香港城市与郊区气候差异分析

香港天文台近年的研究显示,香港的气温上升是由温室效应增强所导致的全球变暖及本地高密度城市发展的共同影响.除温度外,香港因受城市化影响,相对湿度在城市与郊区之间亦有很明显的差异.选取1989-2006年较能代表香港市区与郊区情况的气象站每小时气温和相对湿度数据,初步比较了香港市郊温度和相对湿度差异的日变化和季节变化,并试图分析这些差异变化与城市化影响的关系.结果显示郊区的气温变化幅度比市区大、变化也较突然,市区晚间至清晨气温较郊区为高;日间情况大致逆转,但气温差别幅度不及晚间.一年之中,城市化效应在冬季最为显著,春季则最不明显.市郊相对湿度的差异同样很明显.晚间至清晨市区相对湿度较郊区为低,日间相反.     

Purely coronal flare-like variations

A detailed study of the quasi-periodical post-flare variations on November 6, 1980 in X-rays, UV lines, microwaves, and metric waves confirms that these variations were predominantly thermal phenomena and occurred solely in the corona. Only the short-lived impulsive components that preceded all or most of the individual variations were of non-thermal character and penetrated down to the transition layer. The chromosphere (in Hα) did not participate in any part of these events, in contrast to a flare that appeared at the same place a few hours later. However, the X-ray emission of these variations was so strong that the transition layer and the chromosphere definitely should have been enhanced through heat conduction along the magnetic field lines. The expected heat flux at the top of the chromosphere coming from some of these coronal brightenings was 60–80% of the flux expected in the flare at 17:26 which gave rise to a 2B flare in Hα (Figure 8). Therefore, we suggest that the variations were produced in a coronal plasmoid with closed field lines completely detached from the lower atmospheric layers (Figure 9b). We also give reasons why such a detached plasmoid can be expected to be formded in the very late phase (some 4–5 hr after the onset) of a major two-ribbon flare.     

Balloon observations of solar ultraviolet irradiance at solar minimum

Balloon observations of solar irradiance between 200 and 240 nm have been performed in 1976 and 1977 corresponding to minimum conditions of solar activity. Ultraviolet spectra have been recorded for different zenith angles at an altitude of 41 km by means of a spectrometer with a spectral bandpass of 0.4 nm. Solar irradiances at 1 a.u. confirm previous values obtained by balloon. They are compared with other measurements and discussed in term of possible long-term variability.     

The short-period eclipsing binary V1010 Ophiuchi does it have an eccentric orbit?

V1010 Oph is an unusually complicated close binary. Leung and Wilson (1977) found the system had an overcontact configuration. Subsequently, Margoniet al. (1981) claimed that the system had an eccentric orbit withe=0.25 based upon their spectroscopic study. We computed a theoretical radial velocity curve (accounting for tidal, reflection, and eclipse effects) based on the photometric parameters (e.g.,e=0) of Leung and Wilson. The computed curve fits the Asiago and Kitt Peak data very well. It is suggested that the asymmetry in the observed radial velocity arose from tidal, reflection, and eclipse effects rather than from orbital eccentricity. Other arguments against an eccentric orbit for V1010 Oph are also discussed. It is concluded that the eccentricity derived from the spectroscopic study may be spurious.On leave from Beijing University, China.     

Simple model for transient soil loading in earthquake analysis. I. Basic model and its application

Several models describing soil response under cyclic loading and the ‘liquefaction’ potential have been introduced in recent years with limited success. Most of these are over-complex for realistic parameter identification and have not been widely adopted for practical use. In this paper we introduce a relatively simple modification of the well-known critical state model which accounts reasonably well for the phenomena observed under cyclic tests and indeed improves the performance of critical state, models in monotonic loading. This model is compared with experimental results and with the ‘densification model’ introduced earlier by the authors and shows good predicitive capacity. The model is of a generalized plasticity-bounding surface type. In its simplest form, suitable for clay-like materials, it requires the identifications of a single parameter additional to those required for a standard, critical state model.     

SHIFTS IN THE WHOLESALE TRADE STATUS OF U.S. METROPOLITAN AREAS*

Considerable instability exists among large U.S. metropolitan areas in their status as wholesale trade centers. Differences in wholesale trade growth rates, changes in national shares, and shifts in rank position reflect not only population growth patterns, but also structural changes in the national economy. In the latter instance, the wholesale product mix of SMSAs is an important factor in explaining their differential fortunes within the wholesaling hierarchy.     

