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.
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.
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.
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.
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.