scholarly journals Spatio-temporal development of large scale auroral electrojet currents relative to substorm onsets

2021 ◽  
Author(s):  
Sebastian Käki ◽  
Ari Viljanen ◽  
Liisa Juusola ◽  
Kirsti Kauristie
Keyword(s):  
Large Scale ◽  
Current System ◽  
Field Measurements ◽  
Low Earth Orbit ◽  
Satellite Mission ◽  
Low Earth Orbit Satellites ◽  
Spatio Temporal ◽  
Substorm Onsets ◽  
Auroral Current ◽  
Swarm Satellite

Abstract. During auroral substorms the electric currents flowing in the ionosphere change rapidly and a large amount of energy is dissipated in the auroral ionosphere. An important part of the auroral current system are the auroral electrojets whose profiles can be estimated from magnetic field measurements from Low Earth Orbit satellites. In this paper we combine electrojet data derived from the Swarm satellite mission of ESA with the substorm database derived from the SuperMAG ground magnetometer network data. We organize the electrojet data in relation to the location and time of the onset and obtain statistics for the development of the integrated current and latitudinal location for the auroral electrojets relative to the onset. The major features of the behaviour of the westward electrojet are found to be in accordance with earlier studies of field aligned currents and ground magnetometer observations of substorm time statistics. In addition we show that after the onset the latitudinal location of the maximum of the westward electrojet determined from Swarm satellite data is mostly located close to the SuperMAG onset latitude in the local time sector of the onset regardless of where the onset happens. We also show that the SuperMAG onset corresponds to a strengthening of the order of 100 kA in the amplitude of the median of the westward integrated current in the Swarm data from 15 minutes before to 15 minutes after the onset.

Spatio-temporal development of large scale auroral electrojet currents relative to substorm onsets

2021 ◽  
Author(s):  
Sebastian Käki ◽  
Ari Viljanen ◽  
Liisa Juusola ◽  
Kirsti Kauristie
Keyword(s):  
Large Scale ◽  
Current System ◽  
Field Measurements ◽  
Low Earth Orbit ◽  
Satellite Mission ◽  
Low Earth Orbit Satellites ◽  
Spatio Temporal ◽  
Substorm Onsets ◽  
Auroral Current ◽  
Swarm Satellite

<p>The electric currents flowing in the ionosphere change rapidly and a large amount of energy is dissipated in the auroral ionosphere during auroral substorms. An important part of the auroral current system are the auroral electrojets whose profiles can be estimated from magnetic field measurements from low Earth orbit satellites. We have combined electrojet data derived from the Swarm satellite mission of ESA with the substorm database derived from the SuperMAG ground network data. We organize the electrojet data in relation to the location of the onset and obtain statistics for the development of the integrated current and latitudinal location for the auroral electrojets relative to the onset. Especially we show that just after the onset the latitudinal location of the maximum of the westward electrojet determined from Swarm satellite data is mostly located close to the onset latitude in the local time sector of the onset regardless of where the onset happens.</p>

scholarly journals An initial ULF wave index derived from 2 years of Swarm observations

2018 ◽  
Vol 36 (2) ◽  
pp. 287-299 ◽  
Author(s):  
Constantinos Papadimitriou ◽  
Georgios Balasis ◽  
Ioannis A. Daglis ◽  
Omiros Giannakis
Keyword(s):  
Methodological Approach ◽  
Low Frequency ◽  
Low Earth Orbit ◽  
Topside Ionosphere ◽  
Satellite Mission ◽  
Time Frequency ◽  
Ulf Wave ◽  
Magnetic Field Model ◽  
Swarm Satellite ◽  
Level 2

Abstract. The ongoing Swarm satellite mission provides an opportunity for better knowledge of the near-Earth electromagnetic environment. Herein, we use a new methodological approach for the detection and classification of ultra low-frequency (ULF) wave events observed by Swarm based on an existing time-frequency analysis (TFA) tool and utilizing a state-of-the-art high-resolution magnetic field model and Swarm Level 2 products (i.e., field-aligned currents – FACs – and the Ionospheric Bubble Index – IBI). We present maps of the dependence of ULF wave power with magnetic latitude and magnetic local time (MLT) as well as geographic latitude and longitude from the three satellites at their different locations in low-Earth orbit (LEO) for a period spanning 2 years after the constellation's final configuration. We show that the inclusion of the Swarm single-spacecraft FAC product in our analysis eliminates all the wave activity at high altitudes, which is physically unrealistic. Moreover, we derive a Swarm orbit-by-orbit Pc3 wave (20–100 MHz) index for the topside ionosphere and compare its values with the corresponding variations of solar wind variables and geomagnetic activity indices. This is the first attempt, to our knowledge, to derive a ULF wave index from LEO satellite data. The technique can be potentially used to define a new Level 2 product from the mission, the Swarm ULF wave index, which would be suitable for space weather applications. Keywords. Space plasma physics (waves and instabilities)

scholarly journals Coded continuous wave meteor radar

2015 ◽  
Vol 8 (7) ◽  
pp. 7879-7907
Author(s):  
J. Vierinen ◽  
J. L. Chau ◽  
N. Pfeffer ◽  
M. Clahsen ◽  
G. Stober
Keyword(s):  
Temporal Resolution ◽  
Large Scale ◽  
Pulse Compression ◽  
Continuous Wave ◽  
Signal To Noise Ratio ◽  
Field Measurements ◽  
Meteor Radar ◽  
Spatio Temporal ◽  
To Receive ◽  
Pulse Spacing

