Orbital Period Changes and Long Term Luminosity Variation in Active Binary CG Cyg

UBV photometric observations of the active binary star CG Cygnus have been presented and analyzed to obtain absolute parameters of both components. Updated O-C diagram analysis by Kalimeris method yielded the values of 1.55× 10^-6 day and 1.4×10^-7day as the amplitudes of orbital period modulation, and P_mod1∼ 52.3 yr and P_mod2 ∼ 15.9 yr as the modulation periodicities. Finally, the consequences of period changes have been discussed on the basis of Applegate mechanism.     

A physically based distributed subsurface–surface flow dynamics model for forested mountainous catchments

This study was designed to develop a physically based hydrological model to describe the hydrological processes within forested mountainous river basins. The model describes the relationships between hydrological fluxes and catchment characteristics that are influenced by topography and land cover. Hydrological processes representative of temperate basins in steep terrain that are incorporated in the model include intercepted rainfall, evaporation, transpiration, infiltration into macropores, partitioning between preferential flow and soil matrix flow, percolation, capillary rise, surface flow (saturation‐excess and return flow), subsurface flow (preferential subsurface flow and baseflow) and spatial water‐table dynamics. The soil–vegetation–atmosphere transfer scheme used was the single‐layer Penman–Monteith model, although a two‐layer model was also provided. The catchment characteristics include topography (elevation, topographic indices), slope and contributing area, where a digital elevation model provided flow direction on the steepest gradient flow path. The hydrological fluxes and catchment characteristics are modelled based on the variable source‐area concept, which defines the dynamics of the watershed response. Flow generated on land for each sub‐basin is routed to the river channel by a kinematic wave model. In the river channel, the combined flows from sub‐basins are routed by the Muskingum–Cunge model to the river outlet; these comprise inputs to the river downstream. The model was applied to the Hikimi river basin in Japan. Spatial decadal values of the normalized difference vegetation index and leaf area index were used for the yearly simulations. Results were satisfactory, as indicated by model efficiency criteria, and analysis showed that the rainfall input is not representative of the orographic lifting induced rainfall in the mountainous Hikimi river basin. Also, a simple representation of the effects of preferential flow within the soil matrix flow has a slight significance for soil moisture status, but is insignificant for river flow estimations. Copyright © 2005 John Wiley & Sons, Ltd.     

水库下游再造床过程的若干问题

取河流动力学与地貌学的分析相结合,并辅之以模型试验作验证的途径,对水库下游河床演变中的纵向冲刷、横向变形和河型变化等问题进行了讨论,获得了苦干形式简单,但有一定实用价值的定量关系和评估方法。     

Diurnal cycle of surface energy fluxes in high mountain terrain: High-resolution fully coupled atmosphere-hydrology modelling and impact of lateral flow

Water and energy fluxes are inextricably interlinked within the interface of the land surface and the atmosphere. In the regional earth system models, the lower boundary parameterization of land surface neglects lateral hydrological processes, which may inadequately depict the surface water and energy fluxes variations, thus affecting the simulated atmospheric system through land-atmosphere feedbacks. Therefore, the main objective of this study is to evaluate the hydrologically enhanced regional climate modelling in order to represent the diurnal cycle of surface energy fluxes in high spatial and temporal resolution. In this study, the Weather Research and Forecasting model (WRF) and coupled WRF Hydrological modelling system (WRF-Hydro) are applied in a high alpine catchment in Northeastern Tibetan Plateau, the headwater area of the Heihe River. By evaluating and intercomparing model results by both models, the role of lateral flow processes on the surface energy fluxes dynamics is investigated. The model evaluations suggest that both WRF and coupled WRF-Hydro reasonably represent the diurnal variations of the near-surface meteorological fields, surface energy fluxes and hourly partitioning of available energy. By incorporating additional lateral flow processes, the coupled WRF-Hydro simulates higher surface soil moisture over the mountainous area, resulting in increased latent heat flux and decreased sensible heat flux of around 20–50 W/m² in their diurnal peak values during summertime, although the net radiation and ground heat fluxes remain almost unchanged. The simulation results show that the diurnal cycle of surface energy fluxes follows the local terrain and vegetation features. This highlights the importance of consideration of lateral flow processes over areas with heterogeneous terrain and land surfaces.     

Stress State, Seismicity and Subduction Geometries of the Descending Lithosphere Below the Hindukush and Pamir

The paper presents an analysis of spatial distribution of 6600 earthquake events which occurred during the period 1964 to 1999 between latitude 34 to 40°N and longitude 68 to 76°E. This large volume event is reported in the International Seismological Centre (ISC) catalog. In addition to this a total of 248 focal mechanism solutions are considered to derive a generalised predominant stress prevailing in the descending lithosphere below the Hindukush and Pamir regions.

The analysis of spatial distribution shows that the epicentres of the events at shallow level (depth<70 km) are sparsely distributed throughout except for a cluster at the northern end of both the Hindukush and Pamir. The concentration of epicentres at intermediate-depth level between 71 and 170 km below the Hindukush takes a strip-like pattern. It trends along SW-NE, and narrows at the northeastern end of the Hindukush. At deeper level (depth>170 km) the epicentres below the Hindukush are mainly concentrated in a triangular-shaped zone, and the mean points of concentration of the epicentres appear to be shifted towards southwest at increasing depth. The distribution of epicentres at the intermediate and deeper layers of the Pamir is observed to be diffused except a cluster of few events in each layer appears to be shifted towards south-southeast at increasing depth. The distribution of hypocentres changes its concentration from lesser to considerably higher at about 70 km depth, and further takes a minimum at about 170 km depth below the Hindukush and Pamir.

The present study further involves in analysing the composite/group effect of stresses associated with the descending lithosphere below the Hindukush and Pamir after deriving the best-fit generalized predominant directions of stresses. It shows that the intermediate-depth seismic zone below the Hindukush is acted upon by maximum compressive stresses (P axes) from two directions while the deeper-depth zone from three directions, and may convincingly be correlated with the changing shape of the respective seismic zones. Another interesting phenomenon observed here is the change in direction of maximum compressive stresses in clockwise fashion from intermediate to deep seismic zones below the Hindukush. At shallow depths below the Pamir the maximum and minimum (T axes) compressive stresses are acting almost along NNW-SSE and ENE-WSW and are oriented horizontally. T-axes for few events at these depths show almost vertical orientation. The observed down-dip extension is predominantly parallel with the descending lithosphere below the Hindukush. The entire analysis along with the observed scattering of P- and T-axes of some events at intermediate-depths might be indicating a slight contortion of the middle layer below the Hindukush. The spatial distribution of seismicity and the generalised stress pattern of both the regions infer the existence of two-isolated subducting lithosphere. It perhaps has created the eastward expulsion or lateral extrusion of Tibet along the major strike-slip faults like Karakorum, Altyn-Tagh, Kunlun and Red River. Finally, the whole analysis confirms the existence of shield-like continental rigid slab at depths greater than 170 km below the Hindukush.     

经纬仪横轴误差对竖直角观测的影响

通过对经纬仪横轴本身不水平和由于竖轴不竖直导致横轴不水平2方面分析横轴倾斜对竖直角观测的影响,推出相应的公式.并通过实验数据得出,通过水准管安置经纬仪,由于横轴倾斜角非常小,不必考虑横轴倾斜对竖直角观测的影响.