One‐Hertz Waves at Mars: MAVEN Observations. Issue 5 (6th May 2018)

• Record Type: Journal Article
• Authors: Ruhunusiri, Suranga; Halekas, J. S.; Espley, J. R.; Eparvier, F.; Brain, D.; Mazelle, C.; Harada, Y.; DiBraccio, G. A.; Thiemann, E. M. B.; Larson, D. E.; Mitchell, D. L.; Jakosky, B. M.; Sulaiman, A. H.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 5(2018)
• Page Start: 3460
• Page End: 3476
• Publication Date: 2018-05-06
• Subjects: Mars -- 1‐Hz waves -- low‐frequency whistler waves -- group‐standing waves -- MAVEN; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2017JA024618
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: We perform a survey of 1‐Hz waves at Mars utilizing Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft observations for a Martian year. We find that the 1‐Hz wave occurrence rate shows an apparent variation caused by masking of the waves by background turbulence during the times when the background turbulence levels are high. To correct for this turbulence masking, we select waves that occur in time intervals where the background turbulence levels are low. We find that the extreme ultraviolet flux does not affect the wave occurrence rate significantly, suggesting that the newly born pickup ions originating in the Mars's exosphere contribute minimally to the 1‐Hz wave generation. We find that the wave occurrence rates are higher for low Mach numbers and low beta values than for high Mach numbers and high beta values. Further, we find that a high percentage of 1‐Hz waves satisfy the group‐standing condition, which suggests that a high percentage of the waves seen as monochromatic waves in the spacecraft frame can be broadband waves in the solar wind frame that have group velocities nearly equal and opposite to the solar wind velocity. We infer that the wave occurrence rate trends with the Mach number and proton beta are a consequence of how the Mach numbers and beta values influence the wave generation and damping or how those parameters affect the group‐standing condition. Finally, we find that the 1‐Hz waves are equally likely to be found in both the quasi‐parallel and the quasi‐perpendicular foreshock regions. Key Points: One‐hertz waves at Mars show an apparent occurrence rate variation due to masking of the waves during times of high background turbulence levels The wave occurrence rates vary significantly with Mach numbers and proton beta values but do not vary significantly with EUV flux levels The 1‐Hz waves are observed in both the quasi‐parallel and quasi‐perpendicular foreshock regions with comparable occurrence rates