Abstract
We study the influence of the large-scale atmospheric
contribution to the dynamics of the convective
boundary layer (CBL) in a situation observed during the
Boundary Layer Late Afternoon and Sunset Turbulence
(BLLAST) field campaign. We employ two modeling approaches,
the mixed-layer theory and large-eddy simulation
(LES), with a complete data set of surface and upper-air atmospheric
observations, to quantify the contributions of the
advection of heat and moisture, and subsidence. We find
that by only taking surface and entrainment fluxes into account,
the boundary-layer height is overestimated by 70 %.
Constrained by surface and upper-air observations, we infer
the large-scale vertical motions and horizontal advection of
heat and moisture. Our findings show that subsidence has a
clear diurnal pattern. Supported by the presence of a nearby
mountain range, this pattern suggests that not only synoptic
scales exert their influence on the boundary layer, but also
mesoscale circulations. LES results show a satisfactory correspondence
of the vertical structure of turbulent variables
with observations. We also find that when large-scale advection
and subsidence are included in the simulation, the
values for turbulent kinetic energy are lower than without
these large-scale forcings. We conclude that the prototypical
CBL is a valid representation of the boundary-layer dynamics
near regions characterized by complex topography and
small-scale surface heterogeneity, provided that surface- and
large-scale forcings are representative for the local boundary
layer.
Original language | English |
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Pages (from-to) | 4241-4257 |
Journal | Atmospheric Chemistry and Physics |
Volume | 15 |
DOIs | |
Publication status | Published - 2015 |
Keywords
- large-eddy simulation
- turbulence
- entrainment
- transition
- radiation
- decay