Throughout his graduate career, Manuel Enrique Cuesta worked on a series of observational research topics that have advanced understanding of solar wind turbulence. There are facets of his work that are traditional, facets that contribute to data archives, and facets that are highly innovative from a theoretical perspective. He began with the historically important Voyager magnetic field data sets and embraced the arduous task of cleaning the data for use in turbulence research. This led to a publicly available data product of great potential use for the space plasma community. He exploited this data set to scrutinize radial variations of the turbulence. Going beyond the standard study of spectra, he included higher-order statistics such as scale-dependent kurtosis, a measure of space-filling by coherent structures such as current sheets. He found, counterintuitively, that kurtosis at a fixed physical increment scale decreases outside of 1 astronomical unit. This itself is interesting, but the real conceptual leap came with his recognition that the effective Reynolds number of the turbulence systematically decreases with increasing radial distance. The effective Reynolds is related to the turbulence bandwidth, and this decreases essentially because density decreases as an inverse square law, while correlation scale increases approximately as the square root of distance. This leads to the remarkable conclusion that the quantitative variation of solar wind magnetic field kurtosis behaves very similarly with Reynolds number as one finds in classic wind tunnel experiments. Manuel then extended his studies much closer to the Sun, using Helios and Parker Solar Probe data sets. After further verification of the radial increase of correlation scale across truly vast spans of heliocentric distance, Manuel also looked at radial variations of correlation lengths parallel to, and perpendicular to, the regional mean magnetic field, finding a remarkable tendency for turbulence to isotropize in the inner heliosphere. These studies provide important extensions to understanding global properties of heliospheric turbulence, connecting inner and outer heliospheric observations. Manuel’s accomplishments not only extend the view that the solar wind represents a natural turbulence laboratory, but also demonstrate a totally new feature: that it is possible to systematically examine Reynolds number effects in the heliosphere by making use of the natural variation of plasma parameters. For these accomplishments, both applied and fundamental, Manuel Cuesta is amply deserving of the 2023 AGU Donald L. Turcotte Award.

—William H. Matthaeus, University of Delaware, Newark

I am deeply honored to be the recipient of the Donald L. Turcotte Award from AGU, as well as receiving recognition from my adviser and friend, Prof. William H. Matthaeus. My research work began during the sophomore year of my undergraduate career where I had first been introduced to the space physics group at the University of Delaware (UD), while I was sponsored by NASA’s Delaware Space Grant. I soon learned that this would be one of the most life-changing moments in my life. Through my experiences with the Delaware group, I learned how to work effectively while enjoying time spent with my peers. My first project, which led to my M.S. thesis, was working to improve the magnetic field data product via Voyager 1 measurements up to 10 astronomical units for space research. This data set was then applied to my doctoral research work and is available freely to the research community. Although I was working on spacecraft data analysis that investigated turbulence properties in the solar wind, I was able to make physical comparisons to wind tunnel experiments. The comparison between the solar wind and wind tunnel experiments with respect to the Reynolds number dependence of the scale-dependent kurtosis had drastically changed my point of view on the applicability of my niche research work. I am very grateful to not only my thesis adviser but also Prof. Tulasi N. Parashar for being another motivating and significant person in my research work, making an invaluable difference in my research career. Thank you to everyone in my research team for making my time at UD unforgettable! Finally, I would like to thank my family for their unwavering support in my pursuit of education. —Manuel Enrique Cuesta, Princeton University, Princeton, N.J.