Latitude migration of solar filaments

ABSTRACT The Carte Synoptique catalogue of solar filaments from March 1919 to December 1989, corresponding to complete cycles 16 to 21 is utilized to show latitudinal migration of filaments at low latitudes ( less than 50), and the latitudinal drift of solar filaments in each hemisphere in each cycle of the time interval is compared with the corresponding drift of sunspot groups. The latitudinal drift of filaments obviously differ from that of sunspot groups. At the beginning of a cycle filaments (sunspot groups) migrate from latitudes of about 40◦ (28◦) with a drift velocity of about 2.4m/s (1.2m/s) toward the solar equator, reach latitudes of about 25◦ (20◦) 4 years later at the cycle maximum with a drift velocity of about 1.0m/s (1.0m/s), and halt at about 8◦ (8◦) at the end of the cycle. When solar activity is programming into a solar cycle, the difference between the appearing latitudes of filaments and sunspot groups becomes smaller and smaller. The difference rapidly decrease in the first and last ∼ 4 years of a cycle, but almost does not decrease in the ∼ 4 years after the maximum time of the cycle. For filaments, the latitudinal drift velocity decreases in the first ∼ 7.5 years of a cycle, but it increases in the last ∼ 3.5 years of the cycle. However, for sunspot groups the drift velocity always decreases in a whole cycle. The different between the latitude drift of filaments in the northern and southern hemispheres is found not to be obvious. The latitudinal drift velocity of filaments slightly differs from each other in the northern and southern hemispheres in a cycle. The physical implication behind the latitudinal drift of filaments is explored.