Regionality of deep low-frequency earthquakes associated with subduction of the Philippine Sea plate along the Nankai Trough, southwest Japan

The Fukuoka District Meteorological Observatory recently logged three possible deep low-frequency earthquakes (LFEs) beneath eastern Kyushu, Japan, a region in which LFEs and low-frequency tremors have never before been identified. To assess these data, we analyzed band-pass filtered velocity seismograms and relocated LFEs and regular earthquakes using the double-difference method. The results strongly suggest that the three events were authentic LFEs, each at a depth of about 50 km. We also performed relocation analysis on LFEs recorded beneath the Kii Peninsula and found that these LFEs occurred near the northwest-dipping plate interface at depths of approximately 29–38 km. These results indicate that LFEs in southwest Japan occur near the upper surface of the subducting Philippine Sea (PHS) plate. To investigate the origin of regional differences in the occurrence frequency of LFEs in western Shikoku, the Kii Peninsula, and eastern Kyushu, we calculated temperature distributions associated with PHS plate subduction. Then, using the calculated thermal structures and a phase diagram of water dehydration for oceanic basalt, the water dehydration rate (wt.%/km), which was newly defined in this study, was determined to be 0.19, 0.12, and 0.08 in western Shikoku, the Kii Peninsula, and eastern Kyushu, respectively; that is, the region beneath eastern Kyushu has the lowest water dehydration rate value. Considering that the Kyushu–Palau Ridge that is subducting beneath eastern Kyushu is composed of tonalite, which is low in hydrous minerals, this finding suggests that the regionality may be related to the amount of water dehydration associated with subduction of the PHS plate and/or differences in LFE depths. Notable dehydration reactions take place beneath western Shikoku and the Kii Peninsula, where the depth ranges for dehydration estimated by thermal modeling agree well with those for the relocated LFEs. The temperature range in which LFEs occur in these regions is estimated to be 400–500 °C.     

THE DIABATIC WAVES IN BAROTROPIC MODEL

The equations of barotropic model are used to discuss the effects of diabatic factors such as heat-ing of convective condensation, evaporation-wind feedback and CISK on the Rossby wave and the Kelvin wave. In low latitudes we have obtained the angular frequency and analyzed the period and stability of waves. The result shows the existence of the diabatic factors not only enlarges the period of adiabatic waves but also changes the stability of waves. Thus we think that the so-called intraseasonal oscillation and some other low-frequency oscillations are a kind of diabatic waves which are important factors producing the long-term weather changes and short-term climatic evolution.     

南海夏季风暴发过程的低频特征

应用1979～1996年共18a的NOAA卫星OLR资料及NCEP/NCAR再分析850hPa风场资料,分析了夏季南海地区及南海季风暴发过程的某些低频特征。认为北半球夏季南海地区的低频活动较活跃,并且具有明显的年际变化,这种年际变化同南海季风的暴发时间有联系。南海地区的低频振荡在南海季风暴发后增强。通过对18a 及K*的时段叠加合成图的分析,发现南海夏季风的暴发同赤道印度洋低频振荡的东传及西太平洋低频扰动西传有密切联系,南海夏季风暴发期间南海地区将印度洋与西太平洋之间的低频活动联系在一起。     

山东大风天气的低频特征及机理分析

利用山东省122个国家级地面气象观测站的风速数据与欧洲中期天气预报中心(ECMWF)提供的ERA-interim再分析数据,采用小波分析、带通滤波等方法对2015年9月—2020年9月山东的大风天气及相应的低频大气环流形势进行分析.结果表明,近几年山东的大风天气有增加的趋势,春季大风发生频次最多,秋季最少;山东半岛东部...     

RELATIONSHIP BETWEEN SUMMER LOW-FREQUENCY RAINFALL OVER SOUTHERN CHINA AND PROPAGATION OF TROPICAL INTRASEASONAL OSCILLATION

This study investigates the relationship between summer low-frequency rainfall over southern China and tropical intraseasonal oscillation (ISO) in the atmosphere by examining systematically the propagation features of the tropical ISO in terms of focusing on five large-scale low-frequency rainfall regimes in summer over southern China. It is demonstrated that there is a close linkage between the five rainfall regimes over southern China and the northward propagation of the tropical ISO. The moist ISO signals, which influence the low-frequency rainfall events in different regions of southern China, mainly propagate northwestward from the tropical ocean to the southeast of China. The southeast China rainfall regime is intimately associated with the moist ISO signals propagating northwestward from the equatorial mid-western Pacific Ocean. For both the Yangtze River regime and South of Yangtze River regime, the moist ISO signals over the northern South China Sea show an evident northward propagation towards the Yangtze River region, and then propagate westward. It is further found that the interaction between the northward propagation of low-latitude ISO signals and the southward propagation of high-latitude ISO signals can also make a clear influence on the low-frequency rainfall in southern China. For the Southern China regime, the moist ISO signals show a significant northward propagation from the Philippines. Moreover, for the rainless regime, southern China is under dry ISO signals’ control, and the latter shows no clear propagation to southern China. This study may provide insights for the extended-range forecasting of summer rainfall in southern China.     

