Modelling the effect of changing precipitation inputs on deep soil water utilization

Forests in the Southeastern United States are predicted to experience future changes in seasonal patterns of precipitation inputs as well as more variable precipitation events. These climate change‐induced alterations could increase drought and lower soil water availability. Drought could alter rooting patterns and increase the importance of deep roots that access subsurface water resources. To address plant response to drought in both deep rooting and soil water utilization as well as soil drainage, we utilize a throughfall reduction experiment in a loblolly pine plantation of the Southeastern United States to calibrate and validate a hydrological model. The model was accurately calibrated against field measured soil moisture data under ambient rainfall and validated using 30% throughfall reduction data. Using this model, we then tested these scenarios: (a) evenly reduced precipitation; (b) less precipitation in summer, more in winter; (c) same total amount of precipitation with less frequent but heavier storms; and (d) shallower rooting depth under the above 3 scenarios. When less precipitation was received, drainage decreased proportionally much faster than evapotranspiration implying plants will acquire water first to the detriment of drainage. When precipitation was reduced by more than 30%, plants relied on stored soil water to satisfy evapotranspiration suggesting 30% may be a threshold that if sustained over the long term would deplete plant available soil water. Under the third scenario, evapotranspiration and drainage decreased, whereas surface run‐off increased. Changes in root biomass measured before and 4 years after the throughfall reduction experiment were not detected among treatments. Model simulations, however, indicated gains in evapotranspiration with deeper roots under evenly reduced precipitation and seasonal precipitation redistribution scenarios but not when precipitation frequency was adjusted. Deep soil and deep rooting can provide an important buffer capacity when precipitation alone cannot satisfy the evapotranspirational demand of forests. How this buffering capacity will persist in the face of changing precipitation inputs, however, will depend less on seasonal redistribution than on the magnitude of reductions and changes in rainfall frequency.     

CCD联合平差方法及其初步实例检验

在常规照相天体测量工作中 ,对暗天体的定位是采用逐级定标星过渡的方法实现的。由于星表系统差和局部差的存在 ,最终定位结果可能包含难以把握的误差积累。在CCD小视场观测情况下时常难以找到足够数量的定标星。鉴于此 ,推导了CCD观测联合平差方法的严格矢量表达式 ,以期通过共同星的过渡 ,实现大天区统一平差。原理上此方法可实现相对于河外天体的定位 ,以削弱星表系统差和局部差对定位结果的影响。讨论了CCD联合平差方法实现中的问题 ,包括底片常数模型选择、切点位置改正、共同星的较差改正和法方程解算方法等 ,并分析了具体的处理措施。用实例初步检验了CCD联合平差方法的效果 ,表明通过对多张CCD观测的联合平差 ,可以削弱单张CCD观测参考星数目过少、单张CCD观测参考星分布不均、个别参考星存在位置偏差和局部区域参考星存在系统性位置偏差等不利因素对归算结果的影响 ,进而达到扩大视场和提高归算精度的目的     

FITS、BMP和SCR图象格式及相互转换

本文详细介绍图象的ＦＩＴＳ格式、ＢＭＰ格式和ＳＣＲ格式。ＦＩＴＳ格式已经是天文界的通用格式，几乎所有的天文软件包都支持这一格式，而ＢＭＰ格式在ＰＣ计算机上有广泛的运用，有大量ＰＣ软件支持ＢＭＰ图象的显示，处理和打印。云南天文台的ＳＣＲ格式是ＰＣ机采集ＣＣＤ图象所使用的格式。实现这三种格式的相互转换，就可以自由的将ＣＣＤ图象在ＰＣ机和工作站上进行各种处理。转换的包括图象头和图象数据的转换，其关键在于交换数据的高低字节。     

A rope-shaped solar filament and a IIIb flare

On September 14–18, 2000, a medium-small solar active region was observed at Ganyu Station of Purple Mountain Observatory. Its spots were not large, but it had a peculiar active filament. On Sep.16, a flare of importance III_b with rather intense geophysical effects was produced. Our computation of the magnetic structure of the active region reveals that the rope-shaped filament was concerned with a low magnetic arc close to magnetic neutral line. An intense shear of magnetic field occurred near magnetic rope. The QSL analysis shows that a 3-D magnetic reconnection might appear in the vicinity of filament, and this can be used to interpret the formation of a large flare.     

