Anna Trevisan (1946, 2016).

Anna was born on January 25th 1946 in Bologna where she maintained her habitual residence for all of her life. Anna was a very energetic person, loved several sports and, although science always played a central role in her life, maintained strong ties with her parents and dedicated time and attention to her family, in particular to her son Luca.

Anna got the Italian degree (Laurea) in physics at the University of Bologna discussing a thesis concerning the application of time series analysis techniques to a historical record of tidal waves in the Adriatic Sea. Although very interested in physics, her strong natural inclination towards mathematics emerged quite soon as she took courses in algebra, mathematical methods, etc. She was also attracted by numerical methods as soon as digital computers begun to be available to her.

Since her thesis work Anna developed and maintained international connections. In the early seventies she spent long periods of time at the University of California, San Diego Institute of Geophysiscs and Planetary Physics, where she studied, under the guidance of Walter Munk, time series analysis applications to tidal waves. The basic problem consisted in inferring, through spectral correlation analysis, the relationship between astronomic and atmospheric (pressure, wind) forcing agents and observed tides. Already at the time of her thesis Anna joined CNR (Italian National Research Council), for which institution she worked till the end of her life.

During the seventies Anna studied meteorology at MIT under the guidance of Jule Charney and further developed her skills in the subject at NCAR in Boulder, where she interacted mostly with Chester Newton, at the University of Oslo, collaborating with Arnt Eliassen, at the University of Miami, with Reiner Bleck. During these years Anna developed the first primitive equation model, using isentropic coordinates, which was applied to numerical studies of orographic cyclogenesis: the 1976 paper (Trevisan, A., 1976: Numerical Experiments on the Influence of Orography on Cyclone Formation with an Isentropic Primitive Equation Model. J. Atmos. Sci., 33, 768–780) is one of the first contributions to the development of a numerical model of orographic cyclogenesis. Another topic of interest of Anna was the upper level frontogenesis, a challenging problem in dynamic meteorology (Buzzi, Trevisan and Salustri, 1980; Newton and Trevisan, 1984, a and b). As for other problems she tackled, Anna’s approach relied upon a combination of semi-analytical and numerical methods, very successful in the understanding of complex phenomena and processes characterizing atmospheric dynamics.

The developing phase of ALPEX allowed further investigation of all the aspects of Alpine cyclogenesis: Anna was actively involved in the preparation phase, the field experiment (in 1982) and the following studies up to the conclusion (in 1985). Anna’s main contribution consisted in developing analytical and numerical representation of the basic mechanisms involved in secondary Alpine cyclogenesis. In those and subsequent years Anna gave a fundamental contribution to studies of the Bologna research group that evolved into a complete theory of the onset of orographic cyclones. The theory considered the modification of baroclinic instability induced by the presence of orography (Tosi, Fantini and Trevisan, 1983; Buzzi, Trevisan and Speranza, 1984; Speranza, Buzzi, Trevisan and Malguzzi, 1985; Malguzzi, Trevisan and Speranza, 1987; Trevisan, Ferranti and Malguzzi, 1988; Buzzi; Malguzzi and Trevisan, 1990; Trevisan and Giostra, 1990).

Since the time of her studies in time series analysis (seventies), Anna’s attention was captured by weakly nonlinear interaction mechanisms (triadic resonance) in regressive spectral analysis and for the dynamics of planetary waves connected with the blocking phenomenon (Trevisan and Buzzi, 1980). But it was not until the middle eighties that she was involved in studies on the local properties in phase space of nonlinear systems (Malguzzi P., A. Trevisan, and A. Speranza, 1990). Anna’s interest in atmospheric flow regimes and their predictability led her to compare paradigmatic system behavior (Trevisan and Legnani, 1995) with observed properties of the real atmosphere (Trevisan, 1995) and of complex numerical models (Trevisan, Pancotti and Molteni, 2001). These studies evolved in successive years into suitable ways to estimate the instabilities in atmospheric models, when Anna introduced the breeding on the data assimilation system, BDAS, methodology (see, e.g., Carrassi, Trevisan and Uboldi, 2007; Uboldi and Trevisan, 2015) and into computational method to estimate the covariant Lyapunov vectors (Trevisan and Pancotti, 1998). The latter study inspired and anticipated the development of some of the efficient methods for the computation of the Lyapunov vectors that appeared later, in the late 2000. The use of the covariant Lyapunov vectors, as a key tool to analyze the atmospheric, oceanic or climate dynamics, has, since then, grown dramatically in recent years.

In early 2000 Anna began to be interested to the problem of combining data with dynamical models, the data assimilation. Here, again, rather than being attracted by the operational dimension of the problem (those were the years of the establishment of variational methods worldwide and the emerging of new the ensemble-based approaches), her angle of view was borrowed by dynamical system approach. She pioneered the class of methods known as assimilation in the unstable subspace (Trevisan and Uboldi, 2004), for assimilating data and selecting target observations using the information on the dynamics (Carrassi, Trevisan, Descamps, Talagrand and Uboldi, 2008). In the last years of her activity, Anna has been much involved in the theoretical and applied-oriented development of the method (see e.g. Carrassi, Ghil, Trevisan and Uboldi, 2008; Trevisan, D’Isidoro and Talagrand, 2010; Trevisan and Palatella, 2011; Palatella and Trevisan, 2015), which is still matter of intense research by several groups worldwide, as testified by the number of related and cross referenced publications.

In all of her work experience Anna proved to be able to work both independently and on a team. Although never involved in formal teaching, she dedicated great attention to the formation of young scientists many of whom play a relevant role in present time research.