Abstract
AbstractThe Northwest Pacific features strong sea surface temperature (SST) gradients providing favourable conditions for wintertime cyclone intensification in the midlatitudes. To estimate the relative contribution of the SST front to the evolution of cyclones and identify the mechanisms for cyclone intensification, we track individual cyclones and categorise them depending on their propagation relative to the SST front. We focus on cyclones remaining on either the cold or warm side of the SST front, as well as those crossing the SST front from the warm to the cold side. Cyclones crossing the SST front or remaining on its warm side propagate near the left exit region of the jet and are associated with higher precipitation, consistent with higher moisture availability and cyclone intensity. Comparing the different cyclone categories, there is no direct effect of the SST front on cyclone intensification. However, the SST front contributes to the climatological low‐level baroclinicity, providing a conducive environment for cyclone intensification for the cyclones crossing the SST front. Compared with the Gulf Stream region, the land–sea contrast plays a less prominent role for the low‐level baroclinicity in the Kuroshio region.
Highlights
The Kuroshio and the Gulf Stream are the western boundary currents in the North Pacific and North Atlantic, respectively, and are associated with maxima in midlatitude air–sea heat exchange along the sea surface temperature (SST) front (Ogawa and Spengler, 2019)
We perform a synoptic analysis to elucidate the different contributions of the aforementioned mechanisms to cyclone intensification in the Kuroshio region, where we focus on wintertime cyclones with maximum intensification in the Kuroshio Extension region
We identified the main characteristics for categories of cyclones differing in their propagation relative to the SST front in the Kuroshio region
Summary
Previous studies confirmed that the land–sea contrast contributes considerably to low-level baroclinicity in the Gulf Stream region (e.g., Cione et al, 1993; Inatsu et al, 2000; Wang and Rogers, 2001; Brayshaw et al, 2009; Tsopouridis et al, 2020) and rapidly developing cyclones over the Northwestern Pacific have been associated with cold continental airmasses (Yoshida and Asuma, 2004). In addition to low-level baroclinicity and upper-level forcing, diabatic heating associated with surface fluxes and latent heat release can contribute to cyclone intensification (e.g., Kuo et al, 1991; Reed et al, 1993; Nakamura et al, 2004). Surface heat fluxes and precipitation data are derived from the twice daily forecasts (initialized at 0000 and 1200 UTC) and are accumulated ±3 hr around the respective timesteps (such as in Ogawa and Spengler, 2019)
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