Identification,distribution and significance of lunar volcanic domes

Over 300 previously unrecognized volcanic domes were identified on Lunar Orbiter photographs using the following criteria: (1) the recognition of land forms on the Moon similar in morphology to terrestrial volcanic domes, (2) structural control, (3) geomorphic discordance, and (4) the recognition of land forms modified by dome-like swellings. Many terrestrial volcanic domes are similar in morphology to lunar domes. This analogy suggests that some lunar hills are in fact extrusive volcanic domes. Many of the domes identified in this paper seem to be related to basins and craters, and with the exception of local tectonic grid control few domes are related to any observable Moon-wide pattern. Domes are not uniquely found on maria. Dome formation probably spans a wide range of lunar time and activity in areas where domes are located may be continuing to the present as revealed by the close correlation of dome distribution with the distribution of lunar transient events. The overall morphology of a lunar dome is a poor indicator of the composition of the rock that forms the dome. Contribution No. 33 Planetary Geology Group, University of New Mexico.     

Meteorite stranding surfaces and the Greenland icesheet

Abstract— Thirty years of recoveries in East Antarctica have led to significant understanding of the regional characteristics associated with meteorite stranding surfaces. In Antarctica these sites are characterized by patches of snow‐free blue ice at high altitude on the icesheet in regions where iceflow is highly restricted. Melting is extremely rare or absent and sublimation rates are high, even though meteorite stranding surfaces are predominantly found within regions where accumulation typically dominates. Localized environmental conditions that persist for thousands of years or longer appear to be the dominant factor rather than shorter‐term or seasonal cycles. In this paper we describe our discovery of regions in Northeast Greenland with blue ice areas that exhibit many of the requisite characteristics, suggesting that they are excellent prospects for future meteorite recovery efforts.     

Accumulation mechanisms of micrometeorites in an ancient supraglacial moraine at Larkman Nunatak,Antarctica

We report the discovery of a large accumulation of micrometeorites (MMs) in a supraglacial moraine at Larkman Nunatak in the Grosvenor Mountains of the Transantarctic Range in Antarctica. The MMs are present in abundances of ~600 particles kg⁻¹ of moraine sediment and include a near-complete collection of MM types similar to those observed in Antarctic blue ice and within bare-rock traps in the Antarctic. The size distribution of the observed particles is consistent with those collected from snow collections suggesting the moraine has captured a representative collection of cosmic spherules with significant loss of only the smallest particles (<100 μm) by wind. The presence of microtektites with compositions similar to those of the Australasian strewn field suggests the moraine has been accumulating for 780 ka with dust-sized debris. On the basis of this age estimate, it is suggested that accumulation occurs principally through ice sublimation. Direct infall of fines is suggested to be limited by snow layers that act as barriers to accumulation and can be removed by wind erosion. MM accumulation in many areas in Antarctica, therefore, may not be continuous over long periods and can be subject to climatic controls. On the basis of the interpretation of microtektites as Australasian, Larkman Nunatak deposit is the oldest known supraglacial moraine and its survival through several glacial maxima and interglacial periods is surprising. We suggest that stationary ice produced by the specific ice flow conditions at Larkman Nunatak explains its longevity and provides a new type of record of the East Antarctic ice sheet.     

用于测量圆顶视宁度的微温脉动仪的研制

为评价云南天文台丽江2.4m望远镜的圆顶视宁度,研制了一种能测量温度、气压和微温脉动的仪器。在天文圆顶附近,望远镜前方光路上,放置几组微温传感器,可以测得圆顶附近影响天文观测的湍流强度的分布情况。介绍了这套仪器的基本原理,电路设计,程序设计,实验定标以及一个简单的测试。     

Development of the Automatic Seeing Monitor for the Site Testing of Dome A

The Antarctic site-testing campaigns have shown that Dome C is an excellent astronomical site on the earth, it is better than any of existing mid-latitude astronomical sites in the world, because of its cold and dry weather, low infrared background radiation, continuously observable time as long as 3–4 months, clear and highly transparent atmosphere, low wind speed, and the absence of dust and light pollution. And in the international astronomical community it is generally believed that Dome A with a higher altitude may be better than Dome C as a potential excellent astronomical site. In the past 3 years, although held by the Center for Antarctic Astronomy of Chinese Academy of Sciences, the site testing at Dome A has preliminarily con?rmed the many advantages of Dome A as an excellent astronomical site, but the data about the atmospheric seeing, which is an important parameter for assessing the site quality for optical observations, have not been obtained until now. Hence, on the basis of a commercial telescope with the diameter of 35 cm, we have made the hardware reformation and software development to have it operate as a DIMM (Differential Image Motion Monitor), which can simultaneously monitor both the seeing and isoplanatic angle at Dome A automatically. At present this instrument has been shipped to Antarctica by the “Xuelong” exploration ship, and will be installed at Dome A, and begin to work in early 2011. Before the shipment, by through the comparative measurements together with an existing seeing monitor at the Xinglong astronomical station, the software, hardware, as well as the installation and adjustment of the instrument, are further veri?ed by testing.     

