scholarly journals Severe Convective Windstorms in Europe: Climatology, Preconvective Environments, and Convective Mode

2020 ◽  
pp. 1-45
Author(s):  
George P. Pacey ◽  
David M. Schultz ◽  
Luis Garcia-Carreras
Keyword(s):  
Convective Available Potential Energy ◽  
Warm Season ◽  
Cold Season ◽  
Lower Percentage ◽  
Convective Storms ◽  
Bow Echo ◽  
Strong Winds ◽  
Convective Mode

Abstract The frequency of European convective windstorms, environments in which they form, and their convective organizational modes remain largely unknown. A climatology is produced using 10 233 severe convective-wind reports from the European Severe Weather Database between 2009–2018. Severe convective-wind days have increased from 50 days yr–1 in 2009 to 117 days yr–1 in 2018, largely because of an increase in reporting. The highest frequency of reports occurred across central Europe, particularly Poland. Reporting was most frequent in summer, when a severe convective windstorm occurred every other day on average. The preconvective environment was assessed using 361 proximity soundings from 45 stations between 2006–2018, and a clustering technique was used to distinguish different environments from nine variables. Two environments for severe convective storms occurred: Type 1, generally low-shear–high-CAPE (mostly in the warm season) and Type 2, generally high-shear–low-CAPE (convective available potential energy; mostly in the cold season). Because convective mode often relates to the type of weather hazard, convective organizational mode was studied from 185 windstorms that occurred between 2013–2018. In Type-1 environments, the most frequent convective mode was cells, accounting for 58.5% of events, followed by linear modes (29%) and the nonlinear noncellular mode (12.5%). In Type-2 environments, the most frequent convective mode was linear modes (55%), followed by cells (36%) and the nonlinear noncellular mode (9%). Only 10% of windstorms were associated with bow echoes, a much lower percentage than other studies, suggesting that forecasters should not necessarily wait to see a bow echo before issuing a warning for strong winds.

scholarly journals A Climatological Study of Extreme Cold Surges along the African Highlands

2017 ◽  
Vol 56 (6) ◽  
pp. 1731-1738 ◽  
Author(s):  
Caitlin C. Crossett ◽  
Nicholas D. Metz
Keyword(s):  
East Coast ◽  
Cold Season ◽  
Meridional Flow ◽  
Extreme Cold ◽  
Cold Surges ◽  
African Highlands ◽  
Hemisphere Winter ◽  
Type 3

AbstractEquatorward-moving cold surges occur along the lee of high terrain during the cold season. Even though the east coast of Africa features high terrain, little research exists on cold surges along the African highlands despite the fact that these surges could have potentially large agricultural and societal effects. This paper examines a 5-yr climatology of the most extreme African-highlands cold surges spanning the 2008–12 period. During these years, 186 cold surges occurred to the lee of the African highlands, with 84 events extending between 30° and 35°S (type 1), 27 extending between 25° and 30°S (type 2), and 75 extending equatorward of 25°S (type 3) based on the 1000–850-hPa thickness pattern. This climatology reveals that extreme African-highlands cold surges have a climatological maximum in September. Cold surges of type 1 and type 2 tend to occur throughout the Southern Hemisphere winter and spring, whereas surges of type 3 are generally confined to the winter months. These cold surges can last from 2 to 8 days, with the highest frequency of events spanning a 3-day period. A typical cold-surge event features maximum 925-hPa meridional flow of 30.0–39.9 kt (1 kt = 0.51 m s−1) that most frequently advects cold Antarctic air to between 15.0° and 24.9°S and at times as far as the equator.

scholarly journals An 18-year climatology of derechos in Germany

2020 ◽  
Vol 20 (5) ◽  
pp. 1335-1351 ◽  
Author(s):  
Christoph P. Gatzen ◽  
Andreas H. Fink ◽  
David M. Schultz ◽  
Joaquim G. Pinto
Keyword(s):  
Mixed Layer ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Warm Season ◽  
The United States ◽  
Cold Season ◽  
Start Time ◽  
Central Germany ◽  
The North ◽  
Wind Events

