scholarly journals Finland HF and Esrange MST radar observations of polar mesosphere summer echoes

2003 ◽  
Vol 21 (4) ◽  
pp. 1047-1055 ◽  
Author(s):  
T. Ogawa ◽  
N. F. Arnold ◽  
S. Kirkwood ◽  
N. Nishitani ◽  
M. Lester
Keyword(s):  
Middle Atmosphere ◽  
Spectral Width ◽  
Hf Radar ◽  
Doppler Velocity ◽  
Short Period ◽  
Mst Radar ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes ◽  
Thermospheric Dynamics ◽  
Atmospheric Gravity

Abstract. Peculiar near range echoes observed in summer with the SuperDARN HF radar in Finland are presented. The echoes were detected at four frequencies of 9, 11, 13 and 15 MHz at slant ranges of 105–250 km for about 100 min. Interferometer measurements indicate that the echoes are returned from 80–100 km altitudes with elevation angles of 20°–60°. Echo power (< 16 dB), Doppler velocity (between –30 and + 30 ms-1) and spectral width (< 60 ms-1) fluctuate with periods of several to 20 min, perhaps due to short–period atmospheric gravity waves. When the HF radar detected the echoes, a vertical incidence MST radar, located at Esrange in Sweden (650 km north of the HF radar site), observed polar mesosphere summer echoes (PMSE) at altitudes of 80–90 km. This fact suggests that the near range HF echoes are PMSE at HF band, although both radars did not probe a common volume. With increasing radar frequency, HF echo ranges are closer to the radar site and echo power becomes weaker. Possible mechanisms to explain these features are discussed.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; thermospheric dynamics; waves and tides; instruments and techniques)

scholarly journals Arctic and Antarctic polar mesosphere summer echoes observed with oblique incidence HF radars: analysis using simultaneous MF and VHF radar data

2004 ◽  
Vol 22 (12) ◽  
pp. 4049-4059 ◽  
Author(s):  
T. Ogawa ◽  
S. Nozawa ◽  
M. Tsutsumi ◽  
N. F. Arnold ◽  
N. Nishitani ◽  
...  
Keyword(s):  
Oblique Incidence ◽  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Radar Data ◽  
Hf Radar ◽  
Doppler Velocity ◽  
Vhf Radar ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes ◽  
Mf Radar

Abstract. Polar mesosphere summer echoes (PMSEs) have been well studied using vertical incidence VHF radars at northern high-latitudes. In this paper, two PMSE events detected with the oblique incidence SuperDARN HF radars at Hankasalmi, Finland (62.3° N) and Syowa Station, Antarctica (69.0° S), are analyzed, together with simultaneous VHF and medium-frequency (MF) radar data. Altitude resolutions of the HF radars in the mesosphere and the lower thermosphere are too poor to know exact PMSE altitudes. However, a comparison of Doppler velocity from the HF radar and neutral wind velocity from the MF radar shows that PMSEs at the HF band appeared at altitudes within 80-90km, which are consistent with those from previous vertical incidence HF-VHF radar results. The HF-VHF PMSE occurrences exhibit a semidiurnal behavior, as observed by other researchers. It is found that in one event, PMSEs occurred when westward semidiurnal winds with large amplitude at 85-88km altitudes attained a maximum. When the HF-VHF PMSEs were observed at distances beyond 180km from MF radar sites, the MF radars detected no appreciable signatures of echo enhancement. Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; thermospheric dynamics; waves and tides)

scholarly journals Frequency domain interferometry mode observations of PMSE using the EISCAT VHF radar

2000 ◽  
Vol 18 (12) ◽  
pp. 1599-1612 ◽  
Author(s):  
P. B. Chilson ◽  
S. Kirkwood ◽  
I. Häggström
Keyword(s):  
Frequency Domain ◽  
Middle Atmosphere ◽  
Lower Boundary ◽  
Doppler Velocity ◽  
Vhf Radar ◽  
Radio Science ◽  
First Results ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes ◽  
Frequency Coherence

