Occurrence Of Mesoscale Convective Systems Research Articles

Hue Channel Mesoscale Convective System Identification Techniques using Kalpana Geostationary Satellite Observations

Climate change is leading to sudden extreme weather events like floods and heavy rain to occur. One of the most significant rain-bearing systems, Mesoscale Convective Systems (MCSs), is in charge of catastrophic rainfall and flood events that may cause loss of life and property. MCSs are one of the vital components of the climate system on Earth. Many studies contributed to two significant steps, MCS identification and tracking. There are a variety of algorithms focused on tracking whereas for MCS identification only limited methods are present. They contribute to global as well as regional climate patterns by transporting heat and moisture. It is necessary to identify MCS properly to track MCS occurrences over time and comprehend their typical lifecycle to get early warnings of their existence. Three MCS identification techniques based on the Hue channel of the Hue Saturation Value (HSV) color model are implemented in this research, and their effectiveness is assessed. These techniques execute segmentation based on Hue channel Thresholding (HT), K means clustering combined with Hue channel Thresholding (KMCHT) and the modified Source Apportionment Technique combined with Hue channel Thresholding (SATHT). Image pixel values are used to depict infrared brightness temperature data obtained from the Indian geostationary satellite Kalpana-1. The generated ground truth images and performance measurements are used to assess the effectiveness of the methods. The proposed SATHT method for multiple cloud segmentation results in superior performance metrics than the HT and KMCHT approaches.

Anthropogenic Aerosols Significantly Reduce Mesoscale Convective System Occurrences and Precipitation Over Southern China in April

AbstractPrecipitation over Southern China in April, largely associated with mesoscale convective systems (MCSs), has declined significantly in recent decades. It is unclear how this decline in precipitation may be related to the concurrent increase of anthropogenic aerosols over this region. Here, using observation analyses and model simulations, we showed that increased levels of anthropogenic aerosols can significantly reduce MCS occurrences by 21% to 32% over Southern China in April, leading to less rainfall. Half of this MCS occurrence reduction was due to the direct radiative scattering of aerosols and the indirect enhancement of non‐MCS liquid cloud reflectance by aerosols, which stabilized the regional atmosphere. The other half of the MCS occurrence reduction was due to the microphysical and dynamical responses of the MCS to aerosols. Our results demonstrated the complex effects of aerosols on MCSs via impacts on both the convective systems and on the regional atmosphere.

Climatology and atmospheric conditions associated with cool season bow echo storms in Poland

Cool season severe wind events may be related to the occurrence of mesoscale convective systems with a bow echo (i.e. arch-shaped band of radar reflectivity). This research provides an insight into the spatial and temporal distribution of bow echoes occurring in the cool season (October–March) between January 2007 and March 2019 over Poland and presents atmospheric conditions (synoptic, kinematic, and thermodynamic) associated with such events. The analysis has been performed utilizing SYNOP (surface observations), ESWD (European Severe Weather Database), radar (CMAX, CAPPI), reanalysis (ERA-5) and sounding data. During the period studied, 27 Cool Season Bow Echoes (CSBEs) were identified across Poland. The area most exposed to the occurrence of CSBEs included south-western Poland, while the north-eastern and eastern part of the country was generally free of this phenomenon. Unlike the warm season cases, CSBEs do not indicate a clear diurnal cycle. As our results have shown, a high shear/low CAPE (Convective Available Potential Energy) environment in combination with a triggering mechanism along the cold front (frontal cases) or along the surface trough (post-frontal cases) can be considered as supportive for CSBE. Such cases were always associated with the presence of strong air flow in the low and mid troposphere. The analysis of 500 hPa geopotential height fields revealed that troughs (often with embedded smaller-amplitude dynamic waves) moving over Central Europe were present in 26 out of 27 cases. The median value of vertical wind shear for identified cases exceeded 30 m/s for deep-layer shear (DLS), was well above 20 m/s for mid-level shear (MLS), and higher than 17 m/s for low-level shear (LLS). A recurring finding was also that post-frontal cases formed in an environment with weaker shear, but higher CAPE. • The spatiotemporal distribution of cool season bow echoes (CSBEs) in Poland. • 27 CSBEs have been identified between 2007 and 2019. • CSBEs are strongly affected by the presence of fast flow from mid to upper level. • CSBEs are characterized by weak instability and strong vertical wind shear.

