Assessment of the AlUla Manara astronomical site in Saudi Arabia using ECMWF ERA5 Reanalysis data

TL;DR

This study evaluates AlUla Manara's suitability as Saudi Arabia's first major astronomical observatory using ECMWF ERA5 reanalysis data, focusing on key atmospheric parameters relevant for optical-IR telescopes.

Contribution

It provides a preliminary assessment of AlUla Manara's astro-meteorological conditions, comparing it with other potential sites in Saudi Arabia, and supports site validation with on-site monitoring.

Findings

Median nighttime seeing of 1.5 arcsec

Over 79% clear sky conditions at night

Mild wind regimes suitable for observatory infrastructure

Abstract

As part of Saudi Arabia Vision 2030 and under the guidance of the Royal Commission for AlUla (RCU), efforts are underway to establish AlUla Manara as the Kingdom first major astronomical observatory. This study presents a preliminary assessment of the site based on ECMWF ERA5 reanalysis data to evaluate its suitability for hosting a 4m-class optical-IR telescope. AlUla Manara is located on a remote plateau 74 km north of the historical town of AlUla and was recently designated as an International Dark Sky Park. The analysis focuses on key astro-meteorological parameters such as seeing, temperature regimes, wind patterns, cloud cover and precipitable water vapor (PWV). Results show a median nighttime seeing of 1.5 arcsec, a median cold season PWV of 3.2 mm, and over 79% of nighttime hours with clear sky conditions. Wind regimes are generally mild, posing no constraints on infrastructure. The analysis includes three further sites in the Kingdom, namely Volcanic Top, Ward Mountain, and Dubba Mountain. These sites exhibit better turbulence conditions, but are located outside RCU jurisdiction. Nevertheless, AlUla Manara remains a competitive candidate thanks to its alignment with broader regional development goals. To validate these preliminary results, a dedicated Astronomical Site Monitor has been deployed on site to support the design and operational planning of the observatory.