Subarctic Boundary Layer and Aeolian Science: Forcings and Responses, 20-R8136

Principal Investigators
Cynthia Dinwiddie
Donald Hooper
Timothy Michaels

Inclusive Dates:  02/04/10 – 06/04/10

Background - This project was undertaken to develop a baseline understanding of the atmospheric forcings on and geomorphologic responses of the Great Kobuk Sand Dunes in Kobuk Valley National Park, Alaska. This aeolian dune system and its thermokarst environs at 67° north latitude are bellwethers for subarctic climate change; the dunes also serve as terrestrial geophysical analogs to Martian dunes potentially affected by movement-arresting permafrost and CO₂ and H₂O frost. Scientific research in this remote park has lulled since the 1980s, so little recent information about park resources was available at the time this project commenced.

Approach - To close this knowledge gap, the project team performed analyses of subarctic aeolian geomorphology, conducted site-specific mesoscale atmospheric modeling, and integrated data at the intersection of these disciplines. A project team member accompanied a NASA-funded SwRI geophysics team in March 2010 to (1) conduct geomorphological field research, (2) collect multilevel meteorological and subsurface temperature data with a new custom, portable weather station acquired by SwRI in 2010, and (3) analyze resulting field data. Also, research was conducted to (1) simulate mesoscale atmospheric forcings on the dune system, (2) compare model results with field collected meteorological data, and (3) analyze model output. Finally, soil moisture curves for the Great Kobuk sands were generated from granulometric data; this constitutive relationship is being used in thermohydrologic modeling of the local cryosphere.

Accomplishments - Prevailing wind direction in March was generally within the range from north-northeast to southeast. Wind speeds were generally less than 10 m/s (with the strongest winds nearly always from the north-northeast/northeast). Measurements suggest a saltation threshold of ~9 m/s. Atmospheric modeling suggests significant wind field complexity, with katabatic winds from the north associated with the Baird Mountain canyons turbulently battling flow from the east along the axis of the Kobuk Valley. During the late-winter season, the winds switch chaotically to either flow regime at the dune field. When dominated by easterly flow, the wind direction and speed across the GKSD tend to be relatively uniform. Conversely, when dominated by northerly flow, more complex wind fields are likely to occur. Project results led to the hypothesis that dune movement is mechanically arrested by the combined influences of (1) longterm annual snowcover, which effectively disconnects much of the aeolian system from atmospheric forcing, (2) a seasonally frozen layer, (3) an underlying liquid water layer found everywhere within the dune field, and probably by (4) underlying permafrost that perches the liquid water layer. Given the anticipated importance of the hydrocryosphere on migration rates, petrophysical parameters were developed from granulometric data to model the subsurface dune environment. The sands were found to be fine grained, as defined by the Wentworth scale, relatively homogeneous, and moderately well sorted to well sorted. Finally, field observations of liquid water overflow/aufeis above the ice cover on Kavet and Anhnewetut Creeks near the dunefield suggest the relatively warm temperatures observed in thermal infrared imagery analyzed during a previous project were probably an indication of relatively warm overflow, which is especially common on subarctic creeks and streams shallow enough to completely freeze to their bed during winter.

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