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Watanabe Y.Y.,Japan National Institute of Polar Research | Watanabe Y.Y.,Graduate University for Advanced Studies
Ecology Letters | Year: 2016

Billions of birds migrate to exploit seasonally available resources. The ranges of migration vary greatly among species, but the underlying mechanisms are poorly understood. I hypothesise that flight mode (flapping or soaring) and body mass affect migration range through their influence on flight energetics. Here, I compiled the tracks of migratory birds (196 species, weighing 12–10 350 g) recorded by electronic tags in the last few decades. In flapping birds, migration ranges decreased with body mass, as predicted from rapidly increasing flight cost with increasing body mass. The species with higher aspect ratio and lower wing loading had larger migration ranges. In soaring birds, migration ranges were mass-independent and larger than those of flapping birds, reflecting their low flight costs irrespective of body mass. This study demonstrates that many animal-tracking studies are now available to explore the general patterns and the underlying mechanisms of animal migration. © 2016 John Wiley & Sons Ltd/CNRS.


Vadas S.,NorthWest Research Associates, Inc. | Yue J.,High Altitude Observatory | Nakamura T.,Japan National Institute of Polar Research
Journal of Geophysical Research: Atmospheres | Year: 2012

We report on six continuous hours of OH airglow imager observations (at z ∼ 87 km) of convectively generated gravity waves (GWs) near Fort Collins, Colorado, on the evening of 08 September 2005. These GWs appeared as nearly concentric rings, and had epicenters near the locations of deep convection in three thunderstorms in Colorado, Nebraska and South Dakota. Using GOES satellite and weather radar observations, we show that the GWs closely follow the thunderstorms. Using the background wind from a nearby radar, the intrinsic wave parameters and vertical wavelengths are calculated. The temperature perturbations are estimated to be T/T̄ ∼ 1-3% for GWs with horizontal wavelengths λh ∼ 20-40 km and horizontal phase speeds ∼40-60 m/s. The horizontal wavelengths of GWs from a convective cluster decreased in time from 30 to 15 km. We employ convective plume and ray-trace models to simulate the GW-induced OH intensity perturbations from convective plumes, clusters and complexes. We find that the results using the background model wind (radiosonde/TIME-GCM) agree well with the late-time observations, when the images are dominated by southwestward, short-wavelength, high-frequency GWs. These late-time GWs propagate against the background wind, and have λh ∼ 30-40 km and periods of τ ∼ 20-30 min. The OH intensity perturbations are enhanced because the vertical wavelengths λz increased, T'/T̄ increased, and the vertical velocity perturbations w' decreased (because the GWs were near their reflection levels). We also find that these short-wavelength GWs were created ∼5 h earlier by an extremely energetic, deep convective plume in South Dakota, thereby showing that small-scale, convective GWs directly link the troposphere and mesopause region. Copyright 2012 by the American Geophysical Union.


Tamura T.,University of Tasmania | Tamura T.,Japan National Institute of Polar Research | Ohshima K.I.,Hokkaido University
Journal of Geophysical Research: Oceans | Year: 2011

High ice production in coastal polynyas over the continental shelves in the Arctic Ocean is responsible for the formation of cold saline water, which contributes to the maintenance of the Arctic Ocean halocline. The accurate detection of coastal polynyas, including an estimate of thin ice thickness, is essential for the estimation of sea ice production. This paper presents an algorithm that estimates thin ice thickness using Special Sensor Microwave/Imager (SSM/I) data in the Arctic Ocean. Detection and estimation of sea ice thicknesses of <0.15 m are based on the SSM/I 85 and 37 GHz polarization ratios (PR85 and PR37) through a comparison with sea ice thicknesses estimated from the advanced very high resolution radiometer (AVHRR) data in the three different Arctic coastal polynyas. Thus, for the entire Arctic Ocean, the algorithm can be used for the detection of coastal polynyas and for the estimation of sea ice production through combination with heat-flux calculation. This study provides the first circumpolar mapping of sea ice production in coastal polynyas over the entire Arctic Ocean. High ice production is confined to the major Arctic coastal polynyas, with the highest ice production rate being in the North Water Polynya. This study also presents the interannual variability of sea ice production in the 10 major coastal polynyas from 1992 to 2007. In general, interannual variability in sea ice production has good correlation with polynya extent rather than surface air temperature. The mapping also provides surface heat- and salt- flux conditions in the ice-covered region, which have not been well understood to date. Copyright 2011 by the American Geophysical Union.


