| 1. |
- Askebjer, P., et al.
(författare)
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UV and optical light transmission properties in deep ice at the South Pole
- 1997
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 24:11, s. 1355-1358
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Tidskriftsartikel (refereegranskat)abstract
- Both absorption and scattering of light at wavelengths 410 to 610 nanometers were measured in the South Pole ice at depths 0.8 to 1 kilometer with the laser calibration system of the Antarctic Muon And Neutrino Detector Array (AMANDA). At the shortest wavelengths the absorption lengths exceeded 200 meters - an order of magnitude longer than has been reported for laboratory ice. The absorption shows a strong wavelength dependence while the scattering length is found to be independent of the wavelength, consistent with the hypothesis of a residual density of air bubbles in the ice. The observed linear decrease of the inverse scattering length with depth is compatible with an earlier measurement by the AMANDA collaboration (at ∼515 nanometers).
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| 2. |
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| 3. |
- Bergbauer, S., et al.
(författare)
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Thermal stress evolution in cooling pluton environments of different geometries
- 1998
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 25:5, s. 707-71-
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Tidskriftsartikel (refereegranskat)abstract
- Thermoelastic displacement potentials and fast Fourier transforms can be combined to rapidly calculate the thermal stresses in 2-D for plutons that cool by conduction. First, temperature distributions over time are computed by solving the diffusion equation. Thermal stresses are then obtained using thermoelastic stress potentials. This method can be applied to a broad range of pluton geometries and initial conditions, and requires far less computation time than finite difference or finite element analyses. Results of 2-D analyses show that pluton geometry strongly influences the thermal stresses that occur in a cooling pluton. Thermal stresses of several tens of MPa arise during cooling and are highest at the corners or where the intrusion is thin. The most tensile stress is greater inside a pluton than in the host rock. Moreover, the orientation of the most tensile stress in a cooling pluton generally changes over time. This could result in multiple fracture sets, which would significantly affect the mechanical and hydraulic behavior of a pluton.
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| 4. |
- Boehm, M. H., et al.
(författare)
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Observations of an upward-directed electron beam with the perpendicular temperature of the cold ionosphere
- 1995
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 22, s. 2103-2106
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Tidskriftsartikel (refereegranskat)abstract
- The Freja TESP electron spectrometer has repeatedly observed similar to 100 eV - 1 keV upward-directed, anti-field-aligned electron beams near 1700 km altitude in the auroral zone. A particularly intense event, at energies up to 2 keV, is described. The beam perpendicular temperature T perpendicular to(e)), was as low as 0.1-0.2 eV at 100-200 eV parallel energy. The 10-15 s period of upward fluxes was coincident with a low density (similar to 10 cm(-3)) period and a similar to 5 keV ion conic. Strong low frequency waves and the lack of any downward motion in the simultaneously observed ion conic suggest a strong element of wave acceleration, while electric field and ion loss cone measurements provide limited evidence of potential acceleration to a fraction of the observed energies.
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| 5. |
- Elgered, Gunnar, 1955, et al.
(författare)
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Measuring regional atmospheric water vapor using the Swedish permanent GPS network
- 1997
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Ingår i: Geophysical Research Letters. - 1944-8007 .- 0094-8276. ; 24:21, s. 2663-2666
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the application of a geodetic network of ground-based GPS receivers in Sweden to the measurement of atmospheric water vapor. Using data acquired during four days in December 1993, we show that it is possible to study the detailed motions of air mass systems. Estimates of water vapor from GPS data agree with those from radiosonde and microwave radiometer data to within 1 mm RMS.
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| 6. |
- Germany, G A, et al.
(författare)
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Remote determination of auroral energy characteristics during substorm activity
- 1997
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 24, s. 995-998
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Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet auroral images from the Ultraviolet Imager (UVI) onboard the POLAR satellite can be used as quantitative remote diagnostics of the auroral regions, yielding estimates of incident energy characteristics, compositional changes, and other higher order data products. Here incident energy estimates derived from UVI are compared with in situ measurements of the same parameters from an overflight by the DMSP F12 satellite coincident with the UVI image times during substorm activity occurring on May 19, 1996. This event was simultaneously observed by WIND, GEOTAIL, INTERBALL, DMSP and NOAA spacecraft as well as by POLAR.
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| 7. |
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| 8. |
- Ivchenko, Nickolay, et al.
(författare)
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Quasiperiodic oscillations observed at the edge of an auroral arc by Auroral Turbulence 2
- 1999
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 26:22, s. 3365-3368
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Tidskriftsartikel (refereegranskat)abstract
- The Auroral Turbulence II (AT2) sounding rocket carried three payloads into the auroral ionosphere where they crossed several are structures. At the border of an auroral are a quasiperiodic structure was observed by the magnetic and electric field instruments as well as by the particle detectors. The variations were temporal oscillations, but existed only in a narrow (approximate to 7 km) region transverse to the are, with a correlation length along the are of at least several km. The relation between the electric and magnetic field amplitude indicates the Alfvenic nature of the variations. Field aligned electron precipitation is correlated to the field variations. The narrow band nature of the oscillations and frequency around 0.6 Hz is consistent with waves confined in the ionospheric Alfven resonator.
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| 9. |
- Karlsson, Tomas, et al.
(författare)
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A statistical study of intense low-altitude electric fields observed by Freja
- 1996
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 23, s. 1005-1008
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Tidskriftsartikel (refereegranskat)abstract
- Extremely intense (up to 2 V/m) and fine-structured (1–5 km) electric fields have been observed by the Freja satellite at altitudes of 1400–1770 km. To study the occurrence and characteristics of these intense electric field events, a database was set up by searching 7 months' worth of Freja data for events with peak values greater than 200 mV/m. The intense electric field events are distributed over all local times, but they are mostly concentrated to the midnight and early morning sector of the auroral oval. The events are seen to be associated with low ambient ionospheric conductivities, but are not activity dependent. The most intense events (located in the midnight sector) are associated with the smallest scale sizes, whereas the less intense events on the day side have larger scale sizes.The findings are consistent with the interpretation that a majority of the intense electric field events observed by Freja are associated with the small-scale, east-west-aligned, low-conductivity bands devoid of auroral emissions, known as black auroral bands, or with the curls that may develop when these bands go unstable. Several observations of diverging electric fields of around 1 V/m at 800 km altitude, within the southern auroral oval, may serve as support for the prediction that intense electric fields should exist also at ionospheric altitudes.
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| 10. |
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