scholarly journals Small-scale characteristics of extremely high latitude aurora

2009 ◽  
Vol 27 (9) ◽  
pp. 3335-3347 ◽  
Author(s):  
J. A. Cumnock ◽  
L. G. Blomberg ◽  
A. Kullen ◽  
T. Karlsson ◽  
Keyword(s):  
High Latitude ◽  
Large Scale ◽  
Small Scale ◽  
Strong Correlations ◽  
Polar Cap ◽  
Plasma Flows ◽  
Ionospheric Convection ◽  
Local Closure ◽  
Scale Characteristics

Abstract. We examine 14 cases of an interesting type of extremely high latitude aurora as identified in the precipitating particles measured by the DMSP F13 satellite. In particular we investigate structures within large-scale arcs for which the particle signatures are made up of a group of multiple distinct thin arcs. These cases are chosen without regard to IMF orientation and are part of a group of 87 events where DMSP F13 SSJ/4 measures emissions which occur near the noon-midnight meridian and are spatially separated from both the dawnside and duskside auroral ovals by wide regions with precipitating particles typical of the polar cap. For 73 of these events the high-latitude aurora consists of a continuous region of precipitating particles. We focus on the remaining 14 of these events where the particle signatures show multiple distinct thin arcs. These events occur during northward or weakly southward IMF conditions and follow a change in IMF By. Correlations are seen between the field-aligned currents and plasma flows associated with the arcs, implying local closure of the FACs. Strong correlations are seen only in the sunlit hemisphere. The convection associated with the multiple thin arcs is localized and has little influence on the large-scale convection. This also implies that the sunward flow along the arcs is unrelated to the overall ionospheric convection.

scholarly journals 3D dynamical structuring of a high latitude erupting prominence: I- Analysis of the cool plasma flows before the eruption

2013 ◽  
Vol 8 (S300) ◽  
pp. 430-432
Author(s):  
Serge Koutchmy ◽  
Boris Filippov ◽  
Ehsan Tavabi ◽  
Cyril Bazin ◽  
Sylvain Weiller
Keyword(s):  
Magnetic Field ◽  
High Latitude ◽  
Large Scale ◽  
Vortex Structures ◽  
Small Scale ◽  
Plasma Flows ◽  
Cool Plasma ◽  
Large Scale Vortex ◽  
Good Proxy

AbstractBoth the origin of the quiescent prominences and their eruption related to CMEs are still a matter of extended studies. The small scale dynamic aspects like vortex structures and counter- flows are now seriously taken into account having in mind that the flows are a good proxy of the line of force of the omnipresent but rather unknown in detail force free or not magnetic field. Large scale vortex has been detected in a high latitude prominence observed on November 13- 14, 2011 before its eruption.

scholarly journals Balanced reconnection intervals: four case studies

2008 ◽  
Vol 26 (12) ◽  
pp. 3897-3912 ◽  
Author(s):  
A. D. DeJong ◽  
A. J. Ridley ◽  
C. R. Clauer
Keyword(s):  
Case Studies ◽  
Large Scale ◽  
The Other ◽  
Small Scale ◽  
Polar Cap ◽  
Reconnection Rate ◽  
Magnetospheric Convection ◽  
The Third ◽  
New Name ◽  
Definition Of

Abstract. During steady magnetospheric convection (SMC) events the magnetosphere is active, yet there are no data signatures of a large scale reconfiguration, such as a substorm. While this definition has been used for years it fails to elucidate the true physics that is occurring within the magnetosphere, which is that the dayside merging rate and the nightside reconnection rate balance. Thus, it is suggested that these events be renamed Balanced Reconnection Intervals (BRIs). This paper investigates four diverse BRI events that support the idea that new name for these events is needed. The 3–4 February 1998 event falls well into the classic definition of an SMC set forth by Sergeev et al. (1996), while the other challenge some previous notions about SMCs. The 15 February 1998 event fails to end with a substorm expansion and concludes as the magnetospheric activity slowly quiets. The third event, 22–23 December 2000, begins with a slow build up of magnetospheric activity, thus there is no initiating substorm expansion. The last event, 17 February 1998, is more active (larger AE, AL and cross polar cap potential) than previously studied SMCs. It also has more small scale activity than the other events studied here.

scholarly journals Statistical study of high-latitude plasma flow during magnetospheric substorms

