Computer Science – Sound
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sa31a05w&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SA31A-05
Computer Science
Sound
2411 Electric Fields (2712), 2415 Equatorial Ionosphere, 2435 Ionospheric Disturbances, 2437 Ionospheric Dynamics
Scientific paper
The prediction of equatorial bubbles, and of the resulting scintillation that disrupts trans-ionospheric communication and radar, is a particularly difficult problem of space weather. The fact that bubbles occur essentially at random prevents the systematic observation of their formation, hence progress in their prediction. However what can be observed systematically is the occurrence of strong bottomside spread F (BSSF), which is a necessary condition for bubble formation, and lower levels of BSSF which preclude this formation. This work records for the first time, spread F conditions on each day of a year at solar maximum. Using an array of ionospheric sounders located in the Western Hemisphere, four levels of spread F are recorded: three BSSF of no, weak, and strong; and the fourth as macroscopic bubbles. Because each irregularity level corresponds to a threshold level of maximum pre-reversal E x B drift velocity, the record of BSSF implies also a record of this fundamental parameter. Of particular importance, a given level of irregularity can persist for periods of as many as 10 successive days. Furthermore these periods can recur with the 27 day solar rotation period. Some of these periods correspond to recurring periods of magnetic activity, strong BSSF and bubbles to the lowest magnetic activity, and weak and no BSSF to the highest magnetic activity. Also considered is the relation to 10.7 cm solar flux which varies between 150-350 solar flux units during the year and often by that amount during a single solar rotation. However the influence of solar flux on irregularity level or on its persistence has yet to be determined. The examination of recurrence with solar rotation is limited because only 13.5 rotations occur during the year. In addition there is the limitation of seasonal dependence, especially because irregularity nearly disappears during Jun. and Jul. In addition, strong BSSF is maximum in Jan. and Dec., whereas strong BSSF accompanied by macroscopic bubbles is maximum in Apr. and Sep.
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