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Theory of Midlatitude Sporadic E
Author(s) -
Layzer David
Publication year - 1972
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/rs007i003p00385
Subject(s) - sporadic e propagation , middle latitudes , classification of discontinuities , wind shear , atmospheric sciences , geophysics , geology , ionosphere , physics , electric field , polarization (electrochemistry) , daytime , ionization , wind speed , slip (aerodynamics) , mechanics , ion , meteorology , chemistry , mathematical analysis , mathematics , quantum mechanics , thermodynamics
A discussion of the observed properties of midlatitude sporadic E leads to the conclusion that vertical redistribution of neutral ionization is the only mechanism by which long‐lived metal ions can be concentrated into thin sheets extending over horizontal distances of several hundred kilometers. However, vertical ion transport occasioned by observed wind shears with vertical scales of a few kilometers fails to account for the vertical structure of E 8 layers and their diurnal and seasonal variations. Experimental evidence indicates that, below 120 km, narrow layers of enhanced ionization coincide with abrupt changes in the magnitude and direction of the wind shear. These changes, marked by corners in the horizontal‐wind hodograph, occur over vertical intervals of 100 meters or less. Two alternative physical interpretations of these quasi‐discontinuities are discussed (I now regard my earlier suggestion that they represent gravity shocks as unlikely): stable contact discontinuities, across which the temperature and density (but not the vertical component of velocity and not the pressure) change abruptly; very narrow (Δ z ≃ 10 meters) sheets of very high shear ( dV/dz ≃ 0.1 sec −1 ). It is shown that in either case the layer could function as an effective ion trap. Strong and variable electric polarization fields, however, would interfere with the action of such a trap. Considerations related to the variable component of the polarization field provide a simple and straightforward qualitative explanation for the double‐peaked diurnal variation of intense summertime sporadic E , its seasonal variation, and its negative correlation with magnetic activity.