Long and short term relationships between solar wind velocity and geomagnetic field at low latitudes

Solar wind velocity control of low latitude geomagnetic field both on long and short term basis is studied. It is shown that semiannual averages of the low latitude field is inversely related to solar wind velocity and that there is a dominant local time dependence of the relationship. Strongest correlation are confined to the local afternoon hours. It is also shown that for a duration when the solar wind velocity exhibits significant recurrent pattern the low latitude geomagnetic field also depicts strong solar synodic rotation periodicity of 27 days with significant coherence with velocity. The low latitude field on a short term basis is influenced by variable solar wind velocity with a delay of about 1–2 days. During the period of systematic recurrent pattern in solar wind velocity even the quiet-time night field at equatorial and low latitudes show a strong dependence on velocity indicative of the solar wind control of the quiet-time proton belt encompassing the earth.