Abstract: Ionospheric delay is one of the most serious error sources in GNSS (Global Navigation Satellite System). For singlefrequency GNSS aircraft users, it is essential to apply an effective and simple broadcast ionospheric model to mitigate the ionospheric delay. The classical Klobuchar ionospheric model has a relative error of 50%～60%. In 45°(N) belt, a higher accuracy of correcting is needed. Considering the significant impact of season on the ionosphere in middle and high latitudes, GIMs (Global Ionospheric Maps) were analyzed for the variation of nighttime TEC (Total Electron Content) valleys with seasons and the variation of daytime TEC peaks with seasons. By improving the amplitudes of the cosine term and nighttime term in the classical model without adding extra coefficient, a Klobucharlike ionospheric model suitable for flightcongested latitudes was proposed. With GIM as a reference, the ionospheric relative errors of the new model for nighttime and for daytime reach 82% and 80% respectively,suggesting the new model has the better accuracy in depicting the ionospheric delay of the area.

Key words: Klobucharlike model, broadcast ionospheric model, ionospheric delay；global positioning system