Magnetic Flux Emergence and Decay Rates for Preceder and Follower Sunspots Observed with HMI

Abstract

We quantify the emergence and decay rates of preceder (p) and follower (f) sunspots within ten active regions from 2010-2014 using Space-weather Helioseismic Magnetic Imager Active Region Patch data. The sunspots are small-to mid-sized regions and contain a signed flux within a single polarity sunspot of (1.1 − 6.5) × 10 21 Mx. The net unsigned flux within the regions, including plage, ranges from (5.1 − 20) × 10 21 Mx. Rates are calculated with and without intensity contours to differentiate between sunspot formation and flux emergence. Signed flux emergence rates, calculated with intensity contours, for the p (f) spots average 6.8 (4.9) ×1019 Mx h −1 , while decay rates are −1.9(−3.4) × 10 19Mx h −1 . The mean, signed flux emergence rate of the regions, including plage, is 7.1 × 10 19 Mx h −1 for a mean peak flux of 5.9 × 10 21 Mx. Using a synthesis of these results and others reported previously, there is a clear trend for larger flux regions to emerge faster than smaller ones. Observed emergence rates (dφ/dt, Mx h −1 ) scale with total signed peak flux,φ max , as a power law with an exponent of 0.36, i.e., dφ/dt = Aφ 0.36 max . The observed rates may assist in constraining the boundary and initial conditions in simulations which already demonstrate increased rates for flux tubes with higher buoyancy and twist, or in the presence of a strong upflow. Overall, the observed emergence rates are smaller than those in simulations, which may indicate a slower rise of the flux in the interior than captured in simulations.

Testing the Accuracy of Data-driven MHD Simulations of Active Region Evolution

“…The majority of previous flux emergence simulations, including those in Leake, Linton, and Török [14] and Leake, Linton, and Antiochos [13], are relatively small, based on the axial flux in the tube and the size of the active region, with a typical flux < 10 20 Mx. Some larger scale simulations have recently been performed, and suggest that the mechanism for emergence is similar to that in the smaller-scale scenarios, and that the emergence rate depends on the field strength, depth, width, and twist of the initial flux tube [17].…”

Emergence of Magnetic Flux Generated in a Solar Convective Dynamo. I. The Formation of Sunspots and Active Regions, and The Origin of Their Asymmetries

“…These results provide a clear evidence that the emergence of magnetic flux bundles in these simulations is mostly con-trolled by the convective upflows. Furthermore, the convective upflow is expect to still play a vital role in the flux emergence process observed at the photosphere and may help people to understand the relation of the flux emergence rate to the total magnetic flux emerged (see e.g., Otsuji et al 2011;Norton et al 2017). …”

Super-flaring Active Region 12673 Has One of the Fastest Magnetic Flux Emergence Ever Observed

“…The flux emergence rate of AR 12673 is greater than any values reported in the literature of which we are aware. Figure 1(b) summarizes the mean signed flux emergence rate and peak signed flux from a collection of observations and simulations (Norton et al 2017). AR 12763 largely follows the established trend, but the extreme values on its evolutionary track are rivaled only by the fastest flux emergence model and AR 12192, which has ∼3.6 times the flux 3 .…”

“…The dataset is affected by systematic artifacts that correlate with daily spacecraft velocity variations (Sun et al 2015), so the instantaneousΦ is less certain. The maximum Φ, meanΦ, and maximum instantaneousΦ are 2.18 Norton et al (2017). Red and blue symbols indicate simulations and observations, respectively.…”