Papers by Tadayasu Ohigashi
Atmospheric Research, May 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
On 28 July 2016, an isolated convective storm produced two downbursts within about 10 km north fr... more On 28 July 2016, an isolated convective storm produced two downbursts within about 10 km north from a Doppler lidar at NICT’s Okinawa Electromagnetic Technology Center in Okinawa, Japan. Concentric circular patterns of the Doppler velocity, spectral width, and carrier-to-noise ratio were detected near the sea surface in the 0°-elevation sector plane position indicator scans of the Doppler lidar. An X-band phased array weather radar (PAWR) detected the first echo approximately 13 min prior to the near-surface divergent signature of the downbursts. The PAWR provided 30-sec volumetric data of the storm and observed rapid evolution of reflectivity cores with >65-dBZ radar reflectivity. The cores descended rapidly toward the sea surface. The associated differential reflectivity minimum was observed by an X-band polarimetric radar. In this paper, we show that the synergetic use of different remote sensing instruments is important for better understanding the physical processes of downb...
Observing System Experiment using T-PARCII dropsondes and JMA Global Forecasting System and Development of Sensitivity Analysis Guidance for Tropical Cyclone Intensity
Japan Geoscience Union, 2018
Journal of the Atmospheric Sciences, 2021
Knowledge of the development and maintenance processes of double warm cores in tropical cyclones ... more Knowledge of the development and maintenance processes of double warm cores in tropical cyclones is important for full understanding of the dynamics of storm intensity changes. During its mature stage, Typhoon Lan (2017) had a clear double warm-core structure, which was observed by dropsondes. In this study, to investigate the intensification and maintenance of the double warm-core structure, a numerical simulation of the storm is performed with a cloud-resolving model and verified by dropsonde and satellite observations. A potential temperature budget and backward trajectories are diagnosed to examine intensification and maintenance processes in the simulated eye. The budget analysis indicates that, during the most rapidly intensifying stage, a double warm core is enhanced by axisymmetric subsidence warming in the eye. In the mature stage, upper-core warming is mostly canceled by ventilation due to vertical wind shear, but the lower core continues to warm by asymmetric advection, p...
SOLA, 2022
The influence of an upper-level trough on a Baiu frontal depression (BFD) that caused a heavy rai... more The influence of an upper-level trough on a Baiu frontal depression (BFD) that caused a heavy rainfall event in southern Kyushu, Japan, on July 4, 2020, was examined using numerical simulations with and without the upper-level trough. The numerical simulation with the upper-level trough (CNTL) reproduced a reasonable well-developed BFD and heavy rainfall in southern Kyushu. Conversely, the numerical simulation without the upperlevel trough (NOUT) produced a weaker BFD and notable southward rainfall shift compared with the situation in the CNTL. The weaker BFD for the NOUT was due to weaker convection than that of the CNTL over mainland China. Thus, strong convection over mainland China was essential for the formation and development of the BFD that caused heavy rainfall in southern Kyushu. Additional sensitivity experiments, in which the strength of the upper-level potential vorticity anomalies was reduced to 75, 50, and 25% of the CNTL, showed that the spatial rainfall distribution shifted southward and resulted in a change in precipitation amounts in southern Kyushu because of the weakening of the BFD.
Natural Hazards and Earth System Sciences, Sep 26, 2011
Weather and Forecasting
Meso-γ-scale (2–20 km) local heavy rain (LHR) can cause fatalities through the sudden rise of riv... more Meso-γ-scale (2–20 km) local heavy rain (LHR) can cause fatalities through the sudden rise of rivers and flooding of roads. To help prevent this loss of life, we developed prediction methods for these types of meteorological hazards. We assimilated ground-based cloud radar (Ka-band radar) data that can capture cloud droplets before raindrops form and attempted to predict LHR with a cloud resolving numerical weather prediction (NWP) model. High-temporal (1-min interval) three-dimensional cloud radar data obtained through special observation were assimilated using a water vapor nudging method in the pre-rain stage of an LHR-causing cumulonimbus. While rainfall was not predicted by the NWP model without assimilation, LHR was predicted approximately 20 min after the conclusion of cloud radar data assimilation cycling. Results suggest that NWP with cloud radar data assimilation in the pre-rain stage has great potential for predicting LHR, and can lead to an early evacuation warning and s...
