2021/05/13 更新

写真a

ウキタ ジンロウ
浮田 甚郎
UKITA Jinro
所属
教育研究院 自然科学系 地球・生物科学系列 教授
自然科学研究科 環境科学専攻 教授
理学部 理学科 教授
職名
教授
外部リンク

学位

  • 博士(理学) ( 1997年9月   北海道大学 )

  • 修士(理学) ( 1990年8月   ワシントン州立大学 )

経歴

  • 新潟大学   理学部 理学科   教授

    2017年4月 - 現在

  • 新潟大学   自然科学研究科 環境科学専攻   教授

    2010年4月 - 現在

  • 新潟大学   自然科学研究科 環境科学専攻   教授

    2010年4月 - 現在

  • 新潟大学   物質循環科学   教授

    2007年9月 - 2017年3月

 

論文

  • On the role of Ural Blocking in driving the Warm Arctic-Cold Siberia pattern 査読

    Evangelos Tyrlis, Juergen Bader, Elisa Manzini, Jinro Ukita, Hisashi Nakamura, Daniela Matei

    QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY146 ( 730 ) 2138 - 2153   2020年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY  

    We use reanalysis data to substantiate the role of Ural blocking (UB) in driving the Warm Arctic-Cold Siberia (WACS) pattern, which represents an anti-correlation of surface temperature between the Barents-Kara Seas and central Asia. We confirm a robust link between UB and the WACS pattern on daily to subseasonal time-scales. UB controls the pace of the WACS pattern; warming over the Barents-Kara Seas and cooling over central Asia peak 3-5 days after the UB onset. The observed sea ice deficit over the Barents-Kara Seas in the weeks prior to UB onset is not statistically significant when the long-term trend in sea ice is removed. Thus, the sea ice deficit may not have a direct impact on UB occurrence but it develops as a delayed response to UB. The interannual variability of the WACS pattern is also strongly linked to UB. We identify an upward trend in wintertime UB in recent decades that accounts for a cooling rate of 1 degrees C/decade over central Asia. Over the Barents-Kara Seas, UB trends explain a small fraction of the warming, which is dominated by Arctic amplification. Finally, the link between UB and the WACS pattern is statistically robust over the ERA-Interim period but weaker during the 1990s when the lowest UB activity was observed.

    DOI: 10.1002/qj.3784

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MISC

  • A tropospheric pathway of the stratospheric quasi-biennial oscillation (QBO) impact on the boreal winter polar vortex 査読

    Koji Yamazaki, Tetsu Nakamura, Jinro Ukita, Kazuhira Hoshi

    ATMOSPHERIC CHEMISTRY AND PHYSICS20 ( 8 ) 5111 - 5127   2020年4月

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    記述言語:英語   出版者・発行元:COPERNICUS GESELLSCHAFT MBH  

    The quasi-biennial oscillation (QBO) is quasiperiodic oscillation of the tropical zonal wind in the stratosphere. When the tropical lower stratospheric wind is easterly (westerly), the winter Northern Hemisphere (NH) stratospheric polar vortex tends to be weak (strong). This relation is known as the Holton-Tan relationship. Several mechanisms for this relationship have been proposed, especially linking the tropics with high latitudes through stratospheric pathway. Although QBO impacts on the troposphere have been extensively discussed, a tropospheric pathway of the Holton-Tan relationship has not been explored previously. Here, we propose a tropospheric pathway of the QBO impact, which may partly account for the Holton-Tan relationship in early winter, especially in the November-December period. The study is based on analyses of observational data and results from a simple linear model and atmospheric general circulation model (AGCM) simulations. The mechanism is summarized as follows: the easterly phase of the QBO is accompanied with colder temperature in the tropical tropopause layer, which enhances convective activity over the tropical western Pacific and suppresses it over the Indian Ocean, thus enhancing the Walker circulation. This convection anomaly generates a Rossby wave train, propagating into the midlatitude troposphere, which constructively interferences with the climatological stationary waves, especially in wavenumber 1, resulting in enhanced upward propagation of the planetary wave and a weakened polar vortex.

    DOI: 10.5194/acp-20-5111-2020

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  • Incorporation of satellite-derived thin-ice data into a global OGCM simulation 査読

    Takahiro Toyoda, Katsushi Iwamoto, L. Shogo Urakawa, Hiroyuki Tsujino, Hideyuki Nakano, Kei Sakamoto, Goro Yamanaka, Yoshiki Komuro, Shigeto Nishino, Jinro Ukita

    CLIMATE DYNAMICS53 ( 11 ) 7113 - 7130   2019年12月

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    記述言語:英語   出版者・発行元:SPRINGER  

    The presence of thin sea ice is indicative of active freezing conditions in the polar ocean. We propose a simple yet effective method to incorporate information of thin-ice category into coupled ocean-sea-ice model simulations. In our approach, the thin-ice distribution restricts thick-ice extent and constrains atmosphere-ocean heat exchange through the sea ice. Our model simulation with the incorporation of satellite-derived thin-ice data for the Arctic Ocean showed much improved representation of sea-ice and upper-ocean fields, including sea-ice thickness in the Canadian Archipelago and the region north of Greenland, mixed-layer depth over the Central Arctic, and surface-layer salinity over the open ocean. Enhanced sea-ice production by the thin-ice data constraint increased the total sea-ice volume of the Arctic Ocean by 5x103-10x103 km(3). Subsequent sea-ice melting was also enhanced, leading to the greater amplitude of the seasonal cycle by approximately 2x103 km(3) (15% of the baseline value from the experiment without the thin-ice data incorporation). Overall, our results demonstrate that the incorporation of satellite-derived information on thin sea ice has great potential for the improvement of coupled ocean-sea-ice simulations.

