Models of Very-High-Energy Gamma-Ray Emission from the Jets of Microquasars: Orbital Modulation     

Markus Böttcher  Charles D. Dermer 《Astrophysics and Space Science》2007,307(1-3):233-236

The recent detection of very-high-energy (GeV – TeV) γ-ray emission from the Galactic black-hole candidate and microquasar LS 5039 has sparked renewed interest in jet models for the high-energy emission in those objects. In this work, we have focused on models in which the high-energy emission results from synchrotron and Compton emission by relativistic electrons in the jet (leptonic jet models). Particular attention has been paid to a possible orbital modulation of the high-energy emission due to azimuthal asymmetries caused by the presence of the companion star. Both orbital-phase dependentγγ absorption and Compton scattering of optical/UV photons from the companion star may lead to an orbital modulation of the gamma-ray emission. We make specific predictions which should be testable with refined data from HESS and the upcoming GLAST mission.  相似文献   

A new model for the periodic outbursts of the BL Lac object OJ287     

Weizhao Shi  Xiang Liu  Huagang Song 《Astrophysics and Space Science》2007,310(1-2):59-63

Recent observations provide strong evidence for the BL Lac object OJ287 exhibiting a 11.6±0.5 yr periodicity with a double-peaked maxima in its optical flux variations. Several models have been proposed for the optical behavior. The 2005 November outburst in OJ287 gives us a surprising result since calculation based on the periodicity was predicting such an outburst in late 2006. Here we suggest a new model, it can not only explain the optical quasi-periodic behavior, but also the radio flares behavior which is and simultaneous with the optical flares. We propose that OJ287 is a binary pair of super-massive black holes, both of them creating a jet. The quasi-periodic double peaks would be due to the relativistic beaming effect on the emission coming from the double helix jets. We used “core flares” to explain the large lags between light curves at different frequencies, and the assumption of two jets appear to be merged with each other partly in the radio frequency emitting regions provides a viable interpretation that we can see only a broad maximum which contains two radio flares that we cannot distinguish.  相似文献   

绿洲边缘夏季小气候特征及地表辐射与能量平衡特征分析   总被引：28，自引：15，他引：13  

张宇  吕世华  陈世强  奥银焕  胡泽勇  韦志刚 《高原气象》2005,24(4):527-533

利用“绿洲系统能量与水分循环过程观测试验”加强期(IOP)在甘肃省酒泉市金塔绿洲观测的资料,分析了夏季金塔绿洲边缘的小气候特征及地表辐射收支和地表能量平衡特征。作为绿洲沙漠相互作用的界面,在白天绿洲边缘的垂直运动仍然是以上升气流为主,并且其小气候主要受土壤湿度的影响。中午前后绿洲边缘的总辐射最大值在1000W.m-2左右,净辐射>700W.m-2;在白天,仅有个别天数的感热通量超过100W.m-2,最大值仅为150W.m-2左右。在整个观测期,有超过70%的天数出现负感热通量。而Bowen比在±10-1量级,地表能量不平衡的差额较大,约28%。  相似文献   

A Model to Calculate what a Remote Sensor ‘Sees’ of an Urban Surface   总被引：2，自引：0，他引：2  

A. Soux  J. A. Voogt  T. R. Oke 《Boundary-Layer Meteorology》2004,112(2):401-424

Whilst the measurement of radiation emissions from a surface is relatively straightforward, correct interpretation and proper utilization of the information requires that the surface area seen be known accurately. This becomes non-trivial when the target is an urban surface, due to its complex three-dimensional form and the different thermal, radiative and moisture properties of its myriad surface facets. The geometric structure creates shade patterns in combination with the solar beam and obscures portions of the surface from the sensor, depending on where it is pointing and its field-of-view (FOV). A model to calculate these surface-sensor-sun relations (SUM) is described. SUM is tested against field and scale model observations, and theoretical calculations, and found to perform well. It can predict the surface area seen by a sensor of known FOV pointing in any direction when placed at any point in space above a specified urban surface structure. Moreover, SUM can predict the view factors of the roof, wall and ground facets seen and whether they are sunlit or shaded at any location and time of day. SUM can be used to determine the optimal placement and orientation of remote sensors to study urban radiation emissions; if the facet temperatures are known or modelled it can calculate the average temperature of the system, and it can determine the directional variation of temperature (anisotropy) due to any particular surface-sensor-sun geometric combination. The present surface geometry used in SUM is relatively simple, but there is scope to make it increasingly realistic.  相似文献   

Derivation of Photosynthetically Available Radiation from METEOSAT data in the German Bight with Neural Nets   总被引：1，自引：0，他引：1  

Kathrin Schiller 《Ocean Dynamics》2006,56(2):79-85

Two different models, a Physical Model and a Neural Net (NN), are used for the derivation of the Photosynthetically Available Radiation (PAR) from METEOSAT data in the German Bight; advantages and disadvantages of both models are discussed. The use of a NN for derivation of PAR should be preferred to the Physical Model because by construction, a NN can take the various processes determining PAR on a surface much better into account than a non-statistical model relying on averaged relations.

