Browsing by Author "Liu, L."
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Item Restricted A new approach to the derivation of dynamic information from ionosonde measurements(European Geosciences Union, 2003-11-30) Liu, L.; Luan, X.; Wan, W.; Ning, B.; Lei, J.A new approach is developed to derive dynamic information near the peak of the ionospheric F-layer from ionosonde measurements. This approach avoids deducing equivalent winds from the displacement of the observed peak height from a no-wind equilibrium height, so it need not determine the no-wind equilibrium height which may limit the accuracy of the deduced winds, as did the traditional servo theory. This approach is preliminarily validated with comparisons of deduced equivalent winds with the measurements from the Fabry-Perot interferometer, the Millstone Hill incoherent scatter radar and with previous works. Examples of vertical components of equivalent winds (VEWs), over Wuhan (114.4° E, 30.6° N, 45.2° dip), China in December 2000 are derived from Wuhan DGS-256 Digisonde data. The deduced VEWs show large day-to-day variations during the winter, even in low magnetic activity conditions. The diurnal pattern of average VEWs is more complicated than that predicted by the empirical Horizontal Wind Model (HWM). Using an empirical electric field model based on the observations from Jicamarca radar and satellites, we investigate the contributions to VEWs from neutral winds and from electric fields at the F-layer peak. If the electric field model is reasonable for Wuhan during this period, the neutral winds contribute mostly to the VEWs, and the contribution from the E × B drifts is insignificant.Item Restricted Modeling the relationship between E × B vertical drift and the time rate of change of hmF2 (ΔhmF2/Δt) over the magnetic equator(American Geophysical Union, 2008-03-13) Yue, Xinan; Wan, Weixing; Lei, Jiuhou; Liu, L.A middle and low latitude ionospheric model is used to model the relationship between E × B vertical drift velocity and time rate of change of hmF2 (ΔhmF2/Δt) over the magnetic equator. F107 (10.7 cm solar radiation flux) is chosen to be equal to 100, 150, and 200 to represent low, middle, and high solar activities, respectively, and Ap is equal to 1 to represent quiet geomagnetic activity. Our simulations show that hmF2 derived vertical drifts over the magnetic equator are in good agreement with the E × B vertical drift imposed in the model during 0600–0730 and 1700–2100 LT. This is consistent with previous comparisons between vertical drift velocities derived from ionosonde, Jicamarca incoherent scatter radar, and AE‐E observations well. However, the amplitudes of hmF2 derived drift are smaller than the given drift velocities during other local times. During disturbed conditions, the variations of hmF2 can be used to determine the occurrence of intense electric field disturbance.