scholarly journals Tomographic Imaging of a Large Scale TID during the Halloween Storm of 2003

2020 ◽  
Author(s):  
Karl Bolmgren ◽  
Cathryn Mitchell ◽  
Talini Pinto Jayawardena ◽  
Gary Bust ◽  
Jon Bruno
Keyword(s):  
Large Scale ◽  
Ionospheric Disturbance ◽  
Tomographic Reconstruction ◽  
Tomographic Imaging ◽  
Spatial And Temporal Variation ◽  
Gps Receiver ◽  
Global Positioning ◽  
Independent Observations ◽  
Improved Accuracy ◽  
Horizontal Wavelength

Abstract. The most intense ionospheric storm observed in recent times occurred between 29–31 October 2003. The disturbances to the high-latitude regions set off several Large-Scale Travelling Ionospheric Disturbances (LSTIDs), wavelike perturbations in the ionospheric electron density. This paper investigates one particular Travelling Ionospheric Disturbance (TID) on 31 October 2003 using North American Global Positioning System (GPS) receiver network data and a tomographic imaging technique. The TID has an estimated period of 30 min, an estimated horizontal wavelength of 700 km and propagates South-Westward over North America. The tomographic reconstruction of the wave is validated using a simulation of the observations and with independent observations from ionosondes and the CHAMP Planar Langmuir Probe. The results are discussed in the context of the magnetic and ionospheric conditions that may have contributed to the launch of the wave. Large-scale TIDs are challenging to study over large regions of the Earth, and the GPS network here is shown to offer a unique perspective on the spatial and temporal variation of the TID. The experimental results are backed up by simulations that show a denser network of receivers, as is available in more recent years, would produce improved accuracy in the TID imaging.

scholarly journals Tomographic imaging of a large-scale travelling ionospheric disturbance during the Halloween storm of 2003

2020 ◽  
Vol 38 (6) ◽  
pp. 1149-1157
Author(s):  
Karl Bolmgren ◽  
Cathryn Mitchell ◽  
Talini Pinto Jayawardena ◽  
Gary Bust ◽  
Jon Bruno ◽  
...  
Keyword(s):  
Large Scale ◽  
Ionospheric Disturbance ◽  
Tomographic Reconstruction ◽  
Tomographic Imaging ◽  
Spatial And Temporal Variation ◽  
Gps Receiver ◽  
Global Positioning ◽  
Independent Observations ◽  
Improved Accuracy ◽  
Horizontal Wavelength

Abstract. The most intense ionospheric storm observed in recent times occurred between 29 and 31 October 2003. The disturbances to the high-latitude regions set off several large-scale travelling ionospheric disturbances (LSTIDs), wave-like perturbations in the ionospheric electron density. This paper investigates one particular TID on 31 October 2003 using North American Global Positioning System (GPS) receiver network data and a tomographic imaging technique. The TID has an estimated period of 30 min and an estimated horizontal wavelength of 700 km and propagates south-westward over North America. The tomographic reconstruction of the wave is validated using a simulation of the observations and with independent observations from ionosondes and the CHAMP planar Langmuir probe. The results are discussed in the context of the magnetic and ionospheric conditions that may have contributed to the launch of the wave. Large-scale TIDs are challenging to study over large regions of the Earth, and the GPS network here is shown to offer a unique perspective on the spatial and temporal variation of the TID. The experimental results are backed up by simulations that show a denser network of receivers, as is available in more recent years, would produce improved accuracy in the TID imaging.

scholarly journals Multi-Scale Ionospheric Anomalies Monitoring and Spatio-Temporal Analysis during Intense Storm

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 215
Author(s):  
Na Cheng ◽  
Shuli Song ◽  
Wei Li
Keyword(s):  
Magnetic Storm ◽  
Large Scale ◽  
Temporal Dynamics ◽  
Ionospheric Disturbance ◽  
Ionospheric Scintillation ◽  
Small Scale ◽  
Electron Content ◽  
Total Electron ◽  
Multi Scale ◽  
Intense Storm

