Two interannual variability modes of the Northwestern Pacific Subtropical Anticyclone in boreal summer

Using the reanalysis data and 20th century simulation of coupled model FGOALS_gl developed by LASG/IAP, we identified two distinct interannual modes of Northwestern Pacific Subtropical Anticyclone (NWPAC) by performing Empirical Orthogonal Function (EOF) analysis on 850 hPa wind field over the northwestern Pacific in summer. Based on the associated anomalous equatorial zonal wind, these two modes are termed as "Equatorial Easterly related Mode" (EEM) and "Equatorial Westerly related Mode" (EWM), respectively. The formation mechanisms of these two modes are similar, whereas the maintenance mechanisms, dominant periods, and the relationships with ENSO are different. The EEM is associated with El Ni o decaying phase, with the anomalous anticyclone established in the preceding winter and persisted into summer through local positive air-sea feedback. By enhancing equatorial upwelling of subsurface cold water, EEM favors the transition of ENSO from El Ni o to La Ni a. The EWM is accompanied by the El Ni o events with long persistence, with the anomalous anticyclone formed in spring and strengthened in summer due to the warm Sea Surface Temperature anomalies (SSTA) forcing from the equatorial central-eastern Pacific. The model well reproduces the spatial patterns of these two modes, but fails to simulate the percentage variance accounted for by the two modes. In the NCEP reanalysis (model result), EEM (EWM) appears as the firstmode, which accounts for 35.6% (68.2%) of the total variance.     

Investigation of upper mantle structure under young regions of the southeast Pacific using long-period Rayleigh waves

Long-period Rayleigh wave group velocity dispersion curves are presented for paths across the east Pacific Ocean. The records are from the IPG site at Pamatai (Tahiti) and the IDA station at Nana. For the first time, direct-path observations of group velocities up to 300 s have been obtained. This study shows that for young oceanic regions group velocities are low even at long periods. The observations are interpreted in terms of an S-wave velocity model by a generalized inversion scheme. In the models for young ages, the low-velocity zone under the asthenosphere lid is well developed, with a strong velocity gradient at the bottom of this zone, followed at larger depths by a plateau representing a lower-velocity zone, and a marked gradient at 400 km.     

西北太平洋岩石圈有效弹性厚度及其构造意义

本文引入滑动窗口导纳技术(MWAT),计算西北太平洋岩石圈有效弹性厚度(Te).首先,基于SIO V15.1海底地形模型,模拟研究了MWAT法计算Te的精度,表明当TeTe≥5 km时,相对误差在10%以内.分别采用GEBCO、SIO V15.1和BAT_VGG海底地形模型,构建了西北太平洋Te,通过对获得的洋壳密度参数和实测导纳与模型导纳之差的均方根进行分析,结果表明,BAT_VGG模型更适用于Te计算.西北太平洋Te均值为13.2 km,标准差为6.9 km,以板块冷却模型为参考,主要分布在150℃~450℃等温线深度范围内.白垩纪和侏罗纪时期岩石圈Te分布在150℃~300℃等温线深度范围内,且未随海山加载时岩石圈年龄增大而增大,说明海山加载时岩石圈年龄不是影响其强度的唯一因素.南太平洋超级海隆活动,以及研究区域广泛存在的断裂带构造,都曾对本区域岩石圈演化产生过重要影响,可能是本地区岩石圈Te较小的构造原因.     

Lapse time and frequency-dependent attenuation characteristics of coda waves in the Northwestern Himalayas

We analyzed the local earthquakes waveform recorded on a broadband seismic network in the northwestern Himalayan Region to compute lapse time and frequency dependence of coda Q (Q _c). The observed Q _c values increase with increasing lapse time at all frequency bands. The increase in Q _c values with lapse time is attributed to an increase in Q _c with depth. This implies that attenuation decreases with increasing depth. The approximate radius of medium contributing to coda generation varies from 55 to 130 km. By comparing the Q _c values with those from other regions of the world, we find that they are similar to those obtained from tectonically active regions. The estimated Q _c values show a frequency-dependent relationship, Q _c = Q ₀ f ⁿ , where Q ₀ is Q _c at 1 Hz and n represents degree of frequency dependence. They represent the level of heterogeneity and tectonic activity in an area. Our results show that northwest Himalayas are highly heterogeneous and tectonically very active. Q ₀ increases from 113 ± 7 to 243 ± 10 and n decreases from 1.01 ± 0.05 to 0.85 ± 0.03 when lapse time increases from 30 to 70 s. As larger time window sees the effect of deeper part of the Earth, it is concluded that Q ₀ increases and n decreases with increasing depth; i.e., heterogeneity decreases with depth in the study area.     

