This paper investigates the effects of geomagnetic disturbances that occurred in August 2017, during the declining phase of Solar Cycle 24, when two geomagnetic storms driven by high-speed stream (HSS) and stream interaction region (SIR) structures and associated with HILDCAA intervals took place on 4–6 August and 17–21 August, together with a coronal mass ejection (CME) embedded in the solar wind that impacted the Earth on 22–23 August. The focus of the study is the ionospheric response over the Brazilian sector. For this purpose, we use CADI ionosonde measurements from an equatorial station (Araguatins) and two low-latitude stations (Jataí and São José dos Campos). The empirical model of Fejer and Scherliess (1997) is applied to estimate the equatorial vertical plasma drifts and to assess the impact of prompt penetration electric fields (PPEFs) and disturbance dynamo electric fields (DDEFs) on the F-region ionosphere over Brazil. The results show pronounced variability in the F-layer height parameters ( h ′ F and hpF 2 ) and in the critical frequency ( foF 2 ) throughout August. At the equatorial station, deviations reached approximately ± 80 –160 km ( ± 20 –40%) in h ′ F , ± 160 –200 km ( ± 40 –50%) in hpF 2 , and decreases of about 1–5 MHz in foF 2 . At the low-latitude stations, the corresponding height variations were smaller, typically ± 40 –80 km ( ± 10 –20%), while foF 2 variations remained within the range of -1–5 MHz, with amplitudes decreasing progressively with increasing distance from the magnetic equator. Because storm-time signatures are not always unambiguously identifiable in the raw ionospheric time series, a wavelet-based coherence analysis is employed to quantify how PPEF- and DDEF-related drifts modulate the ionospheric parameters ( h ′ F and foF 2 ) in the time–frequency domain. The time–frequency results support the interpretation that recurrent HSS/SIR structures modulate both the intensity of PPEFs and the equatorial F-layer height. A latitudinal comparison of the wavelet-coherence patterns demonstrates the increasing importance of DDEFs away from the magnetic equator, particularly at Jataí and São José dos Campos. In addition, an analysis of the occurrence of intermediate layers (CIs) is carried out. The CIs, which formed predominantly by detachment from the lower part of the F region followed by downward motion into the ionospheric valley region, exhibited typical virtual heights between 140 and 170 km and peak frequencies between 3 and 4.5 MHz. At Araguatins, the largest number of CI occurrences coincides with geomagnetically disturbed intervals, suggesting that storm-time PPEFs and DDEFs may contribute to the formation or maintenance of CIs near the magnetic equator. At Jataí and São José dos Campos, however, such correspondence is not evident, indicating that additional drivers, such as neutral wind shear, atmospheric tides, and gravity waves, likely play a relatively more important role at those latitudes.