The ionosphere is a significant component of the geospace environment. Storm-induced ionospheric anomalies severely affect the performance of Global Navigation Satellite System (GNSS) Positioning, Navigation, and Timing (PNT) and human space activities, e.g., the Earth observation, deep space exploration, and space weather monitoring and prediction. In this study, we present and discuss the multi-scale ionospheric anomalies monitoring over China using the GNSS observations from the Crustal Movement Observation Network of China (CMONOC) during the 2015 St. Patrick’s Day storm. Total Electron Content (TEC), Ionospheric Electron Density (IED), and the ionospheric disturbance index are used to monitor the storm-induced ionospheric anomalies. This study finally reveals the occurrence of the large-scale ionospheric storms and small-scale ionospheric scintillation during the storm. The results show that this magnetic storm was accompanied by a positive phase and a negative phase ionospheric storm. At the beginning of the main phase of the magnetic storm, both TEC and IED were significantly enhanced. There was long-duration depletion in the topside ionospheric TEC during the recovery phase of the storm. This study also reveals the response and variations in regional ionosphere scintillation. The Rate of the TEC Index (ROTI) was exploited to investigate the ionospheric scintillation and compared with the temporal dynamics of vertical TEC. The analysis of the ROTI proved these storm-induced TEC depletions, which suppressed the occurrence of the ionospheric scintillation. To improve the spatial resolution for ionospheric anomalies monitoring, the regional Three-Dimensional (3D) ionospheric model is reconstructed by the Computerized Ionospheric Tomography (CIT) technique. The spatial-temporal dynamics of ionospheric anomalies during the severe geomagnetic storm was reflected in detail. The IED varied with latitude and altitude dramatically; the maximum IED decreased, and the area where IEDs were maximum moved southward.

scholarly journals Equatorial ionospheric disturbance observed through a transequatorial HF propagation experiment

2006 ◽  
Vol 24 (5) ◽  
pp. 1401-1409 ◽  
Author(s):  
T. Maruyama ◽  
M. Kawamura
Keyword(s):  
Large Scale ◽  
Ionospheric Disturbance ◽  
Great Circle ◽  
Rate Of Change ◽  
Spatial Distance ◽  
Propagation Path ◽  
Multiple Signal Classification ◽  
Radio Broadcasting ◽  
Equatorial Plasma Bubbles ◽  
Propagation Experiment

Abstract. A transequatorial radio-wave propagation experiment at shortwave frequencies (HF-TEP) was done between Shepparton, Australia, and Oarai, Japan, using the radio broadcasting signals of Radio Australia. The receiving facility at Oarai was capable of direction finding based on the MUSIC (Multiple Signal Classification) algorithm. The results were plotted in azimuth-time diagrams (AT plots). During the daytime, the propagation path was close to the great circle connecting Shepparton and Oarai, thus forming a single line in the AT plots. After sunset, off-great-circle paths, or satellite traces in the AT plot, often appeared abruptly to the west and gradually returned to the great circle direction. However, there were very few signals across the great circle to the east. The off-great-circle propagation was very similar to that previously reported and was attributed to reflection by an ionospheric structure near the equator. From the rate of change in the direction, we estimated the drift velocity of the structure to range mostly from 100 to 300 m/s eastward. Multiple instances of off-great-circle propagation with a quasi-periodicity were often observed and their spatial distance in the east-west direction was within the range of large-scale traveling ionospheric disturbances (LS-TIDs). Off-great-circle propagation events were frequently observed in the equinox seasons. Because there were many morphological similarities, the events were attributed to the onset of equatorial plasma bubbles.

scholarly journals A study of atmospheric gravity waves and travelling ionospheric disturbances at equatorial latitudes

1997 ◽  
Vol 15 (8) ◽  
pp. 1048-1056 ◽  
Author(s):  
R. L. Balthazor ◽  
R. J. Moffett
Keyword(s):  
Gravity Waves ◽  
Large Scale ◽  
Ionospheric Disturbance ◽  
Magnetic Equator ◽  
Ionospheric Disturbances ◽  
Atmospheric Gravity Waves ◽  
Opposite Hemisphere ◽  
Travelling Ionospheric Disturbances ◽  
F Region ◽  
Atmospheric Gravity

Abstract. A global coupled thermosphere-ionosphere-plasmasphere model is used to simulate a family of large-scale imperfectly ducted atmospheric gravity waves (AGWs) and associated travelling ionospheric disturbances (TIDs) originating at conjugate magnetic latitudes in the north and south auroral zones and subsequently propagating meridionally to equatorial latitudes. A 'fast' dominant mode and two slower modes are identified. We find that, at the magnetic equator, all the clearly identified modes of AGW interfere constructively and pass through to the opposite hemisphere with unchanged velocity. At F-region altitudes the 'fast' AGW has the largest amplitude, and when northward propagating and southward propagating modes interfere at the equator, the TID (as parameterised by the fractional change in the electron density at the F2 peak) increases in magnitude at the equator. The amplitude of the TID at the magnetic equator is increased compared to mid-latitudes in both upper and lower F-regions with a larger increase in the upper F-region. The ionospheric disturbance at the equator persists in the upper F-region for about 1 hour and in the lower F-region for 2.5 hours after the AGWs first interfere, and it is suggested that this is due to enhancements of the TID by slower AGW modes arriving later at the magnetic equator. The complex effects of the interplays of the TIDs generated in the equatorial plasmasphere are analysed by examining neutral and ion winds predicted by the model, and are demonstrated to be consequences of the forcing of the plasmasphere along the magnetic field lines by the neutral air pressure wave.

