ITCZ的季节内振荡及其与热带气旋发生阶段性的关系

利用中国气象局提供的热带气旋资料和NCEP/NCAR再分析等资料, 研究了热带辐合带(Intertropical Convergence Zone, 简称ITCZ)上对流强度的季节内振荡特征及其与热带气旋生成频数阶段性变化的关系, 并进一步研究了它与越赤道气流、 赤道西风和ITCZ北侧偏东风季节内振荡的关系。研究发现: (1) ITCZ对流强度的变化有明显的30～60 d振荡, 西太平洋 (5°N～20°N, 120°E～150°E) 范围内的热带气旋约有2/3发生在30～60 d振荡的活跃位相。(2) ITCZ季节内振荡在热带地区表现为向东传播的特征, 而在副热带地区 (25°N～35°N) 表现出清晰的西传特征。在ITCZ季节内振荡较强年, 振荡在由赤道传播至15°N左右时, 与北面向南传播的振荡在该纬度附近汇合, 对流强度增强, 使热带气旋在此期间频繁发生。而在弱年, 振荡由赤道一直向北传播至30°N附近, 15°N附近的ITCZ对流较弱, 热带气旋生成偏少。(3) 赤道西风、105°E～110°E越赤道气流和ITCZ北侧的偏东风气流本身也存在30～60 d振荡。这三支气流的30～60 d振荡与ITCZ的季节内强弱变化密切相关。然而, 相比之下偏东风气流的30～60 d振荡和ITCZ对流强弱的30～60 d振荡对应关系略差。

Characteristics of the Intraseasonal Oscillation of Intertropical Convergence Zone and Its Influence on the Periodical Tropical Cyclogenesis

Based on the tropical cyclone data from the China Meteorological Administration and the NCEP/NCAR reanalysis data, the characteristics of the Intraseasonal Oscillation (ISO) of the intensity of convection over Intertropical Convergence Zone (ITCZ) and its influence on the periodical tropical cyclogenesis over the western North Pacific are studied. In addition, the relationships between the ISO of ITCZ and equatorial westerly, cross-equatorial flow averaged from 105°E to 110°E, and the easterly to the north of ITCZ are investigated. The results show that: (1) The significant signal of 30－60-d oscillation exists in the intensity of convection over ITCZ. The active and inactive convections over ITCZ occur in turn at the period of 30－60 d. About two-thirds of tropical cyclones over the western North Pacific (5°N－20°N, 120°E－150°E) occur in the active phase of ISO. (2) It is quite clear that the 30－60-d oscillation of ITCZ propagates eastwards slowly in the equatorial region, but westwards in the subtropical regions over 25°N－35°N. And it is also noticed that there are obvious differences of ISO between the strong ISO years and the weak ISO years. In the strong ISO years, the oscillation spreads from the equator to 15°N, and merges here with the oscillation from north to enhance the convection over ITCZ. Therefore more tropical cyclones originate during this period. On the contrary, in the weak ISO years, the oscillation directly propagates northwards to the vicinity of 30°N, results in the inactive convection over ITCZ near 15°N. At the same time, the frequency of tropical cyclogenesis decreases. (3) There are also remarkable 30－60-d oscillation features for the equatorial westerly, the equatorial flow averaged from 105°E to 110°E, and the easterly to the north of ITCZ. Generally, the 30－60-d oscillations of the three flows are consistent with the ISO of ITCZ. However, the relationship between the easterly wind and the ISO of ITCZ is slightly weaker than the other two flows.