Abstract
Abstract. The Far Ultraviolet (FUV) imaging system on board the IMAGE satellite provides a global view of the north auroral region in three spectral channels, including the SI12 camera sensitive to Doppler shifted Lyman-α emission. FUV images are used to produce instantaneous maps of electron mean energy and energy fluxes for precipitated protons and electrons. We describe a method to calculate ionospheric Hall and Pedersen conductivities induced by auroral proton and electron ionization based on a model of interaction of auroral particles with the atmosphere. Different assumptions on the energy spectral distribution for electrons and protons are compared. Global maps of ionospheric conductances due to instantaneous observation of precipitating protons are calculated. The contribution of auroral protons in the total conductance induced by both types of auroral particles is also evaluated and the importance of proton precipitation is evaluated. This method is well adapted to analyze the time evolution of ionospheric conductances due to precipitating particles over the auroral region or in particular sectors. Results are illustrated with conductance maps of the north polar region obtained during four periods with different activity levels. It is found that the proton contribution to conductance is relatively higher during quiet periods than during substorms. The proton contribution is higher in the period before the onset and strongly decreases during the expansion phase of substorms. During a substorm which occurred on 28 April 2001, a region of strong proton precipitation is observed with SI12 around 14:00MLT at ~75° MLAT. Calculation of conductances in this sector shows that neglecting the protons contribution would produce a large error. We discuss possible effects of the proton precipitation on electron precipitation in auroral arcs. The increase in the ionospheric conductivity, induced by a former proton precipitation can reduce the potential drop along field lines in the upward field-aligned currents by creating an opposite polarization electric field. This feedback mechanism possibly reduces the electron acceleration. Key words. Ionosphere (auroral ionosphere; ionospheremagnetosphere interactions; particle precipitation)
Highlights
The calculation of the ionosphere height integrated conductivities is important in evaluating the ionosphere electrodynamics and in modeling the interactions between magnetosphere, ionosphere and thermosphere
In this study we examine if conductances due the auroral proton precipitation can influence the electron precipitation as the background ionospheric conductance
We developed a model using IMAGE-Far Ultraviolet (FUV) observations to evaluate instantaneous ionospheric conductivity profiles and conductances induced by auroral precipitation on a global scale
Summary
The calculation of the ionosphere height integrated conductivities is important in evaluating the ionosphere electrodynamics and in modeling the interactions between magnetosphere, ionosphere and thermosphere. Frey et al (2001) used in situ measurements from two orbits of the FAST satellite to model the auroral brightness and compared them with simultaneous FUV-WIC observations They concluded a good agreement between predicted and observed emission rates, both in morphology and in intensity. From the proton transport code and with some assumptions about the proton mean energy we calculate the proton energy flux maps from SI12 images Another difficulty stems from the airglow contribution in the WIC and SI13 observations. This contribution must be removed before deriving the precipitating flux, since we seek evaluation of the contribution of auroral particles only This important step when using the WIC and SI13 observations to evaluate the electron mean energy is discussed in Sect.
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