Namiko Sakurai

National Research Institute for Earth Science and Disaster Resilience

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Manabu D. Yamanaka

Jumonji University

Shuichi Mori

Japan Agency for Marine-Earth Science and Technology

Shingo Shimizu

National Research Institute for Earth Science and Disaster Resilience

Takeshi Maesaka

National Research Institute for Earth Science and Disaster Resilience

Koyuru Iwanami

National Research Institute for Earth Science and Disaster Resilience

Shinichi Suzuki

Fukushima Medical University

Yukari Shusse

National Research Institute for Earth Science and Disaster Resilience

Tien Sribimawati

Information and Communication Technology Agency

Fumie Murata

Kōchi University

Hiroyuki Hashiguchi

Kyoto University

Cooperative Institutions

National Research Institute for Earth Science and Disaster Resilience

Meteorological Research Institute

Japan Meteorological Agency

Japan Agency for Marine-Earth Science and Technology

Nagoya University

The University of Tokyo

Hokkaido University

Kyoto University

Information and Communication Technology Agency

Tohoku University

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Internal Structures of Migratory Cloud Systems with Diurnal Cycle over Sumatera Island during CPEA-I Campaign

Journal of the Meteorological Society of Japan Ser II (2009)

Namiko Sakurai Masayuki Kawashima Yasushi Fujiyoshi Hiroyuki Hashiguchi Toyoshi Shimomai

There is a diurnal cycle of systematic cloud migration over Sumatera Island, i.e., cloud systems developing in the mountainous area in the afternoon migrate westward and/or eastward for several hundreds of kilometers (about 500 km) from night to morning. The regional characteristics and internal structure of migratory cloud systems with a diurnal cycle over Sumatera Island during CPEA-I were examined using data from an X-band Doppler radar (XDR), a VHF wind pro?ler (Equatorial Atmosphere Radar (EAR)), rawinsondes, and Geostationary Operational Environmental Satellite (GOES9).During CPEA-I, the cloud system had a horizontal scale of several hundred kilometers and migrated both westward and eastward over nearly all of Sumatera Island except for the southernmost part. The cloud system migrated only westward over southernmost Sumatera Island during CPEA-I.From a case study on April 17 and 18, 2004, precipitation systems with horizontal scales of several tens of kilometers were observed in a cloud system by XDR, and they migrated in a direction similar to that of the cloud system at a speed of about 3 m s-1, which roughly corresponded to the wind direction and speed in the lower troposphere. Convective precipitation was observed mainly in the forward region of the precipitation systems, and stratiform precipitation was observed in the rearward region. The convective precipitation successively generated new convective cells in front of old convective cells. These results suggest that the migratory mechanism of the precipitation systems is self-replication of convective cells and the advection of background wind in the lower troposphere.

Diurnal cycle

10.2151/jmsj.87.157

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Citations (22)

Positive Cloud-to-Ground Lightning Characteristics in the Eyewall of Typhoon Faxai (2019) Observed by Tokyo Lightning Mapping Array

Journal of the Meteorological Society of Japan Ser II (2022)

Namiko Sakurai Hironori Fudeyasu P. R. Krehbiel Ronald J. Thomas W. Rison

Although a number of studies have been conducted of the lightning activity in hurricanes and typhoons, little information has been obtained on the 3-dimensional structure of the lightning, or how it is related to the precipitation structures within the storms. Here we utilize observational data from the 3-D Tokyo Lightning Mapping Array (Tokyo LMA), a Japan Meteorological Agency C-band Doppler radar, and the Japanese Lightning Detection Network (JLDN) to conduct a study of the lightning activity during Typhoon Faxai (2019) in comparison with the storm's precipitation structure. This is done for the dissipating stage of the typhoon, when the eyewall was well within the range of the instruments and undergoing a surge in lightning activity. Of particular interest in the surge was the occurrence of numerous positive cloud-to-ground (+CG) lightning flashes. Detailed study of the Tokyo LMA and JLDN data show that, out of 52 flashes during the surge, 29 flashes or 56 % produced positive strokes to ground, an unheard-of number considering that, from the lightning and 3-D radar structures, the storm appeared to be normally-electrified, and under such circumstances would produce negative rather than positive strokes to ground. It also focuses attention on the question of how +CGs are produced in tropical cyclones in the first place. Based on a lack of −CG strokes and the LMA observations showing that the +CG strokes are produced mid-way or toward the end of normal-polarity intracloud (IC) flashes, it appears that the dissipating storm cells have a depleted or horizontally-sheared mid-level negative charge, such that an IC flash propagating into and through upper positive storm charge effectively funnels a steadily increasing amount of positive charge into the mid-level initiation region, eventually causing the positive breakdown of the IC flash to turn downward toward ground, producing a +CG stroke.

