Abstract
Abstract. The influence of the recent deep and prolonged solar minimum on the daytime zonal and vertical plasma drift velocities during quiet time is investigated in this work. Analyzing the data obtained from incoherent scatter radar from Jicamarca (11.95° S, 76.87° W) we observe an anomalous behavior of the zonal plasma drift during June 2008 characterized by lower than usual daytime westward drift and its early afternoon reversal to eastward. As a case study the zonal drift observed on 24 June 2008 is modeled using a realistic low-latitude ionosphere simulated by the Sheffield University Plasmasphere-Ionosphere Model-INPE (SUPIM-INPE). The results show that an anomalously low zonal wind was mainly responsible for the observed anomalous behavior in the zonal drift. A comparative study of the vertical plasma drifts obtained from magnetometer data for some periods of maximum (2000–2002) and minimum solar activity (1998, 2008, 2010) phases reveal a considerable decrease on the E-region conductivity and the dynamo electric field during 2008. However, we believe that the contribution of these characteristics to the unusual behavior of the zonal plasma drift is significantly smaller than that arising from the anomalously low zonal wind. The SUPIM-INPE result of the critical frequency of the F layer (foF2) over Jicamarca suggested a lower radiation flux than that predicted by solar irradiance model (SOLAR2000) for June 2008.
Highlights
The zonal drift on 24 June reversed to east around 2 h earlier than such reversal time predicted by the drift model of Fejer et al (2005) that calculated by SUPIM-INPE based on HWM zonal wind
The zonal drift analyzed for a few other available days in June 2008 showed earlier eastward reversal as compared to those of similar day groups examined during other solar activity minimum epochs, thereby confirming the unique nature of the effects due to the extremely low activity period of June 2008
Model calculations of the zonal drift based on a realistic low-latitude ionosphere simulated by SUPIM-INPE showed that the major contribution to the drift arises from the Pedersen conductivity-weighted F-region zonal wind, rather than from E-layer dynamo electric field with associated Hall conduction effect
Summary
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, 2010, 2012; Chuo et al, 2013; Fejer et al, 2013) and incoherent scatter radar (Aponte et al, 2013; Kotov et al, 2015; Santos et al, 2016a). It was shown that while in the eastern hemisphere the longitudinal dependence is largely season independent, in the western hemisphere the longitudinal dependence changes considerably with season probably due to the large magnetic declination that characterize this region and thermospheric wind effects Another interesting point observed by Fejer et al (2013) was that the evening reversal time of the zonal drift to east (∼ 17:00 LT) was nearly independent of the longitude during the equinox, but during the winter solstice the reversal occurred before 16:00 LT in the longitude sector between 210 and 360◦. The present study concerns the earlier eastward reversal (in the afternoon) of the zonal plasma drift observed during the daytime on 24 June, which was under magnetic quiet condition unlike the disturbed night condition (of the same day) that was analyzed by Santos et al (2016a). Our results suggest considerably weakened E-region dynamo as well as corresponding reduced zonal wind, which may be responsible for the weak westward zonal drift during the day and, for the early reversal of the drift to eastward in the afternoon time
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