Transition of solar cycle length in association with the occurrence of grand solar minima indicated by radiocarbon content in tree-rings     

Hiroko Miyahara  Kentaro Nagaya  Kimiaki Masuda  Yasushi Muraki  Hiroyuki Kitagawa  Toshio Nakamura 《Quaternary Geochronology》2008,3(3):208-212

In this paper, we review the variation of the 11-year solar cycle since the 15th century revealed by the measurement of radiocarbon content in single-year tree-rings of Japanese cedar trees. Measurements of radiocarbon content in absolutely dated tree-rings provide a calibration curve for accurate dating of archaeological matters, but at the same time, enable us to examine the variations of solar magnetic activity in the pre-historical period. The Sun holds several long-term quasi-cyclic variations in addition to the fundamental 11-year sunspot activity cycle and the 22-year polarity reversal cycle, and it is speculated that the property of the 11-year and the 22-year solar cycle varies in association with such long-term quasi-cycles. It is essential to reveal the details of solar variations around the transition time of solar dynamo for illuminating the mechanisms of the long-term solar variations. We therefore have investigated the property of the 11-year and 22-year cycles around the two grand solar minima; the Maunder Minimum (1645–1715 AD) and the Spoerer Minimum (1415–1534 AD), the periods of prolonged sunspot minima. As a result, slight stretching of the “11-year” and the “22-year” solar cycles was found during these two grand solar activity minima; continuously during the Maunder Minimum and only intermittently during the Spoerer Minimum. On the contrary, normal or slightly shortened 11-year cycles were detected during the interval period of these two minima. It suggests the inverse correlation between the solar cycle length and solar magnetic activity level, and also the change of meridional flow during the grand solar activity minima. Further measurements for the beginning of the grand solar minima will provide a clue to the occurrence of such prolonged sunspot disappearance. We also discuss the effect of solar variations to radiocarbon dating.  相似文献   

Spatial variability and correlation of environmental proxies during the past 18,000 years among multiple cores from Lake Pumoyum Co,Tibet, China   总被引：3，自引：0，他引：3  

Junbo Wang  Liping Zhu  Mitsugu Nishimura  Toshio Nakamura  Jianting Ju  Manping Xie  Watanabe Takahiro  Matsunaka Testsuya 《Journal of Paleolimnology》2009,42(3):303-315

Multiple cores from Lake Pumoyum Co, southern Tibet, provide an improved understanding of the spatial distribution of lake sediments, and how well they represent the paleo-climate. Comparative study of these cores using AMS ¹⁴C dating and environmental proxies clarified their relationships with environmental changes. Our work focused on understanding the spatial similarities among cores covering different time scales, and evaluating variations in sedimentary processes across sites. The four studied cores demonstrate different sedimentation rates, but environmental proxies help synchronize the timing of environmental variations. Sediment variables such as total organic carbon (TOC), inorganic carbon (IC), and grain size in different cores correlate well and corroborate changing trends over the past 10,000 cal years. Differences in sedimentation rates and facies among core sites probably result largely from differences in water depth. The core from the deepest site displays the highest average sedimentation rates and the highest accumulation rates of TOC, but lowest content of IC. Two cores from somewhat shallower sites have plant residues in their lower sections and record similar variations in both the number of layers and their depositional ages. Our results do not indicate any significant variation in sedimentation pattern or its related factors among the three sites. A single core from the deepest site could adequately represent the total lake environment over the time span covered. But cores from somewhat shallower sites might reveal important shifts in the environment over a longer time period.  相似文献   

Cyclicity of Solar Activity During the Maunder Minimum Deduced from Radiocarbon Content     

Hiroko Miyahara  Kimiaki Masuda  Yasushi Muraki  Hideki Furuzawa  Hiroaki Menjo  Toshio Nakamura 《Solar physics》2004,224(1-2):317-322

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New canonical variables for orbital and rotational motions     

Toshio Fukushima 《Celestial Mechanics and Dynamical Astronomy》1994,60(1):57-68

A new canonical transformation of freedom two was found. By using this, we derived three new sets of canonical variables for the orbital motion and two for the rotational motion. New canonical variables have clear physical meanings and remain well-defined in the case when the classical sets become ill-defined, for example, when the eccentricity and/or the inclination is small for the elliptic orbital motion.  相似文献   

Observations of an intrusion of a warmer and less saline water mass into a bay     

Toshio Yamagata  Shin-Ichiro Umatani  Noriaki Masunaga  Tomonori Matsuura 《Continental Shelf Research》1984,3(4):475-488

Detailed hydrographic observations were made in Wakasa Bay, Japan, in August 1979 as the first of a series on the topic of bay intrusions. An anomalous water tongue, evident at a depth of 50 m, was observed to move eastward into the bay at a speed of about 10 km day⁻¹. The width of the tongue was about 20 to 30 km in agreement with the Rossby internal radius of deformation. The results of current meter measurements and the observed temporal and spatial evolution of the temperature field near the front of the anomalous water tongue have suggested that ageostrophic cross-frontal motion, in balance with the along-front acceleration, may be important in our understanding of intrusion processes.  相似文献   

