Anomalies and Fluctuations of Near-surface Air Temperature at Tianhuangping (Zhejiang), China, Produced by the Longest Total Solar Eclipse of the 21st Century Under Cloudy Skies

Abstract

During a total eclipse of the Sun, the solar disk blocked by the lunar disk produces an instant and strong decline of energy at the surface. This loss of energy leads to a decreasing air temperatures near the surface. Anyone under a completely clear sky, with a total solar eclipse (TSE) in progress, feels a cooling, whose minimum is reached a few minutes after totality. This drop in temperature is known as an anomaly and this delay is called thermal lag. During a TSE air temperature changes appreciably not only in magnitude but also in timing, depending on weather and geographical conditions. If the eclipse is partially or totally obscured by clouds, some effects are produced on the thermal lag. Under clear skies, the temperature response lags behind the change in solar flux as one expects in TSE; however, under cloudy skies, the lag can reverse in early and/or late stages of partial phases. The normal heating of the surface by the Sun, which drives turbulent motion in the air layer near the surface, is disrupted during the eclipse. The 2009 TSE in China provided an opportunity to have a look at these kinds of perturbations caused by this eclipse. In this paper, the second of a series of three, we analyze the near-surface air temperature response, at three different heights over the ground, recorded by the Williams College expedition under meteorological conditions characterized by cloudy skies during the longest total solar eclipse of the 21st century on 2009 July 22, at Tianhuangping (Zhejiang), China. An analysis of the relationship between solar radiation and air temperature was made by applying a study previously published in the first paper of this series in which we evaluated the cloudiness contribution in estimating the impact on global solar radiation throughout this phenomenon at that site. The analysis of this response includes linear and absolute negative anomalies as well as fluctuations, which was undertaken through a statistical study to get information on the convection activity produced by the latter. The fluctuations generated by turbulence were studied by analyzing variance and residuals. The results, indicating a steady decrease and recovery of both perturbations, were consistent with those published by other studies for this total solar eclipse.