Semi annual anomaly and annual asymmetry: a consequence of the Sun-Earth electrodynamics interaction?

AZPILICUETA F.; BRUNINI C.

Foz do Iguazzu

Congreso; American Geophysical Union 2010 Scientific Meeting; 2010

American Geophysical Union

During the first decades of ionospheric research, the physical description of the ionospheric free electron vertical density was mainly given by the Chapman theory in which the main driving parameters were the solar irradiance level and the solar zenith distance from the observation point. Whatever a new observed phenomenon that could not be explained by the Chapman theory was considered an ‘anomaly’. After more than 50 years of continuous aeronomic research, many of these phenomena then called ‘anomalies’ were physically explained but some of them are still open to discussions, like the so called Semi-annual Anomaly that produces global mean TEC values larger for Equinoxes than for Solstices; and the Annual Asymmetry that causes larger mean global TEC during the December than June solstice (far larger than the 7% that would be expected from the change on the Sun-Earth relative distance). Several works of the specialized literature have analyzed these anomalies as individual effects, and several of them propose explanations associated to an enhancement on the ionization rate by radiation, caused by hydro-dynamics processes of the neutral species. In this work, we will present some evidences that show that both anomalies in fact could form part of a unique phenomenon that produces a TEC annual pattern. We will also describe the physical process that could lead to a drift of ions that, by means of particle-collision processes, produce the free-electron density enhancement.