12 Solar radiation & structure

1997 ◽  
Vol 23 (1) ◽  
pp. 149-163
Keyword(s):  
High Resolution ◽  
Recent Work ◽  
Spatial Resolution ◽  
Mean Free Path ◽  
Solar Photosphere ◽  
Image Correction ◽  
Resolution Limit ◽  
Earth’S Atmosphere ◽  
Earth's Atmosphere ◽  
Solar Telescopes

Spatial structures in the solar photosphere are likely to be seen down to scales of the order of the photon mean free path, which is about 70 km in the lower photosphere. This scale corresponds to an angle of O.”1 at disk center. Structures associated with magnetic fields may be expected on even smaller scales. Existing solar telescopes typically have diameters of slightly less than one meter. Hence, even in the visible part of the spectrum, the scales of solar structures extend out to the diffraction limit of current solar telescopes. Therefore, the achievable spatial resolution is limited by turbulence in the Earth’s atmosphere (seeing). This has led to the development of various techniques to overcome this resolution limit and achieve diffraction-limited resolution. This report covers selected highlights and recent work done in the context of high-resolution techniques published in the period from July 1, 1993 to June 30, 1996. Due to the lack of space the report remains necessarily incomplete, and I apologize to all the authors of important contributions that are not cited here. This review does not cover space and balloon-borne instruments that try to achieve high spatial resolution by observing from above the Earth’s atmosphere. Recent work on ground-based high-resolution techniques has been collected in the proceedings of the 13thSacramento Peak Summer Workshop on Real Time and Post Facto Solar Image Correction (Radick 1993).

scholarly journals An Update on The Problem of Small Comets

1998 ◽  
Vol 11 (1) ◽  
pp. 237-238
Author(s):  
J.C. Brandt ◽  
M.F. A’Hearn
Keyword(s):  
Recent Work ◽  
Terrestrial Planets ◽  
Indirect Methods ◽  
Earth’S Atmosphere ◽  
Direct Observations ◽  
Icy Bodies ◽  
Earth's Atmosphere ◽  
Search Program ◽  
Volatile Materials

The evidence for a major population of small comets (SCs) is summarized in two steps. First, we briefly summarize our previous work. Second, we describe recent work that continues to find SCs. When new capabilities become available that can detect SCs, we expect to find them and this is occurring. At present, their detection is a haphazard process and we advocate a dedicated, optimized search program. We define SCs as those icy bodies (i.e., sublimating bodies) with radius less than 1000 meters. Often the existence of SCs is inferred from effects ascribed to them. These “effects” include: lunar cratering; cratering on Ganymede; excess interplanetary hydrogen; delivery of volatile materials to the terrestrial planets; and a source of fragile bodies entering the Earth’s atmosphere. While some of these indirect methods support the existence of SCs, direct observations are clearly preferred.

scholarly journals The second solar spectrum and the hidden magnetism

2008 ◽  
Vol 4 (S259) ◽  
pp. 211-222
Author(s):  
Jan O. Stenflo
Keyword(s):  
Magnetic Flux ◽  
Spatial Resolution ◽  
Zeeman Effect ◽  
Solar Spectrum ◽  
Coherent Scattering ◽  
Small Scale ◽  
Solar Photosphere ◽  
Resolution Limit ◽  
New Paradigm ◽  
Hanle Effect

AbstractApplications of the Hanle effect have revealed the existence of vast amounts of “hidden“ magnetic flux in the solar photosphere, which remains invisible to the Zeeman effect due to cancellations inside each spatial resolution element of the opposite-polarity contributions from this small-scale, tangled field. The Hanle effect is a coherency phenomenon that represents the magnetic modification of the linearly polarized spectrum of the Sun that is formed by coherent scattering processes. This so-called “Second Solar Spectrum” is as richly structured as the ordinary intensity spectrum, but the spectral structures look completely different and have different physical origins. One of the new diagnostic uses of this novel spectrum is to explore the magnetic field in previously inaccessible parameter domains. The earlier view that most of the magnetic flux in the photosphere is in the form of intermittent kG flux tubes with tiny filling factors has thereby been shattered. The whole photospheric volume instead appears to be seething with intermediately strong fields, of order 100G, of significance for the overall energy balance of the solar atmosphere. According to the new paradigm the field behaves like a fractal with a high degree of self-similarity between the different scales. The magnetic structuring is expected to continue down to the 10m scale, 4 orders of magnitude below the current spatial resolution limit.

