author = "Negreti, Patr{\'{\i}}cia Mara de Siqueira and Paula, Eurico 
                         Rodrigues de and Candido, Cl{\'a}udia Maria Nicoli",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto 
                         Nacional de Pesquisas Espaciais (INPE)} and {Instituto Nacional de 
                         Pesquisas Espaciais (INPE)}",
                title = "Total electron content responses to HILDCAAs and geomagnetic 
                         storms over South America",
              journal = "Annales Geophysicae",
                 year = "2017",
               volume = "35",
               number = "6",
                pages = "1309--1326",
                month = "Dec.",
             abstract = "Total electron content (TEC) is extensively used to monitor the 
                         ionospheric behavior under geomagnetically quiet and disturbed 
                         conditions. This subject is of greatest importance for space 
                         weather applications. Under disturbed conditions the two main 
                         sources of electric fields, which are responsible for changes in 
                         the plasma drifts and for current perturbations, are the 
                         short-lived prompt penetration electric fields (PPEFs) and the 
                         longer-lasting ionospheric disturbance dynamo (DD) electric 
                         fields. Both mechanisms modulate the TEC around the globe and the 
                         equatorial ionization anomaly (EIA) at low latitudes. In this work 
                         we computed vertical absolute TEC over the low latitude of South 
                         America. The analysis was performed considering HILDCAA 
                         (high-intensity, long-duration, continuous auroral electrojet (AE) 
                         activity) events and geomagnetic storms. The characteristics of 
                         storm-time TEC and HILDCAA-associated TEC will be presented and 
                         discussed. For both case studies presented in this work (March and 
                         August 2013) the HILDCAA event follows a geomagnetic storm, and 
                         then a global scenario of geomagnetic disturbances will be 
                         discussed. Solar wind parameters, geomagnetic indices, 
                         O\ \∕\ N2 ratios retrieved by GUVI instrument 
                         onboard the TIMED satellite and TEC observations will be analyzed 
                         and discussed. Data from the RBMC/IBGE (Brazil) and IGS GNSS 
                         networks were used to calculate TEC over South America. We show 
                         that a HILDCAA event may generate larger TEC differences compared 
                         to the TEC observed during the main phase of the precedent 
                         geomagnetic storm; thus, a HILDCAA event may be more effective for 
                         ionospheric response in comparison to moderate geomagnetic storms, 
                         considering the seasonal conditions. During the August HILDCAA 
                         event, TEC enhancements from 
                         \ \∼\ \ 25 to 80\ % (compared 
                         to quiet time) were observed. These enhancements are much higher 
                         than the quiet-time variability observed in the ionosphere. We 
                         show that ionosphere is quite sensitive to solar wind forcing and 
                         considering the events studied here, this was the most important 
                         source of ionospheric responses. Furthermore, the most important 
                         source of TEC changes were the long-lasting PPEFs observed on 
                         August 2013, during the HILDCAA event. The importance of this 
                         study relies on the peculiarity of the region analyzed 
                         characterized by high declination angle and ionospheric gradients 
                         which are responsible for creating a complex response during 
                         disturbed periods.",
                  doi = "10.5194/angeo-35-1309-2017",
                  url = "http://dx.doi.org/10.5194/angeo-35-1309-2017",
                 issn = "0992-7689",
             language = "en",
        urlaccessdate = "27 nov. 2020"