scholarly journals Ensemble cloud-resolving modelling of a historic back-building mesoscale convective system over Liguria: The San Fruttuoso case of 1915

2016 ◽  
Author(s):  
Antonio Parodi ◽  
Luca Ferraris ◽  
William Gallus ◽  
Maurizio Maugeri ◽  
Luca Molini ◽  
...  
Keyword(s):  
Extreme Event ◽  
Flash Flood ◽  
Wrf Model ◽  
Mediterranean Area ◽  
Western Mediterranean ◽  
Mesoscale Convective Systems ◽  
Convective System ◽  
Convective Systems ◽  
Position Errors ◽  
Mesoscale Convective

Abstract. Highly localized and persistent back-building mesoscale convective systems represent one of the most dangerous flash-flood producing storms in the north-western Mediterranean area. Substantial warming of the Mediterranean Sea in recent decades raises concerns over possible increases in frequency or intensity of these types of events as increased atmospheric temperatures generally support increases in water vapor content. However, analyses of the historical record do not provide a univocal answer, but these are likely affected by a lack of detailed observations for older events. In the present study, 20th Century Reanalysis Project initial and boundary condition data in ensemble mode are used to address the feasibility of performing cloud-resolving simulations with 1 km horizontal grid spacing of a historic extreme event that occurred over Liguria: The San Fruttuoso case of 1915. The proposed approach focuses on the ensemble Weather Research and Forecasting (WRF) model runs that show strong convergence over the Liguria sea, as these runs are the ones most likely to best simulate the event. It is found that these WRF runs generally do show wind and precipitation fields that are consistent with the occurrence of highly localized and persistent back-building mesoscale convective systems, although precipitation peak amounts are underestimated. Systematic small north-westward position errors with regard to the heaviest rain and strongest convergence areas imply that the Reanalysis members may not be adequately representing the amount of cool air over the Po Plain outflowing into the Liguria Sea through the Apennines gap. Regarding the role of historical data sources, this study shows that in addition to Reanalysis products, unconventional data, such as historical meteorological bulletins newspapers and even photographs can be very valuable sources of knowledge in the reconstruction of past extreme events.

scholarly journals Ensemble cloud-resolving modelling of a historic back-building mesoscale convective system over Liguria: the San Fruttuoso case of 1915

2017 ◽  
Vol 13 (5) ◽  
pp. 455-472 ◽  
Author(s):  
Antonio Parodi ◽  
Luca Ferraris ◽  
William Gallus ◽  
Maurizio Maugeri ◽  
Luca Molini ◽  
...  
Keyword(s):  
Extreme Event ◽  
Flash Flood ◽  
Western Mediterranean ◽  
Mesoscale Convective Systems ◽  
Convective System ◽  
Water Vapour Content ◽  
Ligurian Sea ◽  
Convective Systems ◽  
Position Errors ◽  
Mesoscale Convective

Abstract. Highly localized and persistent back-building mesoscale convective systems represent one of the most dangerous flash-flood-producing storms in the north-western Mediterranean area. Substantial warming of the Mediterranean Sea in recent decades raises concerns over possible increases in frequency or intensity of these types of events as increased atmospheric temperatures generally support increases in water vapour content. However, analyses of the historical record do not provide a univocal answer, but these are likely affected by a lack of detailed observations for older events. In the present study, 20th Century Reanalysis Project initial and boundary condition data in ensemble mode are used to address the feasibility of performing cloud-resolving simulations with 1 km horizontal grid spacing of a historic extreme event that occurred over Liguria: the San Fruttuoso case of 1915. The proposed approach focuses on the ensemble Weather Research and Forecasting (WRF) model runs that show strong convergence over the Ligurian Sea (17 out of 56 members) as these runs are the ones most likely to best simulate the event. It is found that these WRF runs generally do show wind and precipitation fields that are consistent with the occurrence of highly localized and persistent back-building mesoscale convective systems, although precipitation peak amounts are underestimated. Systematic small north-westward position errors with regard to the heaviest rain and strongest convergence areas imply that the reanalysis members may not be adequately representing the amount of cool air over the Po Plain outflowing into the Ligurian Sea through the Apennines gap. Regarding the role of historical data sources, this study shows that in addition to reanalysis products, unconventional data, such as historical meteorological bulletins, newspapers, and even photographs, can be very valuable sources of knowledge in the reconstruction of past extreme events.