    DOI: 10.1007/s00382-019-04979-8

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  • Ural Blocking Driving Extreme Arctic Sea Ice Loss, Cold Eurasia, and Stratospheric Vortex Weakening in Autumn and Early Winter 2016-2017 査読

    Evangelos Tyrlis, Elisa Manzini, Juergen Bader, Jinro Ukita, Hisashi Nakamura, Daniela Matei

    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES124 ( 21 ) 11313 - 11329   2019年11月

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    記述言語:英語   出版者・発行元:AMER GEOPHYSICAL UNION  

    This study investigates the dynamics that led to the repeated cold surges over midlatitude Eurasia, exceptionally warm conditions and sea ice loss over the Arctic, and the unseasonable weakening of the stratospheric polar vortex in autumn and early winter 2016-2017. We use ERA-Interim reanalysis data and COBE sea ice and sea surface temperature observational data to trace the dynamical pathways that caused these extreme phenomena. Following abnormally low sea ice conditions in early autumn over the Pacific sector of the Arctic basin, blocking anticyclones became dominant over Eurasia throughout autumn. Ural blocking (UB) activity was four times above climatological levels and organized in several successive events. UB episodes played a key role in the unprecedented sea ice loss observed in late autumn 2016 over the Barents-Kara Seas and the weakening of the stratospheric vortex. Each blocking induced circulation anomalies that resulted in cold air advection to its south and warm advection to its north. The near-surface warming anomalies over the Arctic and cooling anomalies over midlatitude Eurasia varied in phase with the life cycles of UB episodes. The sea ice cover minimum over the Barents-Kara Seas in 2016 was not observed in late summer but rather in mid-November and December shortly after the two strongest UB episodes. Each UB episode drove intense upward flux of wave activity that resulted in unseasonable weakening of the stratospheric vortex in November. The surface impact of this weakening can be linked to the migration of blocking activity and cold spells toward Europe in early winter 2017.

    DOI: 10.1029/2019JD031085

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  • Memory effects of Eurasian land processes cause enhanced cooling in response to sea ice loss 査読

    Tetsu Nakamura, Koji Yamazaki, Tomonori Sato, Jinro Ukita

    NATURE COMMUNICATIONS10   2019年11月

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    記述言語:英語   出版者・発行元:NATURE PUBLISHING GROUP  

    Amplified Arctic warming and its relevance to mid-latitude cooling in winter have been intensively studied. Observational evidence has shown strong connections between decreasing sea ice and cooling over the Siberian/East Asian regions. However, the robustness of such connections remains a matter of discussion because modeling studies have shown divergent and controversial results. Here, we report a set of general circulation model experiments specifically designed to extract memory effects of land processes that can amplify sea ice-climate impacts. The results show that sea ice-induced cooling anomalies over the Eurasian continent are memorized in the snow amount and soil temperature fields, and they reemerge in the following winters to enhance negative Arctic Oscillation-like anomalies. The contribution from this memory effect is similar in magnitude to the direct effect of sea ice loss. The results emphasize the essential role of land processes in understanding and evaluating the Arctic-mid-latitude climate linkage.

    DOI: 10.1038/s41467-019-13124-2

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  • Uncertainties in Arctic Sea Ice Thickness Associated with Different Atmospheric Reanalysis Datasets Using the CICE5 Model 査読

    Su-Bong Lee, Baek-Min Kim, Jinro Ukita, Joong-Bae Ahn

    ATMOSPHERE10 ( 7 )   2019年7月

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    記述言語:英語   出版者・発行元:MDPI  

    Reanalysis data are known to have relatively large uncertainties in the polar region than at lower latitudes. In this study, we used a single sea-ice model (Los Alamos' CICE5) and three sets of reanalysis data to quantify the sensitivities of simulated Arctic sea ice area and volume to perturbed atmospheric forcings. The simulated sea ice area and thickness thus volume were clearly sensitive to the selection of atmospheric reanalysis data. Among the forcing variables, changes in radiative and sensible/latent heat fluxes caused significant amounts of sensitivities. Differences in sea-ice concentration and thickness were primarily caused by differences in downward shortwave and longwave radiations. 2-m air temperature also has a significant influence on year-to-year variability of the sea ice volume. Differences in precipitation affected the sea ice volume by causing changes in the insulation effect of snow-cover on sea ice. The diversity of sea ice extent and thickness responses due to uncertainties in atmospheric variables highlights the need to carefully evaluate reanalysis data over the Arctic region.

    DOI: 10.3390/atmos10070361

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  • The role of stratospheric ozone for Arctic-midlatitude linkages 査読

    Erik Romanowsky, Doerthe Handorf, Ralf Jaiser, Ingo Wohltmann, Wolfgang Dorn, Jinro Ukita, Judah Cohen, Klaus Dethloff, Markus Rex

    SCIENTIFIC REPORTS9   2019年5月

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    記述言語:英語   出版者・発行元:NATURE PUBLISHING GROUP  

    Arctic warming was more pronounced than warming in midlatitudes in the last decades making this region a hotspot of climate change. Associated with this, a rapid decline of sea-ice extent and a decrease of its thickness has been observed. Sea-ice retreat allows for an increased transport of heat and momentum from the ocean up to the tropo- and stratosphere by enhanced upward propagation of planetary-scale atmospheric waves. In the upper atmosphere, these waves deposit the momentum transported, disturbing the stratospheric polar vortex, which can lead to a breakdown of this circulation with the potential to also significantly impact the troposphere in mid- to late-winter and early spring. Therefore, an accurate representation of stratospheric processes in climate models is necessary to improve the understanding of the impact of retreating sea ice on the atmospheric circulation. By modeling the atmospheric response to a prescribed decline in Arctic sea ice, we show that including interactive stratospheric ozone chemistry in atmospheric model calculations leads to an improvement in tropo-stratospheric interactions compared to simulations without interactive chemistry. This suggests that stratospheric ozone chemistry is important for the understanding of sea ice related impacts on atmospheric dynamics.

