The seasonal pattern of thermal characteristics of four of the Bishoftu crater lakes, Ethiopia

Abstract

Summary Measurements of temperature/depth profiles in four Ethiopian crater lakes were made during 1964, 1965 and 1966 at fairly regular intervals. Several more intensive diurnal studies, with observations at 3‐h intervals during periods of about 48 h, were also carried out. Results show a pattern of heating leading to thermal stratification from February to September and cooling from September to December with possible overturn at the end of that period. Thermal stability was never great and thermoclines were often poorly defined and multiple. Net daily changes in heat content during both heating and cooling can be a small fraction (c. 3%) of the diurnal heat flux and depend upon the relative magnitudes of solar radiation and evaporative heat loss. These are such that cooling may occur during periods of highest solar input and vice versa. However, meteorological conditions could easily reverse the cooling process before the December overturn so that complete mixing is by no means a predictably regular annual event.