Tracking Mesoscale Convective Systems that are Potential Candidates for Tropical Cyclogenesis

2020 ◽  
Vol 148 (2) ◽  
pp. 655-669 ◽  
Author(s):  
Kelly M. Núñez Ocasio ◽  
Jenni L. Evans ◽  
George S. Young
Keyword(s):  
Propagation Speed ◽  
Extreme Rainfall ◽  
Life Cycles ◽  
Mesoscale Convective Systems ◽  
Tropical Cyclogenesis ◽  
Convective System ◽  
Background Flow ◽  
Extreme Rainfall Events ◽  
Convective Systems ◽  
Mesoscale Convective

Abstract This study introduces the development of the Tracking Algorithm for Mesoscale Convective Systems (TAMS), an algorithm that allows for the identifying, tracking, classifying, and assigning of rainfall to mesoscale convective systems (MCSs). TAMS combines area-overlapping and projected-cloud-edge tracking techniques to maximize the probability of detecting the progression of a convective system through time, accounting for splits and mergers. The combination of projection on area overlapping is equivalent to setting the background flow in which MCSs are moving on. Sensitivity tests show that area-overlapping technique with no projection (thus, no background flow) underestimates the real propagation speed of MCSs over Africa. The MCS life cycles and propagation derived using TAMS are consistent with climatology. The rainfall assignment is also more reliable than with previous methods as it utilizes a combination of regridding through linear interpolation with high temporal and spatial resolution data. This makes possible the identification of extreme rainfall events associated with intense MCSs more effectively. TAMS will be utilized in future work to build an AEW–MCS dataset to study tropical cyclogenesis.

scholarly journals On the Predictability of Mesoscale Convective Systems: Two-Dimensional Simulations

2008 ◽  
Vol 23 (5) ◽  
pp. 773-785 ◽  
Author(s):  
Matthew S. Wandishin ◽  
David J. Stensrud ◽  
Steven L. Mullen ◽  
Louis J. Wicker
Keyword(s):  
Wind Speed ◽  
Relative Humidity ◽  
Ensemble Member ◽  
Mesoscale Convective Systems ◽  
Convective System ◽  
Forecast Errors ◽  
Two Dimensional ◽  
Substantial Impact ◽  
Convective Systems ◽  
Mesoscale Convective

Abstract Mesoscale convective systems (MCSs) are a dominant climatological feature of the central United States and are responsible for a substantial fraction of warm season rainfall. Yet very little is known about the predictability of MCSs. To help alleviate this situation, a series of ensemble simulations of an MCS are performed on a two-dimensional, storm-scale (Δx = 1 km) model. Ensemble member perturbations in wind speed, relative humidity, and instability are based on current 24-h forecast errors from the North American Model (NAM). The ensemble results thus provide an upper bound on the predictability of mesoscale convective systems within realistic estimates of environmental uncertainty, assuming successful convective initiation. The simulations are assessed by considering an ensemble member a success when it reproduces a convective system of at least 20 km in length (roughly the size of two convective cells) within 100 km on either side of the location of the MCS in the control run. By that standard, MCSs occur roughly 70% of the time for perturbation magnitudes consistent with 24-h forecast errors. Reducing the perturbations for all fields to one-half the 24-h error values increases the MCS success rate to over 90%. The same improvement in forecast accuracy would lead to a 30%–40% reduction in maximum surface wind speed uncertainty and a roughly 20% reduction in the uncertainty in maximum updraft strength, and initially slower growth in the uncertainty in the size of the MCS. However, the occurrence of MCSs drops below 50% as the midlayer mean relative humidity falls below 65%. The response of the model to reductions in forecast errors for instability, moisture, and wind speed is not consistent and cannot be easily generalized, but each can have a substantial impact on forecast uncertainty.

scholarly journals Characteristics of Mesoscale Convective Systems over China and Its Vicinity Using Geostationary Satellite FY2

2015 ◽  
Vol 28 (12) ◽  
pp. 4890-4907 ◽  
Author(s):  
Xiangrong Yang ◽  
Jianfang Fei ◽  
Xiaogang Huang ◽  
Xiaoping Cheng ◽  
Leila M. V. Carvalho ◽  
...  
Keyword(s):  
Warm Season ◽  
The United States ◽  
Geostationary Satellite ◽  
Mesoscale Convective Systems ◽  
Convective System ◽  
Convective Systems ◽  
Diurnal Cycles ◽  
Mesoscale Convective ◽  
Positive Correlations ◽  
Monthly Variations

Abstract This study investigates mesoscale convective systems (MCSs) over China and its vicinity during the boreal warm season (May–August) from 2005 to 2012 based on data from the geostationary satellite Fengyun 2 (FY2) series. The authors classified and analyzed the quasi-circular and elongated MCSs on both large and small scales, including mesoscale convective complexes (MCCs), persistent elongated convective systems (PECSs), meso-β circular convective systems (MβCCSs), meso-β elongated convective system (MβECSs), and two additional types named small meso-β circular convective systems (SMβCCSs) and small meso-β elongated convective systems (SMβECSs). Results show that nearly 80% of the 8696 MCSs identified in this study fall into the elongated categories. Overall, MCSs occur mainly at three zonal bands with average latitudes around 20°, 30°, and 50°N. The frequency of MCSs occurrences is maximized at the zonal band around 20°N and decreases with increase in latitude. During the eight warm seasons, the period of peak systems occurrences is in July, followed decreasingly by June, August, and May. Meanwhile, from May to August three kinds of monthly variations are observed, which are clear northward migration, rapid increase, and persistent high frequency of MCS occurrences. Compared to MCSs in the United States, the four types of MCSs (MCCs, PECSs, MβCCSs, and MβECSs) are relatively smaller both in size and eccentricity but exhibit nearly equal life spans. Moreover, MCSs in both countries share similar positive correlations between their duration and maximum extent. Additionally, the diurnal cycles of MCSs in both countries are similar (local time) regarding the three stages of initiation, maturation, and termination.