    DOI: 10.1038/s41598-019-43823-1

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  • The Polar Amplification Model Intercomparison Project (PAMIP) contribution to CMIP6: investigating the causes and consequences of polar amplification 査読

    Doug M. Smith, James A. Screen, Clara Deser, Judah Cohen, John C. Fyfe, Javier Garcia-Serrano, Thomas Jung, Vladimir Kattsov, Daniela Matei, Rym Msadek, Yannick Peings, Michael Sigmond, Jinro Ukita, Jin-Ho Yoon, Xiangdong Zhang

    GEOSCIENTIFIC MODEL DEVELOPMENT12 ( 3 ) 1139 - 1164   2019年3月

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    記述言語:英語   出版者・発行元:COPERNICUS GESELLSCHAFT MBH  

    Polar amplification - the phenomenon where external radiative forcing produces a larger change in surface temperature at high latitudes than the global average - is a key aspect of anthropogenic climate change, but its causes and consequences are not fully understood. The Polar Amplification Model Intercomparison Project (PAMIP) contribution to the sixth Coupled Model Intercomparison Project (CMIP6; Eyring et al., 2016) seeks to improve our understanding of this phenomenon through a coordinated set of numerical model experiments documented here. In particular, PAMIP will address the following primary questions: (1) what are the relative roles of local sea ice and remote sea surface temperature changes in driving polar amplification? (2) How does the global climate system respond to changes in Arctic and Antarctic sea ice? These issues will be addressed with multi-model simulations that are forced with different combinations of sea ice and/or sea surface temperatures representing present-day, pre-industrial and future conditions. The use of three time periods allows the signals of interest to be diagnosed in multiple ways. Lower-priority tier experiments are proposed to investigate additional aspects and provide further understanding of the physical processes. These experiments will address the following specific questions: what role does ocean-atmosphere coupling play in the response to sea ice? How and why does the atmospheric response to Arctic sea ice depend on the pattern of sea ice forcing? How and why does the atmospheric response to Arctic sea ice depend on the model background state? What have been the roles of local sea ice and remote sea surface temperature in polar amplification, and the response to sea ice, over the recent period since 1979? How does the response to sea ice evolve on decadal and longer timescales?A key goal of PAMIP is to determine the real-world situation using imperfect climate models. Although the experiments proposed here form a coordinated set, we anticipate a large spread across models. However, this spread will be exploited by seeking "emergent constraints" in which model uncertainty may be reduced by using an observable quantity that physically explains the intermodel spread. In summary, PAMIP will improve our understanding of the physical processes that drive polar amplification and its global climate impacts, thereby reducing the uncertainties in future projections and predictions of climate change and variability.

    DOI: 10.5194/gmd-12-1139-2019

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  • Weak Stratospheric Polar Vortex Events Modulated by the Arctic Sea-Ice Loss 査読

    Kazuhira Hoshi, Jinro Ukita, Meiji Honda, Tetsu Nakamura, Koji Yamazaki, Yasunobu Miyoshi, Ralf Jaiser

    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES124 ( 2 ) 858 - 869   2019年1月

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    記述言語:英語   出版者・発行元:AMER GEOPHYSICAL UNION  

    We characterize the differences in the upward planetary-scale wave propagation during observed weak polar vortex (WPV) events between heavy- and light-sea-ice years in the Barents-Kara Sea based on a composite analysis for the period of 1979-2015. Upward wave propagation during WPV events in heavy-ice years is dominated by the wavenumber 1 component. In contrast, WPV events occurring in light-ice years are characterized by stronger wavenumber 2 propagation, which is caused by the tropospheric wavenumber 2 response to sea-ice reduction in the Barents-Kara Sea. The above observed features are supported by an Atmospheric General Circulation Model experiment. Thus, under present climate conditions, Arctic sea-ice loss is a possible factor modulating the wave propagation during the WPV events. We also find that the WPV events in light-ice years have stronger stratosphere-troposphere coupling, followed by colder midlatitude surface conditions particularly over Eurasia.

    DOI: 10.1029/2018JD029222

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  • Detection of a climatological short break in the polar night jet in early winter and its relation to cooling over Siberia 査読

    Yuta Ando, Koji Yamazaki, Yoshihiro Tachibana, Masayo Ogi, Jinro Ukita

    ATMOSPHERIC CHEMISTRY AND PHYSICS18 ( 17 ) 12639 - 12661   2018年8月

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    記述言語:英語   出版者・発行元:COPERNICUS GESELLSCHAFT MBH  

    The polar night jet (PNJ) is a strong stratospheric westerly circumpolar wind at around 65 degrees N in winter, and the strength of the climatological PNJ is widely recognized to increase from October through late December. Remarkably, the climatological PNJ temporarily stops increasing during late November. We examined this "short break" in terms of the atmospheric dynamical balance and the climatological seasonal march. We found that it results from an increase in the upward propagation of climatological planetary waves from the troposphere to the stratosphere in late November, which coincides with a maximum of the climatological Eliassen-Palm (EP) flux convergence in the lower stratosphere. The upward propagation of planetary waves at 100 hPa, which is strongest over Siberia, is related to the climatological strengthening of the tropospheric trough over Siberia. We suggest that longitudinally asymmetric forcing by land-sea heating contrasts caused by their different heat capacities can account for the strengthening of the trough.

