# On the Pulse Shape of Ground Level Enhancements

## TL;DR

This study analyzes the pulse shape of cosmic ray ground level enhancements, revealing a linear relation between decay and rise times and emphasizing the importance of interplanetary transport effects in shaping GLE temporal profiles.

## Contribution

It introduces a model linking GLE pulse shapes to interplanetary scattering, highlighting how transport effects can dominate observed profiles and challenge traditional event classification.

## Key findings

- A linear relation $ au_d \\approx 3.5 \\tau_r$ is observed between decay and rise times.
- Interplanetary scattering can fully determine GLE pulse shapes under certain conditions.
- Transport effects can obscure initial acceleration signatures, affecting event classification.

## Abstract

We study the temporal intensity profile, or pulse shape, of cosmic ray ground level enhancements (GLEs) by calculating the rise $(\tau_\mathrm{r})$ and decay $(\tau_\mathrm{d})$ times for a small subset of all available events. Although these quantities show very large inter-event variability, a linear dependence of $\tau_\mathrm{d} \approx 3.5 \tau_\mathrm{r}$ is found. We interpret these observational findings in terms of an interplanetary transport model, thereby including the effects of scattering (in pitch-angle) as these particles propagate from (near) the Sun to Earth. It is shown that such a model can account for the observed trends in the pulse shape, illustrating that interplanetary transport must be taken into account when studying GLE events, especially their temporal profiles. Furthermore, depending on the model parameters, the pulse shape of GLEs may be determined entirely by interplanetary scattering, obscuring all information regarding the initial acceleration process, and hence making a classification between impulsive and gradual events, as is traditionally done, superfluous.