Morphology of ionospheric scintillations during geomagnetically disturbed periods

Abstract

Since 2006 the Space Physics Group of the Laboratory of Physics and Astronomy from UNIVAP has conducted ionospheric monitoring by using ground-based receivers from Global Navigation Satellite Systems (GNSS). These receivers are currently installed on a network of observatories located in the Brazilian sector. For example, are operating the observatories of Manaus (AM), Ji-Paraná (RO), São José dos Campos (SP) and São Martinho da Serra (RS). From the records in the data of these GNSS receivers have been possible to identify the signatures of the irregularities (or inhomogeneities) present in the ionospheric plasma density, and to study the behavior of the equatorial ionosphere and low latitude ionosphere during quiet and disturbed geomagnetic periods. In this research study, the irregularities of greater interest will be those typically nocturnal, formed shortly after dusk over the magnetic equator and extending to the ionosphere at low latitudes. It is called plasma bubbles, the large-scale irregularities that exist in the tropical ionosphere. These plasma bubbles occur due to the non-linear development of the irregularities present at the bottom of the ionospheric F region. The collisional Rayleigh-Taylor instability is the most accepted mechanism to explain the development of such irregularities. However, it is attributed to a hierarchy of other secondary mechanisms the presence in the ionosphere of structures with different scale sizes. For example, in the edges of the bubbles the plasma density gradients tend to be more intense, and during the growth phase of the bubbles, these gradients become unstable under the action of secondary instability processes, thus favoring the appearance of irregularities from a few meters to a dozen of kilometers. Irregularities in the order of hundreds of meters to a few kilometers are those that most affect the signals from GNSS satellites. In this work, the proposal is to analyze the signatures of ionospheric irregularities on the data collected by the GNSS receivers installed in the observatories managed by UNIVAP. However, the database will be formed by the disturbed geomagnetic days that occurred since 2006, and when observations were available in one or more stations. During geomagnetically disturbed periods, the thermodynamics of the equatorial and low latitude ionosphere can be strongly affected due to direct penetration of electric fields from the magnetospheric origin, and/or due to electric fields of disturbance dynamo associated with the dynamic action of thermospheric neutral winds produced by auroral heating. As a result of the increase in the geomagnetic activity, and depending on the local time and the phase of the storm, the generation of ionospheric irregularities can be inhibited or enhanced. Thus, it is possible to investigate the morphological characteristics and physical properties that govern the occurrence of irregularities during geomagnetically disturbed periods. The topic of this research is of great interest to the community involved in space weather studies, and in the understanding of the phenomena and mechanisms that favor the formation or not of the ionospheric irregularities. (AU)