Seita Emori

The next generation of scenarios for climate change research and assessment

Advances in the science and observation of climate change are providing a clearer understanding of the inherent variability of Earth’s climate system and its likely response to human and natural influences. The implications of climate change for the environment and society will depend not only on the response of the Earth system to changes in radiative forcings, but also on how humankind responds through changes in technology, economies, lifestyle and policy. Extensive uncertainties exist in future forcings of and responses to climate change, necessitating the use of scenarios of the future to explore the potential consequences of different response options. To date, such scenarios have not adequately examined crucial possibilities, such as climate change mitigation and adaptation, and have relied on research processes that slowed the exchange of information among physical, biological and social scientists. Here we describe a new process for creating plausible scenarios to investigate some of the most challenging and important questions about climate change confronting the global community.

Tropical Intraseasonal Variability in 14 IPCC AR4 Climate Models Part I: Convective Signals

Abstract This study evaluates the tropical intraseasonal variability, especially the fidelity of Madden–Julian oscillation (MJO) simulations, in 14 coupled general circulation models (GCMs) participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). Eight years of daily precipitation from each model’s twentieth-century climate simulation are analyzed and compared with daily satellite-retrieved precipitation. Space–time spectral analysis is used to obtain the variance and phase speed of dominant convectively coupled equatorial waves, including the MJO, Kelvin, equatorial Rossby (ER), mixed Rossby–gravity (MRG), and eastward inertio–gravity (EIG) and westward inertio–gravity (WIG) waves. The variance and propagation of the MJO, defined as the eastward wavenumbers 1–6, 30–70-day mode, are examined in detail. The results show that current state-of-the-art GCMs still have significant problems and display a wide range of skill in simulating the tropical intraseasonal va...

Improved Climate Simulation by MIROC5: Mean States, Variability, and Climate Sensitivity

Abstract A new version of the atmosphere–ocean general circulation model cooperatively produced by the Japanese research community, known as the Model for Interdisciplinary Research on Climate (MIROC), has recently been developed. A century-long control experiment was performed using the new version (MIROC5) with the standard resolution of the T85 atmosphere and 1° ocean models. The climatological mean state and variability are then compared with observations and those in a previous version (MIROC3.2) with two different resolutions (medres, hires), coarser and finer than the resolution of MIROC5. A few aspects of the mean fields in MIROC5 are similar to or slightly worse than MIROC3.2, but otherwise the climatological features are considerably better. In particular, improvements are found in precipitation, zonal mean atmospheric fields, equatorial ocean subsurface fields, and the simulation of El Nino–Southern Oscillation. The difference between MIROC5 and the previous model is larger than that between th...

Development of the minimal advanced treatments of surface interaction and runoff

Abstract A land surface model (LSM), minimal advanced treatments of surface interaction and runoff (MATSIRO), has been developed for climate studies at the global and regional scales. The canopy has a single layer, whose albedo and bulk coefficients are evaluated on the basis of a multilayer canopy model. The fluxes are calculated from the energy balance at the ground and canopy surfaces in snow-free and snow-covered portions considering the subgrid snow distribution. The interception evaporation from canopy and the transpiration on the basis of photosynthesis are treated. A simplified TOPMODEL is used to calculate runoff. The snow has the variable number of layers from one to three in accordance with snow water equivalent (SWE), and the snow temperature is calculated by a thermal conduction equation. Besides, the snowmelt, the refreeze of snowmelt, and the freeze of rainfall in snow are taken into consideration. It is found in the PILPS 2e experiment that some parameters in the runoff scheme, such as the surface hydraulic conductivity and the river channel fraction, have a considerable impact on the partitioning of the surface runoff and the base flow. The snow albedo is prognosticated from the time passage since last snowfall and the snow temperature. The soil has five layers in this version, and the soil temperature, the soil moisture, and the frozen amount of moisture are calculated.

Global projections of changing risks of floods and droughts in a changing climate

Abstract Simulated daily discharge derived from a relatively high-resolution (approximately 1.1-degree) general circulation model was used to investigate future projections of extremes in river discharge under global warming. The frequency of floods was projected to increase over many regions, except those including North America and central to western Eurasia. The drought frequency was projected to increase globally, while regions such as northern high latitudes, eastern Australia, and eastern Eurasia showed a decrease or no significant changes. Changes in flood and drought are not explained simply by changes in annual precipitation, heavy precipitation, or differences between precipitation and evapotranspiration. Several regions were projected to have increases in both flood frequency and drought frequency. Such regions show a decrease in the number of precipitation days, but an increase in days with heavy rain. Several regions show shifts in the flood season from springtime snowmelt to the summer period of heavy precipitation.

