scholarly journals Analysis of lightning outliers in the EUCLID network

2017 ◽  
Vol 10 (11) ◽  
pp. 4561-4572 ◽  
Author(s):  
Dieter R. Poelman ◽  
Wolfgang Schulz ◽  
Rudolf Kaltenboeck ◽  
Laurent Delobbe
Keyword(s):  
Lightning Discharge ◽  
Major Axis ◽  
Radar Data ◽  
Spatial Behavior ◽  
Semi Major Axis ◽  
Total Percentage ◽  
Lightning Detection ◽  
Current Events ◽  
Location Algorithm ◽  
Wrong Place

Abstract. Lightning data as observed by the European Cooperation for Lightning Detection (EUCLID) network are used in combination with radar data to retrieve the temporal and spatial behavior of lightning outliers, i.e., discharges located in a wrong place, over a 5-year period from 2011 to 2016. Cloud-to-ground (CG) stroke and intracloud (IC) pulse data are superimposed on corresponding 5 min radar precipitation fields in two topographically different areas, Belgium and Austria, in order to extract lightning outliers based on the distance between each lightning event and the nearest precipitation. It is shown that the percentage of outliers is sensitive to changes in the network and to the location algorithm itself. The total percentage of outliers for both regions varies over the years between 0.8 and 1.7 % for a distance to the nearest precipitation of 2 km, with an average of approximately 1.2 % in Belgium and Austria. Outside the European summer thunderstorm season, the percentage of outliers tends to increase somewhat. The majority of all the outliers are low peak current events with absolute values falling between 0 and 10 kA. More specifically, positive cloud-to-ground strokes are more likely to be classified as outliers compared to all other types of discharges. Furthermore, it turns out that the number of sensors participating in locating a lightning discharge is different for outliers versus correctly located events, with outliers having the lowest amount of sensors participating. In addition, it is shown that in most cases the semi-major axis (SMA) assigned to a lightning discharge as a confidence indicator in the location accuracy (LA) is smaller for correctly located events compared to the semi-major axis of outliers.

scholarly journals Analysis of lightning outliers in the EUCLID network

2017 ◽  
Author(s):  
Dieter R. Poelman ◽  
Wolfgang Schulz ◽  
Rudolf Kaltenboeck ◽  
Laurent Delobbe
Keyword(s):  
Lightning Discharge ◽  
Major Axis ◽  
Radar Data ◽  
Semi Major Axis ◽  
Total Percentage ◽  
Lightning Detection ◽  
Current Events ◽  
Location Algorithm ◽  
Temporal And Spatial ◽  
Wrong Place

Abstract. Lightning data as observed by the European Cooperation for Lightning Detection network EUCLID are used in combination with radar data to retrieve the temporal and spatial behaviour of lightning outliers, i.e. discharges located on a wrong place, over a 5-year period from 2011 to 2016. Cloud-to-ground stroke and intracloud pulse data are superimposed on corresponding 5-min radar precipitation fields in two topographically different areas, being Belgium and Austria, in order to extract lightning outliers based on the distance between each lightning event and the nearest precipitation. It is shown that the percentage of outliers is sensitive to changes in the network and to the location algorithm itself. The total percentage of outliers for both regions varies over the years between 0.8 % and 1.7 % for a distance to the nearest precipitation of 2 km, with an average of approximately 1.2 % in Belgium and Austria. Outside the European summer thunderstorm season the percentage of outliers tends to increase somewhat and could result from the fact that more sensor upgrades occur during winter or that precipitation of winter thunderstorms is underestimated compared to the vertically extended summer storms. The majority of all the outliers are low peak current events with absolute values falling between 0 to 10 kA. More specifically, positive cloud-to-ground strokes are more likely to be classified as outliers compared to all other type of discharges. Furthermore, it turns out that the number of sensors participating in locating a lightning discharge is different for outliers versus correctly located events, with outliers having the least amount of sensors participating. In addition, it is shown that in most cases the semi-major axis assigned to a lightning discharge as a confidence indicator in the location accuracy is smaller for correctly located events compared to the semi-major axis of outliers.

scholarly journals A performance analysis of the North American Lightning Detection Network using CN Tower lightning data

2021 ◽  
Author(s):  
Alexandru Lafkovici
Keyword(s):  
North American ◽  
Detection Efficiency ◽  
Lightning Discharge ◽  
Location Error ◽  
Error Ellipse ◽  
Semi Major Axis ◽  
North East ◽  
The North ◽  
Lightning Detection ◽  
Triggered Lightning

