scholarly journals Improvement of Heavy Rainfall Simulated with SST Adjustment Associated with Mesoscale Convective Complexes Related to Severe Flash Flood in Luwu, Sulawesi, Indonesia

Atmosphere ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 1445
Author(s):  
Erma Yulihastin ◽  
Danang Eko Nuryanto ◽  
Trismidianto ◽  
Robi Muharsyah
Keyword(s):  
Heavy Rainfall ◽  
Flash Flood ◽  
Wrf Model ◽  
Flash Floods ◽  
Heavy Rainfall Event ◽  
Limited Area ◽  
Pressure System ◽  
The North ◽  
Mesoscale Convective ◽  
Persistent Heavy Rainfall

Flash flooding is an important issue as it has a devastating impact over a short time and in a limited area. However, predicting flash floods is challenging because they are connected to convection systems that rapidly evolve and require a high-resolution forecasting system. In addition, modeling a case study of a mesoscale convective complex (MCC) is the key to improving our understanding of the heavy rainfall systems that trigger flash floods. In this study, we aim at improving modeling skills to simulate a heavy rainfall system related to flash-flood-producing MCCs. We simulated a heavy rainfall event related to a severe flash flood in Luwu, Sulawesi, Indonesia, on 13 July 2020. This flood was preceded by persistent heavy rainfall from 11 to 13 July 2020. In this case, we investigated the role of sea surface temperature (SST) in producing the persistent heavy rainfall over the region. Therefore, we explore the physical and dynamic processes that caused the heavy rainfall using a convection-permitting model with 1 km resolution and an experiment comparing the situation with and without updated SST. The results show that the heavy rainfall was modulated by the development of a pair of MCCs during the night. The pair of MCCs was triggered by a meso-low-pressure system with an anti-cyclonic circulation anomaly over the Makassar Strait and was maintained by the warm front passing between the sea and land over central Sulawesi. This front was characterized by moist–warm and cold–dry low-level air, which may have helped extend the lifetime of the MCCs. The north-westward propagation of the MCCs was due to the interaction between predominantly a south-easterly monsoon and SST anomalies. This study suggested that the long-lived (>10 h) MCCs (>80,000 km2 cloud shield) and persistent precipitation are reproduced well in the updated SST scenario in the WRF model. This relatively simple technique in the running model provides a new strategy for improving flash flood forecasting by better predicting rainfall as an input in the hydrological model. Our findings also indicated a long-lived MCC maintained by back-building mechanisms from night to morning inland as an exceptional MCC, which does not correspond to a previous study.

scholarly journals The Role of Local Orography on the Development of a Severe Rainfall Event over Western Peninsular Malaysia: A Case Study

2020 ◽  
Vol 148 (5) ◽  
pp. 2191-2209
Author(s):  
Mohd Fadzil Firdzaus Mohd Nor ◽  
Christopher E. Holloway ◽  
Peter M. Inness
Keyword(s):  
Heavy Rainfall ◽  
Flash Floods ◽  
Peninsular Malaysia ◽  
Rainfall Event ◽  
Heavy Rainfall Event ◽  
Limited Area ◽  
Rainfall Events ◽  
Low Level ◽  
Sumatra Island ◽  
Strait Of Malacca

Abstract Severe rainfall events are common in western Peninsular Malaysia. They are usually short and intense, and occasionally cause flash floods and landslides. Forecasting these local events is difficult and understanding the mechanisms of the rainfall events is vital for the advancement of tropical weather forecasting. This study investigates the mechanisms responsible for a local heavy rainfall event on 2 May 2012 that caused flash floods and landslides using both observations and simulations with the limited-area high-resolution Met Office Unified Model (MetUM). Results suggest that previous day rainfalls over Peninsular Malaysia and Sumatra Island influenced the development of overnight rainfall over the Strait of Malacca by low-level flow convergence. Afternoon convection over the Titiwangsa Mountains over Peninsular Malaysia then induced rainfall development and the combination of these two events influenced the development of severe convective storm over western Peninsular Malaysia. Additionally, anomalously strong low-level northwesterlies also contributed to this event. Sensitivity studies were carried out to investigate the influence of the local orography on this event. Flattened Peninsular Malaysia orography causes a lack of rainfall over the central part of Peninsular Malaysia and Sumatra Island and produces a weaker overnight rainfall over the Strait of Malacca. By removing Sumatra Island in the final experiment, the western and inland parts of Peninsular Malaysia would receive more rainfall, as this region is more influenced by the westerly wind from the Indian Ocean. These results suggest the importance of the interaction between landmasses, orography, low-level flow, and the diurnal cycle on the development of heavy rainfall events.

scholarly journals Characteristics of Mesoscale Convective Complexes that Triggered Heavy Rainfall Related to Severe Flash Flood in Luwu, Sulawesi, Indonesia

