Comparison between solar cycles 23 and 24 from various observations. (Top) An overview of solar cycle 24 with respect to cycle 23 using three sets of observations: the international sunspot number (SSN in gray), polar magnetic field strength in the north and south polar regions (B, averaged over the latitude range 60° to 90°, thick lines), and the low-latitude microwave brightness temperature (Tb, averaged over 0 to 40°, thin lines). The low-latitude Tb is due to active regions. N and S point to the time when the polar magnetic fields vanished before the sign reversal. (bottom) Polar microwave brightness temperature (Tb, averaged over the latitude range 60° to 90°) and the unsigned polar magnetic field strength (B). The horizontal dashed and solid lines roughly indicate the average levels of Tb and B, respectively for the two cycles. The time of vanishing polar B occurs first in the north and then in the south during cycle 23 and 24. However, the lag is more pronounced in cycle 24. Note that the maximum phase has ended in the northern hemisphere (indicated by the steady increase in polar Tb by the end of 2013). All quantities are smoothed over 13 Carrington rotations.