Vertical shear at the equatorial F-region ionosphere during post-sunset hours

The characteristics of the equatorial F-region zonal plasma drift during post-sunset period have been investigated using the multi-frequency HF Doppler radar. The pattern of the zonal plasma drift is such that it starts with a westward drift during the pre-sunset hours, followed by an eastward drift shortly after the E-region sunset. The zonal plasma drift is characterized by the presence of a positive vertical shear around the post-sunset period and maximum shear is observed at the time of the peak of the pre-reversal enhancement in the vertical drift. The presence of vertical shear in the zonal drift is associated with the post-sunset velocity vortex existing at the equatorial F-region.     

Earthquake induced dynamics at the ionosphere in presence of magnetic storm

The modifications induced in the dynamics of the ionosphere by the major Japan earthquake (EQ) of March 11, 2011 (epicenter at 38.322°N, 142.369°E, M = 8.9) in presence of a magnetic storm are examined by mapping latitudinal variations of F-layer ionization density (NmF2) from 22 stations covering the epicenter zone. The changes forced into the Total Electron Content (TEC) by the major EQ in the magnetic storm ambiance are also examined from the GPS data collected at Guwahati (26° 10′ N, 91° 45’ E), situated in the major fault system of East Asia. The contributions of pre-seismic electric field as well as of magnetic storm time electric field in the observed density variations are brought into the ambit of discussion. The influence of lower atmosphere in shaping TEC features during the study case is highlighted. The effects of solar activity on density variations during such complex ambiances are also addressed.     

Variability of foF2 in the African equatorial ionosphere

This paper presents the impact of diurnal, seasonal and solar activity effects on the variability of ionospheric foF2 in the African equatorial latitude. Three African ionospheric stations; Dakar (14.8°N, 17.4°W, dip: 11.4°N), Ouagadougou (12.4°N, 1.5°W, dip: 2.8°N) and Djibouti (11.5°N, 42.8°E, dip: 7.2°N) were considered for the investigation. The overall aim is to provide African inputs that will be of assistance at improving existing forecasting models. The diurnal analysis revealed that the ionospheric critical frequency (foF2) is more susceptible to variability during the night-time than the day-time, with two peaks in the range; 18–38% during post-sunset hours and 35–55% during post-midnight hours. The seasonal and solar activity analyses showed a post-sunset September Equinox maximum and June Solstice maximum of foF2 variability in all the stations for all seasons. At all the stations, foF2 variability was high for low solar activity year. Overall, we concluded that equatorial foF2 variability increases with decreasing solar activity during night-time.     

Four-peak longitudinal distribution of the equatorial plasma bubbles observed in the topside ionosphere: Possible troposphere tide influence

In this paper we consider an idea of the troposphere tide influence on the character of the longitudinal variations in the distribution of the equatorial plasma bubbles (EPBs) observed in the topside ionosphere. For this purpose, the obtained EPB longitudinal patterns were compared with the thermosphere and ionosphere characteristics having the prominent “wave-like” longitudinal structures with wave number 4, which are uniquely associated with the influence of the troposphere DE3 tides. The characteristics of the equatorial mass density anomaly (EMA), equatorial ionization anomaly (EIA), zonal wind and pre-reversal E?×?B drift enhancement (PRE) were used for comparison. The equinox seasons during high solar activity were under consideration. It was obtained that the longitudinal patterns of the EMA and zonal wind show the surprising similarity with the EPB distributions (R???0.8, R???0.72). On the other hand, the resemblance with the ionosphere characteristics (EIA, PRE) is rather faint (R???0.37, R???0.12). It was shown that the thermosphere zonal winds are the most possible transfer mediator of the troposphere DE3 tide influence. The most successful moment for the transfer of the troposphere DE3 tide energy takes place in the beginning of the EPB production, namely, during the seed perturbation development.     

Variability of foE in the equatorial ionosphere with solar activity

This research examined the variability of f_oE in the equatorial ionosphere with solar activity within the equatorial ionospheric anomaly region. Ionosonde data recorded at Ouagadougou (lat. 12.4°N, long. 1.5°W and magnetic dip 1.43°N) were engaged to study the transient variations of the critical frequency of the E-layer (f_oE) and its dependence on solar activity. The study revealed that f_oE increases with the increase in solar intensity of the sun. The variability of the f_oE decreases with increases in the solar activity. The maximum value of the f_oE is at local noon when the ionosphere is stable; the variability at this local time is minimal. The minimum value of the f_oE is at sunrise and sunset, at this period on local time the equatorial ionosphere recorded its maxima variability. Irrespective of the degree of solar activity, f_oE is observed to be maximum in June solstice, followed by the equinoxes and minimum in December solstice. Equinoctial asymmetry occurred in the variation of the relative standard deviation of f_oE with maximum in September/March equinox for low/high solar activity.     

