大気科学コロキウム

概要

2018年度より大気圏物理学講座(気象学研究室・物理気候学研究室)の合同コロキウムを実施しています(不定期開催)。どなたでもご参加頂けますので、多くの皆様のお越しをお待ちしています。発表者も随時募集しています(世話人(坂崎)までご連絡ください)。

発表リスト

2019 (H31,R0) 年度

実施回(月日) 発表者(所属・身分): タイトル 写真
【予定】
第6回 (2019年 5月13日 14:45-16:15)
於 1-563
Tobias Spiegl (ベルリン自由大学・研究員): "Hotspots of future climate change under Grand Solar Minimum conditions"

[要旨] Observations and model projections suggest heterogeneous warming patterns due to the rise of anthropogenic greenhouse gases, revealing different degrees of regional climate vulnerability. However, climate vulnerability in a certain region is not only defined by single parameters, e.g. near surface temperature, but also depends on seasonal changes in the variability and occurrence of extreme events. While the magnitude of 21st century climate change will be dominated by the amount of carbon dioxide emissions, external climate forcing may amplify or dampen the human induced signal. The main source of external variability in the terrestrial climate system is the Sun. Satellite measurements show a gradual decrease in solar output over the last three decades. This raises the question whether a prolonged downturn in solar activity and an associated hypothetical global cooling might counteract a man-made global warming. Like the anthropogenic imprints, the effects of a solar downturn are multidimensional. Here, we quantify the multidimensional climate change due to both, the future anthropogenic and solar forcing. We found, that the regional climate hotspots start to emerge during the early 21st century within the tropics. Throughout the 21st century the hotspot spread to the lower latitudes. Whereby the midlatitudes show a response to the rise of greenhouse gases which is below-average, even at the end of the century. Our findings suggest, that an extreme solar downturn is needed for a longer-term mitigation of the anthropogenic climate effects. In the course of that, the thermal inertia of the oceans is responsible for the delay in the anthropogenic climate signal.
 

2018 (H30) 年度

  
実施回(月日) 発表者(所属・身分): タイトル 写真

第5回 (2019年 2月21日 16:00-17:30)
於 1-462
Ulrike Langemaz (ベルリン自由大学・教授): "The 'ozone hole' ? still a risk? Changes in stratospheric ozone and their implications for the troposphere"

[要旨] The stratospheric ozone layer protects life on Earth by absorbing harmful ultraviolet radiation from the sun. 90% of the atmospheric ozone abundance reside in the stratosphere, however changes in stratospheric ozone may directly impact the troposphere.

Concurrently with an increasing industrial production of chlorine-containing halogens in the 1960/70s, stratospheric ozone began to decrease. Several studies showed that halogens cause chemical ozone depletion in the stratosphere, and the fast growth of their concentrations led to a strong decline in stratospheric ozone during the 1980s and 1990s. The most dramatic example is the so-called Antarctic ozone hole, a severe ozone decrease occurring over Antarctica each spring. In response, regulations of the production and use of the so-called ozone depleting substances (ODSs) were adopted by the United Nations in the Montreal Protocol of 1987. As a result of the Montreal Protocol and further amendments and adjustments, the ODS concentrations began to level off and slowly decline. Since the beginning of the century, there is also evidence from measurements that stratospheric ozone has started to increase. Models consistently project a full return of global mean stratospheric ozone to undisturbed, historical values in the first half of the 21st century. However, because of complex dynamical and chemical interactions, the date of ozone recovery in different atmospheric regions will strongly depend on the future greenhouse gas scenario.

Here, an overview on the evolution of the ozone layer in the recent past is given and new model projections of the future ozone from the upcoming “WMO/UNEP Scientific Assessment of Ozone Depletion” are presented. The role of climate change for future ozone is discussed as well as the impacts of future ozone changes on the troposphere.

第4回 (2018年 12月20日 16:00-17:30)
於 1-563
Bjorn Stevens (マックスプランク研究所・所長/教授): "Experiences with RCE: Convective Aggregation, Land Surface Interactions, Cloud Feedbacks and Climate Sensitivity"

[要旨] Radiative Convective Equilibrium was introduced as a model problem fifty years ago to study the sensitivity of Earths surface temperature to radiative forcing. Today it has re-emerged as a popular framework which brings together a hierarchy of models: one-dimensional models with parameterized convection, large-eddy simulation, cloud-resolving models over large-domains, global cloud-resolving models and coupled climate models, to explore they dynamics of the Earth System. I will show snapshots from our work on RCE, how it identifies the role of shallow circulations in convective self aggregation on the one hand, and the convective dispersal over land on the other hand. We will show the important role of convective aggregation in modifying how the climate system responds to forcing, and explore the possibility of using this framework to study atmosphere-stratosphere interactions.
第3回 (2018年 11月26日 10:00-11:30)
於 1-563
Kevin Hamilton (ハワイ大・名誉教授): "What Do We Know About the QBO Behavior Over the Last 150 Years and What Does it Mean?"

