Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Ionospheric electron heating, optical emissions, and striations induced by powerful HF radio waves at high latitudes: Aspect angle dependence
AU - Rietveld, M. T.
AU - Kosch, Mike J.
AU - Blagoveshchenskaya, N. F.
AU - Kornienko, V. A.
AU - Leyser, T. B.
AU - Yeoman, T. K.
N1 - Copyright (2003) American Geophysical Union.
PY - 2003/4
Y1 - 2003/4
N2 - In recent years, large electron temperature increases of 300% (3000 K above background) caused by powerful HF-radio wave injection have been observed during nighttime using the EISCAT incoherent scatter radar near Tromsø in northern Norway. In a case study we examine the spatial structure of the modified region. The electron heating is accompanied by ion heating of about 100 degrees and magnetic field-aligned measurements show ion outflows increasing with height up to 300 m s−1 at 582 km. The electron density decreases by up to 20%. When the radar antenna was scanned between three elevations from near field-aligned to vertical, the strongest heating effects were always obtained in the field-aligned position. When the HF-pump beam was scanned between the same three positions, the heating was still almost always strongest in the field-aligned direction. Simultaneous images of the 630 nm O(1D) line in the radio-induced aurora showed that the enhancement caused by the HF radio waves also remained localized near the field-aligned position. Coherent HF radar backscatter also appeared strongest when the pump beam was pointed field-aligned. These results are similar to some Langmuir turbulence phenomena which also show a strong preference for excitation by HF rays launched in the field-aligned direction. The correlation of the position of largest temperature enhancement with the position of the radio-induced aurora suggests that a common mechanism, upper-hybrid wave turbulence, is responsible for both effects. Why the strongest heating effects occur for HF rays directed along the magnetic field is still unclear, but self-focusing on field-aligned striations is a candidate mechanism, and possibly ionospheric tilts may be important.
AB - In recent years, large electron temperature increases of 300% (3000 K above background) caused by powerful HF-radio wave injection have been observed during nighttime using the EISCAT incoherent scatter radar near Tromsø in northern Norway. In a case study we examine the spatial structure of the modified region. The electron heating is accompanied by ion heating of about 100 degrees and magnetic field-aligned measurements show ion outflows increasing with height up to 300 m s−1 at 582 km. The electron density decreases by up to 20%. When the radar antenna was scanned between three elevations from near field-aligned to vertical, the strongest heating effects were always obtained in the field-aligned position. When the HF-pump beam was scanned between the same three positions, the heating was still almost always strongest in the field-aligned direction. Simultaneous images of the 630 nm O(1D) line in the radio-induced aurora showed that the enhancement caused by the HF radio waves also remained localized near the field-aligned position. Coherent HF radar backscatter also appeared strongest when the pump beam was pointed field-aligned. These results are similar to some Langmuir turbulence phenomena which also show a strong preference for excitation by HF rays launched in the field-aligned direction. The correlation of the position of largest temperature enhancement with the position of the radio-induced aurora suggests that a common mechanism, upper-hybrid wave turbulence, is responsible for both effects. Why the strongest heating effects occur for HF rays directed along the magnetic field is still unclear, but self-focusing on field-aligned striations is a candidate mechanism, and possibly ionospheric tilts may be important.
KW - heating DCS-publications-id
KW - art-458
KW - DCS-publications-credits
KW - iono
KW - DCS-publications-personnel-id
KW - 7
U2 - 10.1029/2002JA009543
DO - 10.1029/2002JA009543
M3 - Journal article
VL - 108
SP - 2/1-2/16
JO - Journal of Geophysical Research
JF - Journal of Geophysical Research
SN - 0148-0227
IS - A4
ER -