2004 ◽  
Vol 22 (10) ◽  
pp. 3607-3624 ◽  
Author(s):  
G. Provan ◽  
M. Lester ◽  
S. B. Mende ◽  
S. E. Milan
Keyword(s):  
Plasma Flow ◽  
Growth Phase ◽  
High Latitude ◽  
Large Scale ◽  
Flow Region ◽  
Substorm Onset ◽  
Return Flow ◽  
Polar Cap ◽  
Magnetospheric Substorms ◽  
Superposed Epoch Analysis

Abstract. We have utilised the near-global imaging capabilities of the Northern Hemisphere SuperDARN radars, to perform a statistical superposed epoch analysis of high-latitude plasma flows during magnetospheric substorms. The study involved 67 substorms, identified using the IMAGE FUV space-borne auroral imager. A substorm co-ordinate system was developed, centred on the magnetic local time and magnetic latitude of substorm onset determined from the auroral images. The plasma flow vectors from all 67 intervals were combined, creating global statistical plasma flow patterns and backscatter occurrence statistics during the substorm growth and expansion phases. The commencement of the substorm growth phase was clearly observed in the radar data 18-20min before substorm onset, with an increase in the anti-sunward component of the plasma velocity flowing across dawn sector of the polar cap and a peak in the dawn-to-dusk transpolar voltage. Nightside backscatter moved to lower latitudes as the growth phase progressed. At substorm onset a flow suppression region was observed on the nightside, with fast flows surrounding the suppressed flow region. The dawn-to-dusk transpolar voltage increased from ~40kV just before substorm onset to ~75kV 12min after onset. The low-latitude return flow started to increase at substorm onset and continued to increase until 8min after onset. The velocity flowing across the polar-cap peaked 12-14min after onset. This increase in the flux of the polar cap and the excitation of large-scale plasma flow occurred even though the IMF Bz component was increasing (becoming less negative) during most of this time. This study is the first to statistically prove that nightside reconnection creates magnetic flux and excites high-latitude plasma flow in a similar way to dayside reconnection and that dayside and nightside reconnection, are two separate time-dependent processes.

Electrodynamics surrounding polar cap auroral arcs

2021 ◽  
Author(s):  
Amalie Ø. Hovland ◽  
Kjellmar Oksavik ◽  
Jone P. Reistad ◽  
Marc R. Hairston
Keyword(s):  
High Latitude ◽  
Optical Data ◽  
Polar Cap ◽  
Ionospheric Convection ◽  
Ion Drift ◽  
Polar Latitude ◽  
Mesoscale Structure ◽  
Radar Network ◽  
Auroral Arcs

<p>This multi-instrument case study investigates the electrodynamics surrounding polar cap auroral arcs. A long-lasting auroral arc is observed in the high latitude dusk-sector at ~80° Apex latitude in the northern hemisphere. Ion drift measurements from the SSIES system on the DMSP spacecraft have been combined with multiple ground-based observations. Line of sight velocity data from three polar latitude high-frequency Super Dual Auroral Radar Network (SuperDARN) radars show mesoscale structure in the ionospheric convection in the region surrounding the arc. The convection electric field in this region is modelled using a Spherical Elementary Convection Systems (SECS) technique, using curl-free basis functions only. The result is a regional model of the ionospheric convection based on the fairly dense and distributed flow observations and the curl-free constraint. The model is compared to optical data of the auroral arc from two high latitude Redline Emission Geospace Observatory (REGO) all-sky imagers as well as UV images and particle measurements from the DMSP spacecraft to describe the local electrodynamics in the vicinity of the high latitude arc throughout the event.</p>

Scale interactions in a mixing layer – the role of the large-scale gradients

2016 ◽  
Vol 791 ◽  
pp. 154-173 ◽  
Author(s):  
D. Fiscaletti ◽  
A. Attili ◽  
F. Bisetti ◽  
G. E. Elsinga
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Large Scale ◽  
Mixing Layer ◽  
Physical Space ◽  
Small Scale ◽  
Velocity Fluctuations ◽  
Small Scales ◽  
Low Pass ◽  
Scale Characteristics

