The interannual variation in the number of heavy rainfall events in Japan in 1976-2022, extracted from 3-hour accumulated precipitation (P3H) data exceeding 130 mm, showed a relatively large ...relationship (correlation coefficient 0.45) with sea surface temperature (SST) around the Japanese Islands. In the Kyushu area during the rainy season (June–July), the correlation coefficient with SST became considerably smaller, while a relatively large relationship (correlation coefficient 0.45) was found with the appearance frequency of 500m-height water vapor flux above 250 g m−2 s−1, suggesting that the interannual variation could be considerably influenced by the synoptic scale pressure pattern. Diurnal variations in the number of heavy rainfall events, including long-term increasing trends, were also investigated. Although less significant diurnal variations were observed on the annual basis, the events in the Kyushu area were more frequent in the morning (7-9 JST: JST = UTC + 9 hours) during the rainy season. In the Kyushu area, the 47-year long-term trend of heavy rainfall events in 4-9 JST was a 7.47-fold increase in June and July, while it was only a 1.35-fold increase in the other months.
This study investigated the representative height of low-level water vapor field that can be used to examine the occurrence possibility of heavy rainfall in East Asia. First, cloud base heights ...(CBHs) of moist convection were statistically examined by performing simulations with a 1-km-resolution numerical model during April–August 2008, with a focus on Kyushu and Shikoku Islands, western Japan. CBHs of moist convection with strong updrafts were simulated mainly around 500 and 300 m heights above sea level over land and over the ocean, respectively. This result indicates that low-level humid air below a height of 500 m is very important for the initiation of strong moist convection. Moreover, the equivalent potential temperature θe at the CBHs was examined to clarify θe values of lifted air parcels initiating cumulonimbus development. This result showed that, below the CBHs, θe was usually around 355 K. Given these results for the CBHs, θe at 500 m height from 10-km-resolution objective analysis data was statistically compared with θe at various heights and pressure levels over the ocean south of 35°N in East Asia during June–September 2008. These comparisons showed that analyses at the 850-hPa level could not represent the low-level water vapor field, while the θe field at 850 hPa in the Baiu season was strongly influenced by convective activity over the Baiu frontal zone. The θe field at 925 hPa also could not adequately represent the low-level water vapor field, but the difference in θe between heights of 250 and 500 m was very small. Because high θe layers must have some thickness, data at 500 m height can be considered representative of the low-level water vapor field in analyses examining the initiation of moist convection leading to heavy rainfall.
We report the case of a 62-year-old male patient with nasal septum cancer invading the anterior skull with formation of a brain abscess and brain edema, who was transported to our hospital for ...disturbance of consciousness and convulsions. Computed tomography and magnetic resonance imaging showed nasal septum cancer invading the anterior skull, with formation of a brain abscess in the frontal lobe, and cerebral edema. Biopsy of the nasal septum tumor led to the diagnosis of non-keratinized squamous cell carcinoma. A neurosurgeon performed resection of the tumor invading the anterior skull base and frontal lobe via a craniotomy, with the cooperation of an otorhinolaryngologist who provided intranasal endoscopic guidance. The anterior skull base was closed using a fascia lata and a pericranial flap. Postoperative radiotherapy was undertaken, and the patient showed a good clinical course, without recurrence.
Recurrent infection of a frontal mucocele can lead to frontal osteomyelitis and subperiosteal abscess formation in the orbit, resulting in orbital complications. We report a case of frontal mucocele ...complicated by formation of a subcutaneous abscess in the upper eyelid that ruptured through the overlying skin. A 51-year-old man visited us complaining of right upper eyelid swelling and tenderness. On examination, we found a subcutaneous abscess of the upper eyelid that had ruptured through the overlying skin. Computed tomography (CT) and magnetic resonance imaging (MRI) revealed a right frontal mucocele and inflammation of the supraorbital margin. Therefore, we made the final diagnosis of frontal mucocele complicated by formation of a right upper eyelid abscess rupturing through the overlying skin. Endoscopic sinus surgery was performed to open the maxillary sinus and frontal mucocele into the nasal cavity. Then, we performed craniotomy, resected the frontal mucocele, and cranialized the frontal sinus by inserting a frontal musculoskeletal flap into the floor of the frontal sinus. The anterior skull base was covered with a pedicled septal mucosal flap. The upper wall of the right orbit was reconstructed by a bone graft taken from the skull. The postoperative course of the patient was satisfactory. At present, 6 months since the surgery, the patient can open his right eye normally. Upper eyelid lesions complicating a frontal mucocele should be managed by collaboration between the departments of otolaryngology and other relevant departments.
