Medium-Scale Traveling Ionospheric Disturbances Observed by Nadir-Viewing 630 nm Airglow Imaging From the International Space Station

Nighttime medium-scale traveling ionospheric disturbances (MSTIDs) were investigated for wave parameters, occurrence, and seasonal–longitudinal climatology using 630 nm OI airglow from the Visible and Near-Infrared Spectral Imager (VISI) aboard the International Space Station. Although MSTIDs are widely studied from the ground, their global behavior remains less understood due to limited geographic coverage. We present new insights into MSTID climatology derived from spaceborne measurements. VISI's two fields of view, pointing forward and backward from nadir, enable discrimination of ionospheric signals from ground-based light contamination. Case studies show that the two views capture subtle structural differences consistent with an equatorward-tilted vertical geometry of MSTIDs. Comparisons with simultaneous total electron content from Japanese nationwide global navigation satellite system receiver network and with all-sky airglow imagers of the Optical Mesosphere Thermosphere Imagers network reveal that measured wave parameters—wavelength, wavefront orientation, phase speed, and amplitude—agree with established MSTID characteristics. Analysis of 3 years (2013–2015) of VISI data yielded 676 MSTID events across both hemispheres, exhibiting strong seasonal and longitudinal variations. Local summer maxima and activity enhancements appear in regions with high sporadic-E (Es) occurrence. In the Northern Hemisphere, the primary peak occurs around the June solstice, with particularly high rates in the Asia–west Pacific sector. In the Southern Hemisphere, a semiannual pattern emerges, featuring a primary peak during the December solstice and a secondary peak during the June solstice in the same Asia–west Pacific sector. These findings suggest Es-related E–F coupling plays a key role in MSTID generation, with conjugate-hemisphere coupling further modulating global distribution.