The Swarm satellites offer an unprecedented opportunity for improving our knowledge about polar cap patches, which are regarded as the main space weather issue in the polar caps. We present a new ...robust algorithm that automatically detects polar cap patches using in situ plasma density data from Swarm. For both hemispheres, we compute the spatial and seasonal distributions of the patches identified separately by Swarm A and Swarm B between December 2013 and August 2016. We show a clear seasonal dependency of patch occurrence. In the Northern Hemisphere (NH), patches are essentially a winter phenomenon, as their occurrence rate is enhanced during local winter and very low during local summer. Although not as pronounced as in the NH, the same pattern is seen for the Southern Hemisphere (SH). Furthermore, the rate of polar cap patch detection is generally higher in the SH than in the NH, especially on the dayside at about 77° magnetic latitude. Additionally, we show that in the NH the number of patches is higher in the postnoon and prenoon sectors for interplanetary magnetic field (IMF) By<0 and IMF By>0, respectively, and that this trend is mirrored in the SH, consistent with the ionospheric flow convection. Overall, our results confirm previous studies in the NH, shed more light regarding the SH, and provide further insight into polar cap patch climatology. Along with this algorithm, we provide a large data set of patches automatically detected with in situ measurements, which opens new horizons in studies of polar cap phenomena.
Key Points
New polar cap patch detection method based on Swarm in situ data provides an unprecedented data set for polar cap patch statistical studies
Polar cap patch occurrence rate is highest during local winter in both hemispheres; in the south it is also significant during local summer
There is a clear IMF By dependency in the spatial distribution of polar cap patches, consistent with the ionospheric flow pattern
Positive political theorists typically deny the possibility of collective agents by understanding aggregation problems to imply that groups are not rational decision-makers. This view contrasts with ...List and Pettit’s view that such problems actually imply the necessity of accounting for collective agents in explanations of group behaviour. In this paper, I explore these conflicting views and ask whether positive political theorists should alter their individualist analyses of groups like legislatures, political parties, and constituent assemblies. I show how we fail to appreciate the significance of strategic voting and agenda control by treating groups as agents. I, therefore, conclude that positive political theorists should cling to their individualist approach and maintain that groups are not agents.
Eliminating Group Agency Moen, Lars J. K.
Economics and philosophy,
03/2023, Letnik:
39, Številka:
1
Journal Article
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Aggregating individuals’ consistent attitudes might produce inconsistent collective attitudes. Some groups therefore need the capacity to form attitudes that are irreducible to those of their ...members. Such groups, group-agent realists argue, are agents in control of their own attitude formation. In this paper, however, I show how group-agent realism overlooks the important fact that groups consist of strategically interacting agents. Only by eliminating group agency from our social explanations can we see how individuals vote strategically to gain control of their groups and produce collective attitudes we cannot make sense of if we treat groups as agents.
We present two examples from the cusp ionosphere over Svalbard, where poleward moving auroral forms (PMAFs) are causing significant phase scintillation in signals from navigation satellites. The data ...were obtained using a combination of ground‐based optical instruments and a newly installed multiconstellation navigation signal receiver at Longyearbyen. Both events affected signals from GPS and Global Navigation Satellite System (GLONASS). When one intense PMAF appeared, the signal from one GPS spacecraft also experienced a temporary loss of signal lock. Although several polar cap patches were also observed in the area as enhancements in total electron content, the most severe scintillation and loss of signal lock appear to be attributed to very intense PMAF activity. This shows that PMAFs are locations of strong ionospheric irregularities, which at times may cause more severe disturbances in the cusp ionosphere for navigation signals than polar cap patches.
Key Points
Intense phase scintillation from dayside poleward moving auroral forms (PMAFs)
PMAFs can have stronger ionospheric irregularities than polar cap patches
PMAFs can cause loss of signal lock
The characteristics of turbulent plasma in the winter cusp ionosphere is studied based on in‐situ data from the Investigation of Cusp Irregularities (ICI) sounding rockets. The electron density ...fluctuations from ICI‐2 and ICI‐3 missions have been analyzed for the whole flight, using advanced time‐series analysis techniques. The analysis of the autocorrelation scale is indicative of the turbulence integral scale and marks the onset of the turbulent cascade from large to small scales in the power spectrum density of the rocket data. The power spectrum is typical for a turbulent field. The turbulent structures are persistent in the data, which are quantified by analyzing the Probability Distribution Functions (PDFs) and their deviations from the Gaussian distribution. The kurtosis analysis indicates the presence of intermittency. These results are compared with the Local Intermittence Measure ‐ LIM, which confirms the presence of small scale intermittent structures. The turbulence measured by rockets appears well developed and covers frequencies between 1 Hz and several hundred Hz. There is a good agreement with the previous results, suggesting that density fluctuations in the ionospheric cusp agree with the turbulence framework in which intermittent processes transfer energy across different scales.
Key Points
Sounding rocket in situ observations show a complex behavior similar to a turbulent field in the ionospheric cusp
The integral scale of the turbulence exhibits large‐scale structures of the order of tens of kilometers
Density fluctuations agree with the turbulence framework in which intermittent processes transfer energy across different scales
A moralised conception of freedom is based on a normative theory. Understanding it therefore requires an analysis of this theory. In this paper, I show how republican freedom as non-domination is ...moralised, and why analysing this concept therefore involves identifying the basic components of the republican theory of justice. One of these components is the non-moralised pure negative conception of freedom as non-interference. Republicans therefore cannot keep insisting that their freedom concept conflicts with, and is superior to, this more basic concept. I demonstrate how we can use pure negative freedom to formulate the republican theory more precisely. This exercise is more fruitful than the common focus on the alleged conflict between the two freedom concepts.
