Lake numbers, temperatures, and coefficient of eddy diffusivity Toolik Lake, Alaska NSF Arctic LTER site
      Lake numbers indicate how much the thermocline is tilting due to wind forcing. If Ln > 10, it is not tilting, if between 10 and 1 it is partially tilting, and if 1 or less, it is upwelling to the surface. They also indicate whether the internal waves which form in the thermocline and hypolimnion are likely to become unstable (e.g., break) and cause mixing. This mixing is most likely when Ln < 3.
       The time series temperature data show the heating and cooling in the surface layer and, at least for most of the summer, the strong stratification across the thermocline. As a result of cooling, the thermocline will be eroded and will deepen until ultimately, in fall, the lake mixes.
      The eddy diffusivities (Kz) are indicative of how much turbulence occurs in the lake. Molecular diffusivity is 1.4 x 10-7 m2 s-1. Thus, values of Kz near 10-7 indicate little mixing is occuring. Values of 10-5 m2 s-1 indicate a lot of mixing is occurring. Note that as Ln drops below 3, Kz increases in the hypolimnion and often in the thermocline.
      The mixing allows replenishment of nutrients to the upper, well lit portions of the lake where phytoplankton grow.

Disclaimer: As this data is being run in real time, some of the final checks for data quality have not yet been performed. Please contact George Kling for updates on the meteorological data, Sally MacIntyre for updates on the temperature data, and Brian Emery for web-related issues.
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 last updated: 8 Aug 2012
Comments: Brian Emery