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第 257回 大気海洋物理学・気候力学セミナー のおしらせ

日　時： 7月 17日(木) 午前 09:30
場　所： 環境科学院 D棟2階 D201号室

発表者： Alex Fraser (ILTS/JSPS Postdoctoral Fellow)
題名：Automation of Antarctic landfast sea ice detection; and Variability in the backscatter of dry Antarctic snow/firn using ASCAT reveals a changing ice sheet.

発表者： 森文洋 (地球圏科学専攻 大気海洋物理学・気候力学コース/DC3)
Fumihiro Mori (Course in atmosphere-ocean and climate dynamics/DC3)
題名：接地境界層におけるPIV法を用いた乱流観測
Turbulent flow measurement in the surface boundary layer using the PIV method

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Automation of Antarctic landfast sea ice detection; and
Variability in the backscatter of dry Antarctic snow/firn using
ASCAT reveals a changing ice sheet.
(Alex Fraser)　発表要旨：


This seminar will cover two separate projects, as indicated in the title.

First presentation:
Recent studies of changes in sea ice production following the dramatic
2010 reorganization of the “icescape” in the Mertz Glacier region,
East Antarctica, have highlighted the complex relationship between
coastal configuration and sea ice production in coastal polynyas.
Landfast sea ice, commonly known as fast ice, plays an especially
important role in this process, due to the exceptional inter- and
intra-seasonal variability compared with other coastal elements such
as glacier tongues iceberg tongues, and large grounded icebergs which
typically vary on much longer timescales, albeit abruptly at times.
Since fast ice frequently forms the boundary between high and low sea
ice production regions, e.g., in coastal polynyas, accurate estimation
of sea ice production rates, heat and salt flux calculations from
satellite-borne passive microwave instruments requires precise
knowledge of fast ice conditions. This presentation details the use of
the NASA Moderate Resolution Imaging Spectroradiometer (MODIS)
visible/thermal infrared radiometer for retrieval of fast ice extent
at high spatio-temporal resolution (1 km spatial, 15-day temporal).
This unprecedented level of detail will facilitate the production of
highly accurate sea ice production and heat/salt flux maps, key
boundary conditions for current and future generation global climate
models.

Second presentation:
C band microwave backscatter has a penetration depth of ?20 metres in
dry snow, so information on the upper snowpack/firn in the Antarctic
dry snow zone can be retrieved from backscatter parameters. The
Advanced Scatterometer allows unprecedented characterisation and
removal of anisotropy, revealing the response of backscatter to cli-
matic forcing in detail. The backscatter parameters investigated here
are the A parameter (isotropic component of backscatter) and the M2
parameter (magnitude of bi-sinusoidal azimuth anisotropy). These were
analysed in conjunction with high-resolution atmospheric model data to
identify the backscatter response to various surface forcing parameters
(wind, precipitation, skin temperature, upper 1 metre mean density and
grain size). Localised case study interpretation is complex, however
analysis of continent-wide Empirical Orthog-onal Functions and dry snow
zone mean time series reveals the close relationship between
backscatter parameters and temperature and precipitation. This
generally under-appreciated short timescale variability should be
considered in studies involving“snapshot” parameter retrieval from
microwave data, e.g., SAR imagery analysis. In addition to a strong
annual cycle, a decreasing A and M2 parameter trend may indicate changes
in snowfall and subsur-face temperature in West Antarctica and along the
Wilkes/Ad ´elie Land coast, regions also showing strong surface lowering
and mass loss trends in gravity data.




接地境界層におけるPIV法を用いた乱流観測
Turbulent flow measurement in the surface boundary layer using the PIV method
(森文洋 Fumihiro Mori)　発表要旨：

地表面近傍における乱流は水蒸気や熱・運動量の輸送過程において非常に
重要な役割を果たしている。この地表面近傍における乱流の時空間構造を
把握するため、従来、風洞などの屋内実験で行われてきた
PIV(Particle Image Velocimetry)と呼ばれる、流れの可視化技術を用い
た観測を実際の地表面上において行った。PIV法は流れの瞬時・多点の速
度分布情報を面的に取得することが可能であり、本研究では水平ー鉛直
断面を対象として観測を行った。
　PIV法を野外観測に適用させる為に新たに野外観測に適用させた観測測器
システムを開発した。また、計側面内に超音波風速計を設置して、PIVと超
音波風速計の両者の同期計測による精度評価を行ったところ、水平風速成
分に関しては高精度な結果となっていたが、鉛直風速成分に関しては誤差
が見られた。
解析の結果から、風洞実験などでみられていたヘアピン渦構造に類似した
構造が地表面上においても確認された。本発表では以上の内容について詳
細に説明する。

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