Behavior of Solar Cycles 23 and 24 Revealed by Microwave Observations
  Using magnetic and microwave butterfly diagrams, we compare the behavior of solar polar regions to show that (i) the polar magnetic field and the microwave brightness temperature during the solar minimum substantially diminished during the cycle 23/24 minimum compared to the 22/23 minimum. (ii) The polar microwave brightness temperature (b) seems to be a good proxy for the underlying magnetic field strength (B). The analysis indicates a relationship, B = 0.0067Tb - 70, where B is in G and Tb in K. (iii) Both the brightness temperature and the magnetic field strength show north-south asymmetry most of the time except for a short period during the maximum phase. (iv) The rush-to-the-pole phenomenon observed in the prominence eruption activity seems to be complete in the northern hemisphere as of March 2012. (v) The decline of the microwave brightness temperature in the north polar region to the quiet-Sun levels and the sustained prominence eruption activity poleward of 60oN suggest that solar maximum conditions have arrived at the northern hemisphere. The southern hemisphere continues to exhibit conditions corresponding to the rise phase of solar cycle 24. 
N. Gopalswamy, S. Yashiro, P. M\"akel\"a, G. Michalek, K. Shibasaki,   and D. H. Hathaway
astro-ph.SR