无外加流体、350℃和差异应力条件下硫化物再活化实验研究

红透山块状硫化物矿石主要成分为黄铁矿、磁黄铁矿、黄铜矿、闪锌矿和石英、角闪石、黑云母等脉石矿物。将此矿石烘干后作为试料置于岩石三轴应力试验机,在13h内将轴压、围压和温度分步升至1276MPa、414MPa和350℃,然后在空气中自然冷却至室温。实验产物中黄铁矿、石英、长石等以脆性碎裂为主,而磁黄铁矿、黄铜矿、闪锌矿和云母等以塑性变形为主。再活化的黄铜矿、磁黄铁矿和少量闪锌矿呈脉和网脉穿插黄铁矿碎斑。实验结果表明,即使没有外来流体加入．构造动力作用所导致的流体包裹体破坏所释出的流体,就足以使成矿物质发生活化转移和再活化。     

采用钻孔倾斜仪监测滑坡深部水平位移方法和仪器的研究

介绍了目前滑坡深部水平位移钻孔倾斜仪人工监测方法存在的问题,钻孔深部位移自动化监测通信方法的选择。地质滑坡灾害监测中广泛使用钻孔倾斜仪,介绍了CZ-2型钻孔倾斜仪的构成及现场测试方法。     

绿片岩-低角闪岩相变质条件下磁铁铁矿与黄铁矿间的Fe同位素分馏

对辽宁省鞍山一本溪地区经历了绿片岩一低角闪岩相变质的新太古代条带状铁建造中磁铁矿和黄铁矿矿物对的Fe同位素分析结果显示:相对于标准IRMM-014,所有样品的磁铁矿和黄铁矿均显示Fe的重同位素富集;且黄铁矿的Fe同位素比值均大于磁铁矿的Fe同位素比值(ε57Fe黄铁矿ε57Fe磁铁矿),两种矿物的Fe同位素比值之差为△57Fe黄铁矿-磁铁矿=2.23～5.13.黄铁矿富集铁的重同位素表明矿物的Fe同位素组成并不代表其原始沉积的特征,而是在区域变质作用过程中Fe同位素发生了交换的结果.由同位素平衡判别图解可知,在绿片岩一低角闪岩相变质作用中,磁铁矿-黄铁矿间的Fe同位素基本达到了平衡,且在平衡条件下黄铁矿比磁铁矿更富集Fe的重同位素,二者之间的Fe同位素平衡分馏系数α黄铁矿-磁铁矿≈1.000 4‰±0.06‰(2σ).这一研究成果是对变质作用过程中Fe同位素的地球化学行为认识的重要进展.     

斜向波对直立式防波堤堤头作用的试验研究

直立式防波堤堤头在斜向波浪作用下波浪力的计算在现行的技术规范中尚属空白。通过物理模型试验给出了堤头结构设计所需的波压分布图，指出了波浪入射方向和地形对堤头所受波浪力的贡献有时可以超过波高和波周期，根据现行规范按波浪正向入射计算堤头所受的波浪力偏于安全。     

棉兰老涡旋的数值模拟

用一个水平分辨率比较高的非线性正压模式,对热带西太平洋海域里的海流进行了数值模拟。计算海流与观测结果颇相一致。结果表明:赤道以北、棉兰老岛以东附近海域中,棉兰老冷涡在一年的大部分时间里都得到发展,但是其范围、强度和中心位置在各个月份并不相同,显示出很强的季节变化;在哈马黑拉岛东北海域,6月份突然出现了一个反气旋式的涡旋;这个涡旋8月份发展得最强,一直持续到10月份,在11月份就消亡了。