Seasonal transition of hydrological processes in a slow‐moving landslide in a snowy region

A comprehensive understanding of seasonal hydrological dynamics is required to describe the influence of pore‐water pressure on the stability of landslides in snowy regions. This study reports on the results of continuous meteorological and hydrological observations over 2 years on a landslide body comprising Neogene sedimentary rocks in northern Japan, where a thick (3–5 m) seasonal snowpack covers the land surface. Monitoring of the volumetric water content in shallow unsaturated zones (<0.8 m depth) and pore‐water pressure in saturated bedrock at depths of 2.0 and 5.2 m revealed clear seasonality in hydrological responses to rainfall and meltwater supply. During snow‐free periods, both the shallow soil moisture and deep pore‐water pressure responded rapidly to intense rainwater infiltration. In contrast, during snowmelt, the deep pore pressure fluctuated in accordance with the daily cycle of meltwater input, without notable changes in shallow moisture conditions. During occasional foehn events that cause intense snow melting in midwinter, meltwater flows preferentially through the layered snowpack, converging to produce a localized water supply at the ground surface. This episodically triggers a significant rise in pore‐water pressure. The seasonal differences in hydrological responses were characterized by a set of newly proposed indices for the magnitude and quickness of increases in the pressure head near the sliding surface. Under snow‐covered conditions, the magnitude of the pressure increase tends to be suppressed, probably owing to a reduction in infiltration caused by a seasonal decrease in the permeability of surface soils, and effective pore‐water drainage through the highly conductive colluvial layer. Deep groundwater flow within bedrock remained in a steady upwelling state, enhanced by increasing moisture in shallow soils under snow cover, reflecting the convergence of subsurface water from surrounding hillslopes.     

Validating a regional climate model’s downscaling ability for East Asian summer monsoonal interannual variability

Performance of a regional climate model (RCM), WRF, for downscaling East Asian summer season climate is investigated based on 11-summer integrations associated with different climate conditions with reanalysis data as the lateral boundary conditions. It is found that while the RCM is essentially unable to improve large-scale circulation patterns in the upper troposphere for most years, it is able to simulate better lower-level meridional moisture transport in the East Asian summer monsoon. For precipitation downscaling, the RCM produces more realistic magnitude of the interannual variation in most areas of East Asia than that in the reanalysis. Furthermore, the RCM significantly improves the spatial pattern of summer rainfall over dry inland areas and mountainous areas, such as Mongolia and the Tibetan Plateau. Meanwhile, it reduces the wet bias over southeast China. Over Mongolia, however, the performance of precipitation downscaling strongly depends on the year: the WRF is skillful for normal and wet years, but not for dry years, which suggests that land surface processes play an important role in downscaling ability. Over the dry area of North China, the WRF shows the worst performance. Additional sensitivity experiments testing land effects in downscaling suggest the initial soil moisture condition and representation of land surface processes with different schemes are sources of uncertainty for precipitation downscaling. Correction of initial soil moisture using the climatology dataset from GSWP-2 is a useful approach to robustly reducing wet bias in inland areas as well as to improve spatial distribution of precipitation. Despite the improvement on RCM downscaling, regional analyses reveal that accurate simulation of precipitation over East China, where the precipitation pattern is strongly influenced by the activity of the Meiyu/Baiu rainfall band, is difficult. Since the location of the rainfall band is closely associated with both lower-level meridional moisture transport and upper-level circulation structures, it is necessary to have realistic upper-air circulation patterns in the RCM as well as lower-level moisture transport in order to improve the circulation-associated convective rainfall band in East Asia.     

Effects of climate change on building energy consumption in cities

Summary Sensitivity of building-energy consumption to changing urban environments is examined by simulating building energy loads in hypothetical urban settings. A modified version of an algorithm developed by the U.S. Army Construction Engineering Research Laboratory is used to evaluate energy requirements. Energy loads for two buildings of interest are estimated for changing climatic conditions (air temperature) as well as changing environments around the building. An isolated building and a building surrounded by several other buildings are considered.Results indicate that climate warming may lead to energy savings in a wide range of climates while savings also depend on the nature of the building and its use. In cool climates, climate warming forces net energy-load decreases through reductions of the winter heating loads. For example, a one-degree increase in annual air temperature in Duluth led to a 10 kWh decrease in net energy loads for a small office building. In warm climates, urbanization tends to accelerate energy consumption although shadowing may contribute significantly to decreases in summer cooling loads. In Phoenix, annual mean daily net energy loads decreased by about 10 kWh due to shadowing for the same office building. Even in relatively cool regions, summer cooling-load reductions caused by shadowing are effective.With 12 Figures     

Gamma-ray luminosity function of blazars and the cosmic gamma-ray background: evidence for the luminosity-dependent density evolution

