Large‐Scale Horizontally Enhanced Sodium Layers Coobserved in the Midlatitude Region of China

Abstract

We report 19 coobserved enhanced sodium layers, including sporadic sodium layers (SSLs) and thermospheric enhanced sodium layers (TeSLs), over Hefei (31.8°N, 117.3°E) and Wuhan (30.5°N, 114.4°E) from 2011 to 2018. The total coobservation time at Hefei and Wuhan was 387.24 hr, and the average occurrence rates were 0.038 hr−1 and 0.028 hr−1 for the SSLs and TeSLs, respectively. The SSL and TeSL occurrence rates in summer were 0.078 and 0.039 hr−1, respectively, which were considerably higher than those in other seasons. Among all 19 cases, 16 cases, including 9 SSL cases and 7 TeSL cases, occurred almost simultaneously over Hefei and Wuhan without a time delay. Seven TeSLs and four out of the nine SSLs were accompanied by ionospheric sporadic E (Es), suggesting that an “Es‐SSL (TeSL)” chain formed via the wave‐induced wind shear mechanism. Three SSLs were modulated by waves and the two other cases were related with gravity wave overturning. In general, the correlation coefficients between Hefei and Wuhan for long‐duration cases (more than 2 hr) were high due to some large‐scale mechanism, and the short‐duration cases (less than 2 hr) had poor correlation due to different local characteristics. In addition, three cases were observed with an apparent time delay over Hefei and Wuhan, which might indicate the possible existence of long‐distance transport processes.

Solitary wave characteristics on the fine structure of mesospheric sporadic sodium layer

“…Since the vertical scale of the NaS is defined less than 10 km, while the horizontal scale is often reported more than 300 km or even over 1000 km (Fan et al, 2007;Ma et al, 2019), this scenario is in consistent with the shallow water model. The solitary waves could Particularly appear at the interface between upper and lower stratifications in the fluid medium [Bogucki and Garrett, 1993] (Bogucki and Garrett, 1993).…”

Derivation of global ionospheric Sporadic E critical frequency ( f o Es) data from the amplitude variations in GPS/GNSS radio occultations

“…So the ionconvergence mechanism does not work efficiently at high magnetic latitudes [19], but the vertical effects of gravity waves and electric field are very efficient in concentrating the ionization of Es layers in the central polar cap where the magnetic-field lines are approximately vertical [20,21]. The wind shear theory has been confirmed by incoherent scatter radar (ISR) [22], meteor radar [23], ionosonde [24], rocket [25], lidar [26] and chemical tracer measurements [27], as well as the measurements [28][29][30][31][32][33][34] and model simulations [35][36][37][38][39][40] of metal ions and atoms in the mesosphere and lower thermosphere (MLT). The main problem of wind shear theory is to explain the global morphology of Es and its seasonal distribution [16,17].…”

Using GNSS radio occultation data to derive critical frequencies of the ionospheric sporadic E layer in real time

“…The global climatology of EsOR was further confirmed by Yeh et al (2012), Chu et al (2014), and Tsai et al (2018). The climatology of EsOR (Dou et al 2010) and short-term variability of ten minutes to one hour in the Es layer (Xue et al 2017;Ma et al 2019) in a local geographic region can be measured by RO signals. The maximum values of the amplitude scintillation S4 index (S4max) derived from 50 Hz L1 amplitude measurements, which occur at the altitude of Es, can be used as a proxy of the intensity of Es layers (Yue et al 2015a).…”