scholarly journals The Atmospheric Limitation on the Precision of Ground-Based Astrometry

1995 ◽  
Vol 166 ◽  
pp. 371-371
Author(s):  
I.S. Guseva
Keyword(s):  
Spectral Analysis ◽  
Gravity Waves ◽  
Systematic Errors ◽  
Upper Atmosphere ◽  
Random Errors ◽  
Critical Problem ◽  
Pulkovo Observatory ◽  
Long Period ◽  
Wide Range ◽  
Period Variations

Anomalous refraction remains to be the most critical problem in the meridian astrometry measuring large angles on the sky. I study slow quasi-periodical variations of refraction caused by the processes in the middle and upper atmosphere, such as gravity waves, etc., which can not be detected and calibrated out by use of any on-ground meteorological measurements. For this study, very old observations at large zenith distances of 80 to 90 degrees made by V. Fuss at Pulkovo Observatory in 1867-1869 [1] were used. The Deeming's method [2] of spectral analysis of data was applied to examine the characteristic variations of refraction in a wide range of periods. Very powerful quasi-periodical processes with periods of 7-8, 11-14, 18-22, 36-44 minutes and with amplitudes of 0.3 to 0.5 arcsec in the zenith were found when short sets of observations (1-5 days) were considered. They increase random errors of astrometric observations with meridian circles, transit instruments, astrolabes, etc. The periods of very slow variations — 152, 122, 93, 82.5, 73, 61 and 50 days, – are close to the well known periods discovered in other astronomical phenomena, for instance, in solar activity and in Earth rotation. I note also, that some of the long-period variations of refraction may cause quasi-systematic errors in astrometric measurements and catalogues.

scholarly journals Random Errors of Tycho Astrometry

1995 ◽  
Vol 166 ◽  
pp. 376-376
Author(s):  
V.V. Makarov ◽  
E. Høg
Keyword(s):  
Experimental Data ◽  
Theoretical Model ◽  
Prior Information ◽  
A Priori ◽  
Systematic Errors ◽  
Random Errors ◽  
Likelihood Estimator ◽  
Major Drawback ◽  
Wide Range ◽  
Input Catalogue

The paper focuses on the problem of estimation of Tycho astrometry random errors, caused by photon noise. A theoretical model for the random errors was developed on the basis of the Maximum Likelihood estimator. The model provides a satisfactory agreement with experimental data in the wide range of star magnitudes from 4 to 10 for both vertical and inclined slit transits. It is confirmed theoretically, that for fainter stars, which constitute a half of the Tycho star sample, this model is not valid. Moreover, it is demonstrated that a reliable astrometry could hardly be achieved for these faint stars, were it not for a kind of Bayesian approach which is in fact implemented in the processing. This approach uses implicitly a priori astrometric information on positions of the stars. A major drawback of the method is that it introduces some bias in astrometry estimation, of presently unknown size. Nonetheless, no transfer of systematic errors from the input catalogue is expected, for the used prior information comes from Recognition, hence it is based purely on the satellite's own observations. – The inadequacy of the pure ML theory leads us to correct the model empirically, in order to provide reliable formal errors for the astrometric parameters in the final catalogue, for all Tycho magnitudes. In this way, a rms normalized residual is used for each star individually as a scale factor or correction to the formal covariances. Corrected in this way, formal errors are compared directly with external errors, calculated from absolute differences between the Tycho provisional parallaxes in a 30 months solution and the Hipparcos parallaxes of some 100 000 common stars. Analysis of a standard external error shows that the corrected formal errors are robust, and probably even overestimated.

On nearly-commensurable periods in the restricted problem of three bodies, with calculations of the long-period variations in the interior 2:1 case

1966 ◽  
Vol 25 ◽  
pp. 197-222 ◽  
Author(s):  
P. J. Message
Keyword(s):  
Periodic Solution ◽  
Periodic Solutions ◽  
Large Amplitude ◽  
Restricted Problem ◽  
Small Amplitude ◽  
Minor Planets ◽  
Long Period ◽  
Numerical Integrations ◽  
Period Variations ◽  
The Mean

An analytical discussion of that case of motion in the restricted problem, in which the mean motions of the infinitesimal, and smaller-massed, bodies about the larger one are nearly in the ratio of two small integers displays the existence of a series of periodic solutions which, for commensurabilities of the typep+ 1:p, includes solutions of Poincaré'sdeuxième sortewhen the commensurability is very close, and of thepremière sortewhen it is less close. A linear treatment of the long-period variations of the elements, valid for motions in which the elements remain close to a particular periodic solution of this type, shows the continuity of near-commensurable motion with other motion, and some of the properties of long-period librations of small amplitude.To extend the investigation to other types of motion near commensurability, numerical integrations of the equations for the long-period variations of the elements were carried out for the 2:1 interior case (of which the planet 108 “Hecuba” is an example) to survey those motions in which the eccentricity takes values less than 0·1. An investigation of the effect of the large amplitude perturbations near commensurability on a distribution of minor planets, which is originally uniform over mean motion, shows a “draining off” effect from the vicinity of exact commensurability of a magnitude large enough to account for the observed gap in the distribution at the 2:1 commensurability.

