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Dive into the research topics where Masashi Niwano is active.

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Featured researches published by Masashi Niwano.


RADIATION PROCESSES IN THE ATMOSPHERE AND OCEAN (IRS2012): Proceedings of the International Radiation Symposium (IRC/IAMAS) | 2013

Numerical simulation of spectral albedos of glacier surfaces covered with glacial microbes in Northwestern Greenland

Teruo Aoki; Katsuyuki Kuchiki; Masashi Niwano; Sumito Matoba; Jun Uetake; Kazuhiko Masuda; Hiroshi Ishimoto

To clarify the effect of light absorbing impurities including glacial microbes spectral albedo measurements using a spectrometer for spectral domains of the ultraviolet, visible and near-infrared have been carried out on ablation area in Qaanaaq Glacier in northwestern Greenland in July 2011. The almost glacier surfaces in the ablation area were covered with cryoconite (biogenic dust) on thin ice grain layer above bare ice. There were also snow-covered surfaces including red snow (snow algae). The measured spectral albedos had a remarkable contrast between red snow surface and cryoconite-covered ice surface in the spectral domain from the ultraviolet to the visible, where red snow albedo increased rapidly with the wavelength, while the cryoconite albedo was relatively flat to the wavelength. We simulated the spectral albedos of these surfaces with a radiative transfer model for the atmosphere-snow system. The single scattering properties are calculated with Mie theory by assuming red snow gains to be sphe...


Journal of Geophysical Research | 2014

In situ measurements of polarization properties of snow surface under the Brewster geometry in Hokkaido, Japan, and northwest Greenland ice sheet

Tomonori Tanikawa; Masahiro Hori; Teruo Aoki; Akihiro Hachikubo; Katsuyuki Kuchiki; Masashi Niwano; Sumito Matoba; Satoru Yamaguchi; Knut Stamnes

Ground-based measurements of spectral degree of linear polarization (DLP) of various snow types were made during intensive field campaigns in a snowfield in Hokkaido, Japan, and on the northwest Greenland ice sheet in 2012. Spectral measurements were conducted under the solar zenith angle of approximately the Brewster angle in order to quantify the polarization properties of light reflected from snow. We obtained spectral DLPs for five different snow types in both field campaigns including precipitation particles, needles, surface hoar, melt forms, and melt freeze crust covering the snow surface. The measurements showed that in the visible region the spectral dependence of the DLP was small while in the near infrared region it increased with increasing snow grain size with some distinct local peaks. The angular dependence indicated that the DLP exhibited small angular dependence in the visible region while in the near-infrared region it exhibited large and broad peaks in the forward direction. Especially for the melt-freeze crust, the DLP approached 1.0 at wavelengths close to λ = 1.5 and 2.0 μm. These features can be explained by (1) the relative contribution of surface versus volume scattering to the reflected light, (2) the incident angle (solar zenith angle) of approximately the Brewster angle, and (3) the ratio between direct and diffuse components of the solar radiation incident on the snow surface. The spectral DLP was found to be quiet sensitive to the incident solar radiation and solar elevation as well as snow optical properties. Comparison between the spectral DLP and snow grain size obtained by snow pit work shows that the DLP for λ > 1.5 μm was very sensitive to large snow grains close to the surface. This finding suggests that polarization measurements obtained from airborne/satellite polarimeters will be useful for surface snow grain size retrievals and help improve the accuracy of such retrievals based on the intensity-only measurements, especially for the large snow grain sizes.


Annals of Glaciology | 2017

Surface mass balance, ice velocity and near-surface ice temperature on Qaanaaq Ice Cap, northwestern Greenland, from 2012 to 2016

Shun Tsutaki; Shin Sugiyama; Daiki Sakakibara; Teruo Aoki; Masashi Niwano

ABSTRACT To better understand the processes controlling recent mass loss of peripheral glaciers and ice caps in northwestern Greenland, we measured surface mass balance (SMB), ice velocity and near-surface ice temperature on Qaanaaq Ice Cap in the summers of 2012–16. The measurements were performed along a survey route spanning the terminus of an outlet glacier to the upper reaches (243–968 m a.s.l.). The ice-cap-wide SMB ranged from −1.10 ± 0.29 to −0.13 ± 0.26 m w.e. a−1 for the years from 2012/13 to 2015/16. Mass balance showed substantially large fluctuations over the study period under the influence of summer temperature and snow accumulation. Ice velocity showed seasonal speedup only in the summer of 2012, suggesting an extraordinary amount of meltwater penetrated to the bed and enhanced basal ice motion. Ice temperature at a depth of 13 m was −8.0°C at 944 m a.s.l., which was 2.5°C warmer than that at 243 m a.s.l., suggesting that ice temperature in the upper reaches was elevated by refreezing and percolation of meltwater. Our study provided in situ data from a relatively unstudied region in Greenland, and demonstrated the importance of continued monitoring of these processes for longer timespans in the future.