    DOI: 10.5194/acp-18-12639-2018

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  • Evaluating Impacts of Recent Arctic Sea Ice Loss on the Northern Hemisphere Winter Climate Change 査読

    Fumiaki Ogawa, Noel Keenlyside, Yongqi Gao, Torben Koenigk, Shuting Yang, Lingling Suo, Tao Wang, Guillaume Gastineau, Tetsu Nakamura, Ho Nam Cheung, Nour-Eddine Omrani, Jinro Ukita, Vladimir Semenov

    GEOPHYSICAL RESEARCH LETTERS45 ( 7 ) 3255 - 3263   2018年4月

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    記述言語:英語   出版者・発行元:AMER GEOPHYSICAL UNION  

    Wide disagreement among individual modeling studies has contributed to a debate on the role of recent sea ice loss in the Arctic amplification of global warming and the Siberian wintertime cooling trend. We perform coordinated experiments with six atmospheric general circulation models forced by the observed and climatological daily sea ice concentration and sea surface temperature. The results indicate that the impact of the recent sea ice decline is rather limited to the high-latitude lower troposphere in winter, and the sea ice changes do not significantly lead to colder winters over Siberia. The observed wintertime Siberian temperature and corresponding circulation trends are reproduced in a small number of ensemble members but not by the multimodel ensemble mean, suggesting that atmospheric internal dynamics could have played a major role in the observed trends.Plain Language Summary Understanding the mechanism governing the ongoing global warming is a major challenge facing our society and its sustainable growth. Together with the CO2-forced warming, the concurrent polar sea ice loss might also have contributed to the observed Arctic warming amplification and also to the cooling trends over Eurasia through a dynamical teleconnection. However, previous individual modeling studies suggest widely different findings on the role of sea ice loss in Northern Hemisphere climate change. To help resolve this controversy, we used satellite-derived sea ice and sea-surface temperature to run coordinated hindcast experiments with five different atmospheric general circulation models. The multimodel ensemble-mean results presented in the paper reduce biases of each model and eliminate atmospheric internal unforced variability, and thus provide the best estimate to date of the signal of the polar sea ice loss. The results suggest that the impact of sea ice seems critical for the Arctic surface temperature changes, but the temperature trends elsewhere seem rather due to either sea-surface temperature changes or atmospheric internal variability. They give clear guidance on how to provide society with more accurate climate change attributions. Our work is of interest to stakeholders of countries in the Northern Hemisphere middle and high latitudes.

    DOI: 10.1002/2017GL076502

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  • Large drainages from short-lived glacial lakes in the Teskey Range, Tien Shan Mountains, Central Asia 査読

    Chiyuki Narama, Mirlan Daiyrov, Murataly Duishonakunov, Takeo Tadono, Hayato Sato, Andreas Kaab, Jinro Ukita, Kanatbek Abdrakhmatov

    NATURAL HAZARDS AND EARTH SYSTEM SCIENCES18 ( 4 ) 983 - 995   2018年4月

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    記述言語:英語   出版者・発行元:COPERNICUS GESELLSCHAFT MBH  

    Four large drainages from glacial lakes occurred during 2006-2014 in the western Teskey Range, Kyrgyzstan. These floods caused extensive damage, killing people and livestock as well as destroying property and crops. Using satellite data analysis and field surveys of this area, we find that the water volume that drained at Kashkasuu glacial lake in 2006 was 194 000 m3, at western Zyndan lake in 2008 was 437 000m(3), at Jeruy lake in 2013 was 182 000m(3), and at Karateke lake in 2014 was 123 000m(3). Due to their subsurface outlet, we refer to these short-lived glacial lakes as the "tunnel-type", a type that drastically grows and drains over a few months. From spring to early summer, these lakes either appear, or in some cases, significantly expand from an existing lake (but non-stationary), and then drain during summer. Our field surveys show that the short-lived lakes form when an ice tunnel through a debris landform gets blocked. The blocking is caused either by the freezing of stored water inside the tunnel during winter or by the collapse of ice and debris around the ice tunnel. The draining then occurs through an opened ice tunnel during summer. The growth-drain cycle can repeat when the ice-tunnel closure behaves like that of typical supraglacial lakes on debris-covered glaciers. We argue here that the geomorphological characteristics under which such short-lived glacial lakes appear are (i) a debris landform containing ice (ice-cored moraine complex), (ii) a depression with water supply on a debris landform as a potential lake basin, and (iii) no visible surface outflow channel from the depression, indicating the existence of an ice tunnel. Applying these characteristics, we examine 60 depressions (>0.01 km(2)) in the study region and identify here 53 of them that may become short-lived glacial lakes, with 34 of these having a potential drainage exceeding 10m(3) s(-1) at peak discharge.