Abstract. Derechos are high-impact convective wind events that can cause fatalities and widespread losses. In this study, 40 derechos affecting Germany between 1997 and 2014 are analyzed to estimate the derecho risk. Similar to the United States, Germany is affected by two derecho types. The first, called warm-season-type derechos, form in strong southwesterly 500 hPa flow downstream of western European troughs and account for 22 of the 40 derechos. They have a peak occurrence in June and July. Warm-season-type derechos frequently start in the afternoon and move either eastward along the Alpine forelands or northeastward across southern central Germany. Associated proximity soundings indicate strong 0–6 and 0–3 km vertical wind shear and a median of mixed-layer convective available potential energy (mixed-layer CAPE) around 500 J kg−1. The second derecho type, the cold-season-type derecho, forms in strong northwesterly 500 hPa flow, frequently in association with mid-tropospheric potential vorticity (PV) intrusions, and accounts for 18 of the 40 derechos. They are associated with a secondary peak from December to February. Cold-season-type derechos start over or close to the North Sea and primarily affect northern and central Germany; their start time is not strongly related to the peak of diurnal heating. Proximity soundings indicate high-shear–low-CAPE environments. A total of 15 warm-season-type and 9 cold-season-type derechos had wind gusts reaching 33 m s−1 in at least three locations. Although warm-season derechos are more frequent, the path length of cold-season-type derechos is on average 1.4 times longer. Thus, these two types of German derechos are likely to have similar impacts.

scholarly journals Cold-Season Tornadoes: Climatological and Meteorological Insights

2018 ◽  
Vol 33 (3) ◽  
pp. 671-691 ◽  
Author(s):  
Samuel J. Childs ◽  
Russ S. Schumacher ◽  
John T. Allen
Keyword(s):  
United States ◽  
Public Awareness ◽  
Warm Season ◽  
Cold Season ◽  
Reanalysis Data ◽  
The Arctic ◽  
Current State ◽  
The Arctic Oscillation ◽  
Bull's Eye ◽  
Convective Mode

Abstract Tornadoes that occur during the cold season, defined here as November–February (NDJF), pose many societal risks, yet less attention has been given to their climatological trends and variability than their warm-season counterparts, and their meteorological environments have been studied relatively recently. This study aims to advance the current state of knowledge of cold-season tornadoes through analysis of these components. A climatology of all (E)F1–(E)F5 NDJF tornadoes from 1953 to 2015 across a domain of 25°–42.5°N, 75°–100°W was developed. An increasing trend in cold-season tornado occurrence was found across much of the southeastern United States, with a bull’s-eye in western Tennessee, while a decreasing trend was found across eastern Oklahoma. Spectral analysis reveals a cyclic pattern of enhanced NDJF counts every 3–7 years, coincident with the period of ENSO. La Niña episodes favor enhanced NDJF counts, but a stronger relationship was found with the Arctic Oscillation (AO). From a meteorological standpoint, the most-tornadic and least-tornadic NDJF seasons were compared using NCEP–NCAR reanalysis data of various severe weather and tornado parameters. The most-tornadic cold seasons are characterized by warm and moist conditions across the Southeast, with an anomalous mean trough across the western United States. In addition, analysis of the convective mode reveals that NDJF tornadoes are common in both discrete and linear storm modes, yet those associated with discrete supercells are more deadly. Taken together, the perspectives presented here provide a deeper understanding of NDJF tornadoes and their societal impacts, an understanding that serves to increase public awareness and reduce human casualty.

scholarly journals Parainfluenza virus infections in the Cirencester Survey: Seasonal and other characteristics

1981 ◽  
Vol 87 (3) ◽  
pp. 393-406 ◽  
Author(s):  
R. Edgar Hope-Simpson
Keyword(s):  
Respiratory Diseases ◽  
Cold Season ◽  
Parainfluenza Virus ◽  
Virus Infections ◽  
Young Infants ◽  
Population Type ◽  
Winter Peak ◽  
Type 3

SummaryParainfluenza viruses were isolated 165 times during 14 years surveillance of the illnesses of a general practice population of around 3700. Type 1 isolations numbered 57, type 2 isolations 22 and type 3 isolations 86, representing annual rates of 33, 13 and 50 infections respectively per 10000 of population. Type 4 parainfluenza virus was not isolated. Three major classes of illness gave the following rates: sore throats (Throats) nine, acute febrile respiratory diseases (FRD) 23, acute non-febrile respiratory diseases (non-FRD) 71. The illnesses caused by the three types isolated were similar. Type 1 infections were most abundant in November and type 2 infections in December, and only 11.4 % of these types were isolated in the warm semester April through September. Type 3 infections were seasonally bi-modal, with a winter peak in January and an even greater prevalence (66% of the total) in the warm semester. Type 3 infections in the warmer months and in the later years of the Survey were usually more severe. Type 3 virus may therefore be heterogeneous, one subtype possessing and the other lacking the genetic mechanism of ‘cold-season’ prevalence. Geographical discontinuity between summer and winter isolations strengthens the case for the existence of the two subtypes of type 3 parainfluenza virus.Type 3 infections caused the majority of the infections in very young infants. Type 2 infections were widely distributed at all ages. Females were attacked more often than males: type 1, 68.4%; type 2,636%; type 3, 53.5%. Type 3 infections in males outnumbered those in females up to 60 years of age, whereas female predominance became apparent in types 1 and 2 before 10 years of age.All types were widely and sparsely distributed, areas of prevalence changing from year to year. Recurrences occurred only twice, both with type 3 infections. Six persons suffered both a type 1 and a type 3 infection, and one person suffered both a type 2 and a type 3 infection.

