Ground-motion prediction for a scenario earthquake requires evaluation of both the average ground-motion level and ground-motion variability due to model uncertainties. This study aims to evaluate the ground-motion variability due to aleatory variability of the source parameters by modeling ground motion of the 2000 Tottori earthquake (strike-slip type) and the 2004 Chuetsu earthquake (reverse-fault type). The source models are based on the characterized source model by the “recipe” (HERP, 2016) with fault location, size, and geometry as given parameters. Aleatory variability for the three source parameters is considered: (1) asperity location, (2) rupture initiation point, and (3) seismic moment. Two asperities are randomly located on the fault with no overlapping. A rupture initiation point is chosen randomly from the 2 km grids on the fault. Seismic moment M0 is sampled from a normal distribution in which the mean value is given by the M0-S relation (S being the fault area) by Irikura and Miyake (2001) and mean+2σ equals to 2M0. Short-period level A, another important parameter in the characterized source model, is derived from A-M0 relation by Dan et al. (2001). Ground motion for each earthquake is simulated by a hybrid approach; 3D FDM (Aoi and Fujiwara, 1999) for long periods (> 1 s) and the stochastic Green’s function method (Dan and Sato, 1998) for short periods (< 1 s), using a set of 50 source models and a 3D velocity model of J-SHIS v2 (Fujiwara et al., 2012). For the 2004 Chuetsu earthquake, simulations using a simple 1D stratified velocity model are also conducted in order to exclude the effects of the complicated subsurface structure around the source area. From the ground-motion simulation results with 50 source models for each earthquake, standard deviation (SD) of ground-motion indexes, ln of 5% damped acceleration response (Sa), PGA, and PGV, are analyzed at 10 km interval mesh. Distance and azimuthal dependence of SD are observed; the characteristics of the spatial distribution of SD differ from short periods to long periods. It is also found that the spatial distribution of SD is largely distorted by the complicated subsurface velocity structure for the Chuetsu earthquake. As a step toward constructing a model of ground-motion variability in ground-motion prediction for a scenario earthquake, we attempt to fit the SD, each for strike-slip type and reverse-fault type, with a simple regression model using the fault distance and directivity parameters. Effects of variability in other source parameters, such as rupture velocity and source time function, should be studied in our future works. Modeling variabilities in such source parameters requires investigation in physicsor empirical-based criteria.
模拟地震的地震动预测需要评估平均地震动水平和由于模式不确定性而引起的地震动变率。本文通过对2000年鸟取县地震(走滑型)和2004年中越地震(逆断层型)的地震动模拟，评价了震源参数突变引起的地震动变异性。源模型基于“配方”(HERP, 2016)的特征源模型，以断层位置、大小和几何形状为给定参数。考虑了三个震源参数的变异性:(1)凸起位置，(2)破裂起始点，(3)地震矩。两个凸起随机分布在断层上，没有重叠。从断层上的2公里网格中随机选择一个破裂起始点。地震矩M0从正态分布中采样，其中平均值由iirikura和Miyake(2001)的M0-S关系给出(S为断层面积)，平均值+2σ等于2M0。短周期水平A是特征源模型中的另一个重要参数，由Dan等人(2001)从A- m0关系推导而来。用混合方法模拟每次地震的地面运动;使用一组50个源模型和J-SHIS v2三维速度模型(Fujiwara et al.， 2012)，长周期(> 1 s)的3D FDM (Aoi and Fujiwara, 1999)和短周期(< 1 s)的随机Green’s函数方法(Dan and Sato, 1998)。对于2004年的中越地震，为了排除震源周围复杂地下结构的影响，也采用了简单的一维分层速度模型进行了模拟。利用50个震源模型对每次地震的地震动模拟结果，分析了10 km间隔网格上地震动指标的标准差(SD)、5%阻尼加速度响应的ln (Sa)、PGA和PGV。观察SD的距离和方位依赖性;短周期和长周期SD的空间分布特征不同。中越地震复杂的地下速度结构极大地扭曲了SD的空间分布。作为构建情景地震地震动预测中地震动变率模型的一步，我们尝试使用断层距离和指向性参数的简单回归模型拟合走滑类型和逆断层类型的SD。其他震源参数(如破裂速度和震源时间函数)变化的影响应在我们未来的工作中加以研究。在这样的源参数建模的可变性需要调查在物理或经验为基础的标准。
