研究者詳細 - 藤田　耕史

論文 - 藤田　耕史

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A shallow ice core re-drilled on the Dunde Ice Cap, western China: recent changes in the Asian high mountains. 査読有り

Takeuchi N, Miyake T, Nakazawa F, Narita H, Fujita K, Sakai A, Nakawo M, Fujii Y, Duan KQ, Yao TD

Environmental Research Letters 4 巻頁： 045207 2009年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

A 51 m deep ice core was re-drilled on the Dunde Ice Cap of western China in 2002, 15 years after the previous ice core drilling in 1987. Dating by seasonal variations in δ18O and particle concentration showed that this 51 m deep ice core covered approximately the last 150 years. The stratigraphy and density showed that more than 90% of the ice core was refrozen ice layers, which comprised less than 5% of the annual accumulation in the older core. This indicates that the ice cap had experienced a more intense melting since 1987, possibly due to climate warming in this region. Mean net accumulation since the last drilling (2002–1987) was 176 mm a-1, which was considerably smaller than that obtained from the 1987 core (390 mm a-1, 1987–1963), indicating a significant decrease of net accumulation on the ice cap in the more recent period. The δ18O record showed an increasing trend in the late 19th century and the highest in the 1950s, which is consistent with the previous core findings. However, there has been no significant increase in δ18O during the last two decades, in contrast to the warming trends suggested by the melt features and other climate records. This discrepancy may be due to the modification of δ18O records by melt water runoff, percolation, and refreezing on the ice cap. Results strongly suggest recent significant mass loss of glaciers in the Asian high mountains and serious shortage of water supply for local people in this arid region in the near future.

http://www.iop.org/EJ/abstract/1748-9326/4/4/045207

A snow algal community on the surface and in an ice core of Rikha-Samba Glacier in Western Nepali Himalayas. 査読有り

Takeuchi N, Fujita K, Nakazawa F, Matoba S, Nakawo M, Rana B

Bulletin of Glaciological Research 27 巻頁： 25-35 2009年12月

Recent changes in Imja Glacial Lake and its damming moraine in the Nepal Himalaya revealed by in-situ surveys and multi-temporal ASTER imagery. 査読有り

Fujita K, Sakai A, Nuimura T, Yamaguchi S, Sharma RR

Environmental Research Letters 4 巻頁： 045205 2009年11月

Total solar eclipse over Antarctica on 23 November 2003 and its effects on the atmosphere and snow near the ice sheet surface at Dome Fuji. 査読有り

Kameda T, Fujita K, Sugita O, Hirasawa N, Takahashi S

Journal of Geophysical Research - Atmospheres 114 巻頁： D18115 2009年9月

記述言語：英語掲載種別：研究論文（学術雑誌）

The Moon cast a long shadow over Antarctica on 23 November 2003 in a total solar eclipse. The eclipse was observed at Dome Fuji Station, located at the highest point of East Dronning Maud Land, Antarctica, and lasted 1 h 41 min 37 s in a cloudless condition, during which the Sun was completely obscured for 1 min 43 s. This was the first total solar eclipse to be observed in the Antarctic ice sheet. During the eclipse at Dome Fuji, the air temperature at 1.5 m above the snow surface and the subsurface snow temperature decreased by 3.0 K and 1.8 K, respectively. Estimated surface snow temperatures decreased by 4.6 K. Atmospheric pressure and wind direction did not change, but the wind speed possibly decreased by 0.3 m/s with decreasing air temperature; natural variations in wind speed before and after the eclipse made it difficult to identify a true effect of the solar eclipse. Variations of energy components (net shortwave and longwave radiations, sensible and latent heat fluxes, and geothermal heat) during the eclipse were investigated. The total loss of global solar radiation during the eclipse was 0.60 MJ m-2, equaling 1.6% of the total daily global solar radiation. Regional effects of the eclipse due to a reduction of global solar radiation for air temperature and snow temperature ranged from 0.015 to 0.020 K (W m-2)-1. We additionally examined the relation between eclipse obscuration (the fraction of the Sun's surface area occulted by the Moon) and the reduction of global solar radiation from the first to second contacts. The eclipse was also observed from space by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors onboard NASA's Terra and Aqua satellites. The observational results of this study will contribute to detailed model calculations for clarifying the meteorological effects of eclipses.

http://www.agu.org/pubs/crossref/2009/2009JD011886.shtml

Simplification of heat balance calculation and its application to the glacier runoff from the July 1st Glacier in northwest China since the 1930s. 査読有り

Sakai A, Fujita K, Nakawo M, Yao T

Hydrological Processes 23 巻 ( 4 ) 頁： 585-596 2009年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

