Latitudinal-altitudinal inter-relationships for the surface temperatures of the Northern hemisphere freshwater lakes

Abstract

Zonal relationships in (φ{symbol}, Z)-space (latitude-altitude) for surface temperature of lakes in the Northern hemisphere were derived from field data for 123 freshwater lakes. Average annual and extreme temperatures were mainly considered. Nonzonal effects (lake morphometry, long-term variability, etc.) contribute to the scatter of the data about derived relationships but do not obscure them. To minimize the effects above, the initial data at Z ≤ 200 m first were zonally averaged. Then the averaged data were fitted by regression-models, which provided boundary values for use both in spline-models and further calculations. They give, e.g., the average southern boundary for freezing lakes and the northern boundary for mictic lakes to be φ{symbol} = 53° and 80° respectively. The spline-models were applied to obtain improved latitudinal representations and to parameterize the altitude effects. They do not fit the data in a least-square-error sense. However, thanks to the appropriate scaling and suitable boundary conditions, their general shape is plausible. The spline-models, based upon several empirical parameters, can also be applied to any meridian strip and, after a certain modification, to the Southern hemisphere. Combination of spline-models provides a quantitative climatological-average lake thermal classification for (φ{symbol}, Z)-space based on the number of full convective overturnings guaranteed in a year cycle. That includes Hutchinson and Löffler's famous scheme as a particular example. Classification provides quantitative boundaries for previously specified classes and possible new ones (cold monomictic non-freezing, moderate tetramictic lakes, etc.) which can appear or disappear in different meridian strips. Some problems of the space/time variability of lake temperatures from the models derived are also discussed. These results provide background for further physical and ecological studies. © 1994.