广州市空气污染的变化特征及预报

利用2002年11月-2004年9月广州市空气污染指数（API）和PM10、NO2、SO2等污染物逐日浓度资料，采用小波分析、相关分析等方法对广州市空气污染的变化特征及与同期地面气象要素的关系进行了分析。并采用最优子集回归方法分别建立冬、夏季API指数及污染物浓度的预报方程。结果表明。PM10是广州市的主要污染物。其次为NO2、SO2。除SO2外，广州市API指数、NO2、PM10等污染物浓度具有冬半年（11-4月）偏高，夏半年（5-10月）偏低的变化规律。API指数及各种污染物浓度均具有明显的年周期振荡及5-7天的准单周、10-20天准双周、30-60天左右的季节内振荡，且30-60天的季节内振荡在冬半年较强而在夏半年较弱。冬半年API指数和PM10、NO2、SO2浓度与气压、风速、降水呈稳定负相关，与温度、相对湿度等呈稳定的正相关，而夏半年主要与风速、降水具有较好且稳定的负相关。增加前一天的污染物浓度作为预报因子后，所建的最优子集回归方程比单选用气象因子要稳定。具有较强的预测能力。     

Wind-driven, double-gyre, ocean circulation in a reduced-gravity, 2.5-layer, lattice boltzmann model

A coupled lattice Boltzmann （LB） model with second-order accuracy is applied to the reduced-gravity, shallow water, 2.5-layer model for wind-driven double-gyre ocean circulation. By introducing the secondorder integral approximation for the collision operator, the model becomes fully explicit. The Coriolis force and other external forces are included in the model with second-order accuracy, which is consistent with the discretization accuracy of the LB equation. The feature of the multiple equilibria solutions is found in the numerical experiments under different Reynolds numbers based on this LB scheme. With the Reynolds number increasing from 3000 to 4000, the solution of this model is destabilized from the anti-symmetric double-gyre solution to the subtropic gyre solution and then to the subpolar gyre solution. The transitions between these equilibria states are also found in some parameter ranges. The time-dependent variability of the circulation based on this LB simulation is also discussed for varying viscosity regimes. The flow of this model exhibits oscillations with different timescales varying from subannual to interannual. The corresponding statistical oscillation modes are obtained by spectral analysis. By analyzing the spatiotemporal structures of these modes, it is found that the subannual oscillation with a 9-month period originates from the barotropic Rossby basin mode, and the interarmual oscillations with periods ranging from 1.5 years to 4.6 years originate from the recirculation gyre modes, which include the barotropic and the baroclinic recirculation gyre modes.     

CISK, EVAPORATION-WIND FEEDBACK MECHANISM AND 30-60 DAY OSCILLATIONS IN THE TROPICAL ATMOSPHERE*

A baroclinic semi-geostrophic model with evaporation-wind feedback mechanism(EWFM) and CISK is established,two non-dimensional parameters a and η are introduced to represent EWFM and CISK,respectively.Analytic solutions of the model system are obtained,dynamics analyses and the model atmosphere calculations further confirm that EWFM and CISK are very important physical processes in leading to the low-frequency oscillations in the tropics.     

MODULATION OF MADDEN-JULIAN OSCILLATION ON TIBETAN PLATEAU VORTEX

This study uses NCEP/NCAR daily reanalysis data, NOAA outgoing long-wave radiation (OLR) data, the real-time multivariate MJO (RMM) index from the Australian Bureau of Meteorology and Tibetan Plateau vortex (TPV) data from the Chengdu Institute of Plateau Meteorology to discuss modulation of the Madden-Julian Oscillation (MJO) on the Tibetan Plateau Vortex (TPV). Wavelet and composite analysis are used. Results show that the MJO plays an important role in the occurrence of the TPV that the number of TPVs generated within an active period of the MJO is three times as much as that during an inactive period. In addition, during the active period, the number of the TPVs generated in phases 1 and 2 is larger than that in phases 3 and 7. After compositing phases 1 and 7 separately, all meteorological elements in phase 1 are apparently conducive to the generation of the TPV, whereas those in phase 7 are somewhat constrained. With its eastward propagation process, the MJO convection centre spreads eastward, and the vertical circulation within the tropical atmosphere changes. Due to the interaction between the mid-latitude and low-latitude atmosphere, changes occur in the baroclinic characteristics of the atmosphere, the available potential energy and eddy available potential energy of the atmosphere, and the circulation structures of the atmosphere over the Tibetan Plateau (TP) and surrounding areas. This results in significantly different water vapour transportation and latent heat distribution. Advantageous and disadvantageous conditions therefore alternate, leading to a significant difference among the numbers of plateau vortex in different phases.     

卫星摄影姿态测定系统低频误差补偿

姿态测定系统不仅存在高频误差,还存在与卫星轨道纬度及时间有关的低频误差,严重影响无地面控制点测量精度。本文分析了产生低频误差的因素及相关解决措施,并在天绘一号(TH-1)卫星工程中,利用光束法平差实现低频误差的自动检测与补偿处理,消除低频误差对定位精度的影响,最后进行了试验验证。试验结果表明:低频误差补偿技术,很好地解决了无地面控制定位系统误差问题,为实现天绘一号卫星全球定位精度的一致性发挥了重要作用。