5:15 PM - 6:45 PM
[PEM15-P13] Observation of dynamical characteristics of sporadic E by HF Doppler sounding system
Keywords:Sporadic E layer, HF Doppler
Sporadic E (Es) layer is a layer of extremely high electron density that occurs mainly in summer at mid-latitudes around 100 km altitude. Es layer has been known to cause long-range anomalous propagation of radio waves in the VHF band because of the reflection due to an extreme increase of the electron density associated with Es layer. Es layer has been studied for more than half a century using various methods such as the MU radar and GPS-TEC because of its influence on aeronautical navigation systems and radio broadcasts that use the VHF band. However, the coverage of the MU radar is limited. The coverage of GPS-TEC is wide, however this techinique cannot observe Es layer directly.
In this research, we used the HF Doppler (HFD) observation in order to observe Es layer in a wide area. The HFD sounding system transmits two continuous waves, 5.006 MHz and 8.006 MHz from Chofu, Tokyo and the reflected waves are received at 11 observation stations in Japan. These observation stations also receive two broadcast waves, 3.925 MHz and 6.055 MHz from Nagara, Chiba. The system can detect the vertical motion of the ionosphere and dynamical characteristics of various ionospheric phenomena from variations of the Doppler frequency and received signal intensity derived from the received signal at multiple stations. The sampling rate of the raw waveform data is 100 Hz. The temporal resolution of the Doppler frequency and received signal intensity is 10 sec. The HFD observation is known to observe characteristic (quasi-periodic) Doppler spectral traces associated with Es layer, mainly at night during the summer season. If it is confirmed that the quasi-periodic Doppler trace is caused by radio waves reflected around 100 km altitude, it would be possible to observe Es layer in a wide area by using the HFD sounders.
We conducted observations of Es layer by using HFD in May and June 2022. On some days, the HFD observation system detected clear Doppler spectral traces. We assumed that Es layer propagated from transmitter sites to observation sites directly and simulated Doppler spectral traces. By comparing the simulation results and observation results, the reflection altitude would be about 100 km and the propagation speed would be about 140 m/s. These results were almost equal to features of Es layer revealed by previous researches. Therefore, we conclude that HFD can observe dynamical characteristics of Es layer.
We plan to estimate the reflection altitude and propagation speed at other observation sites and reveal dynamical characteristics of Es layer in a wide area.
In this research, we used the HF Doppler (HFD) observation in order to observe Es layer in a wide area. The HFD sounding system transmits two continuous waves, 5.006 MHz and 8.006 MHz from Chofu, Tokyo and the reflected waves are received at 11 observation stations in Japan. These observation stations also receive two broadcast waves, 3.925 MHz and 6.055 MHz from Nagara, Chiba. The system can detect the vertical motion of the ionosphere and dynamical characteristics of various ionospheric phenomena from variations of the Doppler frequency and received signal intensity derived from the received signal at multiple stations. The sampling rate of the raw waveform data is 100 Hz. The temporal resolution of the Doppler frequency and received signal intensity is 10 sec. The HFD observation is known to observe characteristic (quasi-periodic) Doppler spectral traces associated with Es layer, mainly at night during the summer season. If it is confirmed that the quasi-periodic Doppler trace is caused by radio waves reflected around 100 km altitude, it would be possible to observe Es layer in a wide area by using the HFD sounders.
We conducted observations of Es layer by using HFD in May and June 2022. On some days, the HFD observation system detected clear Doppler spectral traces. We assumed that Es layer propagated from transmitter sites to observation sites directly and simulated Doppler spectral traces. By comparing the simulation results and observation results, the reflection altitude would be about 100 km and the propagation speed would be about 140 m/s. These results were almost equal to features of Es layer revealed by previous researches. Therefore, we conclude that HFD can observe dynamical characteristics of Es layer.
We plan to estimate the reflection altitude and propagation speed at other observation sites and reveal dynamical characteristics of Es layer in a wide area.