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We use microwave imaging observations from the Nobeyama Radioheliograph at 17GHz for long-term studies of solar activity. In particular, we use the polarand low-latitude brightness temperatures as proxies to the polar magnetic fieldand the active-regions, respectively. We also use the location of prominenceeruptions as a proxy to the filament locations as a function of time. We showthat the polar microwave brightness temperature is highly correlated with thepolar magnetic field strength and the fast solar wind speed. We also show thatthe polar microwave brightness at one cycle is correlated with the low latitudebrightness with a lag of about half a solar cycle. We use this correlation topredict the strength of the solar cycle: the smoothed sunspot numbers in thesouthern and northern hemispheres can be predicted as 89 and 59, respectively.These values indicate that cycle 25 will not be too different from cycle 24 inits strength. We also combined the rush to the pole data from Nobeyamaprominences with historical data going back to 1860 to study the north-southasymmetry of sign reversal at solar poles. We find that the reversal asymmetryhas a quasi-periodicity of 3-5 cycles.

Long-term Solar Activity Studies using Microwave Imaging Observations and Prediction for Cycle 25