5:15 PM - 6:45 PM
[PEM12-P20] Analysis of Ionospheric Disturbances Associated with Typhoon NANMADOL in 2022 Using HF Doppler and GPS Radio Occultation Observations
Keywords:Typhoon Nanmadol, Ionospheric Disturbances, HF Doppler Sounding, GPS Occultation Observation
Ionospheric disturbances caused by typhoons are often examined by GPS-TEC data. Therefore, detailed propagation characteristics at the temporal scale of seconds have not been studied yet. This study aims to examine the detailed propagation characteristics of ionospheric disturbances caused by typhoons using HF Doppler observations, which have good temporal resolution, and GPS radio occultation observations, which allow the altitude profile of electron density to be calculated.
The target of the analysis is Typhoon No. 14 (NANMADOL), which occurred in September 2022. This typhoon formed as a tropical cyclone in the south of Japan on September 12 and dissipated at 6:00 UT on September 20. The analysis covers the period from September 15 to September 21. We utilized it by HFD sounding system operated by five institutions and GPS radio occultation observations using Formosat-7/COSMIC-2 data provided by Taiwan analysis center for COSMIC (TACC). The HFD observation system can observe variations in ionospheric altitude using the Doppler effect. The frequency characteristics of typhoons were investigated by dynamic spectral analysis of the time series data of HF Doppler frequencies produced by the HFD observations. GPS radio occultation observations yielded altitude profiles of electron density. The wavelength of the variation was analyzed using wavelet transforming in the altitude direction.
Concurrent analysis of HF Doppler observation and GPS Occultation revealed an increase in the variation component at a wavelength of 16 km during the typhoon’s approach and an increase in the component of variation at a wavelength of 2 km at the closest approach. The frequency spectrum of the variation between 2 and 32 km corresponds to several 10 to several 100 mHz, and the analysis of the HFD observation results also showed a similar increase in the high-frequency component of the variation. Next, we examined ionospheric disturbances during the daytime hours using HFD data observed at Sugadaira. The low-frequency component also intensified with the typhoon's intensity in addition to the high-frequency component. Atmospheric gravity waves generated by typhoons can be categorized into two propagation modes: acoustic mode and gravity mode. The increase in fluctuations of high-frequency components of several 10 mHz can be attributed to the acoustic mode. On the other hand, the increase in low-frequency components observed at the Sugadaira station can be attributed to the gravity wave mode. From these results, it is considered that internal gravity waves generated by typhoons affect the ionosphere with two types of propagation characteristics.
The target of the analysis is Typhoon No. 14 (NANMADOL), which occurred in September 2022. This typhoon formed as a tropical cyclone in the south of Japan on September 12 and dissipated at 6:00 UT on September 20. The analysis covers the period from September 15 to September 21. We utilized it by HFD sounding system operated by five institutions and GPS radio occultation observations using Formosat-7/COSMIC-2 data provided by Taiwan analysis center for COSMIC (TACC). The HFD observation system can observe variations in ionospheric altitude using the Doppler effect. The frequency characteristics of typhoons were investigated by dynamic spectral analysis of the time series data of HF Doppler frequencies produced by the HFD observations. GPS radio occultation observations yielded altitude profiles of electron density. The wavelength of the variation was analyzed using wavelet transforming in the altitude direction.
Concurrent analysis of HF Doppler observation and GPS Occultation revealed an increase in the variation component at a wavelength of 16 km during the typhoon’s approach and an increase in the component of variation at a wavelength of 2 km at the closest approach. The frequency spectrum of the variation between 2 and 32 km corresponds to several 10 to several 100 mHz, and the analysis of the HFD observation results also showed a similar increase in the high-frequency component of the variation. Next, we examined ionospheric disturbances during the daytime hours using HFD data observed at Sugadaira. The low-frequency component also intensified with the typhoon's intensity in addition to the high-frequency component. Atmospheric gravity waves generated by typhoons can be categorized into two propagation modes: acoustic mode and gravity mode. The increase in fluctuations of high-frequency components of several 10 mHz can be attributed to the acoustic mode. On the other hand, the increase in low-frequency components observed at the Sugadaira station can be attributed to the gravity wave mode. From these results, it is considered that internal gravity waves generated by typhoons affect the ionosphere with two types of propagation characteristics.