(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 50, No. 1, pp. 31-41, 2003
In this study, secular variation in the occurrence property of summertime daily rainfall amount in and around the Tokyo metropolitan area was demonstrated based on the accumulated rainfall amount in five daily rainfall classes. The geographical structure of the increase tendency of heavy daily rainfall, which is found in recent years at the central part of Tokyo, has been also presented.
Contribution of large daily rainfall classes (high-order classes) to total rainfall amount increased from 1880's to 1940's, and then decreases except around 1960. Contribution of high-order classes, however, changed to an increase in around 1980. Namely, the rainfall property has changed from the stage with daily rainfall of low-order classes prevailed in late 1970's-early 1980's to the stage with large contribution of daily rainfall of high-order classes to total rainfall amount in recent years. It is noted that the secular variation in the summertime rainfall property of Tokyo is characterized by decadal scale vacillation.
The possibility of urban influence is suggested since the recent increasing tendency of rainfall amount of high-order classes is more obvious in the densely populated areas. However, this increasing tendency is considered to be affected basically by larger scale atmospheric variation, because the trend is recognized in the whole area of southern part of Kanto district and is corresponding to only the recent part of decadal scale variation in rainfall property.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 50, No. 3, pp. 161-174, 2003
Developed is a new method of moment estimation applied to a wind profiler that measures Doppler spectra as a function of range in order to reject some clutter noise that corrupts the wind measurements. This method is based on lattice model inspired by both self-organization and Hopfield model in the neural network field and detects atmospheric signals in Doppler spectra to estimate radial velocity. Radial velocity estimated using this method from clutter-contaminated spectral data measured by a boundary layer radar showed a very smooth change along range. It was found that (1) horizontal winds converted from the radial velocity were more continuous in space and in time than those from conventional estimates and showed wind shear clearly;and (2) horizontal wind showed good agreement with rawinsonde-wind.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 50, No. 3, pp. 175-187, 2003
Remarkable progress of study on risk management using weather information has been made in recent days in United States and some other countries. In Japan, Tatehira (1999) showed the way to advanced use of weather information referring to western studies. In turn, requisites for the weather information will become to be clear. The purpose of this paper is a prescriptive modeling of risk management using the probabilistic forecast of temperature.
This study will illustrate the peak load control of electric power co-operation as an example. In this case, risk arises accompanied to the uncertainty of temperature forecast. Risk is quantified based on cost/loss model. It is assumed that decision making controls the size of reserved facilities for power generation. Decision making is assumed to be done using the probabilistic forecast of temperature. The part of cost/loss related to the uncertainty of temperature forecast is called marginal loss which is used as an index measuring the performance of decision making.
This case study will show the possibility of saving about 25% of marginal loss.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 50, No. 4, pp. 243-247, 2003
The AMeDAS data for eight years were used to compare maximum 60-minute precipitation amount in each precipitation event based on hourly data sampling and that based on ten-minutely sampling. On the average over 363993 precipitation cases in which maximum 60-minute precipitation was at least 5mm, the maximum 60-minute precipitation amount based on hourly data was 87.6% of that obtained from ten-minutely data. This ratio was dependent on the duration of precipitation, and was as low as 0.82 for precipitation with duration of 60 minutes. Comparison was also made for the number of cases in which 60-minute precipitation reached some threshold values. The ratio of the numbers of cases based on ten-minutely and hourly sampling was found to be larger for heavier precipitation, and was about 2:1 for precipitation of 100 mm or more.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 50, No. 5, pp. 327-334, 2003
To forecast strong turbulence which gives a serious influence to aircraft, a couple of indices, TSI and TPI, calculated from the vector product of wind vector which reflects the difference of wind direction are proposed to estimate the potential of turbulence occurrence. TSI is related to the thermal advection, and TPI is an index in consideration of the curvature of flow. Verification indicates that these indices have higher accuracy than the conventional ones at the high probability of detection(60-90%), and that these indices are more effective than TI1(the product of horizontal deformation and vertical wind shear)for the turbulence that a forecast was insufficient in VS(vertical wind shear). Therefore, both when separate and when combined with VS, TSI and TPI are more effective than the conventional ones. These indices improve the accuracy of turbulence forecast.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 50, No. 6, pp. 437-445, 2003
A hot-air balloon is handy, needs only low cost to operate, and has considerably large loading capacity. Then we tried to use a hot-air balloon as a platform for measuring atmospheric temperature in a planetary boundary layer.
