Rieger-type Periodic Phase Analysis of Sunspot Areas in the Northern and Southern Hemispheres Using Empirical Mode Decomposition

Empirical mode decomposition (EMD) technique is used to study the Rieger-type cycle in the sunspot area data from the 12th to 24th solar cycles and their phase relations in the northern and southern hemispheres. It is found that:(1) the Rieger-type cycle scale and the time scale are different in the two hemispheres, which leads to the asymmetry of the hemispheric distribution; (2) the average Rieger-type cycle length in the northern hemisphere is slightly longer than that in the southern hemisphere; (3) the phase of the dominant hemisphere is not necessarily ahead of time. The hemispherical Rieger-type with similar cycle scales is not necessarily a strong correlation.