COSMIC observations of dayside total electron content enhancements in response to moderate disturbances in the solar wind

We have analyzed measurements from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites acquired during an 81 day interval in late 2007 to study total electron content (TEC) responses of the dayside ionosphere during three consecutive passes of a high‐speed stream (HSS) in the solar wind by Earth. During the second encounter the HSS arrival was closely preceded by the arrival at the first Lagrange point L 1 of an interplanetary coronal mass ejection (ICME). In all cases the corotating interaction region (CIR) at the HSS's leading edge was characterized by increases in both n SW and T P above predisturbance levels, and large‐amplitude oscillations in all interplanetary magnetic field (IMF) components. The solar wind events induced moderate magnetic storm activity; the minimum Dst of −71 nT occurred during the second encounter. TEC enhancements appeared at low‐magnetic to midmagnetic latitudes during the ICME/CIR‐driven storm. Some increases exceeded quiet time values by factors of ∼110%. In the absence of local auroral electron precipitation to create new plasma in the magnetic latitude domain of COSMIC measurements, the detected TEC increases must reflect transport effects. The COSMIC main phase observations of dayside TEC enhancement are explained as being caused by an ionospheric storm time “fountain” effect driven by weak (<1 mV/m) penetration electric fields. Our observations suggest that penetration dawn‐to‐dusk electric fields cause plasma to drift upward and toward higher latitudes. Plasma and field measurements from the Advanced Composition Explorer (ACE) allow estimates of penetration electric fields that we mapped to the ionosphere to calculate plasma transport velocities. We argue that observed TEC dynamics reflect the interplay between storm time transport and the production/loss histories of plasma parcels as they rotate around Earth.