NASA-CR-204564 Structures in ionospheric number density and velocity associated with polar cap ionization patches C )
Spectral characteristics of polar cap F region irregularities on large density gradients associated with polar ionization patches are studied using in situ measurements made by the Dynamics Explorer 2 (DE 2) spacecraft. The • 18 patches studied in this paper were identified by the algorithm introduced by Coley and Heelis [1995], and they were encountered during midnight-noon passes of the spacecraft. Density and velocity spectra associated with these a_tisunward convecting patches are analyzed in detail. Observations indicate the presence of structure on most patches regardless of the distance between the patch and the cusp where they are believed to develop. Existence of structure on both leading and trailing edges is established when such edges exist. Results, which show no large dependence of AN/N power on the sign of the edge gradient VN, do not allow the identification of leading and trailing edges of the patch. The AN/N is an increasing function of VN regardless of the sign of the gradient. The correlation between AN/N and AV is generally poor, but for a given intensity in AV, AN/N maximizes in regions of large gradients in N. There is evidence for the presence of unstructured patches that seem to coexist with unstructured horizontal velocities. Slightly smaller spectral indices for trailing edges support the presence of the E×B drift instability. Although this instability is found to be operating in some cases, results suggest that stirring may be a significant contributor to kilometer-size structures in the polar cap. C/) "D .//' "" "--"
Sudden Enhancements of F-Layer Ionization in Polar Regions
Abstract A study of the morphology of large sporadic enhancements of F-region electron density in the darkened portions of the polar cap reveals a close connection between “sporadic F” and ionospheric current systems. This connection arises from electric fields which are set up by these currents and then transferred to the F-region along an essentially vertical magnetic field. Under the influence of the electric and magnetic fields, a horizontal drift of ionization may become sufficiently strong to cause the development of sporadic F. Drift velocities obtained from synoptic analyses range between 2000 and 5000 kilometers per hour and agree with theoretical estimates. Criteria are presented for the development of sporadic F events, and the general diurnal and seasonal variations in the frequency of occurrence are inferred.
5.63 and 5.80 MeV levels of Ne20; de-excitation branching
Abstract The ratio Г γ /Г for the 5.63 and 5.80 MeV levels of Ne 20 has been determined to be 0.077 (±0.008) and −4 , respectively, by using the C 12 (C 12 , α)Ne 20 reaction and determining the fraction of the events in which the alpha-particle and the Ne 20 recoil are present in coincidence at the kinematically correct angles. In both cases these results in themselves are shown to imply radiative E1 transition (5.63→1.63 and 5.80→0, respectively) probabilities ⪡5 × 10 −5 Weisskopf units. When taken together with the life-time for the 5.63 MeV level measured by Evans et al . values of Г( E1 ) ≲ 5 × 10 −6 and Г α ≈ 6% of the particle estimate are obtained for this state.