[要旨] The quasi-biennial oscillation (QBO) of the tropical stratospheric circulation was discovered in 1960 by analyzing the daily pilot balloon observations of the zonal wind over Kanton Island (2.8oS) that began in January 1953. By the mid-1960s investigators had analyzed the available observational data sets to provide information on the typical characteristics of the QBO and also to address the question of the “permanence” of the recently discovered oscillation in the period before 1953. Today, even with more than 65 years of daily balloon observations of the near-equatorial wind now available, it is not certain that we have a complete picture of the cycle-to-cycle and longer term variability of the QBO, an issue that was highlighted in 2016 when the QBO winds displayed a disruption of the usual pattern that was unprecedented in the post-1953 record. The types of evidence that may be used to extend knowledge of the QBO zonal wind into the past include: (i) the scattered pilot balloon observations from low latitudes available before 1953, (ii) the zonal wind inferred by tracking the stratospheric aerosol following large low-latitude volcanic eruptions, and (iii) barometric observations of the near-equatorial solar semidurnal tide which we know is affected by the winds in the tropical stratosphere. Fairly recently at least one investigator has made a tentative detailed reconstruction of the QBO winds back to 1900 based primarily on the barometric record. This talk will review earlier work and introduce my recent investigations into the pre-1953 QBO. I will consider speculations that the familiar QBO may have been subject to extensive interruptions in earlier times and place this in the context of projections of future QBO behavior changes in response to global warming.
第2回(2018年 09月28日 15:00-16:30
於 1-563
倉本圭 (北海道大・教授):"ハビタブル惑星の成立を探る火星衛星探査計画MMX"
第1回(2018年 6月15日 10:00-11:30)
於 1-563
David W.J. Thompson (コロラド州立大・教授): "A key constraint on the depth of the extratropical troposphere"

[要旨] In this talk, I will argue that the depth of extratropical troposphere is primarily constrained by the same physics that govern the temperature of tropical anvil clouds. That is: The extratropical tropopause is constrained by the rapid decrease with height of radiative cooling by water vapor in clear sky regions, and thus by the thermodynamic constraints placed on saturation water vapor pressure. The results suggest that the climate feedbacks associated with high cloud in the tropics are also important in the extratropics, thus roughly doubling the surface area affected by the positive high cloud feedback. They also imply that the extratropical tropopause should stay at roughly the same temperature and thus lift under climate change.
(2018年 5月28日 14:30-16:00)
於 1-236
Hai Bui Hoang (ベルゲン大学・ポスドク研究員) "Influence of Sea Surface Temperature on Mid-Latitude Cyclones in an Idealized Framework"

[要旨] Mesoscale oceanic features such as sea surface temperature (SST) fronts have potential impacts on mid-latitude cyclones evolution and trajectory. There is a need for a better understanding of how these mesoscale features interact with cyclones. While the essential mechanisms are sometimes difficult to be isolated from observations data and complex models, an idealized framework may serve as a useful tool. In this study, we investigate the influence of SST on mid-latitude cyclones using an idealized framework of moist baroclinic channel simulation. The initial balanced atmospheric fields are derived from an initial profile of zonal wind that resembles the jet stream. A series of experiments is designed to simulate different conditions of the SST including changes in the SST front location and strength.
(2018年 4月13日 13:00-14:30)
於 1-563
Yohai Kaspi (ワイツマン科学研究所・准教授): "Mechanisms controlling the spatial structure of midlatitude storm tracks and their dependence on climate change"

[要旨] Midlatitude storm tracks dominate the transport of momentum, heat and water-vapor in the extratropics. Therefore, identifying the mechanisms governing their temporal and spatial structure is vital for understanding weather and climate. In this talk, we analyze the spatial structure of midlatitude storm tracks by tracking transient cyclonic eddies in an idealized GCM with several levels of complexity and in CMIP5 simulations. The localized atmospheric response is decomposed in terms of a time-zonal mean background flow, a stationary wave and a transient eddy field. The Lagrangian tracks are used to construct cyclone composites and perform a spatially varying PV budget. Three distinct mechanisms that contribute to the spatial structure emerge: transient nonlinear advection, latent heat release and stationary advection. The downstream evolution of the PV composites shows the different role of these mechanisms as the storm tracks evolve downstream. We demonstrate that the poleward motion of individual cyclones increases with increasing global mean temperatures, and by this provide an alternate quantitative explanation to the poleward shift of storm tracks under climate change.