Advanced Technology Solar Telescope: A status report

Magnetic fields control the inconstant Sun. The key to understanding solar variability and its direct impact on the Earth rests with understanding all aspects of these magnetic fields. The Advanced Technology Solar Telescope (ATST) has been design specifically for magnetic remote sensing. Its collecting area, spatial resolution, scattered light, polarization properties, and wavelength performance all insure ATST will be able to observe magnetic fields at all heights in the solar atmosphere from photosphere to corona. After several years of design efforts, ATST has been approved by the U.S. National Science Foundation to begin construction with a not to exceed cost cap of approximately $298M. Work packages for major telescope components will be released for bid over the next several months. An application for a building permit has been submitted (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Lead angles and emitting electron energies of Io-controlled decameter radio arcs

The Io-controlled radio arcs are emissions in the decametric radio range which appear arc shaped in the time-frequency plane. Their occurrence is controlled by Io's position, so it has been for long inferred that they are powered by the Io-Jupiter electrodynamic interaction. Their frequency ranges correspond to the electron cyclotron frequencies along the Io Flux tube, so they are expected to be generated by cyclotron maser instability (CMI). The arc shape was proposed to be a consequence of the strong anisotropy of the decametric radio emissions beaming, combined with the topology of the magnetic field in the source and the observation geometry. Recent papers succeeded at reproducing the morphologies of a few typical radio arcs by modeling in three dimensions the observation geometry, using the best available magnetic field model and a beaming angle variation consistent with a loss-cone driven CMI. In the continuation of these studies, we present here the systematic modeling of a larger number of observations of the radio arcs emitted in Jupiter's southern hemisphere (including multiple arcs or arcs exhibiting abrupt changes of shape), which permits to obtain a statistical determination of the emitting field line localization (lead angle) relative to the instantaneous Io field line, and of the emitting particle velocities or energies. Variations of these parameters relative to Io's longitude are also measured and compared to the location of the UV footprints of the Io-Jupiter interaction. It is shown that the data are better organized in a reference frame attached to the UV spot resulting from the main Alfvén wing resulting from the Io-Jupiter interaction. It is proposed that the radio arcs are related to the first reflected Alfvén wing rather than to the main one.     

成山头海域潮流能资源可开发量评估

针对潮流能资源较丰富的成山头外海域,利用FVCOM数值模式,在良好模拟该海域潮流场的基础上,运用能量耗散原理,对该海域的潮流能资源可开发量进行了评估。结果表明,在转换装置的拖拽系数为0.07时,面积为27km2的成山头近岸海域的可开发潮流能资源约为17.9MW,其中大潮期间的可开发量高达37.7MW,而小潮期间则为7.3MW。在此条件下,该海域大潮期间涨急和落急时刻的流速分别减小了40%和38%,但发电装置对潮汐的影响较小,在成山头顶端的高潮潮位仅下降了4cm。     

Rainfall effect on wind waves and the turbulence beneath air-sea interface

Rainfall effects on wind waves and turbulence are investigated through the laboratory experiments in a large wind-wave tank. It is found that the wind waves are damped as a whole at low wind speeds, but are enhanced at high wind speeds. This dual effect of rain on the wind waves increases with the increase of rain rate, while the influence of rainfall-area length is not observable. At the low wind speed, the corresponding turbulence in terms of the turbulent kinetic energy （TKE） dissipation rate is significantly enhanced by rain- fall as the waves are damped severely. At the high wind speed, the augment of the TKE dissipation rate is suppressed while the wind waves are enhanced simultaneously. In the field, however, rainfall usually hin- ders the development of waves. In order to explain this contradiction of rainfall effect on waves, a possibility about energy transfer from turbulence to waves in case of the spectral peak of waves overlapping the inertial subrange of turbulence is assumed. It can be applied to interpret the damping phenomenon of gas trans- fer velocity in the laboratory experiments, and the variation of the TKE dissipation rates near sea surface compared with the law of wall.     

