Akimasa Sumi

A diagnostic study of the impact of El Niño on the precipitation in China

The impact of El Niño on the precipitation in China for different seasons are investigated diagnostically. It is found that El Niño can influence the precipitation in China significantly during its mature phase. In the Northern winter, spring and autumn, the positive precipitation anomalies are found in the southern part of China during the El Niño mature phase. In the Northern summer, the patterns of the precipitation anomalies in the El Niño mature phase are different from those in the other seasons. The negative precipitation anomalies appear in both southern and northern parts of China, while in between around the lower reaches of the Yangtze River and the Huaihe River valleys the precipitation anomalies tend to be positive.In the Northern winter, spring and autumn, the physical process by which El Niño affects the precipitation in the southern part of China can be explained by the features of the circulation anomalies over East Asia during the El Niño mature phase (Zhang et al., 1996). The appearance of an anticyclonic anomaly to the north of the maritime continent in the lower troposphere during the El Niño mature phase intensifies the subtropical high in the western Pacific and makes it shift westward. The associated southwesterly flow is responsible for the positive precipitation anomalies in the southern part of China. In the Northern summer, the intensified western Pacific subtropical high covers the southeastern periphery of China so that the precipitation there becomes less. In addition, the weakening of the Indian monsoon provides less moisture inflow to the northern part of China.

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.

Intercomparison of Atmospheric GCM Simulated Anomalies Associated with the 1997/98 El Nino

A wide angle trapezoidal periscope is disclosed having an upper trapezoidal housing and a smaller lower trapezoidal housing secured to said upper housing having optics sealed therein which include parallel upper and lower windows and parallel upper and lower mirrors. When used on military vehicles, the lower trapezoidal periscope housings are inserted within evenly and closely spaced trapezoidal openings in the rim of a hatch and are secured to the hatch with corner connectors to clamp non-parallel walls of said upper housings within about 1/8 of an inch of the adjacent non-parallel walls of the next adjacent trapezoidal housing. Each periscope provides a vertical field of view of about 43 DEG and a horizontal field of view of about 140 DEG .

Arctic dipole anomaly and its contribution to sea ice export from the Arctic Ocean in the 20th century

[1] The winter dipole anomaly (DA) in the Arctic atmosphere and its contribution to sea ice export are investigated by using a high-resolution coupled global general circulation model. The spatial distributions of the first two leading EOF modes of winter mean sea level pressure (SLP) and geopotential height at 500 hPa north of 70N obtained by the long-term simulation (1900–2010) are highly similar to those derived from the National Center for Environmental Prediction and the National Center for the Atmospheric Research (NCEP/NCAR) reanalysis datasets (1948–2004). The first-leading mode corresponds to the Arctic Oscillation (AO). The DA is defined as the second-leading mode. The AO and DA account for 59% and 19% of the total variance, respectively. Composite spatial patterns of SLP, sea ice thickness and velocity in the extreme years when both the absolute values of principal component (PC1 and PC2) exceed 1.0 standard deviation indicate that the DA plays a great important role in sea ice export from the Arctic Ocean to the Greenland Sea due to its strong meridionality. Sea ice export is highly promoted (restricted) in the positive (negative) DA phase. The dependence of sea ice export on the DA is comparable to or rather larger than that on the AO. Citation: Watanabe, E., J. Wang, A. Sumi, and H. Hasumi (2006), Arctic dipole anomaly and its contribution to sea ice export from the Arctic Ocean in the 20th century, Geophys. Res. Lett., 33, L23703, doi:10.1029/ 2006GL028112.

Comparison of equilibrium and transient responses to CO2 increase in eight state-of-the-art climate models

We compared the climate response of doubled CO2 equilibrium experiments (2 × CO2) by atmosphere—slab ocean coupled general circulation models (ASGCMs) and that of 1% per year CO2 increase experiments (1%CO2 by atmosphere—ocean coupled general circulation models (AOGCMs) using eight state-of-the-art climate models. Climate feedback processes in 2 × CO2 are different from those in 1%CO2, and the equilibrium climate sensitivity (T2×) in 2 × CO2 is different from the effective climate sensitivity (T2×, eff) in 1%CO2. The difference between T2× and T2×, eff is from −1.3 to 1.6 K, a large part of which can be explained by the difference in the ice-albedo and cloud feedback. The largest contribution is cloud SW feedback, and the difference in cloud SW feedback for 2 ×CO2 and 1%CO2 could be determined by the distribution of the SAT anomaly which causes differences in the atmospheric thermal structure. An important factor which determines the difference in ice-albedo feedback is the initial sea ice distribution at the Southern Ocean, which is generally overestimated in 2 ×CO2 as compared to 1%CO2 and observation. Through the comparison of climate feedback processes in 2 ×CO2 and 1%CO2, the possible behaviour of the time evolution of T2×, eff is discussed.

