[P-EM12] [EE] Space Weather, Space Climate, VarSITI

[PEM12-33] Forecasting the day-to-day occurrence of equatorial spread F in Southeast Asia

*Prayitno Abadi¹, Yuichi Otsuka¹, Kazuo Shiokawa¹ (1.Institute for Space-Earth Environmental Research (ISEE), Nagoya University)

Keywords:Forecasting spread F, Pre-reversal enhancement, Threshold method, Space Weather

We used ionosondes in Chumphon (CPN) (10.72°N, 99.37°E; Mag. Lat: 3°N), Thailand; Bac Lieu (BCL) (9.30°N, 105.71°E; Mag. Lat: 1.5°N), Vietnam; and Cebu (CEB) (10.35°N, 123.91°E; Mag. Lat: 3.09°N), Philippines during equinox seasons from 2010 to 2016 to develop a forecast technique for equatorial spread F or plasma bubble generation. We considered that enhancement of vertical E × B drift after sunset in the equatorial region, so-called pre-reversal enhancement (PRE), is a primary factor for plasma bubble generation. We then used a "PRE threshold" to determine ESF whether generates or not. We collected 264, 121, and 206 nights for CPN, BCL, and CEB ionosondes, respectively. We used change of h'f in time (dh'f/dt) during 18-19 LT from three ionosonde sites as a proxy for the vertical drift. The threshold is simply defined with a average value of vertical drifts obtained from all stations, and the value is 24 m/s. We defined the PRE ≥ 24 m/s and PRE < 24 m/s for the ESF on and off, respectively. We then compared our threshold method with the real occurrence of ESF for all stations, and the skill score is ~0.7 for each station. We have also analyzed the skill scores by changing the threshold, and we found that the skill score of ~0.7 is a maximum for each station. Thus, our study show that, using the average value of PRE as a threshold, it is enough to forecast ESF occurrence in Southeast Asian longitude with the maximum skill score in the "PRE threshold" method.