scholarly journals High-order ionospheric effects on electron density estimation from Fengyun-3C GPS radio occultation

2017 ◽  
Vol 35 (3) ◽  
pp. 403-411 ◽  
Author(s):  
Junhai Li ◽  
Shuanggen Jin
Keyword(s):  
Electron Density ◽  
Density Estimation ◽  
Radio Occultation ◽  
Second Order ◽  
High Order ◽  
Electron Content ◽  
Total Electron ◽  
Ionospheric Effects ◽  
Gps Radio Occultation ◽  
Ionosphere Model

Abstract. GPS radio occultation can estimate ionospheric electron density and total electron content (TEC) with high spatial resolution, e.g., China's recent Fengyun-3C GPS radio occultation. However, high-order ionospheric delays are normally ignored. In this paper, the high-order ionospheric effects on electron density estimation from the Fengyun-3C GPS radio occultation data are estimated and investigated using the NeQuick2 ionosphere model and the IGRF12 (International Geomagnetic Reference Field, 12th generation) geomagnetic model. Results show that the high-order ionospheric delays have large effects on electron density estimation with up to 800 el cm−3, which should be corrected in high-precision ionospheric density estimation and applications. The second-order ionospheric effects are more significant, particularly at 250–300 km, while third-order ionospheric effects are much smaller. Furthermore, the high-order ionospheric effects are related to the location, the local time, the radio occultation azimuth and the solar activity. The large high-order ionospheric effects are found in the low-latitude area and in the daytime as well as during strong solar activities. The second-order ionospheric effects have a maximum positive value when the radio occultation azimuth is around 0–20°, and a maximum negative value when the radio occultation azimuth is around −180 to −160°. Moreover, the geomagnetic storm also affects the high-order ionospheric delay, which should be carefully corrected.

scholarly journals Topside Ionosphere and Plasmasphere Modelling Using GNSS Radio Occultation and POD Data

2021 ◽  
Vol 13 (8) ◽  
pp. 1559
Author(s):  
Fabricio S. Prol ◽  
M. Mainul Hoque
Keyword(s):  
Solar Activity ◽  
Electron Density ◽  
Radio Occultation ◽  
Geomagnetic Latitude ◽  
Low Earth Orbit ◽  
Activity Level ◽  
Topside Ionosphere ◽  
Electron Content ◽  
Total Electron ◽  
Solar Activity Level

A 3D-model approach has been developed to describe the electron density of the topside ionosphere and plasmasphere based on Global Navigation Satellite System (GNSS) measurements onboard low Earth orbit satellites. Electron density profiles derived from ionospheric Radio Occultation (RO) data are extrapolated to the upper ionosphere and plasmasphere based on a linear Vary-Chap function and Total Electron Content (TEC) measurements. A final update is then obtained by applying tomographic algorithms to the slant TEC measurements. Since the background specification is created with RO data, the proposed approach does not require using any external ionospheric/plasmaspheric model to adapt to the most recent data distributions. We assessed the model accuracy in 2013 and 2018 using independent TEC data, in situ electron density measurements, and ionosondes. A systematic better specification was obtained in comparison to NeQuick, with improvements around 15% in terms of electron density at 800 km, 26% at the top-most region (above 10,000 km) and 26% to 55% in terms of TEC, depending on the solar activity level. Our investigation shows that the developed model follows a known variation of electron density with respect to geographic/geomagnetic latitude, altitude, solar activity level, season, and local time, revealing the approach as a practical and useful tool for describing topside ionosphere and plasmasphere using satellite-based GNSS data.