Dataset for mammatus-like radar echoes along the bases of upper-tropospheric outflow-layer clouds of typhoons
PPI and RHI data of radar observations of mammatus-like echoes at the cloud bases of upper-level ... more PPI and RHI data of radar observations of mammatus-like echoes at the cloud bases of upper-level clouds of typhoons observed by the Nagoya-University cloud radar. The observations were carried out at Okinawa, Japan in 2016 and 2019, and Kobe, Japan in 2018 This dataset includes raw data at polar coordinates and grid data interpolated to Cartesian coordinates. This dataset also includes upper-level sounding observation data during the appearance of mammatus-like echoes at Okinawa, Japan in 2016.
Journal of the Meteorological Society of Japan. Ser. II, 2021
In this study, the polarimetric variables of clear-air echoes (CAEs), that appeared on May 21, 20... more 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 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 (Z e ) 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, Z e decreased rapidly. Range-height indicator observations showed that CAEs were restricted to heights of < 1.5 km. The differential reflectivity (Z DR ) 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 ( ρ hv ) of the CAEs was smaller (< 0.9), whereas the variability of the total differential phase (Ψ DP ) in the range direction was larger. The upper limit of Z e and the distributions of Z DR and ρ hv were inconsistent with the characteristics of the Bragg scattering observed by the S-band (10-cm-wavelength) radar in previous studies. However, the larger Z DR , smaller ρ hv , and larger variability of Ψ DP in the range direction, associated with the hor- izontally widespread echoes, were consistent with the characteristics of insect echoes. The depolarization ratio defined using Z DR and ρ hv 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. Keywords clear-air echo; insect echo; Ka-band cloud radar; polarimetric radar
Japan Geoscience Union, 2015
Cloud ice composing cirrus clouds and aerosol have large impacts on climate and weather by an int... more Cloud ice composing cirrus clouds and aerosol have large impacts on climate and weather by an interaction with radiation. They are one of the large uncertainties for the projections of the climate change. Upper layer cirrus clouds surrounding a typhoon strongly control the upper layer temperature around the typhoon. Consequently, their characteristics are related to typhoon intensity. So far, we have been using hydrometeor videozondes (HYVISs) to observe cloud particles in the upper troposphere. The HYVISs can observe cloud particles ranging from 10 micrometer to 1 mm. It shows size, shape and number concentration of cloud particles with high vertical resolution. We conducted field observations using HYVISs for various types of clouds associated with heavy rainfall systems and typhoons in Okinawa, Japan and Palau in the tropics. The observation results show characteristics of cloud particles and are used to improve the cloud processes in a cloud-resolving model. To perform simulatio...
Polarimetric radars are useful instrument to obtain microphysical information of precipitation sy... more Polarimetric radars are useful instrument to obtain microphysical information of precipitation systems and there have been many researches of hydrometeor classification (hereafter, HC) using polarimetric radars. For X-band polarimetric radars (X-pols), there have been a few researches of HC (for example, Dolan and Rutledge, 2009) but few HC methods were validated with in situ observational data. On the other hand, there have been some researches of HC method for Sor C-band polarimetric radars validated with aircraft and/or ground observational data (for example, Liu and Chandrasekar, 2000), targeting heavy solid precipitation: graupel or hail. X-pols are sensitive to weak solid precipitation with low reflectivity (snowflake and ice crystal). In moist environmental area, for example East Asia, non-hail-producing precipitations are dominant and X-pols are suitable to observation in such environmental area. Therefore, development and validation of HC method for X-pols in East Asia are ...
