scholarly journals Light ring grounded

Nature ◽  
1988 ◽  
Vol 331 (6153) ◽  
pp. 204-204
Author(s):  
PAUL MURDIN
Keyword(s):  
Light Ring

Relationship of Temperature and Light Ring Formation at Subarctic Treeline and Implications for Climate Reconstruction

1993 ◽  
Vol 39 (2) ◽  
pp. 256-262 ◽  
Author(s):  
David K. Yamaguchi ◽  
Louise Filion ◽  
Melissa Savage
Keyword(s):  
Black Spruce ◽  
Threshold Temperature ◽  
Climate Data ◽  
New Approach ◽  
The Past ◽  
Summer Temperatures ◽  
Instrumental Records ◽  
Relationship Of ◽  
Visual Assessments ◽  
Light Ring

AbstractDuring the past 8 centuries, light rings (LRs) have occasionally formed in black spruce (Picea mariana) at treeline near Bush Lake, northern Quebec (L. Filion, S. Payette, L. Gauthier, and Y. Boutin, 1986, Quaternary Research 26, 272-279; A. Delwaide, L. Filion, and S. Fayette, 1991, Canadian Journal of Forest Research 21, 1828-1832). New analyses of climate data compiled during the period of overlapping tree-ring and instrumental records show that years of LR formation at Bush Lake have unusually cool May, June, August, and September temperatures. The analyses also show that August-September temperatures strongly correlate with May-July temperatures. Thus, late spring and entire growing-season temperatures influence LR formation at subarctic treeline. LRs formed in at least 5% of the trees at Bush Lake when May-September mean temperatures at Inukjuak fell below 4.2°C and August-September mean temperatures fell below 6.7°C. These threshold temperature/LR relationships can be used to infer limiting summer temperatures during the period preceding instrumental records. For example, the LR record suggests that May-September temperatures at northern Quebec treeline dropped below 4.2°C in A.D. 1601 after a major volcanic eruption of unknown source. Visual assessments of LR occurrence provide a new approach for extracting quantitative paleoclimatic information from tree rings.

scholarly journals Cloud detection and classification based on MAX-DOAS observations

2013 ◽  
Vol 6 (6) ◽  
pp. 10297-10360 ◽  
Author(s):  
T. Wagner ◽  
S. Beirle ◽  
S. Dörner ◽  
U. Friess ◽  
J. Remmers ◽  
...  
Keyword(s):  
Classification Scheme ◽  
Scattered Light ◽  
Trace Gases ◽  
Colour Index ◽  
Optical Absorption Spectroscopy ◽  
Cloud Detection ◽  
Clear Sky ◽  
Cloud Classification ◽  
Good Agreement ◽  
Light Ring

Abstract. Multi-AXis-Differential Optical Absorption Spectroscopy (MAX-DOAS) observations of aerosols and trace gases can be strongly influenced by clouds. Thus it is important to identify clouds and characterise their properties. In this study we investigate the effects of clouds on several quantities which can be derived from MAX-DOAS observations, like the radiance, the colour index (radiance ratio at two selected wavelengths), the absorption of the oxygen dimer O4 and the fraction of inelastically scattered light (Ring effect). To identify clouds, these quantities can be either compared to their corresponding clear sky reference values, or their dependencies on time or viewing direction can be analysed. From the investigation of the temporal variability the influence of clouds can be identified even for individual measurements. Based on our investigations we developed a cloud classification scheme, which can be applied in a flexible way to MAX-DOAS or zenith DOAS observations: in its simplest version, zenith observations of the colour index are used to identify the presence of clouds (or high aerosol load). In more sophisticated versions, also other quantities and viewing directions are considered, which allows sub-classifications like e.g. thin or thick clouds, or fog. We applied our cloud classification scheme to MAX-DOAS observations during the CINDI campaign in the Netherlands in Summer 2009 and found very good agreement with sky images taken from ground.

scholarly journals Upper bounds on the compactness at the innermost light ring of anisotropic horizonless spheres

2020 ◽  
Vol 80 (8) ◽  
Author(s):  
Yan Peng
Keyword(s):  
Energy Condition ◽  
Upper Bounds ◽  
Dominant Energy Condition ◽  
Anisotropic Spheres ◽  
Analytical Proof ◽  
Light Ring

Abstract In the background of isotropic horizonless spheres, Hod recently provided an analytical proof of a bound on the compactness at the innermost light ring with the dominant energy condition. In this work, we extend the discussion of isotropic spheres to anisotropic spheres. With the dominant energy and non-negative trace conditions, we prove that Hod’s bound also holds in the case of anisotropic horizonless spheres.

scholarly journals Threat to Astronomy by Space Art

1991 ◽  
Vol 112 ◽  
pp. 139-144 ◽  
Author(s):  
Paul Murdin
Keyword(s):  
Solid Angle ◽  
Night Sky ◽  
Space Art ◽  
Optical Astronomy ◽  
Light Ring

ABSTRACTThe Light Ring, proposed as a celebration of the centenary of the Eiffel Tower, and now withdrawn by its sponsors, demonstrated the feasibility to launch relatively inexpensive satellites which subtend an appreciable solid angle as seen from earth. Other satellites in the competition organized by the Eiffel Tower proposed configurations under the name of Space Art which could unacceptably increase the night sky background. Satellites of this nature, launched for noble but essentially frivolous motives, pose a threat to optical astronomy.

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