An investigation of analysis of variance as a tool for exploring regional differences in strong ground motions

The statistical technique known as analysis of variance is applied to a large set of European strong-motion data to investigate whether strong ground motions show a regional dependence. This question is important when selecting strong-motion records for the derivation of ground motion prediction equations and also when choosing strong-motion records from one geographical region for design purposes in another. Five regions with much strong-motion data (the Caucasus region, central Italy, Friuli, Greece and south Iceland) are investigated here. For the magnitude and distance range where there are overlapping data from the five areas (2.50 M_s 5.50, 0 d 35 km) and consequently analysis of variance can be performed, there is little evidence for a regional dependence of ground motions. There is a lack of data from moderate and large magnitude earthquakes (M_s > 5.5) so analysis of variance cannot be performed there. Since there is uncertainty regarding scaling ground motions from small to large magnitudes whether ground motions from large earthquakes are significantly different in different parts of Europe is not known. Analysis of variance has the ability to complement other techniques for the assessment of regional dependence of ground motions.     

Solar radiative output and its variability: evidence and mechanisms

Electromagnetic radiation from the Sun is Earths primary energy source. Space-based radiometric measurements in the past two decades have begun to establish the nature, magnitude and origins of its variability. An 11-year cycle with peak-to-peak amplitude of order 0.1 % is now well established in recent total solar irradiance observations, as are larger variations of order 0.2 % associated with the Suns 27-day rotation period. The ultraviolet, visible and infrared spectral regions all participate in these variations, with larger changes at shorter wavelengths. Linkages of solar radiative output variations with solar magnetism are clearly identified. Active regions alter the local radiance, and their wavelength-dependent contrasts relative to the quiet Sun control the relative spectrum of irradiance variability. Solar radiative output also responds to sub-surface convection and to eruptive events on the Sun. On the shortest time scales, total irradiance exhibits five minute fluctuations of amplitude %, and can increase to as much as 0.015 % during the very largest solar flares. Unknown is whether multi-decadal changes in solar activity produce longer-term irradiance variations larger than observed thus far in the contemporary epoch. Empirical associations with solar activity proxies suggest reduced total solar irradiance during the anomalously low activity in the seventeenth century Maunder Minimum relative to the present. Uncertainties in understanding the physical relationships between direct magnetic modulation of solar radiative output and heliospheric modulation of cosmogenic proxies preclude definitive historical irradiance estimates, as yet.Received: 26 August 2004, Published online: 16 November 2004 Correspondence to: Claus Fröhlich     

丘陵区土壤热通量遥感估算模型适应性分析

利用具有丘陵区典型特征的四川省乐至县气象站的土壤热通量和净辐射观测数据,分析了二者的变化特征,并验证了土壤热通量遥感估算模型的适用性。分析结果表明：晴空土壤热通量G与净辐射Rn存在明显日变化,最大值出现13时左右;其比值G／Rn受土壤湿润程度和地表覆盖的影响,地表湿润、覆盖率高,比值小。在干旱时,瞬时比值可高达0．7,而湿润情况,可低至0．05。对目前广泛使用的G／Rn卫星遥感模型估算结果与实测值的对比分析表明,不同的G／Rn卫星遥感估算模型估算结果存在明显的差异,仅依靠植被指数的模型不适合南方丘陵区。本研究认为Bastiaanssen等的模型较适合丘陵区的土壤热通量遥感估算模型。     

河南省紫外线辐射分布规律及影响因素研究

利用2005年以来的河南省18个地市级气象台站的紫外线辐射监测数据,分析了河南省紫外线辐射的时空分布特征,并定量分析了云量、能见度及相对湿度等因素对紫外线辐射的影响.结果表明:河南省紫外线辐射年平均值总体表现为中部和南部较高;冬季西北地区紫外线辐射较高,夏季在西部、豫东南到豫北西部有两个高值带;季紫外线辐射均值表现为春夏季高、秋冬季低的特点.紫外线辐射强度与总云量、低云量及相对湿度呈显著负相关,而与能见度呈显著正相关.     

