Japanese scientific activities in the Arctic in retrospect and prospect

第3回極域科学シンポジウム/特別セッション「これからの北極研究」11月28日（水） 国立極地研究所 2階大会議

Enhanced temperature variability in high-altitude climate change

In the present article, monthly mean temperature at 56 stations assembled in 18 regional groups in 10 major mountain ranges of the world were investigated. The periods of the analysis covered the last 50 to 110years. The author found that the variability of temperature in climatic time scale tends to increase with altitude in about 65% of the regional groups. A smaller number of groups, 20%, showed the fastest change at an intermediate altitude between the peaks (or ridges) and their foot, while the remaining small number of sites, 15%, showed the largest trends at the foot of mountains. This tendency provides a useful base for considering and planning the climate impact evaluations. The reason for the amplification of temperature variation at high altitudes is traced back to the increasing diabatic processes in the mid- and high troposphere as a result of the cloud condensation. This situation results from the fact that the radiation balance at the earth's surface is transformed more efficiently into latent heat of evaporation rather than sensible heat, the ratio between them being 4 to 1. Variation in the surface evaporation is converted into heat upon condensation into cloud particles and ice crystals in the mid- and high troposphere. Therefore, this is the altitude where the result of the surface radiation change is effectively transferred. Further, the low temperature of the environment amplifies the effect of the energy balance variation on the surface temperature, as a result of the functional shape of Stefan-Boltzmann law. These processes altogether contribute to enhancing temperature variability at high altitudes. The altitude plays an important role in determining the temperature variability, besides other important factors such as topography, surface characteristics, cryosphere/temperature feedback and the frequency and intensity of an inversion. These processes have a profound effect not only on the ecosystem but also on glaciers and permafros

Observed Mass Balance of Mountain Glaciers and Greenland Ice Sheet in the 20th Century and the Present Trends

Glacier mass balance and secular changes in mountain glaciers and ice caps are evaluated from the annual net balance of 137 glaciers from 17 glacierized regions of the world. Further, the winter and summer balances for 35 glaciers in 11 glacierized regions are analyzed. The global means are calculated by weighting glacier and regional surface areas. The area-weighted global mean net balance for the period 1960-2000 is −270±34mma−1w.e. (water equivalent, in mm per year) or (−149±19km3a−1w.e.), with a winter balance of 890±24mma−1w.e. (490±13km3a−1w.e.) and a summer balance of −1,175±24mma−1w.e. (−647±13km3a−1w.e.). The linear-fitted global net balance is accelerating at a rate of −9±2.1 mm a−2. The main driving force behind this change is the summer balance with an acceleration of −10±2.0mm a−2. The decadal balance, however, shows significant fluctuations: summer melt reached its peak around 1945, followed by a decrease. The negative trend in the annual net balance is interrupted by a period of stagnation from 1960s to 1980s. Some regions experienced a period of positive net balance during this time, for example, Europe. The balance has become strongly negative since the early 1990s. These decadal fluctuations correspond to periods of global dimming (for smaller melt) and global brightening (for larger melt). The total radiation at the surface changed as a result of an imbalance between steadily increasing greenhouse gases and fluctuating aerosol emissions. The mass balance of the Greenland ice sheet and the surrounding small glaciers, averaged for the period of 1950-2000, is negative at −74±10 mma−1w.e. (−128±18km3a−1w.e.) with an accumulation of 297±33mma−1w.e. (519±58km3a−1w.e.), melt ablation −169±18mma−1w.e. (−296±31km3a−1w.e.), calving ablation −181±19mma−1w.e. (−316±33km3a−1w.e.) and the bottom melt-21±2mma−1w.e. (−35±4km3a−1w.e.). Almost half (−60±3km3a−1) of the net mass loss comes from mountain glaciers and ice caps around the ice sheet. At present, it is difficult to detect any statistically significant trends for these components. The total mass balance of the Antarctic ice sheet is considered to be too premature to evaluate. The estimated sea-level contributions in the twentieth Century are 5.7±0.5cm by mountain glaciers and ice caps outside Antarctica, 1.9±0.5cm by the Greenland ice sheet, and 2cm by ocean thermal expansion. The difference of 7cm between these components and the estimated value with tide-gage networks (17cm) must result from other sources such as the mass balance of glaciers of Antarctica, especially small glaciers separated from the ice shee

The Global Energy Balance Archive (GEBA) version 2017: a database for worldwide measured surface energy fluxes

