52 research outputs found
Cluster and THEMIS studies of Dayside Magnetospheric Boundary Layer Phenomena
No full textThe solar wind carries plasma and magnetic fields from the Sun. Being a gas of electrically charged particles, it will interact strongly with the magnetic field of the Earth. The main consequence of the interaction is that most of the solar wind is deflected around the Earth, but a detailed look reveals an abundance of complex processes which may, in extreme cases, affect our infrastructure by interfering with or destroying satellites and power grids. Fortunately, a more commonly observed effect is the generation of light in the upper parts of the atmosphere, known as Aurora. This thesis aims to increase our knowledge of the processes occurring in the boundary layers that connect the solar wind to the near-Earth environment. Of the three papers in this thesis, the first examines the consequences of a seemingly small change in the interplanetary magnetic field, which triggers a cascade of events that seriously disturb the magnetospheric boundary layers. This in turn leads to local disturbances of the magnetic field at the ground level. A large part of the field of space physics is the study of Magnetosphere–Ionosphere coupling (M-I coupling). Through waves, precipitating plasma and electrical currents, the forces applied to the magnetosphere by its interaction with the solar wind are transmitted down to the ionosphere. The second and third papers investigate interactions between the electric field, plasma and currents in the cusp, a region where solar wind plasma precipitates into the upper atmosphere
The impact of different sampling rates and calculation time intervals on ROTI values
No full textThe ROTI (Rate of TEC index) is a commonly used measure of ionospheric irregularities level. The algorithm to calculate ROTI is easily implemented, and is the same from paper to paper. However, the sample rate of the GNSS data used, and the time interval over which a value of ROTI is calculated, varies from paper to paper. When comparing ROTI values from different studies, this must be taken into account. This paper aims to show what these differences are, to increase the awareness of this issue. We have investigated the effect of different parameters for the calculation of ROTI values, using one year of data from 8 receivers at latitudes ranging from 59° N to 79° N.
We have found that the ROTI values calculated using different parameter choices are strongly positively correlated. However, the ROTI values are quite different. The effect of a lower sample rate is to lower the ROTI value, due to the loss of high-frequency parts of the ROT spectrum, while the effect of a longer calculation time interval is to remove or reduce short-lived peaks due to the inherent smoothing effect. The ratio of ROTI values based on data of different sampling rate is examined in relation to the ROT power spectrum.
Of relevance to statistical studies, we find that the median level of ROTI depends strongly on sample rate, strongly on latitude at auroral latitudes, and weakly on time interval. Thus, a baseline “quiet” or “noisy” level for one location or choice or parameters may not be valid for another location or choice of parameters
Observed effects of a geomagnetic storm on an RTK positioning network at high latitudes
No full textAt high latitudes, above 60° N, in the vicinity of the auroral oval, the ionosphere frequently experiences disturbed conditions that impact GNSS-based services. The Norwegian Mapping Authority (NMA) is operating a national real-time kinematic (RTK) positioning network and an ionosphere monitoring software. This paper presents the ionospheric observations during a geomagnetic storm, and the observed consequences for the positioning service. Significant disruptions that can be clearly related to the ionospheric disturbances were observed. They tend to occur in roughly longitudinal bands, which is expected for disturbances caused by the particle and energy precipitation in the auroral oval. The position error is found to increase exponentially with increasing rate of TEC index (ROTI). The disturbances are compared to auroral electrojet measurements and results from an operational auroral oval forecasting model. The disturbances are found to be strongly related to auroral electrojet currents
A study of low-energy plasma in the inner magnetosphere of Saturn
No full textIn this thesis the inner magnetosphere of Saturn has been studied using
data from the Langmuir probe on the spacecraft Cassini.
A program has been developed to analyze data from the Langmuir probe.
Using this program, three topics have been investigated.
The first topic is the effect of photoelectrons on Langmuir probe measurements.
Photoelectron current from the probe is found to depend on spacecraft attitude.
It is found that a leakage current from the stub is a likely cause of this.
Because the probe is relatively close to Cassini, photoelectrons emitted from
Cassini can dominate over plasma electrons under certain conditions.
The second topic is the analysis of Langmuir probe data
from Saturn orbit insertion, from 20 R to closest
approach and back out to 15 R.
The results reveal a diverse plasma environment
showing signs of interaction with the rings and moons of Saturn.
The last topic concerns velocity measurements by the Langmuir probe, which
in certain areas differ from the velocity measured by other instruments.
A combination of ions moving at corotation velocities
and ions moving at Keplerian velocities can produce the results and explain why
other instruments did not get the same results as the Langmuir probe
Statistics of ionospheric disturbances and their correlation with GNSS positioning errors at high latitudes
No full textThe Rate Of TEC Index (ROTI) is a commonly used measure of ionospheric activity. ROTI values have been computed every 5 min for the year 2012, for 10 receivers at latitudes from 59° to 79° North. We present the results in geomagnetic coordinates, showing that elevated ROTI values occur mainly in the cusp and nightside auroral oval regions. Elevated ROTI values are more common in the cusp, but in the nightside auroral oval they are stronger.
To investigate the relation to positioning errors, receiver coordinates were computed using the GIPSY software, for the same receivers and time resolution. We found that there is a strong positive correlation between Precise Point Positioning (PPP) error and ROTI for receivers that are affected by space weather. The 3D position error increases exponentially with increasing ROTI.
