Disturbance zonal and vertical plasma drifts in the Peruvian sector during solar minimum phases

Abstract

In the present work, we investigate the behavior of the equatorial F region zonal plasma drifts over the Peruvian region under magnetically disturbed conditions during two solar minimum epochs, one of them being the recent prolonged solar activity minimum. The study utilizes the vertical and zonal components of the plasma drifts measured by the Jicamarca (11.95°S; 76.87°W) incoherent scatter radar during two events that occurred on 10 April 1997 and 24 June 2008 and model calculation of the zonal drift in a realistic ionosphere simulated by the Sheffield University Plasmasphere‐Ionosphere Model‐INPE. Two main points are focused: (1) the connection between electric fields and plasma drifts under prompt penetration electric field during a disturbed periods and (2) anomalous behavior of daytime zonal drift in the absence of any magnetic storm. A perfect anticorrelation between vertical and zonal drifts was observed during the night and in the initial and growth phases of the magnetic storm. For the first time, based on a realistic low‐latitude ionosphere, we will show, on a detailed quantitative basis, that this anticorrelation is driven mainly by a vertical Hall electric field induced by the primary zonal electric field in the presence of an enhanced nighttime E region ionization. It is shown that an increase in the field line‐integrated Hall‐to‐Pedersen conductivity ratio ()∑H∑P, which can arise from precipitation of energetic particles in the region of the South American Magnetic Anomaly, is capable of explaining the observed anticorrelation between the vertical and zonal plasma drifts. Evidence for the particle ionization is provided from the occurrence of anomalous sporadic E layers over the low‐latitude station, Cachoeira Paulista (22.67°S; 44.9°W)—Brazil. It will also be shown that the zonal plasma drift reversal to eastward in the afternoon two hours earlier than its reference quiet time pattern is possibly caused by weakening of the zonal wind system during the prolonged solar minimum period.

Climatology and modeling of ionospheric scintillations and irregularity zonal drifts at the equatorial anomaly crest region

“…Since the maximum contribution of the scintillationproducing irregularities occurs at the heights of peak electron density, any change in the evening peak of the F region is expect to affect the dynamic evolution of these irregularities. Theoretical formulations have predicted that the nighttime eastward irregularity drift, which can be considered equivalent to the background plasma drift, depends essentially on a ratio of flux-tube-integrated Pedersen conductivity weighted by the F-region zonal neutral wind velocity (Anderson and Mendillo, 1983;Haerendel et al, 1992;Eccles, 1998;Santos et al, 2016). Thus, the years with larger mean irregularity zonal velocities during the December solstice (summer) months over Cachoeira Paulista are possibly associated with a stronger vertical polarization electric field owing to a larger thermospheric zonal wind, which then drives the irregularities zonally.…”

Latitude-dependent delay in the responses of the equatorial electrojet and <i>S</i><sub><i>q</i></sub> currents to X-class solar flares

“…We have modeled the field line-integrated Cowling conductivity using the SUPIM-INPE Sellek, 1990, 1997;Souza et al, 2000Souza et al, , 2013Nogueira et al, 2013;Santos et al, 2016). The SUPIM-INPE solves the time-dependent equations of continuity, momentum and energy along magnetic field lines to obtain the electron and ion densities of the low-latitude ionosphere.…”

“…We seek an explanation for this delay by modeling the Cowling conductivity variations produced by the flare enhanced X-ray and EUV fluxes in the equatorial and low-latitude ionosphere close to midday. We used the Sheffield University Plasmasphere-Ionosphere Model at National Institute for Space Research (SUPIM-INPE; Bailey et al, 1978Bailey et al, , 1993Nogueira et al, 2013;Santos et al, 2016), which has been found to simulate realistically the equatorial-low-latitude ionosphere. The modeling results showed that the flare-induced temporal delays in the EEJ response (and in turn in its ground manifestation) cannot be attributed to a corresponding delay in the flare-induced enhanced Cowling conductivity development.…”

Unusual behavior of quiet-time zonal and vertical plasma drift velocities over Jicamarca during the recent extended solar minimum of 2008

“…The impacts of the recent deep and prolonged solar minimum on the electron density, temperature, spread F, and total electron content, as well as the vertical and zonal plasma drifts, over the equatorial and low-latitude ionosphere have been studied using different types of observational data, such as digisondes (Liu Libo et al, 2011;Candido et al, 2011;Chuo et al, 2013;Solomon et al, 2013;Narayanan et al, 2014), satellites (Solomon et al, 2011;Huang et al, 2010Huang et al, , 2012Chuo et al, 2013;Fejer et al, 2013) and incoherent scatter radar (Aponte et al, 2013;Kotov et al, 2015;Santos et al, 2016a). During the period of June 2008 the mean monthly F10.7 radio index reached an extremely low value of ∼ 65.7 × 10 −22 W m −2 Hz −1 , which represented a solar extreme ultraviolet (EUV) irradiance that was lower than during previous solar cycles.…”

“…They reported average values of 5-15 m s −1 between 07:00 and 09:00 LT and a maximum drift to west of ∼ 25 m s −1 at ∼ 13:00 LT. In this case, the reversal of the drift in the afternoon occurred at about 16:30 LT. Santos et al (2016a) investigated the ionospheric plasma drifts during the low-solar-activity period of 2008. They showed that an extra ionization in the nighttime E region can have a significant impact on the zonal plasma drift during a disturbed period and suggested that the sporadic E layers that they observed (around 100-130 km) could be considered as strong evidence for extra ionization due to energetic particle precipitation leading to the development of Hall electric field that modified the zonal drift.…”