tokens: opposite polarity (see the orange and black arrows in Figures 5 (f) and (g), respectively). Noticeably, at the end of the penumbra formation process (Figure 5 (j)), the penumbra covers only half of the umbra, the one facing the opposite polarity. 3.2. Velocity Pattern In Table 2 we report the presence of the inverse Evershed flow. In particular, in 11 spots we observe a flow of opposite sign with respect to that observed when the penumbra has formed, i.e., an inverse Evershed flow. In Figure 6 , we show images of the continuum and LOS velocity maps for the following polarities of the AR 11610 and 11630, respectively. In these cases the inverse Evershed flow was clearly detected before the penumbra formation, although this process has already started. Figure 6. From top to bottom: zoom of the continuum and LOS velocity maps of the following sunspot of AR 11610 ((a)–(h)) and of the following sunspot of AR 11630 ((i)–(p)). The boxes in all of the panels indicate the regions where we calculated the values of the velocity reported in Table 3 . Table 3 reports the mean values of the velocity before and after the penumbra formation, calculated inside the boxes shown in Figure 6 . Table 3 LOS Velocity around Sunspots In fact, in AR 11610, despite that the penumbra surrounds almost all of the umbra, there is a sector without penumbra on the eastern side of the following spot where we observe the onset of the Evershed flow in about 6 hr. The mean velocity before the onset of the Evershed flow is around −160 m s −1 , which becomes 210 m s −1 when the penumbra is completely formed. Concerning AR 11630 (Figure 6 (i)–(p)), we observe at 11:00 UT (Figure 6 (m)), when no penumbra filament is present (Figure 6 (i)), that most of the area inside the black square is redshifted, with a mean velocity of about 220 m s −1 . After 1 hr, filaments appear and the area becomes blueshifted (see Figures 6 (j) and (n)). 4. Discussion and Conclusions In this paper we studied the penumbra formation in 12 ARs. We followed the evolution of the preceding and following spots using continuum and LOS velocity maps and, depending on where the first penumbral sector started to form, we classified the following and preceding polarities of each AR. Despite the fact that not all of the spots in our sample are fully surrounded by a penumbra, we found that the last penumbral sector does not always appear on the side toward the opposite polarity (see the preceding polarity of AR 11150 in Figure 5 ), contrarily to what was reported by Zwaan ( 1992 ). We found that in eight spots the first stable penumbral sector formed on the side toward the opposite polarity, and in nine spots it formed away from the opposite polarity (see Table 2 ). We can also note that the time needed to form the penumbra seems to be related to the side where the penumbra appears. In particular, it seems that the penumbra formation in B-type spots is quicker (about 21 hr) than in the A-type spots (about 39 hr). In
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