2,806 research outputs found
GPS Ionospheric mapping and tomography: A case of study in a geomagnetic storm
The ionosphere has been normally detected by traditional instruments, such as
ionosonde, scatter radars, topside sounders onboard satellites and in situ
rocket. However, most instruments are expensive and also restricted to either
the bottomside ionosphere or the lower part of the topside ionosphere (usually
lower than 800 km), such as ground based radar measurements. Nowadays, GPS
satellites in high altitude orbits (~20,200 km) are capable of providing
details on the structure of the entire ionosphere, even the plasmasphere. In
this paper, a Regional Ionospheric Mapping and Tomography (RIMT) tool was
developed, which can be used to retrieve 2-D TEC and 3-D ionospheric electron
density profiles using ground-based or space-borne GPS measurements. Some
results are presented from the RIMT tool using regional GPS networks in South
Korea and validated using the independent ionosonde. GPS can provide
time-varying ionospheric profiles and information at any specified grid related
to ionospheric activities and states, including the electron density response
at the F2-layer peak (the NmF2) during geomagnetic storms.Comment: Proceeding of IEEE International Geoscience and Remote Sensing
Symposium (IGARSS), 24-29 July, 2011, Vancouver, Canad
Estimation of 3D electron density in the Ionosphere by using fusion of GPS satellite-receiver network measurements and IRI-Plas model
GPS systems can give a good approximation of the Slant Total Electron Content in a cylindrical path between the GPS satellite and the receiver. International Reference Ionosphere extended to Plasmasphere (IRI-Plas) model can also give an estimation of the vertical electron density profile in the ionosphere for any given location and time, in the altitude range from about 50 km to 20000 km. This information can be utilized to obtain total electron content between any given receiver and satellite locations based on the IRI-Plas model. This paper explains how the fusion of measurements obtained from a GPS satellite-receiver network can be utilized together with the IRI-Plas model in order to obtain a robust 3D electron density model of the ionosphere. © 2013 ISIF ( Intl Society of Information Fusi
Real-time geophysical applications with Android GNSS raw measurements
The number of Android devices enabling access to raw GNSS (Global Navigation Satellite System) measurements is rapidly increasing, thanks to the dedicated Google APIs. In this study, the Xiaomi Mi8, the first GNSS dual-frequency smartphone embedded with the Broadcom BCM47755 GNSS chipset, was employed by leveraging the features of L5/E5a observations in addition to the traditional L1/E1 observations. The aim of this paper is to present two different smartphone applications in Geoscience, both based on the variometric approach and able to work in real time. In particular, tests using both VADASE (Variometric Approach for Displacement Analysis Stand-alone Engine) to retrieve the 3D velocity of a stand-alone receiver in real-time, and VARION (Variometric Approach for Real-Time Ionosphere Observations) algorithms, able to reconstruct real-time sTEC (slant total electron content) variations, were carried out. The results demonstrate the contribution that mass-market devices can offer to the geosciences. In detail, the noise level obtained with VADASE in a static scenario-few mm/s for the horizontal components and around 1 cm/s for the vertical component-underlines the possibility, confirmed from kinematic tests, of detecting fast movements such as periodic oscillations caused by earthquakes. VARION results indicate that the noise level can be brought back to that of geodetic receivers, making the Xiaomi Mi8 suitable for real-time ionosphere monitoring
Auroral vortex street formed by the magnetosphere-ionosphere coupling instability
By performing three-dimensional nonlinear MHD simulations including Alfven
eigenmode perturbations most unstable to the ionospheric feedback effects, we
reproduced the auroral vortex street that often appears just before substorm
onset. We found that an initially placed arc splits, intensifies, and rapidly
deforms into a vortex street. We also found that there is a critical convection
electric field for growth of the Alfven eigenmodes. The vortex street is shown
to be a consequence of coupling between the magnetospheric Alfven waves
carrying field-aligned currents and the ionospheric density waves driven by
Pedersen/Hall currents.Comment: 7 pages, 6 figures, submitted to Ann. Geophy
Response of convection electric fields in the magnetosphere to IMF orientation change
[1] The transient response of convection electric fields in the inner magnetosphere to southward turning of the interplanetary magnetic field (IMF) is investigated using inâsitu electric field observations by the CRRES and Akebono spacecraft. Electric fields earthward of the inner edge of the electron plasma sheet show quick responses simultaneously with change in ionospheric electric fields, which indicates the arrival of the first signal related to southward turning. A coordinated observation of the electric field by the CRRES and Akebono spacecraft separated by 5 RE reveals a simultaneous increase in the dawnâdusk electric field in a wide region of the inner magnetosphere. A quick response associated with the southward turning of the IMF is also identified in inâsitu magnetic fields. It indicates that the southward turning of the IMF initiates simultaneous (less than 1 min) enhancements of ionospheric electric fields, convection electric fields in the inner magnetosphere, and the ring or tail current and region 2 FACs. In contrast, a quick response of convection electric fields is not identified in the electron plasma sheet. A statistical study using 161 events of IMF orientation change in 1991 confirms a prompt response within 5 min for 80% of events earthward of the electron plasma sheet, while a large time lag of more than 30 min is identified in electric fields in the electron plasma sheet. The remarkable difference in the response of electric fields indicates that electric fields in the electron plasma sheet are weakened by high conductance in the magnetically conjugated auroral ionosphere.https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2009JA014277https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2009JA014277Published versio
Cluster observations of the midaltitude cusp under strong northward interplanetary magnetic field
We report on a multispacecraft cusp observation lasting more than 100 min. We
determine the cusp boundary motion and reveal the effect on the cusp size of the
interplanetary magnetic field (IMF) changing from southward to northward. The cusp
shrinks at the beginning of the IMF rotation and it reexpands at the rate of 0.40°
invariant latitude per hour under stable northward IMF. On the basis of plasma signatures
inside the cusp, such as counterstreaming electrons with balanced fluxes, we propose
that pulsed dual lobe reconnection operates during the time of interest. SC1 and
SC4 observations suggest a long-term regular periodicity of the pulsed dual reconnection,
which we estimate to be ~1â5 min. Further, the distances from the spacecraft to
the reconnection site are estimated on the basis of observations from three satellites. The
distance determined using SC1 and SC4 observations is ~15 RE and that determined
from SC3 data is ~8 RE. The large-scale speed of the reconnection site sunward motion is
~16 km s-1. We observe also a fast motion of the reconnection site by SC1, which
provides new information about the transitional phase after the IMF rotation. Finally, a
statistical study of the dependency of plasma convection inside the cusp on the IMF clock
angle is performed. The relationship between the cusp stagnation, the dual lobe
reconnection process, and the IMF clock angle is discussed
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