Kathrin SchillerEmail:

  相似文献   

辐射和积云对流过程对大气辐射通量的影响   总被引：4，自引：1，他引：3  

李剑东  刘屹岷  孙治安  吴国雄 《气象学报》2009,67(3):355-369

基于中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室发展的全球大气环流谱模式(SAMIL-R42L26),研究了澳大利亚气象局研究中心(BMRC)新辐射方案和新Zhang-McFaflane积云对流方案对大气辐射通量模拟的影响.新辐射方案相比原辐射方案在辐射计算光谱分辨率、气体吸收和计算效率等方面作了很多改进,其对大气辐射通量的模拟能力相应提高.在晴空条件下,大气顶出射长波、大气吸收短波和地表入射短波等与观测的偏差较原辐射方案明显减小,尤其是在对流活跃区域.在云天条件下大气辐射通量与观测的偏差也较原辐射方案减小,但其偏差依然较大,这与模式中积云对流参数化方案模拟能力不足引起的辐射通量偏差有关.为此,换用了新Zhang-McFarlane积云对流方案,其结果表明,对流活跃区水汽含量显著增加,原对流方案中偏强的"双赤道辐合带"现象明显减弱,赤道辐合带地区的大气辐射通量偏差有明显减小,在海洋地区晴空大气顶出射长波和地表入射短波的量值及空间分布均接近观测结果,同时大气顶全球平均能量收支的年变化和观测结果趋于一致,其中模拟的伞球年平均大气顶能量收支和观测的偏差不到0.6 W/m2.试验结果同时表明,在未来研究中引入气溶胶分布、调整相关的云物理和陆面过程等物理参数化方案是进一步提高SAMIL-R42L26辐射通最模拟性能的关键.  相似文献   

Difference in the Interdecadal Variability of Spring and Summer Sensible Heat Flux over Northwest China          下载免费PDF全文

ZHOU Liantong 《大气和海洋科学快报》2009,2(2):119-123

The present study investigates the difference in interdecadal variability of the spring and summer sensible heat fluxes over Northwest China by using station observations from 1960 to 2000. It was found that the spring sensible heat flux over Northwest China was greater during the period from the late 1970s to the 1990s than during the period from the 1960s to the mid-1970s. The summer sensible heat flux was smaller in the late 1980s through the 1990s than it was in the 1970s through the early 1980s. Both the spring and summer land-air temperature differences over Northwest China displayed an obvious interdecadal increase in the late 1970s. Both the spring and summer surface wind speeds experienced an obvious interdecadal weakening in the late 1970s. The change in the surface wind speed played a more important role in the interdecadal variations in sensible heat flux during the summer, whereas the change in the land-air temperature difference was more important for the interdecadal variations in sensible heat flux in the spring. This difference was related to seasonal changes in the mean land-air temperature difference and the surface wind speed. Further analysis indicated that the increase in the spring land surface temperature in Northwest China was related to an increase in surface net radiation.  相似文献   

Synchrotron emission model of RX J1856.5-3754     

Nino Chkheidze 《New Astronomy》2012,17(2):227-231

A plasma emission model is presented interpreting the observational properties of RX J1856.5-3754. In particular, on the basis of the Vlasov’s kinetic equation we study the process of the quasi-linear diffusion (QLD) developed by means of the cyclotron instability. This mechanism provides simultaneous generation of optical and X-ray emission on the light cylinder scales, in one location of the pulsar magnetosphere. It is assumed that the observed X-ray spectrum of this source is generated via the synchrotron mechanism. A different approach of the synchrotron theory is considered, giving a spectral energy distribution that is in a good agreement with the observational data.  相似文献   

利用辐射数据构建云物理结构     

霍娟 《大气科学》2018,42(5):1013-1022

本文运用CloudSat卫星上搭载的雷达探测数据和AQUA卫星搭载的辐射光谱仪探测数据,选择2007年1月至2010年12月期间,地理位置位于（15°~45°N,145°~165°E）区域内（远海）发生的云场数据开展分析,研究云的物理结构特征与其光谱辐射特性的相互关系。不同光谱波段对云物理结构变化的响应情况各有不同,首先从MODIS光谱仪22个云相关光谱波段中分析并选择出与云物理结构特征密切相关的光谱组合（包含13个波段）,而后开展了这些光谱波段的云辐射特性与云物理结构特征的相互变化关系研究。统计分析表明,在外部大气、地表条件以及太阳入射辐射变化不大情况下,云的结构变化与其光谱辐射变化之间总体存在单调相关关系,物理结构变化不大的云廓线之间其光谱辐射的变化也小,反之也成立,即光谱辐射变化小的云廓线之间物理结构变化也小。从而,对于某些内部物理结构特征未知的云,利用与其光谱辐射特性相近的云结构数据可实现自身垂直结构信息的重建。基于光谱辐射相近则云物理结构很可能相近的特点,本文对未知云场的物理结构重建开展了模拟试验,试验结果表明光谱相近原则匹配物理结构的方法一定程度上能够实现云物理结构的构建,为利用被动遥感数据推测云物理结构特征研究提供参考。  相似文献   

卫星遥感海南岛气候特性的研究          下载免费PDF全文

王宣吉  凭常恭 《应用气象学报》1994,5(2):184-189

利用NOAA极轨气象卫星的AVHRR资料，研究了海南岛干、湿两季在无云情况下的下垫面短波反射率、植被指数、下垫面温度和射出长波辐射的分布及变化特征。结果表明利用气象卫星资料可以较详细地了解气候形成的主要因素之一——下垫面状况。  相似文献