Es Characteristics Of The Ionosphere In Low Latitudes (hainan)

Ionosphere is a very important region in solar-terrestrial space. Physical processes in this region are very complicated. Ionosphere is coupled with the upper neutral atmosphere and influencing its dynamics, and is highly responding to the solar and geomagnetic activities. Es are the irregularities in E-layer. The study of observational characteristic and physical mechanism about sporadic-E has a significant importance in understanding the physical processes in Es-layer and establishing the space weather model.Ionosphere can have notable influence on the electromagnetic wave propagation, refraction and its energy loss. Plasma frequency in ionosphere would influence the long wave, medium wave and short wave propagation. Ionospheric effects would also affect long-distance early warning and guidance radars.In this study, by using the observational data (Mar. 2002 - Feb. 2006) from DPS-4 at Hainan ionospheric station, a statistical analysis for sporadic-E(Es) occurrence frequency in Hainan region during the fall phase of solar cycle has been performed. The seasonal and annual occurrence variations of Es are mainly studied. Those statistical results have been compared with the Dst index to illustrate the relationship between Es occurrence and geomagnetic field. There are 6 types of Es in our statistical results, which are c, f, h, l, q, r. The main results are following: 1.Seasonal variationIn spring (March and April), the total occurrence frequency of Es is 670, there are 49 for type c,103 for type f, 44 for type h, 242 for type l, 141 for type q, and 91 for type r. We can note that Type l is the most frequent in all types, there is 36% q type Es; and the rarest is the c type Es, which take only 7%. In summer (May to August), the total occurrence of Es is 1829, there are 167 for type c, 85 for type f, 44 for type h, 412 for type l, 762 for type and 279 for type r. We can note that type q is most frequent in all types, there is 36% q type Es; and the rarest is the c type Es, which takes only 5%.In autumn (September and October), the total occurrence of Es is 570, there are 56 for type c,5 for type f, 16 for type h, 154 for type l, 170 for type q and 169 for type r. We can note that type q is most frequently in all types, there is 30% q type Es; and the rarest is the f type Es, which takes only 1%.In winter (November to next February), the total occurrence of Es is 1389, there are 75 for type c,132 for type f, 54 for type h, 503 for type l, 424 for type q and 201 for type r. We can note that type l is most frequently in all types, there is 36% q type Es; and the rarest is the h type Es, which takes only 4%.2.Annual variationThere are 989 Es occur in May 2002 to February 2003, including 80 times type c, 54 times type f, 17 times type h, 475 times type l, 267 times type q and 96 times type r. In this year, the most frequent is type l which takes 48%, and the rarest type is h which takes only 2%.There are 1118 Es occur in May 2003 to February 2004, including 40 times type c, 31 times type f, 35 times type h, 522 times type l, 463 times type q and 97 times type r. In this year, the most frequent is the type l which takes 44%, and the rarest type is f which takes only 3%.There are 1280 Es occur in May 2004 to February 2005, including 86 times type c, 127 times type f, 66 times type h, 220 times type l, 413 times type q and 368 times type r. In this year, the most frequent is type q which takes 32%, and the rarest type is h which takes only 5%.There are 1001 Es occurs in May 2005 to February 2006, including 98 times type c, 195 times type f, 81 times type h, 94 times type l, 354 times type q and 179 times type r. In this year, the most frequent is type q which takes 35%, and the rarest type is h which takes only 8%. 3.Relation between Es and geomagnetic activities All types of Es occurrences are positively related to Dst index. But the relationship between Dst index and total Es occurrences as well as the types which are dominating in every season, like type q and r, are very weak. In contrary, rare types, like type h, l, and c show very close relationship to Dst index. Some types of Es are positively related to Kp index, while others negatively. Type r shows close negative relation, and type l shows close positive relation. Type c, type f, and type h show weak negative relation to Kp index. Type q is a very typical Es in equator region, but it shows very weak positive relation to Kp index.As, during the period from 2002 to 2005 solar activity reduces, so all the conclusions we get can only adapt to the same time slice. The data in this paper is from a single ionosphere observation station. To further study the physical mechanism about ionosphere over equator region, we need data from different stations at the same time.