Kashiwa, Japan
Kashiwa, Japan

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Ogawa T.,Meiji University | Okuda T.,Meteorological college
Networks and Heterogeneous Media | Year: 2012

Oscillatory dynamics in a reaction-diffusion system with spatially nonlocal effect under Neumann boundary conditions is studied. The system provides triply degenerate points for two spatially non-uniform modes and uniform one (zero mode). We focus our attention on the 0:1:2-mode interaction in the reaction-diffusion system. Using a normal form on the center manifold, we seek the equilibria and study the stability of them. Moreover, Hopf bifurcation phenomena is studied for each equilibrium which has a Hopf instability point. The numerical results to the chaotic dynamics are also shown. © American Institute of Mathematical Sciences.

Zhu C.,Hokkaido University | Yoshikawa-Inoue H.,Hokkaido University | Matsueda H.,Meteorological Research Institute | Sawa Y.,Meteorological Research Institute | And 3 more authors.
Atmospheric Environment | Year: 2012

Atmospheric 222Rn was monitored from December 2008 to November 2010 on Rishiri Island (45°07'N, 141°12'E), northernmost Japan. Seasonal 222Rn variation was characterized by high concentrations from November to February and low concentrations from May to July, caused by the alternation of continental and maritime fetch regions. 222Rn tracer and back trajectory cluster analyses indicated that the predominant continental fetch region was southeastern Siberia and northeastern China. 222Rn emitted from China and South Korea, whose economies are growing rapidly, did not significantly affect the Rishiri site. The major maritime fetch region was the Sea of Okhotsk and the Bering Sea. A global three-dimensional model (NICAM-TM) accurately simulated 222Rn concentrations on Rishiri Island and in the seasonal fetch regions. The time series of 222Rn data will make it possible to evaluate the sources and sinks of atmospheric greenhouse gases being monitored at Rishiri Island, which complements other sites in the Asia-Pacific rim region, and to validate model simulations used to examine trans-boundary air pollution. © 2011 Elsevier Ltd.

Wada A.,Meteorological College | Matsueda H.,Meteorological Research Institute | Sawa Y.,Meteorological Research Institute | Tsuboi K.,Meteorological Research Institute | Okubo S.,Japan Meteorological Agency
Atmospheric Environment | Year: 2011

We analyzed seasonal and geographical variations of the enhancement ratios of trace gases of the Asian continental pollution (ACP) events observed over the western North Pacific region. The ACP events were identified by using continuous carbon monoxide (CO) measurements taken at three monitoring stations of Minamitorishima (MNM), Yonagunijima (YON), and Ryori (RYO) in Japan for more than 10 years. The frequency of ACP events at MNM and YON increased in the winter and early spring seasons, but not at RYO. The enhanced concentrations of CO (ΔCO) associated with the ACP events showed a clear seasonal variation at MNM and YON, but not at RYO. Other trace gases of methane (CH4), carbon dioxide (CO2), and ozone (O3) were simultaneously enhanced for many of the ACP events, and were highly correlated with ΔCO. The frequency distributions of the enhancement ratios of ΔCH4/ΔCO, ΔCO/ΔCO2, and ΔO3/ΔCO depended largely on the geographical locations of the stations. Distinct seasonal variations in the enhancement ratios showed a decrease in ΔCH4/ΔCO but an increase in ΔCO/ΔCO2 in the winter and early spring at all three stations, although their seasonal amplitudes were different each station. These results indicate that the chemical compositions associated with the ACP events were considerably influenced by the seasonal variations in the trace gas emission ratios of the Asian continental source regions, with increased fluxes of CH4 in summer and CO in winter. Contributions to the ΔCH4/ΔCO and ΔCO/ΔCO2 ratios from the photochemical evolution during atmospheric transport were estimated to be not significant, while the seasonal changes in the ΔO3/ΔCO ratio were controlled significantly by the photochemistry. © 2011 Elsevier Ltd.

Hira S.,Japan Meteorological Agency | Kanehisa H.,Meteorological College
Journal of the Meteorological Society of Japan | Year: 2015

In this study, an analytical solution of nocturnal low level jets (LLJs) is presented. The present model is an extension of Blackadar, who described the nocturnal LLJ as a result of an inertial oscillation. In the present model, the momentum equation in the daytime atmospheric boundary layer includes a term representing convective mixing in addition to mixing with a constant diffusion coefficient. With the convective mixing, the daytime equilibrium wind velocity becomes vertically more uniform than the Ekman solution. In the nighttime atmospheric boundary layer, the convective mixing is assumed to be absent and the diffusion coefficient, which is assumed to be a constant, is smaller than that in the daytime. Without the convective mixing, the nighttime equilibrium wind velocity is the same as that of the Ekman solution. The analytical solution describes the temporal evolution of nighttime wind velocity as a damped inertial oscillation around the nighttime equilibrium wind velocity, starting from daytime equilibrium wind velocity. By appropriately selecting the values of parameters in the analytical solution, some previously published results are reproduced. For example, the height of maximum wind speed decreases as time goes on. There exist backward inertial oscillations in addition to the well-known forward inertial oscillations. In the lower levels, the oscillations are rapidly damped. © 2015, Meteorological Society of Japan.

