Statistics for size and radial wind profile of tropical cyclones in the western North Pacific

Abstract

The 6-yr best-track data of tropical cyclones (TCs) in the western North Pacific are used to study the statistical features of TC size and radial wind profile. A TC size is defined as the azimuthal mean radius of 34-kt surface wind.On average, the TCs in the western North Pacific have a size of 203 km, and the size is larger for stronger TCs. Further analyses show that larger TCs tend to move faster than smaller ones, with a 23-24 km difference in size corresponding to a difference of about 10 km h −1 in moving speed. The TCs that recurve from westward to eastward moving have a mean size of 218 km, significantly larger than that of those without a turning point (179 km). Regional TC distributions demonstrate that the TCs affecting the Korean Peninsula and southwestern Japan have the largest mean size (250-280 km). There are also some large TCs affecting southern Philippines, while TCs over the South China Sea are generally small in size. Comparison of intensity and size of all TCs during their lifespan demonstrates that a TC tends to reach its maximum size 6 h after it reaches its maximum intensity, and the decrease rate of size during the weakening stage of a TC is much smaller than the increase rate of size during its developing stage. Thus, linear regression relations between TC size and intensity are established for its developing and weakening stages respectively, which can be used as a forecast tool for TC size.Features of TC radial wind profile are studied by analyzing a parametric wind model based on the radius data of 34-, 50-, and 64-kt surface winds. The results show that the shape parameter d most frequently takes the values of 0.3, 0.4, and 0.5. It generally increases (decreases) as the TC develops (weakens), implying a sharper (flatter) radial wind profile. Changes in d leads the tendency of intensity. The two parameters for the asymmetric model, namely p and q, are mostly 0.85-1.05 and 0-0.2, respectively, embodying the fact that the asymmetric component is generally much smaller than the symmetric component. The asymmetry in 34-kt surface wind is much stronger than that in 50-and 64-kt surface winds, with the maximum radius often in the northeast quadrant.

Monthly variation and spatial distribution of quadrant tropical cyclone size in the Western North Pacific

“…The shortcoming of the ROCI method is obvious owing to the subjectivity and method dependence (Knaff et al, 2014). At present, the general consensus on the definition of TC size is the radius of the area with a wind speed of 15 mÁs −1 (R15: Shoemaker, 1989;Cocks and Gray, 2002;Lee et al, 2010) or of 17 mÁs −1 (R17: Lu et al, 2011;Chan, 2012, 2015;Guo and Tan, 2017). At present, the general consensus on the definition of TC size is the radius of the area with a wind speed of 15 mÁs −1 (R15: Shoemaker, 1989;Cocks and Gray, 2002;Lee et al, 2010) or of 17 mÁs −1 (R17: Lu et al, 2011;Chan, 2012, 2015;Guo and Tan, 2017).…”

The effects of initial vortex size on tropical cyclogenesis and intensification

“…Observations have shown that tropical cyclones have a wide range of sizes, as measured, for example, by the radius of near‐surface gale force winds or the radius of the outermost closed isobar at the surface (Merrill, 1984; Weatherford and Gray, 1988; Liu and Chan, 1999; Kimball and Mulekar, 2004; Rudeva and Gulev, 2007; Yuan et al , 2007; Chavas and Emanuel, 2010, Lu et al , 2011, Chan and Chan, 2012). At one end of the size spectrum is the occurrence of so‐called midget storms, in which even the extent of gale‐force winds is no more than 100 km from the storm centre (for example, the radius of gales in Tropical Cyclone Tracy that devastated the Australian city of Darwin on Christmas Day in 1974 was a mere 50 km).…”

Optical Properties and Spatial Variation of Tropical Cyclone Cloud Systems From TRMM and MODIS in the East Asia Region: 2010–2014

“…Englehart and Douglas () also found that there are about 90% TC cases' radius less than 550–600 km from the center of a storm to the outer edge TCCS. In different stages, there are remarkable correlation between the scale and intensity of TC (Lu et al, ). Overall, a truncation of 500 km could reflect the mean state characteristics of TCs to some degree.…”