2021 ◽  
Author(s):  
Erma Yulihastin ◽  
Danang Eko Nuryanto ◽  
- Trismidianto ◽  
Robi Muharsyah
Keyword(s):  
Surface Temperature ◽  
Heavy Rainfall ◽  
Flash Flood ◽  
Sea Surface ◽  
Cyclonic Vorticity ◽  
Mesoscale Convective ◽  
Sea Surface Temperature Anomalies ◽  
Persistent Heavy Rainfall ◽  
Vorticity Anomaly ◽  
Central Sulawesi

A severe flash flood hit Luwu, Sulawesi, Indonesia, on 13 July 2020. This flood was preceded by persistent heavy rainfall from 11 to 13 July 2020. In this study, we explore both the physical and dynamical processes that caused the heavy rainfall using a convection-permitting model with 1-km resolution. The heavy rainfall was modulated by the development of a pair of Mesoscale Convective Complexes (MCCs) during the night. The pair of MCCs was triggered by an anti-cyclonic vorticity anomaly over the Makassar Strait and was maintained by the warm front passing between the sea and land over central Sulawesi. This front was characterized by moist-warm and cold-dry low-level air, which may have helped to extend the lifetime of the MCCs. The northwestward propagation of the MCCs was due to the interaction between predominantly southeasterly monsoon and sea surface temperature anomalies.

scholarly journals The MISTRAL Project provides a new tool for Flash Flood Forecasting in Italy 

2021 ◽  
Author(s):  
Estíbaliz Gascón ◽  
Andrea Montani ◽  
Tim Hewson
Keyword(s):  
Heavy Rainfall ◽  
Positive Impact ◽  
Flash Flood ◽  
Flash Floods ◽  
Processing Technique ◽  
Added Value ◽  
Limited Area ◽  
The European Union ◽  
Post Processing ◽  
The World

<p>Localized heavy rainfall, which can be associated with flash floods, is difficult to predict accurately: both the predicted location and the intensity can exhibit large errors. Moreover, weather forecasts should be provided for points and not for the large regions represented by global model grid boxes. This mismatch can in principle be addressed using high-resolution limited-area models, or by applying some post-processing to global forecast models, as used in “ecPoint-rainfall”, a new ECMWF probabilistic post-processing technique to improve precipitation forecasts. One novel premise of ecPoint, which has a major positive impact on the calibration, is that the forecast-versus-point-observation relationship depends on “gridbox weather types” that could potentially occur in many parts of the world.</p><p>The MISTRAL (Meteo Italian SupercompuTing PoRtAL) project, funded under the Connecting Europe Facility (CEF) – Telecommunication Sector Programme of the European Union came to its end in January 2021. The main project goal was to facilitate and foster the re-use of datasets by weather-dependent communities, to provide added value services using HPC resources. ECMWF participated in the project with the goal of improving probabilistic 6-h rainfall forecast products, to improve the prediction of flash floods in Italy and nearby Mediterranean regions. One of the objectives was to exploit the CINECA supercomputer facilities in Bologna to extract maximum benefit from ecPoint-Rainfall and from a 2.2km resolution COSMO limited area ensemble. To address that, we applied a new and innovative scale-selective neighbourhood post-processing technique to the COSMOS output, which, on the one hand, identifies and preserves the most reliable heavy rainfall signals and, on the other, spreads out those signals which are less consistently handled. Then, it is blended with a new 6h ecPoint-Rainfall product in order to leverage the most skilful aspects of the two systems. The 6-h ecPoint Rainfall forecasts were also developed during the project, building on the pre-existing ecPoint-Rainfall 12h product (already delivered to ECMWF customers in real-time). The final blended product includes, for lead times of 1-10 days, 6-h accumulated rainfall for each COSMO gridbox in percentiles (1, 2,..99) and probabilities of exceeding certain thresholds.</p><p>The main objective of this work was to improve forecasts and support weather-alert decisions for flash flood prediction. As a legacy of the project, we are now providing forecast data for Italy and nearby regions with a higher level of quality and resolution than has hitherto been possible,  and we are also delivering a robust gateway to products for the European community within the MISTRAL portal (https://meteohub.hpc.cineca.it/app/maps/flashflood). The principles could also be usefully applied in other parts of Europe, or indeed the world, where limited area ensembles are running operationally.</p><p>In this presentation, we will introduce the methodologies, the verification results and will illustrate with forecast examples.</p>

scholarly journals Assimilating X- and S-Band Radar Data for a Heavy Precipitation Event in Italy

Water ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 1727
Author(s):  
Valerio Capecchi ◽  
Andrea Antonini ◽  
Riccardo Benedetti ◽  
Luca Fibbi ◽  
Samantha Melani ◽  
...  
Keyword(s):  
Extreme Event ◽  
Wrf Model ◽  
Heavy Precipitation ◽  
Radar Data ◽  
Flash Floods ◽  
Precipitation Event ◽  
Weather Research And Forecasting ◽  
Limited Area ◽  
Heavy Precipitation Event ◽  
The Town