Statistics and parallaxes

1978 ◽  
Vol 48 ◽  
pp. 7-29
Author(s):  
T. E. Lutz
Keyword(s):  
Experimental Design ◽  
Statistical Methods ◽  
Review Paper ◽  
Systematic Errors ◽  
Past Experience ◽  
Random Errors ◽  
Trigonometric Parallaxes ◽  
Systematic And Random Errors

This review paper deals with the use of statistical methods to evaluate systematic and random errors associated with trigonometric parallaxes. First, systematic errors which arise when using trigonometric parallaxes to calibrate luminosity systems are discussed. Next, determination of the external errors of parallax measurement are reviewed. Observatory corrections are discussed. Schilt’s point, that as the causes of these systematic differences between observatories are not known the computed corrections can not be applied appropriately, is emphasized. However, modern parallax work is sufficiently accurate that it is necessary to determine observatory corrections if full use is to be made of the potential precision of the data. To this end, it is suggested that a prior experimental design is required. Past experience has shown that accidental overlap of observing programs will not suffice to determine observatory corrections which are meaningful.

On the Long-Period Variations in the F2Region of the Ionosphere

1938 ◽  
Vol 26 (11) ◽  
pp. 1340-1346 ◽  
Author(s):  
Keikitiro Tani ◽  
Y. Ito ◽  
H. Sinkawa
Keyword(s):  
Long Period ◽  
Period Variations

Investigation of acoustic gravity waves in the upper atmosphere by the artificial periodic inhomogeneities method at Nizhny Novgorod

1996 ◽  
Vol 39 (3) ◽  
pp. 224-228
Author(s):  
N. V. Bakhmet'eva ◽  
V. V. Belikovich ◽  
E. A. Benediktov ◽  
V. N. Bubukina ◽  
N. P. Goncharov ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Upper Atmosphere ◽  
Acoustic Gravity Waves ◽  
Periodic Inhomogeneities

scholarly journals Lidar observations of persistent gravity waves with periods of 3–10 h in the Antarctic middle and upper atmosphere at McMurdo (77.83°S, 166.67°E)

2016 ◽  
Vol 121 (2) ◽  
pp. 1483-1502 ◽  
Author(s):  
Cao Chen ◽  
Xinzhao Chu ◽  
Jian Zhao ◽  
Brendan R. Roberts ◽  
Zhibin Yu ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Upper Atmosphere ◽  
The Antarctic ◽  
Lidar Observations

scholarly journals Aircraft measurements of gravity waves in the upper troposphere and lower stratosphere during the START08 field experiment

2015 ◽  
Vol 15 (13) ◽  
pp. 7667-7684 ◽  
Author(s):  
Fuqing Zhang ◽  
Junhong Wei ◽  
Meng Zhang ◽  
K. P. Bowman ◽  
L. L. Pan ◽  
...  
Keyword(s):  
Power Law ◽  
Gravity Waves ◽  
Lower Stratosphere ◽  
Potential Temperature ◽  
Shear Instability ◽  
Aircraft Measurements ◽  
Upper Troposphere ◽  
Airborne Measurements ◽  
Wide Range

Abstract. This study analyzes in situ airborne measurements from the 2008 Stratosphere–Troposphere Analyses of Regional Transport (START08) experiment to characterize gravity waves in the extratropical upper troposphere and lower stratosphere (ExUTLS). The focus is on the second research flight (RF02), which took place on 21–22 April 2008. This was the first airborne mission dedicated to probing gravity waves associated with strong upper-tropospheric jet–front systems. Based on spectral and wavelet analyses of the in situ observations, along with a diagnosis of the polarization relationships, clear signals of mesoscale variations with wavelengths ~ 50–500 km are found in almost every segment of the 8 h flight, which took place mostly in the lower stratosphere. The aircraft sampled a wide range of background conditions including the region near the jet core, the jet exit and over the Rocky Mountains with clear evidence of vertically propagating gravity waves of along-track wavelength between 100 and 120 km. The power spectra of the horizontal velocity components and potential temperature for the scale approximately between ~ 8 and ~ 256 km display an approximate −5/3 power law in agreement with past studies on aircraft measurements, while the fluctuations roll over to a −3 power law for the scale approximately between ~ 0.5 and ~ 8 km (except when this part of the spectrum is activated, as recorded clearly by one of the flight segments). However, at least part of the high-frequency signals with sampled periods of ~ 20–~ 60 s and wavelengths of ~ 5–~ 15 km might be due to intrinsic observational errors in the aircraft measurements, even though the possibilities that these fluctuations may be due to other physical phenomena (e.g., nonlinear dynamics, shear instability and/or turbulence) cannot be completely ruled out.