Past 45 years’ long-term trend of the occurrence frequency of heavy rainfall events (HREs) in Japan was examined. The HREs were extracted using a threshold value of 130 mm for three-hourly ...accumulated precipitation amounts observed at 1178 AMeDAS stations between 1976 and 2020; AMeDAS is the Automated Meteorological Data Acquisition System operated by the Japan Meteorological Agency. We also compared the results with the trend of the occurrence frequency for hourly accumulated precipitation amounts (P1H) of 68 mm or more, which was determined to correspond to the number of the extracted HREs. Annual change of the occurrence frequency for the HREs and P1H≥68 mm showed a long-term increasing trend at a significant level of 1%, and the increase rate was higher by about 10% for the HREs than for P1H≥68 mm. For monthly changes, a long-term increasing trend for the HREs was remarkable during the rainy season (June and July) in Japan, especially the long-term increase rate during 45 years in July reached about 3.8 times at a significant level of 5%; it was about 2.8 times for P1H≥68 mm. In August no significant increasing trend was found for the HREs, but the frequency of P1H≥68 mm increased. Conversely no increasing trend was found for P1H≥68 mm in September, but the HREs became more frequent.
This study investigated characteristics of atmospheric environmental fields in the occurrence of quasi-stationary convective bands (QSCBs) in Kyushu, western Japan during the July 2020 heavy rainfall ...event. We performed case studies of extreme rainfall subevents in the Kumamoto and Kagoshima prefectures on 3-4 July (2020KK) and northern Kyushu on 6-7 July 2020 (2020NK), compared with two heavy rainfall events in northern Kyushu in 2017 and 2018.Nine QSCBs were objectively extracted during the July 2020 heavy rainfall event, causing hourly precipitation amounts exceeding 100 mm twenty times. In 2020KK, the environmental field with extremely large precipitable water due to low-level and middle-level humidity was affected by the upper-level cold airflow, which resulted in favorable condition for the deep convection development. Consequently, the lightning activity became high, and cloud tops were the highest in comparison to previous events. QSCBs in 2020KK and 2020NK were located along a low-level convergence line/zone associated with an inflow that had extremely large water vapor flux on the south side of the mesoscale Baiu frontal depressions. In most of the QSCB cases in 2020, mesoscale depressions were observed and enhanced horizontal winds, which led to extremely large low-level water vapor flux to produce short-term heavy rainfall.
An extreme rainfall event brought precipitation amounts exceeding 1000 mm in Kyushu district, southwestern Japan, in early July 2020. Especially, an elongated and stagnated mesoscale convective ...system formed around the Kuma River in central Kyushu district produced localized heavy rainfall with precipitation amounts larger than 600 mm in 13 hours. Characteristics of this extreme rainfall event were investigated using distributions of radar/raingauge-analyzed precipitation amounts (RAP) and statistically compared with those during the warm seasons (April–November) in 2009-2019. The results are shown as follows; (1) nine heavy rainfall areas of linear-stationary type (LS-HRAs) were extracted, (2) spatial and temporal scales of two LS-HRAs among them respectively exceeded 270 km and 10 hours, (3) the maximum RAP exceeding 100 mm in LS-HRAs were comparable to those in previous extreme rainfall events, (4) large accumulated three-hour precipitation amounts exceeding 200 mm were more frequently observed than those in the previous events, and (5) the accumulated five-day precipitation amount integrated around Kyushu Island was the largest since 2009. This study also showed that the large area-integrated precipitation amount was produced mainly from widespread precipitation systems associated with the Baiu front, while the nine LS-HRAs significantly contributed localized heavy rainfall.
