A Numerical Investigation on the Variation of Sodium Ion and Observed Thermospheric Sodium Layer at Cerro Pachón, Chile During Equinox

Abstract

The extension of the neutral sodium (Na) layer into the thermosphere (up to 170 km) has recently been observed at low and high latitudes using a Na lidar. However, the geophysical mechanisms and implications of its formation are currently unknown. In this study, we conduct an advanced two-dimensional numerical simulation of the Na and Na + variations in the E and F regions at low latitudes. The numerical simulations are used to investigate the contributions of the electromagnetic force, neutral wind, diffusion, and gravity. The simulations lead to three major findings. First, Na + in the subtropical region of the geomagnetic equator acts as the major reservoir of the neutral sodium, and its distribution during nighttime is mostly below 200 km due to the combined effect of the vertical component of the E ! × B ! drift and Coulomb-induced drift. Second, we find that the fountain effect has little influence on the behavior of Na in the nighttime. Third, the probable explanation for the frequent generation of the thermospheric sodium layer during spring equinox at Cerro Pachón, Chile is attributed to the large vertical neutral transport generated by large vertical wind perturbations of unknown origin, with a magnitude exceeding 10 m/s that is closely associated with the semidiurnal tide.

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

“…This varying pattern is similar to those reported in the previous works about the SSLs and Es [21,30,35]. Comparing the statistical parameters of the LTSLs with the statistical parameters of the SSLs observed at Yanqing [11,32], three differences become clear. The altitude of the LTSLs (ranging from 105 to 120 km with an average altitude of 109.5 km) are higher than those of the SSLs (ranging from 90 to 100 km with an average of 95.7 km); the densities of the LTSLs (which are much lower than that of the main sodium layer) are less than those of the SSLs (which are much greater than that of the main sodium layer); and the FWHMs of the LTSLs (distributed from 1 to 12 km with an average width of approximately 4.7 km) are broader than those of the SSLs (approximately 0.2-3.0 km with an average value of 1.7 km).…”

Self-consistent Global Transport of Metallic Ions with WACCM-X

“…Instead of being redistributed along the magnetic field lines to the subtropical region by the "classical" fountain effect (e.g., Pi et al, 2009), the Mg + shows a more complex downward trajectory, i.e., the ions are not transported symmetrically to both sides of the geomagnetic equator, which is closer to the scenario proposed by Cai et al (2019).…”

Investigation on the Distinct Nocturnal Secondary Sodium Layer Behavior Above 95 km in Winter and Summer Over Logan, UT (41.7°N, 112°W) and Arecibo Observatory, PR (18.3°N, 67°W)

“…In addition, we only solve for the continuity equations of Na, Na + , and NaHCO 3 because the densities of other Na related species such as NaOH and NaO are much smaller than these three major species and can be solved using chemical equilibrium without transport during the courses of major species calculations (Plane, 2004). The details of the transport velocity of Na and Na + can be found in Cai, Yuan, and Eccles (2017) and Cai et al (2019). The Na neutral and ion chemistry are adopted from Plane (2004), which also provides the production rate of Na due to Na + .…”