We present the results of experimental studies of the generation peculiarities and features of the Langmuir and ion–acoustic turbulence in the F region of the high-latitude ionosphere excited by ...high-power HF O-mode radio waves emitted by the EISCAT/Heating facility (Tromsø, Norway) in the direction of the Earth’s magnetic field. The experiment was carried out at frequencies fH close to the fourth gyroharmonic, f
H
< 4f
ce
, and the cutoff frequency of the F
2
layer, f
oF2
, f
H
< f
oF2
< f
H
+f
ce
/2, where f
ce
is the electron gyrofrequency. By using the EISCAT incoherent scatter radar (930 MHz), a joint analysis of the plasma and ion line spectra simultaneously below and above the F
2
-layer maximum was performed. The excitation of the HF-induced plasma lines outshifted by 0.35–0.45 MHz from the pump-wave frequency and HF-enhanced ion lines simultaneously below and above the F
2
-layer maximum was found for the first time. The mechanisms of the pump-wave propagation to altitudes above the F
2
-layer maximum and a plausible mechanism for the excitation of the instability responsible for the generation of HF-enhanced ion lines and HF-induced plasma lines above the F
2
-layer maximum are discussed.
It has been long established that high‐power O‐mode HF pumping of the ionosphere can produce artificial optical emissions. 630 nm O(1D) photons are produced by pump‐accelerated electrons colliding ...with the F‐layer neutral oxygen. However, the mechanism for artificial electron acceleration remains unclear. Competing theories include Langmuir and upper‐hybrid turbulence. Pump‐induced HF coherent radar backscatter power is closely linked with upper‐hybrid turbulence, both of which are known to reduce when pumping on an electron gyro‐harmonic frequency. On 3 November 2000, the EISCAT HF facility was systematically stepped in frequency through the 3rd gyro‐harmonic. A significant reduction in the artificial optical intensity coincides with that of CUTLASS radar backscatter power. This is conclusive proof that upper‐hybrid turbulence is intimately linked to the mechanism for high‐latitude pump‐induced aurora, at least for 630 nm photons and the steady state.
A statistical analysis has been made of 26 Polar Mesospheric Summer Echoes (PMSE) active modulation experiments between 2002 and 2007. Observed with the EISCAT VHF radar the PMSE signature can be ...reduced by means of heating the ionosphere with powerful high frequency (HF) radio waves. However, PMSE modulation experiments sometimes fail. We use a computational model to estimate the enhanced electron temperatures due to ionospheric heating from HF radio waves in the D-region. We show that the statistical PMSE modulation for a fixed HF heater-induced electron temperature enhancement appears to be independent of altitude. In addition, for experiments where the PMSE modulation experiment failed, we show that the atmospheric attenuation of the HF heater wave was too great for the HF wave to have any effect on the PMSE layer.
► A statistical analysis of 26 historical PMSE modulation experiments. ► Estimates of enhanced electron temperatures due to ionospheric heating. ► PMSE modulation for fixed temperature enhancement is independent of altitude. ► Failed PMSE modulation due to high attenuation of the HF heater wave.
Powerful high‐frequency radio waves can heat the electrons in the D region of the ionosphere. This heating increases the electron‐neutral collision frequency which modifies the absorption of other ...radio waves propagating through the heated plasma. A high spatial resolution imaging riometer was used to observe changes in cosmic radio noise absorption (CNA) induced by heating from the European Incoherent Scatter (EISCAT) HF facility, and the results were compared to a theoretical model using observed electron densities as an input. The model is found to overestimate the observed effect by a factor close to 2, despite different background electron density profiles and heater powers. However, the model reproduced the spatial morphology of the change in CNA rather well, and the same absorption calculation used in the heating model also reproduced the changes in CNA due to electron precipitation in the absence of heating well. When the assumption of a perfectly conducting ground is replaced with a more realistic model in the calculation of the HF radiated power, the power is reduced to about 75% of its original value, and the model overestimate of the CNA change is reduced to a factor of about 1.3.
Key Points
A high‐resolution imaging riometer can observe radio heating of the D region
Existing models of D region radio heating reproduce observed behavior well
The radiated power of the EISCAT HF facility may have been overestimated
High-frequency electromagnetic pumping of ionospheric F-region plasma at high and mid latitudes gives
the strongest plasma response in magnetic zenith,
antiparallel to the geomagnetic field in the ...Northern Hemisphere.
This has been observed in optical emissions from
the pumped plasma turbulence, electron temperature enhancements,
filamentary magnetic field-aligned plasma density irregularities,
and in self-focusing of the pump beam in magnetic zenith.
We present results of EISCAT (European Incoherent SCATter association) Heating-induced magnetic-zenith effects
observed with the EISCAT UHF incoherent scatter radar.
With heating transmitting a left-handed circularly polarized pump beam towards
magnetic zenith, the UHF radar was scanned in elevation in steps of 1.0 and 1.5∘
around magnetic zenith.
The electron energy equation was integrated to model the electron temperature and associated electron heating rate and
optimized to fit the plasma parameter values measured with the radar.
The experimental and modelling results are consistent with pump wave propagation in the L mode in magnetic zenith,
rather than in the O mode.
Abstract Introduction To advise laryngeal carcinoma patients on the most appropriate form of treatment, a tool to predict survival and local control is needed. Materials and methods We performed a ...population-based cohort study on 994 laryngeal carcinoma patients, treated with RT from 1977 until 2008. Two nomograms were developed and validated. Performance of the models is expressed as the Area Under the Curve (AUC). Results Unfavorable prognostic factors for overall survival were low hemoglobin level, male sex, high T-status, nodal involvement, older age, lower EQD2T (total radiation dose corrected for fraction dose and overall treatment time), and non-glottic tumor. All factors except tumor location were prognostic for local control. The AUCs were 0.73 for overall survival and 0.67 for local control. External validation of the survival model yielded AUCs of 0.68, 0.74, 0.76 and 0.71 for the Leuven ( n = 109), the VU Amsterdam ( n = 178), the Manchester ( n = 403) and the NKI cohort ( n = 205), respectively, while the validation procedure for the local control model resulted in AUCs of 0.70, 0.71, 0.72 and 0.62. The resulting nomograms were made available on the website www.predictcancer.org. Conclusions For patients with a laryngeal carcinoma treated with RT alone, we have developed visual, easy-to-use nomograms for the prediction of overall survival and primary local control. These models have been successfully validated in four external centers.
HF‐induced airglow at 630 nm was observed by the Digital All‐sky Imager, located near Skibotn in Norway, at F‐region altitudes above the EISCAT HF facility near Tromsø on 21 February 1999. The ...transmitter was operated in a 4‐min on, 4‐min off sequence at 4.04 MHz O‐mode with the beam pointing vertically. The airglow reached a peak intensity of about 100 R above background and appeared equatorward of the HF beam's projection on the reflection altitude, which was obtained from ionograms. Generally, the region of maximum airglow was displaced towards the magnetic field line (zenith angle = 12.8°S) passing through the HF facility. This is a unique feature of these observations. From mid‐latitude studies, such airglow is thought to be excited either by electrons energised to several eV by plasma turbulence, or by thermal electron temperature enhancement. Such localisation towards the magnetic field is unexpected for both mechanisms of airglow generation and suggests this feature may be important at high latitudes.
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