(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 58, No. 2, pp. 131-141, 2011
The present study showed the atmospheric pressure distribution in the Tokyo ward area at nighttime in summer using observational data. The data from Tokyo's high density observation system (METROS: Metropolitan Environmental Temperature and Rainfall Observation System) was used. It was necessary to correct the METROS data to show the detailed pressure distribution in the city, because the data has the specific instrument error at each station. However, the observational instruments of METROS had already been removed. Then, we corrected the atmospheric pressure data using the pressure data difference when the sea level pressure at the Tokyo Meteorological Observatory was equal to that at each METROS station, assuming hydrostatic equilibrium. It is thought that the corrected pressure distribution given in this study is reasonable because it is consistent with the air temperature distribution, wind system, and convergence zone. In the case study analysis during which a typical heat island existed in the center of Tokyo, we detected a significant pressure difference where the atmospheric pressure in the center of Tokyo is 0.2 or 0.3 hPa lower than that in the surrounding areas.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 58, No. 4, pp. 305-316, 2011
Features of meso-scale precipitation systems of intense rainfalls on August 17, 1968 over the Kiso-Hida and Nagara River Basin are studied.
The intense rainfalls occurred within a long cloud belt that formed with a low-level moist belt (LMB). The intense rainfalls were accompanied by the intensification of the convective instability due to the southeastward intrusion of mid tropospheric dry airs over the LMB.
Under the synoptic-scale conditions mentioned above, meso-scale precipitation systems developed successively over the river basin, in association with the southerly moist flow into the basin. These precipitation systems caused intense precipitation of 30-100 mm h-1, and resulted in maximum total precipitation of ~300 mm. Most intense precipitation occurred in the night time along the southern edge of inland cold pool. Each meso-scale precipitation system consisted of a few intense precipitation cells, which caused intense precipitation of ~20 mm per 10 min. Significant temperature drop and change in surface wind were not observed in the present case. The intense precipitation was over, simultaneously with the weakening of the southerly moist flow into the basin.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 58, No. 7, pp. 577-598, 2011
Climate geoengineering is defined as "deliberate large-scale manipulation of the planetary environment to counteract anthropogenic climate change." The slow progress of greenhouse gas emissions reduction and a heightened recognition of the risk of dangerous global warming have led to increasing attention to this novel approach, although it cannot substitute for mitigation nor adaptation. The IPCC will review geoengineering as part of its fifth assessment report.
There are two main categories of climate engineering options: carbon dioxide removal (CDR) , which reduces the concentration of the atmospheric carbon dioxide, a primary cause of global warming; and solar radiation management (SRM) that reduces the incoming solar radiation, thereby cooling the earth system. An example of the CDR approach is to add iron to the ocean to increase photosynthesis.
Amongst many proposed approaches, the most promising is arguably the stratospheric aerosol injection, an SRM option. Its physics is similar to that of global cooling following volcanic eruptions. Research has shown that it would be accompanied with undesired effects such as changes in precipitation patterns. The GeoMIP, an international effort to climate model intercomparison on this approach, has recently been launched.
Though intended as a cure of global warming, climate geoengineering confronts the human society with a number of problems. It would require an international framework since, if conducted unilaterally, it would affect the global climate as a whole. In the short run, guidelines for experiments in the natural environment would be crucial, on which international discussions just commenced.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 58, No. 9, pp. 765-775, 2011
A frequently used method in extreme value analysis is to select a distribution function that gives a best fit to data. To evaluate the performance of this approach, a series of Monte Carlo simulation was made by randomly sampling data from the Gumbel distribution or the square-root-exponential type maximum (SQRT-ET) distribution, and applying five candidate functions to calculate return values that were compared with exact values. It was found that two-parameter functions (Gumbel and SQRT-ET) cause biased results if they differ from the true distribution, while three-parameter functions (the generalized extreme value (GEV), log-Pearson type III (LP3), and generalized normal (GNO) distributions) have little bias that is much smaller than the range of uncertainty due to sample variability, indicating the unimportance of fitness analysis for these three-parameter distributions. Then the performance of the standard least-squares criterion (SLSC), which is widely used to quantify the fitness of extreme distribution functions to data, and also of the jackknife method, which is used for evaluating the range of uncertainty of return values, was examined by Monte Carlo simulation. It was found that the value of SLSC is dependent on data length, so that it is not appropriate to test the fitness using a constant threshold of SLSC. The jackknife method gives an almost correct value of the uncertainty range, but it is not suitable for fitness analysis because fitness and uncertainty are irrelevant to each other.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 58, No. 12, pp. 1037-1054, 2011
In the afternoon of 28 April 2007, the Kanto District in Japan was struck by a severe storm accompanied by thunder, wind gusts, and hail. Analyzing this event using Doppler radar data, sounding data, wind profiler data, surface observation data, and a damage survey, we obtained the following results:
(1) The mesoscale convective system that caused the damage was a bow echo.
(2) The dual-Doppler analysis showed a region with strong vertical vorticity and strong horizontal convergence at the apex of the bow echo. The form and behavior of this region were very similar to those of mesocyclones in past studies. The region first stayed aloft in the midlevel (2-4 km AGL), but later, its southwestern part reached to the ground. At that point, two misocyclones were detected at its base by low-level plan-position indicator (PPI) data. They moved with the region toward the east-southeast.
(3) One misocyclone that passed over the southern part of the Tokyo Bay area resulted in wind damage at several locations in the area. Analyses using low-level PPI data showed that the damage occurred at places where the misocyclone wind and its movement were linearly superposed to produce strong wind. The maximum wind speed at this point is estimated to have reached 40 m s-1. The length of the wind-damage swath was about 18 km.
(4) Previous numerical studies on the genesis of mesovortices have suggested that cyclonic mesovortices form from the tilting of horizontal vorticity acquired by downdraft parcels entering the mesovortex. The horizontal vorticity is solenoidally generated by the baroclinic zone across the gust front. Our analysis using Doppler radar data indicates that this mechanism was realized in nature in this case.
(5) About 10 minutes before the first damage occurred, PPI data of the higher elevation angle showed strong radial convergence at the apex of the bow echo. The convergence aloft can be regarded as a precursor to the outbreak of the misocyclone and will provide useful information for severe wind nowcasting.