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 ∼10–11‐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.

Seasonal features of geomagnetic activity and their solar-wind–interplanetary drivers are studied using more than five solar cycles of geomagnetic activity and solar wind observations. This study involves a total of 1296 geomagnetic storms of varying intensity identified using the Dst index from January 1963 to December 2019, a total of 75 863 substorms identified from the SuperMAG AL/SML index from January 1976 to December 2019 and a total of 145 high-intensity long-duration continuous auroral electrojet (AE) activity (HILDCAA) events identified using the AE index from January 1975 to December 2017. The occurrence rates of the substorms and geomagnetic storms, including moderate ($-\mathrm{50}\mathrm{nT}\ge \text{Dst}>-\mathrm{100}\mathrm{nT}$ ) and intense ($-\mathrm{100}\mathrm{nT}\ge \text{Dst}>-\mathrm{250}\mathrm{nT}$ ) storms, exhibit a significant semi-annual variation (periodicity ∼6 months), while the super storms ($\text{Dst}\le -\mathrm{250}$ nT) and HILDCAAs do not exhibit any clear seasonal feature. The geomagnetic activity indices Dst and ap exhibit a semi-annual variation, while AE exhibits an annual variation (periodicity ∼1 year). The annual and semi-annual variations are attributed to the annual variation of the solar wind speed V_sw and the semi-annual variation of the coupling function VB_s (where V = V_sw, and B_s is the southward component of the interplanetary magnetic field), respectively. We present a detailed analysis of the annual and semi-annual variations and their dependencies on the solar activity cycles separated as the odd, even, weak and strong solar cycles.