T. Grydeland

Cavitating Langmuir turbulence in the terrestrial aurora.

Langmuir cavitons have been artificially produced in Earths ionosphere, but evidence of naturally occurring cavitation has been elusive. By measuring and modeling the spectra of electrostatic plasma modes, we show that natural cavitating, or strong, Langmuir turbulence does occur in the ionosphere, via a process in which a beam of auroral electrons drives Langmuir waves, which in turn produce cascading Langmuir and ion-acoustic excitations and cavitating Langmuir turbulence. The data presented here are the first direct evidence of cavitating Langmuir turbulence occurring naturally in any space or astrophysical plasma.

MIDAS-W: a workstation-based incoherent scatter radar data acquisition system

The Millstone Hill Incoherent Scatter Data Acquisition System (MIDAS) is based on an abstract model of an incoherent scatter radar. This model is implemented in a hierarchical software system, which serves to isolate hardware and low-level software implementation details from higher levels of the system. Inherent in this is the idea that implementation details can easily be changed in response to technological advances. MIDAS is an evolutionary system, and the MIDAS hardware has, in fact, evolved while the basic software model has remained unchanged. From the earliest days of MIDAS, it was realized that some functions implemented in specialized hardware might eventually be implemented by software in a general-purpose computer. MIDAS-W is the realization of this concept. The core component of MIDAS-W is a Sun Microsystems UltraSparc 10 workstation equipped with an Ultrarad 1280 PCI bus analog to digital (A/D) converter board. In the current implementation, a 2.25 MHz intermediate frequency (IF) is bandpass sampled at 1 μs intervals and these samples are multicast over a high-speed Ethernet which serves as a raw data bus. A second workstation receives the samples, converts them to filtered, decimated, complex baseband samples and computes the lag-profile matrix of the decimated samples. Overall performance is approximately ten times better than the previous MIDAS system, which utilizes a custom digital filtering module and array processor based correlator. A major advantage of MIDAS-W is its flexibility. A portable, single-workstation data acquisition system can be implemented by moving the software receiver and correlator programs to the workstation with the A/D converter. When the data samples are multicast, additional data processing systems, for example for raw data recording, can be implemented simply by adding another workstation with suitable software to the high-speed network. Testing of new data processing software is also greatly simplified, because a workstation with the new software can be added to the network without impacting the production system. MIDAS-W has been operated in parallel with the existing MIDAS-1 system to verify that incoherent scatter measurements by the two systems agree. MIDAS-W has also been used in a high-bandwidth mode to collect data on the November, 1999, Leonid meteor shower.

HF-pump-induced parametric instabilities in the auroral E-region

Abstract In November 1999 the EISCAT high-power, high-frequency (HF) facility located near Tromso, Norway, was used to create artificial plasma turbulence in the ionosphere. During the experiment the EISCAT 224 MHz radar and sometimes the 931 MHz radar were used to obtain measurements of incoherent scatter ion and plasma lines, and artificially enhanced spectra of E-region plasma waves were measured for the first time at auroral latitudes with both radars. During periods with suitable peak E-region electron density, Z-mode propagation of the HF pump wave to the topside E-region occurred, and topside instability-enhanced plasma waves were observed. In addition to HF-pump-induced effects, an unusual F-region echo was seen in both the ion and plasma line channels, which appears to be due to an auroral arc intersecting the radar beam.

Conditional integration of Incoherent Scattering in relation to flickering aurora

[1] In this report we present incoherent scatter radar (ISR) observations of ionospheric response to precipitation causing flickering aurora. Flickering aurora is caused by electron precipitation with modulations at frequencies higher than 5 Hz. To resolve the variation at these short time-scales with ISR we have integrated together pulses at the same phase of the optical intensity variation observed with high-speed narrow field-of-view imaging in white light to determine the intensity variation in the field aligned direction, which is also the direction of the beam of the EISCAT Svalbard Radar (ESR). Further we show that the 3% modulation in ISR back-scattered power can be explained with electron heating by temporally modulated electron precipitation and electron cooling in collisions with ions and neutrals.

Use of Satellite and Ground Based InSAR in Hazard Classification of Unstable Rock Slopes

A newly developed hazard classification system for large unstable rock slopes depends on the evaluation of a number of criteria. These criteria include both displacement rates and the structural development of the unstable slope. Satellite and ground-based interferometric radars have the potential to measure the displacement of active rockslides. By using several complimentary InSAR datasets, with different viewing geometries, we are able to assess both movement criteria and a number of criteria related to structural development of the bounding surfaces.

Satellite and Ground-Based Interferometric Radar Observations of an Active Rockslide in Northern Norway

Satellite and ground-based interferometric radars have the potential to measure the displacement of active rockslides. Data describing the spatial- and temporal displacement patterns of a rockslide are essential contributions to the total understanding of a rockslide. A better overview of the kinematics will in turn improve the quality of a risk assessment. In this study we have processed TerraSAR-X satellite data, collected since 2009, from both ascending and descending satellite tracks together with ground-based interferometric radar observations of an active rockslide in Northern Norway. Findings show that both the satellite and the ground-based data delimit the active rockslide area and that the displacement rates are highest in the upper part of the rockslide. In the lower parts of the rockslide, the displacement pattern shows a possible compressional toe-zone together with a fast moving lobate shaped landform.