Contrasting longitudinal variation in equatorial spread‐F (ESF) density irregularity distribution has been observed by ROCSAT‐1 during high solar activity year of 2000 against moderate solar activity year of 2003. The monthly averaged solar flux intensity F10.7 was higher every month in 2000 than in 2003, but the irregularity occurrence rate did not always correlate with solar activity at every longitude in a season. For the equinox seasons, the occurrence rate was higher at every longitude in 2000 than in 2003. Higher occurrence rate was also observed in 2000 than in 2003 during a solstice season at longitudes of the so‐called ESF longitudes. On the other hand, higher occurrence rates were observed in 2003 at the so‐called low‐ESF longitudes from 230° to 10° during the June solstice season and from 90° to 260° during the December solstice season, where the magnetic flux tube makes a large‐angle alignment with the sunset terminator during the respective solstice season. Such anti‐solar activity correlation of ESF irregularity occurrences at these low‐ESF longitudes could be due to transequatorial meridional wind‐induced instability suppression agent which becomes more effective to offset the Rayleigh‐Taylor instability growth rate in a solstice season during a high solar activity period than during a low solar activity period.