Mauna Kea Sky Transparency from CFHT SkyProbe Data

TL;DR

This study reports on Mauna Kea's sky transparency over three years using SkyProbe data, showing that skies are clear enough for observations 76% of the time, with photometric conditions averaging 56%.

Contribution

It provides an empirical model of cloud attenuation and duration, enhancing understanding of Mauna Kea's atmospheric conditions for astronomical observations.

Findings

Skies were clear 76% of nights during the study period.

Photometric conditions occurred 56% of the time on average.

Attenuations less than 0.2 magnitudes occurred up to 60% of the time.

Abstract

Nighttime sky transparency statistics on Mauna Kea are reported based on data from the Canada-France-Hawaii Telescope SkyProbe monitor. We focus on the period beginning with the start of MegaCam wide-field optical imager operations in 2003, and continuing for almost three years. Skies were clear enough to observe on 76% of those nights; attenuations were less than 0.2 magnitudes up to 60% of the time. An empirical model of cloud attenuation and duration is presented allowing us to further characterize the photometric conditions. This is a good fit tothe SkyProbe data, and indicates that Mauna Kea skies are truly photometric (without cloud) an average of 56% of the time, with moderate seasonal variation. Continuous monitoring of transparency during the night is necessary to overcome fluctuations in attenuation due to thin cloud.