Field-aligned Diffusive Fluxes Of O~+ Ions In The Mid-and Low-latitude Topside Ionosphere

This thesis includes two parts. One part is the study of O+ field-aligned diffusive fluxes in the topside ionosphere. In this part, the statistical characteristics of the diffusive fluxes in the mid- and low-latitude topside ionosphere are analyzed under low and high solar activity conditions from radio occultation measurements by CHAMP and COSMIC, respectively. The characteristics of diffusive fluxes during two geomagnetic storms are analyzed using the measurements by incoherent scatter radar. In the other part, the in-situ measurements, including atmospheric densities, electron densities and electron temperatures, are analyzed. A method of retrieving atmospheric density is introduced. The preliminary result of atmospheric density model is given. The study in this part has important applied values.1. The study of field-aligned O+ diffusive fluxes.The knowledge of plasma diffusive fluxes is not only important to the study of the dynamical and mass coupling between the ionosphere and plasmasphere/inner magnetosphere, but it is helpful to the research of the dynamical coupling between the ionosphere and thermosphere. It also helps to elucidate the relative contributions of each physical process, including neutral wind, electric field, chemistry and ambipolar diffusion, to variations of the global ionosphere during both storm and quite times. Topside diffusive fluxes are also one of the primary top boundary conditions for many global thermosphere/ionosphere models, such as the NCAR-TIEGCM and TING model.(1) The statistical characteristics of diffusive fluxes under high solar activity conditions are analyzed. O+ field-aligned diffusive velocities and fluxes in the topside ionosphere are calculated from electron density profiles retrieved from CHAMP radio occultation measurements and empirical predicts from IRI2007 and NRLMSISE00 models. The velocities and fluxes from January 2002 to December 2003 at low- and mid-latitudes have been statistically analyzed. The results show that the averaged velocities were between -15ms-1~25 ms-1. The diffusive fluxes during the daytime changed gradually from downwardto upward as altitude increases. The transition heights from downward flows to upward flows were about hmF2+50 km. The largest values of the upward diffusive fluxes and velocities occurred at around±25o geomagnetic latitude. The diffusive fluxes near the equator were small. During solstices the plasma fluxes in the winter hemisphere were larger than those in the summer hemisphere.(2) The statistical characteristics of diffusive fluxes under low solar activity conditions are analyzed. O+ field-aligned diffusive velocities and fluxes in the topside ionosphere have been calculated from electron density profiles retrieved from COSMIC radio occultation measurements. The diffusive velocities and fluxes from October 2006 to October 2007 at low- and mid-latitudes have been statistically analyzed. The results show that the directions of diffusive fluxes are upward in the daytime, but downward at night. The largest values of the upward diffusive fluxes and velocities during daytime occur at at geomagnetic latitudes from 10°to 20°above hmF2+80 km , whereas for the nighttime the maximum downward fluxes occur at geomagnetic latitudes from 30°to 40°. Diffusive fluxes are roughly symmetric around the magnetic equator during equanoxes. But they are asymmetric during solstices, the winter hemisphere has smaller fluxes than the summer hemisphere does above hmF2+80 km. In addition, the diurnal variations have latitudinal dependences. The values from CHAMP data are compared with those from COSMIC data, and the results show that during the daytime the maximum diffusive fluxes under low solar activity conditions are less than those under high solar activity conditions.(3) The variations of diffusive fluxes during geomagnetic storms are analyzed. A 30-day ISR experiment was conducted at Millstone Hill (288.5°E, 42.6°N) from 4 October to 4 November 2002. O+ field-aligned diffusive velocities and fluxes in the topside ionosphere have been calculated from the altitude profiles of electron density, ion and electron temperature during this experiment. The characteristics of Vd,Фd and some other ionospheric parameters are analyzed during two geomagnetic storms. Upward Vd andФd during the storm main phases were significantly less than the averaged values in quiet time at 500 km height. In the nighttime of the storm main phases, downward Vd was larger than the averaged value sometimes. During the recovery phases, the decrease of Vd andФd, and the changes of their directions in the nighttime are observed.2. The thermospheric and ionospheric parameters are analyzed using in-situ measurements by CHAMP.(1) A method of retrieving the upper-atmospheric densities using the measurements from the accelerometer is introduced. A test model is constructed. Since many satellites will carry accelerometers, this method can be widely used in the future.(2) The annual and semiannual variations of electron densities and electron temperatures from Langmuir probe and their dependences of the solar activity are analyzed.