scholarly journals Enhanced incoherent scatter plasma lines

1996 ◽  
Vol 14 (12) ◽  
pp. 1462-1472 ◽  
Author(s):  
H. Nilsson ◽  
S. Kirkwood ◽  
J. Lilensten ◽  
M. Galand
Keyword(s):  
High Plasma ◽  
Collision Term ◽  
Vhf Radar ◽  
Detailed Model ◽  
Model Calculations ◽  
Incoherent Scatter ◽  
Incoherent Scatter Radars ◽  
Plasma Line ◽  
E Region ◽  
Radar Measurements

Abstract. Detailed model calculations of auroral secondary and photoelectron distributions for varying conditions have been used to calculate the theoretical enhancement of incoherent scatter plasma lines. These calculations are compared with EISCAT UHF radar measurements of enhanced plasma lines from both the E and F regions, and published EISCAT VHF radar measurements. The agreement between the calculated and observed plasma line enhancements is good. The enhancement from the superthermal distribution can explain even the very strong enhancements observed in the auroral E region during aurora, as previously shown by Kirkwood et al. The model calculations are used to predict the range of conditions when enhanced plasma lines will be seen with the existing high-latitude incoherent scatter radars, including the new EISCAT Svalbard radar. It is found that the detailed structure, i.e. the gradients in the suprathermal distribution, are most important for the plasma line enhancement. The level of superthermal flux affects the enhancement only in the region of low phase energy where the number of thermal electrons is comparable to the number of suprathermal electrons and in the region of high phase energy where the suprathermal fluxes fall to such low levels that their effect becomes small compared to the collision term. To facilitate the use of the predictions for the different radars, the expected signal- to-noise ratios (SNRs) for typical plasma line enhancements have been calculated. It is found that the high-frequency radars (Søndre Strømfjord, EISCAT UHF) should observe the highest SNR, but only for rather high plasma frequencies. The VHF radars (EISCAT VHF and Svalbard) will detect enhanced plasma lines over a wider range of frequencies, but with lower SNR.

scholarly journals A Proposed Solution to the Range–Doppler Dilemma of Weather Radar Measurements by Using the SMPRF Codes, Practical Results, and a Comparison with Operational Measurements

2005 ◽  
Vol 44 (9) ◽  
pp. 1375-1390 ◽  
Author(s):  
Juha Pirttilä ◽  
Markku S. Lehtinen ◽  
Asko Huuskonen ◽  
Markku Markkanen
Keyword(s):  
High Resolution ◽  
Pulse Repetition Frequency ◽  
Weather Radar ◽  
Simplified Model ◽  
Measured Spectrum ◽  
Model Calculations ◽  
Incoherent Scatter ◽  
Incoherent Scatter Radars ◽  
Working Principle ◽  
Radar Measurements

Abstract Based on the measurement principles used on incoherent scatter radars, the authors have developed the Simultaneous Multiple Pulse Repetition Frequency (SMPRF) code that is intended to solve the range–Doppler dilemma and that can be used with modern magnetron radars. The working principle of the code is explained in mathematical terms and with the help of a simplified model. Results from the SMPRF and traditional fixed PRF weather radar measurements are compared, and the reasons for the differences are explained. The practical results show that the SMPRF code seems to work in the manner that is predicted by the theoretical and model calculations. The SMPRF code provides enough information to produce a high-resolution measured spectrum for each range gate. The shape of these measured spectra are seldom purely Gaussian. It is possible that more advanced raw products, other than just reflectivity, velocity, and width, can be produced with the help of these high-resolution spectra.

scholarly journals Plasma convection at high latitudes using the EISCAT VHF and ESR incoherent scatter radars

2000 ◽  
Vol 18 (9) ◽  
pp. 1088-1096 ◽  
Author(s):  
J. M. Holt ◽  
A. P. van Eyken
Keyword(s):  
Three Dimensional ◽  
Data Sets ◽  
Plasma Convection ◽  
Vhf Radar ◽  
Common Assumption ◽  
Incoherent Scatter ◽  
Incoherent Scatter Radars ◽  
The Common ◽  
Convection Patterns

Abstract. The recent availability of substantial data sets taken by the EISCAT Svalbard Radar allows several important tests to be made on the determination of convection patterns from incoherent scatter radar results. During one 30-h period, the Svalbard Radar made 15 min scans combining local field aligned observations with two, low elevation positions selected to intersect the two beams of the Common Programme Four experiment being simultaneously conducted by the EISCAT VHF radar at Tromsø. The common volume results from the two radars are compared. The plasma convection velocities determined independently by the two radars are shown to agree very closely and the combined three-dimensional velocity data used to test the common assumption of negligible field-aligned flow in this regime.Key words: Ionosphere (auroral ionosphere; polar ionosphere) - Magnetospheric physics (plasma convection)

scholarly journals EISCAT Svalbard radar observations of SPEAR-induced E- and F-region spectral enhancements in the polar cap ionosphere

2007 ◽  
Vol 25 (8) ◽  
pp. 1801-1814 ◽  
Author(s):  
R. S. Dhillon ◽  
T. R. Robinson ◽  
T. K. Yeoman
Keyword(s):  
High Power ◽  
Polar Cap ◽  
Incoherent Scatter ◽  
F Region ◽  
Sporadic E Layers ◽  
First Results ◽  
Plasma Line ◽  
E Region ◽  
Sporadic E ◽  
Overdense Plasma

