scholarly journals A comparison of velocity measurements from the CUTLASS Finland radar and the EISCAT UHF system

1999 ◽  
Vol 17 (7) ◽  
pp. 892-902 ◽  
Author(s):  
J. A. Davies ◽  
M. Lester ◽  
S. E. Milan ◽  
T. K. Yeoman
Keyword(s):  
Total Duration ◽  
Field Of View ◽  
Simultaneous Occurrence ◽  
Plasma Convection ◽  
Contributing Factors ◽  
Plasma Irregularities ◽  
Incoherent Scatter ◽  
F Region ◽  
Initial Comparison ◽  
E Region

Abstract. The CUTLASS Finland radar, which comprises an integral part of the SuperDARN system of HF coherent radars, provides near continuous observations of high-latitude plasma irregularities within a field-of-view which extends over some four million square kilometres. Within the Finland radar field-of-view lie both the EISCAT mainland and EISCAT Svalbard incoherent scatter radar facilities. Since the CUTLASS Finland radar commenced operation, in February 1995, the mainland EISCAT UHF radar has been run in common programme 1 and 2 modes for a total duration exceeding 1000 h. Simultaneous and spatially coincident returns from these two radars over this period provide the basis for a comparison of irregularity drift velocity and F-region ion velocity. Initial comparison is limited to velocities from four intervals of simultaneous radar returns; intervals are selected such that they exhibit a variety of velocity signatures including that characteristic of the convection reversal and a rapidly fluctuating velocity feature. Subsequent comparison is on a statistical basis. The velocities measured by the two systems demonstrate reasonable correspondence over the velocity regime encountered during the simultaneous occurrence of coherent and incoherent scatter; differences between the EISCAT UHF measurements of F-region ion drift and the irregularity drift velocities from the Finland radar are explained in terms of a number of contributing factors including contamination of the latter by E-region echoes, a factor which is investigated further, and the potentially deleterious effect of discrepant volume and time sampling intervals.Key words. Ionosphere (ionospheric irregularities; plasma convection)

scholarly journals Simultaneous observations at different altitudes of ionospheric backscatter in the eastward electrojet

1998 ◽  
Vol 16 (1) ◽  
pp. 55-68 ◽  
Author(s):  
S. E. Milan ◽  
M. Lester
Keyword(s):  
Spectral Characteristics ◽  
Temporal Variations ◽  
Approximate Determination ◽  
Spectral Signature ◽  
Plasma Convection ◽  
Flow Angle ◽  
F Region ◽  
Ion Acoustic ◽  
E Region ◽  
Acoustic Speed

Abstract. A common feature of evening near-range ionospheric backscatter in the CUTLASS Iceland radar field of view is two parallel, approximately L-shell-aligned regions of westward flow which are attributed to irregularities in the auroral eastward electrojet region of the ionosphere. These backscatter channels are separated by approximately 100–200 km in range. The orientation of the CUTLASS Iceland radar beams and the zonally aligned nature of the flow allows an approximate determination of flow angle to be made without the necessity of bistatic measurements. The two flow channels have different azimuthal variations in flow velocity and spectral width. The nearer of the two regions has two distinct spectral signatures. The eastern beams detect spectra with velocities which saturate at or near the ion-acoustic speed, and have low spectral widths (less than 100 m s–1), while the western beams detect lower velocities and higher spectral widths (above 200 m s–1). The more distant of the two channels has only one spectral signature with velocities above the ion-acoustic speed and high spectral widths. The spectral characteristics of the backscatter are consistent with E-region scatter in the nearer channel and upper-E-region or F-region scatter in the further channel. Temporal variations in the characteristics of both channels support current theories of E-region turbulent heating and previous observations of velocity-dependent backscatter cross-section. In future, observations of this nature will provide a powerful tool for the investigation of simultaneous E- and F-region irregularity generation under similar (nearly co-located or magnetically conjugate) electric field conditions.Key words. Auroral ionosphere · Ionospheric irregularities · Plasma convection

scholarly journals Simultaneous HF measurements of E- and F-region Doppler velocities at large flow angles

2004 ◽  
Vol 22 (4) ◽  
pp. 1177-1185 ◽  
Author(s):  
R. A. Makarevitch ◽  
F. Honary ◽  
A. V. Koustov
Keyword(s):  
Hf Radar ◽  
Doppler Velocity ◽  
Plasma Convection ◽  
Aspect Angle ◽  
F Region ◽  
Significant Difference ◽  
E Region ◽  
The Difference ◽  
New Feature ◽  
Large Flow