    DOI: 10.5194/nhess-18-983-2018

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  • Regional Geomorphological Conditions Related to Recent Changes of Glacial Lakes in the Issyk-Kul Basin, Northern Tien Shan 査読

    Mirlan Daiyrov, Chiyuki Narama, Tsutomu Yamanokuchi, Takeo Tadono, Andreas Kaab, Jinro Ukita

    GEOSCIENCES8 ( 3 )   2018年3月

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    記述言語:英語   出版者・発行元:MDPI  

    To assess the current state of glacial lakes, we examine the seasonal lake-area changes of 339 glacial lakes in the Teskey and Kungoy Ranges of the Issyk-Kul Basin, Kyrgyzstan, during 2013-2016 based on optical satellite images (Landsat7/ETM+ and 8/OLI). The glacial lakes are classified into six types based on their seasonal variations in area: stable, increasing, decreasing, appearing, vanishing, and short-lived. We then track the number of each type in a given year and examine how each number changes from one year to the next. We find that many appearing, vanishing, and short-lived types occurred in both mountain ranges, having a large variability in number that is not directly related to the local short-term summer temperature anomaly, nor to precipitation or glacier recession. However, those in the Teskey Range vary significantly more than those in the Kungoy Range. To determine if the changing number and distribution of the various lake types may be due to changes in ground ice, we apply differential interferometric synthetic aperture radar (DInSAR) analysis using ALOS-2/PALSAR-2 for the debris landforms behind which glacial lakes appear. In the Teskey Range, ground ice occurs in 416 out of a total of 557 debris landforms, whereas in the Kungoy Range, ground ice occurs in 71 out of 131. In zones with predominant glacier-retreat during 1971-2010 (from Corona KH-4B and ALOS/PRISM), the Teskey Range had 180 new lake depressions as potential lake-basins, whereas the Kungoy Range had just 22. Existing depressions also expanded when melting ice produced subsidence. Such subsidence, together with debris landforms containing ground ice and ice tunnels, appear to cause the observed large number variability. In particular, the deposition of ice and debris by tunnel collapse or the freezing of storage water in a debris landform may close-off an ice tunnel, causing a lake to appear. Subsequent re-opening via melting of such blockage would produce either a vanishing or a short-lived type. In this way, the large variability in the number of each lake type and the distribution of types over this four-year period arises from regional geomorphological conditions and not directly from the local short-term summer temperature anomaly and precipitation or glacier recession.

    DOI: 10.3390/geosciences8030099

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  • Can preferred atmospheric circulation patterns over the North-Atlantic-Eurasian region be associated with arctic sea ice loss? 査読

    Berit Crasemann, Doerthe Handorf, Ralf Jaiser, Klaus Dethloff, Tetsu Nakamura, Jinro Ukita, Koji Yamazaki

    POLAR SCIENCE14   9 - 20   2017年12月

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    記述言語:英語   出版者・発行元:ELSEVIER  

    In the framework of atmospheric circulation regimes, we study whether the recent Arctic sea ice loss and Arctic Amplification are associated with changes in the frequency of occurrence of preferred atmospheric circulation patterns during the extended winter season from December to March. To determine regimes we applied a cluster analysis to sea-level pressure fields from reanalysis data and output from an atmospheric general circulation model. The specific set up of the two analyzed model simulations for low and high ice conditions allows for attributing differences between the simulations to the prescribed sea ice changes only. The reanalysis data revealed two circulation patterns that occur more frequently for low Arctic sea ice conditions: a Scandinavian blocking in December and January and a negative North Atlantic Oscillation pattern in February and March. An analysis of related patterns of synoptic-scale activity and 2 m temperatures provides a synoptic interpretation of the corresponding large-scale regimes. The regimes that occur more frequently for low sea ice conditions are resembled reasonably well by the model simulations. Based on those results we conclude that the detected changes in the frequency of occurrence of large-scale circulation patterns can be associated with changes in Arctic sea ice conditions. (C) 2017 The Authors. Published by Elsevier B.V.

    DOI: 10.1016/j.polar.2017.09.002

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  • Evaluating the Scale and Potential of GLOF in the Bhutan Himalayas Using a Satellite-Based Integral Glacier-Glacial Lake Inventory 査読

    Hiroto Nagai, Jinro Ukita, Chiyuki Narama, Koji Fujita, Akiko Sakai, Takeo Tadono, Tsutomu Yamanokuchi, Nobuhiro Tomiyama

    GEOSCIENCES7 ( 3 )   2017年9月

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    記述言語:英語   出版者・発行元:MDPI AG  

    A comprehensive glacier-glacial lake inventory was developed for the Bhutan Himalayas based on satellite observations between 1987-1990 and 2006-2011. In total, 733 lakes (covering 82.6 km(2)) were delineated between 4000 and 6000 m a.s.l. and their relationships to associated glaciers were documented. Using this new inventory, the scale and potential for glacial lake outburst flooding (GLOF) based on multiple criteria was examined. This included a history of connectivity characteristics of glacial lakes to mother glaciers, potential flood volumes, and debris-cover of mother glaciers in addition to the conventional criteria of expansion rate and lake size. The majority of the lakes with high expansion rates (more than double in size) and large areas (> 0.1 km(2)) met the conditions of being continuously in contact with a mother debris-covered glacier for nearly 20 years. Based on these multiple criteria, two lakes were identified as having potential for large-scale GLOF. Potentially dangerous glacial lakes listed in the International Centre for Integrated Mountain Development (ICIMOD) study were re-visited, and some overlaps with the glacier-glacial lake inventory were found.

