(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 71, No. 1, pp. 5-9, 2024
Variations of the cloud-amount and latitude of Baiu frontal cloud zone (BFCZ) in July 1982 is studied using satellite observed cloud data CH (cloud-cover of the cloud higher than 400hPa). "LAT-BFCZ (t, λ): latitude of BFCZ" is obtained as the latitude of the maximum CH zone, and "CH-BFCZ (t, λ): cloud-amount in the BFCZ" is obtained from CH (t, φ, λ). Variation of the CH-BFCZ and LAT-BFCZ are studied by the time-spectral analysis. Variation of CH-BFCZ at period of ~7-day and ~4-day, is large in 140-170°E, and 125-150°E, respectively. Variation of LAT-BFCZ at period of ~4-day, ~2.5-day is large over 130-170°E and 130-165°E respectively. Longitudinal wave-length of CH-BFCZ is estimated by longitude-spectral analysis at each observation time. Short wave (wave length of 10-30°) were significant in 7, 10, 12, 18, 23 and 27 July.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 71, No. 2, pp. 57-68, 2024
Scenarios, a tool for analyzing uncertain futures, play a central role in assessing long-term climate change issues. Interdisciplinary scenario studies have been conducted to evaluate future climate change, possible impacts and adaptation, and mitigation, and these strands of research have been the core of assessment reports of the Intergovernmental Panel on Climate Change (IPCC). Recently, interest in scenarios has been growing also among stakeholders such as companies and local governments. Here, we review the framework of the Representative Concentration Pathways (RCPs) and Shared Socioeconomic Pathways (SSPs), which have been the main focus of the IPCC reports, and summarize the current status and future issues. In Japan, there are issues to be addressed, such as making models open-source, collaboration with stakeholders, human resource development, and inter-agency funding.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 71, No. 4, pp. 143-152, 2024
Mt. Fuji radar observed mesoscale precipitation systems aligned at intervals of ~150km, along the Baiu front at 23 UTC Jun 25, 1970. Observational data showed that these precipitation systems located along the northside of the moist stream associated with low-level jet-stream. The mesoscale variations of precipitation and wind, related with the mesoscale precipitation shown by the radar observation, are found at Oshima Island station. Baiu frontal precipitation zone and low-level jet stream are clearly shown by reanalysis data and mesoscale numerical model. However, neither reanalysis data nor mesoscale numerical model express features of the mesoscale precipitation systems observed by the radar observation.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 71, No. 5, pp. 191-195, 2024
The relationship between mean summer temperature and infant/neonatal mortality in Japan was statistically investigated using the Vital Statistics data from 1951 to 2020. Contrary to the general feature for adults, mortality rates of newborns from 1 to 4 weeks old were found to be negatively correlated with summer temperatures since the 2000s. This negative correlation was found for both boys and girls, and in July and August, and was mainly observed in regions in central Honshu. No correlation with summer temperature was observed for mortality rates of infants from 4 weeks to 1 year old, nor newborns less than 1 week old.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 71, No. 6, pp. 229-237, 2024
This is a lecture the author delivered upon receiving the 2023 Fujiwhara Award. The Meiyu-Baiu rain band of June-July accounts for much of the annual rainfall in a large swath of densely populated East Asia from the eastern foothills of the Tibetan Plateau through Japan. Distinct from the tropical monsoon of India, the Meiyu-Baiu rain band is anchored by the westerly Asian Jet, which advects warm air from the Tibetan Plateau and induces upward motions. The termination of the Meiyu-Baiu rainy season in late July coincides with the onset of deep convection to the south over the tropical Northwest Pacific. The seesaw relationship between the Meiyu-Baiu and Northwest Pacific convection is also found in interannual variability, associated with a large-scale anomalous anticyclonic circulation (AAC) astride the Indo-Northwest Pacific oceans that recurs in post-El Nino summers. The coupling with the ocean allows the AAC to outlast El Nino while the background confluence between the monsoon westerlies and easterly trades makes the AAC an intrinsic mode of monsoon variability across a wide range of timescales. The great strides made over the recent decades in understanding coupled atmosphere-ocean dynamics have culminated in skillful prediction of monsoon variability a season in advance, sometimes without El Nino as a predictor. This calls for further efforts are needed to fill the gaps between excessive theoretical idealizations on one hand and uncritical interpretation of nonstationary statistics of short observational records on the other.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 71, No. 7, pp. 281-295, 2024
In this paper, an estimation method of time variation of refractive index (RI), which is a function of temperature and humidity etc., from radio wave phase is explained. It is shown that the time variation of RI can be obtained for more than one month by this method using the airport meteorological Doppler radar at Tokyo International Airport, around which a lot of phase data is available.
It is found that the spatial smoothing of time variation of radio wave phases is needed during estimation. Comparisons with the surface observations obtained from the Tokyo Skytree, the broadcasting tower with observation decks at the heights of 150m and 325m, and from the Tokyo District Meteorological Observatory, indicate that the altitude at which the radar RI is obtained is lower than 150m, and that the radar RI expresses the slow variation with timescale of a few hours. As for the relation between the time variation of RI and meteorological phenomena, the radar RI increases rapidly in response to the onset of rainfall. The spatial distribution of radar RI shows that the range of RI affected by the rainfall was within 10-20km from the rainfall area in the case events shown in this paper.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 71, No. 8, pp. 317-329, 2024
A numerical analysis of the mesoscale environment of heavy rainfall event around the upper Chikuma-gawa river basin caused by Typhoon Hagibis (2019) was carried out using the mesoscale meteorological model MM5. The heavy rainfall was enhanced by a mesoscale front that formed at just east of the Kanto Mountains when the mountain area was placed in the northeast part of Hagibis. A sensitivity experiment without the evaporative cooling of precipitation particles indicated that the evaporative cooling effects by precipitation particles falling from the upper layers contributed to the development of the low-level mesoscale front. A backward trajectory analysis on the near-surface cold air masses that formed the mesoscale front revealed that the significant heavy rainfall in the upper Chikuma-gawa river basin was intensified by the following mechanisms: 1) dry air masses flowed into the vicinity of Maebashi in the Kanto Plain due to the Foehn over-mountain winds from the east-northeast, 2) evaporative cooling of falling precipitation particles from the upper-level convective clouds occurred at the northeast of Hagibis, 3) the increase in horizontal temperature gradient enhanced the mesoscale front, and 4) upward motion and precipitation activity were enhanced on the low-level mesoscale front.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 71, No. 10, pp. 437-446, 2024
Observational case study is made on a rain-zone which elongated from NW to SE formed over western Japan on 1 July 1971. The rain-zone formed under the influence of a ridge over western Japan and the northwesterly in the middle troposphere. In the lower troposphere, a weak depression which formed over China moved over western Japan Sea under the ridge on July 1. The moist southwesterly flowed into the southeastern side of the depression, and the rain zone was formed. Simultaneously, strong wind shear between the low-level southerly and middle-level northerly, strong upward velocity, and moist neutral zone formed over the rain-zone. The rain-zone weakened 20 hours after its formation. The features of this rain-zone are significantly different from features of intense rain systems in the Baiu frontal zone associated with the large-scale southwesterly flows.