For designing a digital High Frequency (HF) radio communication system in the skywave propagation mode, Delay spread and Doppler spread are the fundamental parameters of ionosphere channel characteristics that need to be known. Although the International Telecommunication Union (ITU) already provides general classification values for three different regions and conditions as a recommendation, the empirical Delay spread and Doppler spread values are still needed for an optimum design. As the role of HF communication in Indonesia is still important and its development technology is continued, the empirical data of ionosphere channel characteristics are also needed. However, the comprehensive empirical data of ionosphere channel characteristics over Indonesia is difficult to find. In this research, we developed an Ionosphere Channel Impulse Response (CIR) measurement system based on Software Defined Radio (SDR) with purpose to obtain the empirical values of Delay spread and Doppler spread. The measurement system is placed in Java Island Indonesia, which is in the Low latitude - Equatorial Ionosphere Anomaly (EIA) region. The specification of the system was determined based on the increased values of ITU parameters for low-latitude regions in order to be able to capture the possibility of higher values. The early measurement result shows slightly different values from ITU recommendation which is probably due to the EIA regions effect. This system is ready to collect further data to characterize the ionospheric communication channel comprehensively and investigate the space weather impact on HF communication systems.

We report our analysis of multi-diagnostic ionospheric observations over Indonesia following the 15 January 2022 Tonga volcano eruption. Observation data from the Indonesian GNSS CORS network, ionosondes, and GISTM receivers, in conjunction with the Himawari-8 satellite imagery, were used in the analysis. The Lamb waves from the eruption, traveling at ~310 m/s, reached eastern part of Indonesia (~5,000 km from Tonga) approximately 4 hours after the eruption. The Lamb waves traversed the Indonesian region for 4 hours and 40 minutes, around sunset period. As a result, some unseasonal equatorial plasma bubbles (EPBs) occurred over this longitude sector, with an earlier-than-usual onset time. There was a directional split in the zonal drift velocity of these EPBs, where some EPBs drifted eastward with a velocity of 138.0 ± 6.9 m/s and others westward with a velocity of 39.6 ± 2.0 m/s. At the same time, traveling ionospheric disturbances (TIDs) from the Tonga eruption also propagated over the Indonesian region with a velocity of 434.6 ± 21.7 m/s. In the total electron content (TEC) data, interactions between EPBs and TIDs were observed over the region. There were enhancements in the rate-of-TEC index (ROTI) and S4 scintillation index, indicating the presence of ionospheric density irregularities. A turbulent ionospheric F-layer, due to these EPBs and TIDs, caused either spread-F echoes or a loss of F-region traces in the ionograms. An intensification of sporadic-E layer, lasting for a few hours, was also observed in the ionograms.