Sensitivity of GPS tropospheric estimates to mesoscale convective systems in West Africa

Abstract. This study analyzes the characteristics of GPS tropospheric estimates (zenith wet delays – ZWDs, gradients, and post-fit phase residuals) during the passage of mesoscale convective systems (MCSs) and evaluates their sensitivity to the research-level GPS data processing strategy implemented. Here, we focus on MCS events observed during the monsoon season of West Africa. This region is particularly well suited for the study of these events due to the high frequency of MCS occurrences in the contrasting climatic environments between the Guinean coast and the Sahel. This contrast is well sampled with data generated by six African Monsoon Multidisciplinary Analysis (AMMA) GPS stations. Tropospheric estimates for a 3-year period (2006–2008), processed with both the GAMIT and GIPSY-OASIS software packages, were analyzed and intercompared. First, the case of a MCS that passed over Niamey, Niger, on 11 August 2006 demonstrates a strong impact of the MCS on GPS estimates and post-fit residuals when the GPS signals propagate through the convective cells as detected on reflectivity maps from the MIT C-band Doppler radar. The estimates are also capable of detecting changes in the structure and dynamics of the MCS. However, the sensitivity is different depending on the tropospheric modeling approach adopted in the software. With GIPSY-OASIS, the high temporal sampling (5 min) of ZWDs and gradients is well suited for detecting the small-scale, short-lived, convective cells, while the post-fit residuals remain quite small. With GAMIT, the lower temporal sampling of the estimated parameters (hourly for ZWDs and daily for gradients) is not sufficient to capture the rapid delay variations associated with the passage of the MCS, but the post-fit phase residuals clearly reflect the presence of a strong refractivity anomaly. The results are generalized with a composite analysis of 414 MCS events observed over the 3-year period at the six GPS stations with the GIPSY-OASIS estimates. A systematic peak is found in the ZWDs coincident with the cold pool crossing time associated with the MCSs. The tropospheric gradients reflect the path of the MCS propagation (generally from east to west). This study concludes that ZWDs, gradients, and post-fit phase residuals provide relevant and complementary information on MCSs passing over or in the vicinity of a GPS station.

Kinematic and thermodynamic conditions related to convective systems with a bow echo in Poland

Severe wind events are often related to the occurrence of mesoscale convective systems with arch-shaped radar reflectivity, i.e., a bow echo. In this research, the kinematic and thermodynamic conditions associated with 91 bow echo cases which occurred in the warm season (i.e., from early April until late September) in Poland (2007–2014) were analyzed. The environmental conditions were determined primarily based on the upper air soundings, and additionally on data obtained from ERA-Interim reanalysis. The results indicate that there is a relatively wide range of shear and instability environments associated with bow echoes over Poland. The identified cases occurred both in weakly forced environments, and as well developed in dynamic synoptic patterns with low instability. We have also found cases with strong instability and significantly increased shear values. The combination of a moist boundary layer and steep mid-tropospheric lapse rate usually resulted in moderate to high CAPE values for identified bow echo cases. The median of surface-based CAPE was equal to 1594 J/kg (Mean Layer CAPE = 1038 J/kg) for soundings, and to 1622 J/kg (Mean Layer CAPE = 1275 J/kg) for ERA-Interim. Bow echo environments also showed significantly increased potential for strong downdrafts and damaging outflow winds (the median Downdraft CAPE reached 849 J/kg for soundings and 734 J/kg for ERA-Interim). Bow echoes were usually associated with the occurrence of strong air flow in the troposphere. The presence of a jet stream in the middle and upper troposphere contributed to the development of increased vertical wind shear values. The median of 0–6-km shear exceeded 15 m/s, whereas for 0–3-km shear, it was approximately equal to 12.5 m/s and to 7 m/s for 0–1-km shear.

