is done when S is constrained to be symmetric, or to be self dual quaternion real, or when S has real elements, or has real quaternion elements. Three methods are used: metric forms; a variant of the Ingham-Seigel matrix integral; and a theorem specifying the Jacobi random matrix ensemble in terms

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presentée a ̀ la Faculte ́ sciences et techniques de l’ingénieur

An EOF analysis is used to intercompare the response of ENSO-like variability to CO 2 doubling in results from 15 coupled climate models assembled for the Intergovernmental Panel on Climate Change Fourth Assessment Report. Under preindustrial conditions, 12 of the 15 models exhibit ENSO amplitudes comparable to or exceeding that observed in the second half of the twentieth century. Under CO 2 doubling, three of the models exhibit statistically significant ( p � 0.1) increases in ENSO amplitude, and five exhibit significant decreases. The overall amplitude changes are not strongly related to the magnitude or pattern of surface warming. It is, however, found that ENSO amplitude decreases (increases) in models having a narrow (wide) ENSO zonal wind stress response and ENSO amplitude comparable to or greater than observed. The models exhibit a mean fractional decrease in ENSO period of about 5%. Although many factors can influence the ENSO period, it is suggested that this may be related to a comparable increase in equatorial wave speed through an associated speedup of delayed-oscillator feedback. Changes in leading EOF, characterized in many of the models by a relative increase in the amplitude of SST variations in the central Pacific, are in most cases consistent with effects of anomalous zonal and vertical advection resulting from warming-induced changes in SST. 1.

(Manuscript submitted on the 26/09/2007) High-resolution models can reproduce mesoscale dynamics and the variability in the Gulf of Mexico (GOM), but cannot provide accurate locations of currents without data assimilation (DA). We use the computationally cheap Ensemble Optimal Inter-polation (En

The role of interannual variations in sea surface temperatures (SSTs) on the Northern Hemisphere winter polar stratospheric circulation is addressed by means of an ensemble of nine simulations performed with the middle atmosphere configuration of the ECHAM5 model forced with observed SSTs during

Distributed rainfall-run-calculation of the Jacobian that relates the states and the observations. The soil moisture substantially. The mean absolute normalised error of the peak flows of six large floods system has been in operational use since early 2006. source systems (Wood, 1980). While

Ensembles for sequence learning

The quasi-operational global ensemble prediction system (GEPS) at NMC has been upgraded since December 2006 by the use of the breeding of growing mode (BGM) as initial perturbation strategy. Since

The relation between thermodynamic phase transitions in classical systems and topology changes in their state space is discussed for systems in which equivalence of statistical ensembles does not hold. As an example, the spherical model with mean field-type interactions is considered. Exact results