Statistical Occurrence and Distribution of High‐Amplitude Whistler Mode Waves in the Outer Radiation Belt. Issue 5 (1st March 2019)

• Record Type: Journal Article
• Authors: Tyler, E.; Breneman, A.; Cattell, C.; Wygant, J.; Thaller, S.; Malaspina, D.
• Is Part Of: Geophysical research letters. Volume 46:Issue 5(2019)
• Page Start: 2328
• Page End: 2336
• Publication Date: 2019-03-01
• Subjects: radiation belt -- whistler waves -- chorus -- Van Allen belt; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2019GL082292
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: We present the first statistical analysis with continuous data coverage and nonaveraged amplitudes of the prevalence and distribution of high‐amplitude (>5 mV/m) whistler mode waves in the outer radiation belt using 5 years of Van Allen Probes data. These waves are most common above L = 3.5 and between magnetic local time of 0–7 where they are present 1–4% of the time. During high geomagnetic activity, high‐amplitude whistler mode wave occurrence rises above 30% in some regions. During these active times the plasmasphere erodes to lower L and high‐amplitude waves are observed at all L outside of it, with the highest occurrence at low L (3.5–4) in the predawn sector. These results have important implications for modeling radiation belt particle interactions with chorus, as large‐amplitude waves interact nonlinearly with electrons. Results also may provide clues regarding the mechanisms which result in growth to large amplitudes. Plain Language Summary: Our Earth is surrounded by a ring of high‐energy electrons, known as the outer radiation belt, which can cause damage to satellites in orbit. These electrons gain such high energy because of a type of electromagnetic waves called "whistler waves, " which exist in the space around Earth. Satellites have recently discovered whistler waves that are tens or hundreds of times as large as the average waves. Such large whistler waves can energize electrons very quickly and also cause electrons to be knocked into our atmosphere, creating aurora. Because these large waves are hard to measure, scientists have not been able to say how often they occur, where they occur, or even how exactly they form. This study uses a unique data set gathered by the Van Allen Probes to find out when and where these very large whistler waves occur. We found that these waves appear mostly in the nightside and morning side of the Earth, and they tend to appear much closer to Earth than smaller whistler waves do. This information offers us clues about how these monster waves form and what impact they might have on the radiation belt and the Earth. Key Points: High‐amplitude whistler mode waves are most prevalent between midnight and dawn and above L of 3.5 During active times, high‐amplitude waves are present over 30% of the time in some regions Waves greater than 20 mV/m preferentially occur at low L shell in the predawn sector