A comparison of simulated monsoon circulations and snow accumulation in Asia during the mid-Holocene and at the Last Glacial Maximum

Tropical climatology through the last glacial cycle is believed to have ranged from colder, windier conditions at the Last Glacial Maximum (LGM) to relatively warm, stable conditions during the Holocene. Changes in strength of the South Asian monsoon have previously been determined from a variety of proxy data and have been attributed primarily to changes in radiative forcing, although tropical sea surface temperature (SST) is known to play a fundamental role in regulating monsoon strength and is also believed to have changed throughout the late Quaternary.In this study, the monsoons simulated in a coupled atmosphere–ocean general circulation model (GCM) configured for the mid-Holocene (6000 years B.P.) and for the LGM (21,000 years B.P.) are compared. The colder and windier conditions simulated for the LGM produced a summer monsoon whose westerly winds are stronger and whose precipitation and snowfall into the eastern Himalaya are increased, with drier conditions over the rest of the Indian subcontinent and over most of southwest Asia.The mid-Holocene monsoon circulation is stronger than today, and annual mean snow accumulation is increased over the northwestern Himalaya. These changes in precipitation and snow accumulation are analyzed in terms of the altered atmospheric circulations, which are in turn driven by changes in radiative forcing, sea surface temperatures, and sea surface height. All of these factors are therefore demonstrated to be important in governing the spatial distribution of snow and ice deposition in the Himalaya during the late Quaternary, and are likely to have contributed to the observed asynchroneity of Himalayan glaciation and Northern Hemisphere ice sheet volume.     

Astronomy from Dome A in Antarctica

Dome A in Antarctica has been demonstrated to be the best site on earth for optical, infrared, and terahertz astronomical observations by more and more evidence, such as excellent free-atmosphere seeing,extremely low perceptible water vapor, low sky background, and continuous dark time, etc. In this paper,we present a complete picture of the development of astronomy at Dome A from the very beginning, review recent progress in time-domain astronomy, demonstrate exciting results of the site testing, and address the challenges in instrumentation. Currently proposed projects are briefly discussed.     

膜圆顶及塔架对南极望远镜风载影响的仿真分析

为了充分利用Dome A地区绝佳的视宁度条件, 计划将南极望远镜安装在15m高的塔架上并使用轻质膜圆顶. 研究了在塔架和膜圆顶作用下风载对望远镜观测环境的影 响, 利用计算流体力学(Computational Fluid Dynamics, CFD)分析了在10m·s^-1稳态风作用下,不同风向角、方位轴转动角以及镜筒转动角时,望远镜周围风速、湍动能的分布情况以及光程差的变化,同时研究了风屏对风速、湍动能的改善作用和带来的温升.结果表明,塔架和圆顶周围的风速与湍动能分布对风向的改变不敏感;迎风状态时望远镜附近的湍流分布与风速分布情况整体优于背风状态;当风速为10m·s^-1时,在距离风屏1m远、3m高的位置处风速降为来流风速的1/3至1/4,望远镜附近的平均温升值为0.044 K.     

Nitrate in Polar Ice: A New Tracer of Solar Variability

Knowledge of the long-term variability of solar activity is of both astrophysical and geoscientific interest. Reconstructions of solar activity over multiple millennia are traditionally based on cosmogenic isotopes ¹⁴C or ¹⁰Be measured in natural terrestrial archives, but the two isotopes exhibit significant differences on millennial time scales, so that our knowledge of solar activity at this time scale remains somewhat uncertain. Here we present a new potential proxy of solar activity on the centennial-millennial time scale, based on a chemical tracer, viz. nitrate content in an ice core drilled at Talos Dome (Antarctica). We argue that this location is optimal for preserving the solar signal in the nitrate content during the Holocene. By using the firn core from the same location we show that the 11-year and Gleissberg cycles are present with the variability of 10??C?25?% in nitrate content in the pre-industrial epoch. This is consistent with the results of independent efforts of modeling HNO₃ and NO _y in Antarctic near surface air. However, meteorological noise on the interannual scale makes it impossible to resolve individual solar cycles. Based on different processes of formation and transport compared to cosmogenic isotopes, it provides new, independent insight into long-term solar activity and helps resolve the uncertainties related to cosmogenic isotopes as diagnostics of solar activity.     

