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Turbulent transport of energy across a forest and a semiarid shrubland

Abstract. The role of secondary circulations has recently been studied in the context
of well-defined surface heterogeneity in a semiarid ecosystem where it was
found that energy balance closure over a desert–forest system and the
structure of the boundary layer was impacted by advection and flux
divergence. As a part of the CliFF (“Climate feedbacks and benefits of
semi-arid forests”, a collaboration between KIT, Germany, and the Weizmann
Institute, Israel) campaign, we studied the boundary layer dynamics and
turbulent transport of energy corresponding to this effect in Yatir Forest
situated in the Negev Desert in Israel. The forest surrounded by small shrubs
presents a distinct feature of surface heterogeneity, allowing us to study
the differences between their interactions with the atmosphere above by
conducting measurements with two eddy covariance (EC) stations and two
Doppler lidars. As expected, the turbulence intensity and vertical fluxes of
momentum and sensible heat are found to be higher above the forest compared
to the shrubland. Turbulent statistics indicative of nonlocal motions are
also found to differ over the forest and shrubland and also display a strong
diurnal cycle. The production of turbulent kinetic energy (TKE) over the
forest is strongly mechanical, while buoyancy effects generate most of the
TKE over the shrubland. Overall TKE production is much higher above the
forest compared to the shrubland. The forest is also found to be more
efficient in dissipating TKE. The TKE budget appears to be balanced on
average both for the forest and shrubland, although the imbalance of the TKE
budget, which includes the role of TKE transport, is found to be quite
different in terms of diurnal cycles for the forest and shrubland. The
difference in turbulent quantities and the relationships between the
components of TKE budget are used to infer the characteristics of the
turbulent transport of energy between the desert and the forest.