The North American Lightning Detection Network (NALDN) is a commercial lightning detection network operated by Vaisala Inc., and is composed of the U.S. National Lightning Detection Network (NLDN) and the Environment Canada owned Canadian Lightning Detection Network (CLDN). The CN Tower is one of the best sites in the world to observe the lightning phenomenon and provides an excellent opportunity to evaluate the performance of the NALDN in the Toronto area. Using CN Tower lightning data acquired during 2005, the performance characteristics of the NALDN were thoroughly evaluated, including the flash detection efficiency (DE), stroke DE, absolute location error, peak current estimation and location accuracy model (50%, 90% and 99% error ellipses) error. Although a similar test was performed using rocket-triggered lightning in Florida at Camp Blanding, this test evaluated a completely different region of the NALDN. Moreover, rocket-triggered lightning artificially initiates a lightning discharge, whereas lightning events to the CN Tower occur naturally and are similar to discharges that occur to tall structures or objects at high altitude or mountainous areas. Excluding two flashes understood to be composed of M-components, the NALDN detected 7 out of 7 flashes recorded at the CN Tower, resulting in a 100% flash DE. Furthermore, the NALDN detected 22 out of 39 strokes recorded at the CN Tower, resulting in a stroke DE of 56%. Relative to the CN Tower, the NALDN was found to have a median absolute location error of 0.356 km and a mean error of 0.390 km for the 22 strokes it detected. It was also demonstrated that the NALDN stroke location error seems to have a large bias towards the north of the CN Tower and a slight bias towards the east, with 19 of the 22 strokes predicted north-east of the CN Tower. The 50%, 90% and 99% error ellipses provided by the NALDN were also evaluated. It was found that 73% (16 out of the 22) detected strokes were enclosed by the 50% error ellipse, 91% (20 out of the 22) detected strokes were enclosed by the 90% error ellipse and 95% (21 out of the 22) detected strokes were enclosed by the 99% error ellipse. The minimum value for the 50% error ellipse axes is set at 0.4 km by Vaisala, and 21 out of the 22 detected strokes had a semi-major axis length of 0.4 km, suggesting that the median location error for CN Tower strokes is 0.4 or less. The 0.356 km median location error obtained for the 22 detected strokes appears to support this.

DETERMINATION OF THE ELEMENTS OF METEOR PATHS FROM RADAR OBSERVATIONS

1949 ◽  
Vol 27a (3) ◽  
pp. 53-67 ◽  
Author(s):  
D. W. R. McKinley ◽  
Peter M. Millman
Keyword(s):  
Sea Level ◽  
Path Length ◽  
Major Axis ◽  
Radar Data ◽  
Semi Major Axis ◽  
Radar Observations ◽  
Short Period ◽  
Single Station

Methods of determining meteor velocities from single-station observations are discussed. Where three-station observations are available both the velocity and the elements of the meteor's path through the atmosphere can be computed in favorable cases. These methods are applied to a selected daytime meteor, recorded by the three radar stations at 17h 59m 48s E.S.T., Aug. 4, 1948. The following elements of the meteor's path have been obtained from the radar data:—Apparent geocentric velocity    35.0 ± 0.4 km. per sec.True bearing of apparent radiant    074° ± 2°Elevation of apparent radiant    2° ± 2°Total radar path length    270 km.Height above sea level    108 − 104 km.These values lead to an orbit similar to one of the short-period comets, with these elements:—Semi-major axis    a    2.66Eccentricity    e    0.87Angle node to perihelion    ω    294°.9Longitude of node        132°.4Inclination    i    33°.6Period    P    4.33 years

scholarly journals A performance analysis of the North American Lightning Detection Network using CN Tower lightning data

2021 ◽  
Author(s):  
Alexandru Lafkovici
Keyword(s):  
North American ◽  
Detection Efficiency ◽  
Lightning Discharge ◽  
Location Error ◽  
Error Ellipse ◽  
Semi Major Axis ◽  
North East ◽  
The North ◽  
Lightning Detection ◽  
Triggered Lightning