基于图像相减和随机森林的AST3巡天暂现源及变源搜寻方法

AST3-2 (Antarctic Survey Telescopes)光学巡天望远镜位于南极大陆最高点冰穹A,其产生的大量观测数据对数据处理的效率提出了较高要求.同时南极通信不便,数据回传有诸多困难,有必要在南极本地实现自动处理AST3-2观测数据,进行变源和暂现源观测的数据处理,但是受到低功耗计算机的限制,数据的快速自动处理的实现存在诸多困难.将已有的图像相减方案同机器学习算法相结合,并利用AST3-2 2016年观测数据作为测试样本,发展一套的暂现源及变源的筛选方法成为可行的选择.该筛选方法使用图像相减法初步筛选出可能的变源,再用主成分分析法抽取候选源的特征,并选择随机森林作为机器学习分类器,在测试中对正样本的召回率达到了97%,验证了这种方法的可行性,并最终在2016年观测数据中探测出一批变星候选体.     

An Automatic Method for Detecting Transients and Variable Sources in AST3 Survey Based on Image Subtraction and Random Forest

AST3-2 (the second Antarctic Survey Telescope) is located in Antarctic Dome A, the loftiest ice dome on the Antarctic Plateau. It produces a huge amount of observational data which require a more efficient data reduction program to be developed. Also the data transmission in Antarctica is much difficult, thus it is necessary to perform data reduction and detect variable and transient sources remotely and automatically in Antarctica, but this attempt is restricted by the unsatisfactory performance of the low power consumption computer in Antarctica. For realizing this purpose, to develop a new method based on the existing image subtraction method and random forest algorithm, taking the AST3-2 2016 dataset as the test sample, becomes an alternative choice. This method performs image subtraction on the dataset, then applies the principle component analysis to extract the features of residual images. Random forest is used as a machine learning classifier, and in the test a recall rate of 97% is resulted for the positive sample. Our work has verified the feasibility and accuracy of this method, and finally found out a batch of candidates for variable stars in the AST3-2 2016 dataset.     

Volcanic eruption frequency over the last 45 ky as recorded in Epica-Dome C ice core (East Antarctica) and its relationship with climatic changes

The sulphate glacio-chemical profiles constitute a reliable proxy marker for reconstruction of past volcanic history, assuming a reliable method to distinguish sulphate spikes and to evaluate the flux of individual events is set up. The resulting volcanic event profile is used to reconstruct past event frequencies, and to investigate possible links between volcanism and climatic changes. Volcanic event signatures are useful also in comparing time scales from ice cores drilled at different locations. In this paper, a new method to pick out volcanic signals is proposed. It improves on methods based on the calculation of a threshold using a general mean value plus a multiple of the standard deviation by adding: (1) quantification of nonvolcanic sulphate contributions; (2) sulphate fluxes, instead of concentrations, accounting for accumulation rate changes; (3) data treatment using a log-normal statistic, instead of a Gaussian-type distribution, to take into account the real sulphate distribution; (4) a smoothed curve (weighted fitting) to better understand the residual variability of the sulphate background.This method is used to detect volcanic events throughout the 45 ky time span of the EDC96 ice core, drilled at Dome C on the East Antarctic plateau. A total of 283 volcanic signatures are recovered, with a mean of 6.3 events per millennium. The temporal event frequencies indicate that the last 2000 years were probably characterized by the highest volcanic activity in the period covered by the core and that there is no clear link between number of events recorded and climatic changes.     

Comparison of the atmosphere above the South Pole, Dome C and Dome A: first attempt

The atmospheric properties above three sites (Dome C, Dome A and the South Pole) on the Internal Antarctic Plateau are investigated for astronomical applications using the monthly median of the analyses from ECMWF (the European Centre for Medium-Range Weather Forecasts). Radiosoundings extended on a yearly time-scale at the South Pole and Dome C are used to quantify the reliability of the ECMWF analyses in the free atmosphere as well as in the boundary and surface layers, and to characterize the median wind speed in the first 100 m above the two sites. Thermodynamic instability properties in the free atmosphere above the three sites are quantified with monthly median values of the Richardson number. We find that the probability to trigger thermodynamic instabilities above 100 m is smaller on the Internal Antarctic Plateau than on mid-latitude sites. In spite of the generally more stable atmospheric conditions of the Antarctic sites compared to mid-latitude sites, Dome C shows worse thermodynamic instability conditions than those predicted above the South Pole and Dome A above 100 m. A rank of the Antarctic sites done with respect to the strength of the wind speed in the free atmosphere (ECMWF analyses) as well as the wind shear in the surface layer (radiosoundings) is presented.     