scholarly journals Biomass burning CCN enhance the dynamics of a mesoscale convective system over the La Plata Basin: a numerical approach

2018 ◽  
Vol 18 (3) ◽  
pp. 2081-2096
Author(s):  
Gláuber Camponogara ◽  
Maria Assunção Faus da Silva Dias ◽  
Gustavo G. Carrió
Keyword(s):  
Biomass Burning ◽  
Amazon Basin ◽  
Cloud Condensation Nuclei ◽  
Mesoscale Convective System ◽  
Mesoscale Convective Systems ◽  
Convective System ◽  
La Plata ◽  
Convective Systems ◽  
La Plata Basin ◽  
Mesoscale Convective

Abstract. High aerosol loadings are discharged into the atmosphere every year by biomass burning in the Amazon and central Brazil during the dry season (July–December). These particles, suspended in the atmosphere, can be carried via a low-level jet toward the La Plata Basin, one of the largest hydrographic basins in the world. Once they reach this region, the aerosols can affect mesoscale convective systems (MCSs), whose frequency is higher during the spring and summer over the basin. The present study is one of the first that seeks to understand the microphysical effects of biomass burning aerosols from the Amazon Basin on mesoscale convective systems over the La Plata Basin. We performed numerical simulations initialized with idealized cloud condensation nuclei (CCN) profiles for an MCS case observed over the La Plata Basin on 21 September 2010. The experiments reveal an important link between CCN number concentration and MCS dynamics, where stronger downdrafts were observed under higher amounts of aerosols, generating more updraft cells in response. Moreover, the simulations show higher amounts of precipitation as the CCN concentration increases. Despite the model's uncertainties and limitations, these results represent an important step toward the understanding of possible impacts on the Amazon biomass burning aerosols over neighboring regions such as the La Plata Basin.

scholarly journals Biomass burning CCNs enhance the dynamics of a Mesoscale Convective System over the La Plata Basin: a numerical approach

2017 ◽  
Author(s):  
Gláuber Camponogara ◽  
Maria Assunção Faus Silva Dias ◽  
Gustavo G. Carrió
Keyword(s):  
Biomass Burning ◽  
Amazon Basin ◽  
Mesoscale Convective System ◽  
Numerical Approach ◽  
Mesoscale Convective Systems ◽  
Convective System ◽  
La Plata ◽  
Convective Systems ◽  
La Plata Basin ◽  
Mesoscale Convective

Abstract. High aerosol loadings are discharged into the atmosphere every year by biomass burning in the Amazon and Central Brazil during the dry season (July–December). These particles, suspended in the atmosphere, can be carried via a low level jet toward the La Plata Basin, one of the largest hydrographic basins in the world. Once they reach this region, the aerosols can affect mesoscale convective systems (MCS), whose frequency is higher during the spring and summer over the basin. The present study is one of the first that seeks to understand the microphysical effects of biomass burning aerosols from the Amazon Basin on mesoscale convective systems over the La Plata Basin. We performed numerical simulations initialized with idealized CCN profiles for an MCS case observed over the La Plata Basin on 21 September 2010. The experiments reveal an important link between CCN number concentration and MCS dynamics, where stronger downdrafts were observed under higher amounts of aerosols, generating more updraft cells in response. Moreover, the simulations show higher amounts of precipitation as the CCN concentration increases. Despite the model’s uncertainties and limitations, these results represent an important step toward the understanding of possible impacts on the Amazon biomass burning aerosols over neighboring regions such as the La Plata Basin.

Modeling of Mesoscale-Convective Systems Downstream of Mountain Regions

2021 ◽  
Author(s):  
Andreas F. Prein
Keyword(s):  
Climate Models ◽  
Flash Flood ◽  
Climate Change Impacts ◽  
Mesoscale Convective Systems ◽  
The Tibetan Plateau ◽  
Mountain Regions ◽  
Convective Initiation ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Model Setup

<p>Mesoscale-Convective Systems (MCSs) are prolific rain-producers and are responsible for most flash flood events in mid-latitudes. Global hotspots of MCS occurrence are downstream of major mountain regions such as the Rocky Mountains, the Andes, and the Himalayas. This is because of the effects of mountain barriers on circulation patterns, moisture transport, and convective initiation. Realistically simulating MCSs in climate models is essential for representing the water and energy cycle and flood and severe convective weather assessments. However, state-of-the-art climate models have substantial biases in simulating MCSs and orographic impacts on downstream environments resulting in large uncertainties and errors in assessing climate change impacts on water availability and extreme events. Here we present that kilometer-scale models, which have an improved representation of orography and can represent deep convective processes explicitly, show a step improvement in simulating organized convective storms compared to coarser-resolution models. We will show examples of these improvements from kilometer-scale simulations over the Tibetan Plateau, North- and South America. We will also show sensitivities to the model setup and feedback processes and end with discussing remaining challenges and future prospects.</p>

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