青藏高原影响亚洲夏季气候研究的最新进展

文中回顾了近 10a来吴国雄等在青藏高原影响亚洲夏季气候研究方面的最新进展。通过分析东西风交界面的演变证明 ,由于青藏高原的春季加热 ,亚洲季风区对流层低层冬季盛行偏东风转变为夏季偏西南风最早发生在孟加拉湾东部 ,与其相伴随的激烈对流降水出现在其东面。因此孟加拉湾东部至中印半岛西部是亚洲季风最早爆发的地区。同时也指出盛夏伊朗高原和青藏高原加热所激发的同相环流嵌套在欧亚大陆尺度的热力环流中 ,从而加强了东亚的夏季风 ,加剧了中西亚的干旱 ;并通过其所激发的波动对夏季东亚的气候格局产生重要影响。文中还比较了夏季南亚高压的伊朗模态和青藏模态性质的异同及其对亚洲夏季降水异常分布的不同影响。     

The impact of hydrological changes on travertine deposits related to thermal springs in the Pamukkale area (SW Turkey)

Pamukkale thermal waters (35 °C), exhibiting calcium-bicarbonate-sulfate composition and high carbon dioxide concentration, are of a predominantly meteoric origin. The meteoric fluid, circulating through faults and fractures, is heated by magmatic intrusions at great depth, and ascends from deep reservoirs to the surface. Mixing with relatively cold groundwater in the near surface zone promotes different saturation conditions with respect to calcium carbonate that later precipitates at depth and/or the surface. Dissolution-deposition processes of calcium carbonate both at surface and depth environments may help to reconstruct past climate direction in the field. During wet climate conditions a high-rate of calcium carbonate accumulation would be expected to occur at the surface because thermal fluid would be under-saturated with respect to calcium carbonate at depth because of a relatively higher mixing ratio with cold groundwater. During dry climate conditions the thermal fluid would be super-saturated at depth because of the highly acidic environment. Hydrometeorological studies reveal that the annual precipitation at the Pamukkale hydrothermal field tends to decrease with time. This climatic change in the area was also detected from geological records. While humid climate conditions prevailed during the late Quaternary, the area has recently been affected by arid/semi-arid climate conditions, followed by some episodic transitions. This study has shown how the system has possibly reacted to different climate conditions since antiquity.     

Dynamics of an active rock glacier (Ötztal Alps, Austria)

The rock glacier Innere Ölgrube, located in a small side valley of the Kauner Valley (Ötztal Alps, Austria), consists of two separate, tongue-shaped rock glaciers lying next to each other. Investigations indicate that both rock glaciers contain a core of massive ice. During winter, the temperature at the base of the snow cover (BTS) is significantly lower at the active rock glacier than on permafrost-free ground adjacent to the rock glacier. Discharge is characterized by strong seasonal and diurnal variations, and is strongly controlled by the local weather conditions. Water temperature of the rock glacier springs remains constantly low, mostly below 1°C during the whole melt season. The morphology of the rock glaciers and the presence of meltwater lakes in their rooting zones as well as the high surface flow velocities of >1 m/yr point to a glacial origin. The northern rock glacier, which is bounded by lateral moraines, evolved from the debris-covered tongue of a small glacier of the Little Ice Age with its last highstand around A.D. 1850. Due to the global warming in the following decades, the upper parts of the steep and debris-free ice glacier melted, whereas the debris-covered glacier tongue transformed into an active rock glacier. Due to this evolution and due to the downslope movement, the northern rock glacier, although still active, at present is cut off from its ice and debris supply. The southern rock glacier has developed approximately during the same period from a debris-covered cirque glacier at the foot of the Wannetspitze massif.     

南极冰貌卫星影像条带噪声的剔除

本文在简要叙述条带噪声形成原因的基础上 ,针对南极地区的ASTER 1A的可见光影像中出现的条带噪声的现象 ,通过设计了基于切比雪夫窗、凯瑟窗的FIR滤波器和约束最小二乘FIR滤波器对其条带噪声进行剔除 ,这两种滤波器能够尽可能地剔除条带 ,同时使影像的灰度分布发生最小畸变。并通过与其他方法 (例如 :低通滤波 ,直方图匹配等 )比较 ,说明这两种滤波的方法优于其他的方法     

利用AMTIS数据反演植被和土壤温度

遥感陆面温度 (LST)是目前遥感界面临的重要课题 ,组分温度反演则为LST反演的主攻目标。如果混合像元组分间的温度及发射率存在明显差别 ,就可以从多角度热辐射亮度变化中分离出组分温度的信息。在热辐射矩阵模型的基础上 ,讨论了确定可反演参数和反演组分温度的方法 ,并以AMTIS多角度热红外图像为数据源 ,在进行几何和大气纠正后 ,尝试利用矩阵反演方法分解混合像元中的植被和土壤温度。误差分析表明土壤温度反演结果较好 ,但植被温度的反演精度不高     

Younger Dryas glaciolacustrine rhythmites and cirque glacier variations at Kråkenes, western Norway: depositional processes and climate

