Interdecadal variation of tropical cyclone genesis and its relationship to the monsoon trough over the western North Pacific

Abstract

Using the European Centre for Medium‐Range Weather Forecasts Interim Reanalysis data set and the tropical cyclone (TC) best track data obtained from the International Best Tracks Archive for Climate Stewardship project from June to November for the epoch of 1979–2013, this study reexamines the recent interdecadal shift in TC genesis over the western North Pacific (WNP) in the late 1990s. An interdecadal decrease in the frequency of the WNP TC genesis was observed during 1998–2013 compared to the period of 1979–1997. The spatial distribution of the interdecadal decrease of the WNP TC genesis running northwest‐southeast, consistent with the monsoon trough (MT) zone. The results imply that the WNP genesis may be closely related to the MT on the interdecadal timescale. After the late 1990s, the intensity of the WNP MT becomes weaker and it extends more westward, thereby providing an unfavourable condition for the TC genesis. Through a diagnosis of the energetics, we suggested that the barotropic energy conversion in the eastern part of the WNP MT tends to be weakened in the late 1990s, hence less energy to support the WNP TC genesis. Both the meridional shear and the convergence of the mean zonal winds over the eastern WNP MT have an important impact on the conversion from mean kinetic energy to eddy kinetic energy, which can be considered as the atmospheric cause of the interdecadal decrease of TC genesis.

Perspective on the northwestward shift of autumn tropical cyclogenesis locations over the western North Pacific from shifting ENSO

“…3c, d, green bars), re-confirming that more and more TCs form over the northwestern WNP since 1998 (Fig. A3) from another angle, which is consistent with previous studies (e.g., Hsu et al 2014;Choi et al 2015Choi et al , 2017He et al 2015;Hong et al 2016;Zhao and Wang 2016;Huangfu et al 2017).…”

“…It was ever pointed out that the mean TCL showed a westward shift over the WNP mainly due to (1) the pronounced westward shift of TUTT (Wu et al 2015) and/or (2) the interdecadal change of the WNP MT (Huangfu et al 2017). On the other hand, Zhang et al (2014) demonstrated that southern China had experienced increasing autumn drought due to the ENSO regime shift in the past decades.…”

“…It is well known that the change in sea surface temperature (SST) related to the ENSO shift not only leads to a change in tropical convective activity pattern (e.g., Hu et al 2016b) and then the remote induction of Rossby waves via the perturbation of upper-level divergence (e.g., Sardeshmukh and Hoskins 1988), but also results in changes of large-range atmospheric and oceanic environments related to TC activity (Gray 1979) such as the Walker circulation, the WNP subtropical high, absolute vorticity, relative humidity, vertical wind shear, vertically-integrated moisture transport, and horizontal distribution of local SST (e.g., Chan 2006;Kim et al 2011;Zhang et al 2014;Choi et al 2015;Wang and Wu 2016;Huangfu et al 2017). For example, it has been found by many studies that a southeastward tendency of WNP TCLs in El Niño cases compared to La Niña cases (e.g., Camargo and Sobel 2005;Camargo et al 2007;Wang et al 2013;Zhao and Wang 2016) in both warm and cold phases of the PDO (Zhao and Wang 2016).…”

“…Existing theories also suggest that the east-west shifts of tropical upper-tropospheric trough (TUTT) and MT may induce changes in WNP TCLs (e.g., Lander 1994;Wu et al , 2015Zhao et al 2014b;Huang et al 2016;Wang and Wu 2016;Deng et al 2017;Huangfu et al 2017) on both interannual and interdecadal timescales. It was ever pointed out that the mean TCL showed a westward shift over the WNP mainly due to (1) the pronounced westward shift of TUTT (Wu et al 2015) and/or (2) the interdecadal change of the WNP MT (Huangfu et al 2017).…”

“…Although the interdecadal shift of WNP TCLs since the late-1990s has been widely studied (e.g., Chan 2013, Hsu et al 2014;Choi et al 2015Choi et al , 2017He et al 2015;Hong et al 2016;Zhao and Wang 2016;Huangfu et al 2017), these studies focused on the TC/typhoon activity associated with either ENSO phases or combined phases of PDO and ENSO (e.g., Zhao and Wang 2016). The combined effects of TUTT and MT modulated by shifting ENSO (i.e., two types of La Niña and two types of El Niño) on the concurrent WNP TCL change, however, have not been well investigated.…”