Solar active regions ( ARs ) are thought to be formed by magnetic fields from the convection zone .
Our flux emergence simulations revealed that a strong horizontal divergent flow ( HDF ) of unmagnetized plasma appears at the photosphere before the flux begins to emerge .
In our earlier study , we analyzed HMI data for a single AR and confirmed presence of this precursor plasma flow in the actual Sun .
In this paper , as an extension of our earlier study , we conducted a statistical analysis of the HDFs to further investigate their characteristics and better determine the properties .
From SDO /HMI data , we picked up 23 flux emergence events over a period of 14 months , the total flux of which ranges from 10 ^ { 20 } to 10 ^ { 22 } { Mx } .
Out of 23 selected events , 6 clear HDFs were detected by the method we developed in our earlier study , and 7 HDFs detected by visual inspection were added to this statistic analysis .
We found that the duration of the HDF is on average 61 minutes and the maximum HDF speed is on average 3.1 { km s } ^ { -1 } .
We also estimated the rising speed of the subsurface magnetic flux to be 0.6 – 1.4 { km s } ^ { -1 } .
These values are highly consistent with our previous one-event analysis as well as our simulation results .
The observation results lead us to the conclusion that the HDF is rather a common feature in the earliest phase of AR emergence .
Moreover , our HDF analysis has capability of determining the subsurface properties of emerging fields that can not be directly measured .