scholarly journals High-resolution transmission spectrum of the Earth's atmosphere-seeing Earth as an exoplanet using a lunar eclipse

2014 ◽  
Vol 14 (2) ◽  
pp. 255-266 ◽  
Author(s):  
F. Yan ◽  
R. A. E. Fosbury ◽  
M. G. Petr-Gotzens ◽  
G. Zhao ◽  
W. Wang ◽  
...  
Keyword(s):  
High Resolution ◽  
Water Vapour ◽  
Transmission Spectrum ◽  
Atmospheric Model ◽  
High Signal ◽  
Absorption Feature ◽  
Lunar Eclipse ◽  
Atmospheric Transmission ◽  
Earth’S Atmosphere ◽  
Earth's Atmosphere

AbstractWith the rapid developments in the exoplanet field, more and more terrestrial exoplanets are being detected. Characterizing their atmospheres using transit observations will become a key datum in the quest for detecting an Earth-like exoplanet. The atmospheric transmission spectrum of our Earth will be an ideal template for comparison with future exo-Earth candidates. By observing a lunar eclipse, which offers a similar configuration to that of an exoplanet transit, we have obtained a high-resolution and high signal-to-noise ratio (SNR) transmission spectrum of the Earth's atmosphere. This observation was performed with the High Resolution Spectrograph at Xinglong Station, China during the total lunar eclipse in December 2011. We compare the observed transmission spectrum with our atmospheric model, and determine the characteristics of the various atmospheric species in detail. In the transmission spectrum, O2, O3, O2 · O2, NO2 and H2O are detected, and their column densities are measured and compared with the satellites data. The visible Chappuis band of ozone produces the most prominent absorption feature, which suggests that ozone is a promising molecule for the future exo-Earth characterization. Due to the high resolution and high SNR of our spectrum, several novel details of the Earth atmosphere's transmission spectrum are presented. The individual O2 lines are resolved and O2 isotopes are clearly detected. Our new observations do not confirm the absorption features of Ca II or Na I which have been reported in previous lunar eclipse observations. However, features in these and some other strong Fraunhofer line positions do occur in the observed spectrum. We propose that these are due to a Raman-scattered component in the forward-scattered sunlight appearing in the lunar umbral spectrum. Water vapour absorption is found to be rather weak in our spectrum because the atmosphere we probed is relatively dry, which prompts us to discuss the detectability of water vapour in Earth-like exoplanet atmospheres.

High resolution infrared spectra of the earth's atmosphere III—airborne observations in the 100–140 cm−1 range

1977 ◽  
Vol 17 (4) ◽  
pp. 283-291 ◽  
Author(s):  
J.P. Baluteau ◽  
A. Marten ◽  
E. Bussoletti ◽  
M. Anderegg ◽  
J.E. Beckman ◽  
...  
Keyword(s):  
High Resolution ◽  
Infrared Spectra ◽  
Earth’S Atmosphere ◽  
Earth's Atmosphere

scholarly journals Towards attosecond imaging at the nanoscale using broadband holography-assisted coherent imaging in the extreme ultraviolet

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Wilhelm Eschen ◽  
Sici Wang ◽  
Chang Liu ◽  
Robert Klas ◽  
Michael Steinert ◽  
...  
Keyword(s):  
High Resolution ◽  
Spatial Resolution ◽  
Extreme Ultraviolet ◽  
High Harmonic ◽  
Ultrafast Dynamics ◽  
Single Shot ◽  
Spectral Bandwidth ◽  
Resolution Limit ◽  
Coherent Imaging ◽  
Large Bandwidth

AbstractNanoscale coherent imaging has emerged as an indispensable modality, allowing to surpass the resolution limit given by classical imaging optics. At the same time, attosecond science has experienced enormous progress and has revealed the ultrafast dynamics in complex materials. Combining attosecond temporal resolution of pump-probe experiments with nanometer spatial resolution would allow studying ultrafast dynamics on the smallest spatio-temporal scales but has not been demonstrated yet. To date, the large bandwidth of attosecond pulses poses a major challenge to high-resolution coherent imaging. Here, we present broadband holography-enhanced coherent imaging, which enables the combination of high-resolution coherent imaging with a large spectral bandwidth. By implementing our method at a high harmonic source, we demonstrate a spatial resolution of 34 nm in combination with a spectral bandwidth of 5.5 eV at a central photon energy of 92 eV. The method is single-shot capable and retrieves the spectrum from the measured diffraction pattern.

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