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121.
It is well known that the interaction of an interplanetary coronal mass ejection (ICME) with the solar wind leads to an equalisation
of the ICME and solar wind velocities at 1 AU. This can be understood in terms of an aerodynamic drag force per unit mass
of the form F
D/M=−(ρe
AC
D/M)(V
i−V
e)∣V
i−V
e∣, where A and M are the ICME cross-section and sum of the mass and virtual mass, V
i and V
e the speed of the ICME and solar wind, ρe the solar wind density, C
D a dimensionless drag coefficient, and the inverse deceleration length γ=ρe
A/M. The optimal radial parameterisation of γ and C
D beyond approximately 15 solar radii is calculated. Magnetohydrodynamic simulations show that for dense ICMEs, C
D varies slowly between the Sun and 1 AU, and is of order unity. When the ICME and solar wind densities are similar, C
D is larger (between 3 and 10), but remains approximately constant with radial distance. For tenuous ICMEs, the ICME and solar
wind velocities equalise rapidly due to the very effective drag force. For ICMEs denser that the ambient solar wind, both
approaches show that γ is approximately independent of radius, while for tenuous ICMEs, γ falls off linearly with distance.
When the ICME density is similar to or less than that in the solar wind, inclusion of virtual mass effects is essential. 相似文献
122.
In this paper, the relationships between paleo-precipitation and the regional influence of El Nino Southern Oscillation (ENSO)
in South America are assessed from a high-resolution calendar varve-thickness record. Two short laminated sediment cores (53
and 61 cm length) from Lago Puyehue (40° S) are analysed by continuous varve measurements through the last 600 years. The
calendar varve years are determined by the occurrence of graded planktonic-rich layers. The annual sediment accumulation rates
are reconstructed by using the standard varve-counting methods on thin sections. The 1980–2000 varve-thickness record is interpreted
in terms of climate through correlation with limnological and local monthly instrumental climate databases. The comparison
between the standardized varve thickness with the instrumental records reveals a strong correlation (r = 0.75, р = 0.07) between the total varve thickness and the austral autumn/winter precipitation. We argue that strong austral winter
winds and precipitation are the forcing factors for the seasonal turn-over and phytoplankton increase in the lake sediments.
During strong El Nino events the precipitation and the winds decrease abnormally, hence reducing the thickness of the biogenic
sediments deposited after the winter turn-over. Our results show one significant regional maximum peak of winter precipitation
(>900 mm) in the mid 20th century and a significant period with lower winter precipitation (<400 mm) before the 15th century,
i.e., the late Medieval Warm Period. The first peak in the mid 20th century is confirmed by the regional precipitation database.
The influence of ENSO cycles over the last 600 years is assessed by spectral analysis in Fagel et al. (2007). The possible influence of the regional volcanism and/or the seismic activity on the local climate record is also discussed.
This is the sixth in a series of eight papers published in this special issue dedicated to the 17,900 year multi-proxy lacustrine record of
Lago Puyehue, Chilean Lake District. The papers in this special issue were collected by M. De Batist, N. Fagel, M. -F. Loutre
and E. Chapron. 相似文献
123.
Lucien von Gunten Oliver Heiri Christian Bigler Jacqueline van Leeuwen Carlo Casty André F. Lotter Michael Sturm 《Journal of Paleolimnology》2008,39(3):283-299
We analysed a 42 cm long sediment record from Lej da la Tscheppa, a high-altitude lake (2,616 m a.s.l.) in the Upper Engadine
valley (Switzerland) for subfossil diatoms, chironomids and pollen. The chronology of the top 21 cm of the record was established
using 210Pb analysis using a constant-rate-of-supply model, and validated with 137Cs measurements and the content of spheroidal carbonaceous particles. A tentative chronology for the lower part of the core
was obtained through extrapolation of the sedimentation rates in the uppermost part of the record. Pollen assemblages in the
record reflect regional changes in forestation and land-use patterns in the Upper Engadine valley and show no evidence of
significant local human activity in the lake’s catchment. Diatom assemblages record a distinct increase in planktonic taxa
since the early 19th century, suggesting a decrease in the duration of ice-cover. In contrast, chironomid assemblages remained
stable during a large part of the record. We applied an established chironomid-based July air temperature transfer function
and a newly developed diatom-based spring air temperature transfer function to reconstruct past seasonal air temperature changes
at Lej da la Tscheppa. The reconstructions indicate a diatom-inferred warming trend in spring temperatures during the past
ca. 400 years, whereas chironomid-inferred summer temperatures suggest a slight cooling trend. These biota-based reconstructions
are in good agreement with the centennial-scale temperature trend in an independent reconstruction of regional temperatures
in the Upper Engadine region based on instrumental records and documentary proxy evidence from the Alps. Our results suggest
that, in high-altitude lakes, independent chironomid- and diatom-based seasonal temperature reconstruction is possible and
can be successfully used to track seasonal temperature trends. 相似文献
124.
