Sudden Sodium Layers: Their Appearance and Disappearance

Abstract

Temperature variation has been proposed to play an important role in the formation of the sporadic sodium layers (SSLs or Na S ) in subtropic area, based on the observed significant correlation between SSLs and high temperatures. The icy-dust particle, which could form in the extremely cold conditions and act as absorbers of sodium species, was proposed to be a possible candidate for the sodium reservoir of the SSLs. In this study, the University of Science and Technology of China temperature/wind lidar and the sodium fluorescence lidar at a subtropic station Hefei (31°N, 117°E), China, were used to observe sodium density, temperature, and wind profiles simultaneously throughout the SSL events. Based on the observations of two SSLs occurring on 12 and 13 May 2013, the possibility of an icy-dust layer existing and acting as the sodium reservoir is tested for the first time in details. Both events experienced an extremely cold temperature (<150 K) several hours before the onset of SSLs, followed by a subsequently fast production of sodium atoms during a large temperature enhancement (>40 K). An empirical model including two main steps is then proposed: first, sodium species are collected by an icy-dust reservoir and stored during the extremely cold phase; second, free sodium atoms could be released from the reservoir by a possible trigger. As a result, this kind of SSLs could possibly be regarded as a quasi-continuous phenomenon caused and modulated by temperature variations with an icy-dust model that can exhibit intermittent time variations related to the water vapor concentration.Plain Language Summary Temperature variation, rather than through the mechanism of cooccurrence of sporadic E layer (ES), has been proposed to play an important role in the formation of the sporadic sodium layers (SSLs or NaS) in subtropic area based on the observed significant correlation between SSLs and high temperatures. But the detailed process and mechanism are still unclear. The icy-dust particle, which could form in the extremely cold temperature conditions and as absorbers of sodium species, was proposed by previous studies to be a possible candidate for the sodium reservoir of the SSLs. However, this most promising scenario has not yet been evaluated in those earlier studies owing to a lack of the relevant observations. In this study, the University of Science and Technology of China temperature/wind lidar and the sodium fluorescence lidar at a subtropic station Hefei (31°N, 117°E), China, were used to observe sodium density, temperature, and wind profiles simultaneously throughout the SSL events and activities. Based on the observations of two SSLs occurring on 12 and 13 May 2013, the possibility of an icy-dust layer existing at the mesopause and acting as the sodium reservoir is tested and verified for the first time in details.

The Comprehensive Study of Low Thermospheric Sodium Layers during the 24th Solar Cycle

“…Moreover, the other LTSL on 4 May 2014, a large temperature enhancement was also present, the temperature raised from 206 K to 277 K at 105 km from 19:30 LT to 21:25 LT. However, the lowest temperature was 169 K at 102 km, is higher than previous reported extremely cold phase 150 K [40] for ice dust. Although tidal waves or other such reasons can have amplitude of 40-60 K in the MLT region.…”

“…The temperature-controlled theory was first proposed by Zhou et al, which suggested the triggering of sodium atoms by some means through temperature enhancement in a narrow altitude region due to energy damping during gravity wave breaking [39]. Recently, an empirical model was proposed that sodium species were collected by an icy-dust reservoir and stored during the extremely cold phase (<150 K) and a large temperature enhancement (>40 K of temperature increase) triggered a generation of sodium atoms [40]. Therefore, we turn to the temperature profiles from SABER.…”

Comparison of middle- and low-latitude sodium layer from a ground-based lidar network, the Odin satellite, and WACCM–Na model

“…The sporadic E (E s ) layers, thin layers of concentrated metallic plasma in the lower E region of the ionosphere, are proposed to be a source of sodium in the mesosphere . Studies show that the SSLs are closely related to the changes in Na + metallic ions within E s layers (Yuan et al, 2014b;Qiu et al, 2018;Cai et al, 2019a, b;Xia et al, 2021). From a laboratory kinetic study, Cox and Plane (1998) demonstrated that the sporadic metal layer is produced when the E s layer descends below 100 km under the influence of tides.…”

Dynamic Properties of a Sporadic Sodium Layer Revealed by Observations Over Zhongshan, Antarctica: A Case Study

“…The other candidates for the source of sodium atoms could be direct meteor deposition, and/or release from aerosol particles, as well as redistribution of existing atoms (e.g., Batista et al, 1991;Clemesha, 1995;Clemesha et al, 1978). However, direct meteor deposition requires a meteor shower with a large mass, and aerosol particle release requires a background temperature increase (Qiu et al, 2015(Qiu et al, , 2018. The redistribution of existing atoms is another good explanation for SSLs.…”