Sources and Characteristics of Medium Scale Traveling Ionospheric Disturbances Observed by a Longitudinally Distributed Chain of SuperDARN Radars Across the United States

Abstract:

Medium Scale Traveling Ionospheric Disturbances (MSTIDs) are wave-like perturbations of the
F-region ionosphere with horizontal wavelengths on the order of 100-250 km and periods between ~15 - 60
min. In SuperDARN data, MSTID signatures are manifested as quasi-periodic enhancements of ground
scatter power moving through the radar FOV. High latitude SuperDARN MSTIDs have been studied for
many years and are generally attributed to atmospheric gravity waves (AGWs) launched by auroral sources.
Recent extension of the SuperDARN network to midlatitudes has revealed that MSTIDs are routinely
observed at midlatitudes as well. Our previous research using the single radar in Blackstone, Virginia
found a primary MSTID propagation direction which suggests that high latitude activity is also the primary
source of midlatitude MSTIDs. However, there is also a population of MSTIDs that could be generated by
tropospheric sources. This study extends this research by surveying multiple midlatitude radars in Oregon
(CVW and CVE), Kansas (FHW and FHW) and Virginia (BKS and WAL) from 1 November 2012 through
1 January 2013 for MSTID signatures in order understand the longitudinal distribution of midlatitude
MSTID characteristics and understand possible influences of varied terrain on MSTID observations.
MSTIDs observed by all radars had typical wavelengths between 250 to 500 km and horizontal velocities
between 100 and 250 m/s. In all radars, the dominant population of MSTIDs propagated in a southward
direction, ranging from 135˚ to 250˚ geographic azimuth. The dominant southward propagation direction
suggests auroral sources are the dominant source of MSTIDs observed by SuperDARN radars at
midlatitudes, which reinforces findings regarding the primary population in previous work.