Reducing discrepancies in ground and satellite-observed eruption heights

The plume height represents a crucial piece of evidence about an eruption, feeding later assessment of its size, character, and potential impact, and feeding real-time warnings for aviation and ground-based populations. There have been many observed discrepancies between different observations of maximum plume height for the same eruption. A comparison of maximum daily height estimates of volcanic clouds over Indonesia and Papua New Guinea during 1982–2005 shows marked differences between ground and satellite estimates, and a general tendency towards lower height estimates from the ground. Without improvements in the quality of these estimates, reconciled among all available methods, warning systems will be less effective than they should be and the world's record of global volcanism will remain hard to quantify. Examination of particular cases suggests many possible reasons for the discrepancies. Consideration of the satellite and radar cloud observations for the 1991 Pinatubo eruptions shows that marked differences can exist even with apparently good observations. The problem can be understood largely as a sampling issue, as the most widely reported parameter, the maximum cloud height, is highly sensitive to the frequency of observation. Satellite and radar cloud heights also show a pronounced clumping near the height of the tropopause and relative lack of eruptions reaching only the mid-troposphere, reinforcing the importance of the tropopause in determining the eruption height in convectively unstable environments. To reduce the discrepancies between ground and satellite estimates, a number of formal collaboration measures between vulcanological, meteorological and aviation agencies are suggested.     

利用多元LBP特征自动提取城市道路边界

车载移动测量系统可采集高精度道路三维点云数据,为道路边界自动化提取提供了支撑.为解决车载激光点云中城市道路边界点云提取困难问题,本文引入局部二值模式LBP(Local Binary Pattern),针对各类城市道路边界特征,设计了高度LBP、高程离散度LBP和空间形状LBP3种改进算子;构建多元LBP特征语义识别模型...     

Short-wave radiation flux divergence in arctic cirrus: a case study

Radiation and particle measurements have been performed with an aircraft in deep cirrus cloud fields near the island of Svalbard. The data of 12 March 1993, when measurements at 10 different levels could be obtained, are used in a comparative study with radiative transfer calculations. In a first analysis, the cirrus cloud field was assumed to be horizontally homogeneous and invariable during the time of measurements (frozen properties). Calculations of the up and downward radiative flux densities showed root mean square differences of 9 Wm⁻² from the measurements. To estimate the possible effect of changes of the optical properties of cirrus with time, the flux densities in the upper part (6000–8500 m) and the lower part (3000–5500 m) of the cirrus cloud were analyzed separately. In these simulations, the optical thickness in the lower (upper) part was increased (decreased) by 50%. By this treatment, most of all calculated flux densities were within one standard deviation of the natural variability in each leg. Finally, the effect of inhomogeneities in the cloud field on the solar flux density has been simulated using a Monte Carlo method, since the upper part of the cirrus field has indeed been very inhomogeneous. This paper is a result of a collaborative effort between the MRI in Tsukuba, Japan, and the GKSS in Geesthacht, Germany.     

刚体自转在巨分子云的聚合形成中的作用

分析在聚合形成机制下,巨分子云在刚体自转盘中的形成过程．研究结果表明,形成的巨分子云主要由其附近的分子云组成．由于速度弥散的作用,非弹性碰撞和自引力使分子云聚会在一起,以这种方式形成的巨分子云是小质量的．如果较差自转存在,这些小质量的巨分子云便有更多的机会聚合在一起形成更大质量的巨分子云．这进一步说明,较差自转在巨分子云的形成中起了很大的积极作用．     

OMC--3的13CO(1--0)和C18O(1--0)分子辐射

利用紫金山天文台青海站的 １３．７ ｍ毫米波望远镜,对 Ｏｒｉｏｎ Ａ分子云中的 ＯＭＣ－３区域,进行了较高分辨率的１３ＣＯ（Ｊ＝１－０）和Ｃ１８Ｏ（Ｊ＝１－０）分子辐射的成图观测．给出了该分子云中１３ＣＯ和 Ｃ１８Ｏ云核分布的整体结构和平均物理参数．观测发现,该分子云的１３ＣＯ和 Ｃ１８Ｏ的云核中心分别与最年轻的天体－Ｃｌａｓｓ ０类源 ＭＭＳＩ, ＭＭＳ４,ＭＭＳ６和ＭＭＳ７,ＭＭＳ８;ＭＭＳ９成协．此外,通过分析ＯＭＣ－３整个区域的速度场结构,发现沿 Ｃ１８Ｏ和１３ＣＯ云核方向从南到北有一个～ １．７ｋｍ／ｓ的速度场梯度,而分子云的红、蓝移团块则分别趋于云的北部和南部．并对ＯＭＣ－３区的恒星形成特征进行了讨论．     

Discovery of a dense bipolar outflow from a new class 0 protostar in NGC 2068/LBS 17

