Wataru Ohfuchi

Significance of a Midlatitude SST Frontal Zone in the Formation of a Storm Track and an Eddy-Driven Westerly Jet*

Abstract In a set of idealized “aquaplanet” experiments with an atmospheric general circulation model to which zonally uniform sea surface temperature (SST) is prescribed globally as the lower boundary condition, an assessment is made of the potential influence of the frontal SST gradient upon the formation of a storm track and an eddy-driven midlatitude polar front jet (PFJ), and on its robustness against changes in the intensity of a subtropical jet (STJ). In experiments with the frontal midlatitude SST gradient as that observed in the southwestern Indian Ocean, transient eddy activity in each of the winter and summer hemispheres is organized into a deep storm track along the SST front with an enhanced low-level baroclinic growth of eddies. In the winter hemisphere, another storm track forms just below the intense STJ core, but it is confined to the upper troposphere with no significant baroclinic eddy growth underneath. The near-surface westerlies are strongest near the midlatitude SST front as observe...

High resolution numerical modelling of the atmosphere and ocean

-Gilbert Brunet (Meteorological Service of Canada): Vortex Rossby wave in hurricanes: On the need for a high resolution Numerical Weather Prediction Strategy -Kazuhisa, Tsuboki (Nagoya University, Japan): High-resolution simulation experiments for typhoons using the cloud-resolving model on the Earth Simulator -Bill Skamarock (National Center for Atmospheric Research, USA): High-resolution numerical weather prediction: Are our models adequate? -Akira Noda (Japan Meteorological Research Institute): Global warming simulated with a super high resolution global climate model -Takeshi Enomoto (Earth Simulator Center, Japan): Meso-scale resolving simulations of global atmosphere -Agathe Untch (European Center for Medium Range Weather Forecasts, UK): High-resolution experimentation at ECMWF -Kevin Hamilton (University of Hawaii, USA): Gravity waves in high resolution atmospheric GCM simulations -John McGregor (CSIRO, Australia): Simulations using the conformal-cubic atmospheric model -Isidoro Orlanski (NOAA Geophysical Fluid Dynamics Laboratory, USA): Why the simulation of mid latitude storm tracks requires high resolution -Nobumasa Komori (Earth Simulator Center, Japan): High-resolution simulation of coupled atmospheric-ocean system using the CFES model -Jing-Jia Luo (Frontier Research Center for Global Change, Japan): Seasonal climate predictability in a high-resolution coupled Ocean-Atmosphere GCM -Keiko Takahashi (earth Simulator Center, Japan): Impact of high resolution interaction between ocean and atmosphere -Hideharu Sasaki (Earth Simulator Center, Japan): Eddy-resolving simulation in the world ocean using the ocean GCM fort he Earth Simulator -Yukio Tanaka (Frontier Research Center for Global Change, Japan): Evaluation of eddy effect in the Southern Ocean using high resolution ocean model -George Nurser (Southhampton University, UK): Diagnosis of theupper ocean in the OCCAM high resolution ocean GCM

Description of AFES 2: Improvements for High-Resolution and Coupled Simulations

This chapter describes the updated version of Atmospheric General Circulation Model for the Earth Simulator (AFES 2). Modifications are intended (1) to increase the accuracy and efficiency of the Legendre transform at high resolutions and (2) to improve the physical performance. In particular, the Emanuel scheme replaces a simplified version of the Arakawa-Schubert scheme for the parametrization of cumulus convection. The Emanuel scheme parametrizes O(100m) drafts within subgrid-scale cumuli and does not have explicit dependency upon the grid size. Therefore the cloud model of the Emanuel scheme allows us to use it at high resolutions of O(10km) where the validity of the ensemble cloud model of the Arakawa-Schubert scheme is questionable. Moreover, 10-year test runs indicate that the use of the Emanuel scheme improve the physical performance at a moderate resolution as well. Anomalies of the geopotential height and zonal winds in the middle to upper troposphere are reduced, although the improvements in terms of the distributions of precipitation and sea-level pressure are not significant. Improvements are attributable to a better vertical structure of temperature in the tropics due to more realistic estimation of mixing of the momentum, temperature, and moisture by the Emanuel scheme.

VIRTUAL ATMOSPHERIC AND OCEANIC CIRCULATION IN THE EARTH SIMULATOR

Abstract High-resolution simulations of the atmospheric and oceanic general circulations on the Earth Simulator are briefly introduced to a wider research and educational community. Some early results have been published and are reviewed in this article. The high-resolution simulations may have more information in certain aspects than observations while the simulations need to be validated. On the other hand, high-resolution observations in which uncertainties are unavoidable are now available. Possible close collaboration between observational and simulation research is proposed.

High-Resolution Simulation of the Global Coupled Atmosphere-Ocean System: Description and Preliminary Outcomes of CFES (CGCM for the Earth Simulator)

We have been developing a global, high-resolution, coupled atmosphereocean general circulation model, named CFES, which was designed to achieve efficient computational performance on the Earth Simulator. A brief description of CFES and some preliminary results obtained from 66-month integration are presented. Although some deficiencies are apparent in the results, realistically simulated smallscale structures such as extratropical cyclones and sea surface temperature fronts in the mid-latitudes, and seasonal variation of tropical sea surface temperature and polar sea-ice extent encourage us to study mechanism and predictability of high-impact phenomena and their relation to the global-scale circulations using CFES.

