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 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 \arcdeg .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 \arcdeg .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 .