The Study On Practicability Of The Intra-seasonal Oscillation Feature Of The Cross-equatorial Flow In The Typhoon Seasonal Forecasting

The cross-equatorial flows are the main passages for exchanges of material and energy between northern and southern hemisphere. And its intra-seasonal oscillations (ISO) have very influences on typhoon, typhoon intensity and the typhoon tracks. The modulation of the cross-equatorial flow in the ISO on the typhoon tracks over the Western North Pacific is studied by NCEP/NCAR1979-20102.5°x2.5°horizontal resolution reanalysis wind data. The authors divide the main classes tracks of typhoon into seven types based on the traditional methods. The results show that the cross-equatorial flow in the ISO may affect the tracks of typhoon. The low-frequency cross-equatorial flow influences the position or strength of the low-frequency cyclone, low-frequency anticyclone and then influences the typhoon tracks. Preliminary view is that different types typhoon track have different low-frequency cross-equatorial flow channels, the low-frequency flows to the north of the low-frequency cyclone around20°N lead the approaching typhoon track. Furthermore, the cycle of cross-equatorial flow in the ISO is quasi-40day. As a whole, the cross-equatorial flow in the ISO can be used as a basis for the typhoon seasonal forecasting.Based on the NCEP/NCAR data with6hours time resolution and2.5°x2.5°horizontal resolution wind filed from1979to2010, useing the space filter make the30-60d time filter result have a system where the typhoon system less than1500km wave length and the large scale system larger than2000km wave length are segregated. It indicate that the large scale wave has the quasi-40day cycle of cross-equatorial flow in the ISO. The cycle of the cross-equatorial flow make the low-frequency cyclone arise and maintenance at20°N, and the system around the low-frequency cyclone and itself will lead the approaching typhoon track. The cycle of the large scale cross-equatorial flow in the ISO indicate that it is a intrinsic system, the typhoon system is controlled by large scale system to affect the system in low latitude, and then have many kinds of tracks.The typhoon wave scale cross-equatorial flow also has the cycle of quasi-40d cycle in the ISO, and it can induce the low-frequency anticyclone arise and maintenance. The low-frequency flow around the low-frequency anticyclone is on the contrary to the typhoon track. The interaction of the large scale wave system and the typhoon scale wave system indicate that the cross-equatorial flow ISO character is a intrinsic system of the large scale system, the typhoon wave system is a anti-phase turbulence system to the large scale system, and the anti-phase turbulence system also has the quasi-40d cycle in the ISO.The cycle of the large scale cross-equatorial flow in the ISO indicate that it is a intrinsic system which is a most important character of the large scale, the anti-phase typhoon system is controlled by large scale system to affect the system in low latitude, and then have many kinds of tracks. As the whole The cross-equatorial flow in the ISO can be used as a basis for the typhoon seasonal forecasting.