tokens: Si iv . Solid contours represent and 1.04. The dotted contour represents T b = 6500 K. An animation of the observations is available. The animation runs from 14:19 to 14:54 UT on 2017 April 29. (An animation of this figure is available.) Panel (b) shows the distribution of the relative brightness in the ALMA 100 GHz data defined aswhereis a temporally averaged brightness over the entire observed period (Δ t ≈ 1 hr). The ALMA 100 GHz relative brightness and its corresponding animation (panel b) show a dynamic thorn-like structure coming from the saw-tooth patterns on the limb. Because these structures show dynamic motion with elongation and shortening, hereafter we call them ALMA jets. Their length reaches at least 8′′, suggesting jet-like activity in the ALMA microwave range. Unfortunately owing to the insufficient signal-to-noise ratio in the data beyond the limb particularly in the area more than 10′′ beyond the limb (see Section 4 ), we can not recognize the maximum height of the elongated jets. The speed of the elongation is 30–40 km s −1 . The width of each jet is less than the spatial resolution of the observation, i.e., less than ≈2′′. The IRIS /SJI Mg ii images (panel d) clearly show the appearance of spicules on the limb. Some of the spicular jets reach more than 20′′ beyond the Mg ii limb. It is noteworthy that the spicular jets show clustered structures, i.e., multiple needle-like features display a collective up-and-down motion. Each needle-like structure has a width less than 1′′ and each cluster has a few to several needle-like structures. In comparison with the ALMA data (contours in panel d), the ALMA jets are in good agreement with the IRIS jet clusters. The IRIS Mg ii limb (panel d) is ≈5′′ below the ALMA limb. Again, this confirms the distribution of cool chromospheric plasmas between the IRIS Mg ii and ALMA limbs (For an IRIS limb analysis, see Alissandrakis et al. 2018 ). In the IRIS /SJI Si data (panel f), one can observe the activities on the solar surface inside the limb. Some of them correspond to the footpoints of the Mg ii spicules. The AIA 304 Å data (panel e) has a low signal-to-noise ratio and is difficult to extract information on jet activities. In one of the tall jets in IRIS Mg ii , an ALMA blob ejection was found. From Figure 2 , one can find the trajectory of the blob co-located with the Mg ii jet. The brightness enhancement in the ALMA images is by 135 K beyond the background (Figure 3 ). The blob shows a systematic proper motion at a speed of 40 km s −1 (panel c), which is similar to the IRIS jet speed (panel e). There are no significant features in the IRIS Si or the AIA data sets co-located with this blob event. However, by the careful inspection of the IRIS Si data, we found short (≈a few arcseconds) elongated structures at the base of this event. They show shifting from east to west changing its inclination angle. Figure 2. ALMA blob-ejection event associated with a tall IRIS Mg ii jet. (a) Brightness
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