Zhang DongHe

Observational study of daytime ionospheric irregularities associated with typhoon

Spread-F is a manifestation of ionospheric irregularities and generally takes place at nighttime. However, it can also be observed seldom at daytime. It is recognized that acoustic gravity waves (AGWs) play an important role in triggering plasma instability which results in spread-F in the ionosphere. The typhoon is a main source of the AGWs. In this paper, two cases of ionospheric daytime spread-F in the period of typhoon were analyzed. One case was on July 29, 1988 and the other was on August 01, 1989. The results showed the following: 1) There were some wave-like disturbances appearing in the HF Doppler records firstly, consequently the Doppler echo traces became scattered, which indicated that the ionospheric spread-F was triggered; 2) the blurred echo traces in the both two cases appeared in the morning (08:30–11:30 Beijing time) and lasted for more than two hours; 3) with the blurred echoes gradually weakening, the traveling ionospheric disturbances (TIDs) still existed and became clearer; 4) the frequency shifts in the two cases were both positive, implying the effective reflecting surface of the radio wave in the ionosphere moved downwards. These results provide good observational evidence for daytime spread-F during the typhoon period in Asian region.

Energetic particle radiations measured by particle detector on board CBERS-1 satellite

Using the data measured by energetic particle detector on board CBERS-01 and-02 for the past five years, statistics was made to show the general features of MeV electrons and protons along a solar synchronous orbit at an altitude of 780 km. This height is in the bottom region of the Earth’s radiation belts. Detectors are inside the satellite cabinet and such continuous monitoring of particle radiation environment inside a satellite has seldom conducted so far. After a proper and careful treatment, it is indicated that the data inside satellite are well correlated with the radiation environment outside. Besides the agreement of the general distribution characteristics of energetic electrons and protons with similar observations from other satellites, attention is particularly paid to the disturbed conditions. Variations of particle fluxes are closely related with solar proton events, in general, electron fluxes of outer belt are well correlated with Dst index after three days’ delay while the electron injection occurred almost at the same day during great magnetic storms. It is confirmed that both energetic electrons and protons appear in the Polar Cap region only after the solar proton events.

Particle bursts in the inner radiation belt related to global lightning activity

Particle bursts (PBs), the phenomena characterized by short-term increases of particle counting rates (CRs), were observed by space-borne radiation belt particle detectors. With the electron CR data obtained by National Oceanic and Atmospheric Administration (NOAA)-18 satellite, the occurrence of PBs in the inner belt (1⩽L⩽2 and B⩾20.5 μT) were derived for years 2006–2011. The monthly occurrence number of PBs exhibits a strong maximum in northern summer (May–August). In association with global lightning data, the seasonal occurrence of PBs is found to be consistent with the lightning activity, especially if only lightning flashes at latitudes >20° are taken into account. The positive correlation between PBs and mid-latitude lightning discharges indicates the role of lightning-induced whistler waves, and is consistent with the expected pitch-angle scattering by wave-particle interactions. The contribution of lightning is so significant that it forms a non-negligible seasonal background of PBs. If one connects PBs to seismoelectromagnetic emissions (SEME) in attempt to find the earthquake precursor, the lightning background needs to be considered with great care.

Ionospheric absorption and planetary wave activity in East Asia sector

In this paper, we focus on ionospheric absorption in the East Asia sector, and look for manifestations of atmospheric influences in this area. First, a 4-year historical record of absorption measurement at Beijing is presented. This record was obtained by a sweep frequency technique, in which 27-days periodic variation of the absorption level was found to be dominant, appearing in most seasons except winters. Instead, unusual enhancements of the absorption level appeared in winters (winter anomaly), at the meantime the level varied with periods mainly in the range of 8–12 days. Comparing to 27-days period from the Sun, the shorter period oscillations should be related to planetary wave activities in lower atmosphere. Second, fmin data from 5 mid-latitude ionosondes in Japan were used as an indirect but long-term measurement. With the fmin data covering two solar cycles, disturbances with various periods were found to be active around solar maximum years, but the 8–12 days oscillations always existed in winter, showing seasonal dependence instead of connection to solar activity. These results given in this paper demonstrate seasonal and solar cycle-dependent features of the ionospheric absorption in East Asia sector, and confirm the existence of influence from atmosphere-ionosphere coupling in this area, as well as the relationship between ionospheric winter anomaly and planetary wave activity.