The sedimentary and tectonic evolution of the Amur River and North Sakhalin Basin: new evidence from seismic stratigraphy and Neogene–Recent sediment budgets 下载免费PDF全文
Uisdean Nicholson Bas van der Es Peter D. Clift Rachel Flecker David I. M. Macdonald 《Basin Research》2016,28(2):273-297
The North Sakhalin Basin in the western Sea of Okhotsk has been the main site of sedimentation from the Amur River since the Early Miocene. In this article, we present regional seismic reflection data and a Neogene–Recent sediment budget to constrain the evolution of the basin and its sedimentary fill, and consider the implications for sediment flux from the Amur River, in particular testing models of continental‐scale Neogene drainage capture. The Amur‐derived basin‐fill history can be divided into five distinct stages: the first Amur‐derived sediments (>21–16.5 Ma) were deposited during a period of transtension along the Sakhalin‐Hokkaido Shear Zone, with moderately high sediment flux to the basin (71 Mt year?1). The second stage sequence (16.5–10.4 Ma) was deposited following the cessation of transtension, and was characterised by a significant reduction in sediment flux (24 Mt year?1) and widespread retrogradation of deltaic sediments. The third (10.4–5.3 Ma) and fourth (5.3–2.5 Ma) stages were characterised by progradation of deltaic sediments and an associated increase in sediment flux (48–60 Mt year?1) to the basin. Significant uplift associated with regional transpression started during this time in southeastern Sakhalin, but the north‐eastward propagating strain did not reach the NE shelf of Sakhalin until the Pleistocene (<2.5 Ma). This uplift event, still ongoing today, resulted in recycling of older deltaic sediments from the island of Sakhalin, and contributed to a substantially increased total sediment flux to the adjacent basinal areas (165 Mt year?1). Adjusted rates to discount these local erosional products (117 Mt year?1) imply an Amur catchment‐wide increase in denudation rates during the Late Pliocene–Pleistocene; however, this was likely a result of global climatic and eustatic effects, combined with tectonic processes within the Amur catchment and possibly a smaller drainage capture event by the Sungari tributary, rather than continental‐scale drainage capture involving the entire upper Amur catchment. 相似文献
125.
Researches on breaking-induced currents by waves are summarized firstly in this paper. Then, a combined numerical model in orthogonal curvilinear coordinates is presented to simulate wave-induced current in areas with curved boundary or irregular coastline. The proposed wave-induced current model includes a nearshore current module established through orthogonal curvilinear transformation form of shallow water equations and a wave module based on the curvilinear parabolic approximation wave equation. The wave module actually serves as the driving force to provide the current module with required radiation stresses. The Crank-Nicolson finite difference scheme and the alternating directions implicit method are used to solve the wave and current module, respectively. The established surf zone currents model is validated by two numerical experiments about longshore currents and rip currents in basins with rip channel and breakwater. The numerical results are compared with the measured data and published numerical results. 相似文献
126.
Anantha Chanumolu Sivarani Thirupathi Damien Jones Sunetra Giridhar Deon Grobler Robert Jakobsson 《Experimental Astronomy》2017,43(1):39-58
As a continuation to the published work on model based calibration technique with HESP(Hanle Echelle Spectrograph) as a case study, in this paper we present the performance results of the technique. We also describe how the open parameters were chosen in the model for optimization, the glass data accuracy and handling the discrepancies. It is observed through simulations that the discrepancies in glass data can be identified but not quantifiable. So having an accurate glass data is important which is possible to obtain from the glass manufacturers. The model’s performance in various aspects is presented using the ThAr calibration frames from HESP during its pre-shipment tests. Accuracy of model predictions and its wave length calibration comparison with conventional empirical fitting, the behaviour of open parameters in optimization, model’s ability to track instrumental drifts in the spectrum and the double fibres performance were discussed. It is observed that the optimized model is able to predict to a high accuracy the drifts in the spectrum from environmental fluctuations. It is also observed that the pattern in the spectral drifts across the 2D spectrum which vary from image to image is predictable with the optimized model. We will also discuss the possible science cases where the model can contribute. 相似文献
127.