Implementation and Performance Assessment of a Vector Tracking Method Based on a Software GPS Receiver

2011 ◽  
Vol 64 (S1) ◽  
pp. S151-S161 ◽  
Author(s):  
Sihao Zhao ◽  
Mingquan Lu ◽  
Zhenming Feng
Keyword(s):  
Global Positioning System ◽  
Carrier Frequency ◽  
Gps Receiver ◽  
Tracking Loop ◽  
Frequency Tracking ◽  
Tracking Method ◽  
Global Positioning ◽  
Vector Tracking ◽  
Tracking Loops ◽  
And Performance

A number of methods have been developed to enhance the robustness of Global Positioning System (GPS) receivers when there are a limited number of visible satellites. Vector tracking is one of them. It utilizes information from all channels to aid the processing of individual channels to generate receiver positions and velocities. This paper analyzes relationships among code phase, carrier frequency, and receiver position and velocity, and presents a vector loop-tracking algorithm using an Extended Kalman filter implemented in a Matlab-based GPS software receiver. Simulated GPS signals are generated to test the proposed vector tracking method. The results show that when some of the satellites are blocked, the vector tracking loop provides better carrier frequency tracking results for the blocked signals and produces more accurate navigation solutions compared with traditional scalar tracking loops.

scholarly journals Opportunities and Challenges of Feature Selection Methods for High Dimensional Data: A Review

2021 ◽  
Vol 26 (1) ◽  
pp. 67-77
Author(s):  
Siva Sankari Subbiah ◽  
Jayakumar Chinnappan
Keyword(s):  
Feature Selection ◽  
Big Data ◽  
Large Scale ◽  
High Dimensional Data ◽  
Research Work ◽  
Basic Feature ◽  
High Dimensional ◽  
Selection Methods ◽  
Fast Development ◽  
Improved Accuracy

Now a day, all the organizations collecting huge volume of data without knowing its usefulness. The fast development of Internet helps the organizations to capture data in many different formats through Internet of Things (IoT), social media and from other disparate sources. The dimension of the dataset increases day by day at an extraordinary rate resulting in large scale dataset with high dimensionality. The present paper reviews the opportunities and challenges of feature selection for processing the high dimensional data with reduced complexity and improved accuracy. In the modern big data world the feature selection has a significance in reducing the dimensionality and overfitting of the learning process. Many feature selection methods have been proposed by researchers for obtaining more relevant features especially from the big datasets that helps to provide accurate learning results without degradation in performance. This paper discusses the importance of feature selection, basic feature selection approaches, centralized and distributed big data processing using Hadoop and Spark, challenges of feature selection and provides the summary of the related research work done by various researchers. As a result, the big data analysis with the feature selection improves the accuracy of the learning.

Causes for Large-Scale Hydrographic Changes at the Hawaii Ocean Time Series Station

2008 ◽  
Vol 38 (9) ◽  
pp. 1931-1948 ◽  
Author(s):  
D. Stammer ◽  
S. Park ◽  
A. Köhl ◽  
R. Lukas ◽  
F. Santiago-Mandujano
Keyword(s):  
Time Series ◽  
Large Scale ◽  
Global Ocean ◽  
Modeling Framework ◽  
Decadal Time Scale ◽  
Quasi Biennial Oscillation ◽  
Salinity Field ◽  
Additional Information ◽  
Independent Observations ◽  
Station Aloha

Abstract Results from Estimating the Circulation and Climate of the Ocean (ECCO)–Scripps Institution of Oceanography (SIO) global ocean state estimate, available over the 11-yr period 1992 through 2002, are compared with independent observations available at the Hawaii Ocean time series station ALOHA. The comparison shows that at this position, the estimated temporal variability has some skill in simulating observed ocean variability and that the quality of future syntheses could benefit from additional information available from the Argo network and from the time series observations themselves. On a decadal time scale, the influence radius of the station ALOHA T–S time series covers large parts of the tropical and subtropical Pacific Ocean and reaches even into the Indian Ocean through the Indonesian Throughflow. Estimated changes in sea surface height (SSH) result largely from thermosteric changes; however, nonsteric (barotropic) variations on the order of 1–2 cm also contribute to SSH changes at station ALOHA. Moreover, changes of similar magnitude can be caused by changes in the salinity field because of a quasi-biennial oscillation in the horizontal flow structure and heaving of the mean salinity structure on seasonal and interannual time scales. The adjoint modeling framework confirms westward-propagating Rossby waves (due to wind forcing) and subduction of water-mass anomalies (due to surface buoyancy forcing) as the primary mechanisms leading to observed changes of T–S structures at station ALOHA. Specifically, the analysis identifies surface freshwater fluxes along the wintertime outcrop of intermediate waters as a primary cause for salinity changes at station ALOHA and wind stress forcing east of the station position as another forcing mechanism of salinity variations around the Hawaiian Archipelago.

