Global Radiation Emerging from a Rayleigh-Scattering Atmoshpere of Large Optical Thickness

1968 ◽  
Vol 151 ◽  
pp. 637 ◽  
Author(s):  
Anne B. Kahle
Keyword(s):  
Optical Thickness ◽  
Rayleigh Scattering ◽  
Global Radiation ◽  
Large Optical Thickness

Reflection and transmission of light by a layer with a large optical thickness

1979 ◽  
Vol 30 (5) ◽  
pp. 646-653
Author(s):  
�. P. Zege ◽  
O. V. Bushmakova ◽  
I. L. Katsev ◽  
N. V. Konovalov
Keyword(s):  
Optical Thickness ◽  
Reflection And Transmission ◽  
Large Optical Thickness

scholarly journals Active Regions at Millimeter Wavelengths and the Measurement of Magnetic Fields

1971 ◽  
Vol 43 ◽  
pp. 642-651 ◽  
Author(s):  
M. R. Kundu
Keyword(s):  
Magnetic Fields ◽  
Electron Density ◽  
Optical Thickness ◽  
Background Radiation ◽  
Active Regions ◽  
Brightness Temperatures ◽  
Millimeter Wavelengths ◽  
Solar Active Regions ◽  
Large Optical Thickness ◽  
Filamentary Material

Some properties of solar active regions at 9 and 3.5 mm wavelengths are discussed. The regions have excess brightness temperatures of up to 1000 and 700K at 9 and 3.5 mm wavelengths respectively. The background radiation at 3.5 mm is often seen to be ‘absorbed’ in regions closely coincident with Hα dark filaments on the disk. Interpretation of this ‘absorption’ as due to the large optical thickness of the overlying filamentary material leads to an estimate of electron density in the filaments. The active regions at millimeter wavelengths show almost one-to-one correspondence with the Ca-plage regions as well as with the regions of longitudinal magnetic fields on Mt. Wilson magnetograms. A comparison of the mm-λ maps with the magnetograms ‘smoothed’ with the beams of mm observations shows this correspondence in a striking manner. This relationship suggests the possibility of measuring chromospheric magnetic fields from the measurement of polarization at millimeter wavelengths.

scholarly journals Contrails of Small and Very Large Optical Depth

2010 ◽  
Vol 67 (9) ◽  
pp. 3065-3073 ◽  
Author(s):  
David Atlas ◽  
Zhien Wang
Keyword(s):  
High Resolution ◽  
Optical Depth ◽  
Optical Thickness ◽  
Extinction Coefficient ◽  
Ice Water Content ◽  
Lower Height ◽  
Equivalent Distance ◽  
Ice Water ◽  
Large Optical Thickness ◽  
Clear Atmosphere

Abstract This work deals with two kinds of contrails. The first comprises a large number of optically thin contrails near the tropopause. They are mapped geographically using a lidar to obtain their height and a camera to obtain azimuth and elevation. These high-resolution maps provide the local contrail geometry and the amount of optically clear atmosphere. The second kind is a single trail of unprecedentedly large optical thickness that occurs at a lower height. The latter was observed fortuitously when an aircraft moving along the wind direction passed over the lidar, thus providing measurements for more than 3 h and an equivalent distance of 620 km. It was also observed by Geostationary Operational Environmental Satellite (GOES) sensors. The lidar measured an optical depth of 2.3. The corresponding extinction coefficient of 0.023 km−1 and ice water content of 0.063 g m−3 are close to the maximum values found for midlatitude cirrus. The associated large radar reflectivity compares to that measured by ultrasensitive radar, thus providing support for the reality of the large optical depth.

scholarly journals On the Detection of Binary Be Stars

1976 ◽  
Vol 70 ◽  
pp. 401-415 ◽  
Author(s):  
R. S. Polidan
Keyword(s):  
Low Temperature ◽  
Optical Thickness ◽  
Spectroscopic Investigation ◽  
Promising Method ◽  
Be Stars ◽  
Binary Nature ◽  
Photometric Observations ◽  
Be Star ◽  
Large Optical Thickness

Possible methods for detecting the presence of a cool companion to a Be star are discussed. Photometric observations are shown to be incapable of detecting companions in all but the most extreme cases. Spectroscopic investigation is also unlikely to yield many new discoveries. It, however, remains the most promising method for the detection of binary Be stars. The four known binary Be stars are also discussed.Infrared calcium triplet emission in Be stars is discussed in detail. The lines are shown to originate in a region of large optical thickness and low temperature (T ~ 5000 K). The possible connection between the presence of calcium triplet emission and binary nature is briefly discussed.

scholarly journals Hourly resolved cloud modification factors in the ultraviolet

2008 ◽  
Vol 8 (1) ◽  
pp. 181-214 ◽  
Author(s):  
H. Staiger ◽  
P. N. den Outer ◽  
A. F. Bais ◽  
U. Feister ◽  
B. Johnsen ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Uv Radiation ◽  
Rayleigh Scattering ◽  
Weather Prediction ◽  
Global Radiation ◽  
Action Spectrum ◽  
Solar Irradiation ◽  
Solar Disc ◽  
Global Irradiance ◽  
The Cost

Abstract. Cloud impacts on the transfer of Ultraviolet (UV) radiation through the atmosphere can be assessed using a cloud modification factor (CMF). The total global solar irradiation has proven to be a solid basis to derive CMF's for the UV radiation (UV_CMF). Total global irradiance is frequently measured and forecasted by numerical weather prediction systems. Its advantage compared to for instance cloud cover is that measured solar global irradiance contains already the effect of multiple reflection between cloud layers, reflection between the sides of the clouds, as well as the distinct difference whether the solar disc is obscured by clouds or not. In the UV range clouds decrease the irradiance to a lesser extent than in the visible and infrared spectral range; Rayleigh scattering in the atmosphere yields a larger fraction of scatter radiation compared to that of light and infrared, hence, obscuring the solar disc will not totally block out the irradiation. Thus the relationship between CMF's for solar radiation and for UV-radiation is not straight forwards, but will depend on e.g. the solar zenith angle (SZA) and wavelength band or action spectrum in the UV considered. Den Outer et al. (2005) provide a UV_CMF algorithm on a daily base accounting for these influences. It requires as input a daily CMF in total global radiation (SOL_CMF) and the SZA at noon. The calculation of SOL-CMF uses the clear sky algorithm of the European Solar Radiation Atlas to account for varying turbidity impacts. The algorithm's capability to derive hourly UV_CMF's based on the SZA at the corresponding hour and its worldwide applicability is validated using hourly resolved observational data retrieved from the databases of the COST-Action 726 on "Long term changes and climatology of UV radiation over Europe" and the USDA UV-B Monitoring and Research Program. The model performance for hourly resolution is shown to be comparable in absolute and relative deviations from a measured mean smoothed dependent on SZA with the well performing daily models of the COST-726 model intercomparison (Koepke et al., 2006).

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