The sporadic E phenomenon as measured by an ionosonde station over Chiang Mai, Thailand

This paper proposes the critical frequency of sporadic E (foEs) measured from the FM/CW ionosonde at Chiang Mai (18.76°N, 98. 93°E, Dip 26. 3°), Thailand. The hourly values of foEs were analyzed by the total number of foEs occurrence and the percentage occurrence (%foEs) during the low solar activity period in 2010. The results show that the highest value of foEs appears 111 times (%foEs=32%) during sunset (18LT). For monthly observation, the most frequent occurrence of foEs occurs in June, when it appears 21 times (%foEs=75%).