{"title":"Spatial distribution of ground-motion variability in broadband ground-motion simulations","authors":"A. Iwaki, T. Maeda, N. Morikawa, H. Fujiwara","doi":"10.1785/0120170150","DOIUrl":"https://doi.org/10.1785/0120170150","url":null,"abstract":"Ground-motion prediction for a scenario earthquake requires evaluation of both the average ground-motion level and ground-motion variability due to model uncertainties. This study aims to evaluate the ground-motion variability due to aleatory variability of the source parameters by modeling ground motion of the 2000 Tottori earthquake (strike-slip type) and the 2004 Chuetsu earthquake (reverse-fault type). The source models are based on the characterized source model by the “recipe” (HERP, 2016) with fault location, size, and geometry as given parameters. Aleatory variability for the three source parameters is considered: (1) asperity location, (2) rupture initiation point, and (3) seismic moment. Two asperities are randomly located on the fault with no overlapping. A rupture initiation point is chosen randomly from the 2 km grids on the fault. Seismic moment M0 is sampled from a normal distribution in which the mean value is given by the M0-S relation (S being the fault area) by Irikura and Miyake (2001) and mean+2σ equals to 2M0. Short-period level A, another important parameter in the characterized source model, is derived from A-M0 relation by Dan et al. (2001). Ground motion for each earthquake is simulated by a hybrid approach; 3D FDM (Aoi and Fujiwara, 1999) for long periods (> 1 s) and the stochastic Green’s function method (Dan and Sato, 1998) for short periods (< 1 s), using a set of 50 source models and a 3D velocity model of J-SHIS v2 (Fujiwara et al., 2012). For the 2004 Chuetsu earthquake, simulations using a simple 1D stratified velocity model are also conducted in order to exclude the effects of the complicated subsurface structure around the source area. From the ground-motion simulation results with 50 source models for each earthquake, standard deviation (SD) of ground-motion indexes, ln of 5% damped acceleration response (Sa), PGA, and PGV, are analyzed at 10 km interval mesh. Distance and azimuthal dependence of SD are observed; the characteristics of the spatial distribution of SD differ from short periods to long periods. It is also found that the spatial distribution of SD is largely distorted by the complicated subsurface velocity structure for the Chuetsu earthquake. As a step toward constructing a model of ground-motion variability in ground-motion prediction for a scenario earthquake, we attempt to fit the SD, each for strike-slip type and reverse-fault type, with a simple regression model using the fault distance and directivity parameters. Effects of variability in other source parameters, such as rupture velocity and source time function, should be studied in our future works. Modeling variabilities in such source parameters requires investigation in physicsor empirical-based criteria.","PeriodicalId":14836,"journal":{"name":"Japan Geoscience Union","volume":"73 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86603646","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-03-10DOI: 10.3319/TAO.2016.08.18.01(EOF5)
Jann‐Yenq Liu, Yang‐Yi Sun, C. Chao, Shih‐Ping Chen, M. Parrot
The ion density probed by IAP (Instrument d'Analyse du Plasma) on board the DEMETER (Detection of ElectroMagnetic Emissions Transmitted from Earthquake Regions) satellite is used to find whether the science payload of Advanced Ionospheric Probe (AIP) on board FORMOSAT-5 can be employed to observe space weather of ionospheric plasma irregularities. The low-latitude irregularities within ±15° dip latitudes of the DEMETER/IAP ion density are nighttime phenomena, and become prominent in the South America-Central Africa sector almost all year round, especially during May to August. The high-latitude irregularities of the DEMETER/ IAP ion density appear around ±65° dip latitude worldwide in both daytime and nighttime, and become very intense in the winter and the equinox month/hemisphere. DEMETER/IAP results show that FORMOSAT-5/AIP can be used to monitor space weather of ionospheric daytime/nighttime plasma irregularities in not only the low-but also high-latitude ionosphere.