利用THEMIS卫星观测结果分析亚暴期间等离子体片尾向膨胀

利用THEMIS卫星观测结果,分析2008年3月13日10：40UT-12：10UT的一次中等亚暴事件在磁尾的全球演化过程.在该过程中,THEMIS的5颗卫星在午夜区附近沿x轴依次排列,离地心距离约8.7~13.2R_e.亚暴触发开始后,磁场偶极化和等离子体片的膨胀依次被在磁尾不同位置的卫星观测到.等离子体尾向膨胀的平均速度约为140km·s^-1.在此次亚暴事件中可观测到两种类型的偶极化.一种为偶极化锋面,其与爆发性整体流（BBF）密切相关;另一种为全球偶极化,其与等离子体片的膨胀密切相关.亚暴触发开始约7min后,THEMIS卫星在低中高纬都可以观测到Pi2脉动的发生,且Pi2脉动的振幅随着纬度的升高逐渐变大.此次亚暴事件中的离子整体流速度主要是由离子电漂移速度引起的,测得的电场为局地磁通量变化导致的感应电场.     

等离子喷涂纳米TiO2涂层及其光催化性能

原始喷涂粉末经过喷雾干燥法造粒,采用等离子喷涂工艺在普通载玻片上制备了纳米TiO₂涂层,并对涂层在300℃,400℃,500℃进行热处理.采用X射线衍射(XRD)方法对TiO₂涂层进行了相结构分析;用扫描电子显微镜(SEM)、透射电子显微镜(TEM)观察涂层的微观形貌;用压汞方法测量涂层的孔隙率.结果表明,喷涂后锐钛矿型TiO₂含量大约在30%~50%,粒径10~30nm,孔隙率小于6%,热处理后涂层更致密,孔隙率降低.喷涂电流为400A且未经过热处理的TiO₂涂层具有最佳光催化效果.     

Investigation of precursory phenomena in the ionosphere,atmosphere and groundwater before large earthquakes of M > 6.5

