Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsa21b..05s&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SA21B-05
Physics
2415 Equatorial Ionosphere, 2439 Ionospheric Irregularities, 2481 Topside Ionosphere
Scientific paper
Monthly variation of global equatorial density irregularity distribution has been obtained with data taken by ROCSAT-1 at the 600 km topside ionosphere from March 1999 to June 2004 during high to moderate solar activity periods. This global longitudinal distribution of monthly irregularity occurrence variation not only provides the best spatial/temporal distribution existed so far but also fills the gap of irregularity distribution missing over eastern Pacific regions where no ground observation is available. The 5½-year result of the monthly occurrence pattern indicates a smooth variation across the longitudes contrary to some beliefs that a drastic change in irregularity occurrence pattern has occurred across the eastern Pacific longitudes. Excellent agreement is noted for the current results with Aarons' conjectured sketch of global scintillation occurrence distributions published in 1993. Furthermore, the seasonal/longitudinal (s/l) variations of quiettime post-sunset vertical drift velocities are found to track closely with the s/l variations of irregularity occurrences except during the September equinox. Linear regression analysis between the vertical drift velocity and the irregularity occurrence rate indicates that the vertical drift velocities at three different longitude zones of different magnetic declinations have good correlations with the irregularity occurrences for all seasons. This implies that the averaged post-sunset vertical drift velocity is indeed a good indicator for the occurrences of equatorial density irregularities in a longitude region that has same magnetic declination. Smooth variation of monthly/seasonal/longitudinal distributions of the vertical drift velocities that results in smooth variation of the topside density irregularity occurrences imply that global occurrence pattern of either distribution is controlled by the global variation of post-sunset ionospheric condition from the magnetic declination effect and the seasonal variation of the dip equator location with respect to the geographic equator. There seems little need to include the global variation of instability perturbation seed distribution from the atmospheric disturbances for the global distribution of topside irregularity occurrences.
Chao Chia-Chun
Liu Chan Chiang
Su Shangguo
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