Impacts of Climatic Factors on Runoff Coefficients in Source Regions of the Huanghe River 总被引:4,自引:0,他引:4
CHEN Liqun LIU Changming LI Yanping WANG Guoqiang 《中国地理科学(英文版)》2007,17(1):047-055
Runoff coefficients of the source regions of the Huanghe River in 1956–2000 were analyzed in this paper. In the 1990s runoff of Tangnaihai Hydrologic Station of the Huanghe River experienced a serious decrease, which had at- tracted considerable attention. Climate changes have important impact on the water resources availability. From the view of water cycling, runoff coefficients are important indexes of water resources in a particular catchment. Kalinin baseflow separation technique was improved based on the characteristics of precipitation and streamflow. After the separation of runoff coefficient (R/P), baseflow coefficient (Br/P) and direct runoff coefficient (Dr/P) were estimated. Statistic analyses were applied to assessing the impact of precipitation and temperature on runoff coefficients (including Dr/P, Br/P and R/P). The results show that in the source regions of the Huanghe River, mean annual baseflow coefficient was higher than mean annual direct runoff coefficient. Annual runoff coefficients were in direct proportion to annual pre- cipitation and in inverse proportion to annual mean temperature. The decrease of runoff coefficients in the 1990s was closely related to the decrease in precipitation and increase in temperature in the same period. Over different sub-basins of the source regions of the Huanghe River, runoff coefficients responded differently to precipitation and temperature. In the area above Jimai Hydrologic Station where annual mean temperature is –3.9oC, temperature is the main factor in- fluencing the runoff coefficients. Runoff coefficients were in inverse relation to temperature, and precipitation had nearly no impact on runoff coefficients. In subbasin between Jimai and Maqu Hydrologic Station Dr/P was mainly affected by precipitation while R/P and Br/P were both significantly influenced by precipitation and temperature. In the area be-tween Maqu and Tangnaihai hydrologic stations all the three runoff coefficients increased with the rising of annual precipitation, while direct runoff coefficient was inversely proportional to temperature. In the source regions of the Huanghe River with the increase of average annual temperature, the impacts of temperature on runoff coefficients be-come insignificant. 相似文献
128.
APPLICATION OF ANALYTIC HIERARCHY PROCESS TO ASSESSING THE ECOLOGICAL VULNERABILITY OF WETLANDS IN THE JIANGHAN PLAIN 总被引:4,自引:1,他引:4
WANGXue-lei NINGLong-mei HUWang-bin 《中国地理科学(英文版)》2003,13(3):272-276
Wetlands in the Jianghan Plain are important components of wetland types in lake area in the middle and lower reaches the Changjiang (Yangtze) River and they fulfill many uses and functions related to hydrology,waste assimilation, ecosystem productivity and biodiversity. Owing to natural factors and human activities, especially excessive reclamation from lakes, the shrinking process of the lakes has been accelerated. Wetland ecosystem has shown the characteristics of vulnerability. According to the analysis of wetland ecological function in the Jianghan Plain, this paper presented an index system related to productivity, stability and environmental capacity. By using the method of Analytic Hierarchy Process, we computed the values of the relative weights of the indexes, and evaluated the vulnerability level of the wetland ecosystem by the method of multi-indexes. The case study showed that the fragile extent of wetland ecosystem in the Jianghan Plain is 5.6. This means that the wetland ecosystem in the Jiang-han Plain is laid to the state of middle vulnerability. Therefore, the wetland conservation and eco-rehabilitation in the JiangJaan Plain should be paid attention to. 相似文献
129.
T. Wiegelmann S. K. Solanki J. M. Borrero H. Peter P. Barthol A. Gandorfer V. Martínez Pillet W. Schmidt M. Knölker 《Solar physics》2013,283(2):253-272
Observations with the balloon-borne Sunrise/Imaging Magnetograph eXperiment (IMaX) provide high spatial resolution (roughly 100 km at disk center) measurements of the magnetic field in the photosphere of the quiet Sun. To investigate the magnetic structure of the chromosphere and corona, we extrapolate these photospheric measurements into the upper solar atmosphere and analyze a 22-minute long time series with a cadence of 33 seconds. Using the extrapolated magnetic-field lines as tracer, we investigate temporal evolution of the magnetic connectivity in the quiet Sun’s atmosphere. The majority of magnetic loops are asymmetric in the sense that the photospheric field strength at the loop foot points is very different. We find that the magnetic connectivity of the loops changes rapidly with a typical connection recycling time of about 3±1 minutes in the upper solar atmosphere and 12±4 minutes in the photosphere. This is considerably shorter than previously found. Nonetheless, our estimate of the energy released by the associated magnetic-reconnection processes is not likely to be the sole source for heating the chromosphere and corona in the quiet Sun. 相似文献
130.
In Asia, the intensity and style of active tectonics appears to depend on the age of the last orogenic activity. The shields have remained essentially undeformed during the India-Eurasian collision, but Paleozoic and Mesozoic orogenic belts apparently have been reactivated by this collision, with a suggestion of greater reactivation and more diffuse deformation of the younger belts. If the greater observed heat flow in regions of more recent orogenic activity reflects, at least in part, a greater heat flow from the mantle beneath the younger belts, then the temperatures in the mantle beneath the younger belts should be higher than beneath older belts and shields. Because of the strong dependence on temperature of the creep strength of minerals, particularly of olivine, the crust and mantle beneath the hotter, younger belts should be much weaker than those beneath older belts. This difference in temperature, and consequent difference in strength, may be the cause of the greater reactivation of younger belts. 相似文献