MELTEX
Fig. 1: Polar 5 landing in Inuvik.
The aircraft campaign MELTEX (Impact of melt ponds on energy and momentum fluxes between atmosphere and sea ice) was a joint project conducted by the Alfred Wegener Institute for Polar and Marine Research (AWI), the Institute for Atmospheric Physics (IPA) at the University of Mainz, and Environment Canada (EC).
Melt ponds at the surface of Arctic sea ice usually form from end of May to end of August. They have a strong impact on the energy exchange between atmosphere, sea ice, and ocean. The most important effect is the enhancement of absorption of solar radiation due to the considerably lower albedo of melt ponds than that of the surrounding snow/ice.
The primary goal of MELTEX was to improve the quantitative understanding of the impact of melt ponds on radiation, heat, moisture, and momentum fluxes over Arctic sea ice. MELTEX aimed
● to determine pond fraction and broadband as well as spectral surface albedo of melt-pond covered sea ice,
● to investigate momentum and heat transport in the atmospheric boundary layer over melting sea ice,
● to collect data that can be used to improve algorithms for the retrieval of sea ice parameters such as melt pond fraction from satellite measurements.
The campaign took place in late spring / early summer, when melt ponds start to form. From 9 May to 8 June 2008, we operated in the Canadian Arctic, mainly over the southern Beaufort Sea with Inuvik as airbase for POLAR 5.
Fig. 2: MODIS-image showing the region of Franklin Bay (left), Parry Peninsula, and Darnley Bay (right) situated in the southern Amundsen Gulf. In early June 2008, wide areas of Franklin and Darnley Bay were covered by fast ice with well-developed melt ponds. Thin black lines mark the area, where measurements took place on 06 June 2008.
The aircraft was equipped with meteorological instrumentation including a spectral albedometer with active horizontal stabilization and with various camera systems and a laser altimeter to obtain information on sea ice surface properties (see Fig. 1). Broadband and spectral surface albedo were derived for clear-sky conditions.
Sea ice conditions changed considerably during the campaign from conditions without any melting to a situation with strong melting, especially on fast ice.
For example, on 06 June 2008 a flight was carried out over fast ice in Franklin and Darnley Bay south of the Cape Bathurst coastal polynya in the Amundsen Gulf (Fig. 2). The surface was mainly covered by melt ponds and bare ice only (Fig. 3). The clear-sky broadband albedo calculated from measurements on low level flight legs varied between 0.25 and 0.50. Broadband albedo decreased with increasing pond fraction (Fig. 4). The correlation coefficient R between broadband albedo and melt pond fraction was -0.84. The dependence of spectral albedo on pond fraction was largest in the visible and near-infrared range (Fig. 5). The shape of the spectral albedo curve did not change significantly with increasing melt pond fraction, presumably because ice thickness and pond depth did not vary considerably in this area of fast ice.
REPORTS ON POLAR AND MARINE RESEARCH, 593, 90 PP., 2009
Fig. 3: Well-developed melt ponds on fast ice in Franklin Bay. The picuture was taken with a hand-held camera at an altitute of approx. 330m.
Fig. 4: Clear-sky broadband albedo as function of melt pond fraction.
Fig. 5: Clear-sky spectral albedo as function of wavelength for three different intervals of melt pond fraction.
