雷暴追踪矢量的准确性是决定短时临近降水外推预报效果的关键。以TREC(Tracking Radar Echoes by Correlation)为代表的区域追踪和以TITAN(Thunderstorm Identifiation, Tracking, Analysis, and Nowcasting)为代表的单体追踪是追踪雷...雷暴追踪矢量的准确性是决定短时临近降水外推预报效果的关键。以TREC(Tracking Radar Echoes by Correlation)为代表的区域追踪和以TITAN(Thunderstorm Identifiation, Tracking, Analysis, and Nowcasting)为代表的单体追踪是追踪雷暴移动矢量的两种典型方法。TREC基于追踪格点雷达回波数据得到,能较好体现层状云降水和对流云降水系统的区域总体移动趋势;TITAN可以识别、分析雷暴的二维和三维属性,自动跟踪雷暴的移动速度和方向,形成雷暴单体移动矢量,能够更好地刻画小尺度雷暴单体的移动速度和方向。将TREC和TITAN两种移动矢量进行融合,生成新的外推移动矢量,既保留了TREC方法在刻画大尺度雷暴总体移动趋势信息方面的特长,又能充分发挥TITAN方法在刻画小尺度雷暴运动细节信息上的优势。融合试验表明,采用TREC和TITAN两种降水移动矢量融合的新技术,可以一定程度改进降水外推移动矢量场估计的准确度,提升降水落区和强度外推预报的准确度,对改善北京地区降水临近预报水平具有一定正效果。展开更多
Our understanding of Titan, Saturn＇s largest satellite, has recently been considerably enhanced, thanks to the Cassini-Huygens mission. Since the Saturn Orbit Injection in July 2004, the probe has been harvesting new...Our understanding of Titan, Saturn＇s largest satellite, has recently been considerably enhanced, thanks to the Cassini-Huygens mission. Since the Saturn Orbit Injection in July 2004, the probe has been harvesting new insights of the Kronian system. In particular, this mission orchestrated a climax on January 14, 2005 with the descent of the Huygens probe into Titan＇s thick atmosphere. The orbiter and the lander have provided us with picturesque views of extraterrestrial landscapes, new in composition but reassuringly Earth-like in shape. Thus, Saturn＇s largest satellite displays chains of mountains, fields of dark and damp dunes, lakes and possibly geologic activity. As on Earth, landscapes on Titan are eroded and modeled by some alien hydrology： dendritic systems, hydrocarbon lakes, and methane clouds imply periods of heavy rainfalls, even though rain was never observed directly. Titan＇s surface also proved to be geologically active - today or in the recent past - given the small number of impact craters listed to date, as well as a few possible cryovolcanic features. We attempt hereafter a synthesis of the most significant results of the Cassini-Huygens endeavor, with emphasis on the surface.展开更多
Cassini observations over the past ten years have revealed that Titan possesses a chemically complex ionosphere. In this study,we investigate the relative contributions of different ion species to the total ion escape...Cassini observations over the past ten years have revealed that Titan possesses a chemically complex ionosphere. In this study,we investigate the relative contributions of different ion species to the total ion escape on Titan, by dividing all ion species probed by the Cassini Ion Neutral Mass Spectrometer(INMS) into six groups according to their mass-to-charge ratios(M/Z). For the three lightest ion groups, with characteristic M/Z of 22, 41, and 52 daltons, the observed scale heights tend to be lower than the scale heights predicted by assuming diffusive equilibrium; for the three heavier groups, observed and predicted scale heights are in general agreement, implying that most ion escape from Titan is by relatively light species, with M/Z < 60 daltons. A diffusion model is constructed to describe the density distribution of each ion group in regions where the effect of ionospheric chemistry could be neglected. The data model comparison predicts an optimal total ion escape rate of 3.1×10^(24)s^(–1), of which more than 99% is contributed by relatively light ions with M/Z < 32 daltons.展开更多
Phosphate glasses of composition 48P<sub>2</sub>O<sub>5</sub>-30CaO-(22<span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span&g...Phosphate glasses of composition 48P<sub>2</sub>O<sub>5</sub>-30CaO-(22<span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span>x)Na<sub>2</sub>O-xTiO<sub>2</sub> (with 0 < x ≤ 3, mol%) were prepared by direct melting at 1080<span style="white-space:nowrap;"><span style="white-space:nowrap;"><span style="white-space:nowrap;">°</span></span></span>C ± 20<span style="white-space:nowrap;"><span style="white-space:nowrap;"><span style="white-space:nowrap;">°</span></span></span>C. The chemical durability of these glasses shows an improvement when the Ti<span style="white-space:normal;">O</span><sub style="white-space:normal;">2</sub> content varies from 0 to 2 mol%. The measurements of differential thermal analysis and density, both, indicate the increase of the glass transition temperature and the density. The increase of Tg leads to an improvement of glass rigidity. X-ray diffraction analysis of the glasses annealed at 650<span style="white-space:nowrap;"><span style="white-space:nowrap;"><span style="white-space:nowrap;">°</span></span></span>C for 48 h, indicates the appearance of a mixture of metaphosphate and pyrophosphate phases when the Ti<span style="white-space:normal;">O</span><sub style="white-space:normal;">2</sub> content varies from 0 to 2 mol%, the last become majority when the Ti<span style="white-space:normal;">O</span><sub style="white-space:normal;">2</sub> content rich 2 mol%. Nevertheless, when the Ti<span style="white-space:normal;">O</span><sub style="white-space:normal;">2</sub> content exceeds 2 mol%, the analysis, both, by infrared spectroscopy and X-ray diffraction, reveals a radical change of structure with the formation of majorities isolated orthophosphate groups. SEM micrographs illustrated that the number of crystallites increased in the glass network when the Ti<span style="white-space:normal;">O</span><sub style="white-space:normal;">2</sub> content increased at the expense of the Na<sub>2</sub>O content. An increase in the TiO<sub>2展开更多