Annals of Glaciology | 2018

Temporal variations of cryoconite holes and cryoconite coverage on the ablation ice surface of Qaanaaq Glacier in northwest Greenland

Nozomu Takeuchi; Ryutaro Sakaki; Jun Uetake; Naoko Nagatsuka; Rigen Shimada; Masashi Niwano; Teruo Aoki

Abstract Cryoconite holes are water-filled cylindrical holes formed on ablation ice surfaces and commonly observed on glaciers worldwide. Temporal changes of cryoconite holes characteristically <5 cm in diameter were monitored with a time-lapse interval camera over 15 d during the melting season on Qaanaaq Glacier in northwest Greenland. The holes drastically changed their dimensions and synchronously collapsed twice during the study period. When the holes collapsed, the coverage of cryoconite on the ice surface increased from 1.0 to 3.5% in the field of view of the camera, and then decreased again to 0.4% after the holes reformed. Comparison with meteorological data showed that the collapses occurred in cloudy and rainy or windy weather conditions, corresponding to low shortwave solar radiation (68–126 W m−2, 40–55% of the incoming flux). In contrast, holes developed in sunny conditions correspond to high solar radiation (186–278 W m−2, 63–88%). Results suggest that the dimensions of holes drastically changed depending on the weather conditions and that frequent cloudy, warm and windy conditions would cause a decay of holes and weathering crust, inducing an increase in the cryoconite coverage on the ice, consequently darkening the glacier surface.


RADIATION PROCESSES IN THE ATMOSPHERE AND OCEAN (IRS2012): Proceedings of the International Radiation Symposium (IRC/IAMAS) | 2013

Possibility to discriminate snow types using brightness temperatures in the thermal infrared wavelength region

Masahiro Hori; Tomonori Tanikawa; Teruo Aoki; Akihiro Hachikubo; Konosuke Sugiura; Katsuyuki Kuchiki; Masashi Niwano

Spectral emissivity of snow surface in the thermal infrared (TIR) wavelength region is an important parameter for monitoring snow surface temperature in cold climate regions and also for discriminating clouds and underlying snow surfaces in polar nights using satellite observed brightness temperature data. Past in-situ observations of snow emissivity revealed that the emissivity of snow surfaces varies depending on snow type [1]. Fine dendrite snow exhibits high emissivity over 0.98 in TIR at all exiting angles (θ). As ice granules of snow surface become large, the snow emissivity in TIR decreases and exhibits a wavelength dependence due to enhanced Fresnel reflectance at a wavelength around 12μm. Reduced snow emissivity is further enhanced as exiting angle increases. For example, emissivities of coarse grain snow at wavelengths of 11μm and 12μm are 0.99 and 0.975 for the zenith direction (θ=0°) but 0.965 and 0.93 for the slant direction of θ=75°. For sun crust snow, wavelength and directional dependences...


Journal of Geophysical Research | 2011

Physically based snow albedo model for calculating broadband albedos and the solar heating profile in snowpack for general circulation models

Teruo Aoki; Katsuyuki Kuchiki; Masashi Niwano; Yuji Kodama; Masahiro Hosaka; Taichu Y. Tanaka


Journal of Geophysical Research | 2012

Snow Metamorphism and Albedo Process (SMAP) model for climate studies: Model validation using meteorological and snow impurity data measured at Sapporo, Japan

Masashi Niwano; Teruo Aoki; Katsuyuki Kuchiki; Masahiro Hosaka; Yuji Kodama


Bulletin of glaciological research | 2014

Light-absorbing snow impurity concentrations measured on Northwest Greenland ice sheet in 2011 and 2012

Teruo Aoki; Sumito Matoba; Satoru Yamaguchi; Tomonori Tanikawa; Masashi Niwano; Katsuyuki Kuchiki; Kouji Adachi; Jun Uetake; Hideaki Motoyama; Masahiro Hori


Journal of Geophysical Research | 2011

Effect of sastrugi on snow bidirectional reflectance and its application to MODIS data

Katsuyuki Kuchiki; Teruo Aoki; Masashi Niwano; Hiroki Motoyoshi; Hironobu Iwabuchi


Remote Sensing of Environment | 2017

A 38-year (1978–2015) Northern Hemisphere daily snow cover extent product derived using consistent objective criteria from satellite-borne optical sensors

Masahiro Hori; Konosuke Sugiura; Kazufumi Kobayashi; Teruo Aoki; Tomonori Tanikawa; Katsuyuki Kuchiki; Masashi Niwano; Hiroyuki Enomoto

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Dive into the Masashi Niwano's collaboration.

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Katsuyuki Kuchiki

Japan Meteorological Agency

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Tomonori Tanikawa

Japan Aerospace Exploration Agency

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Masahiro Hori

Japan Aerospace Exploration Agency

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Yuji Kodama

National Institute of Polar Research

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Akihiro Hachikubo

Kitami Institute of Technology

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Konosuke Sugiura

Japan Agency for Marine-Earth Science and Technology

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Hiroki Motoyoshi

Graduate University for Advanced Studies

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