scholarly journals Radar observations of density gradients, electric fields, and plasma irregularities near polar cap patches in the context of the gradient‐drift instability

2017 ◽  
Vol 122 (3) ◽  
pp. 3721-3736 ◽  
Author(s):  
Leslie J. Lamarche ◽  
Roman A. Makarevich
Keyword(s):  
Electric Fields ◽  
Density Gradients ◽  
Polar Cap ◽  
Radar Observations ◽  
Plasma Irregularities ◽  
Gradient Drift ◽  
Drift Instability

scholarly journals Observation of polar cap patches and calculation of gradient drift instability growth times: A Swarm case study

2015 ◽  
Vol 42 (2) ◽  
pp. 201-206 ◽  
Author(s):  
A. Spicher ◽  
T. Cameron ◽  
E. M. Grono ◽  
K. N. Yakymenko ◽  
S. C. Buchert ◽  
...  
Keyword(s):  
Polar Cap ◽  
Instability Growth ◽  
Gradient Drift ◽  
Drift Instability

scholarly journals Non-magnetic aspect sensitive auroral echoes from the lower E region observed at 50 MHz

1999 ◽  
Vol 17 (10) ◽  
pp. 1284-1292 ◽  
Author(s):  
R. Rüster ◽  
K. Schlegel
Keyword(s):  
Magnetic Field ◽  
Electric Fields ◽  
Middle Atmosphere ◽  
Magnetic Field Direction ◽  
Ionosphere Plasma ◽  
E Region ◽  
Strong Electric Fields ◽  
Gradient Drift ◽  
Drift Instability ◽  
The Magnetic Field

Abstract. Backscatter from E-region irregularities was observed at aspect angles close to 90° (almost parallel to the direction of the magnetic field) using the ALOMAR SOUSY radar at Andoya/Norway. Strong electric fields and increased E-region electron temperatures simultaneously measured with the incoherent scatter facility EISCAT proved that the Farley-Buneman plasma instability was excited. In addition, strong particle precipitation was present as inferred from EISCAT electron densities indicating that the gradient drift instability may have been active, too. Backscatter at such large aspect angles was not expected and has not been observed before. The characteristics of the observed echoes, however, are in many aspects completely different from usual auroral radar results: the Doppler velocities are only of the order of 10 m/s, the half-width of the spectra is around 5 m/s, the echoes originate at altitudes well below 100 km, and they seem to be not aspect-sensitive with respect to the magnetic field direction. We, therefore, conclude that the corresponding irregularities are not caused by the mentioned instabilities and that other mechanism have to be invoked.Key words. Ionosphere (plasma waves and instabilities; ionosphere irregularities; particle precipitaion) · Meteorology and atmospheric dynamics (middle atmosphere dynamics)

scholarly journals HF Doppler radar observations of sporadic E at an Indian low latitude station, Visakhapatnam

2009 ◽  
Vol 27 (2) ◽  
pp. 537-545 ◽  
Author(s):  
M. S. S. R. K. N Sarma ◽  
C. Raghava Reddy ◽  
K. Niranjan
Keyword(s):  
Doppler Radar ◽  
Doppler Velocity ◽  
Night Time ◽  
Low Latitude ◽  
Radar Observations ◽  
Latitude Station ◽  
Velocity Variations ◽  
Sporadic E ◽  
Gradient Drift ◽  
Drift Instability

Abstract. 5.5 MHz HF Doppler radar observations of Sporadic E over an Indian low latitude station, Visakhapatnam (17.7° N, 83.3° E and Dip 20°) with 10 s resolution showed quasi-periodic variations of the echo strength and Doppler velocity variations with periods of a few minutes to a few tens of minutes. The echo strength and Doppler velocity variations with time in different range bins of the ES echo showed variations which are some times similar and some times significantly different in successive range bins at intervals of 7.5 km. The ES echo occurs with the height of maximum echo strength in the range of 100 km to 120 km and some times at 130 km. The altitude variation of the average Doppler velocity is highly variable and the height of maximum echo strength is not the same as the height of maximum Doppler velocity. Observations of ES echoes at different times of the day are presented to bring out the differences between the day and night time ES echoes. The relationship between Radar and ES parameters derived from Ionograms is poorer than that of mid latitudes which is quite consistent with the expectations based on gradient drift instability.

scholarly journals On a new process for cusp irregularity production

2008 ◽  
Vol 26 (9) ◽  
pp. 2871-2885 ◽  
Author(s):  
H. C. Carlson ◽  
K. Oksavik ◽  
J. Moen
Keyword(s):  
Additional Data ◽  
Current System ◽  
Velocity Shear ◽  
Polar Cap ◽  
Plasma Irregularities ◽  
The Past ◽  
F Region ◽  
New Process ◽  
Compound Process ◽  
Gradient Drift

Abstract. Two plasma instability mechanisms were thought until 2007 to dominate the formation of plasma irregularities in the F region high latitude and polar ionosphere; the gradient-drift driven instability, and the velocity-shear driven instability. The former mechanism was accepted as accounting for plasma structuring in polar cap patches, the latter for plasma structuring in polar cap sun aligned arcs. Recent work has established the need to replace this view of the past two decades with a new patch plasma structuring process (not a new mechanism), whereby shear-driven instabilities first rapidly structure the entering plasma, after which gradient drift instabilities build on these large "seed" irregularities. Correct modeling of cusp and early polar cap patch structuring will not be accomplished without allowing for this compound process. This compound process explains several previously unexplained characteristics of cusp and early polar cap patch irregularities. Here we introduce additional data, coincident in time and space, to extend that work to smaller irregularity scale sizes and relate it to the structured cusp current system.

