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 Aspect sensitive E- and F-region SPEAR-enhanced incoherent backscatter observed by the EISCAT Svalbard radar

2009 ◽  
Vol 27 (1) ◽  
pp. 65-81 ◽  
Author(s):  
R. S. Dhillon ◽  
T. R. Robinson ◽  
T. K. Yeoman
Keyword(s):  
High Latitude ◽  
Polar Cap ◽  
Electrostatic Waves ◽  
Incoherent Scatter ◽  
F Region ◽  
High Latitude Ionosphere ◽  
Plasma Line ◽  
Sporadic E Layer ◽  
Sporadic E ◽  
Field Aligned Irregularities

Abstract. Previous studies of the aspect sensitivity of heater-enhanced incoherent radar backscatter in the high-latitude ionosphere have demonstrated the directional dependence of incoherent scatter signatures corresponding to artificially excited electrostatic waves, together with consistent field-aligned signatures that may be related to the presence of artificial field-aligned irregularities. These earlier high-latitude results have provided motivation for repeating the investigation in the different geophysical conditions that obtain in the polar cap ionosphere. The Space Plasma Exploration by Active Radar (SPEAR) facility is located within the polar cap and has provided observations of RF-enhanced ion and plasma line spectra recorded by the EISCAT Svalbard UHF incoherent scatter radar system (ESR), which is collocated with SPEAR. In this paper, we present observations of aspect sensitive E- and F-region SPEAR-induced ion and plasma line enhancements that indicate excitation of both the purely growing mode and the parametric decay instability, together with sporadic E-layer results that may indicate the presence of cavitons. We note consistent enhancements from field-aligned, vertical and also from 5° south of field-aligned. We attribute the prevalence of vertical scatter to the importance of the Spitze region, and of that from field-aligned to possible wave/irregularity coupling.

Investigation on the role of E-F region coupling processes on the generation of nighttime MSTIDs: Case studies over northern Germany

2021 ◽  
Author(s):  
Mani Sivakandan ◽  
Jorge L Chau ◽  
Carlos Martinis ◽  
Yuichi Otsuka ◽  
Jens Mielich ◽  
...  
Keyword(s):  
Gps Tec ◽  
F Region ◽  
Perkins Instability ◽  
Sporadic E Layers ◽  
Spread F ◽  
E Region ◽  
Sporadic E ◽  
Low Latitude Ionosphere ◽  
Atmospheric Gravity

<p>Northwest to southeast phase fronts with southwestward moving features are commonly observed in the nighttime midlatitude ionosphere during the solstice months at low solar activity. These features are identified as nighttime MSTIDs (medium scale traveling ionospheric disturbances). Initially, they were considered to be a manifestation of neutral atmospheric gravity waves. Later on, investigations showed that the nighttime MSTIDs are electrified in nature and mostly confined to the mid and low latitude ionosphere. Although the overall characteristics of the nighttime MSTIDs are mostly well understood, the causative mechanisms are not well known. Perkins instability mechanism was believed to be the cause of nighttime MSTIDs, however, the growth rate of the instability is too small to explain the perturbations observed. Recently, model simulations and observational studies suggest that coupling between sporadic-E layers and other type of E-region instabilities, and the F region may be relevant to explain the generation of the MSTIDs.</p><p>In the present study simultaneous observation from OI 630 nm all-sky airglow imager, GPS-TEC, ionosonde and Meteor radars, are used to investigate the role of E and F region coupling on the generation of MSTIDs .Nighttime MSTIDs observed on three nights (14 March 2020, 23 March 2020 and 28 May 2020) in the OI 630 nm airglow images over Kuehlungsborn (54°07'N; 11°46'E, 53.79N  mag latitude), Germany, are presented. Simultaneous detrended GPS-TEC measurements also shows presence of MSTIDs on these nights. In addition, simultaneous ionosonde observations over Juliusruh (54°37.7'N 13°22.5'E) show spread-F in the ionograms as well as sporadic-E layer occurrence.  Furthermore, we also investigate the MLT region wind variations during these nights. The role of Es-layers and the interplay between the winds and Es-layers role on the generation of the MSTIDs will be discussed in detail in this presentation.</p><p> </p>

scholarly journals Multistation digisonde observations of equatorial spread F in South America

