@Article{HajraFranEcheBolz:2021:CoThSt,
               author = "Hajra, Rajkumar and Franco, Adriane Marques de Souza and Echer, 
                         Ezequiel and Bolzan, Maur{\'{\i}}cio Jos{\'e} Alves",
          affiliation = "{Indian Institute of Technology Indore} and {Instituto Nacional de 
                         Pesquisas Espaciais (INPE)} and {Instituto Nacional de Pesquisas 
                         Espaciais (INPE)} and {Universidade Federal de Jata{\'{\i}}}",
                title = "Long-Term Variations of the Geomagnetic Activity: A Comparison 
                         Between the Strong and Weak Solar Activity Cycles and Implications 
                         for the Space Climate",
              journal = "Journal of Geophysical Research: Space Physics",
                 year = "2021",
               volume = "126",
               number = "4",
                pages = "e2020JA028695",
                month = "Apr.",
             abstract = "We study the long-term variations of geomagnetic activity using 
                         more than five solar cycles of geomagnetic and solar wind 
                         observations. From the Dst index variation, 1523 geomagnetic 
                         storms were identified during January 1957 through December 2019, 
                         and 145 high-intensity long-duration continuous auroral electrojet 
                         (AE) activity (HILDCAA) events were identified using the AE index 
                         from January 1975 through December 2017. Among the storms, 
                         \∼3/4th were moderate (\−50 nT \≥ Dst > 
                         \−100 nT), and only \∼1/4th were stronger in 
                         intensity (Dst \≤ \−100 nT). Cross-correlation 
                         analysis reveals a strong correlation (r = 0.58\−0.78) 
                         between the magnetic storms and the F10.7 solar flux at 
                         0\−1-year time lag and a weaker correlation (r = 0.59) 
                         between HILDCAAs and F10.7 at a \∼3-year lag. This result 
                         is consistent with the magnetic storm occurrence rate centered 
                         around the solar cycle maximum with a secondary peak after the 
                         maximum, and HILDCAAs peaking around the descending phase. Wavelet 
                         analysis reveals a dominating \∼1011-year periodicity in 
                         the number of geomagnetic storms and HILDCAAs, geomagnetic 
                         activity indices, solar wind, and interplanetary parameters. The 
                         periodicity is attributed to the solar activity cycle variation. 
                         Solar wind speed induces additional longer (\∼15\−16 
                         years) and shorter (\∼3\−5 years) scale variations 
                         in geomagnetic activity. Solar cycles 20 and 24 are found to be 
                         significantly weaker compared to the cycles 19, 21, 22, and 23 in 
                         solar flux, solar wind-magnetosphere coupling, and resultant 
                         geomagnetic activity. If the decreasing trend of the solar and 
                         geomagnetic activities continues in cycle 25, this may have 
                         important implications for the space weather science and 
                         operations.",
                  doi = "10.1029/2020JA028695",
                  url = "http://dx.doi.org/10.1029/2020JA028695",
                 issn = "2169-9402",
             language = "en",
           targetfile = "2020JA028695.pdf",
        urlaccessdate = "09 maio 2024"
}