Nonthermal Velocity in the Transition Region of Active Regions and Its Center-to-limb Variation

Abstract We derive the nonthermal velocities (NTVs) in transition region of an active using Si iv 1393.78 Å line observed by Interface Region Imaging Spectrograph and compare them with line-of-sight photospheric magnetic fields obtained Helioseismic Magnetic Imager on board Solar Dynamics Observatory. The consists two strong field regions opposite polarity, separated a weak corridor that widened as evolved. means NTV distributions (weak corridors) range between ?18–20 (16–18) km s ?1 , albeit maps show much larger range. In addition, we identify narrow lane middle significantly reduced NTV. NTVs do not center-to-limb variation, they somewhat values near disk center. are well correlated redshifts intensities. results here those presented our companion paper Doppler shifts suggest populations plasma emitting . first population exists extends partway into them. attribute this to spicules heated ?0.1 MK (often called type II spicules). They have inclinations relative vertical. second center corridor, is relatively faint, has smaller velocities, likely horizontal. These provide further insights heating region.