The interaction between the large and the small scales of turbulence is investigated in a mixing layer, at a Reynolds number based on the Taylor microscale ($Re_{{\it\lambda}}$) of $250$, via direct numerical simulations. The analysis is performed in physical space, and the local vorticity root-mean-square (r.m.s.) is taken as a measure of the small-scale activity. It is found that positive large-scale velocity fluctuations correspond to large vorticity r.m.s. on the low-speed side of the mixing layer, whereas, they correspond to low vorticity r.m.s. on the high-speed side. The relationship between large and small scales thus depends on position if the vorticity r.m.s. is correlated with the large-scale velocity fluctuations. On the contrary, the correlation coefficient is nearly constant throughout the mixing layer and close to unity if the vorticity r.m.s. is correlated with the large-scale velocity gradients. Therefore, the small-scale activity appears closely related to large-scale gradients, while the correlation between the small-scale activity and the large-scale velocity fluctuations is shown to reflect a property of the large scales. Furthermore, the vorticity from unfiltered (small scales) and from low pass filtered (large scales) velocity fields tend to be aligned when examined within vortical tubes. These results provide evidence for the so-called ‘scale invariance’ (Meneveau & Katz, Annu. Rev. Fluid Mech., vol. 32, 2000, pp. 1–32), and suggest that some of the large-scale characteristics are not lost at the small scales, at least at the Reynolds number achieved in the present simulation.

scholarly journals Removal of Large-Scale Stripes Via Unidirectional Multiscale Decomposition

2019 ◽  
Vol 11 (21) ◽  
pp. 2472
Author(s):  
He ◽  
Wang ◽  
Chang ◽  
Zhang ◽  
Feng
Keyword(s):  
Large Scale ◽  
Imaging Systems ◽  
Small Scale ◽  
Layer By Layer ◽  
Multiscale Decomposition ◽  
Cumulative Error ◽  
Scale Characteristics ◽  
The Difference ◽  
Color Cast ◽  
Error Suppression

Stripes are common in remote sensing imaging systems equipped with multichannel time delay integration charge-coupled devices (TDI CCDs) and have different scale characteristics depending on their causes. Large-scale stripes appearing between channels are difficult to process by most current methods. The framework of column-by-column nonuniformity correction (CCNUC) is introduced to eliminate large-scale stripes. However, the worst problem of CCNUC is the unavoidable cumulative error, which will cause an overall color cast. To eliminate large-scale stripes and suppress the cumulative error, we proposed a destriping method via unidirectional multiscale decomposition (DUMD). The striped image was decomposed by constructing a unidirectional pyramid and making difference maps layer by layer. The highest layer of the pyramid was processed by CCNUC to eliminate large-scale stripes, and multiple cumulative error suppression measures were performed to reduce overall color cast. The difference maps of the pyramid were processed by a designed filter to eliminate small-scale stripes. Experiments showed that DUMD had good destriping performance and was robust with respect to different terrains.

scholarly journals Modulation of sporadic E layers by small-scale atmospheric waves in Earth’s high-latitude ionosphere

2019 ◽  
Vol 5 (3) ◽  
pp. 116-129
Author(s):  
Владимир Губенко ◽  
Vladimir Gubenko ◽  
Иван Кириллович ◽  
Ivan Kirillovich
Keyword(s):  
High Latitude ◽  
Radio Occultation ◽  
Small Scale ◽  
Polar Cap ◽  
Atmospheric Waves ◽  
Sporadic E Layers ◽  
High Latitude Ionosphere ◽  
Sporadic E Layer ◽  
Sporadic E ◽  
Good Agreement

We have used radio occultation measurements of the satellite CHAMP (Challenging Minisatellite Payload) to examine sporadic E layers (altitudes 90–130 km) in Earth’s high-latitude ionosphere. We have developed a new method for determining characteristics of internal atmospheric waves based on the use of inclined sporadic E layers of Earth’s ionosphere as a detector. The method relies on the fact that an internal wave propagating through the initially horizontal sporadic E layer causes the plasma density gradient to rotate in the direction of the wave vector, which leads to the fact that the layer ionization plane is set parallel to the phase wave front. The developed method enables us to study the interrelations between small-scale internal waves and sporadic E layers in Earth’s ionosphere and significantly expands the capabilities of traditional radio occultation monitoring of the atmosphere. We have found that the internal atmospheric waves under study have periods from 35 to 46 min and vertical phase speeds from 1.2 to 2.0 m/s, which are in good agreement with the results of independent experiments and simulation data on sporadic E layers at a height of ~100 km in Earth’s polar cap.

