Magnotospheric imaging of high latitude ion outflows

Abstract. High latitude ion outflows mostly consist of upward streaming O⁺ and He⁺ emanating from the ionosphere. At heights above 1000 km, these flows consist of cold and hot components which resonantly scatter solar extreme ultraviolet (EUV) light, however, the ion populations respond differently to Doppler shifting resulting from the large relative velocities between the ions and the Sun. The possibility of optical detection of the Doppler effect on the scattering rate will be discussed for the O⁺ (83.4 nm) ions. We have contrasted the EUV solar resonance images of these outflows by simulations of the 30.4 nm He⁺ and 83.4 nm O⁺ emissions for both quiet and disturbed geomagnetic conditions. Input data for the 1000 km level has been obtained from the EICS instrument aboard the Dynamics Explorer satellite. Our results show emission rates of 50 and 56 milli-Rayleighs at 30.4 nm for quiet and disturbed conditions and 65 and 75 milli-Rayleighs at 83.4 nm for quiet and disturbed conditions, respectively, obtained for a polar orbiting satellite and viewing radially outward. We also find that an imager at an equatorial distance of 9 R_E or more is in a favourable position for detecting ion outflows, particularly when the plasmapause is depressed in latitude. However, an occultation disk is necessary to obscure the bright plasmaspheric emissions.