Temporal autocorrelation functions of solar speckle pattern

Abstract A study of day-time temporal autocorrelation functions of speckles was performed on the solar granulation with the McMath telescope of the Kitt Peak National Observatory. In the space of only a few minutes, rapid variations of time constants are observed. For some observations, a single and high value T of time-constant is obtained: average = 170 ms, standard deviation = 80 ms. The temporal autocorrelation functions are consistent with theoretical curves obtained from a single layer atmospheric turbulence model. For other observations, a super-imposed short time-constant τ, showing little variations around 5.5 ms (standard deviation 1 ms), is also present. It is shown that T depends on the diameter of the telescope D and that the value τ of the short time scale, when it occurs, is correlated with the Fried parameter r 0 .