A5101935409- Ionosphere and magnetosphere dynamics
- Earthquake Detection and Analysis
- Solar and Space Plasma Dynamics
- GNSS positioning and interference
- Geophysics and Gravity Measurements
- Geomagnetism and Paleomagnetism Studies
- Magnetic confinement fusion research
- Plasma Diagnostics and Applications
- Astro and Planetary Science
- History and Developments in Astronomy
- Dust and Plasma Wave Phenomena
- Seismic Waves and Analysis
- Historical Geography and Cartography
- Planetary Science and Exploration
- Experimental and Theoretical Physics Studies
- Historical and Architectural Studies
- Radio Astronomy Observations and Technology
- Maritime and Coastal Archaeology
- Atmospheric Ozone and Climate
- Synthetic Aperture Radar (SAR) Applications and Techniques
- Meteorological Phenomena and Simulations
- Radar Systems and Signal Processing
- Social and Demographic Issues in Germany
- Astrophysics and Cosmic Phenomena
- earthquake and tectonic studies
University of Leicester
2003-2017
Rutherford Appleton Laboratory
1996
Max Planck Institute for Astronomy
1996
UiT The Arctic University of Norway
1985
Armagh Observatory & Planetarium
1836-1877
Royal Irish Academy
1853
Simultaneous observations are presented of stimulated electromagnetic emission (SEE) spectra and the anomalous absorption a diagnostic HF wave, caused by powerful radio waves generated Tromsø heating facility. The pump frequency was varied in small steps around third, fourth, fifth harmonic electron gyrofrequency. Systematic variations with were observed data entirety SEE properties. exhibits pronounced minimum at certain near (or at) gyroharmonic question. Of properties strength...
Abstract. Interferometric techniques allow the SuperDARN coherent HF radars to determine elevation angles of returned backscatter, giving information on altitude scatter volume, in case ionospheric or reflection altitude, ground backscatter. Assumptions have be made determination angles, including direction arrival, azimuth, signals, usually taken forward look-direction (north) radars, specified by phasing antenna arrays. It is shown that this assumption not always valid and significant...
Cassini magnetic field observations show that few‐nT oscillations near the planetary rotation period, first observed in Pioneer‐11 and Voyager‐1 ‐2 fly‐by data, are essentially ubiquitous Saturn's magnetosphere, though their character differs between quasi‐dipolar ring current region dawn tail. Examination of data from ring‐current shows, however, oscillation period is not fixed at but has smaller values on inbound pass spacecraft, increasing to larger beyond periapsis. These variations...
We present evidence that shows some aspects of the global atmospheric dynamic responses to eruption Mount St. Helens on May 18, 1980. Although events such as volcanic eruptions may excite a number acoustic‐gravity wave modes in atmosphere, observed surface pressure perturbations and distant ionospheric can be explained only terms propagation Lamb with horizontal velocity slightly above 300 m/s. Results from model computations show good agreements observational data. Ground level created by...
Abstract. Recent observations suggest that there may be a causal relationship between solar activity and the strength of winter Northern Hemisphere circulation in stratosphere. A three-dimensional model atmosphere 10–140 km was developed to assess influence minimum maximum conditions on propagation planetary waves subsequent changes Ultraviolet heating middle kept constant order emphasise importance non-linear dynamical coupling. realistic thermosphere achieved by relaxing upper layers...
The phenomenon of wide band attenuation, i.e., anomalous absorption an HF wave in the F region subjected to modification by a powerful wave, has been measured using Tromsø heating facility. Two types results were found. In quiet situation, attenuation amounted approximately 15 dB and did not change when effective radiated power was lowered from 160 20 MW. variable region, indicated high fading rate diagnostic considerably less than showed strong dependence on power. An explanation for both...
Experimental results concerning European incoherent scatter observations of heater‐induced electron temperature enhancements, anomalous absorption low‐power HF probe waves, and the spectrum stimulated electromagnetic emission (SEE) in sidebands a high‐power wave are presented. For experiments reported this paper, an O mode pump was transmitted vertically into F region above Tromsø, Norway, while injected frequency varied small steps around third harmonic gyrofrequency. Systematic variations...
