Case study of apparent longitudinal differences of spread F occurrence for two midlatitude stations

Abstract

[1] Spread F is a widely studied subject, and the occurrence of spread F is affected by many factors. One of these factors is acoustic gravity waves (AGWs) which are very important in seeding spread F. Since most of the AGWs in the ionosphere originate from the lower atmosphere, there should be some regional features of spread F due to the different meteorological or ground conditions immediately beneath the local ionosphere. In this paper, a data set with a time coverage of one solar cycle from two Chinese stations located at exactly the same latitude and a 38 degrees separation in longitude, and having sharp contrasts of ground meteorological conditions, are used to make comparisons of spread F occurrence rates. The results showed that the total number of occurrence or occurrence percentage at Changchun station (very near the coast) is always much higher than that at Urumqi station (in the very center of the Europe-Asia continent). The annual maxima of spread F occurrence are in summer and winter. Other features of spread F occurrence at these two stations are in agreement with known properties of spread F. However, the great difference of occurrence frequency between the two stations is striking and worth further studying.

Multi-station investigation of spread F over Europe during low to high solar activity

“…The occurrence of nighttime midlatitude spread F has been well documented in the literature considering seasonal, solar and geomagnetic variability (Bowman, 1960, Singleton, 1968Rastogi, 1977;1990;Huang et al, 2011). In the present study, efforts have also been made to examine the monthly occurrence of different types of spread F. It can often be observed that in the nighttime midlatitude ionosphere, various mechanisms are considered as candidates to initiate instability conditions for the formation of irregularities at the bottom of F layer which develop into certain diffused irregularity traces termed as RSF.…”

“…It can be observed that during 21:15 to 21:30 UT, the nighttime F region plasma density distribution was affected by irregularity distributions, which reappeared during 22:30 to 22:45 UT and could be related to spread F development over the European longitudes. As 3rdAugust 2015 was a magnetically quiet day, the sudden plasma depletion observed may indicate the generation of local irregularities under the influence of gravity waves which may originate from the lower atmosphere and trigger the instability at the bottom of the F layer (Huang et al, 2011).The focus of the present paper is limited to three ionosonde stations of European longitude sector, namely, Nicosia, Athens and Pruhonice. The stations at Nicosia and Athens are situated at around 35°to 37°N latitude whereas Pruhonice is at higher latitude (∼50°N).…”

“…The occurrence of nighttime spread F irregularities with various scale sizes (from less than a meter to several kilometers) was first observed by Booker & Wells (1938). Later, various different instruments such as ground-based ionosondes, coherent and incoherent scatter radars, MU radars, satellite-borne top-side sounders, HF Doppler radars, GNSS satellite receivers and in-situ measurements (Fejer & Kelley, 1980;Basu & Basu, 1985;Kelly, 1989;Fukao et al, 1991;Mathews et al, 2001;Swartz et al, 2002;Chandra et al, 2003;Xiao et al, 2007) were used to reveal the morphological features of spread F occurrence including its long term characteristics such as its dependence on solar activity, diurnal, seasonal and latitude/longitude variations (Rastogi, 1977;Bowman, 1984Bowman, , 1986Bowman, , 1988aBowman, , 1988bBowman, , 1990Huang et al, 2011). These morphological features of spread F still need the attention of the scientific community, as spread F significantly complicates ionospheric predictions.…”

Ionospheric longitudinal variations at midlatitudes: Incoherent scatter radar observation at Millstone Hill

“…This difference is exactly the same as shown here and in ref. [5] Further indication of the longitudinal difference between the two stations was shown in the spread-F occurrence [21]. With proper zonal wind information, it will be possible to explain the observed differences in electron density over the two stations in terms of magnetic declination and zonal winds.…”

Low-latitude equinoctial spread-F occurrence at different longitude sectors under low solar activity

“…Hoang et al (2010) performed a comparative study of the ESF characteristics over two equatorial sites, Ho Chi Minh in Vietnam and São Luis in Brazil, showing that the spread-F occurrence is significantly less frequent at Ho Chi Minh than at São Luis throughout the year. Huang et al (2011) considered two Chinese stations, Changchun and Urumqi, at the same latitude and separate in longitude by 38 degrees, and they showed that the spread-F occurrence is always larger at Changchun than at Urumqi. This paper describes a comparative study of spread-F occurrence over five low-latitude sites ( Fig.…”