Typhoon

Lightning

Upper-atmospheric lightning

Storm Surge

Eye

10.2151/jmsj.2022-051

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Citations (3)

Case Study of Misoscale Convective Echo Behavior Associated with Cumulonimbus Development Observed by Ka-band Doppler Radar in the Kanto Region, Japan

SOLA (2012)

Namiko Sakurai Koyuru Iwanami Takeshi Maesaka Shinichi Suzuki Shingo Shimizu

Simultaneous observations of cumulonimbi by a Ka-band Doppler radar (KaDR) and an X-band polarimetric Doppler radar (MP-X) were performed during the summer of 2011 in the Kanto region, Japan to study the process of cumulonimbus initiation and development. A cumulonimbus developed up to 12 km above sea level (ASL) in the mountainous western part of the Kanto region on the morning of 18 August 2011, and its initiation and development were observed by the two radars. A misoscale convective echo which was newly detected in an RHI or PPI scan and developed vertically (RHI scan) or spatially (PPI scan) was labeled as a 'new misoscale convective echo' (NMCE). In the developing stage (DS), NMCEs occurred one after another, and the echo top height and maximum reflectivity of each individual echo gradually increased. In the first half of the DS, the NMCEs appeared between 2 and 5 km ASL. In contrast, in the second half of the DS, the NMCEs' appearance height stepped up to between 5 and 12 km ASL. These results suggest that the ascent of NMCE appearance height is one of the key factors in the prediction of deep convection, which later causes localized heavy rainfall.

Echo (communications protocol)

10.2151/sola.2012-027

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Citations (42)

Diurnal Land–Sea Rainfall Peak Migration over Sumatera Island, Indonesian Maritime Continent, Observed by TRMM Satellite and Intensive Rawinsonde Soundings

Monthly Weather Review (2004)

Shuichi Mori Jun-ichi Hamada Yudi Iman Tauhid Manabu D. Yamanaka Noriko Okamoto

The diurnal cycle of rainfall and its regional variation over Sumatera Island, Indonesian Maritime Continent, are examined using Tropical Rainfall Measuring Mission (TRMM) satellite precipitation radar (PR) and intensive rawinsonde sounding data. The TRMM PR sensor can detect raindrops directly, regardless of ground and cloud conditions, and can distinguish between convective and stratiform types of rainfall. Rainfall variation over this area was found to have the following characteristics: 1) convective rainfall with a broad peak between 1500 and 2000 LT predominates over the land region of Sumatera Island, whereas rainfall in the early morning, composed almost equally of stratiform and convective types, is predominant over the surrounding sea region. 2) A rainfall peak in the daytime and one in the nighttime migrate with time starting from the southwestern coastline of the island into the inland and offshore regions, respectively. The distance of each rainfall peak migration from the coastline is up to 400 km, and the average speed of migration is approximately 10 m s−1. 3) Using intensive rawinsonde sounding data, it was also found that remarkable diurnal variations of wind, humidity, and stability appear in the lower troposphere corresponding to the migrating rainfall peaks over both the inland and the coastal sea regions. The mechanism of the diurnal land–sea rainfall peak migration is discussed comprehensively using TRMM PR, intensive rawinsonde soundings, Geostationary Meteorological Satellite (GMS) data, objective reanalysis, and ground-based observation data. Finally, a crucial difference in rainfall peak migrating mechanisms is suggested between those toward the inland region in the daytime and the offshore region in the nighttime.

