Michael Ghil | École Normale Supérieure (original) (raw)

Papers by Michael Ghil

Journal of the Atmospheric Sciences, 1994

Abstract A short-wave instability theory is applied to secondary waves on a narrow cold-front rai... more Abstract A short-wave instability theory is applied to secondary waves on a narrow cold-front rainband observed during the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA). The basic mean state is approximated by the parabolic, geostrophically balanced interface between two layers of homogeneous density. The observed wavelength of perturbations along the ERICA cold front is about 20-30 km and their doubling time is about 2 hours. The observed wavelength is well within the short-wave regime of the theory, ...

Applied Mathematical Sciences, 1981

From the reviews:'Each of the 19 chapters in this book is written by a knowledgeable exp... more From the reviews:'Each of the 19 chapters in this book is written by a knowledgeable expert urologist with additional expertise in robotic and laparoscopic pediatric urology.... It is specifically designed for novices and those wishing to gain more experience in pediatric laparoscopic and robotic minimally invasive urological surgeries.... The references are useful and up to date.... The figures are of excellent quality and the index is easy to use.'(Martin Allan Koyle, Doody's Review Service, December, 2009)'Edited by Cleveland ...

Journal of the Atmospheric Sciences, 1988

Résumé/Abstract Expériences numériques pour clarifier le mécanisme d'excitation des onde... more Résumé/Abstract Expériences numériques pour clarifier le mécanisme d'excitation des ondes mixtes de Rossby-gravité (ondes de Yanai) dans la troposphère tropicale, ainsi que celui de sélection des nombres zonaux d'ondes 4-5 et de la période de 5 jours. Le modèle utilisé est régi par les équations primitives sur un plan bêta équatorial. Le budget d'humidité est calculé explicitement. Résultats: un mécanisme «wave-CISK» non linéaire produit des ondes de Yanai avec les mêmes pics spectraux en nombres d'ondes et en fréquences ...

Journal of Physical Oceanography, 1994

Résumé/Abstract A major error source in the numerical simulation of tropical oceans is the uncert... more Résumé/Abstract A major error source in the numerical simulation of tropical oceans is the uncertainty in wind stress forcing. A reduced-gravity shallow-water model has been used to test how assimilated ocean data correct simulation errors caused by erroneous wind stress in the tropics. The geometry of the basin is rectangular and symmetric about the equator, and the long-wave approximation is applied. All experiments are of the identical-twin type: the «observations» are generated by sampling the desired reference solution, and the ...

We concentrate here on two aspects of advanced Kalman--filter-related methods: (i) the stability ... more We concentrate here on two aspects of advanced Kalman--filter-related methods: (i) the stability of the forecast- assimilation cycle, and (ii) parameter estimation for the coupled ocean-atmosphere system. The nonlinear stability of a prediction-assimilation system guarantees the uniqueness of the sequentially estimated solutions in the presence of partial and inaccurate observations, distributed in space and time; this stability is shown to

7 ( 1) Oceanic variability on interannual, interdecadal, and 8 longer timescales plays a key role... more 7 ( 1) Oceanic variability on interannual, interdecadal, and 8 longer timescales plays a key role in climate variability and 9 climate change. Paleoclimatic records suggest major 10 changes in the location and rate of deepwater formation in 11 the Atlantic and Southern oceans on timescales from 12 millennia to millions of years. Instrumental records of 13 increasing duration and

The present work applies several advanced spectral methods (Ghil et al., Rev. Geophys., 2002) to ... more The present work applies several advanced spectral methods (Ghil et al., Rev. Geophys., 2002) to the analysis of macroeconomic fluctuations in Italy, The Netherlands, and the United Kingdom. These methods provide valuable time-and-frequency-domain tools that complement traditional time-domain analysis, and are thus fairly well known by now in the geosciences and life sciences, but not yet widespread in quantitative economics.

Decadal Climate Variability, 1996

Spectral Methods: What They Can and Cannot Do for Climatic Time Series. M Ghil, P Yiou NATO ASI S... more Spectral Methods: What They Can and Cannot Do for Climatic Time Series. M Ghil, P Yiou NATO ASI SERIES I GLOBAL ENVIRONMENTAL CHANGE 44, 445-482, SPRINGER, 1996.

Climate Dynamics, 1994

Stable-isotope records from seven marine cores and one ice core provide invaluable information on... more Stable-isotope records from seven marine cores and one ice core provide invaluable information on the intricate behavior of the climatic system over time scales of 104 to 105 years. These records, in conjunction with a simple coupled climate model, help us understand major mechanisms of paleoclimatic variability. The time intervals covered by the records include the last glacial-interglacial cycle. In

Physics of Fluids A: Fluid Dynamics, 1991

A stability analysis based on Arnol'd–Lyapunov arguments in a gauge‐variable formalism is ap... more A stability analysis based on Arnol'd–Lyapunov arguments in a gauge‐variable formalism is applied to a generalized form of propagating modons. The method was previously applied to the special case of Stern's modon in a quiescent background flow. The analysis presented here shows that propagating‐modon solutions in the shallow‐water equations are stable to small‐amplitude perturbations, regardless of the sign of their translational speed, as long as this is much smaller in magnitude than the solid‐rotation speed of the Earth. Sufficient ...

