Occurrence climatology of F region field‐aligned irregularities in middle latitudes as observed by a 40.8 MHz coherent scatter radar in Daejeon, South Korea

Abstract

A new 40.8 MHz coherent scatter radar was built in Daejeon, South Korea (36.18°N, 127.14°E, dip latitude: 26.7°N) on 29 December 2009 and has since been monitoring the occurrence of field‐aligned irregularities (FAIs) in the northern middle latitudes. We report on the occurrence climatology of the F region FAIs as observed by the Daejeon radar between 2010 and 2014. The F region FAIs preferentially occur around 250–350 km at 18:00–21:00 local time (postsunset FAI), around 350–450 km near midnight (nighttime FAI), around 250–350 km before sunrise (presunrise FAI), and around 160–300 km after 05:00 local time (postsunrise FAI). The occurrence rates of nighttime and presunrise FAIs are maximal during summer, though the occurrence rates of postsunset and postsunrise FAIs are maximal during the equinoxes. FAIs rarely occur during local winter. The occurrence rate of F region FAIs increases in concert with increases in solar activity. Medium‐scale traveling ionospheric disturbances (MSTIDs) are known as an important source of the F region FAIs in middle latitudes. The high occurrence rate of the nighttime FAIs in local summer is consistent with the high occurrence rate of MSTIDs in that season. However, the dependence of the FAI activity on the solar cycle is inconsistent with the MSTID activity. The source of the F region FAIs in middle latitudes is an open question. Our report of different types of FAIs and their occurrence climatology may provide a useful reference for the identification of the source of the middle latitude FAIs.

Statistical Characteristics of Mid‐Latitude Ionospheric Irregularities at Geomagnetic Quiet Time: Observations From the Jiamusi and Hokkaido East SuperDARN HF Radars

“…Point 1 is similar to previous studies by Yang et al. (2015), but our results have a wider region of latitude distribution at mid‐latitudes. These seasonal characteristics are the results of many factors, such as electron density gradient, the occurrence rate of MSTIDs, and the presence of Es in the middle latitudes.…”

“…The seasonal variation in the F region irregularity occurrence rate in the middle latitude obtained in this study is consistent with the results of Yang et al. (2015). They used the data from a VHF coherent radar located in Daejeon, South Korea, which is close to the Jiamusi radar.…”

On using a double-thin-shell approach and TEC perturbation component to sound night-time mid-latitude E–F coupling

“…Considering the ionospheric irregularities usually occur at altitudes ~ 95-125 km (~ 250-350 km) in E (F) region (Haldoupis et al 2006;Yang et al 2015), the maximum uncertainty of the phase front structures manifested in the projections on the ground is about 20 km (45 km), under the double-thin-shell approximation with two constant heights. At a given shell ( i = E, F ), the relationship between vertical TECP ( TECP V i ) and slant TECP is…”