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

Abstract

AbstractWe 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.