An Observed Trend Between Mid‐Latitudes Km‐Scale Irregularities and Medium‐Scale Traveling Ionospheric Disturbances

Abstract

AbstractWe describe observations of a trend between the level of km‐scale irregularity activity and the amplitudes of medium‐scale traveling ionospheric disturbances (MSTIDs) at mid‐latitudes using data from December 2019 through June 2021. These include measurements of both heigh‐specific and vertically integrated quantities. Region‐specific, bottom‐side measurements were made with the dynasonde system near Wallops Island (WI) and included phase structure function parameters related to km‐scale irregularities as well as height‐specific tilts/density gradients, which are especially sensitive to MSTIDs. A complementary data set was derived from the nearby Deployable Low‐band Ionosphere and Transient Experiment (DLITE) array in southern Maryland. The DLITE array was used to measure the vertically integrated irregularity index, CkL, via scintillometry of bright cosmic radio sources at 35 MHz. Transverse gradients in the line‐of‐sight total electron content (TEC) were also measured with DLITE using apparent shifts in the sources' sky positions. Relatively simple layer‐based models for the vertical distribution of km‐scale irregularities applied to dynasonde‐measured properties yielded results that correlated well with DLITE measurements of CkL. Similarly, spectral analysis showed that fluctuation amplitudes of vertically integrated bottom‐side density gradients derived from dynasonde data were well correlated with DLITE TEC gradient measurements. A significant trend was found between CkL and TEC gradient MSTID amplitudes among DLITE‐based data as well as among the extrapolated dynasonde measurements. Additionally, within the bottom‐side F‐region, irregularity levels were found to be well correlated with fluctuation amplitudes for the tilt as measured with the WI dynasonde.