Formation of Multilayered Sporadic E under an Influence of Atmospheric Gravity Waves (AGWs)

Abstract

The formation of multilayered sporadic E by atmospheric gravity waves (AGWs), propagating in the mid-latitude lower thermosphere, is shown theoretically and numerically. AGWs with a vertical wavelength smaller than the width of the lower thermosphere lead to the appearance of vertical drift velocity nodes (regions where the ions’ vertical drift velocity, caused by these waves, is zero) of heavy metallic ions (Fe+). The distance between the nearest nodes is close to the AGWs’ vertical wavelength. When the divergence of the ion vertical drift velocity at its nodes has a minimal negative value, then these charged particles can accumulate into Es-type thin layers and the formation of multilayered sporadic E is possible. We showed the importance of the ions’ ambipolar diffusion in the formation of Es layers and control of their densities. Oblique downward or upward propagation of AGWs causes downward or upward motion of the ion vertical drift velocity nodes by the vertical propagation phase velocity of these waves. In this case, the formed Es layers also descend or move upward with the same phase velocity. The condition, when the horizontal component of AGWs’ intrinsic phase velocity (phase velocity relative to the wind) and background wind velocity have same magnitudes but opposite directions, is favorable for the formation of the multilayered sporadic E at fixed heights of the sublayers. When the AGWs are absent, then horizontal homogeneous wind causes the formation of sporadic E but with a single peak. In the framework of the suggested theory, it is shown that, in the lower thermosphere, the wind direction, magnitude, and shear determine the development of the processes of ion/electron convergence into the Es-type layer, as well as their density divergence. Consideration of arbitrary height profiles of the meridional and zonal components of the horizontal wind velocity, in case of AGW propagation, should be important for the investigation of the distribution and behavior of heavy metallic ions on regional and global scales.

Multilayered Sporadic‐E Response to the Annular Solar Eclipse on June 21, 2020

“…The multilayered echoes are similar to those of the E s simulation by Didebulidze et al. (2020). Their simulation results show that the E s can be multilayered under the influence of the small‐scale AGWs in nighttime.…”

“…The agreement between the observation (Figures 2 and 4c) and the independent numerical simulations performed by Didebulidze et al. (2020) suggests that the appearance of the multilayered E s can be attributed to the small‐scale AGWs due to the obscuration. Chen et al.…”

“…Figure 4c shows that the multilayered echoes consist of the 3-5 sublayers with the corresponding spans ranging from 11.4 to 22.6 km distributed also within a wide altitude range. The agreement between the observation (Figures 2 and 4c) and the independent numerical simulations performed by Didebulidze et al (2020) suggests that the appearance of the multilayered E s can be attributed to the small-scale AGWs due to the obscuration. Chen et al (2011) also showed E s being largely scattered around the 137-190 km altitude between the one-and two-hop regular E s echoes by employing the HF fixed frequency ionosonde during the 2009 solar eclipse.…”

Altitudinal and Latitudinal Variations in Ionospheric Sporadic‐E Layer Obtained From FORMOSAT‐3/COSMIC Radio Occultation

“…Back to this study, the discrepancies between the EsOR/EsI and CWS (Figure 9) also imply that the wind shear cannot explain the vertical evolution of the Es layer fully. The formation and evolution of the Es layer can be affected by other factors including the electric field, background metallic ion distribution, and gravity waves (Cai et al, 2017;Chu et al, 2014;Didebulidze et al, 2020;Gubenko & Kirillovich, 2020;Resende et al, 2016).…”

Sounding of sporadic E layers from CSES radio occultation and comparing with ionosonde measurements

“…The name Sporadic E and its abbreviation Es refer to thin layers of metallic ion plasma which accumulates in the dynamo region of the Earth's ionosphere, mostly between 100 and 125 km, where ion motion is controlled mainly by collisions with the neutrals, thus the ions move with the winds while electrons remain strongly magnetized (Haldoupis 2012). The formation of sporadic E layer was traditionally attributed to the "windshear theory" (Whitehead 1961;Axford 1963;Whitehead 1989), in which vertical shears in the horizontal wind play a key role in forming these layers from long-lived metallic ions through (Haldoupis, 2011;Yeh et al, 2014, Didebulidze et al, 2020. Meanwhile, the ionospheric E region has a relatively higher electrical conductivity and therefore plays a crucial role in the ionosphere electron dynamics at both E-and F-region altitudes (Yue et al 2015).…”