Boundary-Layer Meteorology

, Volume 141, Issue 3, pp 333-347

First online:

The Fallacy of Drifting Snow

  • Edgar L. AndreasAffiliated withNorthWest Research Associates, Inc. (Seattle Division) Email author 

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A common parametrization over snow-covered surfaces that are undergoing saltation is that the aerodynamic roughness length for wind speed (z 0) scales as \({\alpha u_\ast^2/g}\), where u * is the friction velocity, g is the acceleration of gravity, and α is an empirical constant. Data analyses seem to support this scaling: many published plots of z 0 measured over snow demonstrate proportionality to \({u_\ast^2 }\). In fact, I show similar plots here that are based on two large eddy-covariance datasets: one collected over snow-covered Arctic sea ice; another collected over snow-covered Antarctic sea ice. But in these and in most such plots from the literature, the independent variable, u *, was used to compute z 0 in the first place; the plots thus suffer from fictitious correlation that causes z 0 to unavoidably increase with u * without any intervening physics. For these two datasets, when I plot z 0 against u * derived from a bulk flux algorithm—and thus minimize the fictitious correlation—z 0 is independent of u * in the drifting snow region, u * ≥ 0.30 ms−1. I conclude that the relation \({z_0 = \alpha u_\ast^2/g}\) when snow is drifting is a fallacy fostered by analyses that suffer from fictitious correlation.


Bulk turbulent flux algorithm Drag coefficient Fictitious correlation Ice Station Weddell Roughness length Saltation Sea ice SHEBA Snow Turbulence measurements