文摘雷暴追踪矢量的准确性是决定短时临近降水外推预报效果的关键。以TREC(Tracking Radar Echoes by Correlation)为代表的区域追踪和以TITAN(Thunderstorm Identifiation, Tracking, Analysis, and Nowcasting)为代表的单体追踪是追踪雷暴移动矢量的两种典型方法。TREC基于追踪格点雷达回波数据得到,能较好体现层状云降水和对流云降水系统的区域总体移动趋势;TITAN可以识别、分析雷暴的二维和三维属性,自动跟踪雷暴的移动速度和方向,形成雷暴单体移动矢量,能够更好地刻画小尺度雷暴单体的移动速度和方向。将TREC和TITAN两种移动矢量进行融合,生成新的外推移动矢量,既保留了TREC方法在刻画大尺度雷暴总体移动趋势信息方面的特长,又能充分发挥TITAN方法在刻画小尺度雷暴运动细节信息上的优势。融合试验表明,采用TREC和TITAN两种降水移动矢量融合的新技术,可以一定程度改进降水外推移动矢量场估计的准确度,提升降水落区和强度外推预报的准确度,对改善北京地区降水临近预报水平具有一定正效果。
文摘Our understanding of Titan, Saturn＇s largest satellite, has recently been considerably enhanced, thanks to the Cassini-Huygens mission. Since the Saturn Orbit Injection in July 2004, the probe has been harvesting new insights of the Kronian system. In particular, this mission orchestrated a climax on January 14, 2005 with the descent of the Huygens probe into Titan＇s thick atmosphere. The orbiter and the lander have provided us with picturesque views of extraterrestrial landscapes, new in composition but reassuringly Earth-like in shape. Thus, Saturn＇s largest satellite displays chains of mountains, fields of dark and damp dunes, lakes and possibly geologic activity. As on Earth, landscapes on Titan are eroded and modeled by some alien hydrology： dendritic systems, hydrocarbon lakes, and methane clouds imply periods of heavy rainfalls, even though rain was never observed directly. Titan＇s surface also proved to be geologically active - today or in the recent past - given the small number of impact craters listed to date, as well as a few possible cryovolcanic features. We attempt hereafter a synthesis of the most significant results of the Cassini-Huygens endeavor, with emphasis on the surface.
基金the National Natural Science Foundation of China(NSFC)through grants 41525015 and 41774186
文摘Cassini observations over the past ten years have revealed that Titan possesses a chemically complex ionosphere. In this study,we investigate the relative contributions of different ion species to the total ion escape on Titan, by dividing all ion species probed by the Cassini Ion Neutral Mass Spectrometer(INMS) into six groups according to their mass-to-charge ratios(M/Z). For the three lightest ion groups, with characteristic M/Z of 22, 41, and 52 daltons, the observed scale heights tend to be lower than the scale heights predicted by assuming diffusive equilibrium; for the three heavier groups, observed and predicted scale heights are in general agreement, implying that most ion escape from Titan is by relatively light species, with M/Z < 60 daltons. A diffusion model is constructed to describe the density distribution of each ion group in regions where the effect of ionospheric chemistry could be neglected. The data model comparison predicts an optimal total ion escape rate of 3.1×10^(24)s^(–1), of which more than 99% is contributed by relatively light ions with M/Z < 32 daltons.
文摘Phosphate glasses of composition 48P<sub>2</sub>O<sub>5</sub>-30CaO-(22<span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span>x)Na<sub>2</sub>O-xTiO<sub>2</sub> (with 0 < x ≤ 3, mol%) were prepared by direct melting at 1080<span style="white-space:nowrap;"><span style="white-space:nowrap;"><span style="white-space:nowrap;">°</span></span></span>C ± 20<span style="white-space:nowrap;"><span style="white-space:nowrap;"><span style="white-space:nowrap;">°</span></span></span>C. The chemical durability of these glasses shows an improvement when the Ti<span style="white-space:normal;">O</span><sub style="white-space:normal;">2</sub> content varies from 0 to 2 mol%. The measurements of differential thermal analysis and density, both, indicate the increase of the glass transition temperature and the density. The increase of Tg leads to an improvement of glass rigidity. X-ray diffraction analysis of the glasses annealed at 650<span style="white-space:nowrap;"><span style="white-space:nowrap;"><span style="white-space:nowrap;">°</span></span></span>C for 48 h, indicates the appearance of a mixture of metaphosphate and pyrophosphate phases when the Ti<span style="white-space:normal;">O</span><sub style="white-space:normal;">2</sub> content varies from 0 to 2 mol%, the last become majority when the Ti<span style="white-space:normal;">O</span><sub style="white-space:normal;">2</sub> content rich 2 mol%. Nevertheless, when the Ti<span style="white-space:normal;">O</span><sub style="white-space:normal;">2</sub> content exceeds 2 mol%, the analysis, both, by infrared spectroscopy and X-ray diffraction, reveals a radical change of structure with the formation of majorities isolated orthophosphate groups. SEM micrographs illustrated that the number of crystallites increased in the glass network when the Ti<span style="white-space:normal;">O</span><sub style="white-space:normal;">2</sub> content increased at the expense of the Na<sub>2</sub>O content. An increase in the TiO<sub>2
