A Statistical Study Of The Ionospheric Bottomside Profile Parameters

The International Reference Ionosphere (IRI) model is one of the most widelyused empirical ionospheric models. The most recent version of the IRI model,IRI-2001, implements new B0 and B1 tables to better determine the bottomsideelectron density profile (Bilitza, 2001). This paper displays a statistical study of B0and B1 over Wuhan and other 15 stations.First, the diurnal, seasonal, annual, and solar activity variations of the bottomsideprofile parameters B0 and B1 are studied using electron density profiles measuredover Wuhan (30.4°N, 114.4°E) with a DGS-256 digisonde during 1999-2004.Comparisons are made with the International Reference Ionosphere model (IRI-2001)using both the standard option (B0-Tab and B1-Tab) and the Gulyeava's option(B0-Gul and B1-Gul). The results show that: (1) In winter and equinox, B0 alsopresents morning and afternoon collapses as reported by Lei et al (2004). (2) B0increases about 18.6 km from low solar activity (LSA, F_10.7p=(F_10.7+F_10.7A)/2＜130) tohigh solar activity (HSA, (F_10.7p=(F_10.7+F_10.7A)/2＞170)). B1 in HSA is smaller thanthat in LSA after 10:00 LT, and its tendency is opposite during the rest time. B0increases with increasing solar activity, but B 1 slightly decreases with increasing solaractivity. (3) A magnetic disturbance has a sensitive effect on B1 and B0. Theamplitude and phase variations of B0 are not in accord with B1 during a magneticdisturbance. (4) Our B0 observations are in better agreement with the B0-Gul optionthan with the B0-Tab, though the B0-Gul option overestimates the observed B0 during09:00 to 17:00 LT in equinox and summer. B0-Tab is larger than the observations12-20 km over Wuhan almost all the time. Meanwhile, B1-Tab is in good agreementwith the observations. Annual variations of B1 have a semiannual cycle on 12:00 LTbut yearly cycle on 00:00 LT.Then, the diurnal, latitudinal and solar activity variations of the 16 stations'bottomside profile parameters B0 and B1 are studied using the data which besideWuhan are downloaded from Digital Ionogram DataBase. Comparisons are made with the International Reference Ionosphere model (IRI-2001). The analysis shows: (1)morning and afternoon collapses is an individual character of individual station. (2)B1 in Southern hemisphere always lager than 3. (3) Most B1 in high solar activity issmaller than that in low solar activity. (4) BO-Gul option always overestimates theobserved B0 near the largest value of diurnal B0. (5) The values of B0 are largest atequatorial latitude, then decreases in mid-latitude, after that it increases slow towardhigh-latitude. Latitudinal variations of IRI underestimate the observed B0 on Northernhemisphere at noon, in high solar activity they underestimate on equator' too, in lowsolar activity they overestimate on Southern hemisphere at midnight.(6) The value ofB 1 decreases from Southern hemisphere's high-latitude toward Southern hemisphere'smid-latitude, then it increases towards equator, next it decreases again towardNorthern hemisphere. B1 has a clear latitudinal variation and solar variation, both areneglected in IRI.In conclusion, the result shows some important result to improve the IRI. This isalso the purpose of this study.