High-speed solar wind stream effects on the topside ionosphere over Arecibo: A case study during solar minimum

The impact of a high-speed solar wind stream (HSS) on the topside near-equatorial ionosphere (Arecibo: 28.17 degrees N, L = 1.3) is investigated for the first time. Although the HSS did not lead to any significant geomagnetic storm activity, the ionosphere over Arecibo became hotter and expanded significantly in altitude as compared to a non-HSS interval. The O+/H+ transition height hT increased by similar to 200 km in the daytime and by similar to 100 km at night. At the hT, the peak ionospheric electron and ion temperatures increased by similar to 200-500 K during day and by similar to 50-70 K at night. While the O+ ion concentration exhibited an overall enhancement, deep penetration of the H+ ions below h(T) are observed during the day. The noontime peak electron density was similar to 4 times higher during the HSS event compared to the non-HSS interval. We present three possible mechanisms to explain this topside ionospheric heating.