Turbulence Characteristics in the Atmospheric Surface Layer for Different Wind Regimes over the Tropical Zongo Glacier (Bolivia, $$16^\circ $$ 16 ∘ S)

Abstract

We investigate properties of the turbulent flow and sensible heat fluxes in the atmospheric surface layer of the high elevation tropical Zongo glacier (\(5,080\) m a.s.l., \(16^\circ \)S, Bolivia) from data collected in the dry season from July to August 2007, with an eddy-covariance system and a 6-m mast for wind speed and temperature profiles. Focus is on the predominant downslope wind regime. A low-level wind-speed maximum, around a height of \(2\) m, is detected in low wind conditions (37 % of the time). In strong wind conditions (39 % of the time), no wind-speed maximum is detected. Statistical and spectral analyses reveal low frequency oscillations of the horizontal wind speed that increase vertical mixing. In strong winds, wavelet analysis shows that coherent structures systematically enhance the turbulent sensible heat fluxes, accounting for 44–52 % of the flux. In contrast, in low wind conditions, the katabatic flow is perturbed by its slow oscillations or meandering motions, inducing erratic turbulent sensible heat fluxes. These motions account for 37–43 % of the flux. On tropical glaciers, the commonly used bulk aerodynamic profile method underestimates the eddy-covariance-based flux, probably because it does not account for low frequency disturbances that influence the surface flow in both wind regimes.