Climate Variability Impact on the Frequency of Occurrence of Mesoscale Convective Systems in Northern Nigeria

Mesoscale Convective Systems (MCSs) form an important component of meteorology in West Africa, and in particular, contribute substantially to precipitation totals. Several authors focused majorly on the contribution of these systems to precipitation and the damages that accompanied it. But in the event of current climate change, it is expected that storm occurrences especially over the tropics will also be impacted due to variability or changing in climate especially in Northern Nigeria which has experienced some extreme weather events over the years. The study was carried out in eight (8) different states within the savannah region of Nigeria. Monthly total rainfall, mean monthly temperature, relative humidity and daily Mesoscale Convective Systems (MCSs) (thunderstorms and line squalls) data of 31 years was used. Man-Kendall and Coefficient of variation (CV) method were used to analyze the data. There were various degrees of variations in some of the data analyzed based on the location of the station. The frequency of occurrence of these systems showed that its number (peals) decreases with an increasing latitude for stations north of 10°N with the north-eastern part of the country recording a decrease of almost one-third between 1981 and 2010. Hence, monsoon type of precipitation can be seen to be contributing more to the total annual rainfall in the northern part of Nigeria in contrast to earlier studies which gave Mesoscale Convective Systems (MCSs) 95% contribution rate.

Observational investigation of relationships between moisture surges and mesoscale‐ to large‐scale convection during the North American monsoon

ABSTRACTThis article consists of a comprehensive climatological study of moisture surges (MSs) in the North American monsoon (NAM) core region using a multiyear (1990–2006) set of surges, surface and upper air data, satellite‐estimated mesoscale convective systems (MCSs), and North American Regional Reanalysis (NARR) products. Composites of surges are created with respect to MCSs occurrence in the NAM core region. MSs are further stratified based on co‐occurrence with tropical easterly waves and tropical storms/tropical cyclones. These results provide new insights into the nature of the Gulf of California (GoC) moisture flux variability and describe the influence of these multi‐scale processes on the occurrence and intensity of surges and the GoC diurnal circulations – especially the Gulf of California low‐level jet (GCLLJ). Results show that over the GoC Coastal Plain, MCSs modulate the diurnal cycle of the GoC low‐level circulation during ‘major surge’, ‘minor surge’, and ‘non‐surge’ environments. We found that MCS activity enhances the offshore flow along the eastern GoC coast, which then enhances the GCLLJ. On the other hand, immediately before major surges onset, the occurrence of MCSs over the southern GoC produces more intense surges. It is also shown that this relationship holds regardless of the intensity and type of tropical synoptic‐scale disturbance forcing the surge.

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

AbstractThis 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.

Variability of mineral dust concentrations over West Africa monitored by the Sahelian Dust Transect

The “Sahelian belt” is known as a region where mineral dust content is among the highest in the world. In the framework of the AMMA international Program, a transect of three ground based stations, the “Sahelian Dust Transect” (SDT), has been deployed in order to obtain quantitative information on the mineral dust content over the Sahel. These three stations: Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) are aligned at 13°N along the east–west main pathway of the Saharan and Sahelian dust toward the Atlantic Ocean. The SDT provides a set of aerosol measurements and local meteorological parameters to describe and understand the mechanisms that control the temporal and regional variability of mineral dust content in these regions.In this work we analyze the seasonal and diurnal variability of the dust concentrations over the period 2006–2010. The analysis of the dust concentrations measured between 2006 and 2010 confirmed a regional seasonal cycle characterized by a maximum in the dry season, with median concentration ranging from 205μgm−3 at Banizoumbou to 144μgm−3 at M'Bour, and a minimum (11–32μgm−3) in the wet season. The five year data set allowed the quantification of the variability of the monthly concentrations. The range between the percentiles 75 and 25 varies linearly with the median concentration: it is of the same order than the median value in M'Bour, 17% slightly higher in Cinzana and 50% higher in Banizoumbou. The range between the accepted maximum and minimum is also correlated with the median value, with slopes ranging from 14 in Banizoumbou to 7 in M'Bour. Part of the variability of the concentration at the monthly scale is due to interannual variability. Extremely high or low monthly concentration can be recorded that significantly impacts the five year median concentration and its range. Compared to the 3-year data set analyzed by Marticorena et al. (2010), the two additional years used in this work appear as the less dusty year (2009) and one of the dustier years (2010).The sampling time step and the high recovery rates of the measurement stations allowed to investigate the diurnal cycle of the dust concentration for the first time. During the dry season, the hourly median concentrations range from 80 to 100μgm−3 during the night to 100–160μgm−3 during the day-time maximum. The diurnal cycle of the PM10 concentrations is phased with the diurnal cycle of the surface wind speed and thus modulated by the interactions between the nocturnal lower level jet (NLLJ) and the surface boundary layer. The NLLJ appears as a major agent to transport Saharan dust toward the Sahel. During the wet season, the median PM10 concentrations are maximum at night-time (<50μgm−3). The night-time concentrations are associated with a large range of variability and coincide with the periods of higher occurrence of meso-scale convective systems. The amplitude of the diurnal cycle is of the order of 60μgm−3 in the dry season and 20μgm−3 in the wet season. Both in the dry and in the wet season, despite a month to month variability of the daily dust concentration, a typical diurnal pattern has been established suggesting that this temporal pattern is mainly driven by local meteorological conditions.