    DOI: 10.3390/geosciences7030077

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  • Seasonal drainage of supraglacial lakes on debris-covered glaciers in the Tien Shan Mountains, Central Asia 査読

    Chiyuki Narama, Mirlan Daiyrov, Takeo Tadono, Minako Yamamoto, Andreas Kaab, Reira Morita, Jinro Ukita

    GEOMORPHOLOGY286   133 - 142   2017年6月

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    記述言語:英語   出版者・発行元:ELSEVIER  

    Using field surveys in 2013, 2014, and 2016 plus satellite data from the 1999-2015 period, we analyze the seasonal drainage cycle of supraglacial lakes on seven debris-covered glaciers in the central Tien Shan. We characterize this cycle by the number of lakes and their water levels. The cycle of the Southern Inylchek Glacier starts to increase in the beginning of April, reaches a maximum in May-June, and decreases sharply in June-July. The increase in April to June comes from an inflow of meltwater from snow and ice, and the subsequent decrease arises from a greater connectivity to the englacial drainage network. For the Southern Inylchek Glacier, 94% of the supraglacial lakes that exist and appear during 2013-2015 drain during all three years, indicating that most lakes could connect to the englacial drainage network for three years. Concerning the water level, lakes in close proximity and with the same base-level tend to synchronize their seasonal water levels through the englacial channels. Although the maximum water level of the three-year, field-measured lake is about the same from 2014 through 2016, the date of maximum water level varies between mid-May and mid-June. During this period, the lifetime and size of the supraglacial lakes are controlled by the timing of their connectivity to the englacial drainage network. (C) 2017 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.geomorph.2017.03.002

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  • Poleward eddy heat flux anomalies associated with recent Arctic sea ice loss 査読

    Kazuhira Hoshi, Jinro Ukita, Meiji Honda, Katsushi Iwamoto, Tetsu Nakamura, Koji Yamazaki, Klaus Dethloff, Ralf Jaiser, Doerthe Handorf

    GEOPHYSICAL RESEARCH LETTERS44 ( 1 ) 446 - 454   2017年1月

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    記述言語:英語   出版者・発行元:AMER GEOPHYSICAL UNION  

    Details of the characteristics of upward planetary wave propagation associated with Arctic sea ice loss under present climate conditions are examined using reanalysis data and simulation results. Recent Arctic sea ice loss results in increased stratospheric poleward eddy heat fluxes in the eastern and central Eurasia regions and enhanced upward propagation of planetary-scale waves in the stratosphere. A linear decomposition scheme reveals that this modulation of the planetary waves arises from coupling of the climatological planetary wavefield with temperature anomalies for the eastern Eurasia region and with meridional wind anomalies for the central Eurasia region. Propagation of stationary Rossby wave packets results in a dynamic link between these temperature and meridional wind anomalies with sea ice loss over the Barents-Kara Sea. The results provide strong evidence that recent Arctic sea ice loss significantly modulates atmospheric circulation in winter to modify poleward eddy heat fluxes so as to drive stratosphere-troposphere coupling processes.

    DOI: 10.1002/2016GL071893

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  • On the atmospheric response experiment to a Blue Arctic Ocean 査読

    Tetsu Nakamura, Koji Yamazaki, Meiji Honda, Jinro Ukita, Ralf Jaiser, Doerthe Handorf, Klaus Dethloff

    GEOPHYSICAL RESEARCH LETTERS43 ( 19 ) 10394 - 10402   2016年10月

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    記述言語:英語   出版者・発行元:AMER GEOPHYSICAL UNION  

    We demonstrated atmospheric responses to a reduction in Arctic sea ice via simulations in which Arctic sea ice decreased stepwise from the present-day range to an ice-free range. In all cases, the tropospheric response exhibited a negative Arctic Oscillation (AO)-like pattern. An intensification of the climatological planetary-scale wave due to the present-day sea ice reduction on the Atlantic side of the Arctic Ocean induced stratospheric polar vortex weakening and the subsequent negative AO. Conversely, strong Arctic warming due to ice-free conditions across the entire Arctic Ocean induced a weakening of the tropospheric westerlies corresponding to a negative AO without troposphere-stratosphere coupling, for which the planetary-scale wave response to a surface heat source extending to the Pacific side of the Arctic Ocean was responsible. Because the resultant negative AO-like response was accompanied by secondary circulation in the meridional plane, atmospheric heat transport into the Arctic increased, accelerating the Arctic amplification.

    DOI: 10.1002/2016GL070526

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  • Atmospheric winter response to Arctic sea ice changes in reanalysis data and model simulations 査読

    Ralf Jaiser, Tetsu Nakamura, Doerthe Handorf, Klaus Dethloff, Jinro Ukita, Koji Yamazaki

    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES121 ( 13 ) 7564 - 7577   2016年7月

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    記述言語:英語   出版者・発行元:AMER GEOPHYSICAL UNION  

    The changes of atmospheric flow patterns related to Arctic Amplification have impacts well beyond the Arctic regional weather and climate system. Here we examine modulations of vertically propagating planetary waves, a major feature of the climate response to Arctic sea ice reduction by comparing the corresponding results of an atmospheric general circulation model with reanalysis data for periods of high and low sea ice conditions. Under low sea ice condition we find enhanced coupling between troposphere and stratosphere starting in November with preferred polar stratospheric vortex breakdowns in February, which then feeds back to the troposphere. The model experiment and ERA-Interim reanalysis data agree well with respect to temporal and spatial characteristics associated with vertical planetary wave propagation including its precursors. The upward propagating planetary wave anomalies resemble a wave number 1 and 2 pattern depending on region and timing. Since our experimental design only allows influences from sea ice changes and there is a high degree of resemblance between model results and observations, we conclude that sea ice is a main driver of observed winter circulation changes.

