Investigation of the role of plasma wave cascading processes in the formation of midlatitude irregularities utilizing GPS and radar observations

Abstract

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 and the Blackstone Super Dual Auroral Radar Network radar, a time series for the growth rate of both TGI and GDI is calculated for observations in the subauroral 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 (kilometer 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.Potential space weather applications have paid attention to the spatial temporal variability of the midlatitude subauroral ionosphere during magnetic storm periods [e.g., Mishin et al., 2003;Ledvina et al., 2002;Foster et al., 2002;Basu et al., 2001Basu et al., , 2008. During disturbed geomagnetic conditions, large regions hosting an ionospheric density gradient exist in the evening sector at subauroral latitudes in the ionosphere [e.g., Coster et al., 2005;Spiro et al., 1979;Evans et al., 1983;Anderson et al., 1991Anderson et al., , 1993. These density gradients are often associated with streams of enhanced plasma convection known as subauroral plasma streams (SAPS) [e.g., Foster and Burke, 2002] and with storm-enhanced densities [e.g., Erickson et al., 2002]. Satellite measurements reveal the existence of wave-like structures embedded within the SAPS [Mishin et al.(2016), Investigation of the role of plasma wave cascading processes in the formation of midlatitude irregularities utilizing GPS and radar observations, Radio Sci., 51, 836-851,

Multi-constellation GNSS scintillation at mid-latitudes

“…In the equation, I is defined as the signal intensity [2]. The operation < * > is the ensemble average, therefore < I 2 > is the variance of the signal intensity and < I > 2 is the mean square.…”

“…Scintillation describes the fluctuations in signal amplitude and phase of the RF signals traveling through ionospheric disturbances often called ionospheric irregularities [2], [19]. The amplitude scintillation equation is presented in equation (12).…”

“…New space science measurement facilities have shown that the physics of ionospheric irregularities are much more complex than have been thought in the past [2].…”

“…SuperDARN collects data using a chain of high frequency (HF) radars to monitor ionospheric conditions at high and mid latitudes [2]. The chain of radars has 16 to 24 beams that scan at rate of 1 to 2 minutes.…”

“…SuperDARN radars are pulse radars that transmit pulses that have a length of 300 microseconds. The radars measure back scatter from ionospheric structure in the E and F regions, typically resulting from plasma irregularities [2], [6]. The SuperDARN radar ionosphere scatter plots provide the signal to noise (SNR) in decibels (dB), which is the ratio of power caused by the back scatter from the ionosphere and noise power interference.…”