Tomikawa Y.,Japan National Institute of Polar Research
Journal of Climate | Year: 2010

This study examines why the persistence of easterly wind during major stratospheric sudden warmings (SSWs) varies from one SSW to another. From the 22 SSWs identified between 1979 and 2009, six long and six short SSWs of easterly wind periods longer than 20 days and shorter than 10 days, respectively, are chosen and their composites are compared. While the polar-night jet is stronger than the climatological jet before long SSWs, the preconditioning of the polar-night jet tends to occur before short SSWs. After the occurrence of SSWs, the easterly wind of short SSWs quickly returns to a westerly wind due to large positive Eliassen-Palm (E-P) flux divergence in the winter polar stratosphere. The easterly wind of long SSWs lasts for 20-40 days because the E-P flux divergence is small whether it is positive or negative. Such a difference in the E-P flux divergence originates from the difference in the upward E-P flux from the troposphere. On the other hand, the positive E-P flux divergence during short SSWs is not caused by the variation of upward E-P flux from the troposphere but could be due to the shear instability caused by the overreflection of zonal wavenumber 1 planetary waves at the critical surface. The difference in the persistence of easterly wind between long and short SSWs also has a large impact on the planetary wave activity in the winter stratosphere. © 2010 American Meteorological Society.


Tani K.,Japan Agency for Marine - Earth Science and Technology | Dunkley D.J.,Japan National Institute of Polar Research | Ohara Y.,Japan Agency for Marine - Earth Science and Technology
Geology | Year: 2011

The Godzilla megamullion is the largest oceanic core complex (OCC) currently known, and is adjacent to the spreading center of the Parece Vela Basin (PVB), an extinct backarc basin in the Philippine Sea. The duration and termination of tectonomagmatic processes during OCC formation are poorly constrained, due to the weak geomagnetic anomalies in the region. Zircon U-Pb dating of gabbroic and leucocratic rocks from the Godzilla megamullion reveals that fault-induced spreading over the ~125 km length of the OCC lasted for ~4 m.y., with continuous magmatic accretion at the spreading axis. The latest magmatism constrains the cessation of PVB spreading to ca. 7.9 Ma or later, significantly younger than a previous estimate of ca. 12 Ma. The new ages show that backarc basin formation migrated to the present-day Mariana Trough soon after the cessation of spreading in the PVB. © 2011 Geological Society of America.


Watanabe Y.Y.,Japan National Institute of Polar Research | Ito M.,Japan National Institute of Polar Research | Takahashi A.,Japan National Institute of Polar Research
Proceedings of the Royal Society B: Biological Sciences | Year: 2014

Food is heterogeneously distributed in nature, and understanding how animals search for and exploit food patches is a fundamental challenge in ecology. The classic marginal value theorem (MVT) formulates optimal patch residence time in response to patch quality. The MVT was generally proved in controlled animal experiments; however, owing to the technical difficulties in recording foraging behaviour in the wild, it has been inadequately examined in natural predator-prey systems, especially those in the three-dimensional marine environment. Using animal-borne accelerometers and video cameras, we collected a rare dataset in which the behaviour of a marine predator (penguin)was recorded simultaneously with the capture timings of mobile, patchily distributed prey (krill).We provide qualitative support for theMVT by showing that (i) krill capture rate diminished with time in each dive, as assumed in the MVT, and (ii) dive duration (or patch residence time, controlled for dive depth) increased with short-term, dive-scale krill capture rate, but decreased with long-term, bout-scale krill capture rate, as predicted from the MVT. Our results demonstrate that a single environmental factor (i.e. patch quality) can have opposite effects on animal behaviour depending on the time scale, emphasizing the importance of multi-scale approaches in understanding complex foraging strategies. © 2014 The Author(s) Published by the Royal Society. All rights reserved.


Watanabe Y.Y.,Japan National Institute of Polar Research
Proceedings. Biological sciences / The Royal Society | Year: 2014

Food is heterogeneously distributed in nature, and understanding how animals search for and exploit food patches is a fundamental challenge in ecology. The classic marginal value theorem (MVT) formulates optimal patch residence time in response to patch quality. The MVT was generally proved in controlled animal experiments; however, owing to the technical difficulties in recording foraging behaviour in the wild, it has been inadequately examined in natural predator-prey systems, especially those in the three-dimensional marine environment. Using animal-borne accelerometers and video cameras, we collected a rare dataset in which the behaviour of a marine predator (penguin) was recorded simultaneously with the capture timings of mobile, patchily distributed prey (krill). We provide qualitative support for the MVT by showing that (i) krill capture rate diminished with time in each dive, as assumed in the MVT, and (ii) dive duration (or patch residence time, controlled for dive depth) increased with short-term, dive-scale krill capture rate, but decreased with long-term, bout-scale krill capture rate, as predicted from the MVT. Our results demonstrate that a single environmental factor (i.e. patch quality) can have opposite effects on animal behaviour depending on the time scale, emphasizing the importance of multi-scale approaches in understanding complex foraging strategies.