Structure of radio sources at wavelengths 10.5 and 12.0 cm from observations of the Solar eclipse on March 29, 2006

The eclipse observations were performed at the Laboratory of Radio Astronomy of the CrAO in Katsiveli with stationary instrumentation of the Solar Patrol at wavelengths of 10.5 and 12.0 cm. The data obtained were used to determine the brightness temperature of the undisturbed Sun at solar activity minimum between 11-year cycles 23 and 24: T _d10.5 = (43.7 ± 0.5) × 10³ K at 10.5 cm and T _d12.0 = (51.8 ± 0.5) × 10³ K at 12.0 cm. The radio brightness distribution above the limb group of sunspots NOAA 0866 was calculated. It shows that at both wavelengths the source consisted of a compact bright nucleus about 50 × 10³ km in size with temperatures T _b10.5 = 0.94 × 10⁶ K and T _b12.0 = 2.15 × 10⁶ K located, respectively, at heights h _10.5 = 33.5 × 10³ km and h _12.0 = 43.3 × 10³ km above the sunspot and an extended halo with a temperature T _b = (230–300) × 10³ K stretching to a height of 157 × 10³ km above the photosphere. The revealed spatial structure of the local source is consistent with the universally accepted assumption that the radiation from the bright part of the source is generated by electrons in the sunspot magnetic fields at the second-third cyclotron frequency harmonics and that the halo is the bremsstrahlung of thermal electrons in the coronal condensation forming an active region. According to the eclipse results, the electron density near the upper boundary of the condensation was N _e ≈ 2.3 × 10⁸ cm^?3, while the optical depth was τ ≈ 0.1 at an electron temperature T _e ≈ 10⁶ K. Thus, the observations of the March 29, 2006 eclipse have allowed the height of the coronal condensation at solar activity minimum to be experimentally determined and the physical parameters of the plasma near its upper boundary to be estimated.     

Ion acceleration and Alfvén wave generation at the Earth’s bow shock

The processes of ion acceleration and Alfvén wave generation by accelerated particles at the Earth’s bow shock are studied within a quasi-linear approach. Steady-state ion and wave spectra are shown to be established in a time of 0.3–4 h, depending on the background level of Alfvénic turbulence in the solar wind. The Alfvén waves produced by accelerated ions are confined within the frequency range 10^?2–1 Hz and their spectral peak with a wave amplitude βB ～ B comparable to the interplanetary magnetic field strength B corresponds to the frequency v = (2–3) × 10^?2 Hz. The high-frequency part of the wave spectrum (v > 0.2 Hz) undergoes damping by thermal ions. The calculated spectra of the accelerated ions and the Alfvén waves generated by them reproduce the main features observed in experiments.     

Solar cycles during the Maunder minimum

We have obtained new consistent versions of the 400-yr time series of the Wolf sunspot number W, the sunspot group number G, and the total sunspot area S (or the total sunspot magnetic flux Φ). We show that the 11-yr cycle did not cease during the Maunder minimum of solar activity. The characteristics of the extrema of individual 11-yr cycles in 1600–2005 have been determined in terms of the total sunspot area index. We provide arguments for using alternating (“magnetic”) time series of indices in investigating the solar cyclicity.     

Paper trails: The Outdoor Recreation Resource Review Commission and the rationalization of recreational resources

This article examines the history of the Outdoor Recreation Resource Review Commission (ORRRC) in the United States between 1955 and 1963 and efforts to make recreational resources legible for federal governance. By drawing on insights from Critical Resource Geography, I highlight the ways that the ORRRC systematically accounted for and categorized recreational resources, creating a “patchwork landscape” that zoned outdoor recreational resources and promoted efficient use and rational resource conservation. I argue that these efforts required a negotiation between abstraction and an awareness of the situated nature of recreational landscapes.     

我国干热岩勘查的有关技术问题

干热岩作为一种可再生的新型能源,具有热能大、分布广、开发利用对环境影响小、不受季节等自然条件的影响等优势。而干热岩的勘查开发利用在我国还基本属于空白,因此对干热岩勘查关键技术开展研究有着非常现实的意义。在简述国内外对干热岩勘查开发利用研究现状的基础上,分析了干热岩开发利用的技术关键,并提出了主要的研究内容和需要做的工作。