The Global Energy Balance Archive (GEBA) is a database for the central storage of the worldwide measured energy fluxes at the Earth's surface, maintained at ETH Zurich (Switzerland). This paper documents the status of the GEBA version 2017 dataset, presents the new web interface and user access, and reviews the scientific impact that GEBA data had in various applications. GEBA has continuously been expanded and updated and contains in its 2017 version around 500 000 monthly mean entries of various surface energy balance components measured at 2500 locations. The database contains observations from 15 surface energy flux components, with the most widely measured quantity available in GEBA being the shortwave radiation incident at the Earth's surface (global radiation). Many of the historic records extend over several decades. GEBA contains monthly data from a variety of sources, namely from the World Radiation Data Centre (WRDC) in St. Petersburg, from national weather services, from different research networks (BSRN, ARM, SURFRAD), from peer-reviewed publications, project and data reports, and from personal communications. Quality checks are applied to test for gross errors in the dataset. GEBA has played a key role in various research applications, such as in the quantification of the global energy balance, in the discussion of the anomalous atmospheric shortwave absorption, and in the detection of multi-decadal variations in global radiation, known as "global dimming" and "brightening". GEBA is further extensively used for the evaluation of climate models and satellite-derived surface flux products. On a more applied level, GEBA provides the basis for engineering applications in the context of solar power generation, water management, agricultural production and tourism. GEBA is publicly accessible through the internet via http://www.geba.ethz.ch. Supplementary data are available at https://doi.org/10.1594/PANGAEA.873078.ISSN:1866-3516ISSN:1866-350

On the relationship between diurnal temperature range and surface solar radiation in Europe

The surface solar radiation (SSR) is an important factor influencing the local and global energy budget. However, information on the spatial and temporal variation of SSR is limited. A more commonly available measure, which may provide such information, is the diurnal temperature range (DTR). In this study we analyze the relationship between DTR and SSR in Europe between 1970 and 2005 on seasonal and decadal scale. When comparing the mean anomalies time series composed of 31 pairs of sites with long-term SSR and DTR measurements, we found a correlation coefficient of 0.87 in the annual mean and between 0.61 and 0.92 in the seasonal mean anomalies. When investigating the individual pairs of SSR and DTR individually, we found that local correlations are mostly lower than the European mean and that they decrease rapidly in seasons and latitudes with low incident angles and at high alpine altitude. The highest correlation on local and seasonal scales seems to be connected with the variability of the large-scale circulation in Europe. The output of 11 simulations of current generation regional climate models over Europe confirms the strong relationship between SSR and DTR. The seasonal dependence of the relationship is well reproduced, but the absolute values of DTR and SSR are mostly too low. The pattern of decrease (dimming) and increase (brightening) in SSR and DTR was not reproduced in the modeled time series. There is still strong evidence from both models and observations that DTR is a reliable representative of SSR

Vegetation type is an important predictor of the arctic summer land surface energy budget

Despite the importance of high-latitude surface energy budgets (SEBs) for land-climate interactions in the rapidly changing Arctic, uncertainties in their prediction persist. Here, we harmonize SEB observations across a network of vegetated and glaciated sites at circumpolar scale (1994-2021). Our variance-partitioning analysis identifies vegetation type as an important predictor for SEB-components during Arctic summer (June-August), compared to other SEB-drivers including climate, latitude and permafrost characteristics. Differences among vegetation types can be of similar magnitude as between vegetation and glacier surfaces and are especially high for summer sensible and latent heat fluxes. The timing of SEB-flux summer-regimes (when daily mean values exceed 0 Wm(-2)) relative to snow-free and -onset dates varies substantially depending on vegetation type, implying vegetation controls on snow-cover and SEB-flux seasonality. Our results indicate complex shifts in surface energy fluxes with land-cover transitions and a lengthening summer season, and highlight the potential for improving future Earth system models via a refined representation of Arctic vegetation types.An international team of researchers finds high potential for improving climate projections by a more comprehensive treatment of largely ignored Arctic vegetation types, underscoring the importance of Arctic energy exchange measuring stations.Peer reviewe

Vegetation type is an important predictor of the arctic summer land surface energy budget

Despite the importance of high-latitude surface energy budgets (SEBs) for land-climate interactions in the rapidly changing Arctic, uncertainties in their prediction persist. Here, we harmonize SEB observations across a network of vegetated and glaciated sites at circumpolar scale (1994–2021). Our variance-partitioning analysis identifies vegetation type as an important predictor for SEB-components during Arctic summer (June-August), compared to other SEB-drivers including climate, latitude and permafrost characteristics. Differences among vegetation types can be of similar magnitude as between vegetation and glacier surfaces and are especially high for summer sensible and latent heat fluxes. The timing of SEB-flux summer-regimes (when daily mean values exceed 0 Wm−2) relative to snow-free and -onset dates varies substantially depending on vegetation type, implying vegetation controls on snow-cover and SEB-flux seasonality. Our results indicate complex shifts in surface energy fluxes with land-cover transitions and a lengthening summer season, and highlight the potential for improving future Earth system models via a refined representation of Arctic vegetation types