We report the discovery of high-velocity dense gas from a bipolar outflow source near NGC 2068 in the L1630 giant molecular cloud. CO and HCO⁺ J =3→2 line wings have a bipolar distribution in the vicinity of LBS 17-H with the flow orientated roughly east–west and perpendicular to the elongation of the submillimetre dust continuum emission. The flow is compact (total extent ∼0.2 pc) and contains of the order of 0.1 M_⊙ of swept-up gas. The high-velocity HCO⁺ emission is distributed over a somewhat smaller area <0.1 pc in extent.
A map of C¹⁸O J =2→1 emission traces the LBS 17 core and follows the ambient HCO⁺ emission reasonably well, with the exception of the direction towards LBS 17-H where there is a significant anticorrelation between the C¹⁸O and HCO⁺. A comparison of beam-matched C¹⁸O and dust-derived H₂ column densities suggests that CO is depleted by up to a factor of ∼50 at this position if the temperature is as low as 9 K, although the difference is substantially reduced if the temperature is as high as 20 K. Chemical models of collapsing clouds can account for this discrepancy in terms of different rates of depletion on to dust grains for CO and HCO⁺.
LBS 17-H has a previously known water maser coincident with it but there are no known near-infrared, IRAS or radio continuum sources associated with this object, leading to the conclusion that it is probably very young. A greybody fit to the continuum data gives a luminosity of only 1.7 L_⊙ and a submillimetre-to-bolometric luminosity ratio of 0.1, comfortably satisfying the criteria for classification as a class 0 protostar candidate.     

Interstellar Na i D lines towards the Southern Coalsack

The interstellar Na  i D absorption-line profiles observed for 15 stars with lines of sight towards the Southern Coalsack are analysed. The method of profile fitting was used in an attempt to determine column densities, linewidths and velocities for the individual interstellar clouds contributing to the observed absorption lines. In common, the observed spectra show a prominent component which is probably associated with the nearest absorbing material composing the Coalsack. The obtained spatial velocity distribution shows great similarity with earlier results from CO emission. In addition, the Na  i D data reveal evidence for the existence of two or three other structures with radial velocities of about −22, −33 and −40 km s⁻¹. Such components may be the counterparts of interstellar structures observed in diffuse H α and CO emission. The assumption that at least one of these components originated in the Carina arm imposes ∼0.9–1.0 kpc as the maximum distance to the near side of that arm.     

广汉机场一次非典型辐射平流雾的天气诊断分析

为探索广汉机场雾发生发展的机制,确保飞行安全,提高预报准确率,利用广汉机场地面观测资料、Mi—caps系统下的常规观测资料、探空资料和NCEP／NCAR再分析资料,采用天气诊断分析方法,对2012年11月13日-15日广汉机场持续性的辐射平流雾进行分析。结果表明,雾是在稳定的天气背景下形成。夜间地面长波辐射冷却触发了这次雾的形成,而在轻雾转大雾期间,地面长波辐射冷却作用明显减弱,低层暖湿平流则起到了主要作用。与典型辐射平流雾不同的是成雾后,机场由脊前西北气流转为南支槽前西南气流控制,天空中云量的迅速增加使得雾进一步加强。     

Anomalously low ozone of 1997 and 2011 Arctic spring: Monitoring results and analysis

Total ozone observations from the Total Ozone Unit （TOU） aboard the Chinese second generation polar orbiting mete- orological satellite, Fengyun-3/A （FY-3/A）, revealed that total column ozone over the Arctic declined rapidly from the beginning of March 2011. An extensive region of low column amount formed around mid March; monthly mean total column ozone in March 2011 was about 30% lower than the average observed during 1979-2010. Daily total column density of ozone near the center of low ozone area in mid March was less than 240 Dobson units, about half the total column ozone amount observed during the same period of the prior 10 years. We analyzed total column ozone data from different satellites during 1979-2011. Results show that the Arctic depletion of ozone in spring 2011 was initiated by the cold polar vortex in the lower stratosphere. The March mean total ozone over the Arctic has shown a decreasing trend over the past 32 years, and its variation is strongly correlated with the polar vortex. A similar low ozone process of spring 1997 was compared to that of 2011, but daily variations of total ozone in March over the Northern Hemisphere in 1997 and 2011 have different patterns.     

分子云磁场与尘埃导致的偏振

磁场对分子云及其中的恒星的形成和演化起到重要的作用.分子云磁场的探测方法主要是谱线塞曼效应、尘埃热辐射的偏振,以及谱线的线偏振观测.利用谱线的塞曼效应可以直接测量视线方向的磁场强度.尘埃热辐射偏振可以有效地示踪磁场方向在天球上的分布.分子云内部的磁场会受到不同物理过程的影响.高分辨率观测可以研究磁场扰动的细节,低分辨率观测可以得到分子云甚至银河系大尺度磁场的宏观信息.只有多波段的观测才能全面地认识分子云磁场与各种物理过程的联系.该文对分子云尘埃热辐射偏振的观测情况做了调研,总结了分子云大尺度磁场的研究现状和发展前景.