Investigation on Properties of Ionospheric Es Layer in Hainan Region

Using the observation data （Mar. 2002-Feb. 2005） from DPS-4 at Hainan ionospheric station, a statistic analysis for sporadic-E （Es） occurrence frequency in Hainan region in the descending phase of solar cycle has been performed. The seasonal variation and annual variation of occurrence of Es are mainly studied. The results show that, in the three years, Es occurrence in Hainan region is increasing with year. Esl and Esq occurs most frequently, next is Esr, then, Esc and Esf occurs lesser, ESh occurs least. Es occurs most frequently in Summer, secondly in Autumn and Winter, and most infrequently in Spring. Different type of Es has different properties, such as Es1 and Esq occurs almost every season, next is Esr, then, Esc, Esf and ESh occurs infrequently in any season, particularly, Esf almost disappears in Autumn. These results provide observation evidence for studying the physics mechanism of the ionospheric irregularity, it is also important to establish space weather predicting model on ionosphere.