Enhanced spectral UV irradiance: a 1 year preliminary study     

J. M. Sabburg  A. V. Parisi  M. G. Kimlin   《Atmospheric Research》2003,66(4):261

The ultraviolet (UV) spectra on cloudy days were compared to those on cloud free days to determine which part of the UV spectrum has the greatest enhancement due to the cloud compared to both corresponding measured clear sky spectra as well as other enhanced spectra. In this preliminary study, cloud enhanced UV spectra selected for maximum UVA enhancement compared to a clear sky UV spectrum at similar solar zenith angle (SZA) and ozone values, showed that the ratio of the two sets of spectral irradiances was approximately wavelength independent (approximately 1.1) above the cut-off wavelength of approximately 306 nm. Similarly, above 306 nm the average ratio of the spectral irradiances of a maximum UVB enhanced UV spectrum compared to a clear sky spectrum was 1.2 with maximum values generally above this average between 316 and 344 nm and generally below 1.2 above the wavelength of 344 nm. The UVA and UVB enhanced spectra were separated into five SZA ranges and the irradiance at each wavelength averaged for each range and compared to clear sky spectra in each of the ranges. Above approximately 306 nm, the ratios are wavelength independent for all SZA. However, with the exception of the SZA range centred on 20°, there is an increasing dependency with shorter wavelengths below the 306 nm. Also there appears to be two distinct groupings of the average irradiance ratios, corresponding to the SZA range centred on 20°, 37° and 49° (ratio of 1.2) and 32° and 42° (ratio 1.0), the latter cases suggesting that on average there is no enhancement for these SZA, except for wavelengths less than 306 nm.  相似文献   

Solar-Blind Diamond Detectors for Lyra, the Solar VUV Radiometer on Board Proba II     

A. Benmoussa  J.-F. Hochedez  W. K. Schmutz  U. SchÜhle  M. NeslÁdek  Y. Stockman  U. Kroth  M. Richter  A. Theissen  Z. Remes  K. Haenen  V. Mortet  S. Koller  J. P. Halain  R. Petersen  M. Dominique  M. D’Olieslaeger 《Experimental Astronomy》2003,16(3):141-148

Fabrication, packaging and experimental results on the calibration of metal-semiconductor-metal (MSM) photodetectors made on diamond are reported. LYRA (Lyman- RAdiometer onboard PROBA-2) will use diamond detectors for the first time in space for a solar physics instrument. A set of measurement campaigns was designed to obtain the XUV-to-VIS responsivity of the devices and other characterizations. The measurements of responsivity in EUV and VUV spectral ranges (40–240 nm) have been carried out by the Physkalisch-Technische Bundesanstalt (PTB) in Germany at the electron storage ring BESSY II. The longer wavelength range from 210 to 1127 nm was measured with monochromatic light by using a Xe-lamp at IMO-IMOMEC. The diamond detectors exhibit a photoresponse which lie in the 35–65 mA/W range at 200 nm (corresponding to an external quantum efficiency of 20–40%) and indicate a visible rejection ratio (200–500 nm) higher than four orders of magnitude.  相似文献   

Near UV absorption spectra and photolysis products of difunctional organic nitrates: Possible importance as NO x reservoirs     

Ian Barnes  Karl H. Becker  Tong Zhu 《Journal of Atmospheric Chemistry》1993,17(4):353-373

