EISCAT Observation of Wave‐Like Fluctuations in Vertical Velocity of Polar Mesospheric Summer Echoes Associated With a Geomagnetic Disturbance

• Published in: Journal of geophysical research. Space physics Vol. 123; no. 6; pp. 5182 - 5194
• Main Authors: Lee, Young‐Sook, Kim, Yong Ha, Kim, Kyung‐Chan, Kwak, Young‐Sil, Sergienko, Timothy, Kirkwood, Sheila, Johnsen, Magnar G.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-06-2018; American Geophysical Union (AGU)
• Subjects: Adiabatic flow; D region; E region; EISCAT; Electron density; Electron precipitation; Fluctuations; Fysikk: 430; geomagnetic storm; Geomagnetism; Gravitational waves; gravity wave; Gravity waves; Ice particles; Incoherent scattering; Ion velocity; Matematikk og Naturvitenskap: 400; Mathematics and natural science: 400; Particle precipitation; Periodic variations; Periodicities; Physics: 430; PMSE; Radar; Radar reflectivity; Updraft; VDP; Velocity; Vertical oscillations; Vertical velocities; Very high frequencies; Wave period
• ISSN: 2169-9380; 2169-9402; 2169-9402
• DOI: 10.1029/2018JA025399

By analyzing a data set from the European Incoherent SCATter (EISCAT) Very High Frequency (VHF) radar at Tromsø, we find that both radar reflectivity and upward ion velocity in a polar mesospheric summer echo (PMSE) layer simultaneously increased at the commencement of a local geomagnetic disturbance, which occurred at midnight on 9 July 2013. The onset of the upward velocity was followed by periodic repetition of ~5 min during the initial 30‐min stage, and then at later stage the vertical velocity oscillated with ~7‐ and ~20‐min periodicities at 85‐ to 90‐km altitudes. The ~5‐min periodicity is close to the buoyancy period, and the ~7‐ and ~20 min periodicities are consistent with gravity waves, thus suggesting that gravity waves can be generated by the effects of the geomagnetic disturbance. On the other hand, the variation of PMSE intensity (85–90 km) was in phase with fluctuations of electron densities (90–110 km) with ~12‐ and ~13‐min periodicities at the initial and later stages, respectively. The initial creation of PMSE can be attributed to both the sudden onset of particle precipitation and ice particles produced by adiabatic cooling during the rapid updraft, as detected by large upward velocity. Our periodogram analysis suggests that variations of PMSE intensity seem to follow the same periods with E region electron density, which is moduled by energetic electron precipitation, while vertical velocity oscillates at atmospheric gravity wave periods.
Key Points
Vertical velocity of PMSE was observed to oscillate at near‐buoyancy period of mesosphere after the onset of substorm
Variation of PMSE intensity is well correlated with that of E region electron density
Initial creation of PMSE is induced by both particle precipitation and air updraft that was observed as large upward velocity