Simulating the night-time astronomical seeing at Dome A using Polar WRF

Abstract

In Antarctica, excellent astronomical observing conditions have been measured at Dome A during nighttime (or polar winter). This study investigates the performance of the Polar-optimized version of the Weather Research and Forecasting (Polar WRF, PWRF hereafter) for simulating the night-time astronomical seeing at Dome A. The seeing values were estimated by a seeing model, which used the PWRF-simulated wind speed and temperature as inputs. And three methods to obtain the boundary layer height in the seeing model have been examined. The estimated seeing agrees well with 50-day measurements from the KunLun Differential Image Motion Monitor at Dome A during the nighttime of 2019; the correlation coefficients range from 0.62 to 0.71. The PWRF-simulated meteorological parameters indicate that, low wind speed and strong temperature inversion (when a large gradient Richardson number always occurs) near the ground can lead to good seeing condition. The results suggest that the PWRF model could be a reliable tool for scheduling observational astronomy at Dome A during nighttime.

Discovery of Calm Astronomical Sites Over the Antarctic Continent

“…As for the temperature, the surface inversion strength increases toward the interior of the plateau (Ma et al 2010), and strong temperature inversion has the close corresponding relation with thin PBLH in Antarctica (Yagüe et al 2001;Petenko et al 2019). Further, the best image quality (corresponding to small seeing values) are observed for small PBLH (Petenko et al 2014;Yang et al 2022b). In sum, strong temperature inversion and weak wind speed produce a thin boundary layer over the high interior, so a calmer atmosphere (or larger CI) could occur and benefit astronomical observation.…”

“…Second, the atmospheric Ri, which can be simply calculated by the routine meteorological parameters (temperature and wind speed profiles), and have been verified on the coast, flank, and summit of the Antarctic continent (Hagelin et al 2008;Yang et al 2021bYang et al , 2022aYang et al , 2022b, with bigger temporal and spatial span than the integrated astroclimatic parameters (Lascaux et al 2009. Third, Both PBLH and Ri seem to be able to an alternative to the integrated astroclimatic parameters, as they were found to be strongly correlated with the observing condition (e.g., seeing) in Antarctica (Petenko et al 2014;Yang et al 2021bYang et al , 2022b. Nevertheless, the correlation between the two parameters and the astronomical seeing will also be validated in this study (Section 3.2.3).…”

“…The AMPS output fields consist mainly of meteorological parameters, without astronomical parameters (e.g., seeing). Helpfully, the Planetary Boundary Layer Height (PBLH; Stull 1988) and the atmospheric Richardson number (Ri; Obukhov 1971;Hunt 1998;Chan 2008), which can be obtained from the AMPS outputs, were found to be closely related to the astronomical seeing in Antarctica (Petenko et al 2014;Yang et al 2021bYang et al , 2022b. Besides, the Richardson number has been motivated as a proxy for evaluating the observing conditions of the Antarctic sites (Geissler & Masciadri 2006;Hagelin et al 2008).…”

“…First, PBLH is a more typical parameter, which can be directly outputted by a numerical model (Xie et al 2012), while the integrated astroclimatic parameters require additional optical turbulence parameterization (Lascaux et al 2009Yang et al 2021aYang et al , 2021b. Second, the atmospheric Ri, which can be simply calculated by the routine meteorological parameters (temperature and wind speed profiles), and have been verified on the coast, flank, and summit of the Antarctic continent (Hagelin et al 2008;Yang et al 2021bYang et al , 2022aYang et al , 2022b, with bigger temporal and spatial span than the integrated astroclimatic parameters (Lascaux et al 2009. Third, Both PBLH and Ri seem to be able to an alternative to the integrated astroclimatic parameters, as they were found to be strongly correlated with the observing condition (e.g., seeing) in Antarctica (Petenko et al 2014;Yang et al 2021bYang et al , 2022b.…”