Abstract
We investigated the effects of the F region bottomside altitude (h’F), maximum upward E × B drift velocity, duration of pre-reversal enhancement and the integral of upward E × B drift on the latitudinal extension of equatorial plasma bubbles in the Southeast Asian sector using the observations recorded by three GPS receivers and two ionosondes. The GPS receivers are installed at Kototabang (0.2°S, 100.3°E; 9.9°S magnetic latitude), Pontianak (0.02°S, 109.3°E; 9.8°S magnetic latitude) and Bandung (6.9°S, 107.6°E; 16.7°S magnetic latitude) in Indonesia. The ionosondes are installed at magnetically equatorial stations, Chumphon (10.7°N, 99.4°E; 0.86°N magnetic latitude) in Thailand and Bac Lieu (9.3°N, 105.7°E; 0.62°N magnetic latitude) in Vietnam. We analysed those observations acquired in the equinoctial months (March, April, September and October) in 2010–2012, when the solar activity index F 10.7 was in the range from 75 to 150. Assuming that plasma bubbles are the major source of scintillations, the latitudinal extension of the bubbles was determined according to the S4 index. We have found that the peak of h’F, maximum upward E × B drift and the integral of upward E × B drift during the pre-reversal enhancement period are positively correlated with the maximum latitude extension of plasma bubbles, but that duration of pre-reversal enhancement does not show correlation. The plasma bubbles reached magnetic latitudes of 10°–20° in the following conditions: (1) the peak value of h’F is greater than 250–450 km, (2) the maximum upward E × B drift is greater than 10–70 m/s and (3) the integral of upward E × B drift is greater than 50–250 m/s. These results suggest that the latitudinal extension of plasma bubbles is controlled mainly by the magnitude of pre-reversal enhancement and the peak value of h’F at the initial phase of development of plasma bubbles (or equatorial spread F) rather than by the duration of pre-reversal enhancement.
Highlights
Plasma bubble refers to depletion of plasma density at the nighttime equatorial and low-latitude region and is generated through the Rayleigh-Taylor instability (RTI) mechanism (Sultan 1996; Fejer et al 1999)
On the basis of the above results for groups 1 and 2, we find that the peak h’F, maximum Vu and integral of Vu at the equatorial region are well positively correlated with the maximum latitudinal extension of plasma bubble
We investigated the effects of the peak h’F and magnitude and duration of pre-reversal enhancement (PRE) on the latitudinal extension of plasma bubble in the Southeast Asian region, under the assumption that region of scintillation coincides with plasma bubble or plasma depletion
Summary
Plasma bubble refers to depletion of plasma density at the nighttime equatorial and low-latitude region and is generated through the Rayleigh-Taylor instability (RTI) mechanism (Sultan 1996; Fejer et al 1999). The eastward electric field is enhanced before the electric field become westward during nighttime. This phenomenon is called pre-reversal enhancement (PRE). PRE causes an enhanced upward E × B drift in the post-sunset sector and affects the plasma bubble generation significantly by lifting the ionosphere to higher altitudes, where the growth rate of the RTI is large because of the small ion-neutral collision. The thresholds of PRE strength under different solar and magnetic activities have been inferred for plasma bubble onset (Farley et al 1970; Jayachandran et al 1993; Fejer et al 1999)
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