Abstract
Traveling ionospheric disturbances (TIDs) are wave-like disturbances in ionospheric plasma density. They are often observed during both quiet (medium-scale TID) and geomagnetically disturbed (large-scale TID) conditions. Their amplitudes can reach double-digit percentages of the background plasma density, and their existence presents a challenge for accurate ionosphere specification. In this study, we examine TID properties using observations obtained during two geomagnetically disturbed periods using multiple ground and space-borne instruments, such as magnetometers, Global Navigation Satellite System (GNSS) receivers, and the SWARM satellite. Reference quiet time observations are also provided for both storms. We use a thermosphere–ionosphere–electrodynamics general circulation model (TIEGCM) results to properly interpret TID features and their drivers. This combination of observations and modeling allows the investigation of variations of TID generation mechanisms and subsequent wave propagation, particularly as a function of different plasma background densities during various geophysical conditions. The trans-equatorial coupling of TIDs in the northern and southern hemispheres is also investigated with respect to attenuation and propagation characteristics. We show that TID properties during trans-equatorial events may be substantially affected by storm time background neutral wind perturbation.
Highlights
IntroductionOver the decades, since the initial work by Hines [1], a large variety of traveling ionospheric disturbances (TIDs) have been observed in the upper atmosphere
From top to bottom: solar wind speed (Vsw) abruptly increased after approximately 15 UT on 27 May 2017; the Bz component of the magnetic field of the interplanetary magnetic field (IMF) went down to −20 nT for more than three hours; the Sym-H index reached a pronounced minimum of −120 nT, which indicates an intense storm; the AE index increased suddenly from approximately 200 to 1500 nT; ∆H (Belem–Petrolina) behaved normally on days 26 and 27, but turned downward on day 28 opposite to the observed trend in plasma density and total electron content (TEC)
The first is relevant to a positive correlation between TID wave amplitude and background ionospheric density [1]; i.e., ∆Ne/Ne is determined primarily by atmospheric gravity wave (AGW) neutral disturbance properties as in the AGW dispersion and polarization relations
Summary
Since the initial work by Hines [1], a large variety of traveling ionospheric disturbances (TIDs) have been observed in the upper atmosphere. Kil and Paxton [14] investigated the role of MSTIDs in the creation of electron density irregularities in the middle latitudes using SWARM observations and concluded that MSTIDs can emerge as a source of irregularities during solstice season Ionospheric disturbances such as TIDs have been detected by many instruments, such as incoherent scatter radars, high-frequency (HF) Doppler sounders, ionosondes, radio telescopes [15], and airglow imagers [16]. Storm time thermospheric perturbations can be significant: using the incoherent scatter radar (ISR) technique to measure thermospheric wind, Vasseur [23] showed that wind speed under disturbance conditions can reach amplitudes as large as 200 m/s This value may exceed the horizontal phase velocity of acoustic waves, and the propagation of such waves in the atmosphere (especially those with a lower phase speed) is correspondingly expected to be influenced to a large degree by thermospheric winds [21]. In(tVesrwpl)anetdaartyamawgneerteic fioelbdta(iBnze)d, aurfororaml electhtreojet A(ACEE), sysmatmelelittreic mmagisnseiotinc: fihetltdpss:t/r/ewnwgtwh.(sSwypmc-.Hno),aian.gteorvp/lpanroedtaurcytse-laenctdri-cdfiateal.dIn(Eteyr)p, alanndeKtapryinmdaicgensewticerfeieoldbt(aBinz)e,daufrroomratlheeleNctAroSjAet d(AatEa)b,assyemnmetwetroirckmatahgnttept:i/c/ofmienldiwsterbe.nggsftch.n(Sasyam.g-oHv)., interplanetary electric field (Ey), and Kp indices were obtained from the NASA database network at http://omniw eb.gsfc.nasa.gov
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