Trans-Pacific yellow sand transport observed in April 1998: A numerical simulation

A yellow sand transport episode from the Asian continent to Japan and North America which occurred in April 1998 is simulated. A new on-line dust tracer model coupled with a regional-scale meteorological model is developed and applied to this dust storm episode. The results for two large dust events that started during April 14–15 and 19–20, 1998, have been analyzed and discussed. The first dust storm was trapped in a cutoff vortex developed over the China plain. A modeled 3-D structure of dust associated with this cutoff vortex agreed with an observed time-height cross section of dust concentration. Results show that the strong subsidence at the backside of the vortex restricted the dust layer below 3 km level. Model analysis revealed that the second dust event that started during April 19–20 over inland China was the origin of a dust episode reported over North America. The trans-Pacific dust transport simulation successfully showed the dust onset near the West Coast of North America. Elevation of the dust layer during the long-range transport was below 3 km. The model is extended to include the transport of an Asian origin anthropogenic tracer over the North Pacific Rim. Both the natural-origin mineral dust and the Asian-origin anthropogenic tracer are simultaneously transported even if their emission regions are different.

Precipitation extreme changes exceeding moisture content increases in MIROC and IPCC climate models

Precipitation extreme changes are often assumed to scale with, or are constrained by, the change in atmospheric moisture content. Studies have generally confirmed the scaling based on moisture content for the midlatitudes but identified deviations for the tropics. In fact half of the twelve selected Intergovernmental Panel on Climate Change (IPCC) models exhibit increases faster than the climatological-mean precipitable water change for high percentiles of tropical daily precipitation, albeit with significant intermodel scatter. Decomposition of the precipitation extreme changes reveals that the variations among models can be attributed primarily to the differences in the upward velocity. Both the amplitude and vertical profile of vertical motion are found to affect precipitation extremes. A recently proposed scaling that incorporates these dynamical effects can capture the basic features of precipitation changes in both the tropics and midlatitudes. In particular, the increases in tropical precipitation extremes significantly exceed the precipitable water change in Model for Interdisciplinary Research on Climate (MIROC), a coupled general circulation model with the highest resolution among IPCC climate models whose precipitation characteristics have been shown to reasonably match those of observations. The expected intensification of tropical disturbances points to the possibility of precipitation extreme increases beyond the moisture content increase as is found in MIROC and some of IPCC models.

Responses of the Kuroshio and the Kuroshio Extension to global warming in a high‐resolution climate model

[1] Using a high-resolution atmosphere-ocean coupled climate model, responses of the Kuroshio and the Kuroshio Extension (KE) to global warming are investigated. In a climate change experiment with atmospheric CO 2 concentration ideally increased by 1% year -1 , the current velocity of the Kuroshio and KE increases, while the latitude of the Kuroshio separation to the east of Japan does not change significantly. The increase of the current velocity is up to 0.3 m s -1 at 150°E. This acceleration of the Kuroshio and KE is due to changes in wind stress over the North Pacific and consequent spin-up of the Kuroshio recirculation gyre. The acceleration of the currents may affect sea level along the southern coast of Japan and northward heat transport under global warming.

Validation, parameterization dependence, and future projection of daily precipitation simulated with a high‐resolution atmospheric GCM

[1] A relatively high-resolution (T106) atmospheric general circulation model (AGCM) was used to simulate the present-day climate with two different assumptions in cumulus parameterization. While the two runs show comparable performance for the annual mean precipitation, one shows much better agreement with satellite-based analysis data for the extreme daily precipitation than the other. Accumulation of convectively available potential energy is shown to be important for more realistic intensities of extreme precipitation. This demonstrates that the performance of an AGCM for extreme precipitation is strongly dependent on cumulus parameterization even when the resolution of the model is as high as 1°, but can be reasonably good with an adequate choice of cumulus parameterization. A time-slice doubled CO 2 experiment was also conducted with the better version of the model. Though the global mean percentage change is larger for extreme precipitation than for the annual mean, this relation is found to vary regionally.

The interaction of cumulus convection with soil moisture distribution: An idealized simulation

In order to investigate the interaction between cumulus convection and soil moisture distribution, two-dimensional numerical experiments using a regional atmospheric model are performed. The model roughly resolves each convective cell and represents cloud processes by a microphysics parameterization. Two long-term (60-day) integrations with relatively dry and wet conditions are made with the atmosphere-land system in a quasi-equilibrium state. Though the initial and boundary conditions are horizontally homogeneous, horizontal contrasts in soil moisture spontaneously develop due to the spotty nature of convective precipitation. When intense soil moisture contrasts develop, they cause surface temperature contrasts through a change in evaporation. As a result, thermally induced local circulations occur in the daytime, with upward branches over the dry and hot regions and downward branches over the wet and cool regions. Most cumulus convection events are initiated by the upward motion of this local circulation over the dry region. They mostly occur in the afternoon (1300–1700 LT), while convection that forms over regions that are wet throughout may occur at any time during the day. The intense precipitation over the dry region “overdamps” the soil moisture contrast, which results in the maintenance of a heterogeneous distribution of soil moisture.