Characteristics of nighttime medium-scale traveling ionospheric disturbances observed over Alaska

Abstract

[1] We focused on propagating wave-like structures which frequently appeared in the O I 630.0 nm airglow images obtained by an all-sky imager installed at Poker Flat Research Range (65.1°N, 147.4°W, magnetic latitude 65.6°) in Alaska. These events are classified as medium-scale traveling ionospheric disturbances (MSTIDs) on the basis of the wavelength and propagating speed. The unique points of our observation are (1) the two-dimensional structures of MSTIDs in the subauroral region are revealed; (2) the horizontal direction of the electric field can be estimated from the motion of the Evening Co-rotating Patch (ECP) aurora appearing simultaneously; and (3) neutral winds are simultaneously observed by a Fabry-Perot spectrometer. Statistical study of these MSTID events from November 2001 to April 2002 indicates the following characteristics. The MSTIDs were observed almost every evening, and sometimes in the morning, but were not observed at midnight. Typical propagating speed, direction, and wavelength of the wave phenomena were about 135 m/s, southwestward, and about 250 km, respectively. When the MSTIDs appeared, northward neutral winds and westward plasma drifts were dominant. This indicates that the Perkins instability does not contribute to the development of MSTIDs in the Alaska region. The vertical wavelength analysis using the dispersion relation of gravity waves with the observed wave parameters and background winds suggests that the observed MSTIDs over Alaska are the atmospheric gravity waves (AGWs). As a case study, temporal variation of an MSTID event on 21 December 2001 is shown. Results of a ray tracing analysis of this event suggest that the AGWs come from the equatorward edge of the auroral oval.

Seasonal Propagation Characteristics of MSTIDs Observed at High Latitudes Over Central Alaska Using the Poker Flat Incoherent Scatter Radar

“…Our findings obtained over several seasons, indicate strong seasonal variability in the MSTID propagation directions at this high‐latitude location. Although there are several previous climatological studies of MSTIDs at middle and low latitudes (e.g., Crowley et al, ; Ding et al, ; Frissell et al, ; Ishida et al, ; Kubota et al, ), seasonal measurements at high latitudes are sparse and their properties are not well known.…”

“…The Ishida et al () measurements were obtained during slightly more active geophysical conditions than in our study (which ranged from ∼1 to 3). In Table , we also include results from Kubota et al (), who observed MSTIDs on 44 nights over central Alaska using OI (630 nm) emission (mean altitude ∼250 km) during one winter season. They reported strong southward propagation with a significant westward component.…”

“…Since these initial observations, the characteristics of TIDs have been investigated using a variety of techniques. These include (a) electron density measurements using vertical and oblique ionosondes (e.g., Afraimovich et al, ; Morgan et al, ; Ogawa et al, ; Tedd et al, ) and incoherent scatter radars (ISRs; e.g., Djuth et al, , ; Fukao et al, ; Nicolls & Heinselman, ), (b) backscatter radar soundings (e.g., Bristow et al, ; Bristow & Greenwald, ; Frissell et al, , ), (c) continuous wave (CW) Doppler measurements (e.g., Georges, ; Hung et al, ; Röttger, ), (d) total electron content (TEC) measurements using Global Positioning System (GPS) satellite constellations (e.g., Galushko et al, ; Nicolls et al, ; Onishi et al, ), and (e) optical airglow measurements (e.g., Kubota et al, ; Paulino et al, ; Shiokawa et al, , ). All of these measurement techniques have their strengths and limitations.…”

Motion of high‐latitude nighttime medium‐scale traveling ionospheric disturbances associated with auroral brightening

“… Bristow et al [1994]made comprehensive studies of MSTIDs, which they called medium‐scale atmospheric gravity waves, in the auroral zone using the SuperDARN HF radar network. However their observations were mainly performed in daytime with less spatial resolution than airglow imagers, as they use ground‐scatter echoes Kubota et al [2011]…”

The geospace response to variable inputs from the lower atmosphere: a review of the progress made by Task Group 4 of CAWSES-II

“…Kubota et al (2011) reported characteristics of MSTIDs observed by an airglow imager at Alaska. They concluded that these southwestward-moving MSTIDs are not caused by ionospheric instabilities, as usually suggested at middle latitudes, but are likely to be caused by auroral disturbances as TADs because the observed background thermospheric wind was poleward, stabilizing the ionospheric instability.…”