2004 ◽  
Vol 22 (9) ◽  
pp. 3145-3153 ◽  
Author(s):  
B. W. Reinisch ◽  
M. Abdu ◽  
I. Batista ◽  
G. S. Sales ◽  
G. Khmyrov ◽  
...  
Keyword(s):  
South America ◽  
Field Line ◽  
Magnetic Equator ◽  
Simple Correlation ◽  
Equatorial Spread F ◽  
F Region ◽  
Sporadic E Layers ◽  
Spread F ◽  
E Region ◽  
Sporadic E

Abstract. Directional ionogram and F-region drift observations were conducted at seven digisonde stations in South America during the COPEX campaign from October to December 2002. Five stations in Brazil, one in Argentina, and one in Peru, monitored the ionosphere across the continent to study the onset and development of F-region density depletions that cause equatorial spread F (ESF). New ionosonde techniques quantitatively describe the prereversal uplifting of the F layer at the magnetic equator and the eastward motion of the depletions over the stations. Three of the Brazilian stations were located along a field line with a 350-km apex over the equator to investigate the relation of the occurrence of ESF and the presence of sporadic E-layers at the two E-region intersections of the field line. No simple correlation was found.

scholarly journals Common volume coherent and incoherent scatter radar observations of mid-latitude sporadic E-layers and QP echoes

2004 ◽  
Vol 22 (9) ◽  
pp. 3277-3290 ◽  
Author(s):  
D. L. Hysell ◽  
M. F. Larsen ◽  
Q. H. Zhou
Keyword(s):  
Large Scale ◽  
Incoherent Scatter Radar ◽  
Coherent Scatter ◽  
Electrostatic Waves ◽  
Incoherent Scatter ◽  
Scatter Radar ◽  
Dual Beam ◽  
Sporadic E Layers ◽  
E Region ◽  
Sporadic E

Abstract. Common-volume observations of sporadic E-layers made on 14-15 June 2002 with the Arecibo incoherent scatter radar and a 30MHz coherent scatter radar imager located on St. Croix are described. Operating in dual-beam mode, the Arecibo radar detected a slowly descending sporadic E-layer accompanied by a series of dense E-region plasma clouds at a time when the coherent scatter radar was detecting quasi-periodic (QP) echoes. Using coherent radar imaging, we collocate the sources of the coherent scatter with the plasma clouds observed by Arecibo. In addition to patchy, polarized scattering regions drifting through the radar illuminated volume, which have been observed in previous imaging experiments, the 30MHz radar also detected large-scale electrostatic waves in the E-region over Puerto Rico, with a wavelength of about 30km and a period of about 10min, propagating to the southwest. Both the intensity and the Doppler shifts of the coherent echoes were modulated by the wave.

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 Type-1 echoes from the mid-latitude E-Region ionosphere

1997 ◽  
Vol 15 (7) ◽  
pp. 908-917 ◽  
Author(s):  
C. Haldoupis ◽  
D. T. Farley ◽  
K. Schlegel
Keyword(s):  
Doppler Radar ◽  
Spectral Component ◽  
Equatorial Electrojet ◽  
Metallic Ions ◽  
Sporadic E Layers ◽  
E Region ◽  
Sporadic E ◽  
The Right

