Arctic clouds strongly influence the regional radiation balance, temperature, melting of sea ice, and freezing of sea water. Despite their importance, there is a lack of systematic and reliabie observations of Arctic ...Arctic clouds strongly influence the regional radiation balance, temperature, melting of sea ice, and freezing of sea water. Despite their importance, there is a lack of systematic and reliabie observations of Arctic clouds. The CloudSat satellite launched in 2006 with a 94GHz Cloud Profiling Radar （CPR） may contribute to close this gap. Here we compare one of the key parameters, the cloud liquid water path （LWP） retrieved from CloudSat observations and from microwave radiometer （MWR） data taken during the ASCOS （Arctic Summer Cloud Ocean Study） cruise of the research vessel Oden from August to September 2008. Over the 45 days of the ASCOS cruise, collocations closer than 3 h and 100 km were found in only 9 d, and collocations closer than 1 h and 30 km in only 2 d. The poor correlations in the scatter plots of the two LWP retrievals can be explained by the patchiness of the cloud cover in these two days （August 5th and September 7th）, as confirmed by coincident MODIS （Moderate-resolution Imaging Spectroradiome- ter） images. The averages of Oden-observed LWP values are systematically higher （40-70 g m-2） than the corresponding CloudSat observations （0-50 g m2）. These are cases of generally low LWP with presumably small droplets, and may be explained by the little sensitivity of the CPR to small droplets or by the surface clutter.展开更多
The atmosphere protects humans, plants, ani- mals, and microorganisms from damaging doses of ultra- violet-B （UVB） solar radiation （280-320 nm） because it modifies the UVB reaching the Earth＇s surface. This modif...The atmosphere protects humans, plants, ani- mals, and microorganisms from damaging doses of ultra- violet-B （UVB） solar radiation （280-320 nm） because it modifies the UVB reaching the Earth＇s surface. This modification is a function of the solar radiation＇s path length through the atmosphere and the amount of each attenuator along the path length. The path length is deter- mined by solar zenith angle （SZA）. The present work ex- plains the dependence of hemispherical transmittance of UVB on SZA. The database used consists of five years of hourly UVB and global solar radiation measurements. From 2001 to 2005, the South Valley University （SVU） meteorological research station （26.20°N, 32.75°E） car- ried out these measurements on a horizontal surface. In addition, the corresponding extraterrestrial UVB （UVBe^d and broadband solar radiation （Gext） were estimated. Consequently, the hemispherical transmittance of UVB （KtuvB） and the hemispherical transmittance of global solar radiation （Kt） were estimated. Furthermore, the UVB redaction due to the atmosphere was evaluated. An analy- sis of the dependence between KtuvB and SZA at different ranges of Kt was performed. A functional dependence between KtuvB and SZA （KtuvB=-a（SZA）＋b） for very narrow Kt-ranges （width of ranges was 0.01） was devel- oped. The results are discussed, and the sensitivity of AKtuvB to △SZA for very narrow Kt-ranges was studied. It was found that the sensitivity of △KtUVB to ASZA slightly increases with increased Kt, which means KtuvB is sensi- tive to SZA as Kt increases. The maximum correlation （R） between KtuvB and SZA was equal to -0.83 for Kt= 0.76.展开更多
Let （V, U） be the vertex-partition of tree T as a bipartite graph. T is called an （m, n）-tree if ｜V｜ = m and ｜U｜ = n. For given positive integers m, n and d, the maximum spectral radius of all （m, n）-trees o...Let （V, U） be the vertex-partition of tree T as a bipartite graph. T is called an （m, n）-tree if ｜V｜ = m and ｜U｜ = n. For given positive integers m, n and d, the maximum spectral radius of all （m, n）-trees on diameter d are obtained, and all extreme graphs are determined.展开更多
基金ASCOS was made possible by grants from DAMOCLES and the Knut and Alice Wallenberg Foundation,and was organized by the Swedish Polar Research Secretariat
文摘Arctic clouds strongly influence the regional radiation balance, temperature, melting of sea ice, and freezing of sea water. Despite their importance, there is a lack of systematic and reliabie observations of Arctic clouds. The CloudSat satellite launched in 2006 with a 94GHz Cloud Profiling Radar （CPR） may contribute to close this gap. Here we compare one of the key parameters, the cloud liquid water path （LWP） retrieved from CloudSat observations and from microwave radiometer （MWR） data taken during the ASCOS （Arctic Summer Cloud Ocean Study） cruise of the research vessel Oden from August to September 2008. Over the 45 days of the ASCOS cruise, collocations closer than 3 h and 100 km were found in only 9 d, and collocations closer than 1 h and 30 km in only 2 d. The poor correlations in the scatter plots of the two LWP retrievals can be explained by the patchiness of the cloud cover in these two days （August 5th and September 7th）, as confirmed by coincident MODIS （Moderate-resolution Imaging Spectroradiome- ter） images. The averages of Oden-observed LWP values are systematically higher （40-70 g m-2） than the corresponding CloudSat observations （0-50 g m2）. These are cases of generally low LWP with presumably small droplets, and may be explained by the little sensitivity of the CPR to small droplets or by the surface clutter.
基金supported by the Deanship of Scientific Research from King Saud University
文摘The atmosphere protects humans, plants, ani- mals, and microorganisms from damaging doses of ultra- violet-B （UVB） solar radiation （280-320 nm） because it modifies the UVB reaching the Earth＇s surface. This modification is a function of the solar radiation＇s path length through the atmosphere and the amount of each attenuator along the path length. The path length is deter- mined by solar zenith angle （SZA）. The present work ex- plains the dependence of hemispherical transmittance of UVB on SZA. The database used consists of five years of hourly UVB and global solar radiation measurements. From 2001 to 2005, the South Valley University （SVU） meteorological research station （26.20°N, 32.75°E） car- ried out these measurements on a horizontal surface. In addition, the corresponding extraterrestrial UVB （UVBe^d and broadband solar radiation （Gext） were estimated. Consequently, the hemispherical transmittance of UVB （KtuvB） and the hemispherical transmittance of global solar radiation （Kt） were estimated. Furthermore, the UVB redaction due to the atmosphere was evaluated. An analy- sis of the dependence between KtuvB and SZA at different ranges of Kt was performed. A functional dependence between KtuvB and SZA （KtuvB=-a（SZA）＋b） for very narrow Kt-ranges （width of ranges was 0.01） was devel- oped. The results are discussed, and the sensitivity of AKtuvB to △SZA for very narrow Kt-ranges was studied. It was found that the sensitivity of △KtUVB to ASZA slightly increases with increased Kt, which means KtuvB is sensi- tive to SZA as Kt increases. The maximum correlation （R） between KtuvB and SZA was equal to -0.83 for Kt= 0.76.
基金Supported by the Department Fund of Science and Technology in Tianjin Higher Education Institutions(20050404)
文摘Let （V, U） be the vertex-partition of tree T as a bipartite graph. T is called an （m, n）-tree if ｜V｜ = m and ｜U｜ = n. For given positive integers m, n and d, the maximum spectral radius of all （m, n）-trees on diameter d are obtained, and all extreme graphs are determined.
