The global climatology of the intensity of ionospheric sporadic <i>E</i> layer

Abstract

On the basis of S4max data retrieved from COSMIC GPS radio occultation measurements, the long-term climatology of the intensity of E s layers is investigated for the period from December 2006 to January 2014. The global maps of E s intensity shows a high spatial resolution geographical distributions and strong seasonal dependence of E s layers.The maximum intensity of E s occurs in the midlatitudes, and its value in summer is 2-3 times larger than that in winter. A relatively strong E s layer is observed at the North and South Poles with a distinct boundary dividing the middle latitudes and high latitudes along 60 • -5 80 • geomagnetic latitude bands. Besides, simulation results shows that the convergence of vertical ion velocity could partially explain the seasonal dependence of E s intensity. Furthermore, some disagreements between the distributions of calculated divergence of vertical ion velocity and observed E s intensity indicate that other processes such as magnetic field effects, meteoric mass influx into the earth's atmosphere and chemical processes of metallic ions should also be considered, which play an important role in the spatial and seasonal variations of E s layers. 10 1 IntroductionThe ionospheric sporadic E (E s ) layers are known as thin-layered structures of intense high electron density at 90-130 km altitudes. Rocket-borne mass spectrometric measurements proved that the E s layer is mostly the ionization of metal atoms such as Fe + , Mg + , and Na + (Kopp, 1997;Grebowsky and Aikin, 2002). The E s layer is mainly at midlatitudes and relatively absent at geomagnetic equator and high latitudes (Whitehead, 1989). It is widely accepted that the mechanism responsible for the E s 15 layer formation at midlatitudes is the windshear theory, in which the zonal and meridional winds provide the vertical windshear convergence nodes. As a result, the long-lived metallic ions are forced to converge towards the wind shear null to form a thin layer of intense metallic ionization (Whitehead, 1961;Macleod, 1966;Whitehead, 1970;Nygren et al., 1984;Whitehead, 1989;Haldoupis, 2012). In the equatoral region, the physical process of E s irregularities is attributed to the gradient-drift instabilities associated with the equatorial electrojet (Tsunoda, 2008). The E s layer generally has a vertical scale of 1 km or less, but its 20 1 Atmos. Chem. Phys. Discuss., https://doi.

Wavenumber‐4 Patterns of the Sporadic E Over the Middle‐ and Low‐Latitudes

“…But it is difficult to be detected, as the Es occurrence rates are generally low during the nighttime. Other physical processes should also be considered in the geographical distribution and spatial and temporal variations in the WN4 pattern, as they play important roles in determining the global morphology of Es, such as the magnetic field, electric field, gravity wave, meteoric influx, the chemical processes of metallic ions, and meteorological processes in the lower atmosphere (Cai et al., 2019; Feng et al., 2013; Haldoupis, 2012; Mathews, 1998; Yu et al., 2019; Yue et al., 2012). Numerical simulations are required to further investigate the relationship between the WN4 structure of the Es layer and the aforementioned causes.…”

VHF Imaging Radar Observations and Theory of Banded Midlatitude Sporadic E Ionization Layers

“…Yu et al. (2019) mapped the global climatology of E s layers using GPS radio occultation measurements from the COSMIC satellites, finding a steep decline in intensity above about 50° geomagnetic latitude. The authors attributed this to the failure of the wind shear mechanism for creating E s layers at higher dip latitudes.…”

Difference in the Sporadic E Layer Occurrence Ratio Between the Southern and Northern Low Magnetic Latitude Regions as Observed by COSMIC Radio Occultation Data

“…In addition, the sporadic E layer intensity is obtained from RO data, which provide a new data source for quantitative analysis that is similar to ionosonde observations (Niu et al, 2015(Niu et al, , 2019Arras and Wickert, 2017;Yu et al, 2019). Tidal behavior has also been investigated in several studies.…”