Changes in trophic flow structure of Independence Bay (Peru) over an ENSO cycle

During the strong warm El Niño (EN) that occurred in 1997/98, Independence Bay (14°S, Peru) showed a ca. 10 °C increase in surface temperatures, higher oxygen concentrations, and clearer water due to decreased phytoplankton concentrations. Under these quasi-tropical conditions, many benthic species suffered (e.g. macroalgae, portunid crabs, and polychaetes) while others benefited (e.g. scallop, sea stars, and sea urchins). The most obvious change was the strong recruitment success and subsequent proliferation of the scallop Argopecten purpuratus, whose biomass increased fiftyfold. To understand these changes, steady-state models of the bay ecosystem trophic structure were constructed and compared for a normal upwelling year (1996) and during an EN (1998), and longer-term dynamics (1996–2003) were explored based on time series of catch and biomass using Ecopath with Ecosim (EwE) software. Model inputs were based on surveys and landings data collected by the Instituto del Mar del Perú (IMARPE). Results indicate that while ecosystem size (total throughput) is reduced by 18% during EN, mainly as a result of decreased total primary production, benthic biomass remains largely unchanged despite considerable shifts in the dominant benthic taxa (e.g. scallops replace polychaetes as secondary consumers). Under normal upwelling conditions, predation by snails and crabs utilize the production of their prey almost completely, resulting in more efficient energy flow to higher trophic levels than occurs during EN. However during EN, the proliferation of the scallop A. purpuratus combined with decreased phytoplankton increased the proportion of directly utilized primary production, while exports and flows to detritus are reduced. The simulations suggest that the main cause for the scallop outburst and for the reduction in crab and macroalgae biomass was a direct temperature effect, whereas other changes are partially explained by trophic interactions. The simulations suggest that bottom-up effects largely control the system.     

Two-Dimensional Spectroscopy of Photospheric Shear Flows in a Small <Emphasis Type="Italic">δ</Emphasis> Spot

In recent high-resolution observations of complex active regions, long-lasting and well-defined regions of strong flows were identified in major flares and associated with bright kernels of visible, near-infrared, and X-ray radiation. These flows, which occurred in the proximity of the magnetic neutral line, significantly contributed to the generation of magnetic shear. Signatures of these shear flows are strongly curved penumbral filaments, which are almost tangential to sunspot umbrae rather than exhibiting the typical radial filamentary structure. Solar active region NOAA 10756 was a moderately complex β δ sunspot group, which provided an opportunity to extend previous studies of such shear flows to quieter settings. We conclude that shear flows are a common phenomenon in complex active regions and δ spots. However, they are not necessarily a prerequisite condition for flaring. Indeed, in the present observations, the photospheric shear flows along the magnetic neutral line are not related to any change of the local magnetic shear. We present high-resolution observations of NOAA 10756 obtained with the 65-cm vacuum reflector at Big Bear Solar Observatory (BBSO). Time series of speckle-reconstructed white-light images and two-dimensional spectroscopic data were combined to study the temporal evolution of the three-dimensional vector flow field in the β δ sunspot group. An hour-long data set of consistent high quality was obtained, which had a cadence of better than 30 seconds and subarcsecond spatial resolution.     

ULF geomagnetic anomalies of possible seismogenic origin observed at Teoloyucan station, México, in 1999–2001: Intermediate and short-time analysis

The analysis of ULF geomagnetic field measured at Teoloyucan station (Central Mexico, 11′35.735″ W, 19 44′45.100″ N, 2280 m height) is presented in an intermediate (± 15 days) and short time scale (the day of the EQ occurrence) in relation to 7 major earthquakes occurred in Mexico in 1999–2001. Local changes in the fractal dynamics of the magnetic field are found to be important: a pronounced fall of the fractal index is frequently observed prior to the main shock. The study of the ULF resonant structure recently discovered in the frequencies f_R1 = 10.2−11.1 mHz and f_R2 = 13.6−14.5 mHz reveals changes in their character probably related to the processes of the earthquakes preparation. The success of the observation of the mentioned anomalies (specially the fractal index decrease) strongly depends on how close is the station from the epicenter, and what is the magnitude of the earthquake.     

