Guanyi Ma

A super bubble detected by dense GPS network at east Asian longitudes

A post sunset bubble manifested by total electron content depletion was observed at midlatitudes (similar to 30 degrees-34 degrees N, similar to 130 degrees-134 degrees E) during the main phase of a storm on 12 February 2000. With loss of lock and the rate of the total electron content index maps, the bubble was seen to bifurcate at its early growth phase. The upward drift speed was observed similar to 300 m/s at similar to 2150 km, and decreasing with increasing altitude and time. The bubble had unusually large latitudinal extension reaching midlatitude of 36.5 degrees N (31.5 degrees N magnetic latitude), indicating an apex height of similar to 2500 km. In process of the evolution, the bubble drifted eastward at a speed of similar to 50 m/s. The F region peak height and density obtained by a meridional ionosonde chain suggested a prompt penetrating magnetospheric electric field helped to trigger the super bubble.

Mid-latitude winds in the mesosphere: a superposed epoch analysis over the geomagnetic storm times

Abstract This study aims at looking for the characteristic patterns of mesospheric wind over the geomagnetic storm times. For this purpose, the geomagnetic storms preceded by a sudden commencement (SSC) have been selected from January 1995 to April 1999. By using the onset of SSC as the timing mark, a superposed epoch analysis has been performed on the available neutral wind data measured with medium frequency (MF) radars at Yamagawa ( 31.2° N , 130.6° E ) and Wakkanai ( 45.4° N , 141.7° E ). In doing so, the length of time chosen for the superposed analysis is from 7 days before the SSC onset to 21 days after the onset; subsets of wind data are superimposed for summer and winter months, respectively. Then with harmonic analysis on the superposed winds the mean winds in both summer and winter months have been obtained. Concerning mean wind characteristics, some interesting details are the reversal heights of the summer zonal winds, which is 79– 80 km at Yamagawa and 84 km at Wakkanai. Strong wavy structures with 2–4 days period are observed at both Yamagawa and Wakkanai in both summer and winter. As for storm effects, significant enhancement of eastward wind is found 5 days after SSC onset at both Yamagawa and Wakkanai in winter. Moreover, the northward wind turns southward at Wakkanai 2 days after the onset of SSC, and the southward wind lasts for several days thereafter. In summer months, the post-storm enhancement tends to be small and mainly in the eastward wind at both Yamagawa and Wakkanai.

Observations of small- to large-scale ionospheric irregularities associated with plasma bubbles with a transequatorial HF propagation experiment and spaced GPS receivers

The results from simultaneous observations of the nighttime transequatorial propagation (TEP) of HF radio waves between Australia and Japan and the GPS scintillation measurements in south China and Vietnam are presented in this paper. The results showed that there was good correspondence between the nighttime eastward traveling off-great circle propagation (OGCP) of broadcasting waves of Radio Australia from Shepparton, Australia, measured at Oarai, Japan, and the scintillations in GPS radio waves at Hainan, China. This shows that the nighttime eastward traveling OGCP in HF TEP is caused by a large- scale ionospheric structure associated with a plasma bubble. The zonal drift velocities of the large- scale ionospheric structure estimated by the change in the direction of arrival of the OGCP were similar to those of the small- scale irregularities associated with plasma bubbles measured by the GPS scintillation spaced- receiver technique. Our results show that the HF TEP measurement is quite useful for monitoring the plasma bubble occurrence over a wide area and for forecasting the arrival of the plasma bubble at places located to the east of it.

The influence of ionospheric thin shell height on TEC retrieval from GPS observation

We investigate the influence of assumed height for the thin shell ionosphere model on the Total Electron Content (TEC) derived from a small scale Global Positioning System (GPS) network. TEC and instrumental bias are determined by applying a grid-based algorithm to the data on several geomagneticlly quiet days covering a 10 month period in 2006. Comparisons of TEC and instrumental bias are made among assumed heights from 250 km to 700 km with an interval of 10 km. While the TEC variations with time follow the same trend, TEC tends to increase with the height of the thin shell. The difference in TEC between heights 250 km and 700 km can be as large as ~8 TECU in both daytime and nighttime. The times at which the TEC reaches its peak or valley do not vary much with the assumed heights. The instrumental biases, especially bias from the satellite, can vary irregularly with assumed height. Several satellites show a large deviation of ~3 ns for heights larger than 550 km. The goodness of fit for different assumed heights is also examined. The data can be generally well-fitted for heights from 350 km to 700 km. A large deviation happens at heights lower than 350 km. Using the grid-based algorithm, there is no consensus on assumed height as related to data fitting. A thin shell height in the range 350 − 500 km can be a reasonable compromise between data fitting and peak height of the ionosphere.

Communication-based positioning systems: past, present and prospects

This paper reviews positioning systems in the context of communication systems. First, the basic positioning technique is described for location based service (LBS) in mobile communication systems. Then the high integrity global positioning system (iGPS) is introduced in terms of aspects of what it is and how the low Earth orbit (LEO) Iridium telecommunication satellites enhance the global positioning system (GPS). Emphasis is on the Chinese Area Positioning System (CAPS) which is mainly based on commercial geostationary (GEO) communication satellites, including decommissioned GEO and inclined geosynchronous communication satellites. Characterized by its low cost, high flexibility, wide-area coverage and ample frequency resources, a distinctive feature of CAPS is that its navigation messages are generated on the ground, then uploaded to and forwarded by the communication satellites. Fundamental principles and key technologies applied in the construction of CAPS are presented in detail from the CAPS validation phase to its experimental system setup. A prospective view of CAPS has concluded it to be a seamless, high accuracy, large capacity navigation and communication system which can be achieved by expanding it world wide and enhancing it with LEO satellites and mobile base stations. Hence, this system is a potential candidate for the next generation of radio navigation after GPS.

