Median TEC
To calculate the variations
of TEC value on one day we used the data of the Madrigal system
capable
of managing and serving archival and real-time data from a wide range
of ground-based instruments
(http://www.openmadrigal.org/). The TEC data is a diurnal file
containing the values of TEC for
different geographic points with a time step of 5 minutes. These data
were averaged by a 15-minute
window and distributed along a 180x360 grid in one-degree increments.
For each time moment, the
median value of TEC (TECmed) was calculated for the 27 previous days.
The TEC deviation from the
median value (∂TEC) was calculated by the formula:
∂TEC (lat, long, t) = (TEC (lat, long, t) - TECmed (lat, long, t))/
TECmed (lat, long, t),
where lat is latitude, long is longitude and t is UT. Thus the
processing of TEC data reproduces the
well-known technique from ionosonde data processing. As far as NmF2
gives the significant part of
TEC then TEC variations can be studied and analyzed in the same manner
as NmF2 temporal dynamics in
ionosonde studies.