scholarly journals Traits of sub-kilometer F-region irregularities as seen with the Swarm satellites

2019 ◽  
Author(s):  
Sharon Aol ◽  
Stephan Buchert ◽  
Edward Jurua
Keyword(s):  
Electron Density ◽  
European Space Agency ◽  
Ionospheric Irregularities ◽  
Magnetic Equator ◽  
Longitudinal Distribution ◽  
Density Data ◽  
Positive Correlation ◽  
F Region ◽  
Weak Positive Correlation ◽  
Swarm Satellites

Abstract. During the night, in the F-region, equatorial ionospheric irregularities manifest as plasma depletions observed by satellites and may cause radio signals to fluctuate. In this study, the distribution characteristics of ionospheric F-region irregularities in the low latitudes were investigated using 16 Hz electron density observations made by the faceplate on board Swarm satellites of the European Space Agency (ESA). The study covers the period from October 2014 to October 2018 when the 16 Hz electron density data were available. For comparison, both the absolute (ΔNe) and relative (ΔNe/Ne) density perturbations were used to quantify the level of ionospheric irregularities. The two methods generally reproduced the local time, seasonal and longitudinal distribution of equatorial ionospheric irregularities as shown in earlier studies, demonstrating the ability of Swarm 16 Hz electron density data. A difference between the two methods was observed based on the latitudinal distribution of ionospheric irregularities where ΔNe showed a symmetrical distribution about the magnetic equator, whereas ΔNe/Ne showed a magnetic equator centered Gaussian distribution. High values of ΔNe and ΔNe/Ne were observed in spatial bins with steep gradients of electron density from a longitudinal and seasonal perspective. The response of ionospheric irregularities to geomagnetic and solar activities was also investigated using Kp index and solar radio flux index (F10.7), respectively. A weak positive correlation was obtained between the occurrence of ionospheric irregularities and Kp index, irrespective of the method adopted to quantify the irregularities. In general, both ΔNe and ΔNe/Ne showed a weak positive correlation with F10.7. However, a higher positive correlation was obtained between ΔNe and F10.7 compared to ΔNe/Ne. Using the high-resolution faceplate data, we were able to identify ionospheric irregularities of scales of only a few hundreds of meters.

scholarly journals Traits of sub-kilometre F-region irregularities as seen with the Swarm satellites

2020 ◽  
Vol 38 (1) ◽  
pp. 243-261 ◽  
Author(s):  
Sharon Aol ◽  
Stephan Buchert ◽  
Edward Jurua
Keyword(s):  
Electron Density ◽  
European Space Agency ◽  
Magnetic Activity ◽  
Ionospheric Irregularities ◽  
Magnetic Equator ◽  
Longitudinal Distribution ◽  
Density Data ◽  
Solar Radio Flux ◽  
F Region ◽  
Swarm Satellites

Abstract. During the night, in the F-region, equatorial ionospheric irregularities manifest as plasma depletions observed by satellites, and they may cause radio signals to fluctuate. In this study, the distribution characteristics of ionospheric F-region irregularities in the low latitudes were investigated using 16 Hz electron density observations made by a faceplate which is a component of the electric field instrument (EFI) onboard Swarm satellites of the European Space Agency (ESA). The study covers the period from October 2014 to October 2018 when the 16 Hz electron density data were available. For comparison, both the absolute (dNe) and relative (dNe∕Ne) density perturbations were used to quantify the level of ionospheric irregularities. The two methods generally reproduced the local-time (LT), seasonal and longitudinal distribution of equatorial ionospheric irregularities as shown in earlier studies, demonstrating the ability of Swarm 16 Hz electron density data. A difference between the two methods was observed based on the latitudinal distribution of ionospheric irregularities where (dNe) showed a symmetrical distribution about the magnetic equator, while dNe∕Ne showed a magnetic-equator-centred Gaussian distribution. High values of dNe and dNe∕Ne were observed in spatial bins with steep gradients of electron density from a longitudinal and seasonal perspective. The response of ionospheric irregularities to geomagnetic and solar activities was also investigated using Kp index and solar radio flux index (F10.7), respectively. The reliance of dNe∕Ne on solar and magnetic activity showed little distinction in the correlation between equatorial and off-equatorial latitudes, whereas dNe showed significant differences. With regard to seasonal and longitudinal distribution, high dNe and dNe∕Ne values were often found during quiet magnetic periods compared to magnetically disturbed periods. The dNe increased approximately linearly from low to moderate solar activity. Using the high-resolution faceplate data, we were able to identify ionospheric irregularities on the scale of only a few hundred of metres.