A statistical analysis presents also the risk of having several satellites observing enhanced ROTI values simultaneously, showing that this risk is greater at high latitudes
High Latitude Ionospheric Gradient Observation Results from a Multi-Scale Network
No full textIn this article, a cluster comprised of eight Continuously Operating Reference Station (CORS) receivers surrounding five supplemental test stations located on much shorter baselines is used to form a composite multi-scale network for the purpose of isolating, extracting, and analyzing ionospheric spatial gradient phenomena. The purpose of this investigation is to characterize the levels of spatial decorrelation between the stations in the cluster during the periods with increased ionospheric activity. The location of the selected receiver cluster is at the auroral zone at night-time (cluster centered at about 69.5° N, 19° E) known to frequently have increased ionospheric activity and observe smaller size of high-density irregularities. As typical CORS networks are relatively sparse, there is a possibility that spatially small-scale ionospheric delay gradients might not be observed by the network/closest receiver cluster but might affect the user, resulting in residual errors affecting system accuracy and integrity. The article presents high level statistical observations based on several hundred manually validated ionospheric spatial gradient events along with low level analysis of specific events with notable temporal/spatial characteristics
Overview of the 2015 St. Patrick’s day storm and its consequences for RTK and PPP positioning in Norway
No full textThe 2015 St. Patrick’s day storm was the first storm of solar cycle 24 to reach a level of “Severe” on the NOAA geomagnetic storm scale. The Norwegian Mapping Authority is operating a national real-time kinematic (RTK) positioning network and has in recent years developed software and services and deployed instrumentation to monitor space weather disturbances. Here, we report on our observations during this event. Strong GNSS (Global Navigation Satellite System) disturbances, measured by the rate-of-TEC index (ROTI), were observed at all latitudes in Norway on March 17th and early on March 18th. Late on the 18th, strong disturbances were only observed in northern parts of Norway. We study the ionospheric disturbances in relation to the auroral electrojet currents, showing that the most intense disturbances of GNSS signals occur on the poleward side of poleward-moving current regions. This indicates a possible connection to ionospheric polar cap plasma patches and/or particle precipitation caused by magnetic reconnection in the magnetosphere tail. We also study the impact of the disturbances on the network RTK and Precise Point Positioning (PPP) techniques. The vertical position errors increase rapidly with increasing ROTI for both techniques, but PPP is more precise than RTK at all disturbance levels
HAPEE, a statistical approach for ionospheric scintillation prediction in the polar region
No full textInternational audienceThrough several studies, CNES, ONERA, NSC and NMA have sought to define a prediction model for ionospheric variations that can disturb e.g. GNSS-based systems. The studies have focused on the high-latitude region, with a particular focus on the auroral oval. A first model was proposed in 2014. The model was a simple empirical model driven by the Kp geomagnetic index, and where the main output was the instantaneous mean Rate-of-TEC Index (ROTI) value. The model was found to not be sufficiently reliable to be used as an operational prediction model. In 2019, an updated model is proposed, where the main inputs are now the solar wind parameters pressure (the solar wind pressure p) and B z (the z component of the solar wind magnetic field). Moreover, a distribution of predicted ROTI or σ φ index is provided instead of a mean value. Thus, the model allows estimating the percentage of time of occurrence for a level of ROTI (or σ φ) to be exceeded in the next 5 minutes or 1 hour, or the exceeded ROTI (or σ φ) for a corresponding percentage of time. This empirical approach is based on 10 years of GNSS/scintillation data collected by more than 15 GNSS stations in Norway
HAPEE, a statistical approach for ionospheric scintillation prediction in the polar region
No full textInternational audienceThrough several studies, CNES, ONERA, NSC and NMA have sought to define a prediction model for ionospheric variations that can disturb e.g. GNSS-based systems. The studies have focused on the high-latitude region, with a particular focus on the auroral oval. A first model was proposed in 2014. The model was a simple empirical model driven by the Kp geomagnetic index, and where the main output was the instantaneous mean Rate-of-TEC Index (ROTI) value. The model was found to not be sufficiently reliable to be used as an operational prediction model. In 2019, an updated model is proposed, where the main inputs are now the solar wind parameters pressure (the solar wind pressure p) and B z (the z component of the solar wind magnetic field). Moreover, a distribution of predicted ROTI or σ φ index is provided instead of a mean value. Thus, the model allows estimating the percentage of time of occurrence for a level of ROTI (or σ φ) to be exceeded in the next 5 minutes or 1 hour, or the exceeded ROTI (or σ φ) for a corresponding percentage of time. This empirical approach is based on 10 years of GNSS/scintillation data collected by more than 15 GNSS stations in Norway
Overview of the 2015 St. Patrick’s day storm and its consequences for RTK and PPP positioning in Norway
No full textThe 2015 St. Patrick’s day storm was the first storm of solar cycle 24 to reach a level of “Severe” on the NOAA geomagnetic storm scale. The Norwegian Mapping Authority is operating a national real-time kinematic (RTK) positioning network and has in recent years developed software and services and deployed instrumentation to monitor space weather disturbances. Here, we report on our observations during this event. Strong GNSS (Global Navigation Satellite System) disturbances, measured by the rate-of-TEC index (ROTI), were observed at all latitudes in Norway on March 17th and early on March 18th. Late on the 18th, strong disturbances were only observed in northern parts of Norway. We study the ionospheric disturbances in relation to the auroral electrojet currents, showing that the most intense disturbances of GNSS signals occur on the poleward side of poleward-moving current regions. This indicates a possible connection to ionospheric polar cap plasma patches and/or particle precipitation caused by magnetic reconnection in the magnetosphere tail. We also study the impact of the disturbances on the network RTK and Precise Point Positioning (PPP) techniques. The vertical position errors increase rapidly with increasing ROTI for both techniques, but PPP is more precise than RTK at all disturbance levels
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