Preliminary Research Of The Inner Core And Outer Size Of Tropical Cyclones And Their Relationship With The Intensity Of Tropical Cyclones

Currently, it is difficult to work out the prediction of tropical cyclone(TC) intensity well in operational forecast, although we can estimate it according to the TC eye's zoom out(in), not every TC will get an eye during its lifetime. Therefore, this paper will extend the TC eye to TC inner core(within the radius of maximum winds), and find out whether there's any relationship between TC inner core size change and intensity change, which might be helpful to TC operational forecast. What's more, structure is an important factor which might influence TC intensity, while TC outer size is a part of TC structure. Size reflects TC's dynamical and thermal condition, so that TC size must have some relation with TC intensity. Absolutely, revealing of the relation and its physical mechanism will be beneficial to the research of TC intensity changing mechanism and operational forecast.Based on the Regional Spectral Model(RSM) re-analysis data from Japan Meteorological Agency (JMA) with a horizontal resolution of 20 km and a time interval of 6h, according to TC's characters, this study works out 2174 samples of TC (occurring over the western North Pacific between 2001 and 2007) size and inner core(within the radius of maximum winds) features. Via contrast with TC size data from Joint Typhoon Warning Center(JTWC), we prove that both the 2174 TC size samples and the definition of TC size are rational.Using the TC size samples, preliminary analysis of the characters of TC inner core and outer size leads to some conclusions: the average of TC outer size is about 263.7km, while the average of TC inner core is about 141.8km. In May, July and August, TC outer size reach the peak, and in April the smallest. TCs in August have the best chance to become large TCs while TCs in April prefer to be small TCs. The size of TC located south of 30°N is larger than the north. From open sea to offing, TC outer size get smaller, while TC inner core become smaller firstly and then larger.Furthermore, analysis of the possible relationship of TC inner core, outer size and TC intensity leads to some conclusions, such as: TCs with large(small) outer size are always strong(weak); strong(weak) TCs prefer to become large(small) TCs; the TC intensity described by maximum winds speed or sea level pressure lead to the same conclusion; when TC has large inner core, zoom out(zoom in)of inner core benefits TC intensifying(weakening); when TC has small inner core, zoom out(zoom in)of inner core is good for TC weakening (intensifying); outer size increment(decrease) helps TC intensifying(weakening); the relativity of TC outer size and intensity is more obvious during TC's decline, while the relativity of TC inner core and intensity is much more notable during TC's developing.On that basis, this paper designs 5 groups of numerical simulation experiments(using high resolution typhoon numerical model) to verify the reliability of statics analysis conclusions, and diagnose the possible mechanism of how TC inner core and outer size influence TC intensity. Results show that: when TC has large inner core, the balance of angular momentum explains that why changing of inner core will course TC intensifying or weakening; when TC has small inner core, the reason why zoom out(zoom in)of inner core leads to TC weakening (intensifying) might be the damage of secondary circulation; the changing of humidity supply and convergence area in low level may be the reason for that outer size increment(decrease) helps TC intensifying(weakening). That is to say: when TC has large inner core, zoom out(zoom in)of inner core leads to the change of TC angular speed, which might influence TC intensity; when TC has small inner core, zoom out(zoom in)of inner core will change the secondary circulation, and then change TC intensity, this may be a mechanism; verifying of TC outer size may influence the quantity of humidity which goes up, so that the latent heat from humidity will change as well, which courses TC intensity changing; the convergence in TC low level will alter when TC outer size shifts, which might lead to TC intensity variation.