Shi Jian-Kui

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.

A Three-Dimensional Ray Tracing Study on Whistler-Mode Chorus During Geomagnetic Activities

A three-dimensional ray tracing study of a whistler-mode chorus is conducted for different geomagnetic activities by using a global core plasma density model. For the upper-band chorus, the initial azimuthal wave angle affects slightly the projection of ray trajectories onto the plane (Z, root(x(2) + y(2))), but controls the longitudinal propagation. The trajectory of the upper-band chorus is strongly associated with the plasmapause and the magnetic local time (MLT) of chorus source region. For the high geomagnetic activity, the chorus trajectory moves inward together with the plasmapause. In the bulge region, the plasmapause extends outward, while the chorus trajectory moves outward together with the plasmapause. For moderately or high geomagnetic activity, the lower-band chorus suffers low hybrid resonance (LHR) reflection before it reaches the plasmapause, leading to a weak correlation with the geomagnetic activity and magnetic local time of the chorus source region. For low geomagnetic activity, the lower-band chorus may be reflected firstly at the plasmapause instead of suffering LHR reflection, exhibiting a propagation characteristic similar to that of the upper-band chorus. The results provide a new insight into the propagation characteristics of the chorus for different geomagnetic activities and contribute to further understanding of the acceleration of energetic electron by a chorus wave.

Acceleration of Ionospheric Out-Flowing Ions in the Substorm in Geo-magnetotail

Using dynamics equation, acceleration of out-flowing ion during dipolarization in a substorm in the magnetotail is simulated. The main results show that: (1) The ion distribution function that is initially exponentially decreasing with increasing speed is turned into a single peak distribution, and with time the peak moves towards higher speed. (2) The peak moves along V⊥ faster than that along V||, and the ion acceleration mainly occurs in the middle of the dipolarization. (3) The higher the initial energy, the faster the peak moves, and the more energy is obtained by the ions. The ion energy theoretically calculated is as high as about 102 keV, this is consistent with the observation.

Field-Aligned Electrons in Polar Region Observed by Cluster on 30 September 2001

The physical process in the Earths polar region is very complex and still needs to be further studied. Using the data from Cluster satellite measurement, an analysis on field-aligned electrons in the mid-latitude cusp on 30 September 2001 has been performed. The satellite observed a down-flowing electron event in the low-latitude boundary and a sequential up-flowing electron event in the high-latitude boundary of the cusp region. The down-flowing electron had a velocity as high as 500 km/s and a flux of 2.0 x 10(9) cm(-2).s(-1). The up-flowing electron had a velocity up to 1200 km/s and a flux of 4.9 x 10(9) cm(-2).s(-1). Both the velocity and the flux observed in this event are the maximum values of the up-flowing electrons observed by all satellites to date. The electron is the main contributor for the field-aligned current in this event. The physical mechanism is also discussed. The down-flowing electron in the low-latitude boundary of the cusp region may result from solar wind injecting during the southward IMF, and the up-flowing electrons in the high-latitude boundary of cusp may result from mirroring of the solar wind, or from the ionospheric up-flowing electrons which have been accelerated.

Properties of Field Aligned Current in Plasma Sheet Boundary Layers in Magnetotail: Cluster Observation

Field aligned current (FAC) distribution in the plasma sheet boundary layers (PSBLs) in the magnetotail is studied statistically by analysing magnetic field data from the Cluster 4-point measurements. The results show that the FAC distribution on the dusk side is not the same as that on the dawn side in the magnetotail. On the each side earthward and tailward, FAC occurrences are different; occurrence and average current density of FACs in the northern hemisphere are different from those in the southern hemisphere. This implies that the FACs have dusk-dawn side asymmetry, polarity asymmetry and inter hemisphere difference in the magnetotail. The present results give a good observation evidence for study on the FAC mechanism.