RADIATIVE COOLING AND BROADBAND PHENOMENON IN LOW-FREQUENCY WAVES

In this paper, we analyze the effects of radiative cooling on the pure baroclinic low-frequency waves under the approximation of equatorial β-plane and semi-geostrophic condition. The results show that radiative cooling does not, exclusively, provide the damping effects on the development of low-frequency waves.Under the delicate radiative-convective equilibrium, radiative effects will alter the phase speed and wave period,and bring about the broadband of phase velocity and wave period by adjusting the vertical profiles of diabaticheating. When the intensity of diabatic heating is moderate and appropriate, it is conductive to the development and sustaining of the low-frequency waves and their broadband phenomena, not the larger, the better. The radiative cooling cannot be neglected in order to reach the moderate and appropriate intensity of diabatic heating.     

Dayside convection and auroral morphology during an interval of northward interplanetary magnetic field

We investigate the dayside auroral dynamics and ionospheric convection during an interval when the interplanetary magnetic field (IMF) had predominantly a positive B_z component (northward IMF) but varying B_y. Polar UVI observations of the Northern Hemisphere auroral emission indicate the existence of a region of luminosity near local noon at latitudes poleward of the dayside auroral oval, which we interpret as the ionospheric footprint of a high-latitude reconnection site. The large field-of-view afforded by the satellite-borne imager allows an unprecedented determination of the dynamics of this region, which has not previously been possible with ground-based observations. The location of the emission in latitude and magnetic local time varies in response to changes in the orientation of the IMF; the cusp MLT and the IMF B_y component are especially well correlated, the emission being located in the pre- or post-noon sectors for B_y < 0 nT or B_y > 0 nT, respectively. Simultaneous ground-based observations of the ionospheric plasma drift are provided by the CUTLASS Finland HF coherent radar. For an interval of IMF B_y 0 nT, these convection flow measurements suggest the presence of a clockwise-rotating lobe cell contained within the pre-noon dayside polar cap, with a flow reversal closely co-located with the high-latitude luminosity region. This pattern is largely consistent with recent theoretical predictions of the convection flow during northward IMF. We believe that this represents the first direct measurement of the convection flow at the imaged location of the footprint of the high-latitude reconnection site.     

Polar ionospheric responses to solar wind IMF changes

Auroral and airglow emissions over Eureka (89° CGM) during the 1997/98 winter show striking variations in relation to solar wind IMF changes. The period January 19 to 22, 1998, was chosen for detailed study, as the IMF was particularly strong and variable. During most of the period, B_z was northward and polar arcs were observed. Several overpasses by DMSP satellites during the four day period provided a clear picture of the particle precipitation producing the polar arcs. The spectral character of these events indicated excitation by electrons of average energy 300 to 500 eV. Only occasionally were electrons of average energy up to 1 keV observed and these appeared transitory from the ground optical data. It is noted that polar arcs appear after sudden changes in IMF B_y, suggesting IMF control over arc initiation. When B_y is positive there is arc motion from dawn to dusk, while B_y is negative the motion is consistently dusk to dawn. F-region (anti-sunward) convections were monitored through the period from 630.0 nm emissions. The convection speed was low (100/150 m/s) when B_z was northward but increased to 500 m/s after B_z turned southward on January 20.     

