Dynamical properties and extremes of Northern Hemisphere climate fields over the past 60 years

Davide Faranda (1, 2, 3) , Gabriele Messori (4) , M Carmen Alvarez-Castro (1, 5) , Pascal Yiou (1, 2)

1 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
2 ESTIMR - Extrèmes : Statistiques, Impacts et Régionalisation
3 LML - London Mathematical Laboratory
4 Bolin Centre for Climate Research
5 CMCC - Centro Euro-Mediterraneo per i Cambiamenti Climatici [Bologna]

Atmospheric dynamics are described by a set of partial differential equations yielding an infinite-dimensional phase space. However, the actual trajectories followed by the system appear to be constrained to a finite-dimensional phase space, i.e. a strange attractor. The dynamical properties of this attractor are difficult to determine due to the complex nature of atmospheric motions. A first step to simplify the problem is to focus on observables which affect-or are linked to phenomena which affect-human welfare and activities, such as sea-level pressure, 2 m temperature, and precipitation frequency. We make use of recent advances in dynami-cal systems theory to estimate two instantaneous dynamical properties of the above fields for the Northern Hemisphere: local dimension and persistence. We then use these metrics to characterize the seasonality of the different fields and their interplay. We further analyse the large-scale anomaly patterns corresponding to phase-space extremes-namely time steps at which the fields display extremes in their instantaneous dynamical properties. The analysis is based on the NCEP/NCAR reanalysis data, over the period 1948-2013. The results show that (i) despite the high dimensionality of atmospheric dynamics, the Northern Hemisphere sea-level pressure and temperature fields can on average be described by roughly 20 degrees of freedom; (ii) the precipitation field has a higher dimensionality; and (iii) the seasonal forcing modulates the variability of the dynamical indicators and affects the occurrence of phase-space extremes. We further identify a number of robust correlations between the dynam-ical properties of the different variables.

Domaines: Climatologie; Océan, Atmosphère

Davide Faranda, Gabriele Messori, M Carmen Alvarez-Castro, Pascal Yiou. Dynamical properties and extremes of Northern Hemisphere climate fields over the past 60 years. Nonlinear Processes in Geophysics, 2017, 24 (4), pp.713-725. ⟨10.5194/npg-24-713-2017⟩. ⟨hal-02886524⟩