Accuracy of temperature measurement in this experiments becomes to be better than±0.2ßC when a thermo-couple is suspended more than 40 m away from the hot-air balloon and the balloon flies horizontally or downward. The response time of the thermo-couple is required to be less than one second in order to make smaller than 0.05ßC the temperature measurement errors caused from vertical movement with the hot-air balloon.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 50, No. 6, pp. 457-460, 2003
An analysis was made on long-term changes in wind speed at AMeDAS (Automated Meteorological Data Acquisition System) stations using data for twenty years from March 1979 to February 1999. On the average over 482 stations, which were judged to be free from changes in site and/or anemometer height, daily maximum wind speed and daily mean wind speed showed a decrease of 0.41%/year and 0.26%/year, respectively. At some stations, wind speed was found to have decreased at a rate of 4-5%/year.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 50, No. 8, pp. 625-633, 2003
The 149 temperature distributions were collected by automobile traverse method in the settlements in Saku city and Asashina village, Nagano, whose populations range from 750 to 23,300 inhabitants, to research the relation between city size and heat island intensity. The analysis shows both of the mean heat island intensity under fine days at day and night to be related to the logarithm of the population (Log P) of the settlements. The same relation can be seen in cloudy nights with smaller slope of regression. The relation between the maximum heat island intensities and log P at night was found to hold remarkably well. This relation is shown to hold in the maximum heat island intensities recently studied in Japanese cities. The regression is to be represented not by two line bending (Park, 1987) at around 300,000 in population but by straight line.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 50, No. 8, pp. 635-640, 2003
Distributions of nocturnal air temperature are observed on days with clear weather and then compared with previous observations of approximately 20 years ago. The observed area lies from downtown Oita to Oita University, located in a suburban hilly area. The warmest area is found in the downtown, located on the western-side estuary region of the Oita River. These features are consistent with the previous observations. However the recent temperature difference between Oita University and the surrounding area is reduced by 1-2ßC compared to the previous ones. It is plausible that this is caused by land use change due to urbanization around Oita University in the last 20 years.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 50, No. 9, pp. 705-714, 2003
The characteristics of tropical cyclone tracks, once exceeding maximum wind speed of 17.2 m/s, including the extratropical cyclones period, are discussed using a new method in this paper. The objective study period is from 1961-1990 in the mid-latitudes of the western North Pacific. Data on the 'TROPICAL CYCLONE TRACKS IN THE WESTERN NORTH PACIFIC 1951-1990,' analyzed by the Japan Meteorological Agency, was used.
In this new method, the zonal position of the tropical cyclone is represented by the longitude when it passes every five parallels from 25ßN to 45ßN, and the level of the northward terminus is indicated by the frequency at which it passes through those parallels. Next, the characteristics of the tropical cyclone tracks are shown by averages of the longitudinal and frequency values. The relationship between the central pressures of tropical cyclones and their tracks is also examined.
The seasonal characteristics of the tropical cyclone tracks in the east-west direction can be attributed to the expansion of the North Pacific subtropical high, but not for those in the northern direction. Instead, an examination of the relationship between central pressures and tracks revealed that the level of the northward terminus has a negative relationship with the central pressure. This result was also confirmed by the analysis of the tropical cyclones, whose maximum wind speed is over 17.2 m/s.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 50, No. 10, pp. 777-786, 2003
Hourly data of the AMeDAS(Automated Meteorological Data Acquisition System)network for 23 years were used to examine the relation between precipitation distribution and surface wind patterns in the Kanto plain in the afternoon of summer. The fuzzy c-means method was applied to classify the precipitation distribution on 239 days, which satisfied the conditions that:(1)the maximum temperature was 28ßC or higher on the average over the plain,(2)precipitation was less than 1mm at all but five stations between 06 and 12 LT, and(3)precipitation was at least 1mm on the average over the plain between 12 and 24 LT. Among the six patterns thus obtained, four were characterized by precipitation in the northern part of the plain. The corresponding surface winds in the early afternoon exhibited southerly winds covering the plain in a similar manner to the "extended sea breeze" which prevails on fine days. However, days with precipitation showed a slightly larger convergence in the central plain than on days without precipitation. The difference of wind fields on days with and without precipitation became more evident after late afternoon, with northeasterly winds in the northern Kanto plain on precipitation days. This northeasterly winds were interpretable to be an outflow from the area cooled by precipitation superimposed on the easterly sea breeze, and also related to synoptic change on the interdiurnal time scale. The other two patterns corresponded to precipitation spreading to the south Kanto plain, including one which had a maximum over Tokyo. The early afternoon wind field in this pattern was characterized by convergence of easterly winds blowing from the east coast and southerly winds from the southern coast.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 50, No. 10, pp. 787-793, 2003
As a category of the surface pressure pattern which is often accompanied by a sustained northeasterly wind with the local cloudiness around the coastal area of the Kanto region, the "reverse-tilting circulation type"(Iwase, 1985a)was discussed, assuming a frontal structure which tilts toward the warm air, i. e., a forward-tilting cold front. A front defined by discontinuity of the gradient of density, can tilt toward the warm air. Such a front is theoretically expected to be accompanied by a frontal zone which is statically less stable, and by a trough and a cyclonic wind shear in the warm air, not in the frontal zone. These features were found as a result of reexamination of Iwase's(1985b)case study(7 April 1984). However, the boundary layer in the warm air was nearly statically neutral, so that the forward-tilt of the cold frontal surface was inferred to be large in the layer of 900-800 hPa.