Tropical cyclones as a possible factor affecting seismic activity in the cyclonic zone of the northwestern Pacific

A possible influence of tropical cyclones on seismic activity in the cyclonic zone of the northwestern Pacific is considered. There is no direct and sufficiently reliable method for calculating the degree of impact of tropical cyclones on the Earth’s crust. Therefore, a sort of inverse problem is solved in the investigation: a possible qualitative influence of tropical cyclones on seismic activity is estimated from its intra-annual dynamics. It is established that for territories of the cyclonic zone, the intra-annual dynamics of cyclonic and seismic activities are similar. Low monthly mean values of the cyclonic and seismic energies are attained in July–October, whereas in the continental territories under consideration (Central Asia), the seismic activity is higher in January–March. The results obtained suggest that cyclones can affect the seismic regime in the cyclonic zone of the northwestern Pacific.     

Source function of stress waves of a spherical explosive source

Summary The source functions of the stress wave patterns at an elastic source of these waves are analysed. The comparison of the properties of the functions with the stress wave records obtained earlier showed that their parameters do not satisfy, to a greater or lesser extent, the stress wave patterns in the neighbourhood of explosive sources. For this reason a new source function (1) was defined, which fully approximates the observed stress wave patterns in gravel sandy soil. The coefficientsP ₀, , , and were experimentally determined as functions of the distance from the source, its size and the radius of the elastic source in the medium considered. The properties of source function (1) are demonstrated on an example.Paper presented at the XIIIth General Assembly of the European Seismological Commission, Braov (Romania), 28 August to 6 September, 1972.     

西北太平洋热带气旋活动对大尺度环境场影响的线性回归分析

本文使用西北太平洋累积气旋能量（ACE）月尺度异常序列,对850 hPa相对涡度、地表纬向风、柱水汽含量、OLR、降水和SST等大尺度环境场变量进行时滞回归分析,讨论了月尺度TC活动对大尺度环境场的影响及其与周尺度的区别和联系.结果表明：（1）月尺度ACE回归出的纬向风无论是强度还是范围都要明显大于周尺度ACE回归结果,TC的频繁发生,尤其是强度大且持续时间长的近赤道TC,对于激发或加强TC活动区域南侧的低纬地区西风异常有一定的积极作用,持续并且强度较大的西风异常可能导致西风的爆发,而西风爆发会在很大程度上影响ENSO事件的发生和演变.（2）在月尺度上,OLR、柱水汽含量、降水和SST等物理量均呈现出较为明显的El Niño型分布,而在周尺度上,仅SST呈现出明显的El Niño型分布,这在一定程度上反映了月尺度TC活动和太平洋ENSO信号之间存在更密切的关联.（3）在TC发生后1-2月,TC的主要生成区域柱水汽含量减少、OLR增大,这会在一定程度上降低该区域生成TC的潜能.虽然TC所引起SST降低的空间尺度很小,但其通过大气和海洋的传导会扩大到更大尺度上,由于这种反馈具有一定的滞后性,所以月尺度TC对大尺度环境场影响的信号更为显著.

     

The Geochemistry of Volcanogenic Mineralization in the Northwestern Segment of the Pacific Ore Belt: Northeast Russia

This paper considers the geochemistry of volcanogenic mineralization in the northeastern segment of the Pacific Ore Belt (Northeast Russia). We give new evidence for the compositions and concentrations of trace and rare-earth elements (REE) in the ores of volcanogenic fields: Au-Ag epithermal (of various types and ages), Cu-Mo-Au porphyritic, Au-Bi related to granitoidal intrusions, Sn-Ag subvolcanic and kies polymetallic enriched in Au and Ag, as well as REEs in alkaline volcanic rocks. Geochemical signatures have been compiled for 17 formation types of volcanogenic fields. It was found that the ore-forming fluids in most fields belonged to an NaCl-H₂O hydrothermal system that was enriched in Cl relative to F; the values of Y/Ho in the ores of nearly all types correspond with the interval of ratios characteristic for present-day hydrothermal fluids in backarc basins; most of the ores that we studied had near-chondrite spectra with configurations similar to those of the REE spectra in volcanic rock sequences of the andesite-diorite series. Comparative analysis of REE spectra in the distribution of trace elements over classes of gold concentration shows synchronous enrichment of ores in similar sets of trace elements. The high Co/Ni ratio in volcanogenic ores probably reflects the superposition of a later magmatic fluid upon an earlier mineralization. Samples from ores of volcanogenic fields, except for Kuroko, show δCe and δEu varying from negative to mildly positive values, thus indicating low-oxidizing conditions during deposition. It was found for Au-Ag epithermal ores that they are enriched in a wide range of trace elements; they have low concentrations of REEs, the light REEs are more abundant than the heavy ones, and the Eu anomalies vary considerably from small negative to low and high positive values. The results provide evidence of an exhalation hydrothermal origin of the Khotoidokh field. It has been shown that the REEs in the ores of the Bol’shoe field are of the type that is most valuable to industry. The results can be used to deal with practical problems: determining the formation type and evaluating the industrial value of a field; detecting accessory components in ores; and discriminating between the types of geochemical anomalies (in rocks or in soil) and stray fluxes as to the potential of a field.     

