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

Abstract

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.

Dynamically Unstable Strong Wind Shears Observed in the Polar Mesosphere Summer Echo Layer Associated With Geomagnetic Disturbances

“…The result gives allegiance to the EISCAT observation in which upward velocity and PMSE reflectivity were remarkably enhanced right after a large excursion of local geomagnetic field as reported by Lee et al (). The EISCAT observation was explained for large upward velocity caused by atmospheric heating due to geomagnetic disturbance and energetic electron precipitation and for PMSE reflectivity enhancement due to the adiabatic cooling.…”

“…Solar wind effects on the PMSE layer seem limited not only to PMSE detectability and its occurrence but also on intensifying horizontal and vertical velocities in the PMSE layer (Lee et al, ; Lee et al, ). The occurrence rate of extreme horizontal speeds in PMSE frequently increases at times of dynamic pressure enhancement (Lee et al, ).…”

“…The occurrence rate of extreme horizontal speeds in PMSE frequently increases at times of dynamic pressure enhancement (Lee et al, ). Evidence for gravity wave generation was observed in the PMSE layer as the effect of energetic electron precipitation (>30 keV) with European Incoherent SCATtering (EISCAT) VHF radar (Lee et al, ). Upward velocity was largely enhanced by the initiation of geomagnetic disturbance, followed by oscillations of vertical velocity.…”

Validation of Multistatic Meteor Radar Analysis Using Modeled Mesospheric Dynamics: An Assessment of the Reliability of Gradients and Vertical Velocities

“…Studies using European Incoherent Scatter (EISCAT) very high requency radars have previously observed vertical velocities in the order of a few m/s (Fritts et al., 1990; Hoppe & Fritts, 1995a, 1995b; Lee et al., 2018; Mitchell & Howells, 1998; Vierinen et al., 2013). Incoherent scatter radars have been used to measure vertical velocities in the mesosphere (Hysell et al., 2014; Zhou, 2000).…”

Polar Mesospheric Summer Echo Characteristics in Magnetic Local Time and Height Profiles

“…Recently, energetic electron precipitation induced by geomagnetic disturbance has been recognized as a significant contributor to PMSE production (Zeller & Bremer 2009;Kirkwood et al 2013;Lee et al 2013Lee et al , 2014Lee et al , 2015Lee et al , 2018Lee et al , 2020. During high-speed solar wind streams (HSSs), PMSE exhibits periodicities of 7, 9, and 13.5 days, in phase with solar wind speed and the auroral electrojet (AE) index (Lee et al 2013).…”