Mesoscale convective systems in NW Mexico during the strong ENSO events of 1997-1999

This study presents an analysis of the summertime mesoscale convective systems (MCSs) that developed in northwestern Mexico during the strong ENSO events of 1997-1999. From the analysis of geostationary data, results indicate that the largest number of MCSs was associated with the 1997 El Niño event throughout a longer active period. During the La Niña event of 1999 fewer MCSs were observed, which had developed over a shorter active period. The occurrence of MCSs is linked to the location of the ridge and the anticyclonic anomalies at 500 hPa and 200 hPa, respectively.

Mean state and kinematic properties of mesoscale convective systems over West Africa

A 17-year (1984 to 2000) dataset of brightness temperature (T b) was employed to study the spatial and temporal scales of mesoscale convective systems (MCS) over West Africa. The kinematic properties of MCS were tested using wind products. A threshold brightness temperature (T b) of ≤213 K and spatial coverage specifications of more than 5000 km2 were used as two set criteria for initiating MCS tracking. MCS occurrences vary in seasons and locations over West Africa, and their activities vary with different weather zones. They can appear at any time of the day, but this study revealed a significant preference for early morning hours and night hours over continental West Africa. The well-organized systems occur between July and September in the Sahel, and between May and September in the Savanna band. MCS activities in the Gulf of Guinea peak between March and April, while the Savanna and Sahel zones peak between June and August. The produced annual atlas gives a spatial account of areas of MCS dominance in West Africa. The presence of African Easterly Jet (AEJ) and Tropical Easterly Jet (TEJ), and deep monsoon depth all characterize an environment where MCS thrive. Kinematic study of a typical MCS reveals that the monsoon depth increases at the passage of MCS, with cyclonic vorticity dominating from the surface to 300 hpa while anticyclonic vorticity was observed around 200 hpa, and this confirms the importance of low level convergence and upper level divergence as the major requirements for storm mobilization and maintenance.

Evaluation of atmospheric turbulence, energy exchanges and structure of convective cores during the occurrence of mesoscale convective systems using MST radar facility at Gadanki

Mesoscale convective systems (MCSs) wreak lots of havoc and severe damage to life and property due to associated strong gusty winds, rainfall and hailstorms even though they last for an hour or so. Planetary boundary layer (PBL) plays an important role in the transportation of energy such as momentum, heat and moisture through turbulence into the upper layers of the atmosphere and acts as a feedback mechanism in the generation and sustenance of MCS. In the present study, three severe thunderstorms that occurred over mesosphere–stratosphere–troposphere (MST) radar facility at National Atmospheric Research Laboratory (NARL), Gadanki, India, have been considered to understand turbulence, energy exchanges and wind structure during the different epochs such as pre-, during and after the occurrence of these convective episodes. Significant changes in the turbulence structure are noticed in the upper layers of the atmosphere during the thunderstorm activity. Identified strong convective cores with varying magnitudes of intensity in terms of vertical velocity at different heights in the atmosphere discern the presence of shallow as well as deep convection during initial, mature and dissipative stages of the thunderstorm. Qualitative assessments of these convective cores are verified using available Doppler Weather Radar imageries in terms of reflectivity. The MST radar derived horizontal wind profiles are in good comparison with observed radiosonde winds. Significant variations in the surface meteorological parameters, sensible heat flux and turbulent kinetic energy as well as horizontal wind profiles are noticed during the different epochs of the convective activity. This work is useful in evaluating the performance of PBL schemes of mesoscale models in simulating MCS.