Low-Earth-Orbit observations for space weather and space climate

2020 ◽  
Author(s):  
Irina Zakharenkova ◽  
Iurii Cherniak ◽  
Sergey Sokolovskiy ◽  
William Schreiner ◽  
Qian Wu ◽  
...  
Keyword(s):  
Electron Density ◽  
Plasma Density ◽  
Space Weather ◽  
Ionospheric Plasma ◽  
Radio Occultation ◽  
Satellite Orbit ◽  
Electron Content ◽  
Gps Measurements ◽  
Total Electron ◽  
Ionospheric Plasma Density

<p>Many of the modern Low-Earth-Orbiting satellites are now equipped with dual-frequency GPS receivers for Radio Occultation (RO) and Precise Orbit Determination (POD). The space-borne GPS measurements can be successfully utilized for ionospheric climatology and space weather monitoring. The combination of GPS measurements, which include RO observations and POD measurements from the upward-looking GPS antenna, provides information about electron density distribution (profile) below the satellite orbit and an integrated Total Electron Content (TEC) above the satellite representing an important data source for electron density climatology above the F2 layer peak on a global scale. We demonstrate the advantages of using space-borne LEO GPS measurements, both RO and upward-looking, for Space Weather activity monitoring including specification of ionospheric plasma density structures at different altitudinal domains of the ionosphere in quiet and disturbed conditions. After the great success of the COSMIC-1 (Constellation Observing System for Meteorology, Ionosphere, and Climate) mission operating since 2006, the six COSMIC-2 satellites were launched into a 24 deg inclination orbit in June 2019. The COSMIC-2 scientific payloads with the advanced Tri-GNSS Radio-Occultation Receiver System provide multiple observation types including multi-GNSS TEC (limb and overhead), RO electron density profiles, amplitude/phase scintillation indices, in-situ ion densities and velocities. The COSMIC-2 advanced instruments allow detection of ionospheric plasma density structures of various scales, and the monitoring of high-rate amplitude and phase scintillations both above and below a satellite orbit. The COSMIC-2 multi-instrumental observations will contribute to a better understanding of the equatorial ionosphere morphology and future forecasting of ionospheric irregularities and radio wave scintillations that harmfully affect satellite-to-Earth communication and navigation systems. We present results of post-event analyses for severe space weather events demonstrating a great potential and contribution of the COSMIC-1/2 missions in combination with the ground-based GNSS receivers and other LEO missions like C/NOFS, DMSP, MetOp, TerraSAR-X, and Swarm for monitoring the space weather effects in the Earth’s ionosphere.</p>

Seismo-ionospheric precursors of the 14 November 2019 M7.1 Indonesia Earthquake detected by FORMOSAT-7/COSMIC-2

2020 ◽  
Author(s):  
Jann-Yenq Liu ◽  
Chi-Yen Lin ◽  
Fu-Yuan Chang ◽  
Yuh-Ing Chen
Keyword(s):  
Electron Density ◽  
Electric Fields ◽  
Radio Occultation ◽  
Electron Content ◽  
Ion Temperature ◽  
Density Profiles ◽  
Ion Density ◽  
Total Electron ◽  
Ion Velocity ◽  
Electron Density Profiles

<p>FORMOSAT-7/COSMIC-2 (F7/C2), with the mission orbit of 550 km altitude, 24-deg inclination, and a period of 97 minutes, was launched on 25 June 2019.  Tri-GNSS Radio occultation System (TGRS), Ion Velocity Meter (IVM), and RF beacon onboard F7/C2 six small satellites allow scientists to observe the plasma structure and dynamics in the mid-latitude, low-latitude, and equatorial ionosphere in detail.  F7/C2 TGRS sounds ionospheric RO (radio occultation) electron density profiles, while F7/C2 IVM probes the ion density, ion temperature, and ion velocity at the satellite altitude.  The F7/C2 electron density profiles and the ion density, ion temperature, and ion velocity, as well as the global ionospheric map (GIM) of the total electron content (TEC) derived from global ground-based GPS receivers are used to detect seismo-ionospheric precursors (SIPs) of the 14 November 2019 M7.1 Indonesia Earthquake.  The GIM TEC and F7/C2 RO NmF2 significantly increase specifically over the epicenter on 25-26 October, which indicates SIPs of the 14 November 2019 M7.1 Indonesia Earthquake being detected.  The F7/C2 RO electron density profiles upward motions suggest that the eastward electric fields have been enhanced during the SIP days of the 2019 M7.1 Indonesia earthquake.  The seismo-generated electric fields of the 2019 M7.1 Indonesia earthquake are 0.34-0.64 mV/m eastward.  The results demonstrate that F7/C2 can be employed to detect SIPs in the ionospheric plasma, which shall shed some light on earthquake prediction/forecast.</p>

scholarly journals Error analysis of Abel retrieved electron density profiles from radio occultation measurements

