... a study in kinematic GNSS

The timevarying ionosphere

The inosphere is in its nature varying over time. Standing on the surface of the Earth and looking up on the medium results in three main characteristics of the variation.

  • Daily
  • Yearly
  • 11 year solar cycle

These three timevarying parameters are not the same observed at different locations. The following data and analysis is based on a midlatitude location in Denmark at app. 56 degree North latitude.

The Total Electron Content (TEC) values are computed using a kalmanfilter with GNSS data from three permanent GNSS receivers as input. The GNSS receivers are operated by the National Survey and Cadastre. (See the full timeserie at TEC timeserie). The three receivers are separated by app. 130-200 km. which gives a good representation of the ionosphere medium above. Data are available from 1999-2007 including the peak of the last solar cycle.

Typical daily variation of the total electron content at winther time at a midlatitude locationA typical observation curve for the daily variation of the electron density is illustrated on the right. The example is from a winther day in 2004 the 28th of January. The values are low almost constant during the night and rise quickly at sunrise with a peak at around 1400 local time. The values degrades slower during the afternoon and last til just after sunset. The value at the peak at 1400 hours local time will vary depending on the soar activity, see section about solar cycle. If you are having difficulties reading the labels, please click on the picture for a full size.

Typical daily variation of the total electron content at summer time at a midlatitude location During the different seasons of the year the daily characteristics will be preserved, despite that the curves do not look alike. A typical daily variation is shown on the left. It is from the 19th of June 2004. It can be seen that the width of the daily peak is longer corresponding to the extended lenght of day. The nighttime constant part has a larger amplitude and the curve is more variable than during winther time. The amplitude of the peak at 1400 local time do not vary significantly though.