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第333回 大気海洋物理学・気候力学セミナー のおしらせ

日　時： 1月23日(木) 9:30 - 12:00
Date ： Thu., 23 Jan. 9:30−12:00　
場　所： 低温科学研究所 3階 講堂
Place ： Institute of Low Temperature Science, 3F Auditorium

発表者：安成 哲平 (北極域研究センター & GI-CoRE 北極域研究グローバルステーション（広域複合災害研究センター兼務助) / 助教)
Speaker:Teppei J. Yasunari (Arctic Research Center & GI-CoRE/Global Station for Arctic Research (Secondary Joint Appointment: Center for Natural Hazards Research) / Assistant Professor)
Title：Wildfire and its air pollution in/around the Arctic under a changing climate

Speaker:Yuan Nan (Course in Atmosphere-Ocean and Climate Dynamics / D1)
Title：Why does the sea ice, in the western area of the Sea of Okhotsk, always survive?

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Wildfire and its air pollution in/around the Arctic under a changing climate
安成 哲平 (Teppei J. Yasunari)  発表要旨：


   This seminar includes a brief introduction of my research career and previous works at NASA
Goddard Space Flight Center, and its connection to my recent works. After that, I'm gonna talk
about the main topic of our recent works on wildfire and its air pollution including data analyses
and field measurements.
    Recently, frequent wildfires have occurred in many places in the world and have been of
large concern under the ongoing global warming. To take better measures for wildfire and
its possible impacts, better understanding of causes of wildfire and its related air pollution
is essential that would lead to accurate prediction of wildfire and its air pollution in the future.
In our recent paper (Yasunari et al., 2018, Sci. Rep.), we examined three large-scale wildfire
over East Eurasia in May 2003, April 2008, and July 2014, respectively. All these wildfire
resulted in significantly increased air pollution in Hokkaido, Japan, due to trans-boundary
transport. The common climate characteristics for all three cases showed that significantly
dryer surface soil conditions at the beginning of the wildfire year and unusually smaller
amount of snow and surface warming a couple months before the wildfire occurrences were
seen, which could eventually make the long-lasting dryer condition and that was preferable
condition for large-scale wildfire on the fire months. This tells us that climate conditions before
the wildfire months would be vital for its better prediction.
    Another smoke event was observed in Sapporo in April 2018. I introduce you the
characteristics of PM2.5 and aerosol during this event, using a portable PM2.5 sensor,
NASA AERONET, and NIES Lidar in Hokkaido University. The wildfire smoke was transported
from Amur and Primorsky Oblasts, and highly increased PM2.5 in Sapporo. In addition,
we have developed a special insulation box for the portable PM2.5 sensor in pretty cold
regions in winter such as Alaska and Russia (i.e., PM2.5 sensor system for cold regions),
and show some performance of the box. The box can automatically keep the air inside warm
above the freezing point even under severely cold air conditions outside.
    In June 2019, we installed the developed PM2.5 sensor system (i.e., the insulation box)
at the roof of the International Arctic Research Center (IARC) in University of Alaska Fairbanks (UAF).
The sensor could capture highly increased PM2.5 during the significantly large-scale wildfire
in this June and July in Alaska. To further understand the high PM2.5 season in the Arctic with
its reason and the relevant climate condition, we further examined the climatic conditions
relevant to higher PM2.5 in the Arctic region for more than one decade during 2003 and 2017
to assess the cause of such higher PM2.5 conditions in the Arctic region. Our analyzed
climatic patterns in the past and the pattern in this summer in the northern hemisphere
indicated interesting common characteristics. The details will be shown on the day of the seminar.



Why does the sea ice, in the western area of the Sea of Okhotsk, always
survive?
Yuan Nan 発表要旨：



　The sea ice extent in the sea of Okhotsk has a clear interannual variation
on record. The maximal sea ice concentration, ever recorded, covered almost the
whole sea, and usually it covers more than half of the area. Conversely, the minimal
sea ice concentration was just along the narrow western boundary lying in the
continental shelf and partial slope where it seems to be warrantable and secure for
the formation of sea ice. In other words, the cold water was conserved there in each
year historically.
　Why is this structure so robust? The difficulty of water exchange comes to mind first.
The inflow from the North Pacific Ocean could determine if the drift ice located in the
central area is melted or not, as whose temperature has a high consistency with the
maximal sea ice concentration (Nakanowatari et al 2010). The formation mechanism
of current varying with topography might somewhat block this inflow go into the
shallow area. For the coastal current, it is identified as the Arrested Topographic
Wave (Nakanowatari, Ohshima et al 2014) whose volume transport is mainly
influenced by the alongshore wind stress. While a stable circulation explained by
Sverdrup Balance persists in the central area, deeper than 500m precisely
(Ohshima,2004), and the geostrophic transport takes an important role in this
circulation. Besides, a sharp temperature gradient is in the low latitude, the north of
the Hokkaido, and close to the coast a cold core holds, according to observation
(Mizuta et al 2004). The same situation might also happen in the higher latitude.
　For clarifying the current pattern inside of the Sea of Okhotsk, we reproduced the
circulation with an Ocean General Circulation Model including stratification and
coupling sea ice set up firstly by Matsuda et al (2015), and the ERA-interim dataset
1980.01.01-2018.12.31 was used as the atmospheric forcing. The simulation
depicted the average sea ice concentration well. With the Tracmass, an out-line
particle tracking toolbox, the horizontal circulation can be seen clearly. In the vertical
profile of East Sakhalin shelf-slope, a sharp isopycnal gradient presented, and for
the along-isobath current, the buoyancy shutdown takes an effect. For the cross-
isobath current, the direction is inverse between the shallow and deep area which is
waiting to be explained.

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