An estimate of the temporal fraction of cloud cover at San Pedro M\'artir Observatory

TL;DR

This paper estimates the daytime cloud-free fraction at San Pedro Mártir Observatory using a novel solar radiation data method, confirming its suitability for optical and infrared astronomy with over 82% clear sky time.

Contribution

The study introduces a new method to estimate cloud cover from solar radiation data, validated with extensive site-testing data at San Pedro Mártir.

Findings

82.4% of daytime is clear of clouds

Results align with previous studies, validating the method

San Pedro Mártir is an excellent astronomical site

Abstract

San Pedro M\'artir in the Northwest of Mexico is the site of the Observatorio Astron\'omico Nacional. It was one of the five candidates sites for the Thirty Meter Telescope, whose site-testing team spent four years measuring the atmospheric properties on site with a very complete array of instrumentation. Using the public database created by this team, we apply a novel method to solar radiation data to estimate the daytime fraction of time when the sky is clear of clouds. We analyse the diurnal, seasonal and annual cycles of cloud cover. We find that 82.4 per cent of the time the sky is clear of clouds. Our results are consistent with those obtained by other authors, using different methods, adding support to this value and proving the potential of the applied method. The clear conditions at the site are particularly good showing that San Pedro M\'artir is an excellent site for optical and infrared observations.