The Dynamics of the Surface-Atmosphere Exchange During and After Snow Melt for Different Arctic Ecosystems: MAGS

The arctic environment and in particular the Mackenzie basin displays a very dynamic interrelationship between the atmosphere and the surface for the different ecosystems represented. The Canadian Twin Otter research aircraft flew a total of 24 grid and long regional transects, over tundra, forest and delta ecosystems, during the period of snow melt (late May - early June) and early summer (early July) as part of the 1999 Mackenzie GEWEX Study (MAGS) field campaign. Observations over tundra showed a sharp rise in the sensible heat flux at the onset of melt, reaching a maximum plateau at the end of the melting period and into early summer. The latent heat flux showed a more gradual rise with a Bowen ratio of 2 during melt, and continuing to rise through to early summer. The forested system demonstrated similar gradual rise in the latent heat flux, while the sensible heat flux was already high with Bowen ratios reaching 3 at the start of the observation period in late May. For both systems, the Bowen ratio stabilizes at approximately 1 by early summer. The gradual rise in latent heat flux can be tied to gradual thawing of the root zone and the significance of transpiration. This is corroborated with a similar gradual trend in the carbon dioxide flux. The relatively low solar elevation angle and earlier start of snow melt in along the regional transect, may account for the much larger sensible heat flux. The closure of the energy balance and the portion of the flux attributed to non-turbulent fluxes and energy consumption is further refined by including flux contributions from low frequency events.

An analysis of the distribution of the turbulent coherent structures along the transect and over the grid area will also be presented. This has the potential of identifying the particular source areas for the different turbulent fluxes. The coincidence of the fluxes within these structures can also indicate co-location of sources. The findings from this study fill gaps in our knowledge about energy partitioning during snow melt, and broadens our contemporary view of evapotranspiration dynamics of wet surfaces.