Quantifying the effects of different cold air events on latent and sensible heat fluxes of Lake Taihu

Abstract

作为冷季主要的天气事件，冷空气过境会改变湖泊上方的气团性质，对湖泊的水热通量产生影响，进而影响湖泊的生物物理和化学过程.以亚热带大型浅水湖泊——太湖为研究对象，基于2012-2017年5个冷季（11月-翌年3月）的太湖中尺度通量网观测数据，量化不同强度冷空气（寒潮、强冷空气和较强冷空气）对太湖水热通量的影响.结果表明：在5个冷季中，寒潮、强冷空气和较强冷空气发生的总次数分别为4、11和33次，累积持续天数分别为14、31和78天.冷空气过境显著增强太湖的水热通量，3种冷空气过境使太湖的感热通量分别增至无冷空气时的10.3、6.0和4.3倍，潜热通量分别增至无冷空气时的4.0、2.1和2.7倍.虽然冷空气影响天数仅占冷季天数的16.4%，但对整个冷季的潜热和感热通量贡献分别为34.9%和51.7%，以较强冷空气贡献最大.冷空气影响时，水-气界面的温度梯度是太湖感热通量的主控因子，而潜热通量的主控因子为风速.与深水湖泊相比，太湖等浅水湖泊对冷空气过境的响应更快，寒潮过境时尤为明显.;As the major synoptic system, cold air events influence the water vapor and heat exchanges between lake and atmosphere by changing the meteorological conditions of air masses over the lake. Then biophysical and biogeochemical cycles in the lake ecosystem would be moderated by cold air passage. Based on dataset of the Taihu Eddy Flux Network observed during the five cool seasons (2012-2017), the effects of different cold air events (cold wave, severe cold air events and strong cold air events) on latent and sensible heat fluxes were quantified on the large subtropical shallow Lake Taihu. The results showed that cold wave, severe cold air events and strong cold air events totally happened 4, 11 and 33 times, and lasted for 14, 31 and 78 days, respectively. The sensible and latent heat exchanges between lake and atmosphere were accelerated significantly by the passage of cold air. The sensible heat flux increased by 10.3, 6.0 and 4.3 times during cold wave, severe cold air events and strong cold air events, respectively. The latent heat flux was increased by 4.0, 2.1 and 2.7 times, respectively. Although cold air passage only occupied 16.4% of entire cool season, the cold air events contributed 34.9% and 51.7% of the total latent and sensible heat fluxes, respectively. Moreover, the strong cold air events were the biggest contributor. During cold air events, the temperature gradient between the air and water is the most significant factor governing the sensible heat exchange rate. While, the latent heat flux is mostly dominated by wind speed. Compared to deep lakes, shallow lakes response faster to cold air activities. Therefore, the latent and sensible heat fluxes of shallow lakes increase much more, especially during cold waves.