When cold air outbreaks occur from the Eurasian Continent, mesoscale lows frequently formed over ... more When cold air outbreaks occur from the Eurasian Continent, mesoscale lows frequently formed over the Sea of Japan, which are also referred to as “polar lows”. A lot of mesoscale lows are associated with the JPCZ (Japan-Sea Polarairmass Convergence Zone) (Asai, 1988). The JPCZ extends from the lee side of the mountains around the joint of the Korean Peninsula to the central coast of the Japan Islands, and is characterized by strong convergence, horizontal shear and an active convevtive cloud band. Snowfall systems within mesoscale lows bring intense and a large amount of snowfall to the coastal region of the Japan Islands in its landing (e.g. Ninomiya and Hoshino 1990). Strong gusts are also caused by mesoscale lows (e.g. Ninomiya and Hoshino 1990; Yamagishi et al. 1992). But there were not many reports for distributions and structures of snowfall systems in mesoscale lows which bring the severe phenomena. The understanding of the detailed characteristics of snowfall systems is impor...
Japan Geoscience Union, 2018
Tropical cyclones (TCs) have positive anomaly of temperature at the storm center (i.e., eye), whi... more Tropical cyclones (TCs) have positive anomaly of temperature at the storm center (i.e., eye), which is known as warm core. The warm anomaly is related to low pressure at the storm center via the hydrostatic balance, and strong cyclonic circulation in the outside of the storm eye in the lower troposphere via the thermal wind relationship. This means that the warm core can control the storm intensity. Thus, full understanding of time evolution of the warm core can be helpful for more accurate numerical prediction of intensity change of TCs including rapid intensification, which is one of the most challenges in the numerical prediction of the storm intensity. Typhoon Lan (2017) underwent a rapid intensification over the western North Pacific. The minimum central pressure was 915 hPa. The mean 50-kt radius of the typhoon in the intensification and mature stages was 160-220 km. In this study, a numerical simulation of the typhoon is performed to investigate the evolution of the typhoon w...
When cold air outbreaks occur from the Eurasian Continent, convective snow clouds develop over th... more When cold air outbreaks occur from the Eurasian Continent, convective snow clouds develop over the Sea of Japan. When snow clouds reach the Japan Island, they are usually modified or intensified around the coastal region. Takeda et al. (1982) showed from the echo structres by a radar in the Hokuriku District, which is located at the south of the Sea of Japan, that most of isolated convective snow clouds had the two stages of mod-
SOLA, 2019
A field observation was carried out along the coast of the Japan Sea in the 2016-2017 and 2017-20... more A field observation was carried out along the coast of the Japan Sea in the 2016-2017 and 2017-2018 winter seasons, using the Ground-based Particle Image and Mass Measurement System (G-PIMMS) to evaluate the Global Precipitation Measurement Mission (GPM) dual-frequency precipitation radar (DPR) precipitation type classification algorithm. The G-PIMMS was installed at Kanazawa University and Ishikawa Prefectural University, which are around 10 km apart from each other. The G-PIMMS observations showed that the major precipitation particle type (graupel or snowflake) was different in the precipitation types classified by the GPM DPR algorithm.
SOLA, 2016
Supercooled liquid droplets (SLDs) not only play important roles in precipitation formation proce... more Supercooled liquid droplets (SLDs) not only play important roles in precipitation formation processes but they also affect the radiation budget. Therefore, it is important to clarify the distribution and quantity of SLDs. Hydrometeor videosonde observations were performed in February 2011 at Rikubetsu in inland Hokkaido, Japan. Five hydrometeor videosondes were released in ice precipitations in stratiform clouds and SLDs were detected in three cases. The clouds in these three cases had SLDs at the cloud tops. The microphysical quantities of the SLD layers were within the ranges of those observed in Arctic mixed-phase clouds. The cloud-top SLDs had potential to cause radiative cooling, which contributed to the formation of upward motion generating ice precipitation. Small water vapor amounts above the cloud tops cannot contribute to moisture supply. Vertical profiles of temperature and moisture showed that the SLD layers were decoupled from surface moisture sources. The absence of additional moisture supply was consistent with short lifetimes, compared with persistent Arctic mixed-phase clouds.