scholarly journals Ionospheric response to magnetar flare: signature of SGR J1550–5418 on coherent ionospheric Doppler radar

2017 ◽  
Vol 35 (3) ◽  
pp. 345-351 ◽  
Author(s):  
Ayman Mahrous
Keyword(s):  
Total Electron Content ◽  
Large Scale ◽  
Doppler Radar ◽  
Ionospheric Disturbance ◽  
Eastern Mediterranean ◽  
Small Scale ◽  
Electron Content ◽  
Total Electron ◽  
Ionospheric Perturbations ◽  
Onset Phase

Abstract. This paper presents observational evidence of frequent ionospheric perturbations caused by the magnetar flare of the source SGR J1550–5418, which took place on 22 January 2009. These ionospheric perturbations are observed in the relative change of the total electron content (ΔTEC/Δt) measurements from the coherent ionospheric Doppler radar (CIDR). The CIDR system makes high-precision measurements of the total electron content (TEC) change along ray-paths from ground receivers to low Earth-orbiting (LEO) beacon spacecraft. These measurements can be integrated along the orbital track of the beacon satellite to construct the relative spatial, not temporal, TEC profiles that are useful for determining the large-scale plasma distribution. The observed spatial TEC changes reveal many interesting features of the magnetar signatures in the ionosphere. The onset phase of the magnetar flare was during the CIDR's nighttime satellite passage. The nighttime small-scale perturbations detected by CIDR, with ΔTEC/Δt  ≥  0.05 TECU s−1, over the eastern Mediterranean on 22 January 2009 were synchronized with the onset phase of the magnetar flare and consistent with the emission of hundreds of bursts detected from the source. The maximum daytime large-scale perturbation measured by CIDR over northern Africa and the eastern Mediterranean was detected after ∼ 6 h from the main phase of the magnetar flare, with ΔTEC/Δt  ≤  0.10 TECU s−1. These ionospheric perturbations resembled an unusual poleward traveling ionospheric disturbance (TID) caused by the extraterrestrial source. The TID's estimated virtual velocity is 385.8 m s−1, with ΔTEC/Δt  ≤  0.10 TECU s−1.

scholarly journals Column water vapor determination in night period with a lunar photometer prototype

2013 ◽  
Vol 6 (1) ◽  
pp. 767-793
Author(s):  
A. Barreto ◽  
E. Cuevas ◽  
B. Damiri ◽  
P. M. Romero ◽  
F. Almansa
Keyword(s):  
Water Vapor ◽  
Comparative Study ◽  
Global Positioning System ◽  
High Mountain ◽  
Positioning System ◽  
Gps Receiver ◽  
Preliminary Results ◽  
Global Positioning ◽  
Lc Filter ◽  
Night Period

Abstract. In this paper we present the preliminary results of atmospheric column integrated water vapor (PWV) obtained with a new Lunar Cimel photometer (LC) at the high mountain Izaña Observatory in the period July–August, 2011. We have compared nocturnal PWV from LC with PWV from a Global Positioning System (GPS) receiver and nighttime radiosondes (RS92). LC data have been calibrated using the Lunar Langley Method (LLM). We complemented this comparative study using quasi-simultaneous daytime PWV from Cimel AERONET (CA), GPS and RS92. Comparison of daytime PWV from CA shows differences against GPS and RS92 up to 0.18 cm. Two different filters, with and approximate bandwidth of 10 nm and central wavelengths at 938 nm (Filter#1) and 937 nm (Filter#2), were mounted into the LC. Filter#1 is currently used in operational AERONET sunphotometers. PWV obtained with LC-Filter#1 showed an overestimation above 0.18 and 0.25 cm compared to GPS and RS92, respectively, meanwhile Filter#2, with a reduced out-of-band radiation, showed very low differences compared with the same references (≤0.03 cm). These results demonstrate the ability of the new lunar photometer to obtain accurate and continuous PWV measurements at night in addition to the notably influence of the filter's transmissivity response on PWV determination at nighttime. The use of enhanced bandpass filters in lunar photometry, which is affected by more important inaccuracies than sun-photometry, is necessary to infer PWV with similar precision than AERONET.

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