Abstract. During the summer of 1997 investigations into the nature of polar mesosphere summer echoes (PMSE) were conducted using the European incoherent scatter (EISCAT) VHF radar in Norway. The radar was operated in a frequency domain interferometry (FDI) mode over a period of two weeks to study the frequency coherence of the returned radar signals. The operating frequencies of the radar were 224.0 and 224.6 MHz. We present the first results from the experiment by discussing two 4-h intervals of data collected over two consecutive nights. During the first of the two days an enhancement of the FDI coherence, which indicates the presence of distinct scattering layers, was found to follow the lower boundary of the PMSE. Indeed, it is not unusual to observe that the coherence values are peaked around the heights corresponding to both the lower- and upper-most boundaries of the PMSE layer and sublayers. A Kelvin-Helmholtz mechanism is offered as one possible explanation for the layering structure. Additionally, our analysis using range-time-pseudocolor plots of signal-to-noise ratios, spectrograms of Doppler velocity, and estimates of the positions of individual scattering layers is shown to be consistent with the proposition that upwardly propagating gravity waves can become steepened near the mesopause.Key words: Ionosphere (polar ionosphere) · Meteorology and Atmospheric Dynamics (middle atmosphere dynamics) · Radio Science (Interferometry)

scholarly journals Super Dual Auroral Radar Network observations of fluctuations in the spectral distribution of near range meteor echoes in the upper mesosphere and lower thermosphere

2001 ◽  
Vol 19 (4) ◽  
pp. 425-434 ◽  
Author(s):  
N. F. Arnold ◽  
T. R. Robinson ◽  
M. Lester ◽  
P. B. Byrne ◽  
P. J. Chapman
Keyword(s):  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Spectral Width ◽  
Hf Radar ◽  
Model Calculations ◽  
Radar Network ◽  
Mesosphere And Lower Thermosphere ◽  
Solar Uv Irradiance ◽  
Thermospheric Dynamics

Abstract. The Doppler shifts of meteor echoes measured by the SuperDARN HF radar network have been used in several studies to observe neutral winds in the upper mesosphere and lower thermosphere region. In the absence of accurate height information for individual meteors, it has been necessary to assume a statistical mean meteor layer where the variations in altitude were not correlated to changes in the horizontal winds. Observations of spectral width distribution variations made by the radars allow an independent determination of the systematic error in the height. We have investigated the dependence of this distribution on a number of factors including the radar geometry, diurnal and seasonal cycles, variations in solar UV irradiance and geomagnetic activity. Changes in the altitude of the mean meteor layer observed at different radar ranges provide us with some insight into the structure of the upper mesosphere and the lower thermosphere within which the meteors are being ablated. An examination of the spectral widths, as measured by the CUT-LASS Finland radar, in the days preceding and following a Storm Sudden Commencement in April 1997, illustrates how the spectral properties of the observed region can be affected. The variations in the widths were consistent with model calculations of the changes to the temperature profile over this interval. Further refinements in the determination of the spectral width are outlined for future experiments.Key words. Meterology and atmospheric dynamics (middle atmosphere dynamics; thermospheric dynamics; instruments and techniques)

scholarly journals Observation of Kelvin–Helmholtz instabilities and gravity waves in the summer mesopause above Andenes in Northern Norway

2018 ◽  
Vol 18 (9) ◽  
pp. 6721-6732 ◽  
Author(s):  
Gunter Stober ◽  
Svenja Sommer ◽  
Carsten Schult ◽  
Ralph Latteck ◽  
Jorge L. Chau
Keyword(s):  
Gravity Waves ◽  
Middle Atmosphere ◽  
Phase Speed ◽  
Velocity Measurements ◽  
Wind Variability ◽  
Short Period ◽  
Strong Shear ◽  
Summer Echoes ◽  
Period Wave ◽  
Horizontal Wavelength

Abstract. We present observations obtained with the Middle Atmosphere Alomar Radar System (MAARSY) to investigate short-period wave-like features using polar mesospheric summer echoes (PMSEs) as a tracer for the neutral dynamics. We conducted a multibeam experiment including 67 different beam directions during a 9-day campaign in June 2013. We identified two Kelvin–Helmholtz instability (KHI) events from the signal morphology of PMSE. The MAARSY observations are complemented by collocated meteor radar wind data to determine the mesoscale gravity wave activity and the vertical structure of the wind field above the PMSE. The KHIs occurred in a strong shear flow with Richardson numbers Ri < 0.25. In addition, we observed 15 wave-like events in our MAARSY multibeam observations applying a sophisticated decomposition of the radial velocity measurements using volume velocity processing. We retrieved the horizontal wavelength, intrinsic frequency, propagation direction, and phase speed from the horizontally resolved wind variability for 15 events. These events showed horizontal wavelengths between 20 and 40 km, vertical wavelengths between 5 and 10 km, and rather high intrinsic phase speeds between 45 and 85 m s−1 with intrinsic periods of 5–10 min.