Abstract. This paper presents more data on the properties of type-1 irregularities in the nighttime mid-latitude E-region ionosphere. The measurements were made with a 50-MHz Doppler radar system operating in Crete, Greece. The type-1 echoes last from several seconds to a few minutes and are characterized by narrow Doppler spectra with peaks corresponding to wave phase velocities of 250–350 m/s. The average velocity of 285 m/s is about 20% lower than nominal E-region ion-acoustic speeds, probably because of the presence of heavy metallic ions in the sporadic-E-layers that appear to be associated with the mid-latitude plasma instabilities. Sometimes the type-1 echoes are combined with a broad spectrum of type-2 echoes; at other times they dominate the spectrum or may appear in the absence of any type-2 spectral component. We believe these echoes are due to the modified two-stream plasma instability driven by a polarization electric field that must be larger than 10 mV/m. This field is similar in nature to the equatorial electrojet polarization field and can arise when patchy nighttime sporadic-E-layers have the right geometry.

scholarly journals Seasonal variability and descent of mid-latitude sporadic E layers at Arecibo

2009 ◽  
Vol 27 (3) ◽  
pp. 923-931 ◽  
Author(s):  
N. Christakis ◽  
C. Haldoupis ◽  
Q. Zhou ◽  
C. Meek
Keyword(s):  
Lower Thermosphere ◽  
Time Base ◽  
Large Set ◽  
Seasonal Behavior ◽  
Incoherent Scatter ◽  
Electron Density Gradient ◽  
Sporadic E Layers ◽  
Sporadic E Layer ◽  
Sporadic E ◽  
Wind Shears

Abstract. Sporadic E layers (Es) follow regular daily patterns in variability and altitude descent, which are determined primarily by the vertical tidal wind shears in the lower thermosphere. In the present study a large set of sporadic E layer incoherent scatter radar (ISR) measurements are analyzed. These were made at Arecibo (Geog. Lat. ~18° N; Magnetic Dip ~50°) over many years with ISR runs lasting from several hours to several days, covering evenly all seasons. A new methodology is applied, in which both weak and strong layers are clearly traced by using the vertical electron density gradient as a function of altitude and time. Taking a time base equal to the 24-h local day, statistics were obtained on the seasonal behavior of the diurnal and semidiurnal tidal variability and altitude descent patterns of sporadic E at Arecibo. The diurnal tide, most likely the S(1,1) tide with a vertical wavelength around 25 km, controls fully the formation and descent of the metallic Es layers at low altitudes below 110 km. At higher altitudes, there are two prevailing layers formed presumably by vertical wind shears associated mainly with semidiurnal tides. These include: 1) a daytime layer starting at ~130 km around midday and descending down to 105 km by local midnight, and 2) a less frequent and weaker nighttime layer which starts prior to midnight at ~130 km, descending downwards at somewhat faster rate to reach 110 km by sunrise. The diurnal and semidiurnal-like pattern prevails, with some differences, in all seasons. The differences in occurrence, strength and descending speeds between the daytime and nighttime upper layers are not well understood from the present data alone and require further study.

scholarly journals A comparison of velocity measurements from the CUTLASS Finland radar and the EISCAT UHF system

1999 ◽  
Vol 17 (7) ◽  
pp. 892-902 ◽  
Author(s):  
J. A. Davies ◽  
M. Lester ◽  
S. E. Milan ◽  
T. K. Yeoman
Keyword(s):  
Total Duration ◽  
Field Of View ◽  
Simultaneous Occurrence ◽  
Plasma Convection ◽  
Contributing Factors ◽  
Plasma Irregularities ◽  
Incoherent Scatter ◽  
F Region ◽  
Initial Comparison ◽  
E Region

Abstract. The CUTLASS Finland radar, which comprises an integral part of the SuperDARN system of HF coherent radars, provides near continuous observations of high-latitude plasma irregularities within a field-of-view which extends over some four million square kilometres. Within the Finland radar field-of-view lie both the EISCAT mainland and EISCAT Svalbard incoherent scatter radar facilities. Since the CUTLASS Finland radar commenced operation, in February 1995, the mainland EISCAT UHF radar has been run in common programme 1 and 2 modes for a total duration exceeding 1000 h. Simultaneous and spatially coincident returns from these two radars over this period provide the basis for a comparison of irregularity drift velocity and F-region ion velocity. Initial comparison is limited to velocities from four intervals of simultaneous radar returns; intervals are selected such that they exhibit a variety of velocity signatures including that characteristic of the convection reversal and a rapidly fluctuating velocity feature. Subsequent comparison is on a statistical basis. The velocities measured by the two systems demonstrate reasonable correspondence over the velocity regime encountered during the simultaneous occurrence of coherent and incoherent scatter; differences between the EISCAT UHF measurements of F-region ion drift and the irregularity drift velocities from the Finland radar are explained in terms of a number of contributing factors including contamination of the latter by E-region echoes, a factor which is investigated further, and the potentially deleterious effect of discrepant volume and time sampling intervals.Key words. Ionosphere (ionospheric irregularities; plasma convection)

