MARCIN CHRUST

European Center For Medium Range Weather Forecasts · Research Department

Skilful Machine Learned weather forecasts have challenged our approach to numerical weather prediction, demonstrating competitive performance compared to traditional physics-based approaches. Data-driven systems have been trained to forecast future weather by learning from long historical records of past weather such as the ECMWF ERA5. These datase...

An Ensemble of Data Assimilations (EDA) can provide valuable information on the analysis and short-range forecast uncertainties. The present ECMWF operational ocean analysis and reanalysis system, called ORAS5, produces an ensemble but does not exploit it for the specification of the background-error covariance matrix $\mathbf{B}$, a key component...

In the last two decades UK research institutes have led a wide range of developments in marine data assimilation (MDA), covering areas from the MDA applications in physics and biogeochemistry, to MDA theory. We review the progress over this period and formulate our MDA vision for both the short-term and the longer-term future. We focus on identifyi...

Recent studies have demonstrated that it is possible to combine machine learning with data assimilation to reconstruct the dynamics of a physical model partially and imperfectly observed. The surrogate model can be defined as an hybrid combination where a physical model based on prior knowledge is enhanced with a statistical model estimated by a ne...

Recent studies have demonstrated that it is possible to combine machine learning with data assimilation to reconstruct the dynamics of a physical model partially and imperfectly observed. Data assimilation is used to estimate the system state from the observations, while machine learning computes a surrogate model of the dynamical system based on t...

This article presents coupled data assimilation (DA) activities at the European Centre for Medium‐Range Weather Forecasts (ECMWF). Coupled DA is an essential component of the ECMWF Earth‐system strategy. It aims at providing consistent initial conditions to the coupled atmosphere, land, and ocean forecast model. The article introduces the different...

As soon as particles, freely falling or ascending under the action of gravity, buoyancy and hydrodynamic forces, reach Reynolds numbers exceeding values of the order of one hundred, path instabilities arise yielding non vertical, mostly oscillating, trajectories. In this paper we focus on the behavior of flat undeformable solid spheroids. Direct nu...

Developing effective ways to model and cycle the background‐error covariance matrix is an active area of research in data assimilation. An important aspect of this problem when using a filter to model the background‐error correlations is the computation of normalization factors to ensure that the diagonal elements of the modelled correlation matrix...

The standard formulation of 4D‐Var assumes random zero‐mean errors for all sources of information used in the analysis. This assumption is usually not well verified in real‐world applications. The performance of a weak‐constraint 4D‐Var formulation ("forcing" formulation) is studied in this paper in a simplified experimental setting using additive...

The efficiency of the forecasting system on future high-performance computing and data handling systems is considered one of the key challenges for implementing ECMWF’s ambitious strategy. This was already recognised by ECMWF in 2013, and has led to the foundation of the Scalability Programme. The programme aims to address this challenge as a conce...

We present a parallel hp-adaptive high order (spectral) discontinuous Galerkin method for approximation of the incompressible Navier-Stokes equations. The spatial discretization consists of equal-order polynomial approximations of the fluid velocity and pressure via discontinuous Galerkin spatial discretizations. For the nonlinear convective term w...

In the present paper, we investigate the path instabilities and the transition scenario for oblate homogeneous spheroids falling (or ascending) freely in a quiescent and unconfined Newtonian fluid under the action of gravity, buoyancy and hydrodynamic forces. The problem depends on three independent external parameters: the aspect ratio $\unicode[S...

Correlation operators based on the solution of an implicitly formulated diffusion equation can be implemented numerically using the Chebyshev iteration method. The attractive properties of the algorithm for modelling correlation functions on high‐performance computers have been discussed in a recent paper. The current paper describes a straightforw...

The transitional regimes of freely falling discs are investigated by direct numerical simulation of the fluid-solid interaction. The discs are assumed to be homogeneous and infinitely thin. The regimes depend on two independent parameters, the Galileo number expressing the ratio between effects of gravity and viscosity and the non-dimensionalized m...

Vortex lattice and panel methods belong to a broad family of aerodynamic codes based on potential flow theory. They are used in preliminary aerodynamic studies in early stages of aircraft design where hundreds of thousands candidate configurations are analyzed. In this paper, we describe their efficient implementation on modern multi- and many-core...

We take up the old problem of Calvert (J. Fluid Mech., vol. 29, 1967, pp. 691-703) concerning the wake of a cylinder inclined with respect to the flow direction, and consider it from the viewpoint of transition to turbulence. For cylinders placed perpendicular to the flow direction, we address the disagreement between numerical simulation of the id...

This paper reports about an experimental investigation of the loss of a fixed plane of symmetry in the wake of a sphere. The symmetry plane appears at the first bifurcation for the Reynolds number Re≈212 and is preserved by a secondary Hopf bifurcation that sets in for Re≈275. Upon increase of the Reynolds number the symmetry plane eventually break...

We present a comprehensive parametric study of the transition scenario of freely falling discs. The motion of the discs is investigated by a direct numerical simulation of the solid-fluid interaction. The discs are assumed to be homogeneous and infinitely thin. The problem is shown to depend on two independent parameters, the Galileo number express...

In 2007 Fernandes et al. reported a surprising delay of the onset of instabilities for freely rising cylinders of aspect ratio (χ=diameter/thickness of the cylinder) 10 and more. At Reynolds numbers at which instabilities develop in the wake of the same body kept fixed, the path was still found to be vertical and the wake axisymmetric. In this pape...

The manuscript presents a numerical study of non-vertical trajectories of bodies fallingor rising freely in a Newtonian fluid initially at rest. The original numerical methodcombining a spectral spatial discretization and the decomposition of the domain wasimplemented. The developed code was used to study fixed and freely moving objects. Forthe fix...

We have performed precise and systematic experiments with PIV in order to measure the velocity field in the wake of a solid sphere and of a disk in a water channel, in the range of intermediate Reynolds number in which stationary and oscillatory instabilities appear, including the hairpin shedding regime. From these experimental data, we study the...

Recently, the wake of a flat disk has regained the interest of researchers.ootnotetextFabre, Auguste and Magnaudet Physics of Fluids 20, 051702 (2008); Meliga, Chomaz and Sipp, J. Fluid Mech. 633, 159 (2009) Simultaneously, some numerical simulations were concerned with cylindrical bodies of finite thickness and showedootnotetextAuguste, Fabre and...