Abstract. Data collected by the CUTLASS Finland HF radar are used to illustrate the significant difference between the cosine component of the plasma convection in the F-region and the Doppler velocity of the E-region coherent echoes observed at large flow angles. We show that the E-region velocity is ~5 times smaller in magnitude and rotated by ~30° clockwise with respect to convection in the F-region. Also, measurements at flow angles larger than 90° exhibit a completely new feature: Doppler velocity increase with the expected aspect angle and spatial anticorrelation with the backscatter power. By considering DMSP drift-meter measurements we argue that the difference between F- and E-region velocities cannot be interpreted in terms of the convection change with latitude. The observed features in the velocity of the E-region echoes can be explained by taking into account the ion drift contribution to the irregularity phase velocity as predicted by the linear fluid theory. Key words. Ionosphere (auroral ionosphere; ionospheric irregularities; plasma convection)

scholarly journals EISCAT Svalbard radar observations of SPEAR-induced E- and F-region spectral enhancements in the polar cap ionosphere

2007 ◽  
Vol 25 (8) ◽  
pp. 1801-1814 ◽  
Author(s):  
R. S. Dhillon ◽  
T. R. Robinson ◽  
T. K. Yeoman
Keyword(s):  
High Power ◽  
Polar Cap ◽  
Incoherent Scatter ◽  
F Region ◽  
Sporadic E Layers ◽  
First Results ◽  
Plasma Line ◽  
E Region ◽  
Sporadic E ◽  
Overdense Plasma

Abstract. The Space Plasma Exploration by Active Radar (SPEAR) facility has successfully operated in the high-power heater and low-power radar modes and has returned its first results. The high-power results include observations of SPEAR-induced ion and plasma line spectral enhancements recorded by the EISCAT Svalbard UHF incoherent scatter radar system (ESR), which is collocated with SPEAR. These SPEAR-enhanced spectra possess features that are consistent with excitation of both the purely growing mode and the parametric decay instability. In this paper, we present observations of upper and lower E-region SPEAR-induced ion and plasma line enhancements, together with F-region spectral enhancements, which indicate excitation of both instabilities and which are consistent with previous theoretical treatments of instability excitation in sporadic E-layers. In agreement with previous observations, spectra from the lower E-region have the single-peaked form characteristic of collisional plasma. Our observations of the SPEAR-enhanced E-region spectra suggest the presence of variable drifting regions of patchy overdense plasma, which is a finding also consistent with previous results.

scholarly journals Assessing the contamination of SuperDARN global convection maps by non-F-region backscatter

2002 ◽  
Vol 20 (1) ◽  
pp. 13-28 ◽  
Author(s):  
G. Chisham ◽  
M. Pinnock
Keyword(s):  
Doppler Velocity ◽  
Plasma Convection ◽  
Data Set ◽  
Radio Science ◽  
Ionosphere Plasma ◽  
F Region ◽  
Mesoscale Structure ◽  
Mapping Process ◽  
E Region ◽  
Instruments And Techniques

Abstract. Global convection mapping using line-of-sight Doppler velocity data from the Super Dual Auroral Radar Network (SuperDARN) is now an accepted method of imaging high-latitude ionospheric convection. This mapping process requires that the flow measured by the radars is defined solely by the convection electric field. This is generally only true of radar backscatter from the ionospheric F-region. We investigate the extent to which the E-region and ground backscatter in the SuperDARN data set may be misidentified as F-region backscatter, and assess the contamination of global convection maps which results from the addition of this non-F-region backscatter. We present examples which highlight the importance of identifying this contamination, especially with regard to the mesoscale structure in the convection maps.Key words. Ionosphere (plasma convection) – Radio science (radio wave propagation; instruments and techniques)

scholarly journals Transient production of F-region irregularities associated with TCV passage

2003 ◽  
Vol 21 (7) ◽  
pp. 1531-1541 ◽  
Author(s):  
R. Kataoka ◽  
H. Fukunishi ◽  
K. Hosokawa ◽  
H. Fujiwara ◽  
A. S. Yukimatu ◽  
...  
Keyword(s):  
Electric Fields ◽  
Current System ◽  
Rapid Evolution ◽  
Three Dimensional ◽  
Leading Edge ◽  
Spectral Width ◽  
Plasma Convection ◽  
Plasma Irregularities ◽  
F Region ◽  
Field Aligned Current

Abstract. Transient production of F-region plasma irregularities due to traveling convection vortices (TCVs) was investigated using the Super Dual Auroral Radar Network (SuperDARN) combined with ground magnetometer networks and the POLAR ultraviolet imager. We selected two large-amplitude (100–200 nT) TCV events that occurred on 22 May 1996 and 24 July 1996. It is found that the TCV-associated HF backscatter arises in blobs with spatial scale of a few hundreds km. They traveled following tailward bulk motion of the TCV across the three fields-of-view of the SuperDARN HF radars in the prenoon sector. The spectra in the blobs showed unidirectional Doppler velocities of typically 400–600 m/s, with flow directions away from the radar. These unidirectional velocities correspond to the poleward and/or eastward convective flow near the leading edge of upward field-aligned current. The backscatter blobs overlapped the poleward and westward part of the TCV-related transient aurora. It is likely that the transient backscatter blobs are produced by the three-dimensional gradient drift instabilities in the three-dimensional current system of the TCV. In this case, nonlinear rapid evolution of irregularities would occur in the upward field-aligned current region. The spectral width of the backscatter blob is typically distributed between 50 and 300 m/s, but sometimes it is over 400 m/s. This suggests that the temporal broad spectra over 400 m/s are produced by Pc1–2 bursts, while the background spectral width of 50–300 m/s are produced by the velocity gradient structure of convection vortices themselves.Key words. Ionosphere (Electric fields and currents; Ionospheric irregularities; Plasma convection)

scholarly journals Intriguing aspects of F-region plasma irregularities revealed by the Gadanki radar observations during the SAFAR campaign

