Probability of ionospheric plasma bubble occurrence as a function of pre-reversal enhancement deduced from ionosondes in Southeast Asia

We employed the data from two ionosondes, one at Chumphon in Thailand and the other at Cebu in Philippines, during March and April from 2011 to 2015 to statistically disclose the probability of ionospheric plasma bubble (PB) occurrence as a function of pre-reversal enhancement (PRE). The PRE was estimated from the vertical motion of ionosphere F-region in the evening sector observed by ionosondes. The PB occurrence was indicated by the observation of spreading echo, so-called spread-F, in the ionograms of ionosondes. We found that the PB occurrence probability generally increases as increasing the PRE strength. From PRE of 0 m/s to 30 m/s, the probability of PB occurrence linearly enhances from 0 to 0.8. When PRE is higher than 30 m/s, the probability of PB occurrence is higher than 0.8. Hence, the PB always almost occurs when the PRE above 30 m/s. In fact, the PB occurrence probability equals to 1 for the PRE ≥40 m/s. Based on these findings, we also emphasize that the PRE of 30 m/s can be a threshold for the PB occurrence for Southeast Asian sector.