The North American Lightning Detection Network (NALDN) is a commercial lightning detection network operated by Vaisala Inc., and is composed of the U.S. National Lightning Detection Network (NLDN) and the Environment Canada owned Canadian Lightning Detection Network (CLDN). The CN Tower is one of the best sites in the world to observe the lightning phenomenon and provides an excellent opportunity to evaluate the performance of the NALDN in the Toronto area. Using CN Tower lightning data acquired during 2005, the performance characteristics of the NALDN were thoroughly evaluated, including the flash detection efficiency (DE), stroke DE, absolute location error, peak current estimation and location accuracy model (50%, 90% and 99% error ellipses) error. Although a similar test was performed using rocket-triggered lightning in Florida at Camp Blanding, this test evaluated a completely different region of the NALDN. Moreover, rocket-triggered lightning artificially initiates a lightning discharge, whereas lightning events to the CN Tower occur naturally and are similar to discharges that occur to tall structures or objects at high altitude or mountainous areas. Excluding two flashes understood to be composed of M-components, the NALDN detected 7 out of 7 flashes recorded at the CN Tower, resulting in a 100% flash DE. Furthermore, the NALDN detected 22 out of 39 strokes recorded at the CN Tower, resulting in a stroke DE of 56%. Relative to the CN Tower, the NALDN was found to have a median absolute location error of 0.356 km and a mean error of 0.390 km for the 22 strokes it detected. It was also demonstrated that the NALDN stroke location error seems to have a large bias towards the north of the CN Tower and a slight bias towards the east, with 19 of the 22 strokes predicted north-east of the CN Tower. The 50%, 90% and 99% error ellipses provided by the NALDN were also evaluated. It was found that 73% (16 out of the 22) detected strokes were enclosed by the 50% error ellipse, 91% (20 out of the 22) detected strokes were enclosed by the 90% error ellipse and 95% (21 out of the 22) detected strokes were enclosed by the 99% error ellipse. The minimum value for the 50% error ellipse axes is set at 0.4 km by Vaisala, and 21 out of the 22 detected strokes had a semi-major axis length of 0.4 km, suggesting that the median location error for CN Tower strokes is 0.4 or less. The 0.356 km median location error obtained for the 22 detected strokes appears to support this.

Detection and Characterization of earth-like Planets

1997 ◽  
Vol 161 ◽  
pp. 299-311 ◽  
Author(s):  
Jean Marie Mariotti ◽  
Alain Léger ◽  
Bertrand Mennesson ◽  
Marc Ollivier
Keyword(s):  
Direct Detection ◽  
Contrast Ratio ◽  
Angular Size ◽  
Physical Nature ◽  
Major Axis ◽  
Infrared Emission ◽  
Space Technology ◽  
Semi Major Axis ◽  
Earth Like Planets ◽  
Visible Wavelengths

AbstractIndirect methods of detection of exo-planets (by radial velocity, astrometry, occultations,...) have revealed recently the first cases of exo-planets, and will in the near future expand our knowledge of these systems. They will provide statistical informations on the dynamical parameters: semi-major axis, eccentricities, inclinations,... But the physical nature of these planets will remain mostly unknown. Only for the larger ones (exo-Jupiters), an estimate of the mass will be accessible. To characterize in more details Earth-like exo-planets, direct detection (i.e., direct observation of photons from the planet) is required. This is a much more challenging observational program. The exo-planets are extremely faint with respect to their star: the contrast ratio is about 10−10at visible wavelengths. Also the angular size of the apparent orbit is small, typically 0.1 second of arc. While the first point calls for observations in the infrared (where the contrast goes up to 10−7) and with a coronograph, the latter implies using an interferometer. Several space projects combining these techniques have been recently proposed. They aim at surveying a few hundreds of nearby single solar-like stars in search for Earth-like planets, and at performing a low resolution spectroscopic analysis of their infrared emission in order to reveal the presence in the atmosphere of the planet of CO H2O and O3. The latter is a good tracer of the presence of oxygen which could be, like on our Earth, released by biological activity. Although extremely ambitious, these projects could be realized using space technology either already available or in development for others missions. They could be built and launched during the first decades on the next century.

scholarly journals Some Special Types of Orbits around Jupiter

Aerospace ◽  
2021 ◽  
Vol 8 (7) ◽  
pp. 183
Author(s):  
Yongjie Liu ◽  
Yu Jiang ◽  
Hengnian Li ◽  
Hui Zhang
Keyword(s):  
Gravity Model ◽  
Small Perturbation ◽  
Equilibrium Points ◽  
Major Axis ◽  
Semi Major Axis ◽  
Ground Track ◽  
The Earth ◽  
Degenerate Equilibrium ◽  
The Mean ◽  
Element Theory