Trends in the distributions of aggregated monthly precipitation over the La Plata Basin

AbstractPositive trends in annual rainfall in the La Plata Basin (LPB), south of 20°S observed in the last four decades of the twentieth century were not reversed and became more statistically significant when calculated until 2005. These trends were part of a more general change in the monthly precipitation distribution including extreme precipitation.Precipitation in dry and extremely dry months (below the 35th percentile) has been decreasing in the whole LPB region south of 22°S. On the contrary, precipitation in the above normal (between the 65th and 90th percentile) and the extremely high rainfall (above the 90th percentile) ranges has been increasing accounting for most of the annual precipitation trends. More than a steady trend, there has been an abrupt change in extreme monthly precipitation concentrated between 1977 and 1983.The analysis of intensity and frequency of extreme events was done fitting Generalized Extreme Values (GEV) and Poisson distributions. Each distribution was fitted with and without trends in the location parameter and tested to determine the best fit in each case. The regions where GEV with a positive trend was the best fit coincide with areas affected by extensive floods during the last decades. Spatially aggregated results highlight the signal of change towards higher maximum monthly precipitations for a wide span of return periods.The atmospheric circulation associated with cases where extreme monthly precipitation was observed in most of the stations was studied through the integrated water vapour transport in the lower troposphere and its associated divergence. During warm months, an intense northern low‐level water vapour flow with two convergence nuclei, one over eastern Argentina, southern Brazil and Uruguay, and the other over western Argentina, along with a weakened south Atlantic Convergence Zone was associated with the more extreme precipitation months favouring the occurrence of Mesoscale Convective Systems. Copyright © 2011 Royal Meteorological Society

Generation processes of mesoscale convective systems following midlatitude troughs around the Sichuan Basin

[1] The generation processes of mesoscale convective systems (MCSs) that occurred over the Sichuan Basin in China were revealed in the early 2008 monsoon season. MCS occurrences detected in METEOSAT geostational satellite images are associated with the traveling of midlatitude troughs after the onset of the Indian monsoon. Three episodes of large-scale MCSs were generated under synoptic conditions of merging southwesterly low-level monsoon flows with a northerly midlatitude air mass following the trough in the leeward of the Tibetan Plateau without direct migration of the vortex generated from the plateau surface. Numerical simulations using a weather research and forecast (WRF) model showed that the MCS was triggered in the evening by strengthening of the low-level wind convergences with horizontal shear between the southerly monsoon flow, with large convective available potential energy, and the northerly dry intrusion. A sudden increase in the northerly winds was confirmed by sonde observation data in the western basin, and the winds were simulated as intrusions passing over the Qinling Mountains when the daytime clouds over the mountain were diminished. Sensitivity experiments by a WRF simulation revealed that the topography of the Sichuan Basin was able to capture the dry intrusion at the bottom to prevent the propagation of disturbances from the plateau and to cause the sudden onset of MCSs apart from the plateau with a heavy precipitation zone.

Climatology of large peak current cloud‐to‐ground lightning flashes in southeastern Brazil

The goal of this article is to present the first climatology of large peak current cloud‐to‐ground (LPCCG) flashes in southeastern Brazil, in terms of flash density, percentage of positive LPCCG flashes, peak current, and diurnal distributions. The results are based on data provided by the Brazilian Lightning Detection Network (BrasilDat) from 1999 to 2006, and only flashes with peak currents &gt;75 kA recorded during the months of December, January, February, and March (the approximate summer season in the Southern Hemisphere) were considered in order to compare with similar data obtained by Lyons et al. (1998) in the contiguous United States. The LPCCG data set, consisting of approximately 122,000 flashes, is currently the largest data set available for the tropical region. The LPCCG flashes represent about 3% of all flashes recorded during this period. All LPCCG distributions were obtained for both negative and positive flashes. The flash density distributions for negative and positive LPCCG flashes are different and furthermore differ from the flash density distributions for all negative and positive cloud‐to‐ground (CG) flashes. This suggests that the flash density distribution of CG flashes is peak current dependent. While the negative LPCCG flash density distribution has no significant dependence on any specific geographical or meteorological feature, the positive LPCCG flash density distribution and the distribution of the percentage of positive LPCCG flashes are closely related to the occurrence of mesoscale convective systems. The peak current and diurnal distributions of LPCCG flashes were found to be similar to those obtained in the contiguous United States.