scholarly journals Magnetic Field and Electron Density Data Analysis from Swarm Satellites Searching for Ionospheric Effects by Great Earthquakes: 12 Case Studies from 2014 to 2016

Atmosphere ◽  
2019 ◽  
Vol 10 (7) ◽  
pp. 371 ◽  
Author(s):  
Angelo De Santis ◽  
Dedalo Marchetti ◽  
Luca Spogli ◽  
Gianfranco Cianchini ◽  
F. Javier Pavón-Carrasco ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electron Density ◽  
Geomagnetic Latitude ◽  
Statistical Correlation ◽  
Satellite Mission ◽  
Strong Earthquakes ◽  
Density Data ◽  
Ionospheric Effects ◽  
Swarm Satellites ◽  
Swarm Satellite

We analyse Swarm satellite magnetic field and electron density data one month before and one month after 12 strong earthquakes that have occurred in the first 2.5 years of Swarm satellite mission lifetime in the Mediterranean region (magnitude M6.1+) or in the rest of the world (M6.7+). The search for anomalies was limited to the area centred at each earthquake epicentre and bounded by a circle that scales with magnitude according to the Dobrovolsky’s radius. We define the magnetic and electron density anomalies statistically in terms of specific thresholds with respect to the same statistical quantity along the whole residual satellite track (|geomagnetic latitude| ≤ 50°, quiet geomagnetic conditions). Once normalized by the analysed satellite tracks, the anomalies associated to all earthquakes resemble a linear dependence with earthquake magnitude, so supporting the statistical correlation with earthquakes and excluding a relationship by chance.

scholarly journals Ionospheric irregularities and scintillations: a direct comparison of in situ density observations with ground-based L-band receivers

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Sharon Aol ◽  
Stephan Buchert ◽  
Edward Jurua
Keyword(s):  
Electron Density ◽  
Satellite Communication ◽  
Density Fluctuations ◽  
Ionospheric Irregularities ◽  
Langmuir Probes ◽  
Amplitude Scintillation ◽  
Swarm Satellites ◽  
L Band ◽  
Electron Density Fluctuations

Abstract Ionospheric irregularities can affect satellite communication and navigation by causing scintillations of radio signals. The scintillations are routinely measured using ground-based networks of receivers. This study presents observations of ionospheric irregularities by Langmuir probes on the Swarm satellites. They are compared with amplitude scintillation events recorded by the Global Positioning System-Scintillation Network and Decision Aid (GPS-SCINDA) receiver installed in Mbarara (Lat: $$0.6^{\circ }\hbox {S}$$ 0 . 6 ∘ S , Lon: $$30.8^{\circ }\hbox {E}$$ 30 . 8 ∘ E , Mag. lat: $$10.2^{\circ }\hbox {S}$$ 10 . 2 ∘ S ). The study covers the years from 2014 to 2018 when both data sets were available. It was found that the ground-based amplitude scintillations were enhanced when Swarm registered ionospheric irregularities for a large number of passes. The number of matching observations was greater for Swarm A and C which orbited at lower altitudes compared to Swarm B. However, some counterexamples, i.e., cases when in situ electron density fluctuations were not associated with any observed L-band amplitude scintillation and vice versa, were also found. Therefore, mismatches between observed irregularity structures and scintillations can occur just over a few minutes and within distances of a few tens of kilometers. The amplitude scintillation strength, characterized by the S4 index was estimated from the electron density data using the well-known phase screen model for weak scattering. The derived amplitude scintillation was on average lower for Swarm B than for A and C and less in accordance with the observed range. Irregularities at an altitude of about 450 km contribute strongly to scintillations in the L-band, while irregularities at about 510-km altitude contribute significantly less. We infer that in situ density fluctuations observed on passes over or near Mbarara may be used to indicate the risk that ionospheric radio wave scintillations occur at that site.

