Examining the Wind Shear Theory of Sporadic E With ICON/MIGHTI Winds and COSMIC‐2 Radio Occultation Data

Abstract

Metallic ion layers are commonly observed in the ionosphere. In particular, those which occur at E-region heights show high plasma concentrations, and they can cause anomalous high frequency (HF) radio propagation, known as Es. The characterization of the phenomenon and the formation mechanism for Es layers have been a subject of study for many decades (see, e.g., reviews by Haldoupis, 2011;Mathews, 1998;Whitehead, 1989). Observations of Es have been made using various instruments and techniques, including ionosondes (e.g., Taguchi, 1961), sounding rockets (e.g., Smith, 1966), incoherent scatter radars (e.g., Miller & Smith, 1978), lidars (e.g., Gardner et al., 1993, and radio occultation measurements (e.g., Hocke et al., 2001). It is now well established that Es layers occur most frequently at mid latitudes (20°-50° latitude) in the summer hemisphere at altitudes of 90-120 km.The formation of an Es layer requires the convergence of ion flux. The wind shear theory (Axford, 1963;Whitehead, 1961) suggests that the required ion flux convergence can be realized by the vertical shear of horizontal neutral winds. The following simple expression can be obtained for the vertical component of the ion velocity, under the assumption of balance between the Lorentz force due to ion motions across the ambient geomagnetic field and the frictional force due to ion-neutral collisions (e.g., Haldoupis, 2011):

Vertical Shears of Horizontal Winds in the Lower Thermosphere Observed by ICON

“…The distribution of wind shears is examined, along with the spatial coherence of the wind shear. This study focuses on the largest wind shears observed, rather than a climatology of the winds and the shears (e.g., Yamazaki et al., 2022). The correspondence between strong shears seen in individual profiles and the climatology of the winds is determined.…”

Statistical Study of F‐Region Short Period Ionospheric Disturbances Related to Convection in the Lower Atmosphere Over Wuhan, China

“…The Es‐layer is an ionized cloud at altitudes from 90 to 130 km that is composed of metallic ions (Haldoupis, 2011; Tang et al., 2021; Zhou et al., 2017). In general, the wind shear is responsible for the formation of the Es‐layer, and wind fields in opposite directions converge the metal ions in a thin layer to form Es‐layer (Wang et al., 2021; Yamazaki et al., 2021). This indicated that the formation of the Es‐layer was closely related to the background wind field conditions.…”

Long Distance Propagation of 162-MHz Shipping Information Links Associated with Sporadic-E

“…Maruyama et al, 2008). Recently, Yamazaki et al (2022) presented convincing evidence linking sporadic-E to zonal wind shears using ICON/MIGHTI interferometer wind profile data and COSMIC-2/RO retrieved electron density profiles. Deacon et al (2022) have linked sporadic-E to long-distance amateur radio propagation reports on frequencies up to 70 MHz, while amateur groups themselves routinely map sporadic-E (e.g.…”