Bio, Shaun Lovejoy, November 2016
Shaun Lovejoy is Professor of Physics at McGill University, Montreal (Canada), which he joined in 1985. He earned his PhD in Physics from the same university in 1981, defending his thesis on The Remote Sensing of Rain following a B.A., M.A. in theoretical physics from Trinity College, Cambridge.
The beginning of Lovejoy’s career coincided with the nonlinear revolution. Chaos, fractals, nonlinear waves, self-organized criticality were new paradigms that promised to transform our understanding of nature, including the geosciences. His 1982 Science paper “Area-perimeter relation for rain and cloud areas” (over 770 citations) marked the beginning of a new era of systematic application of scaling and fractal ideas to the atmospheric and hydrological sciences. His 1986 paper “Scale invariance in climatological temperatures and the local spectral plateau” did the same for climate science by showing that atmospheric motions could be systematically understood over huge ranges of space-time scales with the help of scale invariance. Recent developments from this paper have notably clarified the notion of “What is climate?” (EOS 2013) and led to the discovery of a third macroweather regime in between the weather and the climate. This was the theoretical basis of the first statistical testing (and rejection at the 99.9% confidence level) of the giant natural fluctuation hypothesis for explaining industrial era global warming. This was the most media and blog “mentioned” Climate Dynamics paper in 2014 (highest Altimetric score out of 759).
Starting in 1983, and for much of his career Shaun collaborated with Daniel Schertzer. Together, they developed and applied scaling ideas in the geosciences, contributing to the explosive growth of nonlinear geophysics including the modeling and in empirical analyses and characterization of geosystems over wide ranges of scales. The most important advances include cascade processes as the generic multifractal process, generalized (anisotropic) scale invariance, universal multifractals, (causal) space-time multifractal modeling of geofields.
Highlights from this work include:
i) The realization that a generic consequence of scale invariant dynamics – where the same basic mechanism repeats scale after scale, from large to small – are multifractal fields i.e.they require the transition from fractal geometry to multifractal processes.
ii) In these “cascades”, the variability is built up scale after scale; the generic result is that the extremes are particularly singular, they generally display “divergence of moments” or equivalently algebraic/power law distributions.
iii) The realization that when – over a finite range of scales – such a scaling process interacts with many others or is iterated enough, the resulting behaviour is stable and attractive. This implies that it does not depend on many of the details of the dynamics; i.e. that there exist “universality classes” for multifractal processes. This essentially reduces the number of exponents from infinity to only three, allowing multifractals to be manageable.
iv) The recognition that scale invariance is a very general (non-classical) symmetry principle. The development of Generalized Scale Invariance (GSI) extended scale invariance from the restrictive and unrealistic isotropic (self-similar) fractals and multifractals to highly anisotropic systems (including the atmosphere and solid earth which are both highly stratified). In GSI systems, the appearance/morphologies of structures systematically change with scale illustrating the error of basing our understanding and modeling on appearances: the “phenomenological fallacy”. GSI provides the theoretical basis for new parameterizations in weather and climate models.
v) These ideas allow us to generalize the classical laws of turbulence allowing the scaling to proceed to scales far larger than previously suspected: literally to planetary scales, demonstrated on numerous satellite, aircraft, reanalysis and numerical model outputs. A consequence is that the solar induced, (classical, Kolmogorov) energy rate density turns out to be the key dimensional quantity governing the dynamics. This allows us to finally understand a basic transition in the earth’s atmosphere (at 5-10 days, noted since the 1950’s) and oceans (at ≈1 year), as simply the typical lifetime of planetary sized structures. The same theory also quantitatively explains the comparable transition on Mars at 2 sols.
vi) In 2015 in a series of papers he showed how scaling provides the basis for new stochastic approaches to macroweather (monthly to decadal) atmospheric forecasts; this is the basis for the revolutionary Stochastic Seasonal and Interannual Prediction System (StocSIPS) that exploits the atmosphere’s huge memory to make forecasts based on the real world (rather than model) climates. He was awarded the prestigious Fessenden professorship (2016) to commercialize this technology.
These and other developments are reviewed in his book entitled The weather and climate: emergent laws and multifractal cascades, 496pp, Cambridge University Press (2013), co-authored by D. Schertzer. In addition, Lovejoy has published over 200 journal papers, 2 books and over 60 book chapters applying these ideas to the Earth and environmental sciences. Nonlinear Geophysics is inherently a highly interdisciplinary area, and a breakdown by primary subject area of Lovejoy’s publications shows that indeed, he has made contributions throughout the geosciences: 74 in atmospheric science, 44 in hydrology, 27 in general nonlinear geoscience, 26 in climate science, 22 in solid earth geoscience and 8 in oceanic science (plus 8 others including finance and astrophysics). These papers have the distinct character of illustrating scaling features through innovative data analyses and are also marked by mathematical depth. Application areas comprise atmospheric dynamics, meteorology, climate, turbulence, hydrology, precipitation, floods and river networks, topography, geogravity, geomagnetism, volcanic activity, earthquakes and biogeosystems.
Lovejoy´s work is widely cited across many scientific disciplines (from Google scholar: over 12200 citations, h-index=55, ISI h-index: 41). According to Google scholar, he is the highest cited person with keyword “multifractal” and the fourth highest with the keyword “fractal”. The unifying theme of his work is that when the notion of scaling is generalized to include anisotropy and multifractality, many key geofields display scaling behavior over enormous ranges of scale. This non-classical extreme variability is a new paradigm for the geosciences. By encouraging the community to examine experimental data from a new perspective, he has helped to achieve better use of observations and a clearer understanding of the nature of statistical variations. Apart from some preconceptions and conventional views, the original approach that he proposes is now being applied to the analysis of numerical models of weather and climate, and is producing significant progress.
In addition to these scientific contributions, Lovejoy has actively promoted nonlinear geophysics. In 1989, he also co-founded the Nonlinear Processes in Geophysics scientific division at the European Geosciences Union (EGU); since 2012, he has been president of this division, and sits on the EGU council. In 1994 was founding co-editor of the joint AGUEGUjournal Nonlinear Processes in Geophysics. From its inception in 1997, was an active member of AGU’s Nonlinear Geophysics (NG) focus group of which he was Vice-president (2006-2008), then President (2008-2012). In 2010 he was honoured with the Borland lectureship in hydrology (Colorado State University) and in 2015 by NG focus group’s Lorenz Lecture and in 2016, he became a fellow of the American Geophysical Union. Also in 2016, he became leader of the new Past Climate change (PAGES) working group on Climate Variability Across Scales that aims to foster the collaboration of scientists from both climate and nonlinear geophysics.
He has served or still serves on the editorial boards of several journals including Nonlinear Processes in Geophysicsand Atmosphere. He has also been involved in the organization of numerous conferences, workshops, seminars and short courses that have helped to disseminate advances in this field, and he has engaged in multiple collaborations with colleagues from different backgrounds across the world. His services extend to promoting and encouraging young scientists in the field by involving them in research projects and publishing with them.