Biography

Colin Joyce was a postdoc interested in the study of solar energetic particles (SEPs) and galactic cosmic rays (GCRs). His Ph.D. thesis work focused on the human impact of energetic particle radiation using measurements from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) aboard the Lunar Reconnaissance Orbiter (LRO) as well as modeling from the Earth-Moon-Mars Radiation Environment Module (EMMREM). As a graduate student, he analyzed the potential threat of large SEP events to manned space missions and also modeled GCR radiation in the Earth and Mars atmospheres. Having studied them as an undergraduate, he is also interested in waves excited by newborn interstellar pickup ions which are fundamental to our current understanding of solar wind heating, and has continued to provide modeling support for numerous studies of this phenomena. While at Princeton Colin worked as a member of the Integrated Science Investigations of the Sun (IS☉IS) team as part of the historic Parker Solar Probe (PSP) mission. IS☉IS is a suite of two instruments designed to answer long-standing questions about the origin, acceleration, and transport of energetic particles in the inner heliosphere.

Research Interests

• Solar energetic particles and galactic cosmic rays
• Coronal mass ejections and solar flares
• Energetic particle radiation and its effect on human exploration
• Wave excitation by newborn interstellar pickup ions

Selected Publications

See full publication list at Google Scholar.

Analysis of the potential radiation hazard of the 23 July 2012 SEP event observed by STEREO A using the EMMREM model and LRO/CRaTER  (2015) by Joyce et al., Space Weather Journal

We present a study of the potential radiation hazard of the powerful, superfast interplanetary coronal mass ejection (ICME) observed by STEREO A on 23 July 2012. Using energetic proton flux data from the High Energy Telescope and Low Energy Telescope instruments aboard STEREO A together with the Earth‐Moon‐Mars Radiation Environment Module, we compute dose rates and accumulated doses during the event for both skin/eye and blood forming organs using four physically relevant levels of shielding. For spacesuit equivalent shielding, we compute a peak skin/eye dose rate of 1970 cGy‐Eq/d, a value far greater than those of the 2003 Halloween storms or the January and March solar energetic particle events of 2012. However, due to the relative brevity of the event, the resulting accumulated dose was just 383 cGy‐Eq, which is more aligned with the total doses of the 2003 Halloween and 2012 January/March events. Additionally, we use dose rates at STEREO B and Lunar Reconnaissance Orbiter/Cosmic Ray Telescope for the Effects of Radiation (LRO/CRaTER) during the event to show how the radiation impact is affected by the position of the ICME relative to the observer. Specifically, we find that the energetic particle event associated with the local shock and ICME passage at STEREO A caused greatly enhanced dose rates when compared to STEREO B and LRO/CRaTER, which were longitudinally distant from the ICME. The STEREO A/B dose rates used here will soon be made available to the community as a tool for studying the energetic particle radiation of solar events from different longitudes as a part of NASA's Heliophysics Virtual Observatories and on the Predictions of radiation from REleASE, EMMREM, and Data Incorporating CRaTER, COSTEP, and other SEP measurements (PREDICCS) and CRaTER websites.

Atmospheric radiation modeling of galactic cosmic rays using LRO/CRaTER and the EMMREM model with comparisons to balloon and airline based measurements (2016) by Joyce et al., Space Weather Journal

We provide an analysis of the galactic cosmic ray radiation environment of Earth's atmosphere using measurements from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) aboard the Lunar Reconnaissance Orbiter (LRO) together with the Badhwar‐O'Neil model and dose lookup tables generated by the Earth‐Moon‐Mars Radiation Environment Module (EMMREM). This study demonstrates an updated atmospheric radiation model that uses new dose tables to improve the accuracy of the modeled dose rates. Additionally, a method for computing geomagnetic cutoffs is incorporated into the model in order to account for location‐dependent effects of the magnetosphere. Newly available measurements of atmospheric dose rates from instruments aboard commercial aircraft and high‐altitude balloons enable us to evaluate the accuracy of the model in computing atmospheric dose rates. When compared to the available observations, the model seems to be reasonably accurate in modeling atmospheric radiation levels, overestimating airline dose rates by an average of 20%, which falls within the uncertainty limit recommended by the International Commission on Radiation Units and Measurements (ICRU). Additionally, measurements made aboard high‐altitude balloons during simultaneous launches from New Hampshire and California provide an additional comparison to the model. We also find that the newly incorporated geomagnetic cutoff method enables the model to represent radiation variability as a function of location with sufficient accuracy.

EXCITATION OF LOW-FREQUENCY WAVES IN THE SOLAR WIND BY NEWBORN INTERSTELLAR PICKUP IONS H⁺ AND He⁺ AS SEEN BY VOYAGER AT 4.5 AU by Joyce et al., Astrophysical Journal

We report the observation of a spectral enhancement in the magnetic field fluctuations measured by the MAG instrument on the Voyager 2 spacecraft during 4.5 hr on DOY 7, 1979 at a heliocentric radial position of 4.5 AU. This time period is contained within a solar wind rarefaction when the large-scale interplanetary magnetic field was nearly radial. The frequency range and polarization of the enhanced fluctuations are consistent with waves generated by newly ionized interstellar H⁺ and He⁺. We show sunward propagation of the waves via a cross-helicity analysis. We compare the observation with a theoretical model and find reasonable agreement given the model assumptions. This event is the first indication of pickup ion-generated waves seen at Voyager. It is also the first identification of pickup He⁺ waves by any spacecraft.