2010 ◽  
Vol 28 (1) ◽  
pp. 217-222 ◽  
Author(s):  
X. Yue ◽  
W. S. Schreiner ◽  
J. Lei ◽  
S. V. Sokolovskiy ◽  
C. Rocken ◽  
...  
Keyword(s):  
Electron Density ◽  
Radio Occultation ◽  
Electron Content ◽  
Electron Densities ◽  
Density Profiles ◽  
Total Electron ◽  
The North ◽  
Spring Equinox ◽  
Electron Density Profiles ◽  
Artificial Plasma

Abstract. This letter reports for the first time the simulated error distribution of radio occultation (RO) electron density profiles (EDPs) from the Abel inversion in a systematic way. Occultation events observed by the COSMIC satellites are simulated during the spring equinox of 2008 by calculating the integrated total electron content (TEC) along the COSMIC occultation paths with the "true" electron density from an empirical model. The retrieval errors are computed by comparing the retrieved EDPs with the "true" EDPs. The results show that the retrieved NmF2 and hmF2 are generally in good agreement with the true values, but the reliability of the retrieved electron density degrades in low latitude regions and at low altitudes. Specifically, the Abel retrieval method overestimates electron density to the north and south of the crests of the equatorial ionization anomaly (EIA), and introduces artificial plasma caves underneath the EIA crests. At lower altitudes (E- and F1-regions), it results in three pseudo peaks in daytime electron densities along the magnetic latitude and a pseudo trough in nighttime equatorial electron densities.

scholarly journals Assessment of electron density profiles over the Brazilian region using radio occultation data aided by global ionospheric maps

2020 ◽  
Author(s):  
Gabriel Jerez ◽  
Fabricio Prol ◽  
Daniele Alves ◽  
João Monico ◽  
Manuel Hernández-Pajares
Keyword(s):  
Refractive Index ◽  
Electron Density ◽  
Radio Occultation ◽  
Electron Content ◽  
Neutral Atmosphere ◽  
Density Profiles ◽  
Total Electron ◽  
Ionospheric Variability ◽  
Electron Density Profiles ◽  
Global Ionospheric Maps

<p>The development of GNSS (Global Navigation Satellite System) and LEO (Low Earth Orbiting) satellites missions enhanced new possibilities of the terrestrial atmosphere probing. The Radio Occultation (RO) technique can be used to retrieve profiles from the neutral and the ionized atmosphere. An important advantage of using RO data is the spatial distribution, which enables global coverage. The signal transmitted by GNSS satellites and tracked by receivers embedded at the LEO satellites is influenced by the atmosphere which causes signal refraction. Due to the signal and atmospheric interaction, instead of a straight line, the signal propagates as a curved line in the path between the transmitter and receiver. The satellites geometry allows the retrieval of atmospheric refractive index, which carries several characteristics from its composition, such as pressure and temperature of the neutral atmosphere, and electron density of the ionosphere. In 1995 GPS/MET (Global Positioning System/Meteorology) experiment was launched to prove the RO concept and, since then, several LEO missions with GNSS receiver embedded were developed, such as CHAMP (Challenging Mini-satellite Payload) (2001-2008), SAC-C (Satélite de Aplicaciones Cientificas-C) (2001-2013) and COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) (2006-present). COSMIC is one of the RO missions with the greatest amount of atmospheric data available, mainly taking into account ionospheric information. In the RO technique, in general, the Abel retrieval is used to retrieve the refractive index. The Abel retrieval assumes a spherical symmetry of the atmosphere. When considering the electron density profiles, the main issue is related to regions with large horizontal gradients, where the spherical assumption presents the biggest degradation. In order to improve the ionospheric horizontal gradient used to retrieve electron density profiles, many researches have performed experiments using data from different sources. In this paper, we aimed to assess the electron density profiles over the Brazilian area (equatorial region), characterized by intense ionospheric variability, considering RO data and Global Ionospheric Maps (GIM). The data used is from COSMIC mission, in a period close to the last solar cycle peak (2013-2014). Ionosonde data were used as reference values to assess the RO with GIM aided data. Total Electron Content (TEC) data from GIM were used to estimate the variability of ionosphere between the ionosonde position and the profile locations. This research builds on a preliminary investigation related to the assessment of RO ionospheric profiles over a region under intense ionospheric variability, such as the Brazilian territory. Future works may take into consideration the use of other ionospheric information such as regional ionospheric maps, with higher resolution, and ionospheric tomography.</p>

