Nonlinear Processes in Geosciences

NPG Paper of the Month: “Empirical evidence of a fluctuation theorem for the wind mechanical power input into the ocean”

Achim Wirth November 4, 2021

The pdf p(z,τ) (left) and the symmetry function normalised by the averaging time S(z,τ)/τ (right) as a function of the power input z for different averaging times τ (see caption). The variable τ gives the length of the averaging interval in terms of observations done every 6 hours. Data are for the recirculation area of the Atlantic subtropical gyre at a resolution of 0.5o in space and 6 hours in time for the period of 1993–2016. Note that the pdfs differ from Gaussian. The symmetry function converges to a straight line for increasing averaging periods, showing evidence of a FT. License: “Empirical evidence of a fluctuation theorem for the wind mechanical power input into the ocean".

This month the NPG Paper of the Month award is achieved by Achim Wirth for his paper “Empirical evidence of a fluctuation theorem for the wind mechanical power input into the ocean“. Achim obtained his PhD at the University of Nice (Franc), doing research on turbulence theory. He then moved to oceanography working at UCLA (USA) and Geomar (Germany). Since 2005 he holds a permanent position a ...[Read More]

NPG Paper of the Month: “Ordering of trajectories reveals hierarchical finite-time coherent sets in Lagrangian particle data: detecting Agulhas rings in the South Atlantic Ocean”

David Wichmann March 16, 2021

Result of the OPTICS algorithm applied to the trajectories modelled in the Bickley Jet model flow. (a), (d) and (g) show the reachability plot with different DBSCAN clustering results, indicated by the black horizontal line. The corresponding clustering results of each choice of DBSCAN parameter is shown on the right of the reachability plots for different times. Grey particles correspond to noise. Axis units in the centre and right column are in 1000 km.

The February 2021 NPG Paper of the Month award goes David Wichmann and his co-authors for their paper “Ordering of trajectories reveals hierarchical finite-time coherent sets in Lagrangian particle data: detecting Agulhas rings in the South Atlantic Ocean“. Understanding the transport of tracers and particulates is an important topic in oceanography and in fluid dynamics in general. Th ...[Read More]

NPG Paper of the Month: “A methodology to obtain model-error covariances due to the discretization scheme from the parametric Kalman filter perspective”

Tommaso Alberti March 11, 2021

Illustration of the transport of a chemical specy by a heterogeneous wind field over a 1D domain (a) and the numerical simulation from a simple discretization scheme (b). The loss of variance due to the spurious numerical diffusion involves an increase of the model-error variance (c) which is coupled with the anisotropy (the correlation length-scale in 1D domain, in panel d).

The January 2021 NPG Paper of the Month award goes to Olivier Pannekoucke and his co-authors for the paper “A methodology to obtain model-error covariances due to the discretization scheme from the parametric Kalman filter perspective“. In geophysics, forecasting is based on solving the equations of physics with the help of a computer. To calculate a forecast we need an initial conditi ...[Read More]

Four reasons for still observing cold spells despite the undeniable global climate change

Davide Faranda February 18, 2021

Stravinsky fountain, near the Centre Pompidou (Paris) frozen by the cold wave of 2021.

The winter of 2020-2021 has been characterized by various cold waves affecting – at different times – Western and Eastern Europe and North America. The most striking pictures show Madrid covered by up to 40 cm of fresh snow, frozen Thames near London and Canal St Martin in Paris, heavy snow in Amsterdam and even on the Eolian Islands, just offshore Sicily. At first this seems contradi ...[Read More]