Abstract. The concept of coded continuous wave meteor radar is introduced. The radar uses a continuously transmitted pseudo-random waveform, which has several advantages: coding avoids range aliased echoes, which are often seen with commonly used pulsed specular meteor radars (SMRs); continuous transmissions maximize pulse compression gain, allowing operation with significantly lower peak transmit power; the temporal resolution can be changed after performing a measurement, as it does not depend on pulse spacing; and the low signal to noise ratio allows multiple geographically separated transmitters to be used in the same frequency band without significantly interfering with each other. The latter allows the same receiver antennas to be used to receive multiple transmitters. The principles of the signal processing are discussed, in addition to discussion of several practical ways to increase computation speed, and how to optimally detect meteor echoes. Measurements from a campaign performed with a coded continuous wave SMR are shown and compared with two standard pulsed SMR measurements. The type of meteor radar described in this paper would be suited for use in a large scale multi-static network of meteor radar transmitters and receivers. This would, for example, provide higher spatio-temporal resolution for mesospheric wind field measurements.

scholarly journals Regular daily variations in satellite magnetic total intensity data

2007 ◽  
Vol 25 (10) ◽  
pp. 2167-2174 ◽  
Author(s):  
J. P. R. Turner ◽  
D. E. Winch ◽  
D. J. Ivers ◽  
R. J. Stening
Keyword(s):  
Local Time ◽  
Field Measurements ◽  
Mean Value ◽  
Low Earth Orbit ◽  
Magnetic Data ◽  
Spherical Harmonic Analysis ◽  
Quiet Time ◽  
Champ Satellite ◽  
Daily Variations ◽  
Low Earth Orbit Satellites

Abstract. Regular magnetic daily quiet time (Sq) variations in total intensity of about 30 nT amplitude are determined in Universal Time (UT) from satellite magnetic field measurements. The CHAMP satellite traverses all hours of local time in 132 days and the Sq variations in total intensity are therefore calculated as an average over the 132 days for each hour of UT. Results are compared with the Sq daily variations in total intensity for the region above the ionosphere calculated from Malin's (1973) spherical harmonic analysis of the Sq Fourier coefficients for hourly mean value magnetic data from a global distribution of ground-based magnetic observatories. From the reasonable agreement between the two calculations, we conclude that low-Earth orbit satellites that traverse all hours of local time can determine Sq variations in total intensity above the ionosphere.

scholarly journals Retrieval of vertical profiles of atmospheric refraction angles by inversion of optical dilution measurements

2015 ◽  
Vol 8 (8) ◽  
pp. 3135-3145 ◽  
Author(s):  
D. Fussen ◽  
C. Tétard ◽  
E. Dekemper ◽  
D. Pieroux ◽  
N. Mateshvili ◽  
...  
Keyword(s):  
Low Earth Orbit ◽  
Vertical Profiles ◽  
Atmospheric Refraction ◽  
Satellite Mission ◽  
Image Deformation ◽  
Satellite Attitude ◽  
Accurate Knowledge ◽  
Celestial Bodies ◽  
Low Earth Orbit Satellites ◽  
Absolute Knowledge

Abstract. In this paper, we consider occultations of celestial bodies through the atmospheric limb from low Earth orbit satellites and we show how the usual change of tangent altitude associated with atmospheric refraction is inseparably connected to a variation of the observed apparent intensity, for extended and pointlike sources. We demonstrate, in the regime of weak refraction angles, that atmospheric optical dilution and image deformation are strictly concomitant. The approach leads to the integration of a simple differential equation related to the observed transmittance in the absence of other absorbing molecules along the optical path. The algorithm does not rely on the absolute knowledge of the radiometer pointing angle that is related to the accurate knowledge of the satellite attitude. We successfully applied the proposed method to the measurements performed by two past occultation experiments: GOMOS for stellar and ORA for solar occultations. The developed algorithm (named ARID) will be applied to the imaging of solar occultations in a forthcoming pico-satellite mission.

scholarly journals Satellite Measured Ionospheric Magnetic Field Variations over Natural Hazards Sites