We examined the source region of dayside large‐scale traveling ionospheric disturbances (LSTIDs) and their relation to cusp energy input. Aurora and total electron content (TEC) observations show ...that LSTIDs propagate equatorward away from the cusp and demonstrate the cusp region as the source region. Enhanced energy input to the cusp initiated by interplanetary magnetic field (IMF) southward turning triggers the LSTIDs, and each LSTID oscillation is correlated with a TEC enhancement in the dayside oval with tens of minutes periodicity. Equatorward‐propagating LSTIDs are likely gravity waves caused by repetitive heating in the cusp. The cusp source can explain the high LSTID occurrence on the dayside during geomagnetically active times. Poleward‐propagating ΔTEC patterns in the polar cap propagate nearly at the convection speed. While they have similar ΔTEC signatures to gravity wave‐driven LSTIDs, they are suggested to be weak polar cap patches quasiperiodically drifting from the cusp into the polar cap via dayside reconnection.
Key Points
The cusp region in the dayside auroral oval has been found to be the source region of dayside LSTIDs
Enhanced energy input to the cusp initiated by IMF southward turning triggers the dayside LSTIDs
Midlatitude LSTIDs are thermospheric gravity waves; polar cap TEC perturbations are weak polar cap patches
First experimental proof of a clear and strong dependence of the standard phase scintillation index (σφ) derived using Global Positioning System measurements on the ionospheric plasma flow around the ...noon sector of polar ionosphere is presented. σφ shows a strong linear dependence on the plasma drift speed measured by the Super Dual Auroral Radar Network radars, whereas the amplitude scintillation index (S4) does not. This observed dependence can be explained as a consequence of Fresnel frequency dependence of the relative drift and the used constant cutoff frequency (0.1 Hz) to detrend the data for obtaining standard σφ. The lack of dependence of S4 on the drift speed possibly eliminates the plasma instability mechanism(s) involved as a cause of the dependence. These observations further confirm that the standard phase scintillation index is much more sensitive to plasma flow; therefore, utmost care must be taken when identifying phase scintillation (diffractive phase variations) from refractive (deterministic) phase variations, especially in the polar region where the ionospheric plasma drift is much larger than in equatorial and midlatitude regions.
Key Points
A clear strong linear dependence of phase scintillation index on the plasma drift speed around noon sector of the polar ionosphere is presented
Observed dependence can be very possibly explained by the dependence of the shifted Fresnel frequency from the relative drift
Amplifies the importance of using dynamic cutoff frequency in detrending the phase of GPS signal in the polar region
We use an automated procedure to identify periods of enhanced dayside reconnection followed by enhanced nightside reconnection in measurements of the polar cap size by the Active Magnetosphere and ...Planetary Electrodynamics Response Experiment between January 2010 and December 2012; we find 490 such events. We investigate the dynamics of the spatial distributions of the total electron content (TEC) and phase scintillations of Global Positioning System (GPS) signals across the northern polar region and here report three important findings: (1) While a TEC enhancement (due to polar cap patches) propagates across the polar cap during these events, this enhancement is not associated with significant GPS phase scintillations. (2) Instead, a significant impact on GPS signal quality is first found when the TEC enhancements cross the nightside auroral boundary. (3) In combination with upward field‐aligned currents, these TEC enhancements cause the strongest GPS phase scintillations. We conclude that polar cap patches are not, as previously thought, a space weather threat inside the polar cap but instead reveal their biggest impact once they reach the nightside auroral oval, in particular when combined with upward field‐aligned currents.
Key Points
During polar cap expansion/contraction, TEC enhancements cross the polar cap
Inside the polar cap, they are not associated with GPS scintillations
Once they enter the auroral oval, they cause significant GPS scintillations
Global Navigation Satellite Systems (GNSS) are subject to disturbances caused by plasma irregularities in the ionosphere. Studies have suggested that in addition to the gradient drift and ...Kelvin‐Helmholtz instabilities, electron precipitation may be important for phase scintillations in the dayside auroral region. This study combines in situ Swarm data with ground GNSS observations to investigate the potential role of filamentary field‐aligned currents (FACs) on phase scintillations in the dayside auroral region by analyzing 22 events with phase scintillations exceeding 0.45 radians. We observe colocation between regions of severe phase scintillations and highly filamented FACs with fluctuations measured in the spacecraft frame of the order of 20 Hz. The observations indicate that filamentary FACs are crucial drivers for irregularities responsible for creating severe phase scintillations measured in the dayside auroral region and are thus of significant importance in the context of space weather impact on satellite communication.
Plain Language Summary
Satellite‐based navigation systems such as Global Positioning System (GPS) are known to be affected by dynamic phenomena in the upper atmosphere. The signals are subject to disturbances, resulting in reduced position accuracy or even a loss of signal reception. Several processes have been suggested as being responsible for these disturbances in the dayside auroral region, but their relative importance is still unclear. Thus, we used Swarm data as well as ground‐based instrumentation to investigate this issue. We identified 22 events with severe disturbances that were located where we could compare data from the satellite and from ground‐based instruments. We find that the occurrences of severe phase scintillation coincide with structured field‐aligned currents (FACs), making them potentially a primary driver for signal disturbances in the daytime auroral region.
Key Points
Severe GNSS phase scintillations in the winter dayside auroral ionosphere coincide with filamentary FACs
Filamentary FACs appear to be essential for the creation of severe phase scintillations
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