5.1 Scenario – 1
In the first scenario, we introduced two Heaviside step functions () with an interval of 60 seconds into the synthetic HYDE04 IRI-TEC at 7:48 UT with an amplitude of 0.3 and 0.5 TECU to test the efficiency of the three methods in detecting sharp static variations.
– (9)
; – (10)
where TECs is synthetic IRI-TEC along HYDE04, is Heaviside step function, t is time and Asis amplitude of the step function in TECU.
Residual method, differential method and SPLA were employed to detect the simulated sharp static variations added to the synthetic TECs (Fig. 2, Top-middle). The efficiency of detecting ionospheric sharp static variations by these three methods was assessed by analyzing the rTEC, dTEC and gROT using a Continuous Wavelet Transform (CWT) described by Grinsted et al. (2004). CWTs with (Fig. 2, middle) and without (Fig. 2, left) sharp static variations show that gROT and dTEC precisely detect the sharp static variations. However, CWT of rTEC shows that the residual method identifies the sharp static variation akin to ionospheric perturbation spread out for a long duration (7.5 UT to 11 UT). Furthermore, the frequencies of the static variations detected by the residual method falls within the characteristic frequency band of acoustic and acoustic gravity wave induced ionospheric perturbations. Such sharp static variations can normally occur as observational errors associated with undetected loss of locks, cycle slips, or scintillation.