Anomalies in MERRA-2 & Automatic Weather Station Data over the East Antarctic Plateau

Abstract:

Scientists published an analysis of recent coldest temperatures recorded on Earth in 2018. Temperatures of the snow surface in the East Antarctica Plateau were observed to reach -98.0 °C from thermal emission. The study estimated about -95°C (±4°C) air temperature at 2 meters above the surface. The discovery inspired this investigation of a discrepancy between NASA's MERRA-2 model data and in situ data from two Automatic Weather Stations (AWS) known as PlateauB (78°39' S, 35°38' E, ~3620 m ) and Pole of Inaccessibility (82°07' S, 55°02' E, ~3730 m), located close to the coldest recorded temperatures discussed by Scambos et al. Comparisons of year by year daily mean 2-meter air temperatures from AWS and climate reanalysis data yielded high overall correlations (most R ≥ 0.84), but consistently MERRA-2 temperatures did not reach the lowest temperatures (below -65°C) during the colder months (April-Sep). During these months, which are periods of low or no sunlight, the difference between MERRA-2 2-meter air temperatures and observed AWS 2-meter air temperature varied systematically with temperature, with the difference being greatest (up to ~ -12°C) at the coldest AWS-recorded conditions. We then examined the difference between AWS Temperatures and wind speeds (data from MERRA-2). The lowest temperatures occur during periods of low wind speed (< 2 ms-1) while the warmest winter days at these sites are periods of high wind speeds (> 10 ms-1). During these periods of high wind, the wind direction is in the direction of gravitationally-driven drainage (i.e. katabatic winds). We hypothesize that slow winds result in a strong inversion, and thus a steep temperature gradient with lowest temperatures near the surface; that moderate winds (4-8 ms-1) in an inversion is close to what the MERRA-2 model estimates, thus with consistent temperatures between MERRA-2 and the AWS; and that fast winds result in the inversion being disrupted or overcome due to turbulent airflow and downward mixing of warm air, thus resulting in temperatures higher than the MERRA-2 estimate. Studying, characterizing, and describing such extremely cold regions can provide insight into polar climate, the interaction of the atmosphere and ice sheet, and be analogous to other locations of extremely cold temperatures in our solar system (e.g. Mars polar regions).