Difunctional organic nitrates are important products of the atmospheric reaction of NO₃ radicals with unsaturated hydrocarbons about which relatively little is known. In a continuation of the investigation of the atmospheric chemistry of such compounds, the UV absorption spectra of the following organic dinitrates and keto nitrates have been quantitively measured in the gas phase at 298±2 K and atmospheric pressure: 1,2-propandiol dinitrate, CH₃CH(ONO₂)CH₂(ONO₂); 1,2-butandiol dinitrate, CH₃CH₂CH(ONO₂)CH₂(ONO₂); 2,3-butandiol dinitrate, CH₃CH(ONO₂)CH(ONO₂)CH₃;cis 1,4-dinitrooxy-2-butene, CH₂(ONO₂)CH=CHCH₂(ONO₂); 3,4-dinitrooxy-1-butene, CH₂(ONO₂CH(ONO₂)CH=CH₂; -nitrooxy acetone, CH₃COCH₂(ONO₂); 1-nitrooxy-2-butanone, CH₃CH₂COCH₂(ONO₂); 3-nitrooxy-2-butanone, CH₃CH(ONO₂)COCH₃.Although the UV spectra of the nitrates are all very similar in shape those of the keto nitrates are red-shifted compared to the dinitrates and in the spectral range of atmospheric interest (>290 nm) their absorption cross-sections are approximately a factor of 5 higher. The cross-sections of the dinitrates are a factor of 2 higher than those reported in the literature for the corresponding alkyl mononitrates.The UV absorption cross-sections of the difunctional nitrates were used in combination with solar actinic flux data to estimate photolysis frequencies and consequently atmospheric lifetimes for these compounds. The results indicate that for the saturated difunctional nitrates studied in this work photolysis will generally be somewhat some important than reaction with OH radicals as an atmospheric removal process. However, for unsaturated nitrates loss due to reaction with OH will dominate over photolysis as an atmospheric sink.Preliminary FT-IR analyses of the photolysis products of -nitrooxy acetone, 3-nitrooxy-2-butanone and 2,3-butandiol dinitrate using both mercury and fluorescent lamps indicate that NO₂ is released in the primary step. The further reactions of the radicals thus produced result in the formation of CO, aldehydes and PAN. The possible significance of the results for difunctional organic nitrate as reservoirs for reactive odd nitrogen NO _y in the atmosphere, especially during the night, is briefly discussed.  相似文献   

The Spectrum-UV Mission: an International Ultraviolet Observatory     

Enrico G. Tanzi  Alexander A. Boyarchuk  Michael Grewing  Nikolaj V. Steshenko 《Experimental Astronomy》1997,7(4):345-359

The Spectrum-UV Mission is an ultraviolet space observatory, scheduled to be launched at the break of the century into a 7-day, highly excentric orbit aboard a Spectrum Series platform. The Observatory is endowed with a 170-cm aperture telescope and a focal plane instrument complement for spectroscopy and imaging in the 912 to 3600 range. The results of an advanced feasibility study, being carried out in the four partecipating Countries (Germany, Italy, Russia and Ukraine) are presented.  相似文献   

The UV cameras on the High Energy Transient Experiment (HETE)     

Roland Vanderspek  Alia Atlas  Tye M. Brady  Geoffrey B. Crew  John P. Doty  Steven E. Kissel  George R. Ricker  Peter C. Tappan  Francois Martel  M. Tim Jones 《Astrophysics and Space Science》1995,231(1-2):479-482

The High Energy Transient Experiment (HETE), scheduled for launch this year, is a small satellite dedicated to multiwavelength observations of -ray and X-ray bursts. The HETE spacecraft will be equipped with gamma-ray detectors, X-ray detectors with a coded mask, and ultraviolet-sensitive CCD cameras. The UV cameras on HETE are wide-field imagers which will a) provide UV images of the regions in which -ray or X-ray bursts are detected, before, duringand after the burst, b) detect UV transients, whether associated with a high-energy transient or not, c) monitor the brightnesses of field stars for variability over a wide range of timescales, and d) serve as star trackers for HETE. In this poster, we describe the HETE UV instrumentation, control software, and data products.  相似文献   

Temperature-dependence of ultraviolet absorption cross-sections of alternative chlorofluoroethanes: 2. The 2-chloro-1,1,1,2-tetrafluoro ethane -HCFC-124     

Didier Gillotay  Baul C. Simon 《Journal of Atmospheric Chemistry》1991,13(3):289-299