R/S分析法在南水北调西线一期工程调水河流径流趋势预测中的应用

南水北调西线一期工程主要是从雅砻江支流鲜水河的达曲、泥曲和大渡河的支流色曲、杜柯河、玛柯河、阿柯河等6条河流上引水40×10⁸m³·a^-1,约占河道年径流的60%~70%,剩余大约30%~40%的径流主要用于河道的生态环境需水.由此可见,这些河流的径流多少直接关系着调水工程的实施.利用域重标度分析法(R/S分析)对这6条支流附近的水文站的径流趋势进行了初步分析,结果表明:大渡河支流的绰斯甲、足木足、泥曲的朱巴、雅砻江的甘孜等水文站月径流序列的赫斯特系数分别为0.4090、0.3884、0.4487、0.4271,都<0.5,即这些径流序列具有反持续性,甘孜和足木足站的径流量将会增加;朱巴、绰斯甲两站的径流将会减少,这对西线调水工程的实施是不利的.     

钦-杭成矿带南段(广东廉江)南和地区区域地质特征及构造演化分析

南和地区位于钦-杭成矿带南段的广东廉江幅范围内,该地区的地质特征记录了钦-杭结合带南段的构造演化过程。根据对地层沉积建造的统计,发现研究区沉积地层形成的水动力环境主要为滨海相、浅海相和深海相3种海相沉积以及少量河流相与沼泽相沉积。研究区的岩浆活动具有明显的多期多阶段特征,总体可划分为加里东期和燕山期两个大的构造岩浆旋回。从研究区的岩性变化可以得到南和地区的变质作用规律,岩浆的参与程度因迁移距离的增加而降低,导致距离越远的变质作用与岩浆的关系越低,形成了变质程度逐级降低的混合岩→片岩→千枚岩(图幅外)→变质砂岩。上述区域地质特征反映南和地区主体经历了伸展-挤压地质演化过程,也指示了钦-杭成矿带南段与北段、中段具有类似的大地构造演化历史,即整体"两开、三合"历程。     

现代黄河三角洲钓口叶瓣不良地质现象

根据对钓口三角洲叶瓣体的钻孔、浅地层剖面调查资料,研究了钓口叶瓣体垂向地层结构特点,分析了因其所导致的潜在不良地质现象,如:地面沉降以及不均匀沉降、土体液化、软弱层及底辟、滑坡、差异冲刷,总结了其特征、成因模式及危害。因钓口叶瓣的地层结构特点与现代黄河三角洲整体地层结构特点相似,其所导致的不良地质现象也普遍存在于现代黄河三角洲。该区为埕岛油田所在地,在该区进行工程建设,应对这些可能存在的不良地质现象引起重视。     

Mixed memory, (non) Hurst effect, and maximum entropy of rainfall in the tropical Andes

Diverse linear and nonlinear statistical parameters of rainfall under aggregation in time and the kind of temporal memory are investigated. Data sets from the Andes of Colombia at different resolutions (15 min and 1-h), and record lengths (21 months and 8-40 years) are used. A mixture of two timescales is found in the autocorrelation and autoinformation functions, with short-term memory holding for time lags less than 15-30 min, and long-term memory onwards. Consistently, rainfall variance exhibits different temporal scaling regimes separated at 15-30 min and 24 h. Tests for the Hurst effect evidence the frailty of the R/S approach in discerning the kind of memory in high resolution rainfall, whereas rigorous statistical tests for short-memory processes do reject the existence of the Hurst effect.Rainfall information entropy grows as a power law of aggregation time, S(T) ∼ T^β with 〈β〉 = 0.51, up to a timescale, T_MaxEnt (70-202 h), at which entropy saturates, with β = 0 onwards. Maximum entropy is reached through a dynamic Generalized Pareto distribution, consistently with the maximum information-entropy principle for heavy-tailed random variables, and with its asymptotically infinitely divisible property. The dynamics towards the limit distribution is quantified. Tsallis q-entropies also exhibit power laws with T, such that S_q(T) ∼ T^β(q), with β(q) ? 0 for q ? 0, and β(q) ? 0.5 for q ? 1. No clear patterns are found in the geographic distribution within and among the statistical parameters studied, confirming the strong variability of tropical Andean rainfall.