Regional Eta model experiments: SALLJEX and MCS development

The rainfall regime over La Plata Basin is strongly influenced by Mesoscale Convective Systems (MCS) that develop during night time, associated with the Low‐Level Jet (LLJ) to the east of the Andes. Since they are mesoscale systems, their predictability depends on the model resolution and its ability to represent the main features associated with their development. This study aimed at finding the best configuration of the regional Eta model applied to the region of frequent MCS development to the east of the Andes and to analyze the performance of the model at high resolution, simulating specific MCS cases using two convection schemes. Three experiments were performed for the South American Low‐Level Jet Experiment (SALLJEX) period. Performance of the nonhydrostatic version was better than the hydrostatic version in cases of MCS development. The use of estimated instead of climatological soil moisture in the model, improved the results for several synoptic variables. Evaluation of the convection parameterization scheme indicated a better simulation using the Kain‐Fritsch (KF) rather than the Betts‐Miller‐Janjic scheme in the cases of MCS development. Therefore the best configuration of the Eta model for the simulation of the MCS occurrences over northern Argentina is the nonhydrostatic version using KF convection scheme and estimated soil moisture. With this configuration, the model was able to simulate the precipitation and the main atmospheric characteristics associated with MCS development, such as the upper level jet, the LLJ, humidity, and associated mechanisms for ascending motion, 72 hours in advance.

Influência dos sistemas de altas e baixas pressões e da Temperatura da Superfície do Mar do Atlântico Sul no desenvolvimento de Sistemas Convectivos de Mesoescala sobre o Rio Grande do Sul

In this work the influences of the positioning of high and low pressures systems centers at South Atlantic Ocean and Sea Surface Temperature (SST) anomalies of Atlantic and Pacific Oceans are analysed in association to the occurrence of Mesoscale Convective Systems (MCS) in Rio Grande do Sul (RS) State. The selected period involves four years of February (2002-2005). It was utilized geostationary satellite imagery, values of Sea Surface Temperature (SST) anomalies of the Atlantic and Pacific Oceans and pluviometric precipitation data observed on the State. The horizontal fields of atmospheric pressure and streamslines were obtained from simulations made with the mesoscale model MM5. The results showed that for the analysed period there was one rainy February in the State and three months of drought. For the drought months, the number of observed MCS was inferior, up to six times, to the observed one in the rainy month. Still, in the dry months, the MCS presented shorter duration in relation to the ones observed in the rainy February. For all the analysed period, the MCS dissipation occurred to the east of its position of formation, in the majority of the cases. Although the differences found between all the analysed MCS, the preferential time in which they formed, 12 and 18 UTC, predominated in all period. The large scale and mesoscale circulation patterns had shown that in the rainy month, the centers of subtropical high pressure systems located on the Atlantic Ocean were positioned near the SSA coast, where the SST anomalies values were positive. The opposite were observed during the drought months.

Comments on “A Preliminary Study of Severe Wind-Producing MCSs in Environments of Limited Moisture”

Corresponding author address: Dr. Charles A. Doswell III, Cooperative Institute for Mesoscale Meteorological Studies, 120 David L. Boren Blvd., Ste. 2100, Norman, OK 73072-7304. Email: cdoswell@gcn.ou.edu

A MASCOTTE-based characterization of MCSs over Spain, 2000–2002

A 3-year Mesoscale Convective Systems (MCSs) database, which extends from 2000 to 2002, has been built for the Iberian Peninsula and the Balearic Islands using the objective method MASCOTTE (MAximum Spatial COrrelation Technique). It was originally developed to track the evolution of convective systems over the Amazon region; after modifications, it is able to track MCS evolution even with an hour and a half of missed images and provides essential information of both dynamical and morphological characteristics of MCSs. MASCOTTE is tested against a visual and subjective method, and is found to offer advantages such as automation and a simple and efficient operation that make it very useful for building large MCS databases. Thirty-five MCSs were found between June and October, most of them originated along the Mediterranean coast and near the Pyrenees, showing an increasing occurrence from June to September, when the maximum is found. The regions most influenced by MCS occurrences are Balearic Islands, Valencia, Catalonia, Murcia and the Basque Country. The MCSs tend to be small, short-lived and linear, usually moving eastward or northeastward with low velocities. The MCSs-associated precipitation presents high variability, ranging from 80 to 0 mm h −1 as maximum hourly records. Two different convective regions are identified based on MCS behavior in extreme precipitation events: Northern Spain (the Basque Country) with abundant and continuous precipitation regime but little MCS influence, and the Mediterranean coast, where precipitation is sporadic but much more intense.