scholarly journals First observations of Polar Mesospheric Echoes at both 31 MHz and 53.5 MHz over Svalbard (78.2°N 15.1°E)

2020 ◽  
Vol 1 ◽  
Author(s):  
Chris Hall ◽  
Chris Adami ◽  
Masaki Tsutsumi
Keyword(s):  
Geographical Location ◽  
Meteor Detection ◽  
First Results ◽  
Summer Echoes ◽  
Meteor Trails

AbstractDuring summer 2020, observations of the mesosphere using a 53.5 MHz radar on Svalbard, at 78.2°N 15.1°E, revealed the well-known Polar Mesospheric Summer Echoes (PMSE). At the same time, a co-located meteor detection radar, operating at 31 MHz detected corresponding echoes very distinct from those associated with meteor trails. Comparing as many days as possible during 2020, incontestable evidence arose to demonstrate that the meteor detection radar was capable of observing PMSE, although not in the optimised fashion of the 53.5 MHz system. We present examples of results from both systems, supplementing the earlier findings of Swarnalingam et al. (2009), and simultaneously show very first results from this particular geographical location.

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 Polar mesospheric summer echoes at 78°N, 16°E, 2008: First results of the refurbished sounding system (SOUSY) Svalbard radar

2009 ◽  
Vol 114 (D11) ◽  
Author(s):  
C. M. Hall ◽  
J. Röttger ◽  
K. Kuyeng ◽  
M. Tsutsumi ◽  
M. Dyrland ◽  
...  
Keyword(s):  
First Results ◽  
Summer Echoes

scholarly journals Diurnal variation of non-specular meteor trails

2009 ◽  
Vol 27 (5) ◽  
pp. 1961-1967 ◽  
Author(s):  
J. Hinrichs ◽  
L. P. Dyrud ◽  
J. Urbina
Keyword(s):  
Electric Fields ◽  
Radar Observations ◽  
Plasma Generation ◽  
Highly Sensitive ◽  
First Results ◽  
Head Echo ◽  
Thermospheric Winds ◽  
The Difference ◽  
Meteor Trails ◽  
Radar Meteor

Abstract. We present results of simulated radar observations of meteor trails in an effort to show how non-specular meteor trails are expected to vary as a function of a number of key atmospheric, ionospheric and meteoroid parameters. This paper identifies which geophysical sources effect the variability in non-specular trail radar observations, and provides an approach that uses some of these parameter dependencies to determine meteoroid and atmospheric properties based upon the radar meteor observations. The numerical model used follows meteor evolution from ablation and ionization to head echo plasma generation and through formation of field aligned irregularities (FAI). Our main finding is that non-specular meteor trail duration is highly sensitive to the presence of lower thermospheric winds or electric fields and the background ionospheric electron density. In an effort to make key predictions we present the first results of how the same meteoroid is expected to produce dramatically different meteor trails as a function of location and local time. For example, we show that mid-latitude trail durations are often shorter lasting than equatorial trail observations because of the difference in mid-latitude wind speed and equatorial drift speed. The simulated trails also account for observations showing that equatorial nighttime non-specular meteor trails last significantly longer and are observed more often than daytime trails.

scholarly journals MAARSY – the new MST radar on Andøya: first results of spaced antenna and Doppler measurements of atmospheric winds in the troposphere and mesosphere using a partial array

2012 ◽  
Vol 10 ◽  
pp. 291-298 ◽  
Author(s):  
G. Stober ◽  
R. Latteck ◽  
M. Rapp ◽  
W. Singer ◽  
M. Zecha
Keyword(s):  
Beam Steering ◽  
Meteor Radar ◽  
Phased Array Antenna ◽  
Mst Radar ◽  
First Results ◽  
Expansion Stage ◽  
Summer Echoes ◽  
Wind Measurements ◽  
Radar Measurements ◽  
Temporal And Spatial

Abstract. MST radars have been used to study the troposphere, stratosphere and mesosphere over decades. These radars have proven to be a valuable tool to investigate atmospheric dynamics. MAARSY, the new MST radar at the island of Andøya uses a phased array antenna and is able to perform spaced antenna and Doppler measurements at the same time with high temporal and spatial resolution. Here we present first wind observations using the initial expansion stage during summer 2010. The tropospheric spaced antenna and Doppler beam swinging experiments are compared to radiosonde measurements, which were launched at the nearby Andøya Rocket Range (ARR). The mesospheric wind observations are evaluated versus common volume meteor radar wind measurements. The beam steering capabilities of MAARSY are demonstrated by performing systematic scans of polar mesospheric summer echoes (PMSE) using 25 and 91 beam directions. These wind observations permit to evaluate the new radar against independent measurements from radiosondes and meteor radar measurements to demonstrate its capabilities to provide reliable wind data from the troposphere up to the mesosphere.