scholarly journals Ionospheric transients observed at mid-latitudes prior to earthquake activity in Central Italy

2010 ◽  
Vol 10 (6) ◽  
pp. 1197-1208 ◽  
Author(s):  
P. Nenovski ◽  
Ch. Spassov ◽  
M. Pezzopane ◽  
U. Villante ◽  
M. Vellante ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Critical Frequency ◽  
Central Italy ◽  
Ionospheric Disturbances ◽  
Earthquake Activity ◽  
Acoustic Gravity Waves ◽  
F Region ◽  
E Region ◽  
Sporadic E ◽  
Layer Development

Abstract. Ionograms from Rome (41.8N, 12.5E) and Sofia (42.4N, 23.2E) ionospheric stations during earthquake (EQ) activity with magnitude (M) between 5 and 6 in Central Italy are analyzed. It is found that several ionospheric disturbances occur in the intermediate E-F region before the EQ shock. In fact, besides sporadic E (Es) layer development (of type h) of short duration (transients), fmin increase, trace gaps near the critical frequencies, and E region trace disappearance are also observed within one to three hours before the EQ shock. Before the EQ shocks we find that the F2 region parameters are practically undisturbed. The only exception is the so-called fork trace that appears mostly near the critical frequency of the F2 region. Acoustic gravity waves (AGW) are suggested as one of the possible sources of transients observed in the ionosphere before the EQ shock.

scholarly journals Observational evidence for new instabilities in the midlatitude <i>E</i> and <i>F</i> region

2016 ◽  
Vol 34 (11) ◽  
pp. 927-941 ◽  
Author(s):  
David L. Hysell ◽  
Miguel Larsen ◽  
Michael Sulzer
Keyword(s):  
Dynamic Instability ◽  
Lower Thermosphere ◽  
Growth Time ◽  
F Region ◽  
Stable Conditions ◽  
Spread F ◽  
E Region ◽  
Sporadic E ◽  
The One ◽  
Arecibo Observatory

Abstract. Radar observations of the E- and F-region ionosphere from the Arecibo Observatory made during moderately disturbed conditions are presented. The observations indicate the presence of patchy sporadic E (Es) layers, medium-scale traveling ionospheric disturbances (MSTIDs), and depletion plumes associated with spread F conditions. New analysis techniques are applied to the dataset to infer the vector plasma drifts in the F region as well as vector neutral wind and temperature profiles in the E region. Instability mechanisms in both regions are evaluated. The mesosphere–lower-thermosphere (MLT) region is found to meet the conditions for neutral dynamic instability in the vicinity of the patchy Es layers even though the wind shear was relatively modest. An inversion in the MLT temperature profile contributed significantly to instability in the vicinity of one patchy layer. Of particular interest is the evidence for the conditions required for neutral convective instability in the lower-thermosphere region (which is usually associated with highly stable conditions) due to the rapid increase in temperature with altitude. A localized F-region plasma density enhancement associated with a sudden ascent up the magnetic field is shown to create the conditions necessary for convective plasma instability leading to the depletion plume and spread F. The growth time for the instability is short compared to the one described by [Perkins(1973)]. This instability does not offer a simple analytic solution but is clearly present in numerical simulations. The instability mode has not been described previously but appears to be more viable than the various mechanisms that have been suggested previously as an explanation for the occurrence of midlatitude spread F.

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