Seasonal differences in tropical cyclone—induced sea surface cooling in the western North Pacific

• Published in: Quarterly journal of the Royal Meteorological Society 2024-01, Vol.150 (758), p.447-461
• Main Authors: Singh, Vineet Kumar, Kim, Hye‐Ji, Moon, Il‐Ju
• Format: Article
• Language: English
• Subjects: Autumn; Cooling; Cyclones; cyclone‐induced cooling; Entrainment; Hurricanes; mixed‐layer depth; Negative feedback; Ocean basins; Predation; Sea surface; Sea surface cooling; Sea surface temperature; seasonal difference; Subsurface water; Summer; Surface temperature; Tropical cyclone intensities; Tropical cyclones; western North Pacific
• ISSN: 0035-9009; 1477-870X
• DOI: 10.1002/qj.4606

Tropical cyclone (TC)‐induced sea surface temperature (SST) cooling plays an important role in controlling the intensity of TCs in ocean basins and can modulate the local weather. This study examined the seasonal differences in TC‐induced SST cooling, especially between summer (June–August) and autumn (September–November), in the western North Pacific for the period 1992–2021. The analysis shows that the average maximum TC‐induced SST cooling along the TC track in autumn is 0.18°C less than in summer, although the mean TC intensity in autumn is 14 knots higher than in summer. This is because in autumn, the average mixed‐layer depth is 10–13 m deeper than in summer, and the TC track shifts equatorward, preventing the entrainment of cooler subsurface water to the surface, thereby causing less SST cooling in autumn at the same TC intensity. Given the negative feedback of TC‐induced SST cooling on TC intensity, these results are crucial to understand the seasonal differences in the intensity of TC in this basin. Schematic illustration of tropical cyclone (TC)‐induced cooling in the western North Pacific (WNP) in summer and autumn. The subsurface ocean temperature profile is indicated by the thick black line. Ocean surface is indicated by wavy lines. TCs are represented by a cyclone symbol (filled TC center represents weak TC, white TC center represents strong TC). In the summer season a shallow mixed layer combined with a sharp thermal gradient led to strong SST cooling with a magnitude of approximately −0.64°C, whereas in autumn the track of TCs is more equatorward and travels over regions of higher mixed‐layer depth and low thermal stratification, resulting in less mixing and reduced SST cooling (approx. −0.48°C) despite of stronger cyclones in this season than in summer.