RedSynA (more details)

Project leader: Rupert Klein
Project members: Eileen Mikusky, Antony Z. Owinoh (Guest, FU Berlin), Vladimir Petoukhov, Stamen Dolaptchiev
Contact informations

This project consists of three subprojects:

• Data Analyses
• Multiple scale models for planetary-synoptic interactions

• Concentrated Vortices in the Atmosphere

Data Analysis

Members: Alexey Eliseev (IAP RAS Moscow), Vladimir Petoukhov, Illia Horenko (FU Berlin), Stamen Dolaptchiev

Statistical dynamical atmospheric models as well as the atmosphere components of some Earth system models of intermediate complexity (EMICs) are derived by averaging over the synoptic length and time scales in a suitable fashion. In this way, the long-term evolution of the relevant variables is obtained. A common problem emerging in this approach is the closure procedure for the synoptic eddy statistics. One often assumes that they are of Gaussian type when deriving parameterizations.
Using ERA 40 reanalysis data for the period 1976-2002 we have analyzed the third order statistical moments of the synoptic variables (periods between 2.5 and 6 days). We found that the deviations from gaussianity are considerable in the regions of synoptic eddy generation. The results of this analysis provide guidelines for the development of improved parameterizations for the synoptic eddy statistics.

Considering the atmosphere as a complicated dynamical system, we analyze the ERA 40 time series in order to identify important metastable states and describe them by simple stochastic differential equations (SDEs). We expect that such metastable states are indicative for various modes of low-frequency atmospheric variability. The applied approach has been derived in an entirely different context originally, namely in the area of molecular dynamics, by I. Horenko and Ch. Schütte. We are currently exploring its potential in atmospheric applications.

•  A. Eliseev, V. Petoukhov, R. Klein: "An evaluation of the contribution from the third-order moments to the synoptic-scale dynamics and fluxes of heat and humidity", to appear in Tellus.
• I. Horenko, R. Klein, S. Dolaptchiev and Ch. Schütte: "Automated generation of reduced stochastic weather models I: simultaneous dimension and model reduction for time series analyses", to appear in SIAM J. Mult. Mod. & Sim. download
  

Multiple Scales Models for planetary-synoptic Interactions

Members: Stamen Dolaptchiev,  Rupert Klein

Observations show the existence of a large number of low-frequency atmospheric regimes (periods longer then 10 days) with planetary spatial scales (scales larger than 3000 km), which have an important influence on the variability of the atmosphere. We attribute to these structures some atmospheric phenomena such as: the thermally and orographically induced quasi-stationary planetary Rossby waves; teleconnection patterns (the North Atlantic Oscillation (NAO), the Pacific North American Oscillation (PNA) and others); monsoon circulations; ultra-long persistent blockings; mean meridional circulations (Hadley, Ferrel and the polar cells); zonal mean flows (subtropical and polar jets). A large body of theoretical and observational studies indicate that the planetary scale dynamics are strongly influenced by interactions with the synoptic scales (periods of 3 to 6 days and spatial scales of 1000 km).
Reduced model equations, describing the above listed phenomena, are of particular interest since they will elucidate general features of the atmosphere dynamics. Their numerical solution will be of less computational cost (compared with a GCM) and this makes them very attractive for studies of ultra-low-frequency variability of the atmosphere. It is also possible to implement them as the atmospheric module of an EMIC.
In our project we use a unified multiple scales asymptotic approach (R. Klein 2004, A. Majda and R.Klein 2003, R.Klein and A.Majda 2005) in order to derive systematically reduced model equations, describing planetary scale flows and their interactions with the synoptic scales. We study effects that result from the sphericity of the Earth and from the presence of a mean meridional background zonal flow. In the asymptotic expansion we resolve both: the planetary and the synoptic spatial and temporal scales. The project aims at model equations for the planetary scales, accounting for the averaged interactions with the synoptic scales, and for equations that reveal the influence of planetary structures on the local synoptic dynamics.

Concentrated Vortices in the Atmosphere 

Members: Eileen Mikusky, Antony Z. Owinoh (Guest, FU Berlin), Rupert Klein

At the focus of the third branch of our studies are concentrated atmospheric vortices. Examples include both hurricanes and midlatitude cyclones. In studying those vortices we aim at explaining the physical mechanisms that determine their three-dimensional structure as well as their large-scale motion. It is well known, that a number of key factors such as stratification, beta-effect, diabatic effects, background flow, etc. play an important role in this context. Regarding the latter it is known from observations and numerical simulations that strong vertical shear is an unfavourable condition for a vortex to remain coherent or vertically aligned.

Up to now the impact of the above key factors have been studied separately (to the best knowledge of the project members), since to combine all these factors one needs to describe complex interactions between different scales. We attempt to overcome this difficulty to some extent and use for our investigations again the unified mathematical approach mentioned above R. Klein 2004. In the context of concentrated vortices, we aim at deriving a common theory for the influence of a vortex' mesoscale dynamics on its own synoptic scale trajectory and vice versa. The theory shall also account for diabatic effects, mainly due to condensation, and for vertically sheared background flows.

• Mikusky, E. ,  Owinoh, A. Z. and  Klein, R. (2005): "On the influence of diabatic effects on the motion of 3D - mesoscale vortices within a baroclinic shear flow"  in  K.J. Bathe (Editor),  Computational Fluid and Solid Mechanics; Proceedings of theThird MIT Conference on Computational Fluid and Solid Mechanics;  download