Regionality of group velocities of Rayleigh waves in the Pacific and thickening of the plate

The relationship between group velocities of Rayleigh waves and the ocean-bottom age in the Pacific is examined. The Pacific basin is divided into four regions by isochrons determined from geomagnetic lineations. A significant change in group velocities of Rayleigh waves is obtained for these four regions by the use of the least-squares method from data for 27 paths in a period range 40–90 s. The present result and other geophysical observations strongly suggest the “thickening of the oceanic plate”, and are well explained by a simple plate-thickness/age relationl(km) = 7.49 t (m.y.)^1/2 inferred from the “mantle gravity anomaly”.     

Frequency content of stress waves in the nearest zone of a spherical explosive source in gravel sandy soil

Zusammenfassung Bei Verfolgung der Entstehung und Formierung der durch eine explosive Kugelquelle erregten Druckwellen steht die Frage ihres Frequenzgehalts im Vordergrund. Der Frequenzgehalt dieser Wellen wurde durch die Abhängigkeit ausgedrückt (2), die die Änderungen der relativen Breite des Amplitudenspektrums (1) vom Gewicht und von der Entfernung der Quelle angibt. Aus(2) erfolgt, dass der Frequenzgehalt der Druckwellen mit wachsender Entfernung und Grösse der Ladung exponential sinkt, wobei die Steilheit dieses Abfalls für höhere Grössen der Ladung kleiner ist. Das Herabsetzen des Frequenzgehalts dieser Wellen verursacht, dass die maximate spektral Dichte in grösseren Entfernungen von der Quelle markanter wird.     

Seismic anisotropy of the Pacific Ocean inferred from long-period surface waves dispersion

The dispersion of surface (Rayleigh and Love) waves in the period range 40–300 s along a large number of paths, allows the estimation of both the azimuthal anisotropy and the shear-wave polarization anisotropy. The regional dispersion is determined, taking into account simultaneously its dependence with age and an azimuthal factor. The Pacific Ocean has been divided into 5 regions for Rayleigh waves and into 3 regions for Love waves. This partition discriminates the regions of extreme age which show a fast variation of dispersion with age, from the regions of intermediate age where the variation is weak. A variation of ～ 2% of Rayleigh-wave group velocity with the azimuth of the path, measured with respect to the direction of spreading is displayed, up to very long-period. On the contrary, the azimuthal anisotropy for Love waves is difficult to resolve. For Rayleigh waves, the present-day direction of plate motion seems to agree best with the direction of maximum velocity. On the other hand, the isotropic inversion of the regional dispersion curves indicates, except for young regions, a discrepancy between Rayleigh-wave and Love-wave models. With this hypothesis, SH-velocities are higher than SV-velocities for the regions older than 23 Ma, down to a depth of 300 km, which is indicative of the presence of polarization anisotropy. The latter, very weak for the young part of the ocean, increases with age and reaches 7%, for the oldest region.     

Tropical cyclones and multiscale climate variability: The active western North Pacific Typhoon season of 2018