This paper intends to show some special types of orbits around Jupiter based on the mean element theory, including stationary orbits, sun-synchronous orbits, orbits at the critical inclination, and repeating ground track orbits. A gravity model concerning only the perturbations of J2 and J4 terms is used here. Compared with special orbits around the Earth, the orbit dynamics differ greatly: (1) There do not exist longitude drifts on stationary orbits due to non-spherical gravity since only J2 and J4 terms are taken into account in the gravity model. All points on stationary orbits are degenerate equilibrium points. Moreover, the satellite will oscillate in the radial and North-South directions after a sufficiently small perturbation of stationary orbits. (2) The inclinations of sun-synchronous orbits are always bigger than 90 degrees, but smaller than those for satellites around the Earth. (3) The critical inclinations are no-longer independent of the semi-major axis and eccentricity of the orbits. The results show that if the eccentricity is small, the critical inclinations will decrease as the altitudes of orbits increase; if the eccentricity is larger, the critical inclinations will increase as the altitudes of orbits increase. (4) The inclinations of repeating ground track orbits are monotonically increasing rapidly with respect to the altitudes of orbits.

scholarly journals Dynamical properties of the Molniya satellite constellation: long-term evolution of the semi-major axis

2021 ◽  
Author(s):  
Jérôme Daquin ◽  
Elisa Maria Alessi ◽  
Joseph O’Leary ◽  
Anne Lemaitre ◽  
Alberto Buzzoni
Keyword(s):  
Major Axis ◽  
Long Term Evolution ◽  
Semi Major Axis ◽  
Satellite Constellation ◽  
Term Evolution ◽  
Dynamical Properties

scholarly journals Creation/destruction of ultra-wide binaries in tidal streams

2020 ◽  
Author(s):  
Jorge Peñarrubia
Keyword(s):  
Globular Clusters ◽  
Galactic Halo ◽  
Local Density ◽  
Formation Rate ◽  
Semimajor Axis ◽  
Major Axis ◽  
Binding Energies ◽  
Semi Major Axis ◽  
The Mean ◽  
Tidal Streams

Abstract This paper uses statistical and N-body methods to explore a new mechanism to form binary stars with extremely large separations (≳ 0.1 pc), whose origin is poorly understood. Here, ultra-wide binaries arise via chance entrapment of unrelated stars in tidal streams of disrupting clusters. It is shown that (i) the formation of ultra-wide binaries is not limited to the lifetime of a cluster, but continues after the progenitor is fully disrupted, (ii) the formation rate is proportional to the local phase-space density of the tidal tails, (iii) the semimajor axis distribution scales as p(a)da ∼ a1/2da at a ≪ D, where D is the mean interstellar distance, and (vi) the eccentricity distribution is close to thermal, p(e)de = 2ede. Owing to their low binding energies, ultra-wide binaries can be disrupted by both the smooth tidal field and passing substructures. The time-scale on which tidal fluctuations dominate over the mean field is inversely proportional to the local density of compact substructures. Monte-Carlo experiments show that binaries subject to tidal evaporation follow p(a)da ∼ a−1da at a ≳ apeak, known as Öpik’s law, with a peak semi-major axis that contracts with time as apeak ∼ t−3/4. In contrast, a smooth Galactic potential introduces a sharp truncation at the tidal radius, p(a) ∼ 0 at a ≳ rt. The scaling relations of young clusters suggest that most ultra-wide binaries arise from the disruption of low-mass systems. Streams of globular clusters may be the birthplace of hundreds of ultra-wide binaries, making them ideal laboratories to probe clumpiness in the Galactic halo.

EFFECTS OF INITIAL INHOMOGENEOUS DENSITY DISTRIBUTION AND VOID SHAPE ON POWDER FORGING OF POROUS METAL

2013 ◽  
Vol 27 (19) ◽  
pp. 1341008
Author(s):  
TAIQING DENG ◽  
LIANXI HU ◽  
YU SUN ◽  
XIAOYA LIU
Keyword(s):  
Density Distribution ◽  
Initial Density ◽  
Porous Metal ◽  
Major Axis ◽  
Average Density ◽  
Semi Major Axis ◽  
Punch Force ◽  
Inhomogeneous Density ◽  
Void Shape ◽  
Initial Density Distribution

The deformation behavior during axisymmetric upsetting of sintered metals has been studied based on the finite-element method. The investigation on the effects of the initial density distribution, void shape and die friction on the density distribution and punch force during deformation have been conducted. It was found that under low-friction conditions, the initial density distribution affects the deformation geometry and the density distribution. However, the effect of the initial density distribution was found to be negligible under high-friction conditions. The initial density distribution did not affect the punch force or the average density, regardless of the friction conditions. When the force is perpendicular to semi-major axis of elliptical void, it is not only good for densification but also decrease the punch force in forging of porous metal.

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