Wave structures of the plasma density and vertical E × B drift in low‐latitude F region

Abstract

[1] We investigate the seasonal, longitudinal, local time (LT), and altitudinal variations of the F region morphology at low latitudes using data from the first Republic of China satellite (ROCSAT-1), Global Ultraviolet Imager (GUVI), on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite, and the Defense Meteorological Satellite Program (DMSP) F13 and F15 satellites. Signatures of the longitudinally periodic plasma density structure emerge before 0900 LT. The wave structure is established before noon and further amplified in the afternoon. The amplitudes of the wave structure start to diminish in the evening. The wave-4 structure is clearly distinguishable during equinox and northern hemisphere summer. During northern hemisphere winter, the density structure can be characterized to either wave-4 or wave-3 structure owing to marginal separation of the two peaks in 180°-300°E. Observations of similar density structures from ROCSAT-1 (600 km) and DMSP (840 km) at 0930 and 1800 LT indicate the extension of the wave structure to altitudes greater than 840 km. The daytime wave structure persists into the night during the equinoxes but is significantly modified during the solstices. The modification is more significant at higher altitudes and is attributed to the effects of interhemispheric winds and the prereversal enhancement. The formation of the wavelike density structure in the morning and its temporal evolution in the afternoon show a close association with the vertical E Â B drift. We conclude that the E Â B drift during 0900-1200 LT determines the formation of the wavelike density structure.

Vertical connection from the tropospheric activities to the ionospheric longitudinal structure simulated by a new Earth's whole atmosphere-ionosphere coupled model

“…As denoted by the thin lines vertical between Figures 4a and 4b, the peak locations of upward E × B drift are close to those of nmf2, at least for the southern EIA crest, while the longitude of the wave 1 peak does not match between the upward E × B drift and the nmf2 at the northern EIA crest; this is discussed later. Compared with observations of vertical drift, the significant existence of the wave 4 structure agrees with existing observations [Hartman and Heelis, 2007;Kil et al, 2007Kil et al, , 2008Ren et al, 2009]. However, the amplitude of wave 4 is considerably lower in our simulation (about 4%) than in the observations (e.g., about 10% is shown in Figure 2 of Ren et al [2009] for a similar local time and season).…”

“…[13] Compared with observations of the F-region plasma density, the wave 4 structure becomes dominant only in the Southern Hemisphere in our simulation, while the wave 4 structure is observed in both hemispheres for a similar situation (September equinox, daytime, moderate solar activity) [Lin et al, 2007;Kil et al, 2008;Liu and Watanabe, 2008;Scherliess et al, 2008]. The amplitude of wave 4 is about 4% in our simulation, which is a degree similar to the total electron content observation by TOPEX (e.g., Figure 8 of Scherliess et al [2008]) but significantly smaller than the electron content integrated over 400-450 km obtained by the FORMOSAT-3/COSMIC observation (e.g., Figure 1 of Lin et al [2007], which shows an amplitude of more than 10%).…”

“…[10] Using the present version of GAIA, described in section 2, we have carried out a 30 day consecutive run in September, which is one of the months when the ionospheric four-peak longitudinal structure becomes dominant according to the observations [e.g., Kil et al, 2008;Liu and Watanabe, 2008;Scherliess et al, 2008;Wan et al, 2008]. As the initial condition, we used results from noncoupled simulations using each atmospheric GCM and ionospheric model.…”

“…The nonmigrating tides, with their climatology, have been observed directly in the lower thermosphere [e.g., Oberheide et al, 2006;Forbes et al, 2008], which confirmed the dominant existence of the DE3 tide during many months. As evidence of modulation in the dynamo, a four-peak structure has been observed in E × B drift [Hartman and Heelis, 2007;Kil et al, 2007Kil et al, , 2008Ren et al, 2009] and in the equatorial electrojet (EEJ) [England et al, 2006b;Luhr et al, 2008] and has been shown in electrodynamic simulations [Jin et al, 2008;Ren et al, 2010]. Furthermore, the four-peak structure of the EIA has been reproduced by a simulation using the ThermosphereIonosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM), in which the nonmigrating tidal forcing derived from the Global-Scale Wave Model was incorporated at its lower boundary [Hagan et al, 2007].…”

The role of the vertical <I><B>E</B></I>×<I><B>B</B></I> drift for the formation of the longitudinal plasma density structure in the low-latitude F region

“…This condition is satisfied in most cases at an altitude of 600 km. The temporal evolution of the wave-like longitudinal density structure in the ROCSAT-1 data showed the occurrence of the most pronounced wave structure just after noon (Kil et al, 2008). In Fig.…”