Interpreting Observations of Large‐Scale Traveling Ionospheric Disturbances by Ionospheric Sounders

Abstract

From July to October 2015, the Australian Defence Science and Technology Group conducted an experiment during which a vertical incidence sounder (VIS) was set up at Alice Springs Airport. During September 2015 this VIS observed the passage of many large‐scale traveling ionospheric disturbances (TIDs). By plotting the measured virtual heights across multiple frequencies as a function of time, the passage of the TID can be clearly displayed. Using this plotting method, we show that all the TIDs observed during the campaign by the VIS at Alice Springs show an apparent downward phase progression of the crests and troughs. The passage of the TID can be more clearly interpreted by plotting the true height of iso‐ionic contours across multiple plasma frequencies; the true heights can be obtained by inverting each ionogram to obtain an electron density profile. These plots can be used to measure the vertical phase speed of a TID and also reveal a time lag between events seen in true height compared to virtual height. To the best of our knowledge, this style of analysis has not previously been applied to other swept‐frequency sounder observations. We develop a simple model to investigate the effect of the passage of a large‐scale TID on a VIS. The model confirms that for a TID with a downward vertical phase progression, the crests and troughs will appear earlier in virtual height than in true height and will have a smaller apparent speed in true height than in virtual height.

A case study of the large-scale traveling ionospheric disturbances in the eastern Asian sector during the 2015 St. Patrick's Day geomagnetic storm

“…It provides clear examples of TIDs crossing the dip equator from the Southern Hemisphere to the Northern Hemisphere at around 09:00-12:00 UT. Their analysis shows that these TIDs may not have exceeded 30 • N. Such a poleward feature was also detected in other longitudinal sectors during this storm (Zakharenkova et al, 2016) and other storms (Pradipta et al, 2016;Jonah et al, 2018). In addition, Ding et al (2013) studied the polewardpropagating LSTIDs in southern China during a mediumscale storm in 2011.…”

“…Ding et al (2012) suggested that LSTIDs experience severe dissipation in southern China region due to viscosity and heat conductivity at low latitudes, which may account for the weakening of the equatorward-propagating wave-like structures. Besides this, Pradipta et al (2016) studied the interaction of the auroral LSTIDs from opposite hemispheres near the dip equator during the 26 September 2011 geomagnetic storm.…”

“…Ionospheric parameters from ionograms have been extensively used since early TID studies. Recently, ionograms and iso-frequency lines with different sampling rates were used in TID studies (Klausner et al, 2009;Ding et al, 2012Ding et al, , 2013Pradipta et al, 2016;Ramsingh et al, 2015;Habarulema et al, 2018). Figure 6 presents the temporal variations in the virtual height for each iso-frequency line.…”

A Study of the F2 Layer Stratification on Ionograms Using a Simple Model of TIDs

“…Therefore, the smaller horizontal wavelength of gravity waves could be more favorable to form the F2 stratification. Cervera and Harris (2014) and Pederick et al (2017) suggested that F2 cusp might be associated with small-and medium-scale TIDs but no significant effect for the large-scale TIDs. However, Figure 10 shows that large-scale TIDs (horizontal wavelength is about 1,200 km) could also form the F2 layer stratification (see blue circles at the observation time of 0, 5, 10, and 15 min).…”

A Robust Feature Extraction and Parameterized Fitting Algorithm for Bottom‐Side Oblique and Vertical Incidence Ionograms

“…The performance around the middle of UT day 95 was made worse by blanketing Es. Characteristic F2 signatures, such as the midday f oF2 bite-out (Kohl & King, 1967;Lynn et al, 2014) and quasiperiodic height fluctuations, in which h 0F2 commonly lags h mF2 due to the downward phase progression of traveling ionospheric disturbances (Cabrera et al, 2010;Pederick et al, 2017;Reinisch et al, 1997), are quite distinct in this data set.…”