(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 55, No. 3, pp. 149-158, 2008
Interannual winter temperature variations over Japan and their relation to large-scale atmospheric circulation field are investigated. By a rotated principal component analysis onto the station temperatures, two dominant variation patterns are detected, both of which relate with the intensity of the northwesterly East Asian winter monsoon. The first mode represents a temperature variation in the Honshu island and the Nansei islands. Horizontal temperature advection by surface wind seems to be related with the temperature anomalies, while sunshine duration tends to be long when temperature is low. The first mode accompanies the Western Pacific teleconnection pattern, and relates with the El Nino/Southern Oscillation. The second mode represents a temperature variation in the Northern Japan, and shows a large change in 1988/89. Horizontal temperature advection by surface wind seems to be related with the temperature anomalies, while correlation with sunshine duration is low. Corresponding atmospheric circulation pattern is similar with the Arctic Oscillation.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 55, No. 3, pp. 159-171, 2008
The relationship between the Madden-Julian Oscillation (MJO) and winter (November-March) climate of Japan is statistically investigated using daily surface observation data (surface temperature, precipitation, sunshine duration) in Japan for 24 years. In order to reveal the relationship with the features of the large scale circulation, reanalysis data is also used.
It is found that the surface air temperature anomaly in Japan in the 20-70 day band tends to be positive (negative) with statistical significance when the convection associated with the MJO is active over the Indian Ocean (over Indonesia). This is especially evident in Western Japan. Although less statistically significant, precipitation, frequency of extreme rainfall and sunshine duration are found to be systematically changed with the MJO phase, mainly along the Pacific coast. Interestingly, activities of the synoptic scale disturbance over the North Pacific also fluctuate with statistical significance, synchronous with the variability of rainfall in Japan. Therefore, it is suggested that the winter climate of Japan is affected by the MJO not only directly but also indirectly through the variability of the extratropical atmospheric circulation.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 55, No. 4, pp. 241-250, 2008
Strong winds frequently occur at Chiba Marine Stadium in Chiba Prefecture. Data analysis at Chiba AMeDAS station revealed that the strong winds during the warm season were caused by the intrusion from the southwest through the Tokyo Bay associated with extratropical cyclones passing to the north of the Kanto area or cold fronts. Field observation confirmed that wind variability at Chiba AMeDAS and the Makuhari area with the stadium showed good agreement in cases of south-southwesterly winds. Three-dimensional wind field in and around a doughnut-shaped building, imitating the Marine Stadium, was simulated by wind tunnel experiments. In the stadium, wind below was in the opposite direction of the general flows above the model, and there was a boundary between the flows with larger turbulence. The height of the boundary changed depending on the roughness on the windward side of the stadium and roof height facing the general flows. The occurrence of the reverse flows with the boundary between the general flows was confirmed by observation conducted in the Marine Stadium.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 55, No. 6, pp. 469-473, 2008
A statistical study was made on the variabilities of precipitation and water storage of the Sameura Dam, which is located in central Shikoku and has often experienced severe water shortage in recent years. The summer precipitation over the dam catchment is characterized by more precipitation and larger temporal variability in comparison to many other regions of Japan. The water demand on the dam is higher than those of dams in other regions, so that larger amount of precipitation is required to maintain the water storage, resulting in rapid decrease of water storage in case of dry weather.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 55, No. 8, pp. 637-649, 2008
Airborne observation revealed vertical structure of the local front, which is often seen over Bouso Peninsula, Japan. Formation process of the local front and aerosol-induced low visibility phenomena were discussed.
The local front measured in the morning 19 December 2003, was formed by the warm advection over the cold air pool in the Kanto plain. The local front transformed to the wind shear around the noon, due to vanishing of the cold air pool and transition of synoptic condition.
The aerosol-dammed layer was observed in the cold air of local front in the afternoon. In that layer, visibility decreased from 20 km in the morning to 5 km in the afternoon. The low visibility observed was due to the high concentration of aerosol.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 55, No. 8, pp. 651-660, 2008
A long-term observations of gusts were carried out on the Hokuriku Coast, Japan using X-band radar and surface weather stations during two winter seasons from 1994 to 1996. Based on the 157 cases of the detected gusts, the features of gusts were revealed as follows.
1) Based on 100,000 data of the 1-minute maximum instantaneous wind speed, 3% of them exceeded 15 m/s and 0.1% exceeded 20 m/s, respectively. About 60% of the detected gusts exceeded the wind speed of 15 m/s.
2) 75% of the gusts were accompanied with radar echoes. Pressure jump of 0.2 hPa and temperature drop of 0.5°C in average were recorded at the time of the gusts with convective echoes.
3) Wind speed of gusts was in proportion to the maximum reflectivity and the height of the echoes. Most of the gusts occurred within 10 km from the edge of the echoes.
4) 70% of the convective echoes that brought the surface gusts had the echo intensity exceeding 28 dBZ and the height of the echo exceeding 4 km AGL during cold air outbreak period.
These results implied that the drag force of graupel particle was the important factor of the downdraft. The layer of convective unstable up to 700 hPa was necessary for the developing of the convective echoes that brought the surface gusts as the environmental conditions.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 55, No. 9, pp. 737-746, 2008
In the 1988-2006 cold seasons (November to March), two structures of cold-air outbreak were observed at Naha: Case N (for which a thick layer of northerly wind was predominant through a cold-air outbreak event) and Case S (for which an initially thin layer of northerly wind was gradually thickened as a cold-air outbreak was developed). We elucidate the interannual variations of cold-air outbreak and winter monsoon and the typical structures of the two different cold-air outbreaks, and investigate the relationship of the cold-air outbreak structures around Naha with sea surface temperature (SST) and monsoon. The NINO3 SST anomaly averaged over the cold season correlates with the meridional wind at 1000 hPa and the precipitation until the '00/01 season. The mean SST around Naha correlates with the sea-level pressure and the specific humidity at 1000 hPa, while the Arctic Oscillation index correlates with the relative humidity at 900 hPa.
The synoptic-scale meteorological analysis elucidates that the Pacific anticyclone at the early stage of the cold-air outbreak determines the structures of Cases N and S. In the cold seasons when the southerly winds are strong at 500 hPa over the East China Sea in the association with El Nino, the cold-air outbreaks for Case S are predominant.