The 2018 typhoon season in the western North Pacific(WNP) was highly active, with 26 named tropical cyclones(TCs) from June to November, which exceeded the climatological mean(22) and was the second busiest season over the past twenty years. More TCs formed in the eastern region of the WNP and the northern region of the South China Sea(SCS). More TCs took the northeast quadrant in the WNP, recurving from northwestward to northward and causing heavy damages in China's Mainland(69.73 billion yuan) in 2018. Multiscale climate variability is conducive to an active season via an enhanced monsoon trough and a weakened subtropical high in the WNP. The large-scale backgrounds in 2018 showed a favorable environment for TCs established by a developing central Pacific(CP) El Ni?o and positive Pacific meridional mode(PMM)episode on interannual timescales. The tropical central Pacific(TCP) SST forcing exhibits primary control on TCs in the WNP and large-scale circulations, which are insensitive to the PMM. During CP El Ni?o years, anomalous convection associated with the TCP warming leads to significantly increased anomalous cyclonic circulation in the WNP because of a Gill-type Rossby wave response. As a result, the weakened subtropical high and enhanced monsoon trough shift eastward and northward, which favor TC genesis and development. Although such increased TC activity in 2018 might be slightly suppressed by interdecadal climate variability, it was mostly attributed to the favorable interannual background. In addition, high-frequency climate signals,such as intraseasonal oscillations(ISOs) and synoptic-scale disturbances(SSDs), interacted with the enhanced monsoon trough and strongly modulated regional TC genesis and development in 2018.     

Attenuation coefficients of the maximum amplitude and the spectral amplitude of stress waves in non-elastic zones of explosive sources

Summary The dependences of the values of coefficients of attenuation of the maximum amplitude and of the spectral amplitude were determined from stress wave records obtained from measurements in gravel sandy soil. These dependences were expressed mathematically and their interrelations are discussed.     

Frequency content of stress waves and physical parameters of the medium in the vicinity of a spherical explosive source

Summary In investigating the dynamic processes of the generation of stress waves in the nearest zone of seismic sources, questions concerned with their frequency pattern are very important. In this paper the frequency content of stress waves is expressed by the relative width of their amplitude spectrum. Measurements of stress waves close to a spherical explosive source in gravel-sandy soil, in loess, and in limestone have been realized earlier. This paper discusses the dependence of the frequency content of stress waves on the physical parameters of the medium, on the size of the charge and on the distance from the source.Paper presented at the XIVth General Assembly of the European Seismological Commission, Trieste (Italy), 16 to 23 September, 1974.     

Targeted observation analysis of a Northwestern Tropical Pacific Ocean mooring array using an ensemble-based method

An important supplement for ocean observing systems, the Northwestern Tropical Pacific Ocean (NWTPO) mooring array including 15 moorings equipped with Acoustic Doppler Current Profilers (ADCP) devices was developed by the Chinese Academy of Sciences and deployed in 2013. This study assessed the performance of this mooring array in monitoring the intra-seasonal and low-frequency (above 91 days) variability of oceanic currents by conducting targeted observation analyses using an ensemble-based method. Key regions for monitoring intra-seasonal variability of the NWTPO circulation are the equator, Indonesian throughflow (ITF), headstream of the North Equatorial Countercurrent (NECC), and Subtropical Countercurrent (STCC). For monitoring intra-seasonal variability, the range of each mooring is confined to a local scale. Therefore, NWTPO moorings cannot adequately resolve intra-seasonal variability in areas of the ITF, the headstream of the NECC, and STCC due to location constraints of the moorings. For monitoring low-frequency variability of NWTPO circulation, the key regions are the Western Boundary Current (WBC), NECC, and the Equatorial Undercurrent (EUC). NWTPO moorings performed relatively well in monitoring the low-frequency variability, as indicated by the strong background correlations between each of the currents. The NWTPO mooring array plays an important role in monitoring the location and intensity of background currents. Because moorings are costly and require a high-density distribution for optimal performance, understanding the multi-timescale dynamical nature of the NWTPO current system is critical for the deploying future moorings in this region.     

《西北地震学报》发展回顾及学术评价指标简述

《西北地震学报》是我国西北地区最早公开出版的地震专业学术刊物。本文简要回顾了《西北地震学报》从1979年创刊到2012年的发展历程,概述了办刊经历和在我国地球科学类学术期刊中的地位,阐述了其在地震科学研究和中国防震减灾事业发展中所发挥的作用,统计给出了《西北地震学报》1998年至2012年主要学术期刊评价指标数据。     

Mid-tropospheric cyclones of the summer monsoon

Mid-tropospheric cyclones are often observed on daily and monthly mean maps over southern Asia during the summer southwest monsson season. Although they are important activators of monsoon rains over certain regions, only a few observational studies are available, and even fewer theoretical and numerical studies have been performed. This article attempts to summarize the present observational knowledge about mid-tropospheric cyclones and reviews current ideas on the formation, maintenance and dissipation of these systems. A recent numerical simulation of a mid-tropospheric cyclone is described. In general, latent heat release plays the dominant role in the dynamics of the cyclone. Much is still to be learned about mid-tropospheric cyclones and several promising areas of future research are suggested.