February 24, 2017, 1:00 pm - 2:00 pm

February 24, 1:00 pm - 2:00 pm

Magnetic Flux Emergence and Decay Rates Observed in Sunspots

Aimee Norton (Stanford University)

Magnetic flux emergence into the solar atmosphere triggers transient events such as flares, coronal mass ejections and jets. The aims of this study are to quantify flux emergence and decay rates of active regions using vector magnetic field data as observed with the Helioseismic Magnetic Imager (HMI/SDO) in order to constrain the simulation conditions and understand the subsurface emergence process that we cannot observe directly. Signed flux emergence rates for sunspots average 5 x 10^{19} Mx per hour, while decay rates are considerably slower at about half that rate. Using a synthesis of the HMI results presented in this paper and results previously reported from observations and simulations, a clear trend is seen that larger flux regions emerge faster than regions containing smaller flux. We find the observed emergence rate scales with peak flux of the region as a power law with an exponent of 0.32. We put the observed rates into context with other observations and multiple simulation efforts. The range of flux emergence rates reported here may assist in constraining the choice of boundary and initial conditions in numerical simulations which have already demonstrated that rates increase when a flux tube has higher buoyancy and twist, or is in the presence of a strong convective upflow.