Fujita S.,Meteorological College | Kikuchi T.,Nagoya University | Tanaka T.,Kyushu University
Journal of Geophysical Research: Space Physics | Year: 2010

Using a self-consistent global magnetohydrodynamic simulation, we investigate the transient behavior of the magnetosphere-ionosphere compound system during deformation of the magnetosphere after a northward turn of the interplanetary magnetic field (IMF). We find that a peculiar Region 2 field-aligned current (R2 FAC) caused by a transient dynamo is enhanced in the ionosphere and, consequently, the convection field in the ionosphere is overshielded after the northward turn of the IMF. On the other hand, in the magnetosphere, the transient dynamo appears on the lower-latitude side of the dayside cleft. This dynamo is driven by the sunward convection flow that descends the enhanced pressure slope in the cleft region. This sunward flow and the enhanced pressure are caused by the release of magnetic tension accumulated in the southward IMF interval. Simultaneously, a counterclockwise vortex on a sphere of r = 8 Re (a clockwise vortex in the equatorial plane) in the afternoon sector appears in the magnetosphere. Consequently, the overshielding potential due to the R2 FAC in the ionosphere is a counterpart of the flow vortex in the magnetosphere. Finally, we note that the effect of the ∇B/curvature drift, which is due to the ring current particles, may be insignificant because the dynamo responsible for the overshielding appears in the higher-latitude region. Copyright 2010 by the American Geophysical Union.

Fujita S.,Meteorological College | Tanaka T.,Kyushu University
Earth, Planets and Space | Year: 2013

The plasmaspheric virtual resonance (PVR) and the transient Alfvén wave bouncing between the ionospheres in both hemispheres (the transient response,TR) are regarded as the possible generation mechanisms of the Pi2 pulsations. However,the global MHD simulation of a substorm (Tanaka et al.,2010) did not reproduce such wave modes because of insufficient ionospheric reflection of the Alfven wave,numerical transfer of the Alfven wave across the field lines,and no plasmasphere. Furthermore,it is noted that the substorm current wedge (SCW) which is a driver of the TR is not reproduced in the global MHD simulation. In this study,we search the sources of the Pi2 pulsations in the global MHD simulation,namely,the compressional wave in the inner magnetosphere for the PVR and the Alfvén wave injected to the ionosphere for the TR. In conclusion,there appears a compressional signal in the inner magnetosphere when the high-speed Earthward flow at the substorm onset surges in the inner edge of the plasma sheet. This simulation result suggests that this compressional wave would be trapped in the plasmasphere as the PVR if the model has the plasmasphere. As for TR,the global MHD simulation provides suddenly increasing field-aligned current (the Alfvén wave) associated with sudden appearance of the shear flow which comes from the high-speed flow in the plasma sheet at the onset of the substorm. If the global MHD simulation correctly lets the Alfvén wave be reflected in the ionosphere and transmitted along the field line,the TR would be established. As the ballooning instability is regarded as one of candidates of the Pi2 pulsation sources,we also briefly investigate whether the simulated plasma sheet in the growth phase is unstable or not for the ballooning instability. Copyright © The Society of Geomagnetism and Earth,Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB.

Motoi T.,Meteorological College | Chan W.-L.,Japan Agency for Marine - Earth Science and Technology
Geological Society Special Publication | Year: 2010

The changes in the sea-ice conditions and sea surface temperatures in the Subarctic Pacific caused by the closure of the Central American Seaway and their influence on the East Asian monsoon are investigated by a series of closed (CE), open (OE) and re-closed (RCE) seaway experiments with a climate model. It is found that a permanent halocline forms in the Subarctic Pacific because of the termination of saline water transport through the seaway in CE and RCE. Efficient cooling by shallow convection in the stratified permanent halocline causes thicker and more extensive sea ice in winter, and leads to colder surface water in summer in the Subarctic Pacific. Colder air, over more extensive sea ice cover in winter and over the colder water in summer, produces higher surface air pressure with anticyclonic wind anomalies in both seasons. Southeasterly and southerly wind anomalies develop around the Japanese archipelago in the East Asian monsoon region and induce warm and humid surface air with increased precipitation over the East Asian continent. These results indicate that the East Asian monsoon is weakened in winter and strengthened in summer as a result of closing the Central American Seaway. © The Geological Society of London 2010.

