HR: 1330h
AN: C12A-0860    [PDF]
TI: Can we Trust Measurements of Turbulence on top of the Greenland Ice Sheet?
AU: * Cullen, N J
EM: cullenn@cires.colorado.edu
AF: Cooperative Institute for Research in Environmental Sciences, UCB 216 University of Colorado, Boulder, CO 80309 United States
AU: Steffen, K
EM: koni@seaice.colorado.edu
AF: Cooperative Institute for Research in Environmental Sciences, UCB 216 University of Colorado, Boulder, CO 80309 United States
AB: The most important challenge to providing new insights into the workings of the atmosphere on the top of the Greenland ice sheet is to demonstrate that its weak and intermittent turbulence can be adequately characterized using existing instrumentation. To tackle this problem, very high temporal resolution measurements of turbulence at two heights near the surface were collected at Summit, Greenland over several field seasons. Two independent tests of stationarity on 1080 30-minute runs revealed that approximately 40% of observations are nonstationary. Nonstationary runs are characterized by periods with significant turbulent fluxes separated be extended inactive periods with little or no flux, with most of the flux during a run realized in small fractions ($<$25%) of the total time. However, spectral analyses of stationary runs show that velocity and temperature data, when non-dimensionalized with appropriate scaling parameters, reduce to a set of universal curves that are functions of z/L. To capture 99% of the turbulent heat flux in stable conditions sampling rates do not need to exceed 15 Hz, which is far less than the sampling frequency of 50 Hz used in this investigation. This is important as it shows that standard fast-response sensors close to the surface (2m) can capture the different scales of turbulent motion in this environment. For these measurements to be useful in other applications, such as establishing flux-profile relationships or energy budgets, the issue of stationarity must be addressed otherwise results may differ from those expected.
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
SC: Cryosphere [C]
MN: 2003 Fall Meeting