Precursory phenomena in the ionosphere, atmosphere and groundwater before large earthquakes (M > 6.5) are extensively investigated toward the earthquake prediction. Upward tornado type seismic clouds occurred near the epicenter associated with strong LF-VLF radio noises from lightning discharges in the evening of January 9, 1995 [Yamada, T., Oike, K. On the increase of electromagnetic noises before and after the 1995 Hyogo-Ken Nanbu earthquake. In: Hayakawa M. (Ed.), Atmospheric and Ionospheric Electromagnetic Phenomena Associated with Earthquakes. TERRAPUB, Tokyo, pp. 417–427, 1999] and anomalous foEs increases up to 10 MHz were detected at Shigaraki, 90 km of the epicenter and at Kokubunji, 500 km east of the epicenter [Ondoh, T. Anomalous sporadic-E layers observed before M7.2 Hyogo-ken Nanbu earthquake; Terrestrial gas emanation model. Adv. Polar Upper Atmos. Res. 17, 96–108, 2003; Ondoh, T. Anomalous sporadic-E ionization before a great earthquake, Adv. Space Research 34, 1830–1835, 2004] associated with strong ELF noises from lightning discharges in the daytime on January 15, 1995 [Hata, M., Fujii, T., Takumi, I. EM precursor of large-scale earthquakes in Japan, in: Abstracts of International Workshop on Seismo Electromagnetics (IWSE 2005), Univ. Electro-Communications, Chofu, Tokyo, Japan, March 15–17, pp. 182–186, 2005] before the M7.2 Hyogoken–Nanbu earthquake of January 17, 1995. The anomalous foEs increases occurred at epicentral distances within 500 km that are the same as those of the terrestrial gas emanations along active faults before large earthquakes [King, C.-Y. Gas geochemistry applied to earthquake prediction: An overview. J. Geophys. Res. 91(B12), 12269–12281, 1986]. The anomalous foEs increases seem to be a seismic precursor because geomagnetic and solar conditions were very quiet all day on January 15,1995 and the normal foEs in Japanese winter is below 6 MHz. No significant pre-seismic geomagnetic field variation was detected at epicentral distance of 100 km before this earthquake [Ondoh, T., Hayakawa, M. Anomalous occurrence of sporadic-E layers before the Hyogoken–Nanbu earthquake, M7.2 of January 17, 1995. In: Hayakawa, M. (Ed.), Atmospheric and Ionospheric Electromagnetic Phenomena Associated with Earthquakes, TERRAPUB, Tokyo, pp. 629–639, 1999; Ondoh, T., Hayakawa, M. Seismo discharge model of anomalous sporadic E ionization before great earthquakes. In: Hayakawa, M., O.A. Molchanov, (Eds.), Seismo Electromagnetics: Lithosphere–Atmosphere–Ionosphere Couplings, TERRAPUB, Tokyo, pp. 385–390, 2002; Ondoh. T., Hayakawa, M. Synthetic study of precursory phenomena of the M7.2 Hyogo-ken Nanbu earthquake. Phys. Chem. Earth 31, 378–388, 2006]. The foF2 decrease and h’F increase occurred before the M7.8 Hokkaido Nansei-Oki earthquake of July 12,1993 in a geomagnetic quiet period [Ondoh, T. Ionospheric disturbances associated with great earthquake of Hokkaido southwest coast, Japan of July 12, 1993. Phys. Earth Planet. Interiors. 105, 261–269, 1998; Ondoh, T. Seismo ionospheric phenomena. Adv. Space Res. 26, 8, 1267–1272, 2000]. Characteristic phase changes at terminator times of Omega 10.2 kHz waves passing 70 km of the epicenter extended toward darker local times by 1 h for 3 days before this earthquake due to lowering of the wave reflection height or ion density increases in the D region [Hayakawa, M., Molchanov, O. A., Ondoh, T., Kawai, E. The precursory signature effect of the Kobe earthquake on VLF subionospheric signals. J. Commun. Res. La., 43, 00. 169–180, 1996]. The radon concentration in the atmosphere over Ashiya fault, Kobe [Yasuoka, Y., Shinogi, M. Anomaly in atmospheric radon concentration: a possible precursor of the 1995 Kobe, Japan, earthquake. Health Phys. 72(5), 759–761, 1997] and in the groundwater at 17 m well in Nishinomiya, Japan [Igarashi, G., Saeki, S., Takahata, N., Sumikawa, K., Tasaki, S., Sasaki, Y., Takahashi, M., Sano, Y. Ground-water radon anomaly before the Kobe earthquake in Japan. Science 269, 60–61, 1995] had gradually increased since 2 months before the M7.2 earthquake, increased suddenly in December 1994, and rapidly returned to the normal low level of October, 1994 [Yasuoka, Y., Shinogi, M. 1997. Anomaly in atmospheric radon concentration: a possible precursor of the 1995 Kobe. Japan, earthquake. Health Phys. 72(5), 759–761.]. Radon concentration changes in the groundwater before the M 7.0 Izu-Oshima-kinkai earthquake, Japan on January 14, 1978 [Wakita, H., Nakamura, Y., Notsu, K., Noguchi, M., Asada, T. 1980. Radon anomaly: a possible precursor of the 1978 Izu-Oshima-kinkai earthquake. Science 207, 882–883] and the M6.8 Chengkung earthquake, Taiwan on December 10, 2003 [Kuo, T., Fan, K., Chen, W., Kuochen, H., Han, Y., Wang, C., Chang, T., Lee, Y. Radon anomaly at the Antung Hot Spring before the Taiwan M6.8 Chengkung earthquake. Proceedings, Thirty-First Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, California, January 30–February 1, 2006, SGP-TR-179, 2006] are also investigated to find common features of the groundwater radon concentration changes before large earthquakes (M > 6.5) in comparison with those before the M7.2 Hyogoken–Nanbu earthquake. Groundwater radon concentrations before the 3 large earthquakes had shown common characteristic changes of gradually initial ones from the normal level since about 2 months before the earthquake onsets, rapid decreases down to the minimum, and quick increases up to the maximum at 7–20 days before the earthquake onsets, respectively. These are very useful characteristics of pre-seismic radon anomaly for the earthquake prediction or warning. Promising observations toward the earthquake prediction are also discussed.