scholarly journals First assimilations of COSMIC radio occultation data into the Electron Density Assimilative Model (EDAM)

2008 ◽  
Vol 26 (2) ◽  
pp. 353-359 ◽  
Author(s):  
M. J. Angling
Keyword(s):  
Electron Density ◽  
Vertical Structure ◽  
Radio Occultation ◽  
Electron Content ◽  
Cosmic Radio ◽  
Data Set ◽  
Total Electron ◽  
Ionospheric Models ◽  
Occultation Data ◽  
Radio Occultation Data

Abstract. Ground based measurements of slant total electron content (TEC) can be assimilated into ionospheric models to produce 3-D representations of ionospheric electron density. The Electron Density Assimilative Model (EDAM) has been developed for this purpose. Previous tests using EDAM and ground based data have demonstrated that the information on the vertical structure of the ionosphere is limited in this type of data. The launch of the COSMIC satellite constellation provides the opportunity to use radio occultation data which has more vertical information. EDAM assimilations have been run for three time periods representing quiet, moderate and disturbed geomagnetic conditions. For each run, three data sets have been ingested – only ground based data, only COSMIC data and both ground based and COSMIC data. The results from this preliminary study show that both ground and space based data are capable of improving the representation of the vertical structure of the ionosphere. However, the analysis is limited by the incomplete deployment of the COSMIC constellation and the use of auto-scaled ionosonde data. The first of these can be addressed by repeating this type of study once full deployment has been achieved. The latter requires the manual scaling of ionosonde data; ideally an agreed data set would be scaled and made available to the community to facilitate comparative testing of assimilative models.

scholarly journals Evidence of gravity waves into the atmosphere during the March 2006 total solar eclipse

2007 ◽  
Vol 7 (18) ◽  
pp. 4943-4951 ◽  
Author(s):  
C. S. Zerefos ◽  
E. Gerasopoulos ◽  
I. Tsagouri ◽  
B. E. Psiloglou ◽  
A. Belehaki ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Electron Density ◽  
Gravity Waves ◽  
Solar Eclipse ◽  
Stratospheric Ozone ◽  
Thermal Fluctuations ◽  
Ozone Layer ◽  
Total Solar Eclipse ◽  
Electron Content ◽  
Total Electron

Abstract. This study aims at providing experimental evidence, to support the hypothesis according to which the movement of the moon's shadow sweeping the ozone layer at supersonic speed, during a solar eclipse, creates gravity waves in the atmosphere. An experiment was conducted to study eclipse induced thermal fluctuations in the ozone layer (via measurements of total ozone column, ozone photolysis rates and UV irradiance), the ionosphere (Ionosonde Total Electron Content – ITEC, peak electron density height – hmF2), and the troposphere (temperature, relative humidity), before, during and after the total solar eclipse of 29 March 2006. We found the existence of eclipse induced dominant oscillations in the parameters related to the ozone layer and the ionosphere, with periods ranging between 30–40 min. Cross-spectrum analyses resulted to statistically significant square coherences between the observed oscillations, strengthening thermal stratospheric ozone forcing as the main mechanism for GWs. Additional support for a source below the ionosphere was provided by the amplitude of the oscillations in the ionospheric electron density, which increased upwards from 160 to 220 km height. Even though similar oscillations were shown in surface temperature and relative humidity data, no clear evidence for tropospheric influence could be derived from this study, due to the modest amplitude of these waves and the manifold rationale inside the boundary layer.

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