{"title":"An observing system simulation experiment for FORMOSAT-5/AIP probing topside ionospheric plasma irregularities by using DEMETER/IAP","authors":"Jann‐Yenq Liu, Yang‐Yi Sun, C. Chao, Shih‐Ping Chen, M. Parrot","doi":"10.3319/TAO.2016.08.18.01(EOF5)","DOIUrl":"https://doi.org/10.3319/TAO.2016.08.18.01(EOF5)","url":null,"abstract":"The ion density probed by IAP (Instrument d'Analyse du Plasma) on board the DEMETER (Detection of ElectroMagnetic Emissions Transmitted from Earthquake Regions) satellite is used to find whether the science payload of Advanced Ionospheric Probe (AIP) on board FORMOSAT-5 can be employed to observe space weather of ionospheric plasma irregularities. The low-latitude irregularities within ±15° dip latitudes of the DEMETER/IAP ion density are nighttime phenomena, and become prominent in the South America-Central Africa sector almost all year round, especially during May to August. The high-latitude irregularities of the DEMETER/ IAP ion density appear around ±65° dip latitude worldwide in both daytime and nighttime, and become very intense in the winter and the equinox month/hemisphere. DEMETER/IAP results show that FORMOSAT-5/AIP can be used to monitor space weather of ionospheric daytime/nighttime plasma irregularities in not only the low-but also high-latitude ionosphere.","PeriodicalId":14836,"journal":{"name":"Japan Geoscience Union","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74728519","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-03-10DOI: 10.1175/JCLI-D-17-0291.1
A. Seiki, Y. Takayabu, T. Hasegawa, K. Yoneyama
AbstractThe lack of westerly wind bursts (WWBs) when atmospheric intraseasonal variability (ISV) events occur from boreal spring to autumn is investigated by comparing two types of El Nino years with unmaterialized El Nino (UEN) years. Although high ocean heat content buildup and several ISV events propagating eastward are observed in all three types of years, few WWBs accompany these in the UEN years. The eddy kinetic energy budget analysis based on ISV shows that mean westerly winds in the lower troposphere facilitate the development of eddy disturbances, including WWBs, through convergence and meridional shear of zonal winds. In the UEN years, these westerly winds are retracted westward and do not reach the equatorial central Pacific mainly due to interannual components. In addition, positive sea surface temperature anomalies in the western Pacific, which are conducive to active convection, spread widely in a meridional direction centered on 15°N. Both westward-retracted mean westerlies and off-equator...
{"title":"The lack of westerly wind bursts in unmaterialized El Niño years","authors":"A. Seiki, Y. Takayabu, T. Hasegawa, K. Yoneyama","doi":"10.1175/JCLI-D-17-0291.1","DOIUrl":"https://doi.org/10.1175/JCLI-D-17-0291.1","url":null,"abstract":"AbstractThe lack of westerly wind bursts (WWBs) when atmospheric intraseasonal variability (ISV) events occur from boreal spring to autumn is investigated by comparing two types of El Nino years with unmaterialized El Nino (UEN) years. Although high ocean heat content buildup and several ISV events propagating eastward are observed in all three types of years, few WWBs accompany these in the UEN years. The eddy kinetic energy budget analysis based on ISV shows that mean westerly winds in the lower troposphere facilitate the development of eddy disturbances, including WWBs, through convergence and meridional shear of zonal winds. In the UEN years, these westerly winds are retracted westward and do not reach the equatorial central Pacific mainly due to interannual components. In addition, positive sea surface temperature anomalies in the western Pacific, which are conducive to active convection, spread widely in a meridional direction centered on 15°N. Both westward-retracted mean westerlies and off-equator...","PeriodicalId":14836,"journal":{"name":"Japan Geoscience Union","volume":"PC-27 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84857821","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-03-10DOI: 10.1002/essoar.10500000.1
N. Tsutsumida
Land surface phenology (LSP) is associated with climate over space and time, and the monitoring of LSP help understandings of the terrestrial environmental changes. The LSP is often inferred by satellite observation, and long-term and regularly composite satellite imagery is now freely available. In this study, we demonstrate how LSP changes over space and time at the global scale over the last three decades by using GIMMS3g datasets. We focus on the magnitude and the timing of the peak of yearly phenological activity, estimated from a harmonic analysis. The first harmonic curve is regarded as a proxy of the overall productivity of vegetation and the second one is interpreted as a sensitive bimodal system changes. Results show the long-term trend of LSP changes; for example the peak of phenogical activity tend to be earlier in high-latitude regions.
