Abstract
We present the observation of tweek atmospherics with harmonics m = 1–8 during the solar maximum year, 2013, at Tay Nguyen University, Vietnam (Geog. 12.65° N, 108.02° E). The analysis of 33,690 tweeks on ten international quiet days during 2 months each season, summer (May, August), winter (February, November), and equinox (March, September), shows that tweeks occur about 51 % during summer, 22 % during winter, and 27 % during equinox. The D-region ionosphere is more sharply bounded for harmonics m = 5–6 around an altitude of 85.5 km. The environment of the D-region is more inhomogeneous during winter and equinox seasons. The mean electron density varies from 28.4–225 cm −3, which corresponds to the harmonics m = 1–8 at the mean reflection height of 81.5–87.7 km. The results reveal that the lower reference height in our work as compared to other works is due to the higher level of solar activity. The equivalent electron density profile of the nighttime D-region ionosphere using tweek method during summer, equinox, and winter seasons shows lower values of electron density by 12–58 %, 3–67 %, and 24–76 % than those obtained using the International Reference Ionosphere (IRI-2012) model.
Highlights
Collisions between charged and neutral particles dominate the physical interaction of the D-region ionosphere (∼60–90 km)
The SpectrumLab v2.77b22 records the sferics with audio files having extension “wav.” The Global Positioning System (GPS) is utilized for time synchronization with an accuracy of 100 ns
The higher harmonic tweeks often occurred during summer season, whereas lower harmonic tweeks mainly occurred during equinox and winter seasons (Table 1)
Summary
Collisions between charged and neutral particles dominate the physical interaction of the D-region ionosphere (∼60–90 km). These activities play an important role in the propagation of the extremely low frequency (ELF; 3–3000 Hz) and the very low frequency (VLF; 3–30 kHz) waves through the Earth-ionosphere waveguide (EIWG) (Hargreaves 1992; Kumar and Kumar 2013). The attachment and recombination processes are too fast and that makes the free electron density very low (
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