Since ancient times meltwater from glaciers in mountain zones has been an important water resource in the arid region of northwest China. Meteorological elements for heat balance calculations at the glacier surface were simplified with the aim of simulating discharge fluctuations from the July 1st Glacier over a span of decades. By estimating relative humidity and downward solar radiation from precipitation, heat balance calculations at the glacier can be made using only daily temperature and precipitation, which are easily obtainable. Calculations of daily discharge using the above method during the melting season in 2002 produced a better simulation than those using the conventional positive degree-day (PDD) factor method. (The ablation of glacier during any particular period is assumed to be proportional to the sum of daily mean temperatures above the melting point during that period.)
We calculated the glacier runoff and mass balance at the July 1st Glacier since 1935 from monthly meteorological data taken near the glacier using the above method. We used three patterns of daily temperature and precipitation to estimate daily meteorological data from monthly or annual data. Calculated mass balance using the patterns of air temperature and precipitation in years when the pressure distributions were similar to its long-term average corresponded well with observed data. Our simulation of the glacier runoff since 1935 also showed good results.

http://www3.interscience.wiley.com/journal/121574898/abstract

Effect of precipitation seasonality on climatic sensitivity of glacier mass balance. 査読有り

Fujita K

Earth and Planetary Science Letters 276 巻 ( 1-2 ) 頁： 14-19 2008年11月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Numerical calculations are described, aimed at evaluating the influence of precipitation seasonality and seasonality concentration on climatic sensitivity of glacier mass balance. Equilibrium line altitudes (ELAs) are modeled using idealized meteorological variables, and then a warming test (+1 °C) is performed, which revealed that the effects of latitude and the annual precipitation amount are less than those of precipitation seasonality and its concentration. Calculation shows higher sensitivities for the glaciers located in a summer precipitation climate than for those located within a winter-precipitation climate. Difference due to seasonality is enhanced with the seasonality concentration. The present study suggests that the earlier parameterization of glacier mass balance with annual precipitation amount is insufficient to describe the response of glaciers to climate change. Distribution of precipitation seasonality and its concentration suggest that many parts of the world have a summer-precipitation climate but their seasonality concentration is not significant worldwide. On the other hand, an extensive region of Asia and part of the Andes are located in the highly concentrated summer-precipitation climate. This suggests the high sensitivity of glacier mass balance in these regions to climate change.

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V61-4TPND5C-1&_user=119029&_coverDate=11/30/2008&_rdoc=3&_fmt=high&_orig=browse&_srch=doc-info(%23toc%235801%232008%23997239998%23701811%23FLA%23display%23Volume)&_cdi=5801&_sort=d&_docanchor=&_ct=25&_acct=C000009318&_version=1&_urlVersion=0&_userid=119029&md5=5e83486055fa5c9d81a457ac60ee1fca

ヒマラヤにおける氷河変動招待有り

藤田耕史

豊田自動織機技報 56 巻頁： 78-84 2008年9月

Rapid decrease of mass balance observed in the Xiao (Lesser) Dongkemadi Glacier, in the central Tibetan Plateau. 査読有り

Pu J, Yao T, Yang M, Tian L, Wang N, Ageta Y, Fujita K

Hydrological Processes 22 巻 ( 16 ) 頁： 2953-2958 2008年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

The mass balance of the Xiao (Lesser) Dongkemadi Glacier located in the Tanggula Mountains, of the central Qinghai-Tibetan Plateau has been monitored since 1989. The results show that the mass balance of the glacier has recently shown a deficit trend, and that the glacial terminus was also retreating. Positive mass balance of the glacier was dominant during the period 1989-1993, and the accumulated mass balance reached 970 mm. However, negative mass balance of the glacier has occurred since 1994, except for the large positive mass balance year 1997. The mass balance was -701 mm in 1998, an extremely negative glacier mass balance year. The equilibrium line altitude showed a significant increasing trend. The mass balance of the glacier has changed from a significantly positive mass balance to a strongly negative mass balance since 1994. Meteorological data suggest that the rapid decrease in the mass balance is related to summer season warming.

http://www3.interscience.wiley.com/journal/116327612/abstract

Influence of precipitation seasonality on glacier mass balance and its sensitivity to climate change. 査読有り

Fujita K

Annals of Glaciology 48 巻頁： 88-92 2008年6月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Numerical calculations are described, aimed at evaluating the influence of precipitation seasonality (summer and winter) on glacier mass balance. First, equilibrium-line altitudes (ELAs) are modeled using idealized meteorological variables. Modeled climatic conditions (summer mean temperature and annual precipitation) at the ELA of glaciers located within a winter accumulation pattern confirm the observational results of earlier studies. However, the ELA of glaciers located within a summer accumulation climate pattern locates in a colder environment than that of glaciers located within a winter accumulation climate pattern. This difference is mainly due to the annual snow accumulation and the surface albedo. A warming test (+1K) reveals higher sensitivities for the glaciers located within a summer accumulation pattern than for the glaciers located within a winter accumulation pattern. In a humid environment, a significant decrease in snow accumulation on the glaciers located within a summer accumulation pattern directly causes higher sensitivities. In an arid environment, on the other hand, the decreased summer snow induces accelerated melting by lowering the surface albedo and thus increasing absorption of solar radiation on the glaciers located within a summer accumulation pattern. Both influences are due to significant differences in summer precipitation. This study shows the importance of precipitation seasonality on the climatic sensitivity of glacier mass balance, which in previous studies has been linked only with annual precipitation.

