ALBERT

Description: In this work, we report for the first time the climatology of intermediate descending layers over Brazilian equatorial and low latitudes regions during the extreme solar minimum period of 2009. The occurrence frequency of this layer is very high, being 〉 60 % over São Luís (2° S; 44° W, I: −5.7°) and 〉 90 % in Cachoeira Paulista (22.42° S; 45° W, I: −34.4°). Our results reveal that in most of the cases the intermediate layers (IL’s) appear during the day at altitudes varying from 130 to 180 km and present a descent movement that reaches the lower altitudes (~ 100 km) in a time interval of a few minutes to hours. Differently from other longitudinal sectors, the diurnal tide (24 h) can be considered as the main cause of IL’s for the low latitude region, followed by a smaller dominance of semidiurnal (12 h), terdiurnal (8 h) and quarter-diurnal (6 h) tide components. In the equatorial sector, similar behavior was found, with the exception of the semidiurnal tide, which in general does not appear to influence the IL’s dynamics (except in summer). The IL’s mean descent velocities over São Luís and Cachoeira Paulista show a day-to-day variability that may be associated with gravity waves propagation. Some peculiarities in the IL’s dynamics have been noted, such as the presence of the IL’s during the night hours, ascending IL’s, simultaneous IL’s, and descending IL’s been formed from some connection with the ionospheric F layer. Quite often, these characteristics are observed in the presence of strong signatures in the ionogram F-layer trace similar to those caused by the gravity wave propagation. We will show further that the descending intermediate layer over Brazil can be formed through a process of F1 layer base detachment. Besides that, we will present an interesting case study in which an ascending IL’s, initially detected at ~ 140 km, reached the base of F2 layer, probably due to the gravity wave propagation and/or due to the effect of the prompt penetration electric field.

Description: 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.

Description: Equatorial plasma bubble/spread F irregularity occurrence can present large variability depending upon the intensity of the evening prereversal enhancement in the zonal electric field (PRE), that is, the F region vertical plasma drift, which basically drives the post-sunset irregularity development. Forcing from magnetospheric disturbances is an important source of modification and variability in the PRE vertical drift and of the associated bubble development. Although the roles of magnetospheric disturbance time penetration electric fields in the bubble irregularity development have been studied in the literature, many details regarding the nature of the interaction between the penetration electric fields and the PRE vertical drift still lack our understanding. In this paper we have analyzed data on F layer heights and vertical drifts obtained from digisondes operated in Brazil to investigate the connection between magnetic disturbances occurring during and preceding sunset and the consequent variabilities in the PRE vertical drift and associated equatorial spread F (ESF) development. The impact of the prompt penetration under-shielding eastward electric field and that of the over-shielding, and disturbance dynamo, westward electric field on the evolution of the evening PRE vertical drift and thereby on the ESF development are briefly examined. Keywords. Ionosphere (ionospheric irregularities)

Description: This work presents an analysis of the climatology of the onset time of ionospheric scintillations at low latitude over the southern Brazilian territory near the peak of the equatorial ionization anomaly (EIA). Data from L1 frequency GPS receiver located in Cachoeira Paulista (22.4∘ S, 45.0∘ W; dip latitude 16.9∘ S), from September 1998 to November 2014, covering a period between solar cycles 23 and 24, were used in the present analysis of the scintillation onset time. The results show that the start time of the ionospheric scintillation follows a pattern, starting about 40 min earlier, in the months of November and December, when compared to January and February. The analyses presented here show that such temporal behavior seems to be associated with the ionospheric prereversal vertical drift (PRVD) magnitude and time. The influence of solar activity in the percentage of GPS links affected is also addressed together with the respective ionospheric prereversal vertical drift behavior. Based on this climatological study a set of empirical equations is proposed to be used for a GNSS alert about the scintillation prediction. The identification of this kind of pattern may support GNSS applications for aviation and oil extraction maritime stations positioning. Keywords. Ionosphere (ionospheric irregularities; modeling and forecasting) – radio science (space and satellite communication)