{"title":"Long-term monitoring of land surface phenological changes","authors":"N. Tsutsumida","doi":"10.1002/essoar.10500000.1","DOIUrl":"https://doi.org/10.1002/essoar.10500000.1","url":null,"abstract":"Land surface phenology (LSP) is associated with climate over space and time, and the monitoring of LSP help understandings of the terrestrial environmental changes. The LSP is often inferred by satellite observation, and long-term and regularly composite satellite imagery is now freely available. In this study, we demonstrate how LSP changes over space and time at the global scale over the last three decades by using GIMMS3g datasets. We focus on the magnitude and the timing of the peak of yearly phenological activity, estimated from a harmonic analysis. The first harmonic curve is regarded as a proxy of the overall productivity of vegetation and the second one is interpreted as a sensitive bimodal system changes. Results show the long-term trend of LSP changes; for example the peak of phenogical activity tend to be earlier in high-latitude regions.","PeriodicalId":14836,"journal":{"name":"Japan Geoscience Union","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89930720","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. Abe, Y. Shibazaki, S. Ozawa, I. Ohira, H. Tobe, A. Suzuki
In situ X–ray diffraction studies of the phase relation of Al2SiO4(OH)2 were conducted within a pressure range of 19.7–32.2 GPa and a temperature range of 800–1600 °C. We observed the coexistence of δ–AlOOH and stishovite at 31.0 GPa and 1500 °C and the formation of phase Egg together with corundum at 30.6 GPa and 1600 °C. Our results indicate that phase Egg is stable at least up to 31 GPa and 1600 °C and should be the important water carrier after the avalanche of the stagnant slab to a depth of approximately 900 km in the lower mantle.
{"title":"In situ X-ray diffraction studies of hydrous aluminosilicate at high pressure and temperature","authors":"R. Abe, Y. Shibazaki, S. Ozawa, I. Ohira, H. Tobe, A. Suzuki","doi":"10.2465/JMPS.170714","DOIUrl":"https://doi.org/10.2465/JMPS.170714","url":null,"abstract":"In situ X–ray diffraction studies of the phase relation of Al2SiO4(OH)2 were conducted within a pressure range of 19.7–32.2 GPa and a temperature range of 800–1600 °C. We observed the coexistence of δ–AlOOH and stishovite at 31.0 GPa and 1500 °C and the formation of phase Egg together with corundum at 30.6 GPa and 1600 °C. Our results indicate that phase Egg is stable at least up to 31 GPa and 1600 °C and should be the important water carrier after the avalanche of the stagnant slab to a depth of approximately 900 km in the lower mantle.","PeriodicalId":14836,"journal":{"name":"Japan Geoscience Union","volume":"27 1","pages":"106-111"},"PeriodicalIF":0.0,"publicationDate":"2017-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73621375","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-03-10DOI: 10.5575/GEOSOC.2017.0069
G. Kimura, H. Tobin, M. Kinoshita
The NanTroSEIZE project has been one of the most complex and challenging scientific ocean drilling projects in history, representing a milestone for the Integrated Ocean Drilling Program (2005–2013) and the current International Ocean Discovery Program (2013–013) and the current International Ocean Discovery Program (2013fic ocseismogenesis of the Nankai Trough is now approaching the final stage; i.e., directly sampling, analyzing, and monitoring the plate boundary fault system responsible for historically recurring megaearthquakes and associated tsunamis. The study area is located southeast of Kii Peninsula and comprises a transect of drill sites extending from the Kumano Basin across the Nankai Trough to the incoming Philippine Sea Plate. The drilling of the Nankai seismogenic subduction zone, initiated in 2007, has resulted in the re-evaluation of previously accepted geological models. The main findings are as follows: 1) The Nankai forearc grew intermittently between ~6 and ~2 Ma due to rapid terrestrial sediment supply, resulting in the formation of a hanging wall wedge as a result of the occurrence of great earthquakes. 2) Slip along the plate boundary megathrust and along the associated splay fault has previously reached as far as the Nankai trough and ocean floor. 3) The fault, composed of clay-rich gouge, is weak in both static and dynamic cases. 4) The in situ stress conditions of the accretionary wedge and incoming Philippine Sea Plate are well constrained, and the horizontal compressional stress, parallel to the direction of plate convergence, suggests tectonic loading of accretionary sediments, implying a possible stress buildup that could result in the next great Nankai earthquake. 5) Borehole observatories and an ocean floor network recorded the earthquake, tsunami, and slow slips along the megathrust on 1 April 2016, and represent a new and innovative technology for application in the field of ocean floor science.
