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<p>Sea surface temperature (SST) fronts exert a strong influence on regional climate, yet their effects over the northern South China Sea (NSCS) remain poorly understood. Using CALIPSO satellite observations, ERA5 reanalysis, and high-resolution numerical simulations, this study investigates the climatology of low cloud transitions and a typical case on 8 January 2022 during a cold air outbreak crossing the SST front. The aim is to clarify how the SST front modulates the marine atmospheric boundary layer (MABL) and low cloud evolution. Results show that: (1) Under the influence of continental cold high pressure, northeasterly flows transport cold air across the SST front, forming a typical MABL structure with a stable upper layer and turbulent lower layer. (2) In the frontal zone, both cloud-top and cloud-base heights rise by up to 500&#xa0;m, and cloud cover increases sharply, mainly due to a boundary-layer secondary circulation induced by the SST front. (3) South of the front, low cloud cover decreases while the cloud layer continuously lifts, associated with MABL decoupling driven by SST warming and latent heat release, consistent with the “deepening–warming–decoupling” mechanism. (4) Under northeasterly winds (i.e., along-frontal wind), the response of the MABL to the SST front is primarily dominated by pressure adjustment mechanism. A relatively weaker secondary circulation across the front still plays an important role in the evolution of low cloud heights and low cloud types across the front. These findings highlight the important role of SST fronts in regulating MABL structure and low cloud transitions over the NSCS.</p>

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Impact of the sea surface temperature front over the northern South China Sea on low cloud transition: an observational and numerical case study

  • 期刊论文

  • 发表日期：

    2026年8月4日

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  • Jingchao Long,
  • Jinghong Lin,
  • Shuqi Zhuang,
  • Lingjing Zhu,
  • Jing Luo,
  • Zihan Xie,
  • Yang Chen,
  • Jianjun Xu

摘要

Sea surface temperature (SST) fronts exert a strong influence on regional climate, yet their effects over the northern South China Sea (NSCS) remain poorly understood. Using CALIPSO satellite observations, ERA5 reanalysis, and high-resolution numerical simulations, this study investigates the climatology of low cloud transitions and a typical case on 8 January 2022 during a cold air outbreak crossing the SST front. The aim is to clarify how the SST front modulates the marine atmospheric boundary layer (MABL) and low cloud evolution. Results show that: (1) Under the influence of continental cold high pressure, northeasterly flows transport cold air across the SST front, forming a typical MABL structure with a stable upper layer and turbulent lower layer. (2) In the frontal zone, both cloud-top and cloud-base heights rise by up to 500 m, and cloud cover increases sharply, mainly due to a boundary-layer secondary circulation induced by the SST front. (3) South of the front, low cloud cover decreases while the cloud layer continuously lifts, associated with MABL decoupling driven by SST warming and latent heat release, consistent with the “deepening–warming–decoupling” mechanism. (4) Under northeasterly winds (i.e., along-frontal wind), the response of the MABL to the SST front is primarily dominated by pressure adjustment mechanism. A relatively weaker secondary circulation across the front still plays an important role in the evolution of low cloud heights and low cloud types across the front. These findings highlight the important role of SST fronts in regulating MABL structure and low cloud transitions over the NSCS.