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.

Is Strategic Planning Worth the Effort? A Study of Firm Performance Versus Planning Comprehensiveness in Australia

2000 ◽  
Vol 6 (1) ◽  
pp. 1-13 ◽  
Author(s):  
Peter Devenish ◽  
Tom Fisher
Keyword(s):  
Strategic Planning ◽  
Financial Performance ◽  
Statistical Tests ◽  
The United States ◽  
Negative Finding ◽  
Positive Correlation ◽  
Listed Firms ◽  
The United Kingdom ◽  
Weak Positive Correlation ◽  
Positive Correlations

AbstractThe planning-performance literature suggests that there is a weak positive correlation between strategic planning and financial performance. This study has been undertaken to determine whether this weak positive correlation is true for Australian firms.Strategic planning for the purposes of this study is arranged in three levels of planning complexity. A sample of 77 listed firms was surveyed to determine their level of planning complexity, and this was correlated with the firm's financial performance over a three year period.A range of statistical tests did not reveal any significant correlation between strategic planning at any of the three levels and the financial performance of the firm. This negative finding is generally in line with other recent studies conducted in Australia, the United States and the United Kingdom.However, positive correlations were found with several subjective performance measures, suggesting that respondents generally believe that strategic planning is helping their company.

Calculation of the electron density of the F region heated by a high-power radio-wave field

1977 ◽  
Vol 20 (12) ◽  
pp. 1267-1270 ◽  
Author(s):  
Yu. A. Ignat'ev ◽  
Z. N. Krotova ◽  
�. E. Mityakova
Keyword(s):  
Radio Wave ◽  
Wave Field ◽  
Electron Density ◽  
High Power ◽  
F Region

scholarly journals Ionosonde Observations of Spread F and Spread Es at Low and Middle Latitudes during the Recovery Phase of the 7–9 September 2017 Geomagnetic Storm

2021 ◽  
Vol 13 (5) ◽  
pp. 1010
Author(s):  
Lehui Wei ◽  
Chunhua Jiang ◽  
Yaogai Hu ◽  
Ercha Aa ◽  
Wengeng Huang ◽  
...  
Keyword(s):  
Geomagnetic Storm ◽  
Large Scale ◽  
Satellite System ◽  
Recovery Phase ◽  
Ionospheric Irregularities ◽  
Middle Latitudes ◽  
Multiple Observations ◽  
Swarm Satellites ◽  
Spread F ◽  
Global Navigation Satellite

This study presents observations of nighttime spread F/ionospheric irregularities and spread Es at low and middle latitudes in the South East Asia longitude of China sectors during the recovery phase of the 7–9 September 2017 geomagnetic storm. In this study, multiple observations, including a chain of three ionosondes located about the longitude of 100°E, Swarm satellites, and Global Navigation Satellite System (GNSS) ROTI maps, were used to study the development process and evolution characteristics of the nighttime spread F/ionospheric irregularities at low and middle latitudes. Interestingly, spread F and intense spread Es were simultaneously observed by three ionosondes during the recovery phase. Moreover, associated ionospheric irregularities could be observed by Swarm satellites and ground-based GNSS ionospheric TEC. Nighttime spread F and spread Es at low and middle latitudes might be due to multiple off-vertical reflection echoes from the large-scale tilts in the bottom ionosphere. In addition, we found that the periods of the disturbance ionosphere are ~1 h at ZHY station, ~1.5 h at LSH station and ~1 h at PUR station, respectively. It suggested that the large-scale tilts in the bottom ionosphere might be produced by LSTIDs (Large scale Traveling Ionospheric Disturbances), which might be induced by the high-latitude energy inputs during the recovery phase of this storm. Furthermore, the associated ionospheric irregularities observed by satellites and ground-based GNSS receivers might be caused by the local electric field induced by LSTIDs.

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