Kråkenes faces the open sea on the west coast of Norway. During the Younger Dryas a cirque glacier deposited a large outer and a smaller inner moraine in a cirque at the site and melt-water entered a small lake depositing glaciolacustrine sediments. The glaciolacustrine succession can be divided into three sub-units corresponding to the advance, the still-stand and the retreat phases of the glacier. The sediment succession contains both varves and other types of rhythmites, the latter being mainly deposited as turbidity underflows caused by localized slumping events. Lee-side accumulation of snow by wind and avalanching into the cirque was crucial to form and maintain the cirque glacier once summer temperatures were low enough. At maximum, the glacier likely was in equilibrium with climate. The initial retreat from the maximum position might have been triggered by fall-out of volcanic ash from Iceland, but the continued retreat was due to increased ablation season temperatures. The most rapid change in climate at the Younger Dryas/Preboreal transition occurred after the cirque glacier had melted away completely.     

Discrimination between climate and human-induced dryland degradation

In this study we present a technique to discriminate between climate or human-induced dryland degradation, based on evaluations of AVHRR NDVI data and rainfall data. Since dryland areas typically have high inter-annual rainfall variations and rainfall has a dominant role in determining vegetation growth, minor biomass trends imposed by human influences are difficult to verify. By performing many linear regression calculations between different periods of accumulated precipitation and the annual NDVI_max, we identify the rainfall period that is best related to the NDVI_max and by this the proportion of biomass triggered by rainfall. Positive or negative deviations in biomass from this relationship, expressed in the residuals, are interpreted as human-induced. We discuss several approaches that use either a temporally fixed NDVI peaking time or an absolute one, a best mean rainfall period for the entire drylands or the best rainfall period for each individual pixel. Advantages and disadvantages of either approach or one of its combinations for discriminating between climate and human-induced degradation are discussed. Depending on the particular land-use either method has advantages. To locate areas with a high likelihood of human-induced degradation we therefore recommend combining results from each approach.     

开封大雾气候特征及预报

利用1961～2000年气象资料，分析了开封市大雾天气分布规律、天气特征，并总结出大雾产生的几种天气形势，找出预报指标。     

Historical measurements of the Earth's magnetic field compared with remanence directions from lava flows in Italy over the last four centuries

Direct measurements of the Earth's magnetic field in Italy since 1640 a.d. have been used to check the remanence directions derived from historically dated volcanic rocks of Etna and Vesuvius. Direct measurements consist of the records of L’Aquila and Pola geomagnetic observatories, the repeat stations of the Italian Magnetic Network and the data base of the Historical Italian Geomagnetic Data Catalogue. All have been relocated to the same reference site (Viterbo — lat. 42.45°N, long. 12.03°E) in order to draw a reference secular variation (SV) curve. The direction of the Earth's field at Viterbo has also been calculated from the historical records (2000-1600) of ref. [Jackson, A., Jonkers, A.R.T., Walker, M.R., 2000. Four centuries of geomagnetic secular variation from historical records. Phil. Trans. R. Soc. London, Ser. A 358, 957-990] database. The remanence directions from Etna show a general agreement with the trend of the SV curve, although their inclination is usually lower than that from the direct measurement. The directions from Vesuvius are more scattered. Large discrepancies occur at both volcanoes and in some cases have been ascribed in the literature to poor geographic information, making it difficult to identify the flows actually emplaced during the eruptions reported in the chronicles. Closer examination shows that the great majority of the best-defined remanence directions (semi-angle of confidence α₉₅ < 2.5°) deviate significantly from the geomagnetic direction measured at the time of the emplacement, the angle between the two directions being larger than the α₉₅ value. The value of 2.5-3.0° can thus be regarded as a conservative evaluation of the error when dealing with dating Etna and Vesuvius lava flows older than 17th century, even when the accuracy attained in remanence measurements is higher. In default of a SV curve for Italy derived from archaeological artefacts, a further error in dating is introduced when reference is made to SV curves of other countries, even if well-established, as these are from regions too far from Italy (>600 km) to confidently relocate magnetic directions.     

Leaf area index retrieval based on canopy reflectance and vegetation index in eastern China

The aim of this paper is to investigate the feasibility of using Landsat TM data to retrieve leaf area index (LAI). To get a LAI retrieval model based ground reflectance and vegetation index, detailed field data were collected in the study area of eastern China, dominated by bamboo, tea plant and greengage. Plant canopy reflectance of Landsat TM wavelength bands has been inversed using software of 6S. LAI is an important ecological parameter. In this paper, atmospheric corrected Landsat TM imagery was utilized to calculate different vegetation indices (VI), such as simple ratio vegetation index (SR), shortwave infrared modified simple ratio (MSR), and normalized difference vegetation index (NDVI). Data of 53 samples of LAI were measured by LAI-2000 (LI-COR) in the study area. LAI was modeled based on different reflectances of bands and different vegetation indices from Landsat TM and LAI samples data. There are certainly correlations between LAI and the reflectance of Tm3, TM4, TM5 and TM7. The best model through analyzing the results is LAI = 1.2097*MSR + 0.4741 using the method of regression analysis. The result shows that the correlation coefficient R2 is 0.5157, and average accuracy is 85.75%. However, whether the model of this paper is suitable for application in subtropics needs to be verified in the future.