Journal article
Variability of Upstream Proton Cyclotron Wave Properties and Occurrence at Mars Observed by MAVEN
Journal of geophysical research. Space physics, Vol.126(2), e2020JA028616
02/2021
DOI: 10.1029/2020JA028616
Abstract
The presence of plasma waves upstream from the Martian bow shock, with frequencies near the local proton cyclotron frequency in the spacecraft frame, constitutes, in principle, an indirect signature for the existence of planetary protons from the ionization of Martian exospheric hydrogen. In this study, we determine the "proton cyclotron wave" (PCW) occurrence rate between October 2014 and February 2020, based on Magnetometer and Solar Wind Ion Analyzer measurements from the Mars Atmosphere and Volatile EvolutioN mission. We characterize its dependence on several wave and solar wind (SW) properties, and solar longitude ranges. We confirm a previously reported long-term trend with more PCWs near perihelion, likely associated with changes in exospheric hydrogen density. Furthermore, we report for the first time a decrease in median PCW amplitude for each consecutive Martian perihelion. Such variability cannot be attributed to differences in the distribution of SW conditions. This trend could be associated with changes in solar inputs, foreshock effects, and asymmetries due to the SW convective electric field influencing newborn protons. In addition, we observe PCWs more frequently for low to intermediate interplanetary magnetic field (IMF) cone angles, slower SW speeds, and higher SW proton densities. The IMF cone angle preference likely results from the trade-off between associated linear wave growth rates, wave saturation energies, and pick-up proton densities. Moreover, the dependencies on SW speed and density indicate the importance of the characteristic SW transit timescale and the charge exchange process coupling SW protons with the hydrogen exosphere.
Details
- Title: Subtitle
- Variability of Upstream Proton Cyclotron Wave Properties and Occurrence at Mars Observed by MAVEN
- Creators
- O. M. Romeo - University of Maryland, College ParkN. Romanelli - University of Maryland, Baltimore CountyJ. R. Espley - Goddard Space Flight CenterC. Mazelle - Institut de Recherche en Astrophysique et PlanétologieG. A. DiBraccio - Goddard Space Flight CenterJ. R. Gruesbeck - Goddard Space Flight CenterJ. S. Halekas - University of Iowa
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.126(2), e2020JA028616
- DOI
- 10.1029/2020JA028616
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Publisher
- Amer Geophysical Union
- Number of pages
- 21
- Grant note
- CRESST II (Center for Research and Exploration in Space Sciences Technology) French Space Agency CNES; Centre National D'etudes Spatiales NASA; National Aeronautics & Space Administration (NASA) University of Maryland, College Park
- Language
- English
- Date published
- 02/2021
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984428799602771
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