In Japan, localized heavy rainfall events producing accumulated three-hour precipitation amounts larger than 200 mm are often observed to cause severe landslides and floods. Such events are mainly ...brought by quasistationary band-shaped precipitation systems, named “senjo-kousuitai” in Japanese. Senjo-kousuitai is defined as a band-shaped heavy rainfall area with a length of 50–300 km and a width of 20 - 50 km, produced by successively formed and developed convective cells, lining up to organize multi-cell clusters, and passing or stagnating at almost the same place for a few hours. The formation processes of senjo-kousuitai are categorized mainly into two types; the broken line type in which convective cells simultaneously form on a quasi-stationary local front by the inflow of warm and humid air, and the back building type in which new convective cells successively forming on the upstream side of low-level winds linearly organize with pre-existing cells.In this study, previous studies of band-shaped precipitation systems are reviewed, and the numerical reproducibility of senjo-kousuitai events and the favorable conditions for their occurrence are examined. In a case of Hiroshima heavy rainfall observed in western Japan on 20 August 2014, the reproduction of the senjo-kousuitai requires a horizontal resolution of at least 2 km, which is sufficient to roughly resolve the formation and development processes of convective cells, while a resolution of 250–500 m is necessary to accurately reproduce their inner core structures. The 2-km model quantitatively reproduced the Hiroshima case when initial conditions 10 hours before the event were used, but the predicted amounts of maximum accumulated precipitation were considerably reduced as the initial time became closer to the occurrence time of the senjo-kousuitai. This reduction was brought from the excessive inflow of low-level dry air that shifted occurrence areas of new multi-cell clusters.Six favorable occurrence conditions of senjo-kousuitai events for their diagnostic forecasts were statistically constructed from environmental atmospheric fields in previous localized heavy rainfall events. Two conditions of (1) large water vapor flux amounts (> 150 g m−2 s−1) and (2) short distances to the level of free convection (< 1000 m) were chosen representatively for the low-level water vapor field that is judged based on 500-m height data. Four other favorable conditions are selected; (3) high relative humidity at midlevels (> 60 % at 500 hPa and 700 hPa), (4) large vertical shear estimated from the storm relative environmental helicity (> 100 m2 s−2), (5) synoptic-scale ascending areas (400 km mean field at 700 hPa), and (6) the exclusion of warm air advection frequently appearing at 700–850 hPa and inhibiting the development of convection (i.e., an equilibrium level > 3000 m).
A global navigation satellite system (GNSS) buoy system for early tsunami warnings has been developed for more than 20 years. The first GNSS buoy system using a real-time kinematic algorithm (RTK) ...was implemented in the Nationwide Ocean Wave information network for Ports and HArbourS (NOWPHAS) wave monitoring system in Japan in 2008. The records of NOWPHAS were used to update the tsunami alert by the Japan Meteorological Agency (JMA), owing to the tsunami generated by the 2011 Tohoku-oki earthquake (Mw9.0). However, considering that the distance limit is less than 20 km for the RTK algorithm, a new system was designed by introducing a new positioning algorithm and satellite data transmission to place the buoy much farther from the coast. A new technique for the continuous monitoring of ocean-bottom crustal movements was also implemented in the new system. The new buoy system can be used for weather forecasting and ionospheric monitoring as well.
We propose a new application method in which radar/raingauge-analyzed precipitation amounts (RAP) produced by the Japan Meteorological Agency are spatially converted into 5km-resolution data, in ...addition to a three-hourly accumulation procedure, in order to statistically analyze localized heavy rainfall areas (HRAs) for a long period. A long-term trend and homogeneity in the appearance frequency of RAP with 5km-resolution converted by several methods, including the conventional method, are statistically evaluated in comparison with rain-gauge observations. The results indicate that the following application method is the most suitable to represent long-term variations in the appearance frequency of HRAs; (1) the converted value of RAP from 1 km to 5 km resolution is set to the 90th percentile value in 30 segments with 1km-resolution included in a grid with 5km-resolution, and (2) this spatial conversion is conducted after accumulating original RAP with 1km-resolution for three hours. Statistical analyses were performed for the appearance frequency of HRAs extracted from 5km-resolution RAP that were produced by the new application method, which indicates that the number of HRAs of the linear-stationary type could be increased without compromising the characteristics of HRAs extracted by the conventional method.
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