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O'Ishi R.,University of Tokyo | O'Ishi R.,Japan National Institute of Polar Research | Abe-Ouchi A.,University of Tokyo | Abe-Ouchi A.,Frontier Research Center for Global Change
Climate of the Past | Year: 2013

When the climate is reconstructed from paleoevidence, it shows that the Last Glacial Maximum (LGM, ca. 21 000 yr ago) is cold and dry compared to the present-day. Reconstruction also shows that compared to today, the vegetation of the LGM is less active and the distribution of vegetation was drastically different, due to cold temperature, dryness, and a lower level of atmospheric CO2 concentration (185 ppm compared to a preindustrial level of 285 ppm). In the present paper, we investigate the influence of vegetation change on the climate of the LGM by using a coupled atmosphere-ocean-vegetation general circulation model (AOVGCM, the MIROC-LPJ). The MIROC-LPJ is different from earlier studies in the introduction of a bias correction method in individual running GCM experiments. We examined four GCM experiments (LGM and preindustrial, with and without vegetation feedback) and quantified the strength of the vegetation feedback during the LGM. The result shows that global-averaged cooling during the LGM is amplified by +13.5 % due to the introduction of vegetation feedback. This is mainly caused by the increase of land surface albedo due to the expansion of tundra in northern high latitudes and the desertification in northern middle latitudes around 30° N to 60° N. We also investigated how this change in climate affected the total terrestrial carbon storage by using offline Lund-Potsdam-Jena dynamic global vegetation model (LPJ-DGVM). Our result shows that the total terrestrial carbon storage was reduced by 597 PgC during the LGM, which corresponds to the emission of 282 ppm atmospheric CO2. In the LGM experiments, the global carbon distribution is generally the same whether the vegetation feedback to the atmosphere is included or not. However, the inclusion of vegetation feedback causes substantial terrestrial carbon storage change, especially in explaining the lowering of atmospheric CO2 during the LGM. © Author(s) 2013.

Nomura M.,Nagoya University | Tsuboki K.,Nagoya University | Tsuboki K.,Frontier Research Center for Global Change
Journal of the Meteorological Society of Japan | Year: 2012

Spiral bands are characteristic meso-beta-scale structures of typhoons in their mature stages. Observational study shows that spiral bands cause strong rainfall. The spiral bands are classified into two types: inner and outer rainbands. The inner rainband is formed near the typhoon center. In this study, we focus on the precipitation process in the inner rainband within the typhoon. Two neighboring spiral bands are often observed near the typhoon center. Previous studies have shown the mechanism of intensifying rainfall in the inner-side spiral band of two neighboring inner rainbands that frequently form in this region. However, the intensification of the outer-side spiral band of two neighboring inner rainbands has not been widely reported. Therefore, to clarify the mechanism of intensifying rainfall in the spiral bands, we focus on cloud microphysical processes and perform a numerical experiment using a cloud-resolving model. We show that cold rain processes are important for the intensification of precipitation in the spiral band. In particular, production and growth of graupel are the most effective processes for the intensification of precipitation in the spiral band. © 2012, Meteorological Society of Japan.

Nomura M.,Nagoya University | Tsuboki K.,Nagoya University | Tsuboki K.,Frontier Research Center for Global Change | Shinoda T.,Nagoya University
Journal of the Meteorological Society of Japan | Year: 2012

This study uses a cloud-resolving model to examine the impact of sedimentation of cloud ice on the cloud-top height and the precipitation intensity of typical precipitation systems in East Asia, including a typhoon, snow clouds over the Sea of Japan, and the Baiu front. The fall velocity of cloud ice is assumed to be 0.1 m s-1. When the sedimentation process of cloud ice is included in the model, the horizontal distribution and frequency of the cloud-top height show significantly better agreement with satellite observations. Furthermore, cloud ice with sedimentation concentrates at a lower level than that without sedimentation, and converts to snow and graupel by microphysical growth processes. More solid water substances located in the thin layer above the 0°C level contribute to intensification of precipitation at the surface by several percent, especially in the convective area. © 2012, Meteorological Society of Japan.

Akter N.,Nagoya University | Akter N.,Bangladesh University of Engineering and Technology | Tsuboki K.,Bangladesh University of Engineering and Technology | Tsuboki K.,Frontier Research Center for Global Change
Monthly Weather Review | Year: 2012

Cyclone Sidr, one of the most devastating tropical cyclones that resulted in several thousand deaths and substantial damages, developed in the north Indian Ocean and made landfall over the Bangladesh coast on 15 November 2007. Observation and simulation results show that Sidr was embedded in a nonuniform environment and contained an intense outer rainband to the east of its center and a significant frontal band to the northwest. A detailed study of the outer rainband is performed by numerical simulation. The eastern band was a long, quasi-straight shape in the meridional direction that remained stationary relative to the cyclone center. This band was composed of convective cells that developed southeast of the center within a synoptic-scale convergence zone and propagated along the band toward the northeast quadrant. The speed of the downwind-propagating cells was greater than that of the cyclone, which resulted in a convective cluster northeast of the center. Only the downwind portion of the band consisted of convection with stratiform rain, whereas the upwind and middle portions contained active convective cells without stratiform rain. The band was located between the synoptic-scale flows of a weakly sheared, gradient-balanced westerly and a strongly sheared, nongradient-balanced prevailing southerly caused by the complex terrain of the Bay of Bengal's southeast region. Low-level convergence along the band was dominated by cross-band flow from both sides of the band and was confined below 3 km. As the cyclone moved northward, the convergence zone resulted in the extension of band length up to;800 km. The southerly at the eastern side of the center gradually accelerated and was directed toward the center by a strong pressure gradient force. The flow accumulated a substantial amount of water vapor from the sea in addition to the increased moisture in the lower troposphere, resulting in further intensification of the convective cells. © 2012 American Meteorological Society.

Neelin J.D.,University of California at Los Angeles | Lintner B.R.,University of California at Los Angeles | Lintner B.R.,Rutgers University | Tian B.,Jet Propulsion Laboratory | And 6 more authors.
Geophysical Research Letters | Year: 2010

Simple prototypes for forced advection-diffusion problems are known to produce passive tracer distributions that exhibit approximately exponential or stretched exponential tails. Having previously found an approximately exponential tail for the column integrated water vapor (CWV) distribution under high precipitation conditions, we conjectured that if such prototypes are relevant to more complex tropospheric tracer problems, we should find such tails for a wide set of tracers. Here it is shown that such tails are indeed ubiquitous in observed, model, and reanalysis data sets for a variety of tracers, either column integrated or averaged through a deep layer, including CO and CO2. The long tails in CWV are associated with vertical transport and can occur independent of a local precipitation sink. These non-Gaussian distributions can have consequences for source attribution studies of anthropogenic tracers, and for mechanisms of precipitation extremes; the properties of the tails may help constrain model tracer simulations. Copyright © 2010 by the American Geophysical Union.

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