Abstract. Resonance features of the Ionospheric Alfvén Resonator (IAR) can be observed in pulsation magnetometer data from Sodankylä, Finland using dynamic spectra visualizations. IAR resonance were identified on 13 30 days October 1998, with structures lasting for 3 or more hours over 10 intervals. The diurnal evolution harmonic was quantified these intervals a manual cursor-clicking technique. displayed strong linear relationships between frequency and number all time studied, enabling...
Examination of Cassini magnetic field and plasma data in the outer boundary regions Saturn's magnetosphere shows that magnetopause oscillations at planetary period commonly occur, phase with pressure variations inside magnetosphere. The peak‐to‐trough amplitude mapped to planet‐Sun line is estimated be typically ∼2 R S , corresponding a ∼10% change radius. internal required produce such motions ∼40% background values. A qualitative physical picture proposed which compressive wave propagates...
Abstract. The Super Dual Auroral Radar Network (SuperDARN) network of HF coherent backscatter radars form a unique global diagnostic large-scale ionospheric and magnetospheric dynamics in the Northern Southern Hemispheres. Currently ground projections radar returns are routinely determined by simple rangefinding algorithm, which takes no account prevailing, or indeed average, propagation conditions. This is spite fact that both direct E- F-region 1½-hop commonly used geophysical...
Observations of the anomalous absorption low‐power HF probe waves caused by action a high‐power ordinary mode radio wave are presented. At pump frequencies in vicinity harmonics electron gyrofrequency measured on exhibit local minima. Also at these frequencies, large‐scale changes deduced from phase measurements and heater self‐absorption reduced, whereas growth time is increased. The estimated frequency minimum compares favorably with that derived International Geomagnetic Reference Field...
Abstract. Results are presented from the first two active experimental campaigns undertaken by new SPEAR (Space Plasma Exploration Active Radar) high-power system that has recently become operational on Spitzbergen, in Svalbard archipelago. SPEAR's beam was used to excite artificial enhancements backscatter detected ESR (EISCAT parallel geomagnetic field, as well coherent both of CUTLASS (Co-operative UK Twin Located Auroral Sounding System) radars, directions orthogonal field. The enhanced...
Abstract We have discovered pulsating emission within Jupiter's main auroral oval, providing evidence of the signature Jovian ULF wave processes. The form comprises a 1° × 2° spot located directly on emission, whose intensity oscillates with period ∼10 min throughout 45 observation. feature appears duskward edge discontinuity, maps to ∼13–14 h LT and ∼20–50 R J , rotates at around half rigid corotation. show that oscillation is similar expected Alfvén travel time between ionosphere upper...
The kinetic theory of the modified two‐stream instability (MTSI) is usually considered more accurate than corresponding fluid theory, for purpose interpreting VHF and UHF coherent radar backscatter measurements. However, recent developments in nonlinear MTSI have retained formalism consequently may not be entirely valid short‐wavelength regime where radars operate. In this paper, a dispersion relation which takes account resonance broadening effects developed. With aid relation, phase speeds...
Abstract. The CUTLASS Finland HF radar has been operated in conjunction with the EISCAT Tromsø RF ionospheric heater facility to examine a ULF wave characteristic of development field line resonance (FLR) driven by cavity mode caused magnetospheric impulse. When is on, striating ionosphere field-aligned electron density irregularities, large enough target generated allow post-integration over only 1 second. combined 15 km range gates, this gives measurements naturally occurring at far better...
Results are reported from an experiment in which the HF high power facility at Tromsø was utilised to inject artificial ULF waves into magnetosphere by means of modulated heating auroral electrojet. Local electric field oscillations associated with artificially stimulated were detected on board FAST spacecraft, altitude 2550 km. In addition, a downward flux electrons also detected. The excited waves, together these energised electrons, observed narrow region only few tens km across...
Abstract. The EISCAT incoherent radar system, which is collocated with the heating facility, used to diagnose ionosphere while experiments are conducted. In late September 2002, an experiment was performed in heater transmitted a 2-min-on/2-min-off cycle its pointing direction kept fixed and UHF beam cycled through five directions. This for three beam-pointing For field-aligned pointing, data indicated gradual decrease, time, altitude at enhanced ion-line scatter occurred. accompanied by...
Some results of recent high‐latitude ionospheric heating experiments are presented. Phase changes were induced in a diagnostic radio wave reflected from the lower F region ionosphere as it passed through which was being illuminated by high‐power electromagnetic wave. From obtained there indications that anomalous absorption contributes much more than deviative to at high latitudes.