http://www.ingentaconnect.com/content/igsoc/agl/2008/00000048/00000001/art00013

ドームふじにおける放射観測. 査読有り

平沢尚彦, 藤田耕史

南極資料 52 巻 ( 特集号 ) 頁： 170-181 2008年6月

記述言語：日本語

第44次南極地域観測隊により,2003年2月1日から2004年1月20日の地上放射観測(短波上向き・下向き,長波上向き・下向き)の結果を報告する.放射計ドームの着霜を回避する目的でファン付き放射計を用いた上向き,下向きの長波放射,及び下向きの短波放射は1997年の観測値と比較的近い値を示し,両年の観測の妥当性を示唆した.しかし,ファンのない放射計を用いた上向き短波放射は,極夜前後の1-2カ月において下向き短波放射を上回るなど,異常値を示している.着霜がこの原因の候補の一つであるが,確かめられない.データの修正については今後の課題とする.また,極夜期の上向き・下向き長波放射について,典型的な地表面放射冷却時期と放射冷却が抑制される時期について,事例を示した.

シーロメータにより観察されたドームふじの雲・降雪の鉛直分布と季節変化. 査読有り

平沢尚彦, 藤田耕史

南極資料 52 巻 ( 特集号 ) 頁： 159-169 2008年6月

記述言語：日本語

第44次南極地域観測隊のドームふじ基地におけるシーロメータ観測の結果から,雲及び降雪粒子の鉛直プロファイルの季節変化の概要をまとめ,特徴的な鉛直プロファイルを示した.夏季の2003年2月,12月,及び2004年1月には高度1000m以下に明瞭な雲底が検出される場合が比較的多かった.4月から10月には高度3000mから5000m(標高約7000-9000m)層で夏季より高頻度に雲が観測された.極夜期には高度1500m以下の層でストリーク状の降雪が観測され,これまでの研究と比較し議論した.このストリーク状の降雪は地上に近いほど後方散乱係数が大きくなる特徴を示した.

水の酸素・水素安定同位体を用いた地球水循環研究と今後の展望. 査読有り

檜山哲哉, 阿部理, 栗田直幸, 藤田耕史, 池田健一, 橋本重将, 辻村真貴, 山中勤

水文・水資源学会誌 21 巻 ( 2 ) 頁： 158-176 2008年3月

記述言語：日本語

水の酸素・水素安定同位体（以下，水の安定同位体）を用いた水循環過程に関する重要な研究および最近の研究のレビューを行った．海水の同位体組成（同位体比）に関する知見，同位体大循環モデルを用いた全球スケールの水循環研究，降水形態による同位体比の差異や局域スケールの降水過程に関する研究，流域スケールでの流出過程，植生に関わる蒸発散過程（蒸発と蒸散の分離）の研究をレビューした．加えて，幅広い時間スケールでの気候変動や水循環変動に関する研究として，氷床コアや雪氷コアを利用した古気候・古環境復元とそれらに水の安定同位体を利用した研究についてもレビューした．最後に，水の安定同位体を利用した水循環研究の今後の展望をまとめた．

http://www.jstage.jst.go.jp/article/jjshwr/21/2/21_158/_article/-char/ja/

Performance of ASTER and SRTM DEMs, and their potential for assessing glacier lakes in the Lunana region, Bhutan Himalayas. 査読有り

Fujita K, Suzuki R, Nuimura T, Sakai A

Journal of Glaciology 54 巻 ( 185 ) 頁： 220-228 2008年3月

七一氷河を巡る

藤田耕史

アジア遊学 99 巻頁： 24-27 2007年

Surfacewater-groundwater interaction in the Heihe River basin, Northwestern China. 査読有り

Akiyama T, Sakai A, Yamazaki Y, Wang G, Fujita K, Nakawo M, Kubota J, Konagaya Y

Bulletin of Glaciological Research 24 巻頁： 87-94 2007年

記述言語：英語掲載種別：研究論文（学術雑誌）

River discharge and groundwater level data were collected in the Heihe River basin, which is the second largest inland river in Northwestern China. The surfacewater-groundwater interaction, particularly in the lower desert reaches, was analyzed with the help of isotope data of water collected from the river. In the non-irrigation period, river water, which originated from the groundwater in the middle oasis reaches, was present throughout the period in the lower desert reaches. During this period, the river water recharged the groundwater not only in the riparian forest region located near the river but also in the desert-riparian fringe region located farther away from the river. In the irrigation period, the river was usually dried up in the lower desert reaches. The river water in the lower reaches appeared just after short-term releases from the middle reaches; the groundwater level in the riparian forest region rose rapidly, but it declined again just after the short-term releases finished. Since the mixing ratio of the short-term released discharge to the groundwater in the desert-riparian fringe region was smaller than that in the riparian forest region, the short-term released discharge did not contribute to the groundwater recharge in the desert-riparian fringe region.