10.1175/1520-0493(2004)132<2021:dlrpmo>2.0.co;2

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Citations (354)

Diurnal Land-Sea Rainfall Peak Migration over Sumatra Island, Indonesian Maritime Continent Observed by TRMM Satellite and Intensive Rawinsonde Soundings

EAEJA (2003)

Shuichi Mori Jun-ichi Hamada Yudi Iman Tauhid Manabu D. Yamanaka Nobuhiko Okamoto

Source

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Citations (21)

Assimilation impact of high‐temporal‐resolution volume scans on quantitative precipitation forecasts in a severe storm: Evidence from nudging data assimilation experiments with a thermodynamic retrieval method

Quarterly Journal of the Royal Meteorological Society (2019)

Shingo Shimizu Koyuru Iwanami Ryohei Kato Namiko Sakurai Takeshi Maesaka

Abstract The assimilation impact of high‐temporal volume scan data (1 min) on very‐short‐range (within 1 h) quantitative precipitation forecasts (QPFs) of a severe storm was investigated using a nudging data assimilation method. This study investigated (a) the assimilation impact of two observational parameters (potential temperature, retrieved using a traditional technique and pseudo‐water vapour, obtained from reflectivity observations), (b) the sensitivity to the temporal resolution of three‐dimensional radar observations, and (c) the assimilation method (re‐initialization at a single time or sequential nudging over 20 min), regarding the predictability of a tornadic storm observed on 2 September 2013 around Koshigaya City, Japan. Our results indicate that (a) data assimilation of both pseudo‐water vapour and potential temperature perturbation demonstrated the highest contribution for up to the first 30 min of the evaluation period (50 min in total), (b) finer temporal resolution provided a better forecast overall, and (c) a nudging scheme provided a better forecast in the first 30 min. Our results showed better predictability than traditional extrapolation‐based nowcasts in the latter 40 min of the evaluation period. The data assimilation with water vapour and potential temperature, determined from a 1 min volume scan, therefore has the potential to extend the cloud‐scale predictability in strong rainfall intensity situations (>20 mm/h) of very‐short‐range QPFs (within 30 min).

Predictability

Initialization

Quantitative precipitation forecast

10.1002/qj.3548

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Citations (6)

Three-dimensional microphysical structure of the lower positive charge region in a thunderstorm: A case study for a supercell observed using dual-polarization radars

Atmospheric Research (2025)

Akihito Umehara Satoru Yoshida Syugo Hayashi Shingo Shimizu Namiko Sakurai

Supercell

Weather radar

10.1016/j.atmosres.2025.108006

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Citations (0)

Relationship between Precipitation Core Behavior in Cumulonimbus Clouds and Surface Rainfall Intensity on 18 August 2011 in the Kanto Region, Japan

Journal of the Meteorological Society of Japan Ser II (2015)

Yukari Shusse Masayuki Maki Shingo Shimizu Koyuru Iwanami Takeshi Maesaka

This paper analyzes the behavior of the precipitation cores (PCOs) in three cumulonimbus clouds that caused localized heavy rainfall on 18 August 2011 in the Kanto region, Japan, and their relationship with temporal variations in surface rainfall intensity. The 3D structure of the cumulonimbus clouds was observed at 2-min intervals using a research X-band dual-polarization radar. A PCO was defined as a 3D contiguous region that contained one local maximum of horizontal radar reflectivity Zh, and the PCOs were automatically detected using adaptive thresholds. Subjective tracking procedures using the PCO dataset, which was based on observations made every 2 min, identified 15 PCOs during the total lifespan of the three cumulonimbus clouds. The PCOs generally descended toward the ground after their appearance aloft. The average appearance height of the PCOs of 5.25 km above sea level (ASL) was slightly above the ambient 0°C level (5.1 km ASL). The duration of each PCO was roughly proportional to its appearance height. Of the 12 temporal peaks at maximum surface rainfall intensity (> 10 mm h-1) recorded from the three cumulonimbus clouds, 10 were associated with the descent of PCOs. In each cumulonimbus cloud, the first PCO was detected 10-12 min before rainfall heavier than 10 mm h-1 was recorded. These results indicate that the behavior of PCOs is closely related to the onset of strong surface rainfall and subsequent fluctuations in surface rainfall intensity.

