Geophysics

Snow Megadunes

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Science  01 Dec 2000:
Vol. 290, Issue 5497, pp. 1653
DOI: 10.1126/science.290.5497.1653a

Dune-like features were noted over some areas of the East Antarctic Plateau more than a decade ago. These megadunes are long-wavelength surface ripples with amplitudes of only a few meters and crests that can extend for 100 kilometers.

Using Advanced Very High Resolution Radiometer (AVHRR) images, Fahnestock et al. find three dune fields located in regions characterized by anomalously low rates of snow accumulation. The largest dune field covers about 300,000 square kilometers, and the crests run perpendicular to the prevailing winds. Low microwave emission derived from annual averages and high back-scattered microwave energy on the downwind slopes of the dunes observed in synthetic aperture radar images indicate that the snow is coarse-grained and probably formed on the downwind slope by recrystallization. They suggest that a standing wave may disrupt the near-surface temperature gradient, which is due to radiative cooling of the snow, and that standing waves would bring warmer air onto the downwind slope of the dunes and thus cause recrystallization over large areas. Therefore, snow dunes may form by a more complex surface-atmosphere interaction than applies to sand dunes, and variations in recrystallization may hamper climate reconstructions. — LR

Geophys. Res. Lett.27, 3719 (2000).

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