Journal of Geophysical Research: Atmospheres, 2015
The vertical distribution of precipitation particles in an intensely precipitating stratiform clo... more The vertical distribution of precipitation particles in an intensely precipitating stratiform cloud associated with the Baiu front around Okinawa Island was observed. X‐band polarimetric radar, disdrometer, and hydrometeor videosonde data were used to examine the precipitation processes. The cloud top was approximately 12 km above sea level, as convection was depressed while stratiform regions developed near Okinawa Island. In the rain region below 3 km, the mean median volume diameter of the raindrop size distribution (DSD) estimated from the radar variables was 1.55 mm, and the mean normalized intercept parameter was 104.12 mm−1 m−3 with a mean radar reflectivity of 40.5 dBZe. The DSD indicates that the stratiform precipitation was characterized by higher number concentrations of smaller drops than observed previously in convective cells in a Baiu frontal convective precipitation region around Okinawa Island. The DSD also suggests the presence of larger raindrops than in convectiv...
Journal of the Meteorological Society of Japan. Ser. II, 2014
A stationary rainband brought heavy rainfall across Gifu and Aichi prefectures, Japan, on 15 July... more A stationary rainband brought heavy rainfall across Gifu and Aichi prefectures, Japan, on 15 July 2010. The orientation of the rainband was initially southwest-northeast, and then changed from west-southwest to east-northeast, before reverting to its original orientation, although the rainband remained stationary over the same area. This study analyzes the organization of the rainband during these three orientation periods using polarimetric Doppler radar. The rainband was maintained by south-southwesterly inflows of high equivalent potential temperature (≥340 K) below 2 km, while southwesterly winds prevailed at middle level during the rainfall. It is suggested that these rainband orientations were determined by the travel directions of the convective cells and positions of cell generation relative to the rainband, which in turn were governed by intensities of low-level inflow and cell-origin outflow. During the first orientation period, convective cells formed over a wide area within the rainband and traveled northeastward. Low-level outflows from deep convective cells in the northern section of the rainband shifted the cell-generation area southward, and enhanced south-southwesterly inflows caused the southwestern portion of the rainband to drift slightly to the north; hence, the rainband was oriented from west-southwest to east-northeast. The convective cells were deeper during the second period and low-level outflows were stronger than those in the first stage. The strong outflows formed a cell generation area on the southern lateral side of the rainband, while enhanced low-level inflows contributed to the north-northeastward motion of the generated cells crossing the rainband at an angle of 45°. The outflows and south-southwesterly inflows then weakened, and convective cells formed successively on the southwestern edge of the rainband and moved to the northeast. As a result, the rainband reverted to its original southwest-northeast orientation.
Journal of Atmospheric and Oceanic Technology, 2015
A fuzzy-logic-based hydrometeor classification (HC) method for X-band polarimetric radar (X-pol),... more A fuzzy-logic-based hydrometeor classification (HC) method for X-band polarimetric radar (X-pol), which is suitable for observation of solid hydrometeors under moist environments producing little or no hail, is constructed and validated. This HC method identifies the most likely hydrometeor at each radar sampling volume from eight categories: 1) drizzle, 2) rain, 3) wet snow aggregates, 4) dry snow aggregates, 5) ice crystals, 6) dry graupel, 7) wet graupel, and 8) rain–hail mixture. Membership functions are defined on the basis of previous studies. The HC method uses radar reflectivity Zh, differential reflectivity Zdr, specific differential phase Kdp, and correlation coefficient ρhv as its main inputs, and temperature with some consideration of relative humidity as supplemental information. The method is validated against ground and in situ observations of solid hydrometeors (dry graupel, dry snow aggregates, and ice crystals) under a moist environment. Observational data from a g...
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Papers by Tadayasu Ohigashi