I am thrilled to be the co-author of Juan Roederer’s latest commentary entitled “Coordinates for representing radiation belt flux”. In a nutshell, the objective of this work is to briefly review the history of radiation belt parametrization, to present some “recipes” on how to compute adiabatic parameters (you may be familiar with L*… but have you ever heard of E*? and what about α*?), and to apply these recipes to a real event in which magnetospheric disturbances adiabatically affect the particle fluxes measured onboard the Van Allen Probes.

Juan G. Roederer is one of the founding fathers of radiation belt science. In the community, he is known primarily (1) for his classic textbook on radiation belt dynamics (*Dynamics of Geomagnetically Trapped Radiation*, 1970) and (2) for the coordinate that he introduced 50 years ago, namely “L-star”, a.k.a. “Roederer-L”.

## One might wonder why I am involved in this work.

In fact, the story is pretty uplifting, so let me tell you how I became Roederer’s coauthor.

During my first year as a phD student in Toulouse, France, my supervisor introduced me to adiabatic theory and I dove into the classics: Northrop, Schulz and Lanzerotti, and (of course!) Roederer, whose book happened to be my supervisor’s favorite. I had precise questions on some aspects of Roederer’s book which I brought to my supervisor. He said I should try asking Roederer directly. “Try sending him an email. Worst case scenario: he won’t answer”.

I spent half a day with Google Translate, trying to formulate the most polite and accurate email in order to maximize my chances for a response.

I got a response!

But the first answer I got was not quite what I had expected. Juan said that I had caught him at the wrong time, that he was giving an organ recital in Göttigen, Germany, and that later he would be traveling to China. He also wrote that he would answer my questions in a month or so. I was a bit confused given that he was supposed to be an 80 year-old scientist living in Fairbanks, Alaska. How could he be more active than me?

About a month later, he did indeed answer my science questions. We started discussing some details of his book, and in particular the time variations of L* (the building block of “radial diffusion”). As a result of these exchanges, Juan invited me to review one appendix of the new edition of his classic textbook. Next thing I knew, he sent me another appendix, then a chapter, and finally he sent me the whole draft version of the book (twice!).

In 2014, we finally met in real life at my first AGU conference in San Francisco, California. I had defended my thesis and was a postdoc. It was more than three years after our first email exchange, and a few months after the publication of the 2^{nd} edition of the *Dynamics of Magnetically Trapped Particles. *Needless to say, I had received my autographed copy*.*

One of my ambitions at the time was to co-author an article with Juan. We were both intrigued by these “zebra stripe” observations that were being advertised by the Van Allen Probe mission. So we met and worked on that topic for a week. Juan made drawings on a paper board, and I elaborated on the equations after work. A few months later, our paper was published. (and yes, I have also a post on the zebra stripes).

## The commentary that we have just published is the continuation of our collaboration.

For this work, I was in charge of the computations, figures, and editing.

First, Juan tells the history of radiation belt parametrization. The differences between “distance to the equatorial point of a field line”, McIlwain’s L-value, and the trapped particle’s adiabatic L*parameter are explained (this can be pretty confusing given that these parameters all merge in a dipole magnetic field!). Then, we present a readjustment on adiabatic theory, and we explain how to reformulate measurements in terms of L*, E*, α* (and j*!). Finally, we illustrate the method on a real event.

It is our hope that this work will send out an “adiabatic wake-up call” to the community, for it demonstrates the importance of a rigorous use of adiabatic theory in order to deliver higher quality research. We are looking forward to your feedback!

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