Differential exhumation in response to episodic thrusting along the eastern margin of the Tibetan Plateau

Thermochronological data from the Songpan-Ganze˛Fold Belt and Longmen Mountains Thrust-Nappe Belt, on the eastern margin of the Tibetan Plateau in central China, reveal several phases of differential cooling across major listric thrust faults since Early Cretaceous times. Differential cooling, indicated by distinct breaks in age data across discrete compressional structures, was superimposed upon a regional cooling pattern following the Late Triassic Indosinian Orogeny. ⁴⁰Ar/³⁹Ar data from muscovite from the central and southern Longmen Mountains Thrust-Nappe Belt suggest a phase of differential cooling across the Wenchuan-Maouwen Shear Zone during the Early Cretaceous. The zircon fission track data also indicate differential cooling across a zone of brittle re-activation on the eastern margin of the Wenchuan-Maouwen Shear Zone during the mid-Tertiary, between 38 and 10 Ma. Apatite fission track data from the central and southern Longmen Mountains Thrust-Nappe Belt reveal differential cooling across the Yingxiu-Beichuan and Erwangmiao faults during the Miocene. Forward modelling of apatite fission track data from the northern Longmen Mountains Thrust-Nappe Belt suggests relatively slow regional cooling through the Mesozoic and early Tertiary, followed by accelerated cooling during the Miocene, beginning at ca. 20 Ma, to present day.

Regional cooling is attributed to erosion during exhumation of the evolving Longmen Mountains Thrust-Nappe Belt (LMTNB) following the Indosinian Orogeny. Differential cooling across the Wenchuan-Maouwen Shear Zone and the Yingxiu-Beichuan and Erwangmiao faults is attributed to exhumation of the hanging walls of active listric thrust faults. Thermochronological data from the Longmen Mountains Thrust-Nappe Belt reveal a greater amount of differential exhumation across thrust faults from north to south. This observation is in accord with the prevalence of Proterozoic and Sinian basement in the hanging walls of thrust faults in the central and southern Longmen Mountains. The two most recent phases of reactivation occurred following the initial collision of India with Eurasia, suggesting that lateral extrusion of crustal material in response to this collision was focused along discrete structures in the LMTNB.     

Hydrochemical and stable isotope evidence for the extent and nature of the effective Chalk aquifer of north Norfolk, UK

In eastern England the Chalk aquifer is covered by extensive Pleistocene deposits which influence the hydraulic conditions and hydrochemical nature of the underlying aquifer. In this study, the results of geophysical borehole logging of groundwater temperature and electrical conductivity and depth sampling for major ion concentrations and stable isotope compositions (δ¹⁸O and δ²H) are interpreted to reveal the extent and nature of the effective Chalk aquifer of north Norfolk. It is found that the Chalk aquifer can be divided into an upper region of fresh groundwater, with a Cl concentration of typically less than 100 mg l⁻¹, and a lower region of increasingly saline water. The transition between the two regions is approximately 50 m below sea-level, and results in an effective aquifer thickness of 50–60 m in the west of the area, but less than 25 m where the Eocene London Clay boundary is met in the east of the area. Hydrochemical variations in the effective aquifer are related to different hydraulic conditions developed in the Chalk. Where the Chalk is confined by low-permeability Chalky Boulder Clay, isotopically depleted groundwater (δ¹⁸O less than −7.5‰) is present, in contrast to those areas of unconfined Chalk where glacial deposits are thin or absent (δ¹⁸O about −7.0‰). The isotopically depleted groundwater is evidence for groundwater recharge during the late Pleistocene under conditions when mean surface air temperatures are estimated to have been 4.5°C cooler than at the present day, and suggests long groundwater residence times in the confined aquifer. Elevated molar Mg:Ca ratios of more than 0.2 resulting from progressive rock-water interaction in the confined aquifer also indicate long residence times. A conceptual hydrochemical model for the present situation proposes that isotopically depleted groundwater, occupying areas where confined groundwater dates from the late Pleistocene, is being slowly modified by both diffusion and downward infiltration of modem meteoric water and diffusive mixing from below with an old saline water body.