    DOI: 10.1002/2015JD024679

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  • The stratospheric pathway for Arctic impacts on midlatitude climate 査読

    Tetsu Nakamura, Koji Yamazaki, Katsushi Iwamoto, Meiji Honda, Yasunobu Miyoshi, Yasunobu Ogawa, Yoshihiro Tomikawa, Jinro Ukita

    GEOPHYSICAL RESEARCH LETTERS43 ( 7 ) 3494 - 3501   2016年4月

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    記述言語:英語   出版者・発行元:AMER GEOPHYSICAL UNION  

    Recent evidence from both observations and model simulations suggests that an Arctic sea ice reduction tends to cause a negative Arctic Oscillation (AO) phase with severe winter weather in the Northern Hemisphere, which is often preceded by weakening of the stratospheric polar vortex. Although this evidence hints at a stratospheric involvement in the Arctic-midlatitude climate linkage, the exact role of the stratosphere remains elusive. Here we show that tropospheric AO response to the Arctic sea ice reduction largely disappears when suppressing the stratospheric wave mean flow interactions in numerical experiments. The results confirm a crucial role of the stratosphere in the sea ice impacts on the midlatitudes by coupling between the stratospheric polar vortex and planetary-scale waves. Those results and consistency with observation-based evidence suggest that a recent Arctic sea ice loss is linked to midlatitudes extreme weather events associated with the negative AO phase.

    DOI: 10.1002/2016GL068330

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  • A negative phase shift of the winter AO/NAO due to the recent Arctic sea-ice reduction in late autumn 査読

    Tetsu Nakamura, Koji Yamazaki, Katsushi Iwamoto, Meiji Honda, Yasunobu Miyoshi, Yasunobu Ogawa, Jinro Ukita

    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES120 ( 8 ) 3209 - 3227   2015年4月

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    記述言語:英語   出版者・発行元:AMER GEOPHYSICAL UNION  

    This paper examines the possible linkage between the recent reduction in Arctic sea-ice extent and the wintertime Arctic Oscillation (AO)/North Atlantic Oscillation (NAO). Observational analyses using the ERA interim reanalysis and merged Hadley/Optimum Interpolation Sea Surface Temperature data reveal that a reduced (increased) sea-ice area in November leads to more negative (positive) phases of the AO and NAO in early and late winter, respectively. We simulate the atmospheric response to observed sea-ice anomalies using a high-top atmospheric general circulation model (AGCM for Earth Simulator, AFES version 4.1). The results from the simulation reveal that the recent Arctic sea-ice reduction results in cold winters in mid-latitude continental regions, which are linked to an anomalous circulation pattern similar to the negative phase of AO/NAO with an increased frequency of large negative AO events by a factor of over two. Associated with this negative AO/NAO phase, cold air advection from the Arctic to the mid-latitudes increases. We found that the stationary Rossby wave response to the sea-ice reduction in the Barents Sea region induces this anomalous circulation. We also found a positive feedback mechanism resulting from the anomalous meridional circulation that cools the mid-latitudes and warms the Arctic, which adds an extra heating to the Arctic air column equivalent to about 60% of the direct surface heat release from the sea-ice reduction. The results from this high-top model experiment also suggested a critical role of the stratosphere in deepening the tropospheric annular mode and modulation of the NAO in mid to late winter through stratosphere-troposphere coupling.

    DOI: 10.1002/2014JD022848

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  • DEVELOPMENT OF GLACIAL LAKE INVENTORY IN BHUTAN USING "DAICHI" (ALOS) 査読

    Takeo Tadono, Masanobu Shimada, Tsutomu Yamanokuchi, Jinro Ukita, Chiyuki Narama, Nobuhiro Tomiyama, Sachi Kawamoto, Koji Fujita, Kouichi Nishimura

    2011 IEEE INTERNATIONAL GEOSCIENCE AND REMOTE SENSING SYMPOSIUM (IGARSS)   3202 - 3205   2011年

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    記述言語:英語   出版者・発行元:IEEE  

    The objective of this study is to develop new glacial lake inventory to understand existing condition using the optical imageries of the Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) and the Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2) onboard the Advanced Land Observing Satellite (ALOS, nicknamed "Daichi"). Glacial lakes can be caused outburst flood when natural dams terminated by moraines are broken, and it represents serious hazard damage in downstream regions. Problems of glacial lake outburst floods (GLOFs) are that anyone does not know when it will occur and how much damage causes by it. To contribute these problems, new glacial lake inventory is currently developing in the Bhutan Himalayan using ALOS imageries. This paper describes procedure of the inventory development including image processing that introduces pan-sharpened and ortho-rectified images by PRISM and AVNIR-2, glacial lakes extraction, and its validation.

    DOI: 10.1109/IGARSS.2011.6049900

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  • Glacial lake inventory of Bhutan using ALOS data: methods and preliminary results 査読

    Jinro Ukita, Chiyuki Narama, Takeo Tadono, Tsutomu Yamanokuchi, Nobuhiro Tomiyama, Sachi Kawamoto, Chika Abe, Tsuyoshi Uda, Hironori Yabuki, Koji Fujita, Kouichi Nishimura

    ANNALS OF GLACIOLOGY52 ( 58 ) 65 - 71   2011年

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    記述言語:英語   出版者・発行元:INT GLACIOL SOC  

    The Advanced Land Observing Satellite (AIDS) is relatively new. Its optical sensors are capable of making high-resolution digital surface models (DSMs). For the first time, the task of constructing a regional-scale inventory of glacial lakes based on AIDS data has been undertaken. This study presents the data-processing methods and the results of validation and analysis on the ALOS-based glacial lake inventory of Bhutan in the Himalaya. The analysis based on GPS measurements taken at Metatshota lake in the Mangde Chu sub-basin, one of the glacial lakes assessed as presenting a potential flood danger, shows a validation estimate of 9.5 m for the location of the AIDS-based polygon, with a root mean square of 11.7 m. A comparison with digitized data from the International Centre for Integrated Mountain Development (ICIMOD) shows that positioning and evaluation of terrain changes can be significantly improved using ALOS data. Preliminary analysis of the glacial lakes in four sub-basins, Mo Chu, Pho Chu, Mangde Chu and Dangme Chu, reveals that the frequency distribution of lake sizes biases towards smaller lakes. Glacial lakes 0.01-0.05 km(2) in area account for similar to 55% of the total number and occupy 13% of the total area. Together our results demonstrate the usefulness of high-resolution ALOS data with accurate DSMs for studying glacial lakes. High priority must be given to continuously improving and updating the glacial lake inventory with high-resolution satellite data.