2009 ◽  
Vol 27 (10) ◽  
pp. 3781-3790 ◽  
Author(s):  
A. K. Patra ◽  
D. V. Phanikumar
Keyword(s):  
Solar Activity ◽  
Electron Density ◽  
Plasma Irregularities ◽  
F Region ◽  
Mst Radar ◽  
E Region ◽  
Summer Time ◽  
Interesting Event ◽  
Region Plasma ◽  
Activity Condition

Abstract. Intriguing new results of F-region irregularities observed using the Gadanki MST radar during the SAFAR campaigns, which were conducted during the equinox and summer of 2008 that corresponds to low solar activity condition, are presented. The summer observations are first of its kind from Gadanki. Observations revealed remarkably different morphology of the F-region irregularities in summer when compared to that in equinox. In summer, the F-region irregularities were observed as horizontally stratified structures, while in equinox they were observed as plume structures. Further, the irregularities in summer commenced during the post-midnight hours in contrast to their commencement in the post-sunset hours and occurrence extending to post-midnight hours in equinox. In addition, an intriguing observation of the summer time irregularities is that they occurred when the background electron density was remarkably low as characterized by the disappearance of the F layer trace in the ionograms. An interesting event of equinox that was observed for 10 h and extended beyond the sunrise time displayed multiple plume structures having periods similar to those of the E-region velocity variations. These observations are discussed with due focus on the genesis of post-midnight F-region irregularities and their possible linkage to the E-region dynamics.

scholarly journals 3-D Radar Imaging of E-Region Field-Aligned Plasma Irregularities by Using Multireceiver and Multifrequency Techniques

2018 ◽  
Vol 56 (10) ◽  
pp. 5591-5599 ◽  
Author(s):  
Jenn-Shyong Chen ◽  
Chien-Ya Wang ◽  
Yen-Hsyang Chu ◽  
Ching-Lun Su ◽  
Hiroyuki Hashiguchi
Keyword(s):  
Radar Imaging ◽  
Plasma Irregularities ◽  
E Region

scholarly journals Effects of solar eclipse on the electrodynamical processes of the equatorial ionosphere: a case study during 11 August 1999 dusk time total solar eclipse over India

2002 ◽  
Vol 20 (12) ◽  
pp. 1977-1985 ◽  
Author(s):  
R. Sridharan ◽  
C. V. Devasia ◽  
N. Jyoti ◽  
Diwakar Tiwari ◽  
K. S. Viswanathan ◽  
...  
Keyword(s):  
Electric Fields ◽  
Solar Eclipse ◽  
Equatorial Ionosphere ◽  
Hf Radar ◽  
F Region ◽  
Large Enhancement ◽  
Temporal Structures ◽  
E Region ◽  
Field Lines ◽  
Electric Fields And Currents

Abstract. The effects on the electrodynamics of the equatorial E- and F-regions of the ionosphere, due to the occurrence of the solar eclipse during sunset hours on 11 August 1999, were investigated in a unique observational campaign involving ground based ionosondes, VHF and HF radars from the equatorial location of Trivandrum (8.5° N; 77° E; dip lat. 0.5° N), India. The study revealed the nature of changes brought about by the eclipse in the evening time E- and F-regions in terms of (i) the sudden intensification of a weak blanketing ES-layer and the associated large enhancement of the VHF backscattered returns, (ii) significant increase in h' F immediately following the eclipse and (iii) distinctly different spatial and temporal structures in the spread-F irregularity drift velocities as observed by the HF radar. The significantly large enhancement of the backscattered returns from the E-region coincident with the onset of the eclipse is attributed to the generation of steep electron density gradients associated with the blanketing ES , possibly triggered by the eclipse phenomena. The increase in F-region base height immediately after the eclipse is explained as due to the reduction in the conductivity of the conjugate E-region in the path of totality connected to the F-region over the equator along the magnetic field lines, and this, with the peculiar local and regional conditions, seems to have reduced the E-region loading of the F-region dynamo, resulting in a larger post sunset F-region height (h' F) rise. These aspects of E-and F-region behaviour on the eclipse day are discussed in relation to those observed on the control day.Key words. Ionosphere (electric fields and currents; equatorial ionosphere; ionospheric irregularities)

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