2021 ◽  
Vol 13 (12) ◽  
pp. 2360
Author(s):  
Christoph Schirninger ◽  
Hans U. Eichelberger ◽  
Werner Magnes ◽  
Mohammed Y. Boudjada ◽  
Konrad Schwingenschuh ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Natural Hazards ◽  
Field Measurements ◽  
Volcanic Eruptions ◽  
Low Earth Orbit ◽  
Near Surface ◽  
The Earth ◽  
Magnetic Field Measurements ◽  
Spatio Temporal ◽  
Magnetic Field Variations

Processes and threats related to natural hazards play an important role in the evolution of the Earth and in human history. The purpose of this study is to investigate magnetic field variations measured at low Earth orbit (LEO) altitudes possibly associated with earthquakes, volcanic eruptions, and artificial outbursts. We focus on two missions with well equipped magnetometer packages, the China Seismo-Electromagnetic Satellite (CSES) and ESA’s three spacecraft Swarm fleet. After a natural hazards survey in the context of this satellites, and consideration of external magnetospheric and solar influences, together with spacecraft interferences, wavelet analysed spatio-temporal patterns in ionospheric magnetic field variations related to atmospheric waves are examined in detail. We provide assessment of the links between specific lithospheric or near surface sources and ionospheric magnetic field measurements. For some of the diverse events the achieved statistical results show a change in the pattern between pre- and post-event periods, we show there is an increase in the fluctuations for the higher frequency (smaller scales) components. Our results are relevant to studies which establish a link between space based magnetic field measurements and natural hazards.

Wind-Blown Sand Streamers and Turbulent Flow Structures

2020 ◽  
Author(s):  
Andreas Baas
Keyword(s):  
Turbulent Flow ◽  
Large Scale ◽  
Sonic Anemometer ◽  
Field Measurements ◽  
High Energy ◽  
Beach Sand ◽  
Flow Structures ◽  
Sand Transport ◽  
Near Surface ◽  
Spatio Temporal

<p>This contribution presents results of field measurements of wind-blown sand streamers and turbulent flow structures in the boundary layer airflow during gale-force winds on a beach. Sand transport and streamers were measured using Large-Scale Particle Image Velocimetry (LSPIV) combined with laser particle sensors (Wenglors), and airflow turbulence was monitored with a co-located sonic anemometer. The data analysis yields insight into the precise spatio-temporal relationships between sand streamers and near-surface airflow turbulence, at a high resolution of 25 Hz and a centimetre scale, including how high-energy sweeps correlate with the passage of fast-moving saltation clusters, and how Turbulent Kinetic Energy (TKE) may be linked to sediment mass flux.</p><p> </p>

scholarly journals Application of the Complete Data Fusion algorithm to the ozone profiles measured by geostationary and low-Earth-orbit satellites: a feasibility study

2021 ◽  
Vol 14 (3) ◽  
pp. 2041-2053
Author(s):  
Nicola Zoppetti ◽  
Simone Ceccherini ◽  
Bruno Carli ◽  
Samuele Del Bianco ◽  
Marco Gai ◽  
...  
Keyword(s):  
Data Fusion ◽  
Large Scale ◽  
Simple Procedure ◽  
Low Earth Orbit ◽  
Complete Data ◽  
Fusion Method ◽  
Fusion Algorithm ◽  
Large Sets ◽  
Ozone Profile ◽  
Low Earth Orbit Satellites

Abstract. The new platforms for Earth observation from space are characterized by measurements made at great spatial and temporal resolutions. While this abundance of information makes it possible to detect and study localized phenomena, it may be difficult to manage this large amount of data for the study of global and large-scale phenomena. A particularly significant example is the use by assimilation systems of Level 2 products that represent gas profiles in the atmosphere. The models on which assimilation systems are based are discretized on spatial grids with horizontal dimensions of the order of tens of kilometres in which tens or hundreds of measurements may fall in the future. A simple procedure to overcome this problem is to extract a subset of the original measurements, but this involves a loss of information. Another option is the use of simple averages of the profiles, but this approach also has some limitations that we will discuss in the paper. A more advanced solution is to resort to the so-called fusion algorithms, capable of compressing the size of the dataset while limiting the information loss. A novel data fusion method, the Complete Data Fusion algorithm, was recently developed to merge a set of retrieved products in a single product a posteriori. In the present paper, we apply the Complete Data Fusion method to ozone profile measurements simulated in the thermal infrared and ultraviolet bands in a realistic scenario. Following this, the fused products are compared with the input profiles; comparisons show that the output products of data fusion have smaller total errors and higher information contents in general. The comparisons of the fused products with the fusing products are presented both at single fusion grid box scale and with a statistical analysis of the results obtained on large sets of fusion grid boxes of the same size. We also evaluate the grid box size impact, showing that the Complete Data Fusion method can be used with different grid box sizes even if this possibility is connected to the natural variability of the considered atmospheric molecule.

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