Influence of Indian Ocean Dipole and Pacific recharge on following year’s El Niño: interdecadal robustness   总被引：1，自引：1，他引：0  

Takeshi Izumo  Matthieu Lengaigne  Jérôme Vialard  Jing-Jia Luo  Toshio Yamagata  Gurvan Madec 《Climate Dynamics》2014,42(1-2):291-310

The Indian Ocean Dipole (IOD) can affect the El Niño–Southern Oscillation (ENSO) state of the following year, in addition to the well-known preconditioning by equatorial Pacific Warm Water Volume (WWV), as suggested by a study based on observations over the recent satellite era (1981–2009). The present paper explores the interdecadal robustness of this result over the 1872–2008 period. To this end, we develop a robust IOD index, which well exploits sparse historical observations in the tropical Indian Ocean, and an efficient proxy of WWV interannual variations based on the temporal integral of Pacific zonal wind stress (of a historical atmospheric reanalysis). A linear regression hindcast model based on these two indices in boreal fall explains 50 % of ENSO peak variance 14 months later, with significant contributions from both the IOD and WWV over most of the historical period and a similar skill for El Niño and La Niña events. Our results further reveal that, when combined with WWV, the IOD index provides a larger ENSO hindcast skill improvement than the Indian Ocean basin-wide mode, the Indian Monsoon or ENSO itself. Based on these results, we propose a revised scheme of Indo-Pacific interactions. In this scheme, the IOD–ENSO interactions favour a biennial timescale and interact with the slower recharge-discharge cycle intrinsic to the Pacific Ocean.  相似文献   

Dynamical seasonal prediction of Southern African summer precipitation     

Chaoxia Yuan  Tomoki Tozuka  Willem A. Landman  Toshio Yamagata 《Climate Dynamics》2014,42(11-12):3357-3374

Prediction skill for southern African (16°–33°E, 22°–35°S) summer precipitation in the Scale Interaction Experiment-Frontier coupled model is assessed for the period of 1982–2008. Using three different observation datasets, deterministic forecasts are evaluated by anomaly correlation coefficients, whereas scores of relative operating characteristic and relative operating level are used to evaluate probabilistic forecasts. We have found that these scores for December–February precipitation forecasts initialized on October 1st are significant at 95 % confidence level. On a local scale, the level of prediction skill in the northwestern and central parts of southern Africa is higher than that in northeastern South Africa. El Niño/Southern Oscillation (ENSO) provides the major source of predictability, but the relationship with ENSO is too strong in the model. The Benguela Niño, the basin mode in the tropical Indian Ocean, the subtropical dipole modes in the South Atlantic and the southern Indian Oceans and ENSO Modoki may provide additional sources of predictability. Within the wet season from October to the following April, the precipitation anomalies in December-February are the most predictable. This study presents promising results for seasonal prediction of precipitation anomaly in the extratropics, where seasonal prediction has been considered a difficult task.  相似文献   

Impacts of South China Sea throughflow on the mean state and El Niño/Southern Oscillation as revealed by a coupled GCM   总被引：1，自引：0，他引：1  

Tomoki Tozuka  Tangdong Qu  Toshio Yamagata 《Journal of Oceanography》2015,71(1):105-114

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An index for tropical temperate troughs over southern Africa     

Satyaban B. Ratna  Swadhin Behera  J. Venkata Ratnam  Keiko Takahashi  Toshio Yamagata 《Climate Dynamics》2013,41(2):421-441

Strong cases of the tropical temperate troughs (TTT) that are responsible for the most of the summer rainfall over subtropical southern Africa are analyzed. An index for identifying the TTT is introduced for the first time using anomalies of outgoing longwave radiation (OLR) and the wind. The TTT is associated with a ridge-trough-ridge wave-like structure in the lower troposphere over southern Africa and the adjoining Indian Ocean. Therefore, the index considers physical processes that occur over southern Africa, adjoining the Atlantic and Indian Oceans to depict the variability of the TTT events. Unusually strong TTT events are identified when the standard deviations of the TTT indices defined by the OLR and wind anomalies in the selected regions are above 1.5 and 0.5 respectively. After applying this criterion and filtering out consecutive events, 55 TTT events are identified during the study period of December–January–February seasons from 1980–1981 to 2009–2010. From the composite analyses of those 55 events, it is found that the TTTs evolve with suppressed (enhanced) convection over the southwest Indian Ocean adjacent to Madagascar (southern Africa). The suppressed convection is, in turn, found to be associated with the enhanced convection around Sumatra in the southeast tropical Indian Ocean. This may explain why more TTT events occur in La Niña years as compared to El Niño years. Time evolution of the canonical TTT event shows that it starts 3 days prior to the mature phase of the event, suggesting possible predictability. After reaching a matured state, the system moves east toward the Indian Ocean and decays within the subsequent couple of days. In addition, the intertropical convergence zone (ITCZ) structure changes over Southern Africa/Madagascar during the TTT event and remains similar to climatology over other regions. The results indicate that the continental part of the ITCZ intensifies prior to the TTT event and then spreads southward following the mid-latitude influence during and after the event.  相似文献