scholarly journals Observations of time dependence and aspect sensitivity of regions of enhanced UHF backscatter associated with RF heating

2005 ◽  
Vol 23 (1) ◽  
pp. 75-85 ◽  
Author(s):  
R. S. Dhillon ◽  
T. R. Robinson
Keyword(s):  
Elevation Angle ◽  
High Amplitude ◽  
Radar System ◽  
Heating Facility ◽  
Subsequent Decrease ◽  
Time Histories ◽  
Constant Altitude ◽  
Coherent Radar ◽  
Uhf Radar ◽  
Field Aligned Irregularities

Abstract. The EISCAT incoherent radar system, which is collocated with the EISCAT heating facility, is used to diagnose the ionosphere while heating experiments are conducted. In late September 2002, an experiment was performed in which the heater transmitted a 2-min-on/2-min-off cycle while its pointing direction was kept fixed and the UHF beam was cycled through five pointing directions. This UHF cycle was used for three heater beam-pointing directions. For field-aligned heater beam and UHF pointing, UHF data indicated a gradual decrease, with time, in the altitude at which enhanced ion-line scatter occurred. This was accompanied by a reduction in the intensity of the scatter. For field-aligned heater pointing and the UHF elevation angle of 6° in the field-aligned direction, a persistent high-amplitude signature was observed, which remained at a fairly constant altitude throughout the period that the heater remained switched on. Different time histories of the backscatter amplitude were observed in other UHF pointing directions, including the "ion-line overshoot", which is characterized by an increase and subsequent decrease in the heater-enhanced backscatter just after heater switch-on. It is suggested that these signatures may be caused by the presence or absence of field-aligned irregularities and reduced recombination caused by heating. The CUTLASS coherent radar system, which operated simultaneously with the UHF radar and the heater, observed backscatter from field-aligned irregularities created by the heater. The intensity of this backscatter was highest from the regions of the ionosphere that were excited by the central part of the heater beam.

scholarly journals Saturation and hysteresis effects in ionospheric modification experiments observed by the CUTLASS and EISCAT radars

2006 ◽  
Vol 24 (2) ◽  
pp. 543-553 ◽  
Author(s):  
D. M. Wright ◽  
J. A. Davies ◽  
T. K. Yeoman ◽  
T. R. Robinson ◽  
H. Shergill
Keyword(s):  
High Frequency ◽  
Radio Waves ◽  
Heating Facility ◽  
Ionospheric Modification ◽  
Radiated Power ◽  
Pump Waves ◽  
Hybrid Waves ◽  
Electron Density Irregularities ◽  
Uhf Radar ◽  
Field Aligned Irregularities

Abstract. The results of high latitude ionospheric modification experiments utilising the EISCAT heating facility at Tromsø are presented. As a result of the interaction between the high power pump waves and upper hybrid waves in the ionosphere, field-aligned electron density irregularities are artificially excited. Observations of these structures with the CUTLASS coherent HF radars and the EISCAT incoherent UHF radar exhibit hysteresis effects as the heater output power is varied. These are explained in terms of the two-stage mechanism which leads to the growth of the irregularities. Experiments which involve preconditioning of the ionosphere also indicate that hysteresis could be exploited to maximise the intensity of the field-aligned irregularities, especially where the available heater power is limited. In addition, the saturation of the irregularity amplitude is considered. Although, the rate of irregularity growth becomes less rapid at high heater powers it does not seem to fully saturate, indicating that the amplification would continue beyond the capabilities of the Tromsø heater - currently the most powerful of its kind. It is shown that the CUTLASS radars are sensitive to irregularities produced by very low heater powers (effective radiated powers <4 MW). This fact is discussed from the perspective of a new heating facility, SPEAR, located on Spitzbergen and capable of transmitting high frequency radio waves with an effective radiated power ~10% of that of the Tromsø heater (28MW).

scholarly journals Kinematics of simulated galaxies II: Probing the stellar kinematics of galaxies out to large radii

2020 ◽  
Vol 493 (3) ◽  
pp. 3778-3799 ◽  
Author(s):  
Felix Schulze ◽  
Rhea-Silvia Remus ◽  
Klaus Dolag ◽  
Sabine Bellstedt ◽  
Andreas Burkert ◽  
...  
Keyword(s):  
High Amplitude ◽  
Ex Situ ◽  
Stellar Kinematics ◽  
Continuous Increase ◽  
Formation Pathway ◽  
Subsequent Decrease ◽  
Stellar Component ◽  
Stellar Halo ◽  
Ordered Motion

ABSTRACT We investigate the stellar kinematics of a sample of galaxies extracted from the hydrodynamic cosmological Magneticum Pathfinder simulations out to five half-mass radii. We construct differential radial stellar spin profiles quantified by the observationally widely used λ and the closely related (V/σ) parameters. We find three characteristic profile shapes: profiles exhibiting a (i) peak within 2.5 half-mass radii and a subsequent decrease; (ii) continuous increase that plateaus at larger radii typically with a high amplitude; (iii) completely flat behaviour typically with low amplitude, in agreement with observations. This shows that the kinematic state of the stellar component can vary significantly with radius, suggesting a distinct interplay between in-situ star formation and ex-situ accretion of stars. Following the evolution of our sample through time, we provide evidence that the accretion history of galaxies with decreasing profiles is dominated by the anisotropic accretion of low-mass satellites that get disrupted beyond ∼2.0 half-mass radii, building up a stellar halo with non-ordered motion while maintaining the central rotation already present at z = 2. In fact, at z = 2 decreasing profiles are the predominant profile class. Hence, we can predict a distinct formation pathway for galaxies with a decreasing profile and show that the centre resembles an old embedded disc. Furthermore, we show that the radius of the kinematic transition provides a good estimation for the transition radius from in-situ stars in the centre to accreted stars in the halo.

