Active Role of Sea Surface Temperature Changes Over the Kuroshio in the Development of Distant Tropical Cyclones in Boreal Fall

Abstract

This study examined the active role of sea surface temperature (SST) changes over the Kuroshio in the development of distant tropical cyclones (TCs) approaching Japan in October, using a cloud‐resolving model. We designed a real SST experiment and SST sensitivity runs by adding and subtracting SST anomalies equivalent to a spread of year‐to‐year October‐mean Kuroshio's SST changes. Under a synoptic environment that low‐level northeasterlies prevailed over the Kuroshio, systematic differences in TC intensity between the real and modified SST runs were simulated despite the developing TCs being far away from the modified SST areas. In the warm (cool) SST runs, active (inactive) moisture import from the Kuroshio increased (decreased) the equivalent potential temperature within the planetary boundary layer (PBL) in the inner core, thereby enhancing (weakening) the latent eyewall heating and the associated secondary circulation. The differences in the secondary circulation led to those in the inward advection of absolute angular momentum in the PBL, affecting a vortex spin‐up in the inner core. We also found that the surface heat and moisture supply from the Kuroshio facilitated the warming and moistening processes of midlatitude air parcels traveling over the underlying current, causing further reinforcement of the moisture import into the distant TC. These thermodynamic processes were more and less apparent in the warm and cool SST runs, respectively. Since the synoptic environment in this study often arises in boreal fall, the Kuroshio's SST warming in recent decades may influence the intensities of TCs approaching Japan in fall.

Subtropical Mode Water south of Japan impacts typhoon intensity

“…This region is north of the main focus areas of previous statistical analyses on tropical cyclones in the western North Pacific ( 43 , 44 ). Our findings are consistent with previous case studies around our study region ( 45 , 46 ) arguing that tropical cyclones’ inner-core processes and air-sea fluxes have an important role in altering TCIRs. The mechanism needs to be further investigated in future studies.…”

“…Thus, the long-term observations have demonstrated that both SST and TCHP in the warm season were significantly modulated by the decadal variation of the STMW thickness. This is expected to affect the development and decay of atmospheric convective systems, such as typhoons, through the probability of exceeding the critical SST or TCHP values for tropical cyclone intensification (33,36,(42)(43)(44)(45)(46).…”

Sensitivity of Typhoon Forecast to Prescribed Sea Surface Temperature Data

“…In addition, we used OISST data, even if the SST estimation of OISST was only exactly obtained in clear-sky conditions. Nevertheless, since many studies have used daily mean OISST data, not only for typhoon forecasting but also for the analysis of typhoon-induced SST cooling [36][37][38][39], this study could provide some perspectives (e.g., the importance of higher temporal-resolution of SST data for typhoon forecast) for improvements in typhoon forecast performance.…”

Intensification of a distant hurricane by warm‐core eddies in the Gulf Stream in boreal fall

“…On the other hand, several recent studies have pointed out the significant role of remote ocean environments in TC strength (Fujiwara et al, 2017, 2020a, 2020b; Hegde et al, 2016). Fujiwara and Kawamura (2021, hereafter FK21) revealed the modulations of TC intensity and structure through the remote impact of large‐scale SST changes over the Kuroshio in boreal fall. Some of northward‐traveling TCs over the Philippine Sea encountered an eastward‐moving anticyclone around Japan in boreal fall, inducing dry and cold northeasterly winds in the lower troposphere over the Kuroshio.…”