## Inertia gravity waves breaking in the middle atmosphere: energy transfer and dissipation tensor anisotropy

Pestana, T., Thalhammer, M., Hickel, S. (2020) *Journal of the Atmospheric Sciences *77: 3193-3210. doi: 10.1175/JAS-D-19-0342.1

We present direct numerical simulations of inertia–gravity waves breaking in the middle–upper mesosphere. We consider two different altitudes, which correspond to the Reynolds number of 28 647 and 114 591 based on wavelength and buoyancy period. While the former was studied by Remmler et al., it is here repeated at a higher resolution and serves as a baseline for comparison with the high-Reynolds-number case.

## Rossby-number effects on columnar eddy formation and the energy dissipation law in homogeneous rotating turbulence

Pestana, T., Hickel, S. (2020)*Journal of Fluid Mechanics *885: A7. doi: 10.1017/jfm.2019.976

Two aspects of homogeneous rotating turbulence are quantified through forced direct numerical simulations in an elongated domain, which, in the direction of rotation, is approximately 340 times larger than the typical initial eddy size. First, by following the time evolution of the integral length scale along the axis of rotation ℓ_{‖}, the growth rate of the columnar eddies and its dependence on the Rossby number 𝑅𝑜_{𝜀} is determined as 𝛾=3.90exp(−16.72𝑅𝑜_{𝜀}) for 0.06⩽𝑅𝑜_{𝜀}⩽0.31, where 𝛾 is the non-dimensional growth rate. Second, a scaling law for the energy dissipation rate 𝜀_{𝜈} is sought.

## A priori investigations into the construction and the performance of an explicit algebraic subgrid-scale stress model

Gnanasundaram, A.K., Pestana, T., Hickel, S. (2019) *11th International Symposium on Turbulence and Shear Flow Phenomena.* TSFP paper 2019-286

We investigate the underlying assumptions of Explicit Algebraic Subgrid-Scale Models (EASSMs) for Large- Eddy Simulations (LESs) through an a priori analysis using data from Direct Numerical Simulations (DNSs) of homogeneous isotropic and homogeneous rotating turbulence. We focus on the performance of three models: the dynamic Smagorinsky (DSM) and the standard and dynamic explicit algebraic models as in Marstorp et al. (2009), here refereed to as SEA and DEA.

## Regime transition in the energy cascade of rotating turbulence

Pestana, T., Hickel, S. (2019) *Phys. Rev. E* 99, 053103. doi: 10.1103/PhysRevE.99.053103

Transition from a split to a forward kinetic energy cascade system is explored in the context of rotating turbulence using direct numerical simulations with a three-dimensional isotropic random force uncorrelated with the velocity field. Our parametric study covers confinement effects in high-aspect-ratio domains and a broad range of rotation rates.

## Benchmarking in a rotating annulus: A comparative experimental and numerical study of baroclinic wave dynamics

Vincze, M., Borchert, S., Achatz, U., Von Larcher, T., Baumann, M., Liersch, C., Remmler, S., Beck, T., Alexandrov, K.D., Egbers, C., Fröhlich, J., Heuveline, V., Hickel, S., Harlander, U. (2015) *Meteorologische Zeitschrift* 23: 611-635. doi: 10.1127/metz/2014/0600

The differentially heated rotating annulus is a widely studied tabletop-size laboratory model of the general mid-latitude atmospheric circulation. The two most relevant factors of cyclogenesis, namely rotation and meridional temperature gradient are quite well captured in this simple arrangement. The radial temperature difference in the cylindrical tank and its rotation rate can be set so that the isothermal surfaces in the bulk tilt, leading to the formation of baroclinic waves.

## Finite-volume models with implicit subgrid-scale parameterization for the differentially heated rotating annulus

Borchert, S., Achatz, U., Remmler, S., Hickel, S., Harlander, U., Vincze, M., Alexandrov, K.D., Rieper, F., Heppelmann, T., Dolaptchiev, S.I. (2014) *Meteorologische Zeitschrift* 23: 561-580. doi: 10.1127/metz/2014/0548

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.

## On the construction of a direct numerical simulation of a breaking inertia-gravity wave in the upper-mesosphere

Fruman, M.D., Remmler, S., Achatz, U., Hickel, S. (2014) *Journal of Geophysical Research *119: 11613-11640. doi: 10.1002/2014JD022046

A systematic approach to the direct numerical simulation (DNS) of breaking upper mesospheric inertia-gravity waves of amplitude close to or above the threshold for static instability is presented. Normal mode or singular vector analysis applied in a frame of reference moving with the phase velocity of the wave (in which the wave is a steady solution) is used to determine the most likely scale and structure of the primary instability

## A conservative integration of the pseudo-incompressible equations with implicit turbulence parameterization

Rieper, F., Hickel, S., Achatz, U. (2013)*Monthly Weather Review* 141: 861-886. doi: 10.1175/MWR-D-12-00026.1

Durran’s pseudo-incompressible equations are integrated in a mass and momentum conserving way with a new implicit turbulence model. This system is soundproof, which has two major advantages over fully compressible systems: the Courant–Friedrichs–Lewy (CFL) condition for stable time advancement is no longer dictated by the speed of sound and all waves in the model are clearly gravity waves (GW).