現温暖化におけるエアロゾルの効果

The cause for the global temperature change of the last one hundred years is investigated in light of the earth’s energy balance. The material used for the present paper is mostly observed at the earth’s surface or from the space. While the enhanced greenhouse effect steadily increased,the aerosol effect fluctuated as a result of the decadal variation in aerosol emission. A cooling period witnessed for 30 years in the middle of the 20th Century is considered to have been caused by aerosol effect that surpassed the enhanced greenhouse effect. This cooling episode coincided with the period of declining surface global solar radiation,which was subsequently coined as the Global Dimming. The Mie-scattering theory can however explain only half of the decrease. The remaining half is considered due to the increase in cloud, which has been confirmed by the observations at the surface and from the space. Thus the ongoing climate warming is caused by a delicate imbalance between the increasing rates of greenhouse gases and of aerosol. The turning point of the total radiation from the negative to the positive phases is estimated to have happened sometime in the 1970s, which corresponds to the end of the cooling period and the beginning of the unprecedented warming. In the near future it is possible that the temperature trend may turn negative, if the aerosol effect overtakes the greenhouse effect. The currently observed slowing down of the warming after 2005 may well be the result of the increasing aerosol.二十世紀初頭以来の百余年間は人為的温室効果による温暖化の時代と言われる. たしかに1900年以来全球平均でほぼ１℃昇温した. しかし, 温度変化を注意して見ると単調増加ではない. 1910年から30年間昇温した後, 1940年から1970年までの30年間昇温が停まっただけでなく, 0.1℃強寒冷化した. その後再び昇温に転じ1970年からの40年間だけで0.9℃温暖化した. これは全球平均の話で, この通りの変化を示した地域はないが, 二十世紀初期の温暖化と, それに続く寒冷化そして最近の顕著な温暖化という三相変化は位相をわずかに異にしてほぼ全球で見られる. 従って, 二十世紀中葉に現れた寒冷化は全球的現象であった. この30年にわたる全球規模での温暖化トレンドからの逸出はENSOやその他多く知られている振動現象では説明できない. この寒冷化の原因が分からなければ二十世紀全般にわたる温度変化の原因も正確には理解できないことになり, 又将来の予測もおぼつかないことになる. したがって, 本論文では, 二相の温暖化に挟まれた寒冷化の原因を極める. そのために, 本論文では甚だ基礎的になるが気候システムにおける温度生成過程を熱力学第一法則に基づいて考える. 地球表面の温度生成における放射の占める役割を認識し, 二十世紀初頭以来観測された全天太陽放射, 直達放射と大気の透過度を分析する. 全天太陽放射の経年変化から二十世紀初頭から1950年にかけての第一次グローバル・ブライトニング（全天太陽放射の増加期）,1950年代から80年代にかけてのグローバル・デイミング（全天太陽放射の減少期）, 更に80年代から2005年にかけての第二次グローバル・ブライトニングの３時代が認識される. その間に観測されたデイミングとブライトニング間の大気の透過度の変化は0.05であった. この透過度の変化に相当するエアロゾルの直接効果（ミー散乱）だけでは全天放射の変動量の約50％しか再現できないことが判り, 残りの50％はエアロゾルの間接効果,即ち雲の経年変化に帰着される. エアロゾルによる光学行程と雲量の相関はきわめて高く, この時期のエアロゾル間接効果と思われる雲の変動は全雲量で４％, 日照時間では日に0.4時間に相当する. この雲量の変動は地上と衛星から観測された結果である. グローバル・デイミングの続いていた期間は全天太陽放射の減少率が長波放射の増加率を上回り全放射率が減少していたことが判明し, これが気温低下を引き起こしたと考えられる. 続く1980年代からの第二次グローバル・ブライトニング期では増加に転じた全天太陽放射と既に増加傾向にあった長波放射が相まって全放射の増加率は6.6Wm-2/decadeとなり, 年間0.035℃となる観測時代最大の気温上昇率をもたらす結果となる. このように現在進行中の温暖化は温室効果ガスの増加率とエアロゾルの増加率のバランスの微妙な崩れの結果であり, 近い将来においてもエアロゾルの増加率がある程度大きくなり温室効果の上昇率を越すことが生じれば, 寒冷化が起こりえる. 現に2000年代に入ってから温暖化が鈍っているのは, 決して温室効果が減少したためではなく, エアロゾルの効果が増加している結果である可能性が高い.Ⅶ. エアロゾルの気候影