{"title":"A new perspective of the subduction zone derived from the Ocean Drilling Program for the Nankai Trough Seismogenic Zone Experiments (NanTroSEIZE)","authors":"G. Kimura, H. Tobin, M. Kinoshita","doi":"10.5575/GEOSOC.2017.0069","DOIUrl":"https://doi.org/10.5575/GEOSOC.2017.0069","url":null,"abstract":"The NanTroSEIZE project has been one of the most complex and challenging scientific ocean drilling projects in history, representing a milestone for the Integrated Ocean Drilling Program (2005–2013) and the current International Ocean Discovery Program (2013–013) and the current International Ocean Discovery Program (2013fic ocseismogenesis of the Nankai Trough is now approaching the final stage; i.e., directly sampling, analyzing, and monitoring the plate boundary fault system responsible for historically recurring megaearthquakes and associated tsunamis. The study area is located southeast of Kii Peninsula and comprises a transect of drill sites extending from the Kumano Basin across the Nankai Trough to the incoming Philippine Sea Plate. The drilling of the Nankai seismogenic subduction zone, initiated in 2007, has resulted in the re-evaluation of previously accepted geological models. The main findings are as follows: 1) The Nankai forearc grew intermittently between ~6 and ~2 Ma due to rapid terrestrial sediment supply, resulting in the formation of a hanging wall wedge as a result of the occurrence of great earthquakes. 2) Slip along the plate boundary megathrust and along the associated splay fault has previously reached as far as the Nankai trough and ocean floor. 3) The fault, composed of clay-rich gouge, is weak in both static and dynamic cases. 4) The in situ stress conditions of the accretionary wedge and incoming Philippine Sea Plate are well constrained, and the horizontal compressional stress, parallel to the direction of plate convergence, suggests tectonic loading of accretionary sediments, implying a possible stress buildup that could result in the next great Nankai earthquake. 5) Borehole observatories and an ocean floor network recorded the earthquake, tsunami, and slow slips along the megathrust on 1 April 2016, and represent a new and innovative technology for application in the field of ocean floor science.","PeriodicalId":14836,"journal":{"name":"Japan Geoscience Union","volume":"57 5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79830059","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
AbstractThe Kuroshio south of Japan shows bimodal path fluctuations between the large meander (LM) path and the nonlarge meander (NLM) path. The transition from the NLM path to the LM path is triggered by a small meander generated off southwestern Japan. The small meander first propagates eastward (downstream) along the Kuroshio and then rapidly amplifies over Koshu Seamount, located about 200 km south of Japan, leading to the formation of the LM path of the Kuroshio. Although Koshu Seamount is essential for the rapid amplification of the small meander, the underlying physical mechanism is not fully understood. In this study, the role of Koshu Seamount is revisited using a two-layer quasi-geostrophic model that takes into account the effects of bottom topography. Numerical experiments show that the transition from the NLM path to the LM path can be successfully reproduced only when bottom topography mimicking Koshu Seamount is incorporated. In this case, the upper-layer meander trough is rapidly amplified...
{"title":"Effects of Koshu Seamount on the Development of Baroclinic Instability Leading to the Kuroshio Large Meander","authors":"Yuki Tanaka, T. Hibiya","doi":"10.1175/JPO-D-17-0050.1","DOIUrl":"https://doi.org/10.1175/JPO-D-17-0050.1","url":null,"abstract":"AbstractThe Kuroshio south of Japan shows bimodal path fluctuations between the large meander (LM) path and the nonlarge meander (NLM) path. The transition from the NLM path to the LM path is triggered by a small meander generated off southwestern Japan. The small meander first propagates eastward (downstream) along the Kuroshio and then rapidly amplifies over Koshu Seamount, located about 200 km south of Japan, leading to the formation of the LM path of the Kuroshio. Although Koshu Seamount is essential for the rapid amplification of the small meander, the underlying physical mechanism is not fully understood. In this study, the role of Koshu Seamount is revisited using a two-layer quasi-geostrophic model that takes into account the effects of bottom topography. Numerical experiments show that the transition from the NLM path to the LM path can be successfully reproduced only when bottom topography mimicking Koshu Seamount is incorporated. In this case, the upper-layer meander trough is rapidly amplified...","PeriodicalId":14836,"journal":{"name":"Japan Geoscience Union","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86992124","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
AbstractDetailed mechanisms for frontogenesis/frontolysis of the sea surface temperature (SST) front in the Agulhas Return Current (ARC) region are investigated using outputs from a high-resolution coupled general circulation model. The SST front is maintained throughout the year through an approximate balance between frontolysis by surface heat flux and frontogenesis by horizontal advection. Although a southward (northward) cross-isotherm flow on the northern (southern) side of the front is weaker than a strong eastward along-isotherm current in the frontal region, this cross-isotherm confluent flow advects warmer (cooler) temperature toward the SST front north (south) of the front and acts as the dominant frontogenesis mechanism. In addition, stronger (weaker) frontogenesis in austral summer (winter) is attributed to the stronger (weaker) cross-isotherm confluence, which may be linked to seasonal variations of the Agulhas Current, ARC, and Antarctic Circumpolar Current. On the other hand, the contributi...