Intensity

Precipitation types

10.2151/jmsj.2015-012

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Citations (10)

Clear-Air Echoes Observed by Ka-band Polarimetric Cloud Radar: A Case Study on Insect Echoes in the Tokyo Metropolitan Area, Japan

Journal of the Meteorological Society of Japan Ser II (2020)

Tadayasu Ohigashi Takeshi Maesaka Shinichi Suzuki Yukari Shusse Namiko Sakurai

In this study, the polarimetric variables of clear-air echoes (CAEs), that appeared on May 21, 2016 in the Tokyo metropolitan area, Japan, were investigated using the Ka-band (8.6-mm-wavelength) polarimetric cloud radar capable of detecting non-precipitating clouds. The objective was to establish the potential for distinguishing CAEs and hydrometeor echoes in the initial stage of cloud formation using a Ka-band polarimetric cloud radar. On the day being studied, CAEs showed evident diurnal variation. There were no CAEs before sunrise. The equivalent radar reflectivity (Ze) increased with time after sunrise, and horizontally widespread echoes (max. value > −15 dBZ) occurred within the radar observation range in the early afternoon. After sunset and into the early part of the night, Ze decreased rapidly. Range-height indicator observations showed that CAEs were restricted to heights of < 1.5 km. The differential reflectivity (ZDR) values of the CAEs were largely positive (1.8 dB) with a large standard deviation at 18:00 local time, i.e., considerably larger than those of cloud/weak precipitation echoes (0.4 dB) observed simultaneously. In comparison with cloud/precipitation echoes, the copolar correlation coefficient (ρhv) of the CAEs was smaller (< 0.9), whereas the variability of the total differential phase (ΨDP) in the range direction was larger. The upper limit of Ze and the distributions of ZDR and ρhv were inconsistent with the characteristics of the Bragg scattering observed by the S-band (10-cm-wavelength) radar in previous studies. However, the larger ZDR, smaller ρhv, and larger variability of ΨDP in the range direction, associated with the horizontally widespread echoes, were consistent with the characteristics of insect echoes. The depolarization ratio defined using ZDR and ρhv could be effective in distinguishing this type of CAE and hydrometeor echoes observed by Ka-band polarimetric cloud radar. The polarimetric variables obtained by Ka-band polarimetric cloud radar are useful in distinguishing between CAEs and hydrometeor echoes.

Ka band

10.2151/jmsj.2021-006

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Citations (2)

Case Study of an Intense Wind Event Associated with a Mesoscale Convective System in West Sumatera during the HARIMAU2006 Campaign

Journal of the Meteorological Society of Japan Ser II (2011)

Masayuki Kawashima Yasushi Fujiyoshi Masayuki Ohi Shuichi Mori Namiko Sakurai

In this study, the processes responsible for an intense wind event that occurred in west Sumatera on November 19, 2006, during the first campaign of the Hydrometeorological ARay for Isv-Monsoon AUtomonitoring (HARIMAU) were investigated.Strong winds of 17 m s-1 and a sudden temperature drop of 5 K were observed at an X-band Doppler radar site associated with the passage of a convective system, and some houses were severely damaged. The convective system developed under an environment of strong low-level easterly vertical shear associated with the easterly region of an equatorial Rossby wave. The northern part of the convective system possessed qualitatively similar structures to midlatitude bow echoes, including the convex shape of the convective line, a descending rear-inflow jet positioned at its apex, and mesoscale vortices on both sides of the rear-inflow jet. The low-level wind behind the convective system formed a channel of strong easterly wind as it passed through an area of relatively low topography in the mountain range. The enhanced easterly wind was thought to contribute to the formation of the bow echo-like structure in the northern part of the convective system. This easterly rear-inflow jet was further accelerated in the convective system and descended near the leading edge, forming divergent strong winds at the surface.The sounding data that were taken after the passage of the convective system indicated that dry air appeared in the lower troposphere associated with an enhancement of the southerly component of the wind. An analysis of objective reanalysis data suggests that the southerly was probably associated with westward-propagating mixed Rossby-gravity waves with a period of approximately 5 days. It is suggested that the dry air intruded into the convective system across the back edge of the precipitation area and caused enhanced evaporative cooling, which resulted in the effective downward transport of the enhanced easterly momentum.

Mesoscale convective system

Squall line

Inflow

African easterly jet

Outflow

10.2151/jmsj.2011-a15

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Citations (12)