Polar Boundary Layer Field Studies

My introduction to polar studies was mostly serendipitous, stemming from a chance conversation about turbulence with a favorite professor (J. Dungan Smith) when I was a first-year graduate student in the geophysics program at the University of Washington in 1971. In March 1972, I thus found myself standing on the flight deck of a C130 Hercules as it made the first nighttime landing on a frozen-lead runway lit with smudge pots about 300 nm north of Barrow, Alaska. My memory of the remainder of that night is the roar (and smell) of C130 turbines as flight after flight landed, and all hands turned out to offload tons of scientific equipment and support materiel. The next day I had a chance to observe what was for me a completely new environment: breathtakingly cold in spite of dazzling sunlight; a terrain of pressure ridges and sastrugi, like miniature landforms; and a color spectrum consisting only of gradations from blue to white. In a fundamental way, I have enjoyed the polar environment ever since.

By any standard, the 1972 AIDJEX Pilot Study was an enormous undertaking. Organized under the leadership of N. Untersteiner, peak occupancy of the station exceeded 80 scientists and support personnel. It was supplied by eighteen C130 and numerous smaller aircraft flights (Heiberg and Bjornert 1972). The AIDJEX Pilot Study also provided me, through my association with J. D. Smith, an opportunity afforded few graduate students: access to an unprecedented data set with simultaneous measurements of turbulent stress and mean velocity at several levels through an entire rotational planetary boundary layer. What Smith realized, and what I came soon to appreciate, was that drifting ice stations provided superb laboratories for studying ocean boundary layer (OBL) physics. Without vertical platform (ship) motion and the complicating factor of surface gravity waves, it was relatively easy to measure small velocity fluctuations across much of the turbulent spectrum. Wind-driven ice typically drifts with the maximum velocity in OBL, and given its considerable momentum, it provides a remarkably steady platform from which to measure the small fluctuations in velocity and scalar contaminants that constitute turbulent exchange.

In the intervening years I have participated in more than 20 polar field programs in both hemispheres. In addition to descriptions of SHEBA and AIDJEX already provided, some of the projects that provided additional data used in this volume were:

Marginal Ice Zone Experiment (MIZEX, June-July 1984): A multinational, multi-ship project in the Greenland Sea/Fram Strait region. We made measurements from two different floes drifting near the ice edge, supported by the M/V Polar Queen. Late in the project, northerly winds blew our floe across an upper-ocean temperature front marking the boundary of an eddy identified later in satellite imagery. After crossing into the warmer water, turbulent heat flux increased dramatically (Section 5.2).

Coordinated Eastern Arctic Experiment (CEAREX, March-April 1989): A late winter project north of Fram Strait established by aircraft. It mostly drifted along the NW flank of Yermak Plateau, and was notable in that in contrast to most of the Arctic Ocean experiments, the main driving was tidal and internal ice stress gradients rather than wind, the mixed layer was relatively deep, with no underlying cold, saline layer.

Ice Station Weddell (ISW, February-April 1992): A drift station following closely the track of HMS Endurance in 1915-1916 east of the Antarctic Peninsula (Gordon et al. 1993). The station was deployed by the Soviet research ice breaker R/V Federov, and recovered during the maiden voyage of the R/V Nathaniel B. Palmer, chartered for the US National Science Foundation. My turbulence apparatus was deployed and operated by R. Andersen and D. Martinson.

The Lead Experiment (LeadEX, March-April 1992): An ambitious experiment designed to move an entire ice camp by helicopters and/or snow machines to the edges of freezing leads within hours of the lead opening. The main station was deployed by air about 300 km NNE of Prudhoe Bay, Alaska. We deployed to four different leads (Section 5.3 and Fig. 5.12).

The Antarctic Zone Flux Experiment (ANZFLUX, June-August 1994): Winter experiment in the eastern Weddell Sea, with two drifts, one west of and the other over Maud Rise (a seamount centered near 65° S, 3° E.) In several storms we encountered extreme conditions of stress and heat flux in the upper ocean (McPhee etal. 1996).

Ice Station Polarstern (ISPOL, November 2004-January 2005): A drift experiment in early summer near the track of ISW (and the Endurance), supported by the German research icebreaker, R/V Polarstern. We drifted with a relatively large heterogeneous floe made up of multiyear and first-year ice fragments. in the western Weddell (Hellmer et al. 2006), forced by a combination of wind, tides, and mean flow.

Maud Rise Nonlinear Equation of State Study (MaudNESS, July-September 2005): A winter experiment in the eastern Weddell Sea designed to study upper ocean mixing in a low stability environment, from the R/V Nathaniel B. Palmer. The experiment comprised a rapid survey of upper ocean properties above and on the flanks of the Maud Rise seamount, two ship-supported drifts with various instrumentation on the ship and adjacent floe, and a series of short drifts with all instrumentation, including turbulence measuring equipment deployed from the ship.

Svalbard Fjord Studies An ongoing series of short field studies from fast ice in Svalbard fjords, usually done in collaboration with the University Center in Svalbard (UNIS). By measuring turbulence during tidal cycles along with ice characteristics, these experiments were designed to look at specific aspects of heat and salt exchange near the ice/ocean interface.

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