A Comparison of Surface Sensible Heat Flux at Atqasuk and Barrow
Shaw, W.J. (a), Doran, J.C. (b), and Hubbe, J.M. (c), Pacific Northwest National Laboratory
Eleventh Atmospheric Radiation Measurement (ARM) Science Team Meeting
As part of the effort to discover the feedbacks between low-level arctic stratus and surface fluxes, we have operated an acoustic anemometer near Barrow, Alaska and a dual wavelength scintillometer near Atqasuk, which is 100 km to the south, in order to measure the surface turbulence heat flux. The systems operated unattended during the spring melt period of 2000, and the data were logged via internet or telephone connections. The acoustic anemometer was mounted on a tower attached to a barge grounded on a low island on the northeast side of Elson Lagoon. The anemometer was 8.5 m above the barge surface, giving an estimated height above the sea/ice surface of 10 m. The fetch was unobstructed, except by the tower and the anemometer itself, in all directions. The scintillometer was installed with a 200 m path between the transmitters and receivers. The path length was 2.5 m above the tundra, and it was oriented perpendicular to the prevailing wind direction. The scintillometer provided data from May until early July, when the transmitter and receiver apparently drifted out of alignment. The acoustic anemometer provided data until early August. Before the spring melt, both Barrow and Atqasuk exhibited a weak (maximum 30 W/m2) but clearly defined diurnal cycle in sensible heat flux and mean temperatures that were comparable. This diurnal cycle was strongly correlated between the sites. The melt occurred about two weeks earlier at Atqasuk than at Barrow. After the melt, the diurnal cycle was no longer evident in the Barrow data, with sensible heat fluxes remaining near zero most of the time. The exceptions were occasional periods of pronounced downward flux when the wind direction indicated advection of air from relatively warm land over relatively cool water. At Atqasuk, on the other hand, the departure of snow from the tundra coincided with a rapid increase in maximum daily sense flux to values as large as 200 W/m2. The daily mean temperature at Atqasuk also increased to values generally 10º C warmer than Barrow during the post-melt period. We expect that these differences in boundary layer temperature and heat flux are involved in feedbacks with the cloud properties at the two sites. A parallel component of this project is using radiometric measurements to establish cloud properties.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