SIAM Journal on Applied Mathematics, 1984

Physica D: Nonlinear Phenomena, 2001

Boolean delay equations (BDEs) provide a mathematical framework to formulate and analyze conceptu... more Boolean delay equations (BDEs) provide a mathematical framework to formulate and analyze conceptual models of complex multi-component systems. This framework is used here to construct a simple conceptual model for the El-Niño/Southern Oscillation (ENSO) phenomenon. ENSO involves the coupling of atmospheric and oceanic processes that are far from being completely understood. Our BDE model uses Boolean variables to represent key atmospheric and oceanic quantities and equations that involve logical operators to ...

Physica D: Nonlinear Phenomena, 1996

An intermediate coupled model for the El Niño/Southern Oscillation (ENSO) phenomenon is used to e... more An intermediate coupled model for the El Niño/Southern Oscillation (ENSO) phenomenon is used to examine the interaction of ENSO with the seasonal cycle and how this is related to the irregularity of ENSO time series. Under annual mean conditions, the mechanisms that give rise to an inherent ENSO frequency and spatial pattern are well understood in this model. When the annual cycle is included, the ENSO cycle tends to lock to rational multiples of the annual frequency. The role of such subharmonic frequency locking in the transition ...

Monthly Weather Review, 1982

ABSTRACT

Journal of the Atmospheric Sciences, 1990

Abstract Experiments were performed in a rotating, differentially heated annulus, with and withou... more Abstract Experiments were performed in a rotating, differentially heated annulus, with and without bottom topography of azimuthal wavenumber 2. Both water and a viscous glycerol-water mixture were used as a working fluid. In one series of experiments, measurements of azimuthal velocity u were carded out by Doppler-laser velocimetry at midradius and at and depth. In the other, temperature measurements were made by a set of thermistors at three different heights and three different radii. Results were analyzed by Fourier transformation, ...

Journal of Statistical Physics, 1986

We present here the abstracts of the talks presented at the conference" Mathematical Pro... more We present here the abstracts of the talks presented at the conference" Mathematical Problems from the Physics of Fluids." Each invited speaker was requested to provide a short abstract of his talk together with a commented bibliography containing the papers of the last decades judged (by the speaker) as particularly relevant for his work and/or his talk. Unfortunately, as the reader can check, not all the speakers interpreted our request in the sense we wanted: nevertheless we think that all the contributions are interesting and ...

Journal of Statistical Physics, 1985

Abstract Boolean delay equations (BDEs) areevolution equations for a vector of discrete variables... more Abstract Boolean delay equations (BDEs) areevolution equations for a vector of discrete variables x (t). The value of each componentX i (t), 0 or 1. depends on previous values of all componentsx j (t− t ij), xi (t)= fi (x 1 (t− t i1),..., xn (t− t in)). BDEs model the evolution of biological and physical systems with threshold behavior and nonlinear feedbacks. The delays model distinct interaction times between pairs of variables. In this paper, BDEs are studied by algebraic, analytic, and numerical methods. It is shown that solutions depend ...

Journal of Geophysical Research, 1988

A simple climate model of Quaternary glaciations is combined with a simple isotopic model in orde... more A simple climate model of Quaternary glaciations is combined with a simple isotopic model in order to study phase relationships between g• 80 records in deep-sea cores and in ice cores. Power spectra of the model&amp;#x27;s climatic and isotopic variables show a dominant peak near 100 kyr (1 kyr= 1000 years), the continuous background of all paleoclimatic spectra, smaller peaks at the orbital periodicities of 41, 23, and 19 kyr, and additional peaks at 14.7, 13, 11.5, 10.4, and 9.5 kyr. Time lags between the model&amp;#x27;s isotopic profiles are highly ...

Journal of Geophysical Research, 2009

Journal of Fluid Mechanics, 1990

Abstract A new Lyapunov stability condition is formulated for the shallow-water equations, using ... more Abstract A new Lyapunov stability condition is formulated for the shallow-water equations, using a gauge-variable formalism. This sufficient condition is derived for the class of perturbations that conserve the total mass. It is weaker than existing stability criteria, ie it applies to a wider class of flows. Formal stability to infinitesimally small perturbations of arbitrary shape is obtained for two classes of large-scale geophysical flows: pseudo-eastward flow with constant shear, and localized coherent structures of modon type.