scholarly journals Computation of daily Penman–Monteith reference evapotranspiration in the Carpathian Region and comparison with Thornthwaite estimates

2020 ◽  
Vol 16 ◽  
pp. 251-259
Author(s):  
Mónika Lakatos ◽  
Tamás Weidinger ◽  
Lilla Hoffmann ◽  
Zita Bihari ◽  
Ákos Horváth
Keyword(s):  
Reference Evapotranspiration ◽  
Potential Evapotranspiration ◽  
Pannonian Basin ◽  
Linear Trend ◽  
Geographical Location ◽  
Research Programme ◽  
First Results ◽  
Seasonal Basis ◽  
Grid Points ◽  
Meteorological Observations

Abstract. The Pannonian Basin Experiment (PannEx) is a Regional Hydroclimate Project (RHP) of the World Climate Research Programme (WCRP) Global Energy and Water Exchanges (GEWEX) Project. A gridded meteorological dataset is available for the PannEx region as part of the CarpatClim database, which consists of homogenized and harmonized daily meteorological observations for several climate parameters with 0.1∘ spatial resolution in the period of 1961–2010. The estimation of the Penman–Monteith reference evapotranspiration (ET0) on the daily scale was performed for the CarpatClim grid as one of the first results in the PannEx initiative. This study compares the already accessible Thornthwaite estimates of potential evapotranspiration (PET_Th) on the monthly scale to the newly derived Penman–Monteith estimates. The comparison is made on an annual and seasonal basis for the 50-year period. The distribution of both estimates is influenced by geographical location and orographic features. The annual time series are similar but the regional-average annual values of ET0 are ∼80 mm greater than the Thornthwaite estimate in the whole CarpatClim region. The relative bias and root mean square error was computed as well. The classical Thornthwaite method underestimates the ET0 by more than 20 % over extensive regions for selected grid points at elevations lower than 200 m in the Pannonian Basin. The slope of the fitted linear trend indicate increasing reference evapotranspiration in the Pannonian/Carpathian Basin due to climate change.

scholarly journals Comparison of D-region Doppler drift winds measured by the SuperDARN Finland HF radar over an annual cycle using the Kiruna VHF meteor radar

2003 ◽  
Vol 21 (10) ◽  
pp. 2073-2082 ◽  
Author(s):  
N. F. Arnold ◽  
P. A. Cook ◽  
T. R. Robinson ◽  
M. Lester ◽  
P. J. Chapman ◽  
...  
Keyword(s):  
Hf Radar ◽  
Meteor Radar ◽  
Meteorology And Atmospheric Dynamics ◽  
Sporadic E Layers ◽  
D Region ◽  
Summer Echoes ◽  
Instruments And Techniques ◽  
Waves And Tides ◽  
Sporadic E ◽  
Meteor Trails

Abstract. The SuperDARN chain of oblique HF radars has provided an opportunity to generate a unique climatology of horizontal winds near the mesopause at a number of high latitude locations, via the Doppler shifted echoes from sources of ionisation in the D-region. Ablating meteor trails form the bulk of these targets, but other phenomena also contribute to the observations. Due to the poor vertical resolution of the radars, care must be taken to reduce possible biases from sporadic-E layers and Polar Mesospheric Summer echoes that can affect the effective altitude of the geophysical parameters being observed. Second, there is strong theoretical and observational evidence to suggest that the radars are picking up echoes from the backward looking direction that will tend to reduce the measured wind strengths. The effect is strongly frequency dependent, resulting in a 20% reduction at 12 MHz and a 50% reduction at 10 MHz. A comparison of the climatologies observed by the Super-DARN Finland radar between September 1999 and September 2000 and that obtained from the adjacent VHF meteor radar located at Kiruna is also presented. The agreement between the two instruments was very good. Extending the analysis to the SuperDARN Iceland East radar indicated that the principles outlined above could be applied successfully to the rest of the SuperDARN network.Key words. Ionosphere (ionosphere-atmosphere interactions; instruments and techniques) – Meteorology and atmospheric dynamics (waves and tides)

Discussion of the Oblique Rotator Model Cases Of 108 Aqr and x Serp.