干旱半干旱区太阳辐射特征

Climatic characteristics of broadband solar radiation （Rs） in Chinese arid and semi-arid areas are reported in this study. The annual average daily Rs in the arid and semi-arid areas is 16.3 ±5.77 and 15.3 ± 5.16 MJ m^-2 d^-1, respectively. The highest value （17.2 ± 5.84 MJ m^-2 d^-1） appears in an arid area at Linze. The lowest value appears in the semi-arid area of Ansai. Pronounced seasonal variation of Rs is observed with the highest value in summer and the lowest in winter. The clearness index showed similar seasonal pattern at most sites, with the minimum observed in the summer and the highest values in winter at both arid and semi-arid areas. The seasonal variation of the ratio of Rs to its extraterrestrial value Kt in the arid area is more significant than that observed in the semi-arid region, and it is caused by the different range of variation of water vapor between arid and semi-arid areas. The seasonal fluctuations in Rs and Kt are mainly controlled by the water vapor content in these areas. The aerosol particles have significant influence on Rs and Kt at stations with higher aerosol burden.     

Spectral variability in Cygnus X-3

We model the broad-band X-ray spectrum of Cyg X-3 in all states displayed by this source as observed by the Rossi X-ray Timing Explorer . From our models, we derive for the first time unabsorbed spectral shapes and luminosities for the full range of spectral states. We interpret the unabsorbed spectra in terms of Comptonization by a hybrid electron distribution and strong Compton reflection. We study the spectral evolution and compare with other black hole as well as neutron star sources. We show that a neutron star accretor is not consistent with the spectral evolution as a function of L _E and especially not with the transition to a hard state. Our results point to the compact object in Cyg X-3 being a massive,  ∼30 M_⊙  black hole.     

Formation of the radio profile components of the Crab pulsar

The induced Compton scattering of radio emission off the particles of the ultrarelativistic electron–positron plasma in the open field line tube of a pulsar is considered. We examine the scattering of a bright narrow radio beam into the background over a wide solid angle and specifically study the scattering in the transverse regime, which holds in a moderately strong magnetic field and gives rise to the scattered component nearly antiparallel to the streaming velocity of the scattering particles. Making use of the angular distribution of the scattered intensity and taking into account the effect of rotational aberration in the scattering region, we simulate the profiles of the backscattered components as applied to the Crab pulsar. It is suggested that the interpulse (IP), the high-frequency interpulse (IP') and the pair of so-called high-frequency components (HFC1 and HFC2) result from the backward scattering of the main pulse (MP), precursor (PR) and low-frequency component (LFC), respectively. The components of the high-frequency profiles, the IP' and HFCs, are interpreted for the first time. The HFC1 and HFC2 are argued to be a single component split by the rotational aberration close to the light cylinder. It is demonstrated that the observed spectral and polarization properties of the profile components of the Crab pulsar as well as the giant pulse phenomenon outside the MP can be explained in terms of our model.     

Some properties of synchrotron radio and inverse-Compton gamma-ray images of supernova remnants

The synchrotron radio maps of supernova remnants (SNRs) in a uniform interstellar medium and interstellar magnetic field (ISMF) are analysed, allowing for different 'sensitivity' of the injection efficiency to the obliquity of the shock. The very-high-energy γ-ray maps arising from inverse Compton processes are also synthesized. The properties of images in these different wavelength bands are compared, with particular emphasis on the location of the bright limbs in bilateral SNRs. Recent High-Energy Stereoscopic System (HESS) observations of SN 1006 show that the radio and inverse Compton γ-ray limbs coincide, and we found that this may happen if (i) injection is isotropic but the variation of the maximum energy of electrons is rather fast to compensate for differences in the magnetic field, or (ii) the obliquity dependence of injection (either quasi-parallel or quasi-perpendicular) and the electron maximum energy are strong enough to dominate the magnetic field variation. In the latter case, the obliquity dependences of the injection and the maximum energy should not be opposite. We argue that the position of the limbs alone, and even their coincidence in radio, X-rays and γ-rays, as discovered by HESS in SN 1006, cannot be conclusive as regards the dependence of the electron injection efficiency, the compression/amplification of the ISMF and the electron maximum energy on the obliquity angle.     

Optical polarization of the Crab pulsar: precision measurements and comparison to the radio emission

The linear polarization of the Crab pulsar and its close environment was derived from observations with the high-speed photopolarimeter Optical Pulsar TIMing Analyser at the 2.56-m Nordic Optical Telescope in the optical spectral range (400–750 nm). Time resolution as short as 11 μs, which corresponds to a phase interval of 1/3000 of the pulsar rotation, and high statistics allow the derivation of polarization details never achieved before. The degree of optical polarization and the position angle correlate in surprising details with the light curves at optical wavelengths and at radio frequencies of 610 and 1400 MHz. Our observations show that there exists a subtle connection between presumed non-coherent (optical) and coherent (radio) emissions. This finding supports previously detected correlations between the optical intensity of the Crab and the occurrence of giant radio pulses. Interpretation of our observations requires more elaborate theoretical models than those currently available in the literature.