{"title":"Frontogenesis in the Agulhas Return Current region simulated by a high-resolution CGCM","authors":"Shun Ohishi, T. Tozuka, M. Cronin","doi":"10.1175/JPO-D-17-0038.1","DOIUrl":"https://doi.org/10.1175/JPO-D-17-0038.1","url":null,"abstract":"AbstractDetailed mechanisms for frontogenesis/frontolysis of the sea surface temperature (SST) front in the Agulhas Return Current (ARC) region are investigated using outputs from a high-resolution coupled general circulation model. The SST front is maintained throughout the year through an approximate balance between frontolysis by surface heat flux and frontogenesis by horizontal advection. Although a southward (northward) cross-isotherm flow on the northern (southern) side of the front is weaker than a strong eastward along-isotherm current in the frontal region, this cross-isotherm confluent flow advects warmer (cooler) temperature toward the SST front north (south) of the front and acts as the dominant frontogenesis mechanism. In addition, stronger (weaker) frontogenesis in austral summer (winter) is attributed to the stronger (weaker) cross-isotherm confluence, which may be linked to seasonal variations of the Agulhas Current, ARC, and Antarctic Circumpolar Current. On the other hand, the contributi...","PeriodicalId":14836,"journal":{"name":"Japan Geoscience Union","volume":"34 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78470462","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-03-10DOI: 10.1175/JCLI-D-16-0435.1
F. Murata, T. Terao, H. Fujinami, Taiichi Hayashi, Haruhisa Asada, J. Matsumoto, H. Syiemlieh
AbstractThe characteristics of active rainfall spells (ARSs) at Cherrapunji, northeast India, where extreme high rainfall is experienced, and their relationships with large-scale dynamics were studied using daily rainfall data from 1902 to 2005 and Japanese 55-Year Reanalysis from 1958 to 2005. Extreme high daily rainfalls occur in association with ARSs. The extremely large amounts of rainfall in the monsoon season are determined by the cumulative rainfall during ARSs. ARSs start when anomalous anticyclonic circulation (AAC) at 850 hPa propagates westward from the South China Sea and western North Pacific, and covers the northern Bay of Bengal. The AAC propagates farther westward and suppresses convection over central India during ARSs at Cherrapunji, and continues for 3 to 14 days. Consequently, a northward shift of the monsoon trough during the “break” in the Indian core region occurs. The westerly wind, which prevails in the northern portion of the AAC, transports moisture toward northeast India and en...