Correction to “Effect of high-latitude ionospheric convection in Sun-aligned polar cap arcs”

1994 ◽  
Vol 99 (A7) ◽  
pp. 13281 ◽  
Author(s):  
J. J. Sojka ◽  
L. Zhu ◽  
D. J. Crain ◽  
R. W. Schunk
Keyword(s):  
High Latitude ◽  
Polar Cap ◽  
Ionospheric Convection

scholarly journals Magnetospheric convection from Cluster EDI measurements compared with the ground-based ionospheric convection model IZMEM

2009 ◽  
Vol 27 (8) ◽  
pp. 3077-3087 ◽  
Author(s):  
M. Förster ◽  
Y. I. Feldstein ◽  
S. E. Haaland ◽  
L. A. Dremukhina ◽  
L. I. Gromova ◽  
...  
Keyword(s):  
High Latitude ◽  
Electric Potential ◽  
Potential Distribution ◽  
Spatial And Temporal Variation ◽  
Convection Pattern ◽  
Polar Cap ◽  
Ionospheric Convection ◽  
Electric Potential Distribution ◽  
Convection Model ◽  
The Imf

Abstract. Cluster/EDI electron drift observations above the Northern and Southern polar cap areas for more than seven and a half years (2001–2008) have been used to derive a statistical model of the high-latitude electric potential distribution for summer conditions. Based on potential pattern for different orientations of the interplanetary magnetic field (IMF) in the GSM y-z-plane, basic convection pattern (BCP) were derived, that represent the main characteristics of the electric potential distribution in dependence on the IMF. The BCPs comprise the IMF-independent potential distribution as well as patterns, which describe the dependence on positive and negative IMFBz and IMFBy variations. The full set of BCPs allows to describe the spatial and temporal variation of the high-latitude electric potential (ionospheric convection) for any solar wind IMF condition near the Earth's magnetopause within reasonable ranges. The comparison of the Cluster/EDI model with the IZMEM ionospheric convection model, which was derived from ground-based magnetometer observations, shows a good agreement of the basic patterns and its variation with the IMF. According to the statistical models, there is a two-cell antisunward convection within the polar cap for northward IMFBz+≤2 nT, while for increasing northward IMFBz+ there appears a region of sunward convection within the high-latitude daytime sector, which assumes the form of two additional cells with sunward convection between them for IMFBz+≈4–5 nT. This results in a four-cell convection pattern of the high-latitude convection. In dependence of the ±IMFBy contribution during sufficiently strong northward IMFBz conditions, a transformation to three-cell convection patterns takes place.

scholarly journals Plasma patches inside the polar cap and auroral oval: the impact on the spaceborne GPS receiver

2019 ◽  
Vol 9 ◽  
pp. A25 ◽  
Author(s):  
Chao Xiong ◽  
Fan Yin ◽  
Xiaomin Luo ◽  
Yaqi Jin ◽  
Xin Wan
Keyword(s):  
Large Scale ◽  
Magnetic Measurements ◽  
Auroral Oval ◽  
Lower Latitude ◽  
Small Scale ◽  
Gps Receiver ◽  
Polar Cap ◽  
Cusp Region ◽  
Swarm Satellites ◽  
The Impact

In this study, we focus on plasma patches with very dense plasma in the southern hemisphere during the main phase of 2015 St. Patrick’s Day storm. With in situ electron densities exceeding 1.5 × 1012 m−3 at 450–500 km altitude, the patches cause strong signal outages of the global positioning system (GPS) receivers on board Swarm satellites. By using the field-aligned currents derived from the Swarm magnetic measurements, we determined whether the satellites fly inside the auroral oval or not. Different influences on the spaceborne GPS receiver are seen when these patches are located at different latitude regions, e.g., inside the polar cap or auroral oval. The simultaneously measurements of 2 Hz electron density as well as 50 Hz magnetic signatures from Swarm show that when large-scale polar cap patches transported from dayside lower latitude entering the cusp region, irregularities with much finer scale-size are generated; associated with various instabilities inside the cusp region, the small-scale irregularities cause much more severe influence on the GPS signals. This is the first direct evidence to show that when plasma patches are located inside the cusp region, the spaceborne receiver experiences stronger outage of GPS signals.

Sign in / Sign up

Export Citation Format

Share Document