I was born in Elefsis, Greece, where I grew up with my brother, Panagiotis. As a young man, I studied physics and mathematics at Aristotelian University in Thessaloniki, where I received my BS in 1976. I then traveled to Montreal, Canada, where I studied atmospheric sciences, receiving my Ph.D in 1982 from McGill University. For the next three years I was a post-doctoral fellow at the Atmospheric Environmental Service, Cloud Physics Division, at Downsview, Ontario, an area in the north end of Toronto.
In 1985, I joined the Department of Geosciences at the University of Wisconsin -Milwaukee (UWM) as an Assistant Professor. I am now an Emeritus Distinguished Professor in the department of Mathematical Sciences, where I helped develop the Atmospheric Sciences program, a subdivision of the Mathematical Sciences, which includes 6 other internationally recognized faculty members, and has become one of the most successful research groups at UWM.

My work has focused on the study of Atmospheric Sciences, specifically in the areas of climate dynamics and global change. I was one of the first scientists to promote the application of Chaos theory and nonlinear data analysis in Atmospheric Sciences. I and my post-doctoral fellow Jim Elsner in a series of papers in the late 1980s popularized and introduced this theory to meteorologists. Our research has led to the Tsonis criterion, a method bearing our names, and two statistical tests bearing our names. The Tsonis Criterion refers to the necessary number of points required in attractor reconstructions. The Tsonis-Elsner method is a method used to distinguish low-dimensional chaos from random fractal processes, and the Elsner-Tsonis test is a statistical test designed to assess the significance of climate oscillations. In addition, we have introduced the notion of connected subsystems in the climate system. This concept is recently gaining significance in studies of climate change. In 2004 I was the first to apply the concepts of “small-world” networks to atmospheric sciences. My research in this area has led to the discovery of a new dynamical mechanism for major climate shifts, which explains all major global temperature shifts in the 20th and 21st century. I have also done significant research in the area of global change, and have published a theory about the relationship of global temperature and the frequency of El Niño.

My interdisciplinary efforts and collaborations in nonlinear methods have resulted in over 15 papers in the subjects of Biology, Economics, Linguistics, and Psychology. With my brother Panagiotis, I have published several important papers on the mathematical properties of DNA sequences, and have developed a hypothesis regarding the mathematical framework for memories and dreams. This hypothesis has recently been verified experimentally.

I have held associate editor positions for Nonlinear Processes in Geophysics and Journal of Hydrology. I have been an invited speaker at over 50 meetings, and have authored 10 books and 140 peer reviewed publications. I have also organized several conferences and many sessions in AGU and EGU on nonlinear dynamics.

In 2022, I won the American Geophysical Union’s Lorenz lecture award for significant contributions to Nonlinear Geosciences. In 2023, I was elected corresponding member of the Academy of Athens.