We present a comprehensive study of the gamma-ray luminosity function (GLF) of blazars and their contribution to the extragalactic diffuse gamma-ray background (EGRB). Radio and gamma-ray luminosity correlation is introduced with a modest dispersion, consistent with observations, to take into account the radio detectability, which is important for blazar identification. Previous studies considered only pure luminosity evolution (PLE) or pure density evolution, but here we introduce the luminosity-dependent density evolution (LDDE) model, which is favored on the basis of the evolution of the X-ray luminosity function (XLF) of AGNs. The model parameters are constrained by likelihood analyses of the observed redshift and gamma-ray flux distributions of the EGRET blazars. Interestingly, we find that the LDDE model gives a better fit to the observed distributions than the PLE model, indicating that the LDDE model is also appropriate for gamma-ray blazars and that the jet activity is universally correlated with the accretion history of AGNs. We then find that only 25–50% of the EGRB can be explained by unresolved blazars with the best-fit LDDE parameters. Unresolved blazars can account for all the EGRB only with a steeper index of the faint-end slope of the GLF, which is marginally consistent with the EGRET data but inconsistent with XLF data. Therefore, unresolved AGNs cannot be the dominant source of the EGRB, unless there is a new population of gamma-ray emitting AGNs that evolves differently from the XLF of AGNs. Predictions for the GLAST mission are made, and we find that the best-fit LDDE model predicts about 3000 blazars in the entire sky, which is considerably fewer (by a factor of more than 3) than a previous estimate.     

Estimation of canopy drying time after rainfall using sap flow measurements in an emergent tree in a lowland mixed‐dipterocarp forest in Sarawak,Malaysia

This study emphasizes the importance of canopy drying time (CDT) after rainfall in a lowland tropical rain forest. In this study, we estimate CDT using sap flow velocities measured by a heat‐pulse method in an emergent tree in a lowland mixed‐dipterocarp forest. Estimated CDT (ECDT) for each rain event has been defined as the time from rainfall cessation to the specific time derived from the difference between diurnal courses of sap flow velocities on a rainy day versus bright days. ECDT could be derived for 22 rain events that were grouped into two types, depending on whether rainfall ceased before or after noon. The ECDTs were distributed more widely and with greater values when rainfall ceased before noon (Type 1) than after noon (Type 2). The ECDTs of both Type 1 and Type 2 decreased with increases in net radiation (Rn) and vapour pressure deficit (VPD) after rainfall. This result shows that ECDT is determined mainly by post‐rainfall evaporation rates. The sap flow velocity as a detector of canopy wetness worked out well because of the specific rainfall characteristics at this site. The practical limitations of the method using sap flow velocities are discussed in relation to rainfall characteristics and time lags between transpirations and sap flow velocities. Copyright © 2005 John Wiley & Sons, Ltd.     

Observations of an intrusion of a warmer and less saline water mass into a bay

Detailed hydrographic observations were made in Wakasa Bay, Japan, in August 1979 as the first of a series on the topic of bay intrusions. An anomalous water tongue, evident at a depth of 50 m, was observed to move eastward into the bay at a speed of about 10 km day⁻¹. The width of the tongue was about 20 to 30 km in agreement with the Rossby internal radius of deformation. The results of current meter measurements and the observed temporal and spatial evolution of the temperature field near the front of the anomalous water tongue have suggested that ageostrophic cross-frontal motion, in balance with the along-front acceleration, may be important in our understanding of intrusion processes.     

Subtelescopic Inhomogeneities of Electron Density in the Solar Corona

The brightness of the solar corona due to Thomson scattering depends linearly on the electron density, while the brightness due to the Balmer continuum is proportional to its square. As a consequence, information on the distribution of the electron density in the corona can be obtained by comparing the radial profiles of the surface brightness in both continua. This idea was explored for the first time in the solar eclipse of November 03, 1994, in Foz do Iguaçu, PR, Brazil. Pictures of the corona were obtained with interference filters, one centered at 477 nm (Thomson continuum) and another one at 347 nm (Balmer continuum). The second filter also transmits the Thomson continuum through its spectral window, so that the Balmer images contain Thomson contamination. This paper reports on the observational results and presents their preliminary analysis. It was found that in certain radial directions, the normalized profiles of both continua (Thomson and contaminated Balmer) coincide, but in other directions they differ significantly. The non-coincident profiles may only occur if Balmer emission becomes important in relation to the Thomson scattering. A simple calculation shows that in such cases the electron density in the inner corona must exceed the values of standard models by up to 6.1 × 10⁴ times, maintaining however the total number of electrons along the line of sight in agreement with the prediction of standard models. It is concluded that the corona contains high electron concentration in cloudlets of subtelescopic sizes down to 10⁶ cm. The varied behavior of the radial profiles of both continua in different radial directions, suggests that the subtelescopic structures might be related to the spatially variable topology of coronal magnetic flux tubes.     

Effect of winter meteorological conditions on the formation of the cold bottom water in the eastern Bering Sea shelf

The cold bottom water, formed in the previous winter on the eastern Bering Sea shelf, remains throughout the summer. in order to examine the mechanism for the formation of the cold bottom water, we used minimum water temperature in the cold bottom water observed over the eastern Bering Sea shelf for 30 years. The interannual variation in the minimum water temperature of the cold bottom water was closely related to that of mean air temperature during cooling period at St. Paul Island. The air temperature in previous winter primarily affects the cold bottom water. We estimated decrement of the water temperature due to ice melting with simple box model. It was found with the box model that decreasing of the water temperature and lowering of the salinity depend on ice melting. To investigate the cause of interannual variation in air temperature in winter, we applied EOF analysis to the 500 hPa height. The Pacific/North American pattern (PNA) was related to mean air temperature at St. Paul Island in cooling season and the cold bottom water temperature. These results suggest the connection between ENSO events and warming or cooling in the Bering Sea shelf in winter.