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.