4 research outputs found
Interactions between gravity waves and cirrus clouds: asymptotic modeling of wave induced ice nucleation
We present an asymptotic approach for the systematic investigation of the
effect of gravity waves (GW) on ice clouds formed through homogeneous
nucleation. In particular, we consider high- and mid-frequency GW in the
tropopause region driving the formation of ice clouds, modeled with a
double-moment bulk ice microphysics scheme. The asymptotic approach allows for
identifying reduced equations for self-consistent description of the ice
dynamics forced by GW including the effects of diffusional growth and
nucleation of ice crystals. Further, corresponding analytical solutions for a
monochromatic GW are derived under a single-parcel approximation. It is
demonstrated that the asymptotic solutions capture the dynamics of the full ice
model and provide a simple expression for the nucleated number of ice crystals.
The present approach is extended to allow for superposition of GW, as well as,
for variable mean mass in the ice crystal distribution. Implications of the
results for an improved representation of GW variability in cirrus
parameterizations are discussed
Rounding errors may be beneficial for simulations of atmospheric flow: results from the forced 1D Burgers equation
Finite-volume models with implicit subgrid-scale parameterization for the differentially heated rotating annulus
The differentially heated rotating annulus is a classical experiment for the investigation of baroclinic flows and can be regarded as a strongly simplified laboratory model of the atmosphere in mid-latitudes. Data of this experiment, measured at the BTU Cottbus-Senftenberg, are used to validate two numerical finite-volume models (INCA and cylFloit) which differ basically in their grid structure. Both models employ an implicit parameterization of the subgrid-scale turbulence by the Adaptive Local Deconvolution Method (ALDM). One part of the laboratory procedure, which is commonly neglected in simulations, is the annulus spin-up. During this phase the annulus is accelerated from a state of rest to a desired angular velocity. We use a simple modelling approach of the spin-up to investigate whether it increases the agreement between experiment and simulation. The model validation compares the azimuthal mode numbers of the baroclinic waves and does a principal component analysis of time series of the temperature field. The Eady model of baroclinic instability provides a guideline for the qualitative understanding of the observations