[1] We report for the first time simultaneous observations of medium-scale traveling ionospheric disturbances (MSTIDs) at geomagnetic conjugate points in both hemispheres, using two all-sky airglow imagers at midlatitudes. A 630-nm all-sky CCD imager at Sata, Japan, detected MSTIDs with a wavefront elongated from NW to SE on the night of August 9, 2002. During this event, MSTIDs with a wavefront elongated from SW to NE were observed at the geomagnetic conjugate point, Darwin, Australia. To investigate geomagnetic conjugacy of the MSTID structures, the Darwin images were mapped The MSTID structures mapped from Darwin to its magnetic conjugate points along the geomagnetic field lines (B) coincide closely with those in the Sata images. This result suggests that polarization electric field (Ep) plays an important role in the generation of MSTIDs. Ep maps along B and moves the F region plasma upward or downward by E × B drifts, causing plasma density perturbations with structures mirrored in the northern and southern hemispheres.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2004GL020262

Geomagnetic conjugate observations of medium-scale traveling ionospheric disturbances at midlatitude using all-sky airglow imagers

[1] In this work we present a simple technique to estimate the medium-scale traveling ionospheric disturbances (MSTIDs) characteristics (such as occurrence, velocity, vertical propagation) with periods lower than 20 min and its application to a set of GPS data both temporally and spatially representative (near one solar cycle and four local networks in the Northern and Southern Hemispheres, respectively). Some of the main results presented in this paper are the MSTIDs which occur at daytime in local winter and nighttime in local summer, related to the solar terminator and modulated by the solar cycle. They present equatorward (from � 100 to 400 m/s) and westward (� 50 to 200 m/s) horizontal propagation velocities, respectively. The corresponding periods are compatible (higher) with the theoretical prediction, which is given by the neutral atmosphere

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2005JA011474

Medium-scale traveling ionospheric disturbances affecting GPS measurements: Spatial and temporal analysis

[1] We have investigated statistical characteristics of the nighttime medium-scale traveling ionospheric disturbances (MSTIDs) observed in 630-nm airglow images at two stations, Rikubetsu (43.5°N, 34.8°MLAT) and Shigaraki (34.9°N, 25.4°MLAT), in Japan for 1998–2000 near the solar maximum period. Most of the observed MSTIDs propagate southwestward in the images. The typical wavelength, velocity, period, and amplitude are 100–300 km, 50–100 m/s, 0.5–1.5 h, and 5–15%, respectively. Seasonal variations in these parameters are not clear. The occurrence rate has a major peak (50–60%) in summer that appears ∼2 months earlier at lower latitudes and a minor peak in winter. Similar occurrence characteristics are obtained from midlatitude spread-F signatures using multipoint ionosonde data in Japan, though the coincidence of the spread-F and the MSTIDs in airglow images is only 10–15%.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002JA009491

Statistical study of nighttime medium‐scale traveling ionospheric disturbances using midlatitude airglow images

: We present, in this paper, an overview of theories of naturally occurring high latitude E and F region ionospheric irregularities. (For a review of artificially-induced irregularities, e.g., from ionospheric 'heating' experiments, see Fejer 1979.) Emphasis is placed on recent results, particularly with regard to sources of high latitude irregularities. Physical mechanisms are stressed with extensive mathematical analysis avoided. Expertise in plasma physics has not been assumed. We summarize the recent and previous theoretical literature dealing with F region irregularities, and we concentrate on E region irregularity phenomena.

Theories of high-latitude ionospheric irregularities: A review

. Two-dimensional structures of medium-scale traveling ionospheric disturbances (MSTIDs) over Europe have been revealed, for the first time, by using maps of the total electron content (TEC) obtained from more than 800 GPS receivers of the European GPS receiver networks. From statistical analysis of the TEC maps obtained 2008, we have found that the observed MSTIDs can be categorized into two groups: daytime MSTID and nighttime MSTID. The daytime MSTID frequently occurs in winter. Its maximum occurrence rate in monthly and hourly bin exceeds 70% at lower latitudes over Europe, whereas it is approximately 45% at higher latitudes. Since most of the daytime MSTIDs propagate southward, we speculate that they could be caused by atmospheric gravity waves in the thermosphere. The nighttime MSTIDs also frequently occur in winter but most of them propagate southwestward, in a direction consistent with the theory that polarization electric fields play an important role in generating the nighttime MSTIDs. The nighttime MSTID occurrence rate shows distinct latitudinal difference: The maximum of the occurrence rate in monthly and hourly bin is approximately 50% at lower latitudes in Europe, whereas the nighttime MSTID was rarely observed at higher latitudes. We have performed model calculations of the plasma density perturbations caused by a gravity wave and an oscillating electric field to reproduce the daytime and nighttime MSTIDs, respectively. We find that TEC perturbations caused by gravity waves do not show dip angle dependencies, while those caused by the oscillating electric field have a larger amplitude at lower latitudes. These dip angle dependencies of the TEC perturbation amplitude could contribute to the latitudinal variation of the MSTID occurrence rate. Comparing with previous studies, we discuss the longitudinal difference of the nighttime MSTID occurrence rate, along with the E- and F-region coupling processes. The seasonal variation, of the nighttime MSTID occurrence rate in Europe, is not consistent with the theory that the longitudinal and seasonal variations of the nighttime MSTID occurrence could be attributed to those of the Es layer occurrence.

/pdf/gps-observations-of-medium-scale-traveling-ionospheric-6pq5fc3iyr.pdf

GPS observations of medium-scale traveling ionospheric disturbances over Europe

A review of theoretical and observational results describing atmospheric gravity wave (AGW)/traveling ionospheric disturbance (TID) phenomena at high latitudes is presented. Some recent experimental studies of AGW's using the Chatanika incoherent scatter radar and other geophysical sensors are reported. Specifically, the following features are described in detail: (1) cause/effect relations between aurorally generated AGW's and TID's detected at mid-latitudes, including probable ‘source signature’ identification, (2) AGW source phenomenology, particularly a semiquantitative assessment of the relative importance of Joule heating, Lorentz forces, intense particle precipitation, and other mechanisms in generating AGW's, and (3) detection of TID's in the auroral ionosphere. Several instances of F region electron density, temperature, and plasma periodicities accompanied by horizontal plasma velocities which were consistent with theoretical AGW/TID models are documented.

Robert D. Hunsucker

Papers

Atmospheric gravity waves generated in the high‐latitude ionosphere: A review