scholarly journals Dynamical critical scaling of electric field fluctuations in the greater cusp and magnetotail implied by HF radar observations of F-region Doppler velocity

2006 ◽  
Vol 24 (2) ◽  
pp. 689-705 ◽  
Author(s):  
M. L. Parkinson
Keyword(s):  
Solar Wind ◽  
Open Field ◽  
Electric Fields ◽  
Spectral Width ◽  
Hf Radar ◽  
Doppler Velocity ◽  
Closed Field ◽  
Scaling Exponent ◽  
Central Plasma ◽  
Field Lines

Abstract. Akasofu's solar wind ε parameter describes the coupling of solar wind energy to the magnetosphere and ionosphere. Analysis of fluctuations in ε using model independent scaling techniques including the peaks of probability density functions (PDFs) and generalised structure function (GSF) analysis show the fluctuations were self-affine (mono-fractal, single exponent scaling) over 9 octaves of time scale from ~46 s to ~9.1 h. However, the peak scaling exponent α0 was a function of the fluctuation bin size, so caution is required when comparing the exponents for different data sets sampled in different ways. The same generic scaling techniques revealed the organisation and functional form of concurrent fluctuations in azimuthal magnetospheric electric fields implied by SuperDARN HF radar measurements of line-of-sight Doppler velocity, vLOS, made in the high-latitude austral ionosphere. The PDFs of vLOS fluctuation were calculated for time scales between 1 min and 256 min, and were sorted into noon sector results obtained with the Halley radar, and midnight sector results obtained with the TIGER radar. The PDFs were further sorted according to the orientation of the interplanetary magnetic field, as well as ionospheric regions of high and low Doppler spectral width. High spectral widths tend to occur at higher latitude, mostly on open field lines but also on closed field lines just equatorward of the open-closed boundary, whereas low spectral widths are concentrated on closed field lines deeper inside the magnetosphere. The vLOS fluctuations were most self-affine (i.e. like the solar wind ε parameter) on the high spectral width field lines in the noon sector ionosphere (i.e. the greater cusp), but suggested multi-fractal behaviour on closed field lines in the midnight sector (i.e. the central plasma sheet). Long tails in the PDFs imply that "microbursts" in ionospheric convection occur far more frequently, especially on open field lines, than can be captured using the effective Nyquist frequency and volume resolution of SuperDARN radars.

scholarly journals CUTLASS HF radar observations of high-velocity E-region echoes

2001 ◽  
Vol 19 (4) ◽  
pp. 411-424 ◽  
Author(s):  
M. V. Uspensky ◽  
A. V. Koustov ◽  
P. Eglitis ◽  
A. Huuskonen ◽  
S. E. Milan ◽  
...  
Keyword(s):  
Electric Fields ◽  
High Velocity ◽  
Power Doppler ◽  
Spectral Width ◽  
Plasma Instability ◽  
Hf Radar ◽  
Doppler Velocity ◽  
Classical Type ◽  
E Region

Abstract. A short event of high-velocity E-region echo observations by the Pykkvibaer HF radar is analysed to study echo parameters and the echo relation to the Farley-Buneman plasma instability. The echoes were detected in several beams aligned closely to the magnetic L-shell direction. Two echo groups were identified: one group corresponded to the classical type 1 echoes with velocities close to the nominal ion-acoustic speed of 400 ms–1 , while the other group had significantly larger velocities, of the order of 700 ms–1 . The mutual relationship between the echo power, Doppler velocity, spectral width and elevation angles for these two groups was studied. Plotting of echo parameters versus slant range showed that all ~700 ms–1 echoes originated from larger heights and distances of 500–700 km, while all ~400 ms–1 echoes came from lower heights and from farther distances; 700–1000 km. We argue that both observed groups of echoes occurred due to the Farley-Buneman plasma instability excited by strong ( ~70 mVm–1 ) and uniformly distributed electric fields. We show that the echo velocities for the two groups were different because the echoes were received from different heights. Such a separation of echo heights occurred due to the differing amounts of ionospheric refraction at short and large ranges. Thus, the ionospheric refraction and related altitude modulation of ionospheric parameters are the most important factors to consider, when various characteristics of E-region decametre irregularities are derived from HF radar measurements.Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; polar ionosphere)

scholarly journals Influence of tides and gravity waves on layering processes in the polar summer mesopause region

