author = "Santos, {\^A}ngela Machado dos and Batista, Inez Staciarini and 
                         Abdu, Mangalathayil Ali and Sobral, Jos{\'e} Humberto Andrade and 
                         Souza, Jonas Rodrigues de and Brum, Christiano Garnett Marques",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto 
                         Nacional de Pesquisas Espaciais (INPE)} and {} and {} and 
                         {Instituto Nacional de Pesquisas Espaciais (INPE)}",
                title = "Climatology of intermediate descending layers (or 150 km echoes) 
                         over the equatorial and low-latitude regions of Brazil during the 
                         deep solar minimum of 2009",
              journal = "Annales Geophysicae",
                 year = "2019",
               volume = "37",
               number = "6",
                pages = "1005--1024",
                month = "Nov.",
             abstract = "In this work, we have performed a study for the first time on the 
                         climatology of the intermediate descending layers (ILs) over 
                         Brazilian equatorial and low-latitude regions during the extreme 
                         solar minimum period of 2009. The result of this study shows that 
                         the occurrence frequency of the ILs is very high, being 
                         >\ 60\ % over S{\~a}o Lu{\'{\i}}s 
                         (2\ĝ\ S, 44\ĝ\ W; inclination: 
                         -3.8\ĝ) and >\ 90\ % in Cachoeira Paulista 
                         (22.42\ĝ\ S, 45\ĝ\ W; inclination: 
                         -33.5\ĝ). In most cases the ILs occur during the day at 
                         altitudes varying from 130 to 180\ km and they may descend 
                         to lower altitudes (\ĝ1/4100\ km) in a time interval 
                         of a few minutes to hours. The main driving force for the ILs at 
                         the low-latitude region, may be considered to be the diurnal tide 
                         (24\ h) followed in smaller dominance by the semidiurnal 
                         (12\ h), terdiurnal (8\ h) and quarter-diurnal 
                         (6\ h) components. In the magnetic equatorial sector, 
                         similar behavior was seen, with the exception of the semidiurnal 
                         tide, which in general does not appear to have influenced the IL's 
                         dynamics (except in summer). Additionally, the IL mean descent 
                         velocity over S{\~a}o Lu{\'{\i}}s and Cachoeira Paulista shows 
                         a day-to-day variability that may be associated with a wave-like 
                         perturbation with a periodicity of some days. Some peculiarities 
                         in the IL dynamics were noted, such as the presence of the ILs 
                         during the night hours. Ascending and descending ILs appeared to 
                         have been formed from some connection with the ionospheric F 
                         layer. Quite often, these characteristics are observed in the 
                         presence of strong signatures of the gravity wave propagation as 
                         suggested by the F layer traces in the ionogram. The descending 
                         intermediate layer over Brazil appears to have been formed through 
                         a process of F1 layer base detachment. An interesting case study 
                         showed that an ascending ILs, initially detected at 
                         \ĝ1/4130\ km, reached the base of the F2 layer, due 
                         probably to the gravity wave propagation and/or the effect of a 
                         prompt penetration electric field.",
                  doi = "10.5194/angeo-37-1005-2019",
                  url = "http://dx.doi.org/10.5194/angeo-37-1005-2019",
                 issn = "0992-7689",
             language = "en",
           targetfile = "santos_climatology.pdf",
        urlaccessdate = "24 jan. 2021"