A new high-resolution atmosphere-ocean coupled general circulation model named MIROC4h has been developed, and its performance in a 120-year control experiment (including a 50-year spin-up) under the present conditions (the year 1950) is examined. The results of the control experiment by MIROC4h are compared with simulations of preindustrial conditions carried out for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) using the previous high- and medium-resolution versions of the model, called MIROC3h and MIROC3m, respectively. A major change in MIROC4h is a doubling of the resolution of the atmospheric component to 0.5625°, compared to 1.125° for MIROC3h. The oceanic components of MIROC4h and MIROC3h are eddy-permitting, with a horizontal resolution of 0.28125° (zonal) × 0.1875° (meridional). In MIROC3m, the horizontal resolution is 2.8125° for the atmospheric component and 1.40625° (zonal) × 0.56°–1.4° (meridional) for the ocean component. Compared with MIROC3h and MIROC3m, many improvements have been achieved; for example, errors in the surface air temperature and sea surface temperature are smaller, there is less drift of the ocean water temperature in the subsurface-deep ocean, and the frequency of heavy rain is comparable to observations. The fine horizontal resolution in the atmosphere makes orographic wind and its effects on the ocean more realistic than those of the former models, and the treatment of coastal upwelling motion in the ocean has been improved. Phenomena in the atmosphere and ocean related to the El Niño and southern oscillation are now closer to observations than was obtained by MIROC3h and MIROC3m. The effective climate sensitivity for CO2 doubling is calculated to be about 5.7 K, which is much larger than the value obtained using the IPCC AR4 models, and is mainly due to a decrease in the low-level clouds at low latitudes.
A layered structure of aerosol particles from surface to 1080 m was observed in Beijing on 8 December 2007. Below 700 m, the particles were well mixed vertically. From 700 to 1000 m was an elevated aerosol layer (EAL), in which the aerosol concentration was remarkably higher than in the lower and upper layers. Electron microscopic analyses of particles in the size range of 0.2–1.3 μm at different altitudes revealed that soot particles were the majority in all layers. There were fresh, young and aged soot particles in the lower layer. In contrast, soot particles in the EAL were well aged, showing the structure of shrunken soot inclusions coated with weakly absorbing materials. The geometric mean equivalent diameter of the soot particles in the EAL was 0.4–0.6 μm while that of their inclusions was about 0.1 μm. The EAL coincided with the remaining nocturnal layer aloft, which was the residual left by the daytime upward convective mixing. These results suggest that the fate of soot particles was closely dependent on the evolution of the boundary layer. While particles emitted from the surface were efficiently mixed upward in daytime, the residual nocturnal layer acted as a cap and produced an EAL abundant in well-aged soot particles. In addition, the lapse rate in the EAL had an obvious decrease. However, estimation of aerosol absorption showed a limited warming effect and the inversion intensification could not be explained by the absorption. Meteorological records indicated that the intensification was more likely the consequence of air subsidence.
This study examines the indirect effect of tropical cyclones (TCs) on cases of heavy rainfall during the Baiu season in Kyushu, Japan using data analyses and numerical experiments. A detailed analysis of the heavy rainfall event that occurred on 7 June 1999 (JST) is performed. This event was remotely affected by Typhoon Maggie (9903), which was located approximately 2000 km from Kyushu at the time. As Typhoon Maggie passed close to Taiwan, a high potential vorticity (PV) zone appeared to the north of Taiwan. A low PV region formed simultaneously to the east of Taiwan, corresponding to a northwestward extension of the Pacific high. These dynamical changes induced an enhanced southerly moisture flux between the high PV zone and the low PV region, leading to moisture convergence and heavy rain in the vicinity of Kyushu. During this time, Typhoon Maggie also caused the northward advection of a separate tropical disturbance. The high PV zone to the north of Taiwan was produced by diabatic heating associated with interplay between the circulation of Typhoon Maggie and the topography of Taiwan. In contrast, the low PV region was formed through the advection of low-PV air from low latitudes by Typhoon Maggie. A piecewise PV inversion diagnostic shows that the low PV region was the largest contributor to the southerly moisture flux, although both Typhoon Maggie and the high PV zone also made positive contributions. Numerical experiments reveal that the precipitation in and around Kyushu was enhanced by both the topography of Taiwan and the northward advection of the additional tropical disturbance. This study identifies a new mechanism as an indirect effect of TCs. The core element of this mechanism is a large moisture flux south of Kyushu, which is termed “moisture road,” and the difference from “atmospheric river” is discussed. This mechanism is not unique to Typhoon Maggie, as other cases of heavy rainfall in and around Kyushu are associated with similar situations.
Water vapor and ozone profiles in the tropical tropopause layer (TTL) are investigated using measurements from balloon-borne frost-point hygrometers and ozone sensors during the Central Equatorial Pacific Experiment campaign. Variations in water vapor, ozone, and temperature are described during soundings taken over a period of two weeks and over a distance of approximately 2,700 km along the equator. These observations indicate that the first and latter halves of the campaign period are characterized as cold and warm phases near the cold point tropopause, respectively. Stationary and eastward-traveling components equally contributed to these temperature anomalies. During the transition between the two phases, the ozone increased around 350–400 K, with the maxima around the 360 K isentrope. The water vapor simultaneously increased and decreased around the 360–400 K and 350–360 K isentropes, respectively. Simultaneous increases in ozone and water vapor around 360–400 K with a reduction in the vertical gradients suggest the possibility of turbulent mixing associated with a large-scale wave structure. The enhancement of vertical shear of zonal wind during the transition between the two phases also supports this idea. The decrease in water vapor around the 350–360 K isentropes could be understood as a result of saturation on the isentropic surface. This study shows the importance of observing variations in isentropic coordinates, rather than altitude coordinates, around the TTL in order to make a quantitative argument concerning mixing and dehydration when a large-amplitude disturbance exists.
To understand the mechanisms of long-term climate and carbon cycle feedback with anthropogenic impact, past simulations (1850–2005) and projection experiments (2006 to 2100) were conducted using a new Earth system model named “MIROC-ESM”, forced by four representative concentration pathway (RCP) scenarios that describe how greenhouse gases (GHGs), aerosols, and land-use will develop in the future. From these projections, temperature rise from 1850 to 2100 ranged from 2.4 K in the RCP2.6 scenario to 6.2 K in the RCP8.5 scenario. We found that there are discrepancies between the RCPs and the estimates of our model in both allowable fossil fuel and land-use change emissions. The former showed systematic discrepancies likely due to strong positive feedbacks in the model, but the latter did not. The likely reason for the difference in land-use emissions is the modeling of land-use change processes or definitions for the emission. Climate response to the increase of atmospheric carbon showed large variation among scenarios, strongly affected by ocean heat uptake efficiency that could depend on the rate of atmospheric CO2 increase in each scenario. Large variation between scenarios was also found in carbon cycle sensitivity measured by cumulative airborne fraction. The variation in carbon cycle sensitivity may be attributable to the dependence of concentration-carbon feedback on the rate of atmospheric CO2 increase. The earth system would show a similar response to emitted carbon during the 21st century if the difference of ocean heat uptake efficiency between scenarios were small. The earth system responds to RCP6.0 with less sensitivity to emitted carbon when compared with other scenarios because of high-efficiency carbon uptakes by land and ocean ecosystems. In contrast, RCP2.6 showed high sensitivity of the earth system to carbon emission, and apparently showed different behavior from other scenarios due to early reduction of GHGs.