(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 68, No. 1, pp. 5-12, 2021
Visibility is important information not only for meteorological analysis but also for operations of transport and monitoring air pollution. In this study, climatological features of visibility in the Tokyo urban area are investigated. The number of days with low visibility decreases year by year. The factors can be drying in urban areas and the improvement of air quality, and the reduction of suspended particle matters contributes more to improve the visibility than the relative humidity. The visibility shows seasonal changes; during summer, visibility decreases when photochemical smog is likely to occur, whereas the visibility increases in winter. Visibility in Tokyo can be largely affected by anthropogenic hygroscopic aerosols, which decrease visibility when relative humidity is high.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 68, No. 3, pp. 131-148, 2021
Development process and structure of the meso-a-scale Baiu frontal depression associated with Kyushu heavy rains in 23-24 July 1982 are studied using observation data and reanalysis data. The depression formed with precipitation, in the week baroclinic field over China (~33ßN, 105ßE). In the formation stage, the depression was not associated with upper trough. The depression developed and moved eastward, and reached over the sea south of the Korean Peninsula on 23 July. The cloud cluster which sustained in the warm-sector of the depression caused intense rainfall. During 23-24 July, a high-pressure zone extended westward from the Okhotsk anticyclone toward the east-side of the depression. Strong southerly low-level jet stream, moisture gradient, vorticity and up-ward velocity were sustained in the eastern periphery of the depression. The depression weakened on 25 July, as it moved in the high-pressure area, and rainfall weakened rapidly. The features of the depression found in this Baiu heavy rainfall event are compared with these in previous studies. Although some of the features in this case are commonly found in other cases, some differences are seen among the cases.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 68, No. 3, pp. 149-163, 2021
Here we investigated features of the Japanese hottest temperature of 41.1ßC observed in Hamamatsu, Shizuoka, Japan, on 17 August 2020. The result suggested that a whale's tail pressure pattern with high-temperature and northwesterly wind above the mixed-layer, as well as continuous clear skies over the Nobi Plain, were necessary conditions for the 41.1ßC event. In addition to these background factors, a foehn-like wind with diabatic heating from urban and the dry ground surface directly contributed to the 41.1ßC. This heated airflow entered Hamamatsu was blocked by the southerly wind east of Hamamatsu, which was the reason why the highest temperature was observed in Hamamatsu. As the mechanism described here is similar to that in past high-temperature events in Japan, any other regions may also experience such high temperatures over 40ßC in near future when the background factors and the foehn-like wind be combined there.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 68, No. 8, pp. 371-389, 2021
The tendency to form a sea of clouds (SOC) with surface meteorological conditions was observed for three-year warm periods at the foot of Mt. Yatsugatake by time-lapse camera and meteorological instruments at the Fujimi Panorama ski resort, Nagano Prefecture. In situ observation revealed large- and small-scale SOCs in the valley. Large-scale SOCs were commonly observed in the early morning, while small-scale SOCs in the eastern valley corresponded with low-level orographic clouds ascending over the slopes of Yatsugatake. An empirical algorithm was developed to detect the occurrence of nocturnal low-level clouds, corresponding to large-scale morning SOCs, using Himawari-8 images on an hourly basis with references to in situ camera observation. SOCs frequently occurred in the large-scale valley or basin in the inland areas of the Japanese Alps region, referred to as 12 target areas, and they were infrequent in the coastal areas or at high elevations over 2000m. When we defined days of wide-ranging SOC occurrence, in which SOCs occurred in half or more of the target areas, 67% were associated with a subsidence inversion layer by a synoptic-scale high pressure system. The low-level cloud-top height determined by two camera images at different altitudes almost corresponded with the height of the inversion layer observed by radio-sounding data at the Wajima station. We concluded that the synoptic-scale subsidence inversion layer plays an important role in forming large-scale SOCs in the Japanese Alps region in addition to nocturnal radiative cooling conditions.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 68, No. 11, pp. 575-590, 2021
Features of meso-b/g-scale circulation and precipitation systems in the meso-a-scale Baiu-frontal (BF) depression associated with Kyushu heavy rains in 23-24 July 1982 are studied mainly using observation data. The depression stayed over the Tsushima Strait in 23-24 July. Successive development of meso-scale convective systems sustained the cloud cluster in the warm-sector of the depression. During 23-24 July, several meso-scale circulation systems developed in the cloud cluster. Among them, a meso-b-scale depression, which formed around 06 UTC 23 to the east of the BF depression center, preceded the heavy rainfall event.
Meso-b/g-scale precipitation systems developed successively in the depression. These precipitation systems are associated with wind shear lines. Satellite IR cloud images show the successive development of convective clouds over the sea to the west of Kyusyu. The marge of the new clouds with the preexisting cloud areas sustains the cloud cluster in the warm sector of the depression.
The features of this heavy rainfall event are compared with these in previous reports. In many cases, successive development of meso-scale precipitation systems in the depressions caused heavy rainfalls. However, features of meso-scale precipitation systems in depressions varied significantly in cases.