T1: Mesoscale energy cascades in the lower and middle atmosphere

Principal investigators: Prof. Erich Becker (Leibniz Institute of Atmospheric Research), Dr. Almut Gassmann (Leibniz Institute of Atmospheric Research), Prof. Franz-Josef Lübken (Leibniz Institute of Atmospheric Research)

This project aims to develop a closure scheme for the atmospheric flow that is suitable for numerical truncation in the regime of stratified macro-turbulence. Particular emphasis is spent on conservation laws and scale invariance.  High-resolution lidar and radar measurements of temperatures and winds, as well as retrievals from other methods, are used to construct horizontal and vertical wavenumber power spectra for the upper troposphere and the mesosphere, and to validate the model results.

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Atmospheric gravity waves from LIDAR observations

My mission is to develop data analysis from our observations and apply it to the output from the Kühlungsborn Mechanistic Circulation Model (KMCM).

Marwa Almowafy, PhD T1

My name is Marwa Almowafy, I am a PhD student in the subproject “T1: Mesoscale energy cascades in the lower and middle atmosphere”.

I am working on temperature perturbations in the upper stratosphere and mesosphere, between 30 and 80 km, caused by atmospheric gravity waves. These waves are mainly generated in the troposphere due to several processes, for example convection and flow of air over mountains. The waves are propagating upward carrying momentum and energy. Eventually this momentum and energy is deposited at higher altitudes. With the help of observations, we address the cycle of gravity propagation and dissipation which is important for understanding their role of modifying the background atmosphere.

At the Leibniz Institute for atmospheric Physics (IAP) we have a variety of observation techniques and facilities such as balloons, sounding rockets, radars and Lidars. In the frame work of my PhD, I am focusing on data from Lidar observations. Our Rayleigh/Mie/Raman (RMR) Lidar is used to study temperatures and winds in the middle atmosphere. This Lidar has the unique capability to operate even under full daylight. IAP is operating several Lidars, one of them being located in Kühlungsborn, Germany, and another one in Andenes, Northern Norway. This allows for studying the impact of latitudinal difference and upper atmospheric dynamics regarding gravity waves. We are comparing the seasonal variability of temperature fluctuations from both locations to available reanalysis and satellite retrievals. A step further will be to approve the results with our highly resolving models at IAP.

My mission as a part of TRR181 is to develop data analysis from our observations and also apply it to the output from the Kühlungsborn Mechanistic Circulation Model (KMCM).  Furthermore, I plan to construct time series of gravity wave spectra from temperature and wind data to study the behavior of power spectral indices and compare them to expectations from theory.

Meso-scale energy cascades in the lower and middle atmosphere

My task is to extend the recently developed parameterization for friction/diffusion for atmospheric flows to the middle atmosphere.

Serhat Can, PhD in T1

Hi, I am Serhat from subproject T1. As a PhD candidate, my task is to extend the recently developed parameterization for friction/diffusion for atmospheric flows to the middle atmosphere, including full accounting of the spectral budget for kinetic and available potential energy. Complex flows cover a wide range of spatial and temporal scales and it becomes practically illogical to expect existing computational technology to simulate a realistic atmosphere for all observed phenomena. Thus, the emergence of accounting for the effects of unresolved scales is inevitable, resulting in what is known as the turbulence closure problem.

Closure is handled via the so-called Dynamic Smagorinsky Model (DSM), in the Kühlungsborn Mechanistic general Circulation Model (KMCM). This scheme eliminates ad hoc tuning for the parameterization and allows a space-time dependent mixing length, fully determined by the resolved flow.

Observational data from Nastrom & Gage point to transition from synoptic -3 slope to -5/3 in mesoscales for horizontal motion and temperature, providing a solid reference information for comparison. Atmosphere being strongly effected by gravity, anisotropic formulation is needed for DSM and the arguments of Stratified Macro Turbulence (SMT) comes into play for the aid, yielding an additional constraint on the dependence of vertical form of DSM on its horizontal part.

On top of all these intertwined descriptions of turbulence, scale invariance sets the tone and dictates equations to keep their forms unchanged for inertial regimes, including parameterizations. A dynamically determined mixing length complies with this requirement and definition of parameterization is completed. It should be emphasized that sub-grid scale motion is considered as a modelling of friction from a thermodynamic point of view. In this manner, only forward energy cascade with no backscatter must result on average from the spectral analyses of the circulation model.

Reasoning for a unidirectional energy cascade stems from the Lorenz Energy Cycle, where the conversions between kinetic, available and unavailable potential energy drives the climate. To appropriately represent this cycle detailed description of entropy production, i.e. friction due to motion is crucial. DSM appears as a comprehensive method to address above-mentioned demands in general circulation modelling. As a result, friction/diffusion in atmosphere represented in the framework of turbulence modelling creates an exciting meeting of seemingly distant fields.