Nighttime ionization enhancements observed with the Tucuman Digisonde

RIOS, VICTOR HUGO; GONZÁLEZ, GILDA DE LOURDES; MEDINA, CESAR; BLAS DE HARO

Rosario

Encuentro; 94º Reunión Anual de Física Argentina; 2009

Asociación de física Argentina

Abstract True height electron density profiles observed with the Tucuman Digisonde were analyzed together with geomagnetic data indices for different period of 2003 in an effort to define the ionospheric  structure during events of nighttime ionization enhancements and to discuss the physical processes that may cause them. An upwelling of the F2-layer, limited to the dark hemisphere, was evident in all events, but nighttime positive effects and nighttime height enhancements are attributed to two distinct mechanisms, according to our findings. Height enhancements are wave-like disturbances and the time delay of their occurrence at middle latitudes depends on the increase rate of the AE index, and consequently, on the rate that the solar wind input energy dissipates in the auroral ionosphere. Thus, they most probably originated in the auroral oval region and propagated toward the equator-like TID disturbances, with a periodicity that depends on the ionization density. On the other hand, foF2 and TEC increases do not share the same wavy appearance, which could mean that they are not connected to TIDs and are not of auroral oval origin. The increased nighttime density can only be speculated to be due to increased downward fluxes from the plasmasphere.