Second-Moment Budgets of the Baroclinic Atmospheric Boundary Layer

The assumption that the atmospheric boundary layer (ABL) is driven by uniform
pressure gradients (barotropic atmosphere) is known to be a critical oversimplification, with
field measurements and numerical simulations showing profound implications of baroclinicity
(height-dependent pressure gradients resulting from large
scale horizontal thermal gradients) on both the mean flow and second-order statistics. As
improved parameterization of velocity and scalar (e.g. temperature) variances, momentum and
heat fluxes is becoming increasingly important in weather and climate modeling, the need for a
deeper understanding of the influence of variable geostrophic forcing
on the ABL becomes also warranted. In this work, we conduct a suite of large eddy simulation
(LES) experiments spanning a range of stratification conditions, and strength and rotation angle
of the thermal wind vector to investigate the effects of geostrophic shear on the canonical
scaling laws of the second-order statistics in the ABL. Special emphasis is devoted to how
baroclinicity modifies the workings of energy redistribution by the pressure-strain and
pressure-temperature gradient terms in the variance and flux budgets, and whether simplified
representations such as Rotta-type and/or rapid distortion theory models remain plausible.
Implications on second-order closure modeling using Mellor-Yamada schemes will also be
discussed.