scholarly journals Multi-frequency HF radar measurements of artificial F-region field-aligned irregularities

2004 ◽  
Vol 22 (10) ◽  
pp. 3503-3511 ◽  
Author(s):  
A. Senior ◽  
N. D. Borisov ◽  
M. J. Kosch ◽  
T. K. Yeoman ◽  
F. Honary ◽  
...  
Keyword(s):  
Wave Interaction ◽  
Operating Mode ◽  
Hf Radar ◽  
Heating Facility ◽  
F Region ◽  
Density Perturbations ◽  
Radar Measurements ◽  
The Mean ◽  
Power Measurements ◽  
Field Aligned Irregularities

Abstract. We present radar backscatter power measurements using the CUTLASS HF radar at Hankasalmi, Finland from F-region field-aligned irregularities induced by HF radio pumping with the EISCAT Heating facility. A novel radar operating mode is used in which the radar frequency is rapidly swept through a number of bands, making use of the varying ionospheric refraction to probe different heights within the heated region. We obtain height profiles of backscatter power which correspond to e-folding scale lengths of around 20km for the mean-square electron density perturbations for pump wave interaction heights in the region of 240-250km in daytime conditions. The results are in agreement with previous measurements made by other techniques. We discuss some problems with the method and suggest improvements for future experiments.

scholarly journals History of EISCAT – Part 5: Operation and development of the system during the first two decades

2021 ◽  
Author(s):  
Gudmund Wannberg
Keyword(s):  
Signal Processing ◽  
Computer System ◽  
Radar System ◽  
Section 8 ◽  
History Of ◽  
Inside View ◽  
Personal Reflections ◽  
Uhf Radar ◽  
Final Closure

Abstract. This paper gives an inside view of the first 20 years of operation of the Kiruna-Sodankylä-Tromsø (KST) part of EISCAT as experienced and remembered by myself. The paper is subdivided into an Introduction and 13 sections. Sections 1 to 6 describe the organization, staffing and responsibilites of the Sites, with particular emphasis on the transmitter-related work at Tromsø and the commuting of staff and equipment between the Sites. The Headquarters operation is treated in Section 7. The UHF radar system is treated in Section 8. Section 9 is a review of the VHF system, including a summary of transmitter and antenna problems not available elsewhere in easily accessed media. Section 10 treats the computer system and the proprietary control languages EROS, TARLAN and CORLAN. Section 11 describes the signal processing hardware, with special emphasis on the Alker correlator, its idiosyncrasies and the gradual unlocking of its capabilities through UNIPROG, the GEN-system and the G2-system, culminating in the ability to run alternating codes experiments routinely. Section 12 presents the time- and frequency keeping, a non-trivial task in the early 1980s. Finally, Section 13 discusses the UHF spectrum problem and relates how the UHF system had to be constantly upgraded in order to be able to co-exist with the emerging cellphone networks until the final closure of UHF reception at Kiruna and Sodankylä in 2012. The paper ends with some personal reflections.

scholarly journals Determination of meteoroid physical properties from tristatic radar observations

2008 ◽  
Vol 26 (8) ◽  
pp. 2217-2228 ◽  
Author(s):  
J. Kero ◽  
C. Szasz ◽  
A. Pellinen-Wannberg ◽  
G. Wannberg ◽  
A. Westman ◽  
...  
Keyword(s):  
Cross Sections ◽  
Equation Of Motion ◽  
Momentum Equation ◽  
Radar System ◽  
Radar Target ◽  
Radar Cross Sections ◽  
The Common ◽  
Head Echo ◽  
Uhf Radar

Abstract. In this work we give a review of the meteor head echo observations carried out with the tristatic 930 MHz EISCAT UHF radar system during four 24 h runs between 2002 and 2005 and compare these with earlier observations. A total number of 410 tristatic meteors were observed. We describe a method to determine the position of a compact radar target in the common volume monitored by the three receivers and demonstrate its applicability for meteor studies. The inferred positions of the meteor targets have been utilized to estimate their velocities, decelerations and directions of arrival as well as their radar cross sections with unprecedented accuracy. The velocity distribution of the meteoroids is bimodal with peaks at 35–40 km/s and 55–60 km/s, and ranges from 19–70 km/s. The estimated masses are between 10−9–10−5.5 kg. There are very few detections below 30 km/s. The observations are clearly biased to high-velocity meteoroids, but not so biased against slow meteoroids as has been presumed from previous tristatic measurements. Finally, we discuss how the radial deceleration observed with a monostatic radar depends on the meteoroid velocity and the angle between the trajectory and the beam. The finite beamwidth leads to underestimated meteoroid masses if radial velocity and deceleration of meteoroids approaching the radar are used as estimates of the true quantities in a momentum equation of motion.

UHF radar system tested on the bridge of Yangtze river

2007 ◽  
Author(s):  
Shen Wei ◽  
Wen Biyang ◽  
Li Zili ◽  
Huang Xiaojing
Keyword(s):  
Yangtze River ◽  
Radar System ◽  
Uhf Radar
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