GPS-based TEC derivation and its dependence on ionospheric height assumption

With GPS observation from a small scale network and the grid-based algorithm to derive TEC and instrumrntal bias, the effects of the thin shell ionospheric height assumption on GPS-based TEC is studied. While the trend of TEC variation with time retains, TEC tends to increase with the height. The times at which the TEC peaks or reaches the minimum do not change significantly with the height. The instrumental biases can vary with the height irregularly. The goodness of fit is different for different height. The fitting is generally good when the height is taken from 350 km to 700 km. There does not exist a best height assumption. It has large deviations for the height lower than 350 km. The goodness of fit worsens monotonously when the height decreases from 280 km to 250 km.

Variation of single-frequency GPS positioning errors at Taiwan based on Klobuchar ionosphere model

In this paper, ten years single-frequency pseudorange observations from one IGS GPS receiver at Taoyuan (121.1°E, 24.6°N), Taiwan, were used to analyze the relation of the positioning error to the changes of the solar activities. The receivers position at each epoch is obtained by solving the pseudorange equation set. Positioning error is defined as the difference between the position from the equation set and the position published by IGS. The Klobuchar model is used the correct the ionospheric range delay during the positioning solution. The results showed that during the high solar activity years the positioning error is larger than that during the low solar activity years. For the single-frequency GPS receiver, the ionospheric delay is the main error source, and the error of the single-frequency GPS receiver is mainly controlled by the solar activity.

A Study of TEC Storm on 13 October 2016

An ionospheric positive storm on 13 October 2016 was studied. The longitude effect of ionospheric storm along 40°N latitude region is studied with 23 GPS stations from 0°E to 360°E. Total electron content (TEC) was calculated with polynomial method, and TEC difference between the storm time and quiet time (ΔTEC) were calculated. The variations of TEC difference were different at different longitudes. There was a positive phase storm at the local time day side region, while the variations were not obvious at the night side longitudes. The maximum value of ΔTEC was about 25 TECU at 330°E at about 1400UT on 13 October 2016. Two Ionosonde data at EB040 (0.5°E, 40°N) and RL052 (51.5°N, 359.4°E) were also used to study the ionospheric storm. The ΔfoF2 of RL052 increased earlier that low latitude ionosonde of EB040. There was a second peak of ΔTEC at the local night time about 2000 LT on 13 October 2016. The latitude effect of ionospheric storm was also studied with 7 GPS stations at 0°E meridian. It was found that the positive storm was obvious at high latitude region, while it was weak at low latitude region. This phenomenon may be caused by the fountain effect. From high latitude to low latitude, ΔTEC gradually began to increase, and ΔTEC at higher latitude reached the maximum value earlier than the low latitude. These show that the positive ionospheric storm may be caused by the equatorward surge.

Comparison of global TEC between IRI TEC and GPS TEC in the spring of 2006

Comparison of the global Total Electron Content (TEC) derived from dual-frequency Global Positioning System (GPS) data and International Reference Ionosphere (IRI) used tomographic models, it has very important significance for IRI upgrading [1]. We investigate the trend of global TEC between IRI TEC and GPS TEC in the spring of 2006. IRI TEC is derived from the IRI-2012 model and GPS TEC is obtained from the International GNSS service (IGS) [1, 2]. By comparing the results, IRI TEC agrees with GPS TEC very well at high latitudes. They are generally in agreement even at low latitudes for the period from evening to morning. However, differences are found from 11:00–17:00 LT at low latitudes. It can be seen that the north-south asymmetry has remarkable effect on both IRI TEC and GPS TEC, especially in the equatorial ionization anomaly (EIA). The strength of EIA crest is obviously higher in north than in south about IRI TEC, it reaches ∼11 TECU around 15° E longitude at 13:00 LT. Meanwhile, EIA crest in daytime is generally exaggerated and the noon-bite out is deep in the IRI TEC than GPS TEC, the difference of noon-bite is about 12 TECU around 105° E longitude at 13:00 LT.

The Effect of GNSS Sites Distribution on TEC Derivation

With worldwide increased Global Navigation Satellite System (GNSS) receivers, it is possible to obtain the ionospheric total electron content (TEC) and hence monitor the ionosphere with GNSS. Using a thin layer assumption of the ionosphere and dual-frequency Global Positioning System (GPS) observations from 16 geomagnetically quiet days in four seasons of 2006, this paper adopts the spherical harmonic model to fit TEC and investigates the effects of two network constitutions on global TEC derivation, one with 275 GPS receivers and the other with 125 GPS receivers. The results show that the data can be well fitted for both network constitutions. The derived TECs are consistent with each other for four seasons. This is especially true for TECs at low- and mid-latitude. The derived satellite and receiver biases are stable during the year. The standard deviation of the satellite and the receiver biases are less than 0.5 and 3 ns, respectively.