Equatorial plasma fountain and its effects: Possibility of an additional layer

Abstract

The importance of diffusion, perpendicular electrodynamic drift, and neutral wind on the generation and modulation of the equatorial plasma fountain of the Earth's ionosphere is studied using the Sheffield University plasmasphere-ionosphere model for the ionosphere above Jicamarca under magnetically quiet equinoctial conditions at medium solar activity. The effects of the fountain, which include the equatorial anomaly, are also investigated. As expected, the F region electrodynamic (E x B) drift generates the plasma fountain and the anomaly, which are symmetric with respect to the magnetic equator. The neutral wind introduces asymmetries, with larger plasma flow (toward the hemisphere of stronger poleward wind) and stronger anomaly crest occurring in opposite hemispheres. During daytime, when the drift is upward, the fountain rises to about 800 km altitude at the equator and covers about +300 magnetic latitude; outside the reach of the fountain, plasma flows toward the equator from both hemispheres. This convergence of plasma leads to the formation of an additional layer (called the G layer) within 4-100 of the magnetic equator during the prenoon hours when the drift is large. At the magnetic equator, the maximum plasma concentration of the G layer can be greater than that of the F layer for a short period of time just before noon and when the drift starts to decrease. In the evening, soon after the drift turns downward, the fountain becomes a reverse fountain with supply of ionization from both hemispheres from regions outside the fountain. The reverse fountain acts as the main source for the nighttime increase in ionization at equatorial anomaly latitudes, with some contribution from the prereversal strengthening of the forward fountain. The importance of the prereversal strengthening of the forward fountain, which rises to about 1000 km altitude at the equator, and the following reverse fountain on the generation and propagation of plasma bubbles and spread F irregularities is discussed. It is also shown that the equatorial anomaly in the vertical ionospheric electron content need not be as pronounced as the interpretation of the observations suggests. Paper number 95JA01555. 0148-0227/95/95JA-015555 05.00 ized by a trough at the equator and crests at about 4-170 magnetic latitude [Appleton, 1946]; the crest-totrough ratio (about 1.5 in daytime peak electron density, N[nax) and the position of the crests vary with various geophysical conditions. Many theories, like the diffusion theory [Mitra, 1946] and the electrodynamic drift theory [Martyn, 1955], have been put forward to explain the anomaly. The diffusion theory has been shown to be important but not sufficient to explain the observations [Rishbelh et al., 1963]. The electrodynamic drift theory, on the other hand, has been successful in explaining the observations [Bramley and Pearl, 1965; Moffett and Hanson, 1965]. According to the drift theory, the north-south geomagnetic field combined with the daytime east--west ionospheric electric field (both being p...

Features of theF3layer in the low-latitude ionosphere at sunset

“…[15] The model result of Balan and Bailey [1995] shows that the F 3 layer starts to form during the morning hours when the upward E × B drift increases. Once formed, the peak concentration of the F 3 layer remains greater than that of the F 2 layer for a short period of time before noon when the drift is large.…”

“…[3] Studies of the stratification of the F 2 layer gradually subsided until recent theoretical work based on the Sheffield University Plasmasphere-Ionosphere Model (SUPIM) suggested that the equatorial plasma fountain could produce a temporary additional layer ("G" layer) above the normal F 2 when the plasma flow is distorted by a meridional neutral wind [Balan and Bailey, 1995]. This additional layer was later renamed the F 3 layer because it has the same chemical composition as the F region .…”

Some features of the equatorial anomaly revealed by ionospheric tomography

“…Recent computer simulations [Balan and Bailey, 1995] and experimental data [Vladimer et al, 1999] show that the fountain created by uplifting electrodynamic ExB drift at the geomagnetic equator must be supplemented by neutral wind effects. During periods of stronger eastward electric field, the fountain will lift the ionospheric plasma to a higher height, resulting in a crest formed at higher latitudes.…”

Solar control of ambient ionization of the ionosphere near the crest of the equatorial anomaly in the Indian zone

“…The electrodynamic ExB drift at the magnetic equator and subsequent diffusion generates the plasma fountain and anomaly (Hanson and Moffett, 1966). The neutral wind makes the fountain and anomaly asymmetric (Balan and Bailey, 1995). An estimate of the equatorial electric field responsible for the fountain effect may be obtained from the electrojet strength.…”

“…The electrodynamic ExB drift produces a trough of ionization at the equator with two crests around 15 • -20 • geomagnetic latitudes -known as the equatorial ionization anomaly. The neutral wind further introduces asymmetries in the anomalous distribution of the ionization with larger plasma flow (towards the hemisphere of the stronger poleward wind) and a stronger anomaly crest occurring in the opposite hemispheres (Balan and Bailey, 1995). The latitudes of the anomaly crests and the strength of the anomaly are found to vary with day, month, season, solar activity, as well as longitudes (Rush and Richmond, 1973;Huang et al, 1989).…”