Meteorological effects of the eclipse of 11 August 1999 in cloudy and clear conditions

Integrated atmospheric measurements were made at two sites in the UK during the total solar eclipse of 11 August 1999. Sensitive high-resolution meteorological observations revealed dynamical atmospheric effects despite the presence of cloud. Short-term eclipse-related changes dominated over temperature, wind speed and wind directions associated with the synoptic conditions, and 35 min period gravity waves were detected in surface-pressure observations. Theoretical calculations for solar radiation changes were compared with observations made during the 97% partial eclipse in clear skies at Reading, Berkshire, and used to predict the radiative changes expected at Camborne, Cornwall, during totality. At Camborne, a vertical array of sensitive fine-wire thermometers was operated with a high-resolution sonic anemometer, logged at 5 Hz. Despite cloudy conditions, which reduced the eclipseinduced thermal perturbations, small temperature and wind changes were detected which were consistent with theory. The cold outflow from the umbra was unambiguously detected for the first time in cloudy conditions.