Publication Date:
2016-06-09
Description:
Recent studies reveal that midlatitude ionospheric irregularities are less understood due to lack of models and observations that can explain the characteristics of the observed wave structures. In this paper, the cascading processes of both the Temperature Gradient Instability (TGI) and the Gradient Drift Instability (GDI) are investigated as the cause of these irregularities. Based on observations obtained during a coordinated experiment between the Millstone Hill Incoherent Scatter Radar (ISR) and the Blackstone SuperDARN radar, a time series for the growth rate of both TGI and GDI is calculated for observations in the sub-auroral ionosphere under both quiet and disturbed geomagnetic conditions. Recorded GPS scintillation data are analyzed to monitor the amplitude scintillations and to obtain the spectral characteristics of irregularities producing ionospheric scintillations. Spatial power spectra of the density fluctuations associated with the TGI from nonlinear plasma simulations are compared with both the GPS scintillation spectral characteristics and previous in-situ satellite spectral measurements. The spectral comparisons suggest that initially TGI or/and GDI irregularities are generated at large scale size (km-scale) and the dissipation of the energy associated with these irregularities occurs by generating smaller and smaller (decameter-scale) irregularities. The alignment between experimental, theoretical, and computational results of this study suggests that, in spite of expectations from linear growth rate calculations, cascading processes involving TGI and GDI are likely responsible for the midlatitude ionospheric irregularities associated with GPS scintillations during disturbed times.
Print ISSN:
0048-6604
Electronic ISSN:
1944-799X
Topics:
Geosciences
,
Physics
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