著者

IWAKIRI Tomoki WATANABE Masahiro

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2020-064, (Released:2020-08-28)

被引用文献数

14

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La Niña is the negative phase of the El Niño-Southern Oscillation (ENSO) cycle. It occurs in the equatorial Pacific, and events known as multiyear La Niña often persist for more than two years. During a conventional La Niña event, the seasonal cycle of surface temperature over Japan is known to be amplified (i.e. hotter summer and colder winter than normal years), but the influence of multiyear events on temperature over Japan has not yet been clarified. In this study, we evaluate the teleconnection associated with multiyear La Niña using composite analyses of observations, reanalysis data, and a large-ensemble of atmospheric general circulation model (AGCM) simulations for 1951-2010 driven by observed boundary conditions, and propose two distinct mechanisms involved in multiyear La Niña causing hot summers over Japan.  Composites of observational data show significant positive temperature anomalies over Japan in the boreal summer season preceding the two consecutive La Niña events reaching their mature phases. This robust summer signal can be reproduced by AGCM large ensemble simulations, which indicates that it is forced by multiyear La Niña. The time evolution of the anomalous summer temperature over Japan differs between the first and second years of multiyear La Niña. In the first summer, warm conditions are found in August–October in the southwestern part of Japan, due to anomalous southwesterly winds in the lower troposphere. This atmospheric circulation anomaly can be explained by a La Niña-induced decrease in precipitation over the equatorial western Pacific. In the second summer, warm anomalies are found in June–August over northeastern Japan, and these are accompanied by an anomalous barotropic high-pressure induced by negative precipitation anomalies over the equatorial Pacific. The seasonal march in atmospheric background states and the delayed effect of a preceding El Niño may explain the distinct teleconnection during multiyear La Niña.

著者

MOGI Atsushi WATANABE Masahiro

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2022-025, (Released:2022-02-03)

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Extremely hot days in Japan are known to persist for a week or more, and they are measured by the temperature anomaly at 850 hPa averaged over Japan derived from the JRA-55 reanalysis data, denoted as T850JP. Severe high-temperature anomalies are often accompanied by multiple teleconnection patterns that affect the weather in Japan, but their relative contribution to individual heat wave events has not yet been quantified. In this study, we examined the effects of three major teleconnection patterns, namely, the Pacific-Japan (PJ), circumglobal teleconnection (CGT), and Siberian patterns, on T850JP in July and August from 1958-2019 using daily low-pass filtered anomalies with 8 days cutoff time-scale derived from the reanalysis. A linear regression analysis demonstrated that T850JP tended to show a large positive anomaly one or two days after the peak of these patterns. Based on this relationship, we reconstructed a daily T850JP time series using a multivariate statistical model wherein the parameters were estimated using regression analyses between T850JP and indices of the three teleconnection patterns. The reconstructed T850JP showed that the three teleconnection patterns together accounted for 50 % of the total variance of T850JP for extremely hot summers, to which each of the three teleconnection patterns were found to have a similar degree of contribution. The statistical model reproduces the interannual variability along with the long-term T850JP trend. The PJ pattern has the largest effect on the interannual variability of T850JP, probably due to the PJ teleconnection occurring over a longer timescale compared with the other two patterns. The reconstructed T850JP also displays a warming trend associated with an increasing trend in the CGT index, which may be a factor, along with the direct thermodynamic effects due to global warming, to explain the long-term increase in the heat wave frequency in Japan.

著者

TAKAHASHI Chiharu IMADA Yukiko WATANABE Masahiro

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2022-014, (Released:2021-11-12)

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The present study found a significant influence of the Madden-Julian Oscillation (MJO) on the occurrence probability of extreme snowfall and precipitation in Japan during boreal winter (December-February) using observational data and the Database for Policy Decision Making for Future Climate Change (d4PDF). The analysis of d4PDF containing 90-member and 50-member ensemble historical simulations by global and high-resolution regional models, respectively, enabled us to quantify and elucidate the geographical distribution of the occurrence probability of extreme weather in Japan related to the MJO. The d4PDF global simulations well represent the MJO and its teleconnection over the Pacific-North America region. Our results show that (1) the probability of extreme snowfall on the Sea of Japan side of northwestern Japan (SJA) increases (decreases) by approximately 20 % (30-40 %) associated with enhanced MJO over the Maritime Continent and western Pacific (western Indian Ocean) relative to that for all winter days; (2) the extreme precipitation on the Pacific Ocean side (PAC) of Japan increases (reduces) by 40-50 % (approximately 30 %) when the MJO is active over the Indian Ocean (western Pacific); and (3) the extreme snowfall on the Kanto area in PAC increases by 30-45 % when the MJO is enhanced over the eastern Indian Ocean and Maritime Continent. Composite analysis reveals that different physical processes associated with the MJO are responsible for the occurrence of extremes in the three regions. The MJO intensifies cold air intrusion from Siberia into Japan associated with a more frequent blocking over East Siberia, causing extreme snowfall in SJA. The MJO stimulates the explosive development of extratropical cyclones due to enhanced moisture flux convergence, leading to extreme precipitation in PAC and extreme snowfall in Kanto. Furthermore, the Kanto snowfall is partly related to a cold air outflow from the blocking induced by the MJO.

著者

Watanabe Masahiro Kaneoka Koji Okubo Yu Shiina Itsuo Tatsumura Masaki Miyakawa Shumpei

出版者

Elsevier

雑誌

Physiotherapy (ISSN:00319406)

巻号頁・発行日

vol.99, no.1, pp.78-83, 2013-03

被引用文献数

11 2

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ObjectiveTo determine trunk muscle activity when lifting an object of greater weight than expected, which may contribute to the development of low back pain.DesignElectromyographic evaluation of trunk muscle activity.SettingUniversity of Tsukuba, Spine laboratory.ParticipantsEleven healthy men with a mean age of 24 (SD 2) years.InterventionsTrunk muscle activity was measured when subjects lifted an object with their right arm in immediate response to a light stimulus. Surface and wire electrodes were used to measure the activity of the rectus abdominis, external oblique and erector spinae muscles, and the transversus abdominis and lumbar multifidus muscles, respectively. The lifting tests were performed in three different settings: lifting an expected 1-kg object, lifting an unexpected 4-kg object (erroneously expected to weigh 1 kg), and lifting an expected 4-kg object.Main outcome measuresThe muscle activity induced when subjects lifted objects of different weights was compared by calculating the root mean square (RMS) of muscle activity at rest and % maximum voluntary contraction.ResultsWhen the subjects were aware of the weight of the object to be lifted, the activity of the external oblique, transversus abdominis, erector spinae and lumbar multifidus muscles increased immediately after lifting. When the subjects were not aware of the weight of the object to be lifted, the increase in muscle activity was delayed (P < 0.05).ConclusionsTrunk muscles may not be able to function appropriately when individuals lift an object that is much heavier than expected.