scholarly journals An 18-year climatology of derechos in Germany

2019 ◽  
Author(s):  
Christoph P. Gatzen ◽  
Andreas H. Fink ◽  
David M. Schultz ◽  
Joaquim G. Pinto
Keyword(s):  
North Sea ◽  
Mixed Layer ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Warm Season ◽  
The United States ◽  
Cold Season ◽  
Central Germany ◽  
The North ◽  
The North Sea

Abstract. Derechos are high-impact convective wind events that can cause fatalities and widespread losses. In this study, 40 derechos affecting Germany between 1997 and 2014 are analysed to estimate the derecho risk. Similar to the United States, Germany is affected by two derecho types. The first derecho type forms in south-westerly 500-hPa flow downstream of intense west-European troughs and accounts for 22 of the 40 derechos. These derechos are named warm-season type due to their peak occurrence in June and July. Warm-season type derechos frequently start over southwestern Germany in the afternoon and move either eastward along the Alpine forelands or north-eastward across southern central Germany. Only one warm-season derecho moved across the North Sea and one moved across the Baltic Sea in the 18-year period. Proximity soundings of German warm-season type derechos indicate strong deep-layer vertical wind shear with a median of 20 m s−1 0–6-km shear and mixed-layer Convective Available Potential Energy (mixed-layer CAPE) between 20 and 2600 J kg−1 with a median around 500 J kg−1. The second derecho type forms in north-westerly 500-hPa flow and accounts for 18 of the 40 derechos. These derechos form in strong north-westerly flow, frequently in association with mid-tropospheric PV intrusions. They are named cold-season type because they are associated with a secondary peak from December to February. Cold-season type derechos start over or close to the North Sea and primarily affect north and central Germany; their start time is not strongly related to the peak of diurnal heating. Proximity soundings indicate high-shear–low-CAPE environments with a median 0–6-km shear of 35 m s−1 and a median mixed-layer CAPE of 3 J kg−1. Environmental CAPE is zero in almost half of cold-season type proximity soundings. Fifteen warm-season type and nine cold-season type derechos had wind gusts reaching 33 m s−1 in at least at three locations. Although warm-season derechos are more frequent, the path length of cold-season type derechos is on average 1.4 times longer. Thus, these two types of German derechos are likely to have similar impacts.

Phosphatidylserine externalization in sickle red blood cells: associations with cell age, density, and hemoglobin F

Blood ◽  
2003 ◽  
Vol 102 (1) ◽  
pp. 365-370 ◽  
Author(s):  
Zahida Yasin ◽  
Scott Witting ◽  
Mary B. Palascak ◽  
Clinton H. Joiner ◽  
Donald L. Rucknagel ◽  
...  
Keyword(s):  
Sickle Cell Disease ◽  
Sickle Cell ◽  
Fetal Hemoglobin ◽  
Lower Percentage ◽  
Cell Disease ◽  
Low Level ◽  
Sickle Cells ◽  
Cell Age

