Z. Ren

Correlation between the ionospheric WN4 signature and the upper atmospheric DE3 tide

[1]xa0The present work studies the correlation relationship between the longitudinal ionospheric structure of wave number 4 (WN4) and the upper atmospheric tide of nonmigrating tidal mode DE3 (diurnal eastward wave number 3). Global ionospheric maps produced by the Jet Propulsion Laboratory were used to deduce the latitudinal integration of total electron content in the low-latitude ionosphere, and TIDI/TIMED observations were used to retrieve the atmospheric zonal and meridional winds. By applying Fourier filtering and fitting techniques, the WN4 wave and DE3 tidal components are derived from the ionospheric and upper atmospheric observations, respectively. We found that the observed WN4 wave and DE3 zonal wind components experience very similar annual and interannual variations, but the DE3 meridional wind component behaves in a quite different manner. Both WN4 and DE3 zonal winds are very intense during northern summer and autumn; they also appear in the later spring, but tend to vanish in winter. Their amplitudes increase as the solar activity decreases, and both are stronger in the quasi-biennial oscillation (QBO) eastward wind phase than in the westward phase. At the same time, the DE3 meridional wind likes to occur only in winter and seems not change with solar activity and QBO phase. We further studied the correlation between the WN4 wave and the two wind components of the DE3 tide. We found that the cross-correlation coefficient between the WN4 wave and the DE3 zonal wind is much larger, while that between the WN4 wave and the DE3 meridional wind is relatively smaller. Such different correlations are attributed to the different latitudinal symmetry of different DE3 wind components. The DE3 zonal wind is likely in latitudinally symmetric tidal mode; hence, it can efficiently affect the F region ion drifts. In contrast, the meridional wind is mainly in antisymmetric mode and thus seldom affects the ionospheric drifts. The present results support the suggestion that the longitudinal WN4 structure in the ionospheric F region originates from the symmetric modes, mainly the zonal wind component, of the upper atmospheric nonmigrating tidal mode DE3 in the ionospheric E region.

Anomalous enhancement of ionospheric electron content in the Asian-Australian region during a geomagnetically quiet day

National Natural Science Foundation of China[40725014]; National Important Basic Research Project[2006CB806306]; Knowledge Innovation Program of the Chinese Academy of Sciences

Westward ionospheric electric field perturbations on the dayside associated with substorm processes

[1]xa0A controversy has risen in the direction of ionospheric electric field perturbation on the dayside caused by substorm expansion phase in recent years, i.e., eastward or westward. To exclude the effect of interplanetary magnetic field northward turning, the substorms without interplanetary field (IMF) trigger are required to investigate this issue. Previous works, such as that by Huang et al. (2004), showed that the eastward electric field perturbations caused by substorms can be observed. However, our case suggests that some substorms can produce strong westward electric field perturbations and drive westward equatorial electrojets on the dayside ionosphere. This westward electric field is created by an overshielding-like imbalance state of field-aligned currents (FACs), Region 2 (R2) FAC greater than Region 1 (R1) FAC, which is built up through R2 FAC enhancement rather than R1 FAC reduction due to IMF northward turning. The substorm processes should be responsible for the westward electric field especially through polar cap shrinkage and magnetic field dipolarization.

Is DE2 the source of the ionospheric wave number 3 longitudinal structure

[1]xa0This study examines the connection of the wave number 3 (wave-3) longitudinal structure in the ionospheric plasma density with diurnal eastward propagating zonal wave number 2 tide (DE2) by examining the annual and diurnal variations of the wave-3 structures in the plasma density and vertical E × B drift. For this purpose, we have utilized the mean plasma density and vertical ion velocity derived from the first Republic of China satellite data during 1999–2004 under Kp < 4 condition. Good correlation between the wave-3 longitudinal structures in the plasma density and vertical E × B drift indicates that the vertical E × B drift (or E-region dynamo electric field) is responsible for the creation of the wave-3 plasma density structure. The annual variation of the amplitude of the ionospheric wave-3 structure in the plasma density and vertical E × B drift shows two peaks near December and May, which is consistent with the annual variation of the DE2 amplitude. However, the diurnal variation of the ionospheric wave-3 structure does not show the eastward phase shift of 120°/24 LT that is predicted by DE2. The amplitude of the ionospheric wave-3 structure is greater than might be predicted by the comparison of the amplitude of the DE3 and DE2 winds. Another mechanism in addition to DE2 is necessary in order to explain the formation of the ionospheric wave-3 longitudinal structure.

Solar wind density controlling penetration electric field at the equatorial ionosphere during a saturation of cross polar cap potential

[1]xa0The most important source of electrodynamic disturbances in the equatorial ionosphere during the main phase of a storm is the prompt penetration electric field (PPEF) originating from the high-latitude region. It has been known that such an electric field is correlated with the magnetospheric convection or interplanetary electric field. Here we show a unique case, in which the electric field disturbance in the equatorial ionosphere cannot be interpreted by this concept. During the superstorm on Nov. 20–21, 2003, the cross polar cap potential (CPCP) saturated at least for 8.2xa0h. The CPCP reconstructed by Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure suggested that the PPEF at the equatorial ionosphere still correlated with the saturated CPCP, but the CPCP was controlled by the solar wind density instead of the interplanetary electric field. However, the predicted CPCPs by Hill-Siscoe-Ober (HSO) model and Boyle-Ridley (BR) model were not fully consistent with the AMIE result and PPEF. The PPEF also decoupled from the convection electric field in the magnetotail. Due to the decoupling, the electric field in the ring current was not able to comply with the variations of PPEF, and this resulted in a long-duration electric field penetration without shielding.