Polar Mesosphere Summer Echoes and Possible Signatures of Pulsating Aurora Detected by the Meteor Radar. Issue 11 (29th October 2021)

• Record Type: Journal Article
• Authors: Kozlovsky, A.; Shalimov, S.; Lester, M.; Belova, E.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 11(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-10-29
• Subjects: polar mesosphere summer echo -- noctilucent clouds -- pulsating aurora -- meteor radar; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2020JA028855
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Using data of the all‐sky interferometric meteor radar (SKiYMET, 36.9 MHz) operating in the Sodankylä Geophysical Observatory (67°22′N, 26°38′E, Finland) we found a specific type of polar mesosphere summer echo (PMSE), the power of which exhibits irregular variations at a frequency of the order of a few Hz. We classified such radar echoes as pulsating PMSE. These echoes were observed in late June‐July in the morning sector (4–12 MLT) during geomagnetic storms. They were received from a narrow range of altitudes near 82 km, which corresponds to the altitude of noctilucent clouds where ice particles of about 50‐nm radii exist. During pulsating PMSE, the SGO ionosonde showed an electron density of the order of 3 × 10 11 m −3 around 82 km, and enhanced D‐region ionization was manifested in the cosmic noise absorption. We suggest that the power of PMSE is modulated by bursts of electron precipitation corresponding to the few‐Hz internal modulation of pulsating aurora. During a short precipitation burst of 50–100 keV electrons, additional electrons can attach to the ice particles due to the presence of hyperthermal electrons according to the hypothesis proposed by Rosenberg et al. (2012, https://doi.org/10.1016/j.jastp.2011.10.011 ). This leads to an increase of the power of PMSE. After the burst is ended, the ice particles are deionized with a characteristic time of about 0.2 s due to attractive interaction with ions. Plain Language Summary: We present rare observations that relate to two different high‐latitude phenomena, aerosol ice particles near the mesopause and pulsating aurora. Because of the global atmospheric circulation, the lowest atmospheric temperature down to about −160°C occurs in the polar mesosphere at altitudes 80–90 km during summer time. Due to this low temperature, ice aerosol particles of the size up to 50‐nm exist there, which can be observed as noctilucent clouds (NLC). The ice particles can accumulate free electrons from surrounding space, so that spatial irregularities of the density of ice particles give rise to irregularities of electron density, which can be detected by radars as polar mesosphere summer echo (PMSE). In the case of pulsating aurora, the power of the PMSE detected by the radar is varying in accordance with the auroral pulsations, in spite of the aurora cannot be seen visually in the sunlight summer sky. This makes possible radar monitoring of the auroral pulsations even when visual auroral observations are impossible. Key Points: Polar mesosphere summer echoes, the power of which varied on the subsecond scale, were received from the altitude of noctilucent clouds Pulsating aurora can modulate power of the polar mesosphere summer echo Meteor radar erroneously accepts variations of the polar mesosphere summer echo at subsecond scale as meteor trails