Role of Transients in the Dynamics of East Asian Summer Seasonal Mean Circulation Anomalies—A Study of 1993 and 1994

Abstract By using the National Centers for Environmental Prediction reanalysis data and a nonlinear barotropic model, the transient activities and the possible role of transient vorticity fluxes in the maintenance of east Asian summer seasonal mean circulation anomalies associated with Japan’s extremely cool and wet summer of 1993 and hot and dry summer of 1994 are examined. Data analysis shows that the summertime atmospheric circulation and the transient activity anomalies exhibit nearly opposite patterns over east Asia during these two years. Vorticity budget calculations indicate that the anomalies of transient activities in these two years produced strong transient vorticity flux forcing anomalies that are comparable in magnitude to the divergent forcing anomalies over east Asia. The nonlinear barotropic model, when forced by the anomalous divergence and transient vorticity flux forcing together, produces simulations that bear resemblance to the observed summertime seasonal mean circulation anomalies ...

Model development for the global warming prediction by using the Earth Simulator

A high resolution atmosphere-ocean coupled model has been developed in order to improve a Global Warming simulation. Based on preliminary experiments, it was decided that an atmospheric component is T106 global spectral model with 56 levels and an ocean component is 1/4/spl deg/ 1/6/spl deg/grid point mode with 46 levels. A land surface model (MATSUSIRO) and a run-off model are incorporated. Corresponding to the increase in horizontal and vertical resolution, subroutines for physical processes are reexamined. Various options have been examined and final specification of the model was decided. Coupling between atmosphere component and ocean component is done through MPMD (multiple program and multiple data) algorithm. 10 nodes in the Earth Simulator (ES) are allocated to the atmospheric component and 76 nodes are allocated to the oceanic component. The version 0 of the coupled model was completed in 2003 and 40 year control run was conducted, and 1% increase of CO2 run was also conducted for 40 years. Simulation of atmospheric and oceanic phenomena was improved at many respects. It is suggested that a regional climate change may be achieved.

A high resolution nonhydrostatic tropical atmospheric model and its performance

A high resolution nonhydrostatic tropical atmospheric model is developed by using a ready-made regional atmospheric modeling system. The motivation is to investigate the convective activities associated with the tropical intraseasonal oscillation (ISO) through a cloud resolving calculation. Due to limitations in computing resources, a 2000 km×2000 km region covering the forefront of an ISO-related westerly is selected as the model domain, in which a cloud-resolving integration with a 5-km horizontal resolution is conducted. The results indicate the importance of stratus-cumulus interactions in the organization of the cloud clusters embedded in the ISO. In addition, comparative integrations with 2-km and 5-km grid sizes are conducted, which suggest no distinctive differences between the two cases although some finer structures of convections are discernible in the 2-km case. The significance of this study resides in supplying a powerful tool for investigating tropical cloud activities without the controversy of cloud parameterizations. The parallel computing method applied in this model allows sufficient usage of computer memory, which is different from the usual method used when parallelizing regional model. Further simulation for the global tropics with a resolution around 5 km is being prepared.

Radar observations of tropical clouds on the Manus Island, Papua New Guinea

During the Intensive Observation Period (IOP) of TOGA-COARE (the Tropical Ocean-Global Atmosphere program, a Coupled Ocean-Atmosphere Response Experiment), Doppler radar observation was carried out on Manus Island, Papua New Guinea. In this study, as a preliminary analysis of tropical cloud in the western part of Pacific Ocean, two cases of convective clouds are analyzed, one is the isolated convective cloud which appeared at the center of the island, the other is linear convective rainband associated with gust front. The common finding of these analyses is the temporal separation of warm rain processes and cold rain processes. This feature causes the timing of the anvil appearance and of the wind gust occurrence.<<ETX>>

Global change and the role of the natural sciences

The basic purpose of the natural sciences is to understand the dynamism of nature by applying deduction based on physical and chemical laws and validating the results with observational and experimental data. Therefore, it is considered important to find the essential phenomenon by filtering the various noises that are included in the natural phenomena, and to analyse it. At the same time, quantitative expression is preferred to qualitative expression. Most discussion and deduction is based on countable quantities. Thus, the analytical method tends to become the dominant method because it applies logic to a target phenomenon and then explores its mechanism. Usually, mathematical expression is used to represent the logic. Of course, the analytical method is not the only method in the natural sciences. Other methods include observation and description, where the emphasis is on knowing nature itself and every detail is well documented. These primary data are organized on the basis of the topic’s characteristics and the scientist’s interest. Through this process, filtering is conducted.