{"title":"Dominant synoptic disturbance in the extreme rainfall at Cherrapunji, northeast India, based on 104 years of rainfall data (1902-2005)","authors":"F. Murata, T. Terao, H. Fujinami, Taiichi Hayashi, Haruhisa Asada, J. Matsumoto, H. Syiemlieh","doi":"10.1175/JCLI-D-16-0435.1","DOIUrl":"https://doi.org/10.1175/JCLI-D-16-0435.1","url":null,"abstract":"AbstractThe characteristics of active rainfall spells (ARSs) at Cherrapunji, northeast India, where extreme high rainfall is experienced, and their relationships with large-scale dynamics were studied using daily rainfall data from 1902 to 2005 and Japanese 55-Year Reanalysis from 1958 to 2005. Extreme high daily rainfalls occur in association with ARSs. The extremely large amounts of rainfall in the monsoon season are determined by the cumulative rainfall during ARSs. ARSs start when anomalous anticyclonic circulation (AAC) at 850 hPa propagates westward from the South China Sea and western North Pacific, and covers the northern Bay of Bengal. The AAC propagates farther westward and suppresses convection over central India during ARSs at Cherrapunji, and continues for 3 to 14 days. Consequently, a northward shift of the monsoon trough during the “break” in the Indian core region occurs. The westerly wind, which prevails in the northern portion of the AAC, transports moisture toward northeast India and en...","PeriodicalId":14836,"journal":{"name":"Japan Geoscience Union","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86833725","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. Hara, S. Matoba, M. Hirabayashi, Tetsuhide Yamasaki
Sea salts and halogens in aerosols, frost flowers, and brine play an important role in atmospheric chemistry in polar regions. Simultaneous sampling and observations of frost flowers, brine, and aerosol particles were conducted around Siorapaluk in northwestern Greenland during December 2013 to March 2014. Results show that watersoluble frost flower and brine components are sea-salt components (e.g., Na, Cl, Mg2+, K, Ca2+, Br, and iodine). Concentration factors of sea-salt components of frost flowers and brine relative to seawater were 1.14–3.67. Sea-salt enrichment of Mg2+, K, Ca2+, and halogens (Cl, Br, and iodine) in frost flowers is associated with sea-salt fractionation by precipitation of mirabilite and hydrohalite. High aerosol number concentrations correspond to the occurrence of higher abundance of sea-salt particles in both coarse and fine modes, and blowing snow and strong winds. Aerosol number concentrations, particularly in coarse mode, are increased considerably by release from the sea-ice surface under strong wind conditions. Sulfate depletion by sea-salt fractionation was found to be limited in sea-salt aerosols because of the presence of non-sea-salt (NSS) SO2− 4 . However, coarse and fine sea-salt particles were found to be rich in Mg. Strong Mg enrichment might be more likely to proceed in fine seasalt particles. Magnesium-rich sea-salt particles might be released from the surface of snow and slush layer (brine) on sea ice and frost flowers. Mirabilite-like and ikaite-like particles were identified only in aerosol samples collected near new sea-ice areas. From the field evidence and results from earlier studies, we propose and describe sea-salt cycles in seasonal sea-ice areas.
{"title":"Frost flowers and sea-salt aerosols over seasonal sea-ice areas in north-western Greenland","authors":"K. Hara, S. Matoba, M. Hirabayashi, Tetsuhide Yamasaki","doi":"10.5194/acp-2016-1094","DOIUrl":"https://doi.org/10.5194/acp-2016-1094","url":null,"abstract":"Sea salts and halogens in aerosols, frost flowers, and brine play an important role in atmospheric chemistry in polar regions. Simultaneous sampling and observations of frost flowers, brine, and aerosol particles were conducted around Siorapaluk in northwestern Greenland during December 2013 to March 2014. Results show that watersoluble frost flower and brine components are sea-salt components (e.g., Na, Cl, Mg2+, K, Ca2+, Br, and iodine). Concentration factors of sea-salt components of frost flowers and brine relative to seawater were 1.14–3.67. Sea-salt enrichment of Mg2+, K, Ca2+, and halogens (Cl, Br, and iodine) in frost flowers is associated with sea-salt fractionation by precipitation of mirabilite and hydrohalite. High aerosol number concentrations correspond to the occurrence of higher abundance of sea-salt particles in both coarse and fine modes, and blowing snow and strong winds. Aerosol number concentrations, particularly in coarse mode, are increased considerably by release from the sea-ice surface under strong wind conditions. Sulfate depletion by sea-salt fractionation was found to be limited in sea-salt aerosols because of the presence of non-sea-salt (NSS) SO2− 4 . However, coarse and fine sea-salt particles were found to be rich in Mg. Strong Mg enrichment might be more likely to proceed in fine seasalt particles. Magnesium-rich sea-salt particles might be released from the surface of snow and slush layer (brine) on sea ice and frost flowers. Mirabilite-like and ikaite-like particles were identified only in aerosol samples collected near new sea-ice areas. From the field evidence and results from earlier studies, we propose and describe sea-salt cycles in seasonal sea-ice areas.","PeriodicalId":14836,"journal":{"name":"Japan Geoscience Union","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84334877","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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