A Statistical Study on Seismo-Ionospheric Anomalies of the Total Electron Content for the Period of 56 M≥6.0 Earthquakes Occurring in China During 1998—2012

This paper reports statistical results of Seismo-Ionospheric Anomalies(SIAs) of the Total Electron Content(TEC) in the Global Ionosphere Map(GIM) associated with 56 M≥6.0 earthquakes in China during 1998—2012.To detect SIA,a quartile-based(i.e.median-based) process is performed.TEC anomalies for the period of earthquakes without being led by magnetic storms about 10 days are further isolated and examined to confirm the SIP existence.Results show that SIA is the TEC significantly decrease in the afternoon period 2—9 days before the earthquakes in China,which is in a good agreement with the SIA appearing before the 12 May 2008 M 8.0 Wenchuan earthquake.

Interferometry observations of low-latitude E-region irregularity patches using the Sanya VHF radar

Interferometry plays an important role in revealing fine-scale structures of ionospheric irregularity.By placing an additional receiving array of four 5-element Yagi antennas in the north of the main East-West array of the Sanya VHF radar,multiple interferometry baselines with components parallel and perpendicular to the magnetic meridian are formed.These baselines allow us to study the three-dimensional(3D)behavior of low-latitude ionospheric field-aligned irregularity(FAI)over Sanya.Using multiple non-collinear receiving baselines,an experiment for which the Sanya VHF radar operated as an interferometer was performed on 10 July 2013.Ionospheric E-region FAI echoes with periods of several minutes were observed during 0745-0915 UT;mean Doppler velocity was around -30 m/s with spectral widths of about 50 m/s.The interferometry results show fine-scale structures of E-region FAI with a zonal scale size of 15 km or less.In addition,we found that the periodic variations of echo intensity shown in radar range-time-intensity(RTI)maps were produced by spatially separated E-region irregularity patches.The patches drifted westward with a velocity of about 40-60 m/s and could be associated with propagating gravity waves.These results provide a clearer picture of the characteristics of FAI and thus help to investigate the generation and dynamics of low-latitude ionospheric irregularities in the Chinese sector.

Monitoring traveling ionospheric disturbances using the GPS network around China during the geomagnetic storm on 28 May 2011

Larger-scale traveling ionospheric disturbances （LSTIDs） are studied using the total electron content （TEC） data observed from 246 GPS receivers in and around China during the medium storm on 28 May 2011. It is the first attempt to get the two-dimensional TEC perturbation maps in China. Two LSTID events are detected： one is in southwestern China before mid- night propagating from low to middle latitude to the distance of about 1200 km with the phase front extending to about 500 km, and the other is in northeastern China after midnight propagating from middle to low latitudes to the distance of about 1200 km with the phase front extending to nearly 1400 km. By using the multichannel maximum-entropy method, we get the propagation parameters of these two LSTIDs. The LSTID that occurs before midnight has a higher horizontal phase velocity and a larger damping rate corresponding to the after midnight LSTID, and this may be caused by the relatively large vertical back- ground TECo and high atmospheric temperature in the southwest of China before midnight. According to the variations of magnetic H component observed in high latitudes, the source region for the after midnight LSTID is likely to be located 1400-2600 km east of 140E and north of 42N; the before midnight LSTID is propably excited by the atmospheric gravity waves （AGWs） generated by the Joule heating of the equatorial electrojet.

3-D numerical calculation of magnetic drag parachute

The concept of using an externally applied magnetic field to add the drag force of a hypersonic reentry vehicle during the blackout was proposed by Bush in 1958.The increased drag force is caused by electromagnetic force that is introduced by interaction between the applied magnetic field and the weakly ionized airflow around the reentry vehicle.We investigated the influences of magnetic field intensities on the drag forces of a reentry vehicle by three dimensional(3-D)magnetohydrodynamics(MHD)simulation.The results showed that the drag fore exerted on the vehicle reached 25 kN when the magnetic field was 0.4 T.The drag force increased with the enhanced intial magnetic field.The bow shock was also pushed far away from the vehicle when the magnetic field was strengthened.

Comparing the diurnal variations in the SuperMAG auroral electrojet indices SML and SMU

Diurnal variations of the SuperMAG auroral electrojet indices(SML and SMU)were examined for the period of 1980–2010,and the differences between SML and SMU were especially analyzed.The diurnal variation of SML with a maximum at around 1100 UT has a prenoonpostnoon asymmetry.At solstices,the diurnal variation of SML is much stronger than that at equinoxes.For the SMU,two maxima are recorded in the diurnal variation with the bigger one at 1700 UT and the smaller one at 0400 UT.The seasonal variations are not obvious in the UT variation characteristics of SMU although the intensity of SMU is changed remarkably season by season.For both SML and SMU,the contributing stations are located at higher geomagnetic latitude around 1600 UT and at lower geomagnetic latitude around 0400 UT.These results indicate that:(1)the SML is mostly controlled by the convection electric field.Its diurnal variation is mainly correlated with the equinoctial and R-M hypothesis;(2)the SMU is largely controlled by the ionospheric conductance.Its diurnal variation is tightly correlated with the solar radiation.

A new technique for deriving the quiet day curve from imaging riometer data at Zhongshan Station, Antarctic

A new technique for estimating quiet day curve(QDC)was suggested.To validate the new approach,QDCs were derived from data acquired by the imaging riometer installed at the Chinese Zhongshan Station in Antarctic.The evaluation was performed by comparing the difference between QDC derived by the new technique and those derived by Tanaka’s technique.The results were discussed in terms of the diurnal variation and discrepancy.Also,cosmic noise absorption(CNA)images were built using both techniques in order to evaluate the implications of the changes when obtaining them using different methods of the QDC determination.The influence of the multiplicative factor value on the QDC determination in Tanaka’s technique was evaluated.