Telescope and instrument robotization at Dome C

This article reviews the situation for robotization of telescopes and instruments at the Antarctic station Concordia on Dome C. A brain‐storming meeting was held in Tenerife in March 2007 from which this review emerged.We describe and summarize the challenges for night‐time operations of various astronomical experiments at conditions “between Earth and Space” and conclude that robotization is likely a prerequisite for continuous astronomical data taking during the 2000‐hour night at Dome C. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Open‐foldable domes with high‐tension textile membranes: The GREGOR dome

Double layers of high‐tensioned textile membranes were applied to the completely open‐foldable dome for the GREGOR telescope for the first time. Simultaneous climate measurements inside and outside the dome have proven the thermalinsulating capability of this double‐layer construction. The GREGOR dome is the result of the continuation of the ESO research on open‐foldable domes with textile structures, followed by the research for the DOT dome with high‐tensioned textile membranes. It cleared the way to extreme stability required for astronomical practice on high mountain sites with heavy storms and ice formation. The storm Delta with 245 km/h 1‐minute mean maximum at the location of the GREGOR caused no problems, nor did other storms afterwards. Opening and closing experiences up to wind speeds of 90 km/h were without problems. New technical developments were implemented and tested at the GREGOR dome, opening the way for application to much larger domes up to the 30 m diameter‐class range (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dome C's Atmospheric Conditions: Implications for Astronomy

The expectation that exceptional conditions for astronomy would be found at Dome C on the high Antarctic plateau has motivated a coordinated effort by a number of international teams to comprehensively measure the atmospheric conditions at this site. This paper presents an overview of the current status of site testing at Dome C. We discuss the past, present, and planned instrumentation, the main results obtained to date, and the implications of these results.     

Evidence of individual solar proton events in Antarctic snow

The high-resolution nitrate analyses of a snow sequence in Antarctica reveals clear evidence that the snow contains a chemical record of ionization from charged particles incident upon the upper atmosphere of the Earth. The Antarctic continent acts as a cold trap that effectively freezes out this signal and retains it in the stratigraphy of the ice shelves and the continental ice sheet. The signal that we measure results from the ionization of nitrogen and oxygen, the two primary constituents of the Earth's atmosphere, which subsequently react to form oxides of nitrogen. A large portion of the nitrogen oxides produced are ultimately oxidized to nitric acid and incorporated in snow crystals together with nitrates from tropospheric sources that also contribute to the general background. The nitrate concentration in a firn core was measured in Antarctica by ultraviolet spectrophotometry under tightly controlled experimental procedures. Based on uninterrupted, high-resolution sampling, variations in nitrate concentration were found to average about 53% (one standard deviation) of the mean concentration for the entire core. Short pulses of high nitrate concentration were found to show a variance of up to 11 standard deviations above the mean. At the series mean, the precision of analysis is better than 2%.The firn core was drilled by hand to a depth of 21.7 m corresponding to 62 years and including more than 5 solar cycles. The time series that resulted from a total of 1393 individual analyses shows a statistically significant modulation of the background signal that is clearly tracable to solar activity. Several anomalously large concentration peaks were observed that have been dated and found to correlate with the major solar proton events of August 1972, July 1946, and the white-light flare of July 1928.     

南极冰穹A首台自动视宁度检测仪的研制

南极冰穹C (Dome C)的选址结果显示:Dome C具有寒冷干燥、红外背景辐射低、可连续3～4个月观测、空气明净、透过率高、风速低等特征,是比地面上任何中纬度台址都好的天文观测台址.而由我国最先登陆的内陆最高点冰穹A (Dome A)被国际天文界广泛认为可能是比Dome C更好的天文台址.近3 yr来,中国科学院南极天文中心领导开展Dome A的台址测量工作,初步结果表明Dome A作为天文台址具有巨大优势.但是到目前还没有获得直接用于衡量天文台址在光学观测方面的主要参数—视宁度数据.介绍了中国科学院南京天文光学技术研究所自行研制的我国首个用于Dome A的自动视宁度测量仪,基于一台口径35 cm的商用望远镜进行硬件改造和软件开发,使其能在Dome A低温低压环境下进行自动观测和数据处理.目前该仪器已随“雪龙号,科考船起运南极,于2011年初安装到Dome A并开始测量.起运前,在兴隆观测站与中国科学院国家天文台(国台)选址组的一台视宁度监测仪进行了对比测量,对软件、硬件和装调方法进行了检验验证.