Critical assessment of the forecasting capability of L-band scintillation over the magnetic equatorial region – Campaign results

• Campaign to assess the L-band scintillation forecast method of Sridharan et al. (2012) conducted.
• The uncertainties due to moving platforms reduced by making use of geo stationary platforms.
• The fluctuating component of f0F2 from ground used as a measure of perturbations.
• The zonal velocity estimated using the time delays in the GPS and GSAT scintillations accounted for.
• Threshold levels have been defined for the upward velocity, h׳F and plasma scale length.

A critical evaluation of the novel method suggested by Sridharan et al. (2012) to forecast L-band scintillation is made using the results from a special campaign conducted from Trivandrum (8.5°N, 76.91°E, dip latitude 0.5°N), India, during April 2012. The significance of the campaign lies in the fact that, (1) efforts are made to minimise the uncertainties due to the movement of the satellite platform (TEC and S4 observations from GNSS satellites) by choosing a recently launched GSAT-8 geostationary satellite for ionospheric scintillation in L1 band, (2) unlike the previous study (Sridharan et al., 2012) wherein the GPS derived TEC fluctuations were treated as representative of ionospheric perturbations, in the present exercise, the fluctuating component of the foF2 data from the ground based digital Ionosonde have been taken as a measure of the perturbations and (3) though both the GSAT and Ionosonde are stationary, still the ionospheric regions they represent are physically separated and in order to correlate the scintillation over the GSAT location to the forecast perturbations over the ionosonde location, the required zonal velocity of the perturbations/irregularities is estimated using GSAT and GPS scintillation data during one of the close-by GPS passes and this is taken to represent the particular solar epoch and season. Following the earlier method of Sridharan et al. (2012) the relative amplitudes and phase integrity of the perturbations have been maintained and extended throughout night. By adopting the above changes, it has been noted that the forecasting capability of L band scintillation has remarkably improved vindicating the role of perturbations in the evolution of the scintillation, thus making it more useful for practical applications. The nonoccurrence of scintillation on occasions in the prescribed time windows has also been understood based on the changes in the background conditions. A threshold upward velocity for the evening F-region as early as 1730–1830 LT, has been worked out to be 5 ms−1 for the ESF to get triggered and for its sustenance, a plasma scale length of <20 km along with a critical base height (h׳F) of 225 km have been evaluated as necessary background conditions.