Temporal Features Of The Turbulent Kinetic Energy Above The Bottom Near The Shore Of Lake Taihu And Explorations On The Possible Mechanism Of Its Changes

Turbulence is not only the key process that leads to the exchange of materials and momentum at the water-air interface and the internal transport of water columns,but also the driving force that promotes sediment resuspension and the evolution of the aquatic ecosystem in shallow lakes.Among them,Turbulent kinetic energy?TKE?can not only scaled the intensity of turbulence,but also is a key physical quantity describing the change of turbulence in water.Based on the long-term high-frequency three-dimensional velocity data collected from March to November 2018 in Lake Taihu,and combining with the meteorological field data of the Taihu station during the same period,the temporal characteristics of turbulent kinetic energy near the bottom of Lake Taihu and its possible change mechanism were discussed.The main conclusions were as follows:?1?The distribution of turbulent kinetic energy near the bottom of Lake Taihu was relatively wide,and the magnitude was between 10^-3cm²/s² to 10 cm²/s².The probability density increased firstly and then decreased with the increase of turbulent kinetic energy.The weak turbulent kinetic energy between 10^-3cm²/s² to 10^-1 cm²/s² showed significant high-frequency characteristics;but the strong turbulent kinetic energy greater than 1 cm²/s²had low-frequency characteristics.Turbulent was strongest in spring,followed by autumn,and the weakest in summer.Cold air and typhoons may be broken the seasonal trend in high-value areas of turbulent kinetic energy.?2?Wind(including wind speed,wind direction,and duration was the most influential factor that was closely related to the change of turbulent kinetic energy,and provided the energy driving turbulent mixing of water column.Wind speed was the primary driving factor,showing a positive correlation with TKE,and the greater the wind speed,the stronger the correlation;Due to the near-shore topography,the wind direction had a more significant effect on TKE:the wind direction affected the near-bottom turbulent kinetic energy through modulating the wind speed effect.The modulating effect can be scaled by a trigonometric function;near-bottom TKE was also affected by the accumulation of the previous wind field.From the correlation coefficient of the two after coupling,the effective period of the accumulation effect of the earlier time was 1-3 h.?3?The effects of net radiation on turbulent kinetic energy were both diurnal and seasonal.The near-bottom turbulent kinetic energy was weakened during the daytime,the heat loss at night was enhanced,and the internal turbulent disturbances increased TKE.The thermal effect in summer is stronger than that in spring and autumn,and the positive and negative effects of net radiation on TKE near the bottom were stronger?4?Under weak wind conditions,the effect of heat on turbulent kinetic energy was stronger than that of strong wind.The negative contribution rate to TKE during the day reaches 58.74%,and the positive contribution rate at night reaches 56.3%;When the wind speed is greater than6 m/s,the wind field becomes the dominant factor affecting the change of TKE,and the effect of net radiation is hardly reflected.?5?When a high wind process such as a typhoon or a cold wave,the large magnitude of??with a very short duration was rapidly strengthen the disturbance near the bottom layer,and TKE reached a peak.These events with large-amplitude??were caused by intermittent bursts of near-bottom turbulent coherent structure?dominated by ejection and sweep?.