Magnetohydrodynamic nature of solar terminator-generated MS TIDs

• download

We analyzed the dynamic and spectral characteristics of the medium-scale travelling ionospheric disturbances
(MS TID). We used total electron content (TEC) measurements from the global network of GPS receivers (up
to 1500 stations) in 1998-2009 and the dense Japanese network GPS/GEONET (1220 stations) in 2008-2009.
Diurnal, seasonal, spectral and spatial-temporal MS TWP characteristics are determined by the solar termi-
nator (ST) dynamics and do not depend on the solar or geomagnetic activity. In the time field, TWPs are
narrow-band TEC oscillations of duration of about 1-2 hours with oscillation periods of 10-20 minutes. In
winter, TWPs in the northern hemisphere are observed 3-4 hours after the morning ST passage, when the TEC
time derivative achieves its maximum. In summer, TWPs are recorded 1.5-2 hours before the evening ST oc-
currence at the point of observations, but at the moment of the evening ST passage in the magneto-conjugated
area. The TWP spatial structure is of a high degree of anisotropy and coherence at the distance of more than
10 wavelengths; the TWP wavelength is about 100-300 km. Both the high quality-factor of oscillatory system
and synchronization of TWP occurrence with solar terminator passage at the point of observations and in the
magneto-conjugated area testify the MHD nature of ST-excited TWP generation. The obtained results are the
first experimental evidence for the hypothesis for the ST-generated ion sound waves (Huba et al., GRL, 2000,
27, 19, 3181).