Characteristics of Quasi-Periodic Oscillations During Sea Fog Events

Based on the high-resolution datasets collected in a sea fog field experiment at the northern coast of South China Sea, the variations of liquid water content (LWC) and net longwave radiation flux (NLRF) during two sea fog events on 16th-17th and 18th-19th March, 2008 are exaimeed by wavelet analysis, and the cooling mechanisms for fog formation and persistence are also investigated. The main results are shown as follows. (1) Sea fog may develop and persist whether it is cloudy or not aloft. However, when there is cloud aloft the LWC is less and wind speed in sea fog is higher than that in the clear sky. (2) The quasi-periodic oscillations (QPOs) of NLRF are observed in the formation stage of the two fogs. QPOs of LWC are only found in the developing stage no matter with cloudless or cloudy condition. (3) It is likely that sea fog forms by the cooling effects of longwave radiation and develops through the vertical mixing induced by the radiative cooling at the upper level. (4) During sea fog development and persistence, other mechanisms could also play important roles in fog-layer cooling, such as turbulent heat transport and radiation transport between air-sea interfaces.     

For whom the disc tolls

Report on the Nordita Workdays on Quasi‐Peridic Oscillations (QPOs). (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

���ظ�Ƶ�ʼ������ʵ����

???????????????????TROS??I?????????????????Ajisai????????й??????????     

中子星X射线双星中kHz QPO现象的理论解释

罗西X射线时变探测器(RXTE)在中子星小质量X射线双星中发现了千赫兹准周期振荡现象(kHzQPO)。kHzQPO的频率一般在几百到上千赫兹,其动力学时标与吸积盘最内部区域物质的运动时标一致,因此普遍认为kHz QPO产生于中子星表面附近区域,携带了来自中心中子星及周围强引力场信息,如质量、自转周期、角动量、半径、磁场等。kHz QpO现象的理解为研究强引力场和致密物质状态开启了一扇新的窗口。着重介绍基于kHz QPO的基本现象和相应的理论模型。     

Seabed characterization through a range of high-resolution acoustic systems – a case study offshore Oman

This study uses three acoustic instruments (different in their operating frequencies, 13, 3.5, and 6–10 kHz, and deployment type, hull-mounted, surface-towed and deep-towed) to investigate and characterize the acoustic response of seafloor NE of Oman in a frequency-independent manner. High-resolution control was achieved by having selected areas of our acoustic transects ground-truthed by sampling and/or sea-floor photography. On the regional scale, the greatest degree of change in backscatter amplitude was correlated with major changes of seabed morphology and lithology. However, small-scale roughness had the biggest effect on amplitude on the local scale, i.e. within each area of specific seafloor type. The study also shows that seafloor reflection amplitude changes are far more easily detected by deep-towed instrument than by surface-towed or hull-mounted systems. Whilst there are significant changes in bioturbation types and density along the transects, the suite of instruments deployed was not able to pick up the effect of the bioturbation on acoustic signals.     

海雾的准周期振荡特征

根据南海北部海雾外场观测获取的高分辨率液态含水量、长波辐射通量数据,采用小波分析方法分析了2008年3月16—17日和18—19日两次海雾中的液态水含量、净长波辐射通量的变化特征,讨论南海北部海雾发展和维持的冷却机制。结果显示:(1)无论在有云或无云条件下,海雾都可发展和维持;但前者的液态含水量明显小于后者,而风速大于后者;(2)在地面海雾的生成之前和生成初期,净辐射通量都存在准周期振荡现象,无论无云/有云,地面海雾液态水的大幅度发展的阶段都存在含水量的准周期振荡现象;(3)含水量的准周期振荡现象与振荡发生时段的长波辐射通量关系不大,而主要通过湍流对液态水的混合作用与高空海雾液态水大量生成阶段的雾顶长波辐射间接相关。(4)海雾的生成都与雾顶长波辐射冷却密切相关,但发展和维持可通过不同的冷却机制,既可通过海气间湍流热量输送和辐射传输,也可通过雾顶长波辐射冷却。     

Difficulties with the QPOs resonance model

High frequency quasi-periodic oscillations (HFQPOs) have been detected in microquasars and neutron star systems. The resonance model suggested by Kluźniak and Abramowicz (2000, 2001) explains twin QPOs as two weakly coupled nonlinear resonant epicyclic modes in the accretion disk. Although this model successfully explains many features of the observed QPOs, it still faces difficulties and shortcomings. Here we summarize the aspects of the theory that remain a puzzle and we briefly discuss likely developments.     

2010年上海天文台卫星激光测距观测报告

介绍了2010年上海天文台卫星激光测距的常规观测和白天千赫兹激光测距情况。在国际上首次对同步轨道卫星开展了千赫兹激光测距,作用距离达38800多千米,测距系统性能达到国际先进水平。利用2套独立的激光测距系统,开展了激光收发分离测距实验,为行星际异步应答式激光测距模拟试验提供了实测数据。最后概述了空间碎片目标激光测距进展情况。     

High-resolution (2–7 kHz) acoustic and geometric characters of submarine creep deposits in the South Korea Plateau, East Sea

A synthesis of high-resolution (Chirp, 2–7 kHz) seismic profiles in the South Korea Plateau reveals that large masses of wavy stratified sediment (≈60–90 m thick) cover broad, gently sloping (<0·5°) ridges in water depths of 1000–2000 m. The wavy stratified sediment (WSS) is characterized by wavy (0·2–5 km in wavelength and <15 m in relief), continuous reflective layers with a basal deformed zone that overlies undeformed, strong reflectors. The WSS exhibits systematic variation in wave dimensions and thickness of internal reflective layers with changes in slope gradient. The troughs of the waves are commonly associated with internal growth faults, and wave amplitude generally increases with subbottom depth. On steep slopes around the ridges, the WSS masses are bounded downslope by slide and slump deposits including slightly translated or rotated WSS blocks. The acoustic and geometric characters, and association with downslope slides and slumps on the steeper slopes, suggest that the WSS masses were most probably formed by slow creep movement before slope failure. In the absence of significant sediment input to the South Korea Plateau, the deep (1000–2000 m in water depth) mass movements were probably triggered by earthquakes that have occurred frequently in this region. Some slightly displaced, intact WSS blocks in the associated slides and slumps downslope reflect a progressive evolution from submarine creep into slide and slump.     

kHz QPOs in LMXBs, relations between different frequencies and compactness of stars

We suggest that the mass of four compact stars SAX J1808.4-3658, KS 1731-260, SAX J1750.8-2900 and IGR J17191-2821 can be determined from the difference in the observed kiloHertz quasi periodic oscillations (kHz QPO-s) of these stars. The stellar radius is very close to the marginally stable orbit R_ms as predicted by Einstein’s general relativity. It may be noted that the first of these stars was suggested to be a strange star more than a decade back by Li et al. (1999a) from the unique millisecond X-ray pulsations with an accurate determination of its rotation period. It showed kHz QPO-s eight years back and so far it is the only set that has been observed. This is the first time we give an estimate of the mass of the star and of three other compact stars in low-mass X-ray binaries using their observed kHz QPO-s.