Influence of Generalized (r, q) Distribution Function on Electrostatic Waves

Non-Maxwellian particle distribution functions possessing high energy tail and shoulder in the profile of distribution function considerably change the damping characteristics of the waves. In the present paper Landau damping of electron plasma (Langmuir) waves and ion-acoustic waves in a hot, isotropic, unmagnetized plasma is studied with the generalized (r,q) distribution function. The results show that for the Langmuir oscillations Landau damping becomes severe as the spectral index r or q reduces. However, for the ion-acoustic waves Landau damping is more sensitive to the ion temperature than the spectral indices.

Investigation of Total Absorption of Radio Waves in High Latitude Ionosphere

Using the digisonde data observed at ionospheric station Norilsk (Dip lat. 60 degrees N) in 2006, a statistical study on the characteristics of the ionospheric plasma total absorption of radio waves (IPTAR) was performed. In the winter and some months of equinox, the IPTAR mainly occurred in the nighttime and the highest occurrence rate could be up to 90%. In the summer, the occurrence was relatively low and the differences between nighttime and daytime occurrence reduced. The total duration of IPTAR seemed longer around the winter than that around the summer. The occurrence of IPTAR events ascended as the Kp index increased. The frequent precipitation of energetic particles into the ionospheric plasma in the auroral belt may be the main cause of the IPTAR events.

A Model for the Sounding Rocket Measurement on an Ionospheric E-F Valley at the Hainan Low Latitude Station

To understand the physics of an ionospheric E-F valley,a new overlapping threeChapman-layer model is developed to interpret the sounding rocket measurement in the morning(sunrise) on May 7,2011 at the Hainan low latitude ionospheric observation station(19.5oN,109.1oE).From our model,the valley width,depth and height are 43.0 km,62.9% and 121.0 km,respectively.From the sounding rocket observation,the valley width,depth and height are 42.2 km,47.0% and 123.5 km,respectively.The model results are well consistent with the sounding rocket observation.The observed E-F valley at Hainan station is very wide and deep,and rapid development of the photochemical process in the ionosphere should be the underlying reason.

Field-Aligned Currents at the PSBL on 17 August 2001 Storm: Relationships with solar Wind Conditions

Using magnetic field and plasma data acquired with Cluster spacecrafts, we investigate the relationship between the field-aligned currents (FACs) at the plasma sheet boundary layer (PSBL) and solar wind dynamic pressure, as well as the interplanetary magnetic field (IMF) B(y) on 17 August 2001 storm. Our studies reveal that FAC density at the PSBL in the magnetotail in the storm time is controlled mainly by the solar wind dynamic pressure rather than IMF B(y) The FACs at the PSBL are associated with the low-altitude region-1 current and have the same polarity as region-1 current in the dawn sector. In the polar region, the footprints of the FACs at the PSBL expand equatorward. The data analysis also shows that a very strong FAC with a density over 40 nA.m(-2) appeared in this storm time when a substorm just occurred.

Clarification on Polarity of Bipolar Electric Field Solitary Structures in Space Plasmas with Satellite Observation

The bipolar electric field solitary (EFS) structures observed frequently in space plasmas by satellites have two different polarities, first positive electric field peak then negative (i.e., positive/negative) and first negative then positive peak (i.e., negative/positive). We provide the physical explanation on the polarity of observed bipolar EFS structures with an electrostatic ion fluid model. The results show that if initial electric field E0 > 0, the polarity of the bipolar EFS structure will be positive/negative; and if E0 < 0, the polarity of the bipolar EFS structure will be negative/positive. However, for a fixed polarity of the EFS, either positive/negative or negative/positive, if the satellite is located at the positive side of the EFS, the observed polarity should be positive/negative, if the satellite is located at the negative side of the EFS, the observed polarity should be negative/positive. Therefore, we provide a method to clarify the natural polarity of the EFS with observed polarity by satellites. Our results are significant to understand the physical process in space plasma with the satellite observation.