence of the global TC, while it only leads to upward or downward trend in some regions in some basins.3. The variation of Western North Pacific Subtropical High (WNPSH) in different time scale can affect the variation of the frequency of occurrence (FOC) of TCs in HFOR in the WNP.The variation of TCs in peak season (JASO) in three HFORs (the region E, region S and region P) is different. In the region S, whatever the FOC, the track number (TN) and the genesis number (GN) all show significant downward trends. In the P region, the FOC, TN and GN all show about 8-11-year decadal variation. Otherwise, in the region E, the significant 3-4 years oscillation appears in the FOC and TN.For the three regions, the TN's variability that influenced by the variation of the WNPSH is the main reason of the variation of the FOC. For the long term trend of the TN of the region S, compare the period 1987 to 2008 with period 1965 to 1986, the WNPSH displays westward and southward, and strengthened. It even expands to the region S. This change of the WNPSH will reduce the number of the tracks which go through the region S. On the decade scale, an anomaly anticyclone appearing in the' northwest of the region P makes the WNPSH stretch northward and westward, and this is suitable for TCs reaching the region P in the larger FOC year of the region P. The interannual variation of the WNPSH results in the interannual variation of the TN of the region E.Otherwise, for the region S, the decreasing trend of the GN of the region S and the region (140°～160°E,5°～20°N) where the TC generating may go through the region S is another reason of the downward trend of the FOC of the region S. The reduced relative humidity and increased meridianal shear of zonal wind may be lead to the trend of the GN in the two regions.4. The GPI is used to predict the change of the genesis of the TCs in JASO when the CO2 is doubling and doubled in the GFDL2.0 mode.The results show that whatever in the doubling of CO2 or doubled, the genesis of TCs in the north Pacific may shift northward (the GPI is positive on the north of 10°N, while negative on the south of 10°N); in the Atlantic, the property of genesis of TCs will decrease on the east of the Gulf of Mexico (GPI, negative), increasing on the south and north the Gulf of Mexico (GPI, positive). The possible reason of these changes may be the change of vertical shear of zonal wind and the relative humidity caused by the inconsistency of the increasing of SST.