Arc echo
The arc echo (from the English bow echo ) is an arc-shaped echo in the precipitation radar image, which mostly consists of a multi-cell line, and more rarely also originates from a super cell .
In connection with the arc echoes, heavy gusts are mostly observed on the back of the echo line, some of which can reach hurricane strength ( downburst ). The cause of the arched structure is a dominant downdraft in the middle, which is intensified by a strong wind in the middle and lower altitude layers, as well as weaker winds in the north and south parts of the echo.
Usually, cyclonic rotation predominates in the northern part of the arc echo, which is supported by the Coriolis force . Then it typically develops to a decimal point , the southern part is weaker because of the anticyclonic rotation .
In Doppler radar , arc echoes can be seen on two adjacent surfaces of different, at best intense colors (mostly green and red in the DWD), which mark the jump in the wind on the arc echo (e.g. red: moving away from the radar; green: moving towards the radar ).
In addition to heavy falling gusts, tornadoes can rarely occur in the rear area of the arc echo when the so-called rear flank downdraft (a downdraft flanking the back) wraps around the rotating updraft in the cyclonic head (northern part) .