Mesoscale resolving simulations of the global atmosphere and ocean on the Earth simulator

Understanding multiscale interactions within the complex hierarchy of various phenomena on wide ranges of temporal and spatial scales is an essential part of the study of the atmosphere and ocean circulation systems. Despite significant progress, the complex interactions have not yet been fully understood, due mainly to the lack of continuous, mesoscale resolving observations of the global three-dimensional circulations, whose realization is difficult, especially for the ocean. However, computer simulations with ultra-high resolution, if possible, would be a powerful tool to tackle this difficult issue. Such simulations are now under way on the Earth Simulator (ES), a Japanese gigantic vectorparallel computer that has been in operation since March 2002 and was the worlds fastest general-purpose supercomputer until early fall 2004. Even though the ES is now the third-fastest supercomputer by both peak performance and UNPACK test, which is a benchmark test by liner algebra computations, our 10-km mesh atmospheric general circulation simulation remains the fastest real-world computation on a general-purpose supercomputer even after two and half years.

The APE atlas

This Atlas presents statistical analyses of the simulations submitted to the Aqua-Planet Experiment (APE) data archive. The simulations are from global Atmospheric General Circulation Models (AGCM) applied to a water-covered earth. The AGCMs include ones actively used or being developed for numerical weather prediction or climate research. Some are mature, application models and others are more novel and thus less well tested in Earth-like applications. The experiment applies AGCMs with their complete parameterization package to an idealization of the planet Earth which has a greatly simplified lower boundary that consists of an ocean only. It has no land and its associated orography, and no sea ice. The ocean is represented by Sea Surface Temperatures (SST) which are specified everywhere with simple, idealized distributions. Thus in the hierarchy of tests available for AGCMs, APE falls between tests with simplified forcings such as those proposed by Held and Suarez (1994) and Boer and Denis (1997) and Earth-like simulations of the Atmospheric Modeling Intercomparison Project (AMIP, Gates et al., 1999). Blackburn and Hoskins (2013) summarize the APE and its aims. They discuss where the APE fits within a modeling hierarchy which has evolved to evaluate complete models and which provides a link between realistic simulation and conceptual models of atmospheric phenomena. The APE bridges a gap in the existing hierarchy. The goals of APE are to provide a benchmark of current model behaviors and to stimulate research to understand the cause of inter-model differences., APE is sponsored by the World Meteorological Organization (WMO) joint Commission on Atmospheric Science (CAS), World Climate Research Program (WCRP) Working Group on Numerical Experimentation (WGNE). Chapter 2 of this Atlas provides an overview of the specification of the eight APE experiments and of the data collected. Chapter 3 lists the participating models and includes brief descriptions of each. Chapters 4 through 7 present a wide variety of statistics from the 14 participating models for the eight different experiments. Additional intercomparison figures created by Dr. Yukiko Yamada in AGU group are available at http://www.gfd-dennou.org/library/ape/comparison/. This Atlas is intended to present and compare the statistics of the APE simulations but does not contain a discussion of interpretive analyses. Such analyses are left for journal papers such as those included in the Special Issue of the Journal of the Meteorological Society of Japan (2013, Vol. 91A) devoted to the APE. Two papers in that collection provide an overview of the simulations. One (Blackburn et al., 2013) concentrates on the CONTROL simulation and the other (Williamson et al., 2013) on the response to changes in the meridional SST profile. Additional papers provide more detailed analysis of the basic simulations, while others describe various sensitivities and applications. The APE experiment data base holds a wealth of data that is now publicly available from the APE web site: http://climate.ncas.ac.uk/ape/. We hope that this Atlas will stimulate future analyses and investigations to understand the large variation seen in the model behaviors.

10-KM MESH GLOBAL ATMOSPHERIC SIMULATIONS

Following the development of an atmospheric general circulation model that runs very efficiently on the Earth Simulator, three meso-scale resolving global 10-km mesh simulations were performed. Three meso-scale phenomena were chosen as simulation and research targets: They were the typhoon genesis, wintertime cyclogenesis and Baiu-Meiyu frontal zone. A brief summary of these results is given in this paper. Generally speaking, the results are realistic, and the figures of precipitation fields from the simulations may look like synthesized pictures from artificial satellites. The results are very encouraging and suggest the usefulness of such ultra-high resolution global simulations for studies on, for example, interaction between large-scale circulation and meso-scale disturbances. Also rationales for this kind of simulations are discussed.

High resolution simulations of atmospheric and oceanic circulation

The pursuit of fine spatial representation in models of the atmospheric and oceanic circulation has been a theme running through the development of the field of numerical simulation. For example, in studies of the global ocean circulation, a longstanding concern has been the issue of adequately resolving particularly energetic eddies, such as Gulf Stream rings. In global and regional atmospheric models, a key issue has been resolving mesoscale circulations that organize clouds and convection. With the recent advent of a new generation of high-performance computing systems, such as the Japan Agency for Marine-Earth Science and Technologys (JAMSTEC) Earth Simulator, some notable thresholds in terms of model resolution have been approached or, in some cases, surpassed. For example, the first long integrations with genuine eddy-resolving global ocean models were reported in 2003. On the atmospheric side, decadal integrations with global models with effective horizontal resolution of approximately 20 kilometers have now become possible, and very short integrations of models that explicitly resolve scales approaching those of individual convective elements were first reported in 2005. These developments in global models have been paralleled by rising research activity with increasingly fine resolution regional atmospheric models for climate and shortrange forecasting applications.