Long-period variations in the magnetic field of small-scale solar structures

2016 ◽  
Vol 56 (8) ◽  
pp. 1052-1059 ◽  
Author(s):  
P. V. Strekalova ◽  
Yu. A. Nagovitsyn ◽  
A. Riehokainen ◽  
V. V. Smirnova
Keyword(s):  
Magnetic Field ◽  
Small Scale ◽  
Long Period ◽  
Period Variations ◽  
The Magnetic Field

Observation of gliding tremors from the Gulf of Guinea might help solve over 50 year old mystery

2021 ◽  
Author(s):  
Charlotte Bruland ◽  
Sarah Mader ◽  
Céline Hadziioannou
Keyword(s):  
Spectral Analysis ◽  
Volcanic Activity ◽  
Rayleigh Waves ◽  
Spectral Characteristics ◽  
Gulf Of Guinea ◽  
Seismic Amplitude ◽  
Long Period ◽  
Amplitude Spectra ◽  
Using Data ◽  
Over Time

<p>In the 1960's a peak in the seismic amplitude spectra around 26 s was discovered and detected on stations worldwide. The source was located in the Gulf of Guinea, with approximate coordinates (0,0), and was believed to be generated continuously. A source with similar spectral characteristics was discovered near the Vanuatu Islands, at nearly the antipodal location of the Gulf of Guinea source. Since it was located close to the volcanoes in Vanuatu, this source is commonly attributed to magmatic processes. The physical cause of the 26 s microseism, however, remains unclear.</p><p>We investigate the source location and evolution of the 26 s microseim using data from permanent broadband stations in Germany, France and Algeria and temporary arrays in Morocco, Cameroon and Botswana for spectral analysis and 3-C beamforming to get closer to resolving the source mechanism responsible for this enigmatic signal. We find that the signal modulates over time and is not always detectable, but occasionally it becomes so energetic it can be observed on stations worldwide. Such a burst can last for hours or days. The signal is visible on stations globally approximately 30 percent of the time. Our beamforming analysis confirms that the source is located in the Gulf of Guinea, as shown in previous studies, and that the location is temporally stable. Whenever the signal is detectable, both Love and Rayleigh waves are generated. We discover a spectral glide effect associated with the bursts, that so far has not been reported in the literature. </p><p>The spectral glides last for about two days and are observed on stations globally. Although at higher frequencies, very long period tremors and gliding tremors are also observed on volcanoes as Redoubt in Alaska and Arenal in Costa Rica, suggesting that the origin of the 26 s tremor is also volcanic. However, there is no reported volcanic activity in the area where the source appears to be located.</p><p> </p>

Etiology of Ventricular Septal Defects: An Epidemiologic Approach

PEDIATRICS ◽  
1985 ◽  
Vol 76 (5) ◽  
pp. 741-749
Author(s):  
Thomas B. Newman
Keyword(s):  
The United States ◽  
Incidence Rates ◽  
Identical Twins ◽  
Random Errors ◽  
Ventricular Septal Defects ◽  
Metabolic Disturbances ◽  
Cardiac Morphogenesis ◽  
Septal Defects ◽  
Wide Range ◽  
History Of

To investigate the recent 150% increase in the reported incidence of ventricular septal defects (VSDs) in the United States, the epidemiology of ventricular septal defects was examined. The apparent incidence of VSDs is highly dependent on case finding methods, and more complete diagnosis and reporting probably account for the increase in reported incidence. Variations in case ascertainment also account for the small differences in incidence in studies from different places. The several known risk factors for VSD, including a family history of congenital heart disease and exposure to certain drugs, infectious agents, and maternal metabolic disturbances, explain few cases. Incidence rates are similar in different races and seasons and are unrelated to maternal age, birth order, sex, and socioeconomic status. VSDs occur naturally in a wide range of mammals and in birds, which also have four-chambered hearts. Despite identical genes and similar prenatal environments, the concordance rate in identical twins is only about 10%. The consistency of incidence among individuals with widely differing genes and environments and the frequency of discordance in identical twins suggest that VSDs often occur as random errors in development, at a frequency largely determined by the complexity of normal cardiac morphogenesis. This hypothesis has two major implications: many VSDs are not preventable and parents need not feel responsible for VSDs in their children.

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