Medium‐scale traveling ionospheric disturbances observed with the SuperDARN Hokkaido radar, all‐sky imager, and GPS network and their relation to concurrent sporadic E irregularities

Abstract

[1] We present midlatitude medium-scale traveling ionospheric disturbances (MSTIDs) observed with a Super Dual Auroral Radar Network (SuperDARN) HF radar at around 10 MHz in Hokkaido, Japan, in combination with a 630-nm all-sky imager and a GPS network (GEONET) that provides total electron content (TEC) data. MSTIDs propagating southward from high latitudes are detected at first with the HF radar and then with the imager and GEONET. We analyze two MSTID events, one in winter (event 1) and the other in summer (event 2), to find that MSTIDs appear simultaneously, at least, at 55°-25°N. It is shown that nighttime MSTIDs propagate toward the southwest over a horizontal distance of about 4000 km, and daytime MSTIDs do so toward the southeast. Daytime radar echoes are due to ground/sea surface (GS) scatter, while nighttime echoes in event 1 return from 15-m-scale F region field-aligned irregularities (FAIs) and those in event 2 are due to GS scatter. Doppler velocities of the nighttime F region FAI echoes in event 1 are negative (motion away from the radar) within strong echo regions and are positive (motion toward the radar) within weak echo regions. This fact suggests that the strong (weak) echoes return from suppressed (enhanced) airglow/TEC areas, in line with previous observations over central Japan. The nighttime MSTIDs in events 1 and 2 are often accompanied by concurrent coherent echoes from FAIs in sporadic E (E s ) layers. The E s echo areas in event 2 rather coincide with suppressed airglow/TEC areas in the F region that are connected with the echo areas along the geomagnetic field, indicating the existence of E and F region coupling at night.Citation: Ogawa, T., N. Nishitani, Y. Otsuka, K. Shiokawa, T. Tsugawa, and K. Hosokawa (2009), Medium-scale traveling ionospheric disturbances observed with the SuperDARN Hokkaido radar, all-sky imager, and GPS network and their relation to concurrent sporadic E irregularities,

On the origin of mesoscale TIDs at midlatitudes

“…Chisham et al (2007) summarized the SUPERDARN observations of many phenomena, including their very common detection of gravity waves at high latitudes. These waves occurred at all levels of magnetic activity, as was also reported later by Ogawa et al (2009). This notion is supported by satellite data showing that plasma irregularities are present 100% of the time above 55 • latitude (Kelley and Mozer, 1972).…”

“…We suspect that sporadic E-layers play a role (Otsuka et al, 2007) as well as the ratio of F-to E-region conductivities. Gravity waves in the E-region may also play a role but were not reported by Ogawa et al (2009).…”

“…The resulting altitude change affects the recombination rate and hence the plasma density. Ogawa et al (2009) report an example of a daytime MSTID that has similar characteristics to large-scale TIDs but does not have F-region irregularities or the E-region effects that characterize nighttime MSTIDs and is likely due to classical gravity wave interaction with the ionosphere. In the remainder of this paper, the term "MSTIDs" refers exclusively to nighttime MSTIDs.…”

“…However, a major breakthrough occurred recently when Ogawa et al (2009) used a Superdarn-type radar to show that MSTIDs seem to be related to gravity waves generated at high latitudes. However, they found no relationship with magnetic activity, that is, the gravity wave amplitude and occurrence rate did not depend on Kp.…”

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Abstract.A recent breakthrough experiment by Ogawa et al (2009) showed that Mesoscale Traveling Ionospheric Disturbances (MSTIDs), a common phenomenon at midlatitudes, originate in the auroral zone as gravity waves. Curiously, however, the latter do not seem to be related to magnetic activity.

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