1976 ◽  
Vol 32 ◽  
pp. 577-588
Author(s):  
C. Mégessier ◽  
V. Khokhlova ◽  
T. Ryabchikova
Keyword(s):  
Mathematical Formulation ◽  
The Other ◽  
Rotator Model ◽  
Oblique Rotator ◽  
First Results

My talk will be on the oblique rotator model which was first proposed by Stibbs (1950), and since received success and further developments. I shall present two different attempts at describing a star according to this model and the first results obtained in the framework of a Russian-French collaboration in order to test the precision of the two methods. The aim is to give the best possible representation of the element distributions on the Ap stellar surfaces. The first method is the mathematical formulation proposed by Deutsch (1958-1970) and applied by Deutsch (1958) to HD 125248, by Pyper (1969) to α2CVn and by Mégessier (1975) to 108 Aqr. The other one was proposed by Khokhlova (1974) and used by her group.

Meridional Circulation, Turbulence, and Diffusion Processes in Stars

1976 ◽  
Vol 32 ◽  
pp. 109-116 ◽  
Author(s):  
S. Vauclair
Keyword(s):  
Convection Zone ◽  
Diffusion Processes ◽  
Meridional Circulation ◽  
Diffusion Time ◽  
Work In Progress ◽  
First Results ◽  
Stellar Envelopes ◽  
And Diffusion ◽  
Turbulence And Diffusion ◽  
Hr Diagram

This paper gives the first results of a work in progress, in collaboration with G. Michaud and G. Vauclair. It is a first attempt to compute the effects of meridional circulation and turbulence on diffusion processes in stellar envelopes. Computations have been made for a 2 Mʘstar, which lies in the Am - δ Scuti region of the HR diagram.Let us recall that in Am stars diffusion cannot occur between the two outer convection zones, contrary to what was assumed by Watson (1970, 1971) and Smith (1971), since they are linked by overshooting (Latour, 1972; Toomre et al., 1975). But diffusion may occur at the bottom of the second convection zone. According to Vauclair et al. (1974), the second convection zone, due to He II ionization, disappears after a time equal to the helium diffusion time, and then diffusion may happen at the bottom of the first convection zone, so that the arguments by Watson and Smith are preserved.

Investigation of cluster layers of small netal particles by TEM, SEM, EELS and by photoacoustic spectroscopy

1990 ◽  
Vol 48 (4) ◽  
pp. 250-251
Author(s):  
H. Seiler ◽  
U. Haas ◽  
K.H. Körtje
Keyword(s):  
Bulk Material ◽  
High Vacuum ◽  
Optical Methods ◽  
Metal Particles ◽  
Silver Particles ◽  
Low Loss ◽  
Plasmon Excitation ◽  
First Results ◽  
Diffraction Patterns ◽  
Small Metal Particles

The physical properties of small metal particles reveal an intermediate position between atomic and bulk material. Especially Ag has shown pronounced size effects. We compared silver layers evaporated in high vacuum with cluster layers of small silver particles, evaporated in N2 at a pressure of about 102 Pa. The investigations were performed by electron optical methods (TEM, SEM, EELS) and by Photoacoustic (PA) Spectroscopy (gas-microphone detection).The observation of cluster layers with TEM and high resolution SEM show small silver particles with diameters of about 50 nm (Fig. 1 and Figure 2, respectively). The electron diffraction patterns of homogeneous Ag layers and of cluster layers are similar, whereas the low loss EELS spectra due to plasmon excitation are quite different. Fig. 3 and Figure 4 show first results of EELS spectra of a cluster layer of small silver particles on carbon foil and of a homogeneous Ag layer, respectively.

Towards 1-Ångstrom-resolution STEM

1993 ◽  
Vol 51 ◽  
pp. 996-997
Author(s):  
H.S. von Harrach ◽  
D.E. Jesson ◽  
S.J. Pennycook
Keyword(s):  
High Resolution ◽  
Field Emission ◽  
Phase Contrast ◽  
Spherical Aberration ◽  
A Priori ◽  
Dark Field ◽  
Image Resolution ◽  
Objective Lens ◽  
Annular Dark Field ◽  
First Results

Phase contrast TEM has been the leading technique for high resolution imaging of materials for many years, whilst STEM has been the principal method for high-resolution microanalysis. However, it was demonstrated many years ago that low angle dark-field STEM imaging is a priori capable of almost 50% higher point resolution than coherent bright-field imaging (i.e. phase contrast TEM or STEM). This advantage was not exploited until Pennycook developed the high-angle annular dark-field (ADF) technique which can provide an incoherent image showing both high image resolution and atomic number contrast.This paper describes the design and first results of a 300kV field-emission STEM (VG Microscopes HB603U) which has improved ADF STEM image resolution towards the 1 angstrom target. The instrument uses a cold field-emission gun, generating a 300 kV beam of up to 1 μA from an 11-stage accelerator. The beam is focussed on to the specimen by two condensers and a condenser-objective lens with a spherical aberration coefficient of 1.0 mm.

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