Abstract Phosphatidylserine (PS) is normally confined to the cytoplasmic leaflet of the red blood cell (RBC) membrane, but some sickle RBCs expose PS in the outer leaflet (PS+ cells). This study examined the relationships among PS externalization, fetal hemoglobin content, hydration state, and cell age. Sickle RBCs exhibit a wide range of PS externalization. Those with low-level exposure (type 1 PS+) include many young transferrin-receptor-positive (TfR+) cells. This is not specific for sickle cell disease because many nonsickle TfR+ cells are also PS+. RBCs with higher PS exposure (type 2 PS+) appear to be more specific for sickle cell disease. Their formation is most likely sickling dependent because type 2 PS+ dense sickle cells have a lower percentage of fetal hemoglobin (HbF) than PS- cells in the same density fraction (1.7 vs 2.9; n = 8; P < .01). In vivo experiments using biotin-labeled sickle cells showed a sharp decrease in the percentage of circulating, labeled PS+ cells in the first 24 hours after reinfusion. This decrease was confined to type 1 PS+ cells and was thus consistent with the reversal of PS exposure in very young cells. As the labeled cells aged in the circulation, the percentages of type 1 and type 2 PS+ cells increased. These studies indicate that PS externalization in sickle cells may be low level, as observed in many immature cells, or high level, which is associated with dehydration and appears to be more specific for sickle RBCs. (Blood. 2003;102: 365-370)

scholarly journals A Case Study of Severe Winter Convection in the Midwest

2009 ◽  
Vol 24 (1) ◽  
pp. 121-139 ◽  
Author(s):  
Brian P. Pettegrew ◽  
Patrick S. Market ◽  
Raymond A. Wolf ◽  
Ronald L. Holle ◽  
Nicholas W. S. Demetriades
Keyword(s):  
Warm Season ◽  
Mesoscale Convective System ◽  
Ground Level ◽  
Cold Season ◽  
Thunderstorm Activity ◽  
Squall Line ◽  
Convective System ◽  
Short Period ◽  
Strong Winds ◽  
Central Illinois

Abstract Between 2100 UTC 11 February 2003 and 0200 UTC 12 February 2003, a line of thunderstorms passed swiftly through parts of eastern Iowa and into north-central Illinois. Although this storm somewhat resembled a warm season, line-type mesoscale convective system, it was unique in that the thunderstorm winds exceeded the severe criterion (50 kt; 25.7 m s−1) during a snowburst. While the parent snowband deposited only 4 cm of snow, it did so in a short period and created a treacherous driving situation because of the ensuing near-whiteout conditions caused by strong winds that reached the National Weather Service severe criteria, as the line moved across central Illinois. Such storms in the cold season rarely occur and are largely undocumented; the present work seeks to fill this void in the existing literature. While this system superficially resembled a more traditional warm season squall line, deeper inspection revealed a precipitation band that failed to conform to that paradigm. Radar analysis failed to resolve any of the necessary warm season signatures, as maximum reflectivities of only 40–45 dBZ reached no higher than 3.7 km above ground level. The result was low-topped convection in a highly sheared environment. Moreover, winds in excess of 50 kt (25.7 m s−1) occurred earlier in the day without thunderstorm activity, upstream of the eventual severe thundersnow location. Perhaps of greatest importance is the fact that the winds in excess of the severe criterion were more the result of boundary layer mixing, and largely coincident with the parent convective line. This event was a case of forced convection, dynamically linked to its parent cold front via persistent frontogenesis and the convective instability associated with it; winds sufficient for a severe thunderstorm warning, while influenced by convection, resulted from high momentum mixing downward through a dry-adiabatic layer.

Biases in the Prediction of Convective Storm Characteristics with a Convection Allowing Ensemble

2021 ◽  
Author(s):  
Joseph A. Grim ◽  
James O. Pinto ◽  
Thomas Blitz ◽  
Kenneth Stone ◽  
David C. Dowell
Keyword(s):  
Warm Season ◽  
Storm Events ◽  
Convective Storm ◽  
Convective Storms ◽  
Convective Systems ◽  
Object Based ◽  
Mesoscale Convective ◽  
Macrophysical Properties ◽  
Storm Characteristics ◽  
Convective Mode

AbstractThe severity, duration, and spatial extent of thunderstorm impacts is related to convective storm mode. This study assesses the skill of the High Resolution Rapid Refresh Ensemble (HRRR-E) and its deterministic counterpart (HRRRv4) at predicting convective mode and storm macrophysical properties using 35 convective events observed during the 2020 warm season across the eastern U.S. Seven cases were selected from each of five subjectively-determined convective organization modes: tropical cyclones, mesoscale convective systems (MCSs), quasi-linear convective systems, clusters, and cellular convection. These storm events were assessed using an object-based approach to identify convective storms and determine their individual size. Averaged across all 35 cases, both the HRRR-E and HRRRv4 predicted storm areas were generally larger than observed, with this bias being a function of storm lifetime and convective mode. Both modeling systems also under-predicted the rapid increase in storm counts during the initiation period, particularly for the smaller-scale storm modes. Interestingly, performance of the HRRRv4 differed from that of the HRRR-E, with the HRRRv4 generally having a larger bias in total storm area than the HRRR-E due to HRRRv4 predicting up to 66% more storm objects than the HRRR-E. The HRRR-E accurately predicted the convective mode 65% of the time, with complete misses being very rare (<5% of the time overall). However, an evaluation of rank histograms across all 35 cases revealed that the HRRR-E tended to be under-dispersive when predicting storm size for all but the MCS mode.

