Modeling temperature inversion in southeastern Yellow Sea during winter 2016

Abstract

A significant temperature inversion with temperature differences larger than 3°C was observed in the southeastern Yellow Sea (YS) during February 2016. By analyzing in situ hydrographic profiles and results from a regional ocean model for the YS, this study examines the spatiotemporal evolution of the temperature inversion and its connection with wind‐induced currents in winter. Observations reveal that in winter, when the northwesterly wind prevails over the YS, the temperature inversion occurs largely at the frontal zone southwest of Korea where warm/saline water of a Kuroshio origin meets cold/fresh coastal water. Our model successfully captures the temperature inversion observed in the winter of 2016 and suggests a close relation between northwesterly wind bursts and the occurrence of the large inversion. In this respect, the strong northwesterly wind drove cold coastal water southward in the upper layer via Ekman transport, which pushed the water mass southward and increased the sea level slope in the frontal zone in southeastern YS. The intensified sea level slope propagated northward away from the frontal zone as a shelf wave, causing a northward upwind flow response along the YS trough in the lower layer, thereby resulting in the large temperature inversion. Diagnostic analysis of the momentum balance shows that the westward pressure gradient, which developed with shelf wave propagation along the YS trough, was balanced with the Coriolis force in accordance with the northward upwind current in and around the inversion area.

Wintertime Large Temperature Inversions in the Yellow Sea Associated With the Cheju and Yellow Sea Warm Currents

“…Large inversions (ΔT ≥ 2.0°C) were observed in late February to March 1986 and in early April 1996. The large inversions have also been observed in February of 2003 and 2016 (Lie et al, 2015;Pang et al, 2017). Conversely, weak inversions with ΔT ≤ 0.5°C were observed in January 1986 and February 1997, despite temperature and salinity patterns (Figures 3 and 5) that demonstrate the formation of a strong frontal zone.…”

“…The inversions northwest of Jeju‐do are not so significantly large as those southeast of the SP and the inversion area is apparently the smallest among the three frontal zones. However, large temperature differences in Δ T > 3.0°C were observed in February of 2003 and 2016 in that area (Lie et al, ; Pang et al, ). The relatively weak inversion there in January 1986 may be closely associated with the coarse spacing of CTD stations across the front between 33°N and 34°N, as CTD measurements were collected at stations with a north‐south distance of about 100 km.…”

“…The east‐to‐west development of the front northwest of Jeju‐do differs from the fronts southeast of SP and northeast of CB on the Chinese side, which develop in an approximately north‐to‐south direction along the coast. Although in February 1997, inversions were observed in a small area due to the sparse north‐south spacing of CTD stations, significant inversions have been frequently observed in February (Lie et al, ; Pang et al, ). Southward‐flowing cold water along the Korean coast comes into contact with the warm CWC water northwest of Jeju‐do and then flows westward along the front (Lie et al, ).…”

“…However, this normal temperature profile is not always maintained and temperature inversions often occur, defined as a specific temperature structure in which the temperature at deeper depths is higher than that at shallower depths (e.g., Lie et al, ; Ueno & Yasuda, ). Recent studies have reported the occurrence of large temperature inversions in winter to the southwest of Korea, with temperature differences across the temperature inversion layer ≥2.0°C (Lie et al, , ; Pang et al, ) as well as frequent temperature inversions southeast of the Shantung Peninsula (SP; Hao et al, ). However, the precise locations and detailed structures of significantly large inversions during the cold season remain unclear.…”

Sea Surface Height and Current Responses to Synoptic Winter Wind in the Bohai, Yellow, and East China Seas: Two Leading Coastal Trapped Waves

“…In winter, the Yellow Sea Warm Current (YSWC) has been widely studied because of its prominent hydrographic and upwind features (Hsueh, ; Huang et al, ; Lin & Yang, ; Tak et al, ). The YSWC significantly influences frontal circulation and the heat and water exchange in the Yellow Sea (Lie et al, , ; Pang et al, ), and its synoptic variation has been studied with numerical models in recent years (Ding et al, ; Hu et al, ; Li et al, ). These studies showed that after a strong northerly wind burst, a strong northward YSWC forms in the Yellow Sea trough and is associated with large‐scale SSH variations.…”