Two years of atmospheric boundary layer observations on a 45‐m tower at Dome C on the Antarctic plateau

Abstract

[1] The lower atmospheric boundary layer at Dome C on the Antarctic plateau has been continuously monitored along a 45-m tower since 2009. Two years of observations (2009 and 2010) are presented. A strong diurnal cycle is observed near the surface in summer but almost disappears at the top of the tower, indicating that the summer nocturnal inversion is very shallow. Very steep inversions reaching almost 1 C m À1 on average along the tower are observed in winter. They are stronger and more frequent during the colder 2010 winter, reaching a maximum in a layer~10-15 m above the surface. Winter temperature is characterized by strong synoptic variability. An extreme warm event occurred in July 2009. The temperature reached À30 C, typical of midsummer weather. Meteorological analyses which agree with the observations near the surface confirm that heat is propagated downward from higher elevations. A high total water column indicates moist air masses aloft originating from the lower latitudes. The coldest temperatures and strongest inversions are associated with characteristic synoptic patterns and a particularly dry atmosphere. Measurement of moisture in the clean and cold Antarctic plateau atmosphere is a challenging task. Supersaturations are very likely but are not revealed by the observations. This is possibly an instrumental artifact that would affect other moisture measurements made in similar conditions. In spite of this, such observations offer a stringent test of the robustness of the polar boundary layer in meteorological and climate models, addressing a major concern raised in the IPCC 2007 report.

Wavelike Structures in the Turbulent Layer During the Morning Development of Convection at Dome C, Antarctica

“…Episodic synoptic perturbations, due to maritime air intrusions produce wind speeds of up to 10 m s −1 , significantly higher temperatures (up to −20 • C) and dense cloudiness (e.g. Argentini et al 2001;Genthon et al 2013). …”

“…The calibration procedure was the same as described in Petenko et al (2014b): based on the validity of the Obukhov-Wyngaard "z −4/3 " height dependence of C 2 T for convective conditions, we calculated the corresponding values for each range gate of the sodar profile from the sonic C 2 T measured at 3.5 m. The converting coefficients C = C 2 T (z)/(I z 2 exp(4az)) at several levels were then averaged providing the value C = (2.67 ± 0.58) × 10 −9 K m −2/3 −2 to give C 2 T values expressed in units of K m −2/3 , where is the analog-to-digital converter count. In addition, temperature and wind-velocity profiles from a 45-m tower located at a distance of approximately 1 km were available; see a description of the tower equipment in Genthon et al (2013).…”

Atmospheric moisture supersaturation in the near-surface atmosphere at Dome C, Antarctic Plateau

“…4). More often than not, when ∼ 100 % RH i is observed at Dome C with conventional instruments (not adapted to sample supersaturation), both models produce significant supersaturation, occasionally reaching more than 150 % (Genthon et al, 2013). The cold microphysics parameterizations differ in the two models (see Sect.…”

“…On the other hand, many reports of relative humidity with respect to ice (RH i ) on the Antarctic Plateau reach but seem to be capped at 100 % (King and Andersen, 1999). Genthon et al (2013) compare RH i observed at Dome C on the Antarctic Plateau, using conventional solid-state sensors, with results from the ECMWF (European Center for Mediumrange Weather forecasts) meteorological analyses and from the MAR (Modèle Atmosphérique Régional) meteorological model. In both models, cold microphysics parameterizations are used which, depending on local conditions, allow for supersaturations (Sect.…”

“…In Sect. 4, simulation results from recent versions of the two atmospheric models discussed in Genthon et al (2013) quent occurrences of supersaturation at all times in the year including in summer. It is also shown that details of the climatology and the statistics of occurrence of supersaturation differ between the models and the observations and between the two models.…”