* Spatial distribution of thermal properties on debris-covered glaciers in the Himalayas derived from ASTER data. 査読有り

Suzuki R, Fujita K, Ageta Y

Bulletin of Glaciological Research 24 巻頁： 13-22 2007年

Characteristics and climatic sensitivities of runoff from a cold-type glacier on the Tibetan Plateau. 査読有り

Fujita K, Ohta T, Ageta Y

Hydrological Processes 21 巻 ( 21 ) 頁： 2882-2891 2007年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Model calculations are made in order to understand the characteristics and response to climate change of runoff from a cold glacier on the Tibetan Plateau. Some 20% of meltwater is preserved at the snow-ice boundary due to refreezing, since the glaciers in mid to northern Tibet are sufficiently cooled during the previous winter.
Sensitivity to alterations in meteorological parameters has revealed that a change in air temperature would cause not only an increase in melting by sensible heat, but also a drastic increase in melting due to lowering of the albedo, since some of the snowfall changes to rainfall. In addition, it was suggested that a decrease in precipitation would cause a lowering of the surface albedo, with a resulting increase in the contribution of glacier runoff to the total runoff of river water. This study shows the first quantitative evaluation of the above effects, though they have been suggested qualitatively. The seasonal sensitivity of glacier runoff was examined by changing the dates given for a meteorological perturbation for a period of only 5 days. It was revealed that changes in both air temperature and precipitation during the melting season strongly affected glacier runoff by changing the surface albedo, though these perturbations only slightly altered the annual averages.

http://www3.interscience.wiley.com/journal/113508995/abstract

Effect of dust event timing on glacier runoff: sensitivity analysis for a Tibetan glacier. 査読有り

Fujita K

Hydrological Processes 21 巻 ( 21 ) 頁： 2892-2896 2007年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

The impact of the timing of dust deposition on glacier runoff was evaluated using a glacier mass-balance model with a newly improved scheme to track a dusted layer in a snow layer of a glacier. The lowering of surface albedo due to the dusted layer appearing leads to a drastic increase of glacier runoff even under the same meteorological conditions. Calculations of seasonal sensitivity, the relationship between dusted date and resulting runoff, have shown that dust deposition during a melting season might cause a drastic mass outflow from a glacier through changing the surface albedo during the melting season.

http://www3.interscience.wiley.com/journal/113509005/abstract

Topographical survey of end-moraine and dead ice area at the Imja Glacial Lake in 2001 and 2002. 査読有り

Sakai A, Saito M, Nishimura K, Yamada T, Iizuka Y, Harada K, Kobayashi S, Fujita K, Gurung CB

Bulletin of Glaciological Research 24 巻頁： 29-36 2007年

記述言語：英語掲載種別：研究論文（学術雑誌）

A survey was carried out at the end moraine and the dead ice area of the Imja Glacial Lake in October 2001 and in April 2002 using a digital theodolite with a laser distance meter and differential Global Positioning System (d-GPS). The survey points covered the whole dead ice area and end moraine of the Imja Glacier, and map contours were produced at 5 m intervals. This topographical map will be a significant means to analyze the time variation of the dead ice area and end moraine in future re-mapping. Changes in the lake level and the spillway on the dead ice area since 1994 were also analyzed in comparison with the measurements in 1994 by Watanabe et al. (1995).

Meteorological observations during 2002-2004 in Lunana region, Bhutan Himalayas. 査読有り

Suzuki R, Fujita K, Ageta Y, Naito N, Matsuda Y, Karma

Bulletin of Glaciological Research 24 巻頁： 71-78 2007年

記述言語：英語掲載種別：研究論文（学術雑誌）

Meteorological observations were carried out in the Lunana region, Bhutan Himalayas, from September 2002 to October 2004. An automatic weather station (Lugge AWS) was installed at 4524 m a.s.l. on the end moraine of Lugge Glacier. In addition, air temperatures, ground temperatures and relative humidity were observed simultaneously around the AWS from late September to early October in 2003 and 2004 to investigate spatial variation of these components. Characteristics of seasonal and diurnal variations of meteorological elements are shown using the data observed by the AWS. Relatively large spatial variability of surface temperature is shown by the data observed at different sites compared to that of air temperature and relative humidity.

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