Properties of Hot Spots for Solar Activity

Hot spots for solar flares are areas of enhanced flare activity in a long term, which rotate rigidly at a certain rate. For example, a double-hot-spot system with a synodic period of 26.73 days persisted for three solar cycles (20 through 22) in the same locations in the northern hemisphere. This paper investigates properties of three hot- spot systems. The first is mentioned above, and the second is a double-hot-spot system with a synodic rotation period of 27.41 days, which operated in the northern hemisphere during cycles 19, 20, and 21. The third one is a double-hot-spot system with a synodic rotation period of 28.24 days, which operated in the southern hemisphere during solar cycle 23. This system was discovered by Bai (2003, ApJ 585, 1114), by analyzing flares observed until June 2002. Analysis of flares observed since then shows that this system operated until the end of January 2004, after which it ceased to operate. A double-hot-spot system has two hot spots, separated by about 180 degrees in longitude, with the same rotation period. The three hot-spot systems show different properties. The 26.73-day hot-spot system mainly influenced distributions of flares from superactive regions, whereas the distribution of flares produced by active regions with three or less major flares did not show a hint of this hot-spot system. On the other hand, for the other two hot-spot systems, distributions of flares from ordinary active regions (with three or less major flares) were also influenced by hot spots. Another interesting discovery is that the two hot spots with the 26.73-day period were not active simultaneously. When one hot spot was active, the other was dormant, and vice versa. Even for a long interval, their activity levels were anti-correlated.