2008 ◽  
Vol 26 (12) ◽  
pp. 4013-4022 ◽  
Author(s):  
P. Hoffmann ◽  
M. Rapp ◽  
J. Fiedler ◽  
R. Latteck
Keyword(s):  
Gravity Waves ◽  
Lower Layer ◽  
Vhf Radar ◽  
Remarkable Feature ◽  
Ice Cloud ◽  
Radar Echoes ◽  
Layer Structures ◽  
Short Period ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes

Abstract. Polar Mesosphere Summer Echoes (PMSE) have been studied at Andenes (69° N, 16° E), Norway, using VHF radar observations since 1994. One remarkable feature of these observations is the fact that {during 50% of the time,} the radar echoes occur in the form of two or more distinct layers. In the case of multiple PMSE layers, statistical analysis shows that the lower layer occurs at a mean height of ~83.4 km, which is almost identical to the mean height of noctilucent clouds (NLC) derived from observation with the ALOMAR Rayleigh/Mie/Raman lidar at the same site. To investigate the layering processes microphysical model simulations under the influence of tidal and gravity waves were performed. In the presence of long period gravity waves, these model investigations predict an enhanced formation of multiple PMSE layer structures, where the lower layer is a consequence of the occurrence of the largest particles at the bottom of the ice cloud. This explains the coincidence of the lowermost PMSE layers and NLC. During periods with enhanced amplitudes of the semidiurnal tide, the observed NLC and PMSE show pronounced tidal structures comparable to the results of corresponding microphysical simulations. At periods with short period gravity waves there is a tendency for a decreasing occurrence of NLC and for variable weak PMSE structures.

scholarly journals VHF radar observations of turbulent structures in the polar mesopause region

1997 ◽  
Vol 15 (8) ◽  
pp. 1028-1036 ◽  
Author(s):  
P. Czechowsky ◽  
R. Rüster
Keyword(s):  
General Relation ◽  
Spectral Width ◽  
Energy Dissipation Rate ◽  
Observation Time ◽  
Inertial Subrange ◽  
Apparent Velocity ◽  
Turbulent Structures ◽  
Vhf Radar ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes

Abstract. The mobile SOUSY VHF Radar was operated in the summer of 1987 during the MAC/SINE campaign in northern Norway to study the polar mesosphere summer echoes (PMSE). Measurements of the spectral width indicate that two types of structures occur. In general mesospheric layers are bifurcated exhibiting a narrow spectral width and a well-defined aspect sensitivity. However, for about 10% of the observation time cells of enhanced turbulence characterized by extremely broad spectral widths appear predominantly in the upper sublayer above 86 km. Identification and separation of beam and shear broadening allows a determination of the turbulence-induced component of the spectral width. This case study reveals that during several events these cloud-like structures of enhanced turbulence move with an apparent velocity of several tens of meters per second which is almost identical with the phase trace velocity of simultaneously observed waves. Since, at that time, the Richardson number was less than a quarter, it was concluded that these turbulent cells were generated by a Kelvin-Helmholtz mechanism. The horizontal extent of these structures was calculated to be less than 40 km. A general relation between spectral width and echo power was not detected. The turbulent component of the spectral width was used to calculate typical values of the energy dissipation rate at times where narrow spectral width dominates and during periods of enhanced turbulence. In addition, the outer scale of the inertial subrange (buoyancy scale) was estimated. For the first time the occurrence and motion of this type of structures of enhanced spectral width is analyzed and discussed in detail.

scholarly journals Observation of Kelvin-Helmholtz Instabilities and gravity waves in the summer mesopause above Andenes in Northern Norway

2018 ◽  
Author(s):  
Gunter Stober ◽  
Svenja Sommer ◽  
Carsten Schult ◽  
Ralph Latteck ◽  
Jorge L. Chau
Keyword(s):  
Gravity Waves ◽  
Vertical Structure ◽  
Middle Atmosphere ◽  
Meteor Radar ◽  
Helmholtz Instability ◽  
Beam Experiment ◽  
Short Period ◽  
Strong Shear ◽  
Summer Echoes ◽  
Period Wave

Abstract. We present observations obtained with the Middle Atmosphere Alomar Radar System (MAARSY) to investigate short period wave-like features using polar mesospheric summer echoes (PMSE) as tracer for the neutral dynamics. We conducted a multi-beam experiment including 67 different beam directions during a 9-day campaign in June 2013. We identified two Kelvin Helmholtz Instability (KHI) events from the signal morphology of PMSE. The MAARSY observations are complemented by collocated meteor radar wind data to determine the mesoscale gravity wave activity and the vertical structure of the wind field above the PMSE. The KHIs occurred in a strong shear flow with Richardson numbers Ri 

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