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Ratnam J.V.,Research Institute for Global Change | Ratnam J.V.,Application Laboratory | Behera S.K.,Research Institute for Global Change | Behera S.K.,Application Laboratory | And 6 more authors.
Climate Dynamics | Year: 2012

The winter months from December 2009 to February 2010 witnessed extreme conditions affecting lives of millions of people around the globe. During this winter, the El Niño Modoki in the tropical Pacific was a dominant climatic mode. In this study, exclusive impacts of the El Niño Modoki are evaluated with an Atmospheric General Circulation Model. Sensitivity experiments are conducted by selectively specifying anomalies of the observed sea surface temperature in the tropical Pacific. Observed data are also used in the diagnostics to trace the source of forced Rossby waves. Both the observational results and the model simulated results show that the heating associated with the El Niño Modoki in the central tropical Pacific accounted for most of the anomalous conditions observed over southern parts of North America, Europe and over most countries in the Southern Hemisphere viz. Uruguay. Unlike those, the model-simulated results suggest that the anomalously high precipitation observed over Australia and Florida might be associated with the narrow eastern Pacific heating observed during the season. © 2011 Springer-Verlag.


Ratnam J.V.,Research Institute for Global Change | Ratnam J.V.,Application Laboratory | Behera S.K.,Research Institute for Global Change | Behera S.K.,Application Laboratory | And 5 more authors.
Climate Dynamics | Year: 2012

The main aim of this paper is to evaluate the Advanced Research Weather Research and Forecasting (WRF) regional model in simulating the precipitation over southern Africa during austral summer. The model's ability to reproduce the southern African mean climate and its variability around this mean state was evaluated by using the two-tier approach of specifying sea surface temperature (SST) to WRF and by using the one-tier approach of coupling the WRF with a simple mixed-layer ocean model. The boundary conditions provided by the reanalysis-II data were used for the simulations. Model experiments were conducted for twelve austral summers from DJF1998-99 to DJF2009-10. The experiments using both the two-tier and one-tier approaches simulated the spatial and temporal distributions of the precipitation realistically. However, both experiments simulated negative biases over Mozambique. Furthermore, analysis of the wet and dry spells revealed that the one-tier approach is superior to the two-tier approach. Based on the analysis of the surface temperature and the zonal wind shear it is noted that the simple mixed-layer ocean model coupled to WRF can be effectively used in place of two-tier WRF to simulate the climate of southern Africa. This is an important result because specification of SST at higher temporal resolutions in the subtropics is the most difficult task in the two-tier approach for most regional prediction models. The one-tier approach with the simple mixed-layer model can effectively reduce the complicacy of finding good SST predictions. © 2011 Springer-Verlag.


Klein P.,French National Center for Scientific Research | Lapeyre G.,French National Center for Scientific Research | Roullet G.,French National Center for Scientific Research | Le Gentil S.,French National Center for Scientific Research | Sasaki H.,Earth Simulator Center
Geophysical and Astrophysical Fluid Dynamics | Year: 2011

High resolution simulations of ocean turbulence with Rossby number of order one have revealed that upper layer dynamics significantly differs from the interior dynamics. As reported before, upper layer dynamics is characterized with shallow velocity spectrum corresponding to kinetic energy distributed over a spectral range from mesoscales to small scales. This dynamics is driven by small-scale frontogenesis related to surface density anomalies. Interior dynamics is characterized by steeper velocity spectrum and is driven by the potential vorticity anomalies set up by the interior baroclinic instability. Impact of the divergent motions related to surface frontogenesis leads to a warming of the upper layers, a cyclone dominance and a negative skewness of the isopycnal displacements. On the contrary, divergent motions in the interior lead to a cooling of the deeper layers, an anticylone dominance and a positive skewness of the isopycnal displacements. These different ageostrophic processes are consistent with an SQG regime extended to Rossby number of order one on one hand and an interior QG regime extended to Rossby number of order one on the other hand, as proposed by previous studies. Synthesis of these characteristics suggest a connection between upper and deeper layers, induced by the divergent motions, through which small scales near the surface interact with mesoscales in the interior. © 2011 Taylor & Francis.


Takahashi K.,Earth Simulator Center | Onishi R.,Earth Simulator Center | Baba Y.,Earth Simulator Center | Kida S.,Earth Simulator Center | And 3 more authors.
Journal of Physics: Conference Series | Year: 2013

Mechanisms of interactions among different scale phenomena play important roles for forecasting of weather and climate. Multi-scale Simulator for the Geoenvironment (MSSG), which deals with multi-scale multi-physics phenomena, is a coupled non-hydrostatic atmosphere-ocean model designed to be run efficiently on the Earth Simulator. We present simulation results with the world-highest 1.9km horizontal resolution for the entire globe and regional heavy rain with 1km horizontal resolution and 5m horizontal/vertical resolution for urban area simulation. To gain high performance by exploiting the system capabilities, we propose novel performance evaluation metrics introduced in previous studies that incorporate the effects of the data caching mechanism between CPU and memory. With a useful code optimization guideline based on such metrics, we demonstrate that MSSG can achieve an excellent peak performance ratio of 32.2% on the Earth Simulator with the single-core performance found to be a key to a reduced time-to-solution.


Takahashi K.,Earth Simulator Center | Onishi R.,Earth Simulator Center | Sugimura T.,Earth Simulator Center | Baba Y.,Earth Simulator Center | And 2 more authors.
High Performance Computing on Vector Systems 2009 | Year: 2010

Multi-Scale Simulator for the Geoenvironment (MSSG), which is a coupled non-hydrostatic atmosphere-ocean-land model, has been developed in the Earth simulator Center. Outline of MSSG is introduced and characteristics are presented. After optimizing computational performance of MSSG, performance analysis has been performed on the Earth Simulator. As the results of optimization, ultra high performance with MSSG has been achieved. Computational performance of the coupled non-hydrostatic atmosphere-ocean-land model has attained 52-55% of theoretical peak performance. Furthermore, results from preliminary validations including forecasting experiments are presented. © Springer-Verlag Berlin Heidelberg 2010.

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