Assessment of Daytime Sky Quality and Atmospheric Refractive Index (Cn2) Analysis at Pico dos Dias Observatory

Cuadros E.T.; Almeida A.P.; Carlesso F.; Pareja-Quispe D.; Guarnieri F.L.; Lago A.D.; Gargaglioni S.R.; Vieira L.E.A. · Astrophysical Journal, Supplement Series (2025) · DOI: 10.3847/1538-4365/ae0a2a

Resumen

Ground-based astronomical and solar observations are strongly influenced by atmospheric turbulence, a dynamic phenomenon that degrades optical resolution through refractive index fluctuations. This study evaluates daytime sky quality and the refractive index structure parameter (Cn2) at the Pico dos Dias Observatory (OPD) in Brazil, integrating in situ meteorological data with the European Centre for Medium-Range Weather Forecasts Reanalysis version 5 product. Variables such as air temperature, wind speed, relative humidity, and cloud cover are analyzed across vertical and temporal scales, providing insights into diurnal, seasonal, and altitudinal atmospheric behaviors. The study highlights the distinct challenges posed by daytime turbulence, driven by solar heating and convection, on adaptive optics (AO) systems and high-precision solar spectropolarimetric instruments, such as the prototype of the Galileo Solar Space Telescope. To provide context for the atmospheric conditions at the OPD, this study characterizes several key meteorological variables. Typical daytime conditions feature median air temperatures of 15°C–20°C and surface winds of 1.0–4.0 m s−1, predominantly from the north, while nighttime conditions are cooler (10°C–15°C) with weaker winds shifting south–southeast. Relative humidity generally remains below 70%, especially in the June–July–August months, making it favorable for astronomical observations. Cloud cover shows seasonality, with clear-sky fractions of about 32% at night and 28% by day, peaking in austral winter and minimizing in summer. Our quantitative analysis of refractive index variability underscores the necessity of advanced AO technologies. Seasonal and vertical profiles of Cn2 present pronounced variability, influenced by solar heating, terrain-induced airflow, and jet stream dynamics. These findings stress the importance of strategic scheduling and turbulence modeling to optimize performance. This comprehensive characterization advances understanding of atmospheric conditions for solar and nighttime astronomy, refining AO systems, and enabling progress in high-precision astrophysics.

Instituciones: Universidad Nacional Mayor de San Marcos