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| Titel |
Surface energy budget over snow and blue ice in Dronning Maud land, Antarctica, during two summer seasons. |
| VerfasserIn |
T. Vihma, R. Pirazzini, M. Johansson |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250027535
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| Zusammenfassung |
| During two Finnish Antarctic expeditions (summers 2006/07 and 2007/08) radiation,
turbulence, and snow properties were measured over a glacier in the vicinity of the Finnish
Station Aboa (73Ë 03’S, 13Ë 24’W), in order to quantify the various component of the
surface energy budget. The main measurement station, located at ~230 a.s.l. in an area
covered by a thick snow pack, was equipped with a weather mast that gave the vertical profile
of temperature and wind speed up to 6.5 m, a 3-dimendional sonic anemometer from which
the turbulent fluxes of heat and momentum, atmospheric stability parameter, drag coefficient
and various statistics of turbulence were calculated, and a set of radiation sensors to measure
the upwelling and downwelling longwave and shortwave radiation fluxes. A second
measurement station was located at the distance of one kilometer from the main station, over
a blue-ice area, and was equipped with a set of radiometers to measure the for components of
the surface radiation budget (plus the downward diffuse shortwave radiation during
the second campaign). A third measurement station was located on bare, rocky
ground on the slope of a nunatak at 480 m a.s.l., at 3 km distance from the main
measurement station on the glacier. The wind, air temperature, humidity, incoming
solar radiation and, in 2007/2008, the turbulent fluxes of heat and momentum were
measured.
Snow temperature and density vertical profiles (down to a depth of 0.5m) were measured
twice a day (in the first campaign) and twice at each other day (in the second campaign).
Occasionally, to quantify the spatial heterogeneity of the snow properties, snow temperature
and density in the uppermost layers were measured along horizontal lines several
meters long. Vertical profile of snow grain size was obtained from digital photos
taken once or twice a day (in the first campaign) or at each other day (in the second
campaign). Cloud cover classification was made every two hours except during night
time.
The preliminary data analysis showed that near-neutral stratification dominated
during both measurement campaigns, with some cases of strong surface-based
temperature inversions over the glacier. Over the bare ground of the nunatak, the surface
was strongly heated, which resulted in upward turbulent heat fluxes, convection
and, occasionally during weak winds under clear skies, formation of convective
Cumulus humilis clouds. Although the Sun was continuously above the horizon, the
surface fluxes, atmospheric surface layer stratification, and the vertical profile of
snow temperature had a pronounced diurnal cycle. Occasionally, much higher wind
speed was observed at Aboa station compared to the glacier, due to the very stable
stratification which prevented the vertical mixing of momentum over the glacier.
Momentum flux and drag coefficient over the glacier were clearly affected by the
sastrugi: high drag was observed when wind direction differed from the usual, i.e.
wind blew perpendicular to the sastrugi. Surface albedo was identical at the snow
and blue ice sites as long as snow was uniformly covering the blue ice area. When
snow disappeared over the blue ice, the albedo significantly dropped, causing a
sharp increase in net shortwave radiation absorbed at the surface. Daily maxima in
upwelling longwave radiation were similar over snow and blue-ice, but over blue ice the
nocturnal minima in upwelling radiation were much higher than over snow, due to
the larger conductive heat flux from the ice/water beneath the surface. We also
observed a large small-scale (< 1 m) horizontal variability in snow temperature and
density, probably due to the presence of sastrugi and the non-uniform wind packing. |
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