    DOI: 10.3189/172756411797252293

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  • Thin sea ice thickness as inferred from passive microwave and in situ observations 査読

    Kazuhiro Naoki, Jinro Ukita, Fumihiko Nishio, Masashige Nakayama, Josefino C. Comiso, Al Gasiewski

    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS113 ( C2 )   2008年2月

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    記述言語:英語   出版者・発行元:AMER GEOPHYSICAL UNION  

    Microwave radiometric signals from sea ice strongly reflect physical conditions of a layer near the ice surface. This study examines the extent to which the relationships of thickness with brightness temperature and with emissivity hold for thin sea ice, approximately <0.2-0.3 m, and how those relationships may arise from changes in brine characteristics through modification of dielectric properties near the ice surface. In order to address these questions we made concurrent measurements of sea ice thickness in the Sea of Okhotsk from a ship and passive microwave radiometry from an over-flying aircraft. The results show that the brightness temperature and emissivity increase with thickness approximately within the thin ice for a frequency range of 10-37 GHz. The relationship is more pronounced at lower frequencies and at the horizontal polarization. We also established an empirical relationship between ice thickness and salinity in the layer near the ice surface from a field experiment, which qualitatively supports the idea that changes in the near-surface brine characteristics contribute to the observed thickness-brightness temperature/emissivity relationship. On the basis of our results, we conclude that for thin ice, passive microwave radiometric signals likely contain indirect information on ice thickness through the dependence of dielectric properties on brine, which provides a plausible and common explanation for previously proposed passive microwave thickness algorithms.

    DOI: 10.1029/2007JC004270

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  • Northern Hemisphere sea ice variability: lag structure and its implications 査読

    Jinro Ukita, Meiji Honda, Hisashi Nakamura, Yoshihiro Tachibana, Donald J. Cavalieri, Claire L. Parkinson, Hiroshi Koide, Kentaro Yamamoto

    TELLUS SERIES A-DYNAMIC METEOROLOGY AND OCEANOGRAPHY59 ( 2 ) 261 - 272   2007年3月

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    記述言語:英語   出版者・発行元:CO-ACTION PUBLISHING  

    An analysis of satellite sea-ice records for recent decades reveals a highly coherent spatial and temporal structure of the Northern Hemisphere (NH) wintertime sea-ice variability and its close link to anomalous atmospheric circulation. The dominant mode of the wintertime sea-ice variability is characterized by a double-dipole composed of one dipole over the North Atlantic and the other over the North Pacific, which are mutually correlated interannually. This dominant sea-ice mode is lag correlated with the winter-averaged North Atlantic Oscillation (NAO) index at lags up to two winters when the NAO leads. In the sub-Arctic, significant lead-lag relationships exist between sea-ice extent (SIE) anomalies on regional scales, which are closely associated with atmospheric circulation anomalies. An eastward evolving pattern is identified in regional SIE anomalies from the Labrador to Nordic and farther to the Okhotsk Sea at multi-year time-scales, led by anomalously weak Aleutian and strong Icelandic lows. The results suggest the presence of climate memories over the North Atlantic and Eurasia, which are crucial for recent downward trends in the NH SIE by transforming atmospheric influences into slower changes in sea-ice conditions. The summer Okhotsk high, which leads to a sea-ice reduction along the east Siberian coast and further affects sea-ice conditions over the Arctic Ocean, is a key link between summer Arctic and winter sub-Arctic sea-ice trends. We also conjecture that variations and changes in the NH sea-ice conditions are linked to climate variability in the tropics.

    DOI: 10.1111/j.1600-0870.2006.00223.x

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  • Intra-seasonal relationship between the Northern Hemisphere sea ice variability and the North Atlantic Oscillation 査読

    Kentaro Yamamoto, Yoshihiro Tachibana, Meiji Honda, Jinro Ukita

    GEOPHYSICAL RESEARCH LETTERS33 ( 14 )   2006年7月

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    記述言語:英語   出版者・発行元:AMER GEOPHYSICAL UNION  

    An intra-seasonal relationship, including a possible feedback, is investigated between the North Atlantic Oscillation (NAO) and a hemispheric-scale seesaw-like pattern dominant in sea ice variability over the wintertime Northern Hemisphere, with one polarity in the Bering and Labrador Seas and the other in the Okhotsk and Greenland-Barents Seas. Statistical analysis using observational data suggests that a particular phase of NAO and anomalous atmospheric circulation in the Pacific during early winter contribute toward the development of the midwinter hemispheric sea-ice seesaw. In contrast, the ice seesaw tends to damp the preexisting NAO signal during late winter, indicating a reversal of the phase relation between them. This NAO damping may be triggered by the Pacific sea-ice anomalies. Results from numerical experiments generally support this notion and further suggests a stationary Rossby wave train emanated from the North Pacific as a dynamical mechanism for damping the NAO signal.

    DOI: 10.1029/2006GL026286

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