Abstract

The air at the surface of the high Antarctic Plateau is very cold, dry and clean. In such conditions the atmospheric moisture can significantly deviate from thermodynamic equilibrium conditions, and supersaturation with respect to ice can occur. Most conventional humidity sensors for meteorological applications cannot report supersaturation in this environment. A simple approach for measuring supersaturation using conventional instruments, one being operated in a heated airflow, is presented. Since 2018, this instrumental setup was deployed at 3 levels in the lower ~40 m above the surface at Dome C on the high Antarctic Plateau. The 3-year 2018–2020 record (Genthon et al. 2021) is presented and analyzed for features such as the frequency of supersaturation with respect to ice, diurnal and seasonal variability, and vertical distribution. As supercooled liquid water droplets are frequently observed in clouds at the temperatures met on the high Antarctic Plateau, the distribution of relative humidity with respect to liquid water at Dome C is also discussed. It is suggested that, while not strictly mimicking the conditions of the high troposphere, the surface atmosphere on the Antarctic Plateau is a convenient natural laboratory to test parametrizations of cold microphysics predominantly developed to handle the genesis of high tropospheric clouds. Data are distributed on the PANGAEA data repository at https://doi.pangaea.de/10.1594/PANGAEA.939425 (Genthon et al., 2021).

Highlights

  • The surface atmosphere of the high Antarctic Plateau is very cold, with an annual average 3-m air temperature of -52°C, ranging from -64°C in June to -31°C in January (Genthon et al 2021)

  • As supercooled liquid water droplets are frequently observed in clouds at the temperatures met on the high Antarctic Plateau, the distribution of relative humidity with respect to liquid water at Dome C is discussed

  • Genthon et al (2021) focus on 150 temperatures from the HMP155 but do not yet report on the moisture data because the sensors are limited to measuring up to 100% relative humidity wri, while it is known for the atmosphere to reach well above saturation at Dome C (Genthon et al, 2017)

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Summary

Introduction

The surface atmosphere of the high Antarctic Plateau is very cold, with an annual average 3-m air temperature of -52°C, ranging from -64°C in June to -31°C in January (Genthon et al 2021). This may be due to stagnant air slowly cooling radiatively, which should result in supersaturation, or air subsiding from above in association with the general convergence and subsidence on the Antarctic Plateau (Bas et al (2019), Vignon et al (2018)) In the latter case, adiabatic warming through subsidence and compression reduces relative humidity at a fixed moisture content, 185 contributing to less frequent supersaturation cases at very cold temperatures.

Seasonal and diurnal cycles and variability
Vertical profiles and gradients
A look at relative humidity with respect to liquid water 400
Findings
Conclusions
Full Text
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