PROPERTIES OF SOLAR EPHEMERAL REGIONS AT THE EMERGENCE STAGE

Abstract

For the first time, we statistically study the properties of ephemeral regions (ERs) and quantitatively determine their parameters at the emergence stage based on a sample of 2988 ERs observed by the \emph{Solar Dynamics Observatory}. During the emergence process, there are three kinds of kinematic performances, i.e., separation of dipolar patches, shift of ER's magnetic centroid, and rotation of ER's axis. The average emergence duration, flux emergence rate, separation velocity, shift velocity, and angular speed are 49.3 min, 2.6 $\times$ 10$^{15}$ Mx s$^{-1}$, 1.1 km s$^{-1}$, 0.9 km s$^{-1}$, and 0$\degr$.6 min$^{-1}$, respectively. At the end of emergence, the mean magnetic flux, separation distance, shift distance, and rotation angle are 9.3 $\times$ 10$^{18}$ Mx, 4.7 Mm, 1.1 Mm, and 12$\degr$.9, respectively. We also find that the higher the ER magnetic flux is, (1) the longer the emergence lasts, (2) the higher the flux emergence rate is, (3) the further the two polarities separate, (4) the lower the separation velocity is, (5) the larger the shift distance is, (6) the slower the ER shifts, and (7) the lower the rotation speed is. However, the rotation angle seems not to depend on the magnetic flux. Not only at the start time, but also at the end time, the ERs are randomly oriented in both the northern and the southern hemispheres. Besides, neither the anticlockwise rotated ERs, nor the clockwise rotated ones dominate the northern or the southern hemisphere.