TY  - JOUR
A1  - Verma, Meetu
A1  - Kummerow, P.
A1  - Denker, Carsten
T1  - On the extent of the moat flow in axisymmetric sunspots
JF  - Astronomische Nachrichten = Astronomical notes
N2  - Unipolar, axisymmetric sunspots are figuratively called “theoretician's sunspots” because their simplicity supposedly makes them more suitable for theoretical descriptions or numerical models. On November 18, 2013, a very large specimen (active region NOAA 11899) crossed the central meridian of the sun. The moat flow associated with this very large spot is quantitatively compared to that of a medium and a small sunspot to determine the extent of the moat flow in different environments. We employ continuum images and magnetograms of the Helioseismic and Magnetic Imager (HMI) as well as extreme ultraviolet (EUV) images at λ160 nm of the Atmospheric Imaging Assembly (AIA), both on board the Solar Dynamics Observatory (SDO), to measure horizontal proper motions with Local Correlation Tracking (LCT) and flux transport velocities with the Differential Affine Velocity Estimator (DAVE). We compute time-averaged flow maps (±6 hr around meridian passage) and radial averages of photometric, magnetic, and flow properties. Flow fields of a small- and a medium-sized axisymmetric sunspot provide the context for interpreting the results. All sunspots show outward moat flow and the advection of moving magnetic features (MMFs). However, the extent of the moat flow varies from spot to spot, and a correlation of flow properties with size is tenuous, if at all present. The moat flow is asymmetric and predominantly in the east–west direction, whereby deviations are related to the tilt angle of the sunspot group as well as to the topology and activity level of the trailing plage.
KW  - activity
KW  - data analysis
KW  - image processing
KW  - photosphere
KW  - sunspots
Y1  - 2018
U6  - https://doi.org/10.1002/asna.201813482
SN  - 0004-6337
SN  - 1521-3994
VL  - 339
IS  - 4
SP  - 268
EP  - 276
PB  - Wiley-VCH
CY  - Weinheim
ER  -