An Investigation on Properties of Ionospheric Es in Hainan Region

In this study, using the DPS-4 digisonde data obtained in Hainan ionosphere observation station from March 2002 to February 2008, diurnal, seasonal and annual occurrence variations of the observed Sporadic E (Es) and its responding to the SSN are studied. The main results are as: The diurnal characteristic of h/c type Es had a single peak which was difierent from the double peak of the Es over Cachoeira Paulista, and the Es-q had two peaks (one in the morning and the other in the evening) which was also difierent from the Es-q occurrence (mainly in daytime) over Fortaleza, Brazil. The frequent season was spring, summer, summer and autumn for the f/l, h/c, q and r type Es, respectively. For the annual occurrence rate, the highest was f/l type Es, while the lowest was r type Es. The f/l and q type Es showed a clear increase with SSN and had a positive correlation with SSN during equinoxes and winter, while during summer the each type of Es showed no correlation with SSN. The mechanisms of the Es are also discussed. The ionosphere Sporadic E-layers (Es) appearing in the E region remain a mystery with their erratic and unpredictable appearance. They can serous afiect the wave propagation in the ionosphere. Some types of Es could often blanket echoes from the F-region. The Es-layer formation at lower latitudes is known to be quite difierent from those at middle and high latitudes. Studies on properties of the difierent type Es were conducted during the last decades. Abdu etal. reported the sporadic E-layer phenomena in the Brazilian geomagnetic anomaly (1). It gives an evidence for a regular particle ionization source. Abdu et. al. also studied the long term trends in the sporadic E- layer occurrences and associated electric flelds over the equatorial station (Fortaleza station) using 16 years (1975{1990) of ionosonde data (2). Reid studied the q-type Es echoes observed in the height region of 105{110Km in the daytime equatorial ionograms and suggested it is a manifestation of the type II irregularities of the equatorial electrojet (3). Wilkinson etal. studied the sporadic E-layers in the lower ionosphere and found that the h-type Es develops around 180Km and descending in sequential ionograms becomes c-type Es. The results also showed that the l and f type occur during the day time and night time, respectively (4). Some authors studied the mechanism of the difierent type of sporadic layers. Indeed, many authors have studied the sporadic E-layers using difierent regional observation data from the ionosphere, but got inconsistent results on the formation and mechanism of Es (2). It is because the ionosphere is complex and has not only globe properties, but also regional properties. Although some authors has studied the ionospheric processes and the mechanism of the Es (5{7), the sporadic E-layers properties and mechanism are still open questions and need to be further studied, especially, by observation. In this study, using digisonde data, a statistical analysis for properties of all type of the observed Es including Es-l/f, Es-h/c, Es-q and Es-r over the Hainan region has been performed. 2. DATA AND METHOD IN THE ANALYSIS The data used in this paper were obtained with the DPS-4 (a Digisonde Portable Sounder) located at Hainan, a low latitude ionospheric observation station with Geo-magnetic 179 - 08'E, 8 - 28'N from