VHF Radar Images of Artificial Field‐Aligned Ionospheric Irregularities in the Subauroral <i>E</i> Region

Hysell, D. L.; Munk, J.; McCarrick, M.

doi:10.1002/2017rs006497

Cited by 1 publication

(2 citation statements)

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“…That QP echoes occur under the midlatitude trough argues that coupled instabilities cannot be uniquely responsible for the phenomena. Observations of QP echoes in the subauroral zone further support the point (Hysell, Munk, & McCarrick, 2018).…”

Section: Discussionsupporting

confidence: 55%

“…The authors attributed this to the failure of the wind shear mechanism for creating E s layers at higher dip latitudes. However, recent observations of QP echoes made during ionospheric modification experiments at the HAARP facility suggest that at least some of the processes at work at lower latitudes also take place in the subauroral E region (Hysell, Munk, & McCarrick, 2018). One of the objectives of the present research is to explore the latitude extent of midlatitude E s ‐layer formation and instability.…”

Section: Introductionmentioning

confidence: 99%

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

Hysell

Larsen

2021

JGR Space Physics

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The altitude range in the mesosphere/lower thermosphere where the turbopause occurs, that is, nearly an altitude of 100 km, is particularly important because of the rapid changes in dynamics, electrodynamics, and chemistry that occur there. The transition from the negative lapse rates in the mesosphere to isothermal, and even positive lapse rates in the lower thermosphere is a natural inhibitor to significant vertical transport across that region due to the inherently more stable air overlying the less stable air in the mesosphere. Layers in the mesosphere frequently show evidence of shear instabilities of the Kelvin-Helmholtz type, as shown in the case studies presented by Hecht et al. (2021) and Chau et al. (2020), for example. See also their discussion of other past observations from that region.Observations from higher altitudes near the critical turbopause transition are much more limited, but the available data indicate that the region is characterized by frequent and persistent shears associated with the large winds that occur there. The shears often meet the criteria for shear instability, as shown by Larsen (2002) using an extensive set of rocket-based wind measurements and by Sherman and She (2006) using a long time series of lidar wind measurements that extended to altitudes of 105 km. Liu (2017) was able to reproduce the essential characteristics of the observed winds and shears in that altitude range and discussed their implications for diffusion and transport. Recently Mesquita et al. (2020) presented an example of a K-H billow observed directly with chemical tracer measurements in the transition altitude where the more stable isothermal lapse rate occurs. One conclusion was that this type of instability can contribute significantly to vertical transport into the more stable portions of the atmosphere in the lower thermosphere, which would otherwise inhibit strong vertical motions.Data from the lower thermosphere are much more limited than data from lower altitudes in the mesosphere, but a long series of observations from the Caribbean have shown that there is a strong relationship between the development of coherent scatter radar echoes associated with sporadic E layers and upward displacements of the ionization layers. Furthermore, the quasi-periodic (QP) scattering structures that are now known to be a common characteristic of sporadic E layers have been tied to unstable shears in many of the observations. The vertical displacements associated with the billow structures are, therefore, the likely driver for the plasma instabilities responsible for the QP structure in the radar scatter.

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Section: Discussionsupporting

confidence: 55%

Section: Introductionmentioning

confidence: 99%