A Statistical Analysis of the Relationship between Upper-Tropospheric Cold Low and Tropical Cyclone Track and Intensity Change over the Western North Pacific

Abstract

The geographical and temporal characteristics of upper-tropospheric cold low (UTCL) and their relationship to tropical cyclone (TC) track and intensity change over the western North Pacific (WNP) during 2000-12 are examined using the TC best track and global meteorological reanalysis data. An analysis of the two datasets shows that 73% of 346 TCs coexist with 345 UTCLs, and 21% of the latter coexist with TCs within an initial cutoff distance of 158. By selecting those coexisted systems within this distance, the possible influences of UTCL on TC track and intensity change are found, depending on their relative distance and on the sectors of UTCLs where TCs are located. Results show that the impact of UTCLs on TC directional changes are statistically insignificant when averaged within the 158 radius. However, left-turning TCs within 58 distance from the UTCL center exhibit large deviated directional changes from the WNP climatology, due to the presence of highly frequent abrupt left turnings in the eastern semicircle of UTCL. The abrupt turnings of TCs are often accompanied by their slow-down movements. Results also show that TCs seem more (less) prone to intensify at early (late) development stages when interacting with UTCLs compared to the WNP climatology. Intensifying (weakening) TCs are more distributed in the southern (northern) sectors of UTCLs, with less hostile conditions for weakening within 98-138 radial range. In addition, rapid intensifying TCs take place in the south-southwest and east-southeast sectors of UTCLs, whereas rapid weakening cases appear in the western semicircle of UTCLs due to their frequent proximity to mainland coastal regions.

Assessing the Influence of Upper-Tropospheric Troughs on Tropical Cyclone Intensification Rates after Genesis

“…After TC genesis occurs, the role an upper-tropospheric PV anomaly plays in TC intensification is ambiguous. While troughs have been found to be unfavorable for the intensification of TCs in general (DeMaria et al 1993;Peirano et al 2016), some studies have documented cases of favorable TC-trough interactions (Molinari and Vollaro 1989;Hanley et al 2001;Leroux et al 2013;Wei et al 2016). The favorable mechanisms for TC intensification in the presence of an uppertropospheric trough include eddy flux convergence of angular momentum (EFC) (Molinari and Vollaro 1989), eddy fluxes of PV (Leroux et al 2013), and PV superposition (Molinari et al 1998).…”

Recent Progress in the Fundamental Understanding of Tropical Cyclone Motion

“…These works suggest that the TC track depends on both of low-frequency flows associated with the MG and the TC vortex itself. Wei et al (2016) statistically investigated the relationship between the upper tropospheric cold low (UTCL) and the TC tracks over the WNP during 2000-2012.…”

“…The quantity with a plus in parentheses shows a significant increase in the mean directional change of the TCs in the shaded distance range over the corresponding WNP climatology. (afterWei et al 2016)…”

Statistical Analysis of the Relationship between Upper Tropospheric Cold Lows and Tropical Cyclone Genesis over the Western North Pacific

“…Another previous study by Wei et al (2016) investigated changes in TC track and intensity due to UCLs over the WNP during the 13 years from 2000 to 2012. The results of this study showed that 73 % of TCs coexisted with UCLs that included an upper tropospheric low originating from TUTT cells and cutoff lows in the mid-latitudes, and 44 % of the TCs had interacted with UCLs during their lifetimes.…”

“…Although Wei et al (2016) have revealed the statistical characteristics of TCs interacting with UCLs throughout the TC lifecycle, few have examined the characteristics of TCs where TCG was influenced by UCLs in the northwest quadrant of the TCG region (hereinafter referred to as UL-TCs). In addition, the analysis period of the statistical study described above was only 4 years, and annual changes in UL-TCs were not investigated.…”