scholarly journals Auroral <i>E</i>-region electron density gradients measured

2000 ◽  
Vol 18 (9) ◽  
pp. 1172-1181 ◽  
Author(s):  
C. Haldoupis ◽  
K. Schlegel ◽  
G. Hussey
Keyword(s):  
Electric Field ◽  
Density Gradient ◽  
Electron Density ◽  
Electric Fields ◽  
Plasma Waves ◽  
Density Gradients ◽  
Electron Density Gradient ◽  
E Region ◽  
Gradient Drift ◽  
Region Plasma

Abstract. In the theory of E-region plasma instabilities, the ambient electric field and electron density gradient are both included in the same dispersion relation as the key parameters that provide the energy for the generation and growth of electrostatic plasma waves. While there exist numerous measurements of ionospheric electric fields, there are very few measurements and limited knowledge about the ambient electron density gradients, ∇Ne, in the E-region plasma. In this work, we took advantage of the EISCAT CP1 data base and studied statistically the vertical electron density gradient length, Lz=Ne/(dNe/dz), at auroral E-region heights during both eastward and westward electrojet conditions and different ambient electric field levels. Overall, the prevailing electron density gradients, with Lz ranging from 4 to 7 km, are found to be located below 100 km, but to move steadily up in altitude as the electric field level increases. The steepest density gradients, with Lz possibly less than 3 km, occur near 110 km mostly in the eastward electrojet during times of strong electric fields. The results and their implications are examined and discussed in the frame of the linear gradient drift instability theory. Finally, it would be interesting to test the implications of the present results with a vertical radar interferometer.Key words: Ionosphere (auroral ionosphere; ionospheric irregularities; plasma waves and instabilities)  

scholarly journals Global Positioning System (GPS) Scintillation Associated with a Polar Cap Patch

2021 ◽  
Vol 13 (10) ◽  
pp. 1915
Author(s):  
Jayachandran P. Thayyil ◽  
Anthony M. McCaffrey ◽  
Yong Wang ◽  
David R. Themens ◽  
Christopher Watson ◽  
...  
Keyword(s):  
Global Positioning System ◽  
Leading Edge ◽  
Signal Amplitude ◽  
Positioning System ◽  
Polar Cap ◽  
Linear Evolution ◽  
Gps Scintillation ◽  
Global Positioning ◽  
Gradient Drift ◽  
Drift Instability

A Global Positioning System (GPS) network in the polar cap, along with ionosonde and SuperDARN radar measurements, are used to study GPS signal amplitude and phase scintillation associated with a polar cap patch. The patch was formed due to a north-to-south transition of the interplanetary magnetic field (IMF Bz). The patch moved antisunward with an average speed of ~600 m/s and lasted for ~2 h. Significant scintillation occurred on the leading edge of the patch, with smaller bursts of scintillation inside and on the trailing edge. As the patch moved, it maintained the integrity of the scintillation, producing irregularities (Fresnel scale) on the leading edge. There were no convection shears or changes in the direction of convection during scintillation events. Observations suggest that scintillation-producing Fresnel scale structures are generated through the non-linear evolution of the gradient drift instability mechanism.

scholarly journals E-Region Field-Aligned Irregularities in the Middle of a Solar Eclipse Observed by a Bistatic Radar

2022 ◽  
Vol 14 (2) ◽  
pp. 392
Author(s):  
Lei Qiao ◽  
Gang Chen ◽  
Wanlin Gong ◽  
Xuesi Cai ◽  
Erxiao Liu ◽  
...  
Keyword(s):  
Solar Eclipse ◽  
Recovery Phase ◽  
Bistatic Radar ◽  
Doppler Shifts ◽  
Propagation Parameters ◽  
E Region ◽  
Gradient Drift ◽  
Drift Instability ◽  
Wave Induced ◽  
Field Aligned Irregularities

The Wuhan Ionospheric Oblique Backscatter Sounding System (WIOBSS) was applied as a bistatic radar to record the ionospheric E-region responses to a solar eclipse on 22 July 2009. The transmitter was located in Wuhan and the receiver was located in Huaian. The receiver observed anomalous echoes with larger Doppler shifts at the farther ranges compared with the echoes reflected by Es. According to the simulated ray propagation paths of the reflected and scattered waves, we considered that the anomalous echoes were scattered by E-region field-aligned irregularities (FAIs). The locations of the FAIs recorded by the WIOBSS were estimated with the International Geomagnetic Reference Field (IGRF) and the observed propagation parameters. These irregularities occurred at around the eclipse maximum and lasted for ~20–40 min. The steep plasma density gradient induced by the fast drop photo ionization under the lunar shadow was beneficial to the occurrence of gradient drift instability to generate the FAIs. They were different from the gravity wave-induced irregularities occurring in the recovery phase of the solar eclipse.

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