Toyokuni G.,Japan National Institute of Polar Research | Takenaka H.,Kyushu University
Physics of the Earth and Planetary Interiors | Year: 2012

We propose a method for modeling global seismic wave propagation through an attenuative Earth model including the center. This method enables accurate and efficient computations since it is based on the 2.5-D approach, which solves wave equations only on a 2-D cross section of the whole Earth and can correctly model 3-D geometrical spreading. We extend a numerical scheme for the elastic waves in spherical coordinates using the finite-difference method (FDM), to solve the viscoelastodynamic equation. For computation of realistic seismic wave propagation, incorporation of anelastic attenuation is crucial. Since the nature of Earth material is both elastic solid and viscous fluid, we should solve stress-strain relations of viscoelastic material, including attenuative structures. These relations represent the stress as a convolution integral in time, which has had difficulty treating viscoelasticity in time-domain computation such as the FDM. However, we now have a method using so-called memory variables, invented in the 1980s, followed by improvements in Cartesian coordinates. Arbitrary values of the quality factor (Q) can be incorporated into the wave equation via an array of Zener bodies. We also introduce the multi-domain, an FD grid of several layers with different grid spacings, into our FDM scheme. This allows wider lateral grid spacings with depth, so as not to perturb the FD stability criterion around the Earth center. In addition, we propose a technique to avoid the singularity problem of the wave equation in spherical coordinates at the Earth center. We develop a scheme to calculate wavefield variables on this point, based on linear interpolation for the velocity-stress, staggered-grid FDM. This scheme is validated through a comparison of synthetic seismograms with those obtained by the Direct Solution Method for a spherically symmetric Earth model, showing excellent accuracy for our FDM scheme. As a numerical example, we apply the method to simulate seismic waves affected by hemispherical variations of P-wavespeed and attenuation in the top 300. km of the inner core. © 2012 Elsevier B.V..


Watanabe T.,Tokai University | Yamazaki K.,Japan National Institute of Polar Research | Yamazaki K.,Hokkaido University
Journal of Climate | Year: 2014

The variation of the summermonsoon onset over South Asia was investigated by using long-term data of the onset over Kerala, India, during the 64-yr period from 1948 to 2011. It was found that the onset over Kerala shows variation on a multidecadal scale. In early-onset years, the sea surface temperature (SST) anomaly over the northern Pacific Ocean was very similar to the negative Pacific decadal oscillation (PDO). The stationarywave train related to the negative PDO reaches into central Asia and generates a warm anomaly, thereby intensifying the land-sea thermal contrast, which promotes summer monsoon onset over South and Southeast Asia. The correlation between the onset date over Kerala and the PDOhas strengthened since 1976.Analysis of zonal wind in the upper-level troposphere for the period 1958-2002 indicates that the change in the correlationis related to the change in the wave train path. The wave train propagating from the northern Pacific Ocean to western Russia could propagate eastward more easily in 1976-2002 than in 1958-75. © 2014 American Meteorological Society.


Mori M.,University of Tokyo | Watanabe M.,University of Tokyo | Shiogama H.,Japan National Institute of Environmental Studies | Inoue J.,Japan National Institute of Polar Research | Kimoto M.,University of Tokyo
Nature Geoscience | Year: 2014

Over the past decade, severe winters occurred frequently in mid-latitude Eurasia, despite increasing global- and annual-mean surface air temperatures. Observations suggest that these cold Eurasian winters could have been instigated by Arctic sea-ice decline, through excitation of circulation anomalies similar to the Arctic Oscillation. In climate simulations, however, a robust atmospheric response to sea-ice decline has not been found, perhaps owing to energetic internal fluctuations in the atmospheric circulation. Here we use a 100-member ensemble of simulations with an atmospheric general circulation model driven by observation-based sea-ice concentration anomalies to show that as a result of sea-ice reduction in the Barents-Kara Sea, the probability of severe winters has more than doubled in central Eurasia. In our simulations, the atmospheric response to sea-ice decline is approximately independent of the Arctic Oscillation. Both reanalysis data and our simulations suggest that sea-ice decline leads to more frequent Eurasian blocking situations, which in turn favour cold-air advection to Eurasia and hence severe winters. Based on a further analysis of simulations from 22 climate models we conclude that the sea-ice-driven cold winters are unlikely to dominate in a warming future climate, although uncertainty remains, due in part to an insufficient ensemble size. © 2014 Macmillan Publishers Limited.

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