scholarly journals Differences between Severe and Nonsevere Warm-Season, Nocturnal Bow Echo Environments

2021 ◽  
Vol 36 (1) ◽  
pp. 53-74
Author(s):  
Ezio L. Mauri ◽  
William A. Gallus Jr.
Keyword(s):  
Convective Available Potential Energy ◽  
Warm Season ◽  
Wind Damage ◽  
Wind Component ◽  
Predictive Skill ◽  
Shear Component ◽  
Wind Potential ◽  
Bow Echo ◽  
Composite Parameter ◽  
Two Parameters

AbstractNocturnal bow echoes can produce wind damage, even in situations where elevated convection occurs. Accurate forecasts of wind potential tend to be more challenging for operational forecasters than for daytime bows because of incomplete understanding of how elevated convection interacts with the stable boundary layer. The present study compares the differences in warm-season, nocturnal bow echo environments in which high intensity [>70 kt (1 kt ≈ 0.51 m s−1)] severe winds (HS), low intensity (50–55 kt) severe winds (LS), and nonsevere winds (NS) occurred. Using a sample of 132 events from 2010 to 2018, 43 forecast parameters from the SPC mesoanalysis system were examined over a 120 km × 120 km region centered on the strongest storm report or most pronounced bowing convective segment. Severe composite parameters are found to be among the best discriminators between all severity types, especially derecho composite parameter (DCP) and significant tornado parameter (STP). Shear parameters are significant discriminators only between severe and nonsevere cases, while convective available potential energy (CAPE) parameters are significant discriminators only between HS and LS/NS bow echoes. Convective inhibition (CIN) is among the worst discriminators for all severity types. The parameters providing the most predictive skill for HS bow echoes are STP and most unstable CAPE, and for LS bow echoes these are the V wind component at best CAPE (VMXP) level, STP, and the supercell composite parameter. Combinations of two parameters are shown to improve forecasting skill further, with the combination of surface-based CAPE and 0–6-km U shear component, and DCP and VMXP, providing the most skillful HS and LS forecasts, respectively.

scholarly journals A 10-Year Radar-Based Climatology of Mesoscale Convective System Archetypes and Derechos in Poland

2020 ◽  
Vol 148 (8) ◽  
pp. 3471-3488
Author(s):  
Artur Surowiecki ◽  
Mateusz Taszarek
Keyword(s):  
Warm Season ◽  
Mesoscale Convective System ◽  
Morphological Type ◽  
Cold Season ◽  
Convective System ◽  
The West ◽  
Convective Systems ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
System Archetypes

Abstract In this study, a 10-yr (2008–17) radar-based mesoscale convective system (MCS) and derecho climatology for Poland is presented. This is one of the first attempts of a European country to investigate morphological and precipitation archetypes of MCSs as prior studies were mostly based on satellite data. Despite its ubiquity and significance for society, economy, agriculture, and water availability, little is known about the climatological aspects of MCSs over central Europe. Our results indicate that MCSs are not rare in Poland as an annual mean of 77 MCSs and 49 days with MCS can be depicted for Poland. Their lifetime ranges typically from 3 to 6 h, with initiation time around the afternoon hours (1200–1400 UTC) and dissipation stage in the evening (1900–2000 UTC). The most frequent morphological type of MCSs is a broken line (58% of cases), then areal/cluster (25%), and then quasi-linear convective systems (QLCS; 17%), which are usually associated with a bow echo (72% of QLCS). QLCS are the feature with the longest life cycle. Among precipitation archetypes of linear MCSs, trailing stratiform (73%) and parallel stratiform (25%) are the most common. MCSs are usually observed from April to September, with a peak in mid-July. A majority of MCSs travels from the west, southwest, and south sectors. A total of 16 derecho events were identified (1.5% of all MCS and 9.1% of all QLCS); the majority of them were produced by a warm-season QLCS, whereas only 4 were produced by cold-season narrow cold-frontal rainbands. Warm-season derechos produced a bigger impact than did cold-season events, even though their damage paths were shorter.

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