## 1 Introduction  
The climate system relies significantly on oceans due to their tremendous heat-storage capacity, compared to the atmosphere. The thermal inertia of oceans is actively transferred to the atmosphere through turbulent and radiative energy exchange at the sea surface [1]. Sea surface temperature (SST), as a singular oceanic parameter, serves as a proxy for these energy fluxes and plays a key role in the regulation of climate and its variability [1]. SSTs are influenced by intricate combinations of atmospheric and oceanic processes, incorporating various dominant factors such as winds and air temperature in the atmosphere as well as thermal advection by surface currents and vertical mixing in the ocean. These factors, either solely or in an interlaced manner, affect SST variability. The East/Japan Sea (EJS) is a semi-enclosed marginal sea, well known as a miniature ocean (Figure 1). According to previous studies [2; 3; 4; 5], the timescale of SST variability in the EJS ranges from annual to multidecadal scales. For interannual-to-decadal timescales, local air-sea interactions and East Asian monsoon variability have been suggested as key factors in generating the long-term SST variations [4; 6]. [PERSON] and [PERSON] [7] reported the oscillations of atmospheric, oceanographic, and hydro-chemical features on quasi-biennial scales, and an El Nino-Southern Oscillation (ENSO) with a time scale of 3-7 years has been confirmed in various studies [3; 8; 9; 10]. There have also been longer temporal scale features ranging from decadal [11] to inter-decadal timescales [3; 4; 12]. There have been reports on oscillatory features of SST variability in the EJS with smaller time scales, such as, intra-annual through interannual time scales [2; 13], and semi-annual through annual time scales [2]. Further, some oscillations, nearly equal to and shorter than half a year, were also reported [14]. The wide-range scales observed in EJS SST variability are mainly due to many forcing factors, which have different spatiotemporal scales and include the monsoon, extratropical air-sea interactions, transportation variability of the TWC, and remote forcing [16]. As for the seasonal variability, there were several studies supporting the critical role of atmospheric forcing relating to the surface wind [17; 18; 19; 20]. Especially, a northwesterly wind starting from the orographic gap located on the north of Vladivostok cools the SST in the ESIW formation site and the northern region of SPF in every late autumn and early winter, greatly contributing to the ESIW formation during the wintertime [21; 22; 23; 24; 25]. However, the  
Figure 1: Surface oceanic current of the EJS, averaged over decades [15]. TWC: Tsushima warm current, EKWC: East Korea warm current, NB: nearshore branch of TWC, OB: offshore branch of TWC, NKCC: North Korea cold current, LCC: Liman cold current, KTS: Korea-Tsushima Strait, TS: Tsugaru Strait, SS: Soya Strait, JB: Japan Basin, YB: Yamato Basin, UB: Ulleung Basin. A gray dashed box for EKB, a green dotted box for SPF, and a black solid box for the ESIW formation site. long-term variability is greatly influenced by the Siberian High (SH), Aleutian Low (AL), North Pacific High, East Asian jet, and East Asian monsoon [3; 4; 13; 26]. That is, different forcing parameters are playing in SST variations, depending on their timescales. Also, there are influences of climate forcing parameters with longer timescales, namely the Arctic Oscillation (AO), North Atlantic Oscillation (NAO), West Pacific (WP) pattern, and ENSO (ENSO) [27; 28; 29; 30]. The volume transport of TWC has a great influence in the southern part of the EJS [15; 31].