Wada A.,Meteorological Research Institute | Midorikawa T.,Geochemical Research Institute | Ishii M.,Geochemical Research Institute | Motoi T.,Meteorological College
Journal of Geophysical Research: Oceans | Year: 2011

A simple chemical scheme was introduced into the Meteorological Research Institute Community Ocean Model (MRI.COM) for investigating the rapid CO 2 flux increase at a moored buoy in the East China Sea caused by the passages of Typhoons Tina and Winnie in 1997. MRI.COM well reproduced variations in the observed water temperature and pCO2 sea at 1 m depth and in the air-sea CO2 flux at the buoy. Even though the analyzed magnitudes of the air-sea CO2 fluxes were of the same order, the sudden CO2 flux change occurred nearly 2 days after Tina and nearly 3 days after Winnie. The increase in pCO2 sea normalized to a temperature of 29C induced by Winnie appeared longer than that induced by Tina. The numerical simulation results showed clear differences in the oceanic response between the two typhoons. In the case of Tina, upwelling along the continental shelf played a crucial role in rapidly decreasing the water temperature and transporting seawater with low pCO2 sea and high dissolved inorganic carbon (DIC) to the upper ocean. In contrast, water with relatively high pCO2 sea and low DIC transported by strong horizontal advection of the Kuroshio Current was vertically mixed by the passage of Winnie, resulting in a cool, deep mixed layer at the buoy. The surface seawater hydrogen ion concentration (pH) temporarily decreased during the passages of Tina and Winnie. In the case of Tina, pH decreased by at most 0.03 and for only 1 day. Copyright 2011 by the American Geophysical Union.

Tsujino H.,Meteorological Research Institute | Hirabara M.,Meteorological Research Institute | Nakano H.,Meteorological Research Institute | Yasuda T.,Meteorological Research Institute | And 2 more authors.
Journal of Oceanography | Year: 2011

A long-term spin-up and a subsequent interannual simulation are conducted for the ocean-ice component of the climate model intercomparison project (CMIP)-class earth system model of the Japan Meteorological Agency/Meteorological Research Institute. This experiment has three purposes: first is to assess the ability of our model with the Coordinated Ocean-ice Reference Experiments (COREs) forcing in reproducing the present ocean-climate; second is to understand the ocean-climate variability for the past 60 years; third is to present an example of evaluating an ocean-ice interannual variability simulation. The Pacific Ocean is focused on for the last two purposes. After integrating for about 1500 years with repeated use of a detrended CORE interannual forcing, the model reaches a quasi-steady state where the present climate is reproduced satisfactorily. Then, the interannual variability simulation is conducted with the retrieved forcing trend and the result is analyzed. The simulation is successful at reproducing the long-term variability in the Pacific and surrounding oceans. Brief analyses of the tropical and mid-latitude upper layer, deep circulation, and the Arctic sea ice are presented. A caveat in treating other parts of the globe is due to the recent intense convection in the Southern Ocean caused by a remarkably increasing trend of the Southern Hemisphere westerly. Overall, the current simulation with our CMIP-class ocean-ice model is shown to be useful for studying the present ocean-climate variability, specifically in the Pacific sector. It could also be used as a benchmark control experiment that facilitates further research, model development, and intercomparison. © 2011 The Oceanographic Society of Japan and Springer.

Oda M.,Meteorological Research Institute | Kanehisa H.,Meteorological College
Journal of the Meteorological Society of Japan | Year: 2015

The interaction between Rossby and gravity waves is examined in a vertical-zonal two-dimensional model, in which the basic state has an upward gradient of buoyancy at a lower level and a downward gradient of horizontal vorticity at a higher level. Because of the gradients, there exist westward-propagating upper Rossby and westward- and eastward-propagating lower gravity waves, where the propagation is relative to the fluid. The initial value problem for the disturbance is analytically solved. The temporal evolution of the analytical solution from an initial value shows the following characteristics. Resonant interaction between the westward-propagating upper Rossby wave and the eastward-propagating lower gravity wave is possible, in the same way as between two counter-propagating Rossby waves in barotropic and baroclinic problems. On the boundary in the parameter space between the unstable region, where resonant exponential growth occurs, and the stable region, where the solution oscillates, the marginal solution grows as a linear function of time. As in other instability problems, the marginal linear growth in the present model is not trivial. For small horizontal wave numbers, the westward-propagating gravity wave makes a non-negligible contribution to the resonant interaction between the westward-propagating Rossby wave and the eastward-propagating gravity waves. © 2015, Meteorological Society of Japan.

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