Simultaneous Generalized and Low-Layer SCIDAR turbulence profiles at San Pedro M\'artir Observatory

TL;DR

This study combines G-SCIDAR and LOLAS turbulence profiles at San Pedro Me1rtir Observatory to analyze atmospheric turbulence with different resolutions, revealing detailed ground-layer turbulence and its impact on astronomical seeing.

Contribution

It provides simultaneous turbulence profiles using G-SCIDAR and LOLAS, offering new insights into the ground-layer turbulence and its variation with local topography and wind.

Findings

Turbulence peaks between 25 and 50 meters above ground.

Stable layers are often detected at 10-15 km altitude.

Median seeing value of 0.79 arcseconds across campaigns.

Abstract

We present optical turbulence profiles obtained with a Generalized SCIDAR (G-SCIDAR) and a Low Layer SCIDAR (LOLAS) at the Observatorio Astron\'omico Nacional in San Pedro M\'artir (OAN-SPM), Baja California, Mexico, during three observing campaigns in 2013, 2014 and 2015. The G-SCIDAR delivers profiles with moderate altitude-resolution (a few hundred meters) along the entire turbulent section of the atmosphere, while the LOLAS gives high altitude-resolution (on the order of tens of meters) but only within the first few hundred meters. Simultaneous measurements were obtained on 2014 and allowed us to characterize in detail the combined effect of the local orography and wind direction on the turbulence distribution close to the ground. At the beginning of several nights, the LOLAS profiles show that turbulence peaks between 25 and 50 m above the ground, not at ground level as was expected. The G-SCIDAR profiles exhibit a peak within the first kilometer. In 55% and 36% of the nights stable layers are detected between 10 and 15 km and at 3 km, respectively. This distribution is consistent with the results obtained with a G-SCIDAR in 1997 and 2000 observing campaigns. Statistics computed with the 7891 profiles that have been measured at the OAN-SPM with a G-SCIDAR in 1997, 2000, 2014 and 2015 campaigns are presented. The seeing values calculated with each of those profiles have a median of 0.79, first and third quartiles of 0.51 and 1.08 arcsec, which are in close agreement with other long term seeing monitoring performed at the OAN-SPM.