Abstract. The Space Plasma Exploration by Active Radar (SPEAR) facility has successfully operated in the high-power heater and low-power radar modes and has returned its first results. The high-power results include observations of SPEAR-induced ion and plasma line spectral enhancements recorded by the EISCAT Svalbard UHF incoherent scatter radar system (ESR), which is collocated with SPEAR. These SPEAR-enhanced spectra possess features that are consistent with excitation of both the purely growing mode and the parametric decay instability. In this paper, we present observations of upper and lower E-region SPEAR-induced ion and plasma line enhancements, together with F-region spectral enhancements, which indicate excitation of both instabilities and which are consistent with previous theoretical treatments of instability excitation in sporadic E-layers. In agreement with previous observations, spectra from the lower E-region have the single-peaked form characteristic of collisional plasma. Our observations of the SPEAR-enhanced E-region spectra suggest the presence of variable drifting regions of patchy overdense plasma, which is a finding also consistent with previous results.

scholarly journals Alternating-code experiment for plasma-line studies

1996 ◽  
Vol 14 (12) ◽  
pp. 1473-1479
Author(s):  
P. Guio ◽  
N. Bjørnå ◽  
W. Kofman
Keyword(s):  
Correction Term ◽  
Good Alternative ◽  
Electron Velocity ◽  
Electron Velocity Distribution ◽  
Vhf Radar ◽  
Pulse Technique ◽  
F Region ◽  
Plasma Line ◽  
E Region ◽  
Long Pulse

Abstract. We present results of the first plasma-line measurement of the incoherent spectrum using the alternating-code technique with the EISCAT VHF radar. This technique, which has earlier mostly been used to measure high-resolution E-region ion-line spectra, turned out to be a very good alternative to other techniques for plasma-line measurements. The experiment provides simultaneous measurement of the ion line and downshifted and upshifted plasma-line spectra with an altitude resolution of 3 km and a temporal resolution of 10 s. The measurements are taken around the peak of the F region, but not necessarily at the peak itself, as is the case with the long-pulse technique. The condition for success is that the scale height should be large enough such that the backscattered signal from the range extent of one gate falls inside the receiver filter. The data are analysed and the results are combined with the results of the ion-line data analysis to estimate electron mean drift velocity and thereafter electric currents along the line of sight of the radar using both the standard dispersion relation assuming a Maxwellian electron velocity distribution and the more recent model including a heat-flow correction term.

scholarly journals Charged dust in the D-region incoherent scatter spectrum

2021 ◽  
Vol 87 (5) ◽  
Author(s):  
Tinna L. Gunnarsdottir ◽  
Ingrid Mann
Keyword(s):  
Electromagnetic Waves ◽  
Dust Particles ◽  
Charged Dust ◽  
Vhf Radar ◽  
Model Calculations ◽  
Incoherent Scatter ◽  
D Region ◽  
Dust Detection ◽  
Dust Component ◽  
Scatter Spectrum

We investigate the influence of charged dust on the incoherent scatter from the D-region ionosphere. Incoherent scatter is observed with high-power, large aperture radars and results from electromagnetic waves scattering at electrons that are coupled to other charged components through plasma oscillations. The influence of charged dust can hence be considered an effect of dusty plasma. The D-region contains meteoric smoke particles that are of nanometre size and form from incoming ablating meteors. Detection of such charged dust in the incoherent scatter spectrum from the D-region has previously been proposed and studied to some degree. We here present model calculations to investigate the influence of the charged dust component with a size distribution, instead of the one size dust components assumed in other works. The developed code to calculate the incoherent scatter spectrum from the D-region including dust particles with different sizes and different positive and negative charge states is made available (https://doi.org/10.18710/GHZIIY). We investigate how sizes, number density and charge state of the dust influence the spectrum during different ionospheric conditions. We consider the ionospheric parameters for the location of the EISCAT VHF radar during a year and find that conditions are most suitable for dust detection in winter below 80 km at times with increased electron densities. The prospects to derive dust parameters increase, when the incoherent scatter observations are combined with those of other instruments to provide independent information on electron density, neutral density and temperature.

scholarly journals Analysis of beam plasma instability effects on incoherent scatter spectra

2010 ◽  
Vol 28 (12) ◽  
pp. 2169-2175 ◽  
Author(s):  
M. A. Diaz ◽  
J. L. Semeter ◽  
M. Oppenheim ◽  
M. Zettergren
Keyword(s):  
Simultaneous Detection ◽  
Plasma Instability ◽  
Recent Model ◽  
Incoherent Scatter ◽  
Beam Plasma ◽  
Baseband Signal ◽  
Incoherent Scatter Radars ◽  
Plasma Line ◽  
Beam Plasma Instability ◽  
Langmuir Decay

Abstract. Naturally Enhanced Ion Acoustic Lines (NEIALs) detected with Incoherent Scatter Radars (ISRs) can be produced by a Langmuir decay mechanism, triggered by a bump on tail instability. A recent model of the beam-plasma instability suggests that weak-warm beams, such those associated with NEIAL events, might produce Langmuir harmonics which could be detected by a properly configured ISR. The analysis performed in this work shows that such a beam-driven wave may be simultaneously detected with NEIALs within the baseband signal of a single ISR. The analysis shows that simultaneous detection of NEIALs and the first Langmuir harmonic is more likely than simultaneous detection of NEIALs and enhanced plasma line. This detection not only would help to discriminate between current NEIAL models, but could also aid in the parameter estimation of soft precipitating electrons.

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