During the night between 9 and 10 September 2017, multiple flash floods associated with a heavy-precipitation event affected the town of Livorno, located in Tuscany, Italy. Accumulated precipitation exceeding 200 mm in two hours was recorded. This rainfall intensity is associated with a return period of higher than 200 years. As a consequence, all the largest streams of the Livorno municipality flooded several areas of the town. We used the limited-area weather research and forecasting (WRF) model, in a convection-permitting setup, to reconstruct the extreme event leading to the flash floods. We evaluated possible forecasting improvements emerging from the assimilation of local ground stations and X- and S-band radar data into the WRF, using the configuration operational at the meteorological center of Tuscany region (LaMMA) at the time of the event. Simulations were verified against weather station observations, through an innovative method aimed at disentangling the positioning and intensity errors of precipitation forecasts. A more accurate description of the low-level flows and a better assessment of the atmospheric water vapor field showed how the assimilation of radar data can improve quantitative precipitation forecasts.

scholarly journals Sensitivity Study of WRF Numerical Modeling for Forecasting Heavy Rainfall in Sri Lanka

Atmosphere ◽  
2018 ◽  
Vol 9 (10) ◽  
pp. 378 ◽  
Author(s):  
Channa Rodrigo ◽  
Sangil Kim ◽  
Il Jung
Keyword(s):  
Sri Lanka ◽  
Heavy Rainfall ◽  
Weather Prediction ◽  
Wrf Model ◽  
Heavy Rain ◽  
Heavy Precipitation ◽  
Sensitivity Study ◽  
Southwest Monsoon ◽  
Northeast Monsoon ◽  
Pressure System

This study aimed to determine the predictability of the Weather Research and Forecasting (WRF) model with different model physics options to identify the best set of physics parameters for predicting heavy rainfall events during the southwest and northeast monsoon seasons. Two case studies were used for the evaluation: heavy precipitation during the southwest monsoon associated with the simultaneous onset of the monsoon, and a low pressure system over the southwest Bay of Bengal that produced heavy rain over most of the country, with heavy precipitation associated with the northeast monsoon associated with monsoon flow and easterly disturbances. The modeling results showed large variation in the rainfall estimated by the model using the various model physics schemes, but several corresponding rainfall simulations were produced with spatial distribution aligned with rainfall station data, although the amount was not estimated accurately. Moreover, the WRF model was able to capture the rainfall patterns of these events in Sri Lanka, suggesting that the model has potential for operational use in numerical weather prediction in Sri Lanka.

scholarly journals NUMERICAL SENSITIVITY EXPERIMENTS ON PRECIPITATION IN A HEAVY RAINFALL EVENT SIMULATED BY USING THE WRF MODEL

2014 ◽  
Vol 70 (4) ◽  
pp. I_541-I_546 ◽  
Author(s):  
Yuji SUGIHARA ◽  
Sho IMAGAMA ◽  
Yohei OHKUMA ◽  
Nobuhiro MATSUNAGA ◽  
Yukiko HISADA ◽  
...  
Keyword(s):  
Heavy Rainfall ◽  
Wrf Model ◽  
Rainfall Event ◽  
Heavy Rainfall Event ◽  
Sensitivity Experiments

scholarly journals On a Flood-Producing Coastal Mesoscale Convective Storm Associated with the Kor’easterlies: Multi-Data Analyses Using Remotely-Sensed and In-Situ Observations and Storm-Scale Model Simulations

2020 ◽  
Vol 12 (9) ◽  
pp. 1532
Author(s):  
Seon Ki Park ◽  
Sojung Park
Keyword(s):  
Heat Waves ◽  
Coastal Region ◽  
Vertical Wind Shear ◽  
Scale Model ◽  
Cold Pool ◽  
Heavy Rainfall Event ◽  
Convective System ◽  
Pressure System ◽  
Mesoscale Convective

A flood-producing heavy rainfall event occurred at the mountainous coastal region in the northeast of South Korea on 5–6 August 2018, subsequent to extreme heat waves, through a quasi-stationary mesoscale convective system (MCS). We analyzed the storm environment via a multi-data approach using high-resolution (1-km) simulations from the Weather Research and Forecasting (WRF) and in situ/satellite/radar observations. The brightness temperature, from the Advanced Himawari Imager water vapor band, and the composite radar reflectivity were used to identify characteristics of the MCS and associated precipitations. The following factors affected this back-building MCS: low-level convergence by the Korea easterlies (Kor’easterlies), carrying moist air into the coast; strong vertical wind shear, making the updraft tilted and sustained; coastal fronts and back-building convection bands, formed through interactions among the Kor’easterlies, cold pool outflows, and orography; mid-level advection of cold air and positive relative vorticity, enhancing vertical convection and potential instability; and vigorous updraft releasing potential instability. The pre-storm synoptic environment provided favorable conditions for storm development such as high moisture and temperature over the coastal area and adjacent sea, and enhancement of the Kor’easterlies by expansion of a surface high pressure system. Upper-level north-northwesterly winds prompted the MCS to propagate south-southeastward along the coastline.

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