The temperature-dependent ultraviolet absorption cross-sections of CF₃-CHFCI (HCFC-124) have been measured between 170 and 230 nm for temperatures ranging from 295 to 210 K, with uncertainties between 2 and 4%. These results are compared with other available sets of determinations. Temperature effects are discussed and the photodissociation coefficients, presented with their temperature dependence, are calculated. Implication of the temperature dependences on the stratospheric chemistry is also discussed. Parametrical formulae are proposed to compute absorption crosssection values for wavelengths and temperatures useful in modelling calculations.  相似文献   

On the use of UV spectrophotometry to assess dissolved organic carbon origin variations in the Upper Rhône River     

J. C. Rostan  B. Cellot 《Aquatic Sciences - Research Across Boundaries》1995,57(1):70-80

To detect temporal changes and the origin of the refractory dissolved organic matter in the Upper Rhône River, UV light absorbance (A) at 285 nm and quantitative dissolved organic carbon (DOC) measurements were carried out. Data from 63 visits to the main channel over a period of two years and from visits to different waterbodies in the alluvial plain before and after a flood are presented. There was a good correlation between A (0.019–0.160) and the DOC content (1.40–9.81 mg/L) for the waterbodies, but not for the river axis with lower A (0.013–0.044) and DOC content (1.13–2.20 mg/L). Due to this good correlation, the DOC content could be quantified for the waterbodies by absorbance measurements only. For the river water this indirect determination of the DOC content was not possible. However, the A/DOC ratio showed changes in the composition of DOC of river water and provided indications about the origin of the dissolved organic matter in the Upper Rhône River.  相似文献   

广州地区太阳分光辐射的某些变化特征   总被引：1，自引：0，他引：1       下载免费PDF全文

熊效振  王新宇  王庚辰  张绍坤  于汇滨  刘旭 《应用气象学报》1994,5(1):98-103

利用广州地区1985—1990年的太阳分光辐射的连续观测资料（观测角度为23°11′），研究了广州地区紫外辐射、可见光辐射（光合有效辐射）、近红外辐射的某些特征。结果指出，每年7—10月份各分光辐射及总辐射总量较大。月总辐射中可见光辐射占总辐射的百分比年平均为47.3%，相应的紫外辐射和近红外辐射分别占7.1%和45.6%。文中还分析了晴天条件下分光辐射的变化和1990年紫外辐射变化的某些特征，并分析和讨论了分光辐射与云量、日照时间等因子的相关。  相似文献   

Induction of thymine dimers by solar radiation in natural freshwater phytoplankton assemblages in Patagonia, Argentina     

Manfred Klisch  Rajeshwar P. Sinha  E. Walter Helbling  Donat-P. Häder 《Aquatic Sciences - Research Across Boundaries》2005,67(1):72-78

  相似文献   

The anomalous intensities of helium lines in the quiet solar transition region     

K. P. Macpherson  C. Jordan 《Monthly notices of the Royal Astronomical Society》1999,308(2):510-526

Previous studies using observations made at low spatial and spectral resolution showed that the resonance lines of He  i and He  ii are anomalously strong in the quiet Sun when compared with other transition region lines formed at similar temperatures. Here, the higher spatial and spectral resolution provided by the Coronal Diagnostic Spectrometer ( cds ) instrument on board the Solar and Heliospheric Observatory ( SOHO ) is used to re-examine the behaviour of the He  i and He  ii lines and other transition region lines, in quiet regions near Sun centre. Supergranulation cell boundaries and cell interiors are examined separately. Near-simultaneous observations with the sumer instrument provide information on the lower transition region and the electron pressure. While the lines of He  i and He  ii have a common behaviour, as do the other transition region lines, the behaviour of the helium lines relative to the other transition region lines is significantly different. The emission measure distributions that account for all transition region lines, except those of helium, fail to produce sufficient emission in the He  i and He  ii resonance lines by around an order of magnitude, in both supergranulation cell boundary and cell interior regions. The electron pressure appears to be higher in the cell interiors than in the average cell boundaries, although the uncertainties are large. While the VAL-D model gives a closer match to the He  i 584.3-Å line, it does not successfully reproduce other transition region lines.  相似文献