Abstract
A climatology of synoptic drylines on the subtropical southern African interior plateau (SAP) is developed using ERA5 reanalysis specific humidity and surface temperature gradients and an ...objective detection algorithm. Drylines are found to occur regularly during spring and summer (September–March), and almost daily during December of that period, but rarely in winter. A westward shift in peak dryline frequency takes place through the summer. Drylines peak first over the eastern parts of the SAP during November with a mean of 10 drylines and then over the central (mean of 12) and western SAP (mean of 20) in December. During midsummer, drylines over the eastern SAP are negatively correlated with drylines in the west. Between 1980 and 2020, a significant correlation exists between ENSO and dryline days over the eastern (
r
= 0.44;
p
value = 0.004) and central (
r
= 0.41;
p
value = 0.008) SAP with fewer drylines (up to 10) occurring during years with increased surface moisture and more drylines (up to 45) occurring during years with decreased surface moisture. Drylines forming over the eastern parts of the SAP were more likely to move westward than drylines over the central and western parts. Onset times across the SAP show that drylines have a tendency to form during either the late morning to early afternoon (1100 and 1400 LST) or during the early evening hours (1700 and 2000 LST), suggesting that the surface heat trough (Kalahari heat low) and westward moisture transport mechanisms, such as the Limpopo low-level jet and ridging highs, are responsible for the formation of most drylines across the SAP.
Significance Statement
“Drylines” are used to describe boundaries separating regions of very dry air from those with much higher moisture content. The importance of these drylines is that they tend to act as a trigger for thunderstorms, which can produce severe weather. In this study, we build a long-term climatological description of drylines in subtropical southern Africa. We find that drylines are most frequent over eastern South Africa during the early summer, a time when storms with large hail and damaging winds are most likely to occur. Drylines are sensitive to moisture circulation patterns and respond differently during El Niño and La Niña years, with generally more drylines during El Niño over eastern South Africa and fewer during La Niña.
Long-term trends in the historical frequency of environments supportive of atmospheric convection are unclear, and only partially follow the expectations of a warming climate. This uncertainty is ...driven by the lack of unequivocal changes in the ingredients for severe thunderstorms (i.e., conditional instability, sufficient low-level moisture, initiation mechanism, and vertical wind shear). ERA5 hybrid-sigma data allow for superior characterization of thermodynamic parameters including convective inhibition, which is very sensitive to the number of levels in the lower troposphere. Using hourly data we demonstrate that long-term decreases in instability and stronger convective inhibition cause a decline in the frequency of thunderstorm environments over the southern United States, particularly during summer. Conversely, increasingly favorable conditions for tornadoes are observed during winter across the Southeast. Over Europe, a pronounced multidecadal increase in low-level moisture has provided positive trends in thunderstorm environments over the south, central, and north, with decreases over the east due to strengthening convective inhibition. Modest increases in vertical wind shear and storm-relative helicity have been observed over northwestern Europe and the Great Plains. Both continents exhibit negative trends in the fraction of environments with likely convective initiation. This suggests that despite increasing instability, thunderstorms in a warming climate may be less likely to develop due to stronger convective inhibition and lower relative humidity. Decreases in convective initiation and resulting precipitation may have long-term implications for agriculture, water availability, and the frequency of severe weather such as large hail and tornadoes. Our results also indicate that trends observed over the United States cannot be assumed to be representative of other continents.
The research was carried out on 3 apple varieties, namely Golden delicious, Jonathan and Starkrimson, grown in the N-E area of Romania, within the Research Station for fruit growing Iasi, on ...Fălticeni development center. The plantation was established in 1990, being in 31 since planting. The trees are grafted on the MM106 rootstock, with a planting distance of 4 meters between rows and 2.5 meters between trees, with a density of 1000 trees/ha. During the agricultural year 2021, hail was observed as an extreme climatic phenomenon, recorded in June, July and August, when the trees were in the phenological stage BBCH 71-74, BBCH 75, BBCH 77 and BBCH 79. Extreme phenomena were accompanied by heavy rains and storms that affected both the quality and quantity of fruit production. The highest degree of damage was recorded in the Golden delicious variety in all four hail falls, with a percentage between 5% and 67%. Therefore, the fruit production was affected, their quality being impaired and not being commercialized as high quality fruit, for fresh consumption, but only industrialized.
Based on the hail data of the China Meteorological Administration, the spatial and temporal distributions of hail disaster eents in China during 2010-2020 are studied by using the statistical method ...and GIS technology. The result is shown below. (1) The number of stations and the days of hails in China increase, while the number of severe hails decreases during 2010-2020. (2) The seasonal change is significant for the number of stations and the days of hails with the maximum in summer and the minimum in winter. In terms of monthly variation, hail occurs most often in June and least often in November. In southwest and central China, the monthly variation of the number of stations and the days of hails is bimodal. The monthly distribution of severe hail is similar to that of hail, but it occurs least often in December. The severe hail occurs most frequently in southwest China. (3) For diurnal variation, hail or severe hail mainly occurrs from afternoon to evening. The peak appears 1-hour later in northwest Chin
We study a transportation network company (TNC) that offers on-demand solo and pooling e-hail services in an aggregate mobility service market, while competing with transit for passengers. The market ...equilibrium is established based on a spatial driver–passenger matching model that determines the passenger wait time for both solo and pooling rides. We prove, under mild conditions, this system always has an equilibrium solution. Built on the market equilibrium, three variants of pricing problems are analyzed and compared, namely, (i) profit maximization, (ii) profit maximization subject to regulatory constraints, and (iii) social welfare maximization subject to a revenue-neutral constraint. A comprehensive case study is constructed using TNC data collected in the city of Chicago. We found pooling is desirable when demand is high but supply is scarce. However, its benefit diminishes quickly as the average en-route detour time (i.e., the difference between the average duration of solo and pooling trips) increases. Without regulations, a mixed strategy—providing both solo and pooling rides—not only achieves the highest profit and trip production in most scenarios, but also gains higher social welfare. The minimum wage policy can improve social welfare in the short term. However, in the long run, the TNC could react by limiting the size of the driver pool, and consequently, render the policy counterproductive, even pushing social welfare below the unregulated level. Moreover, by maintaining the supply and demand of ride-hail at an artificially high level, the minimum wage policy tends to exacerbate traffic congestion by depressing the use of collective modes (transit and pooling). A congestion tax policy that penalizes solo rides promotes pooling, but may harm social welfare. However, it promises to increase both social welfare and pooling ratio when jointly implemented with the minimum wage policy.
•We study a transportation network company that offers solo and pooling e-hail services and competes with transit.•The market equilibrium is established based on a novel spatial driver–passenger matching model.•We analyze the platform’s pricing strategies under various objectives and regulatory constraints.•The minimum wage policy can improve social welfare in the short term but could be harmful in the long run.•A congestion tax policy that penalizes solo rides promotes pooling, but may harm social welfare.
Severe hailstorms represent some of Australia's most costly natural disasters. In particular, the densely populated east‐coast cities of Brisbane and Sydney have both been impacted by events that ...individually produced over AU$1 billion in insured losses. In this study, the frequency of damaging hailstorms in these regions is assessed over an eight‐year period using single‐polarisation radar observations. Reflectivity data from multiple radars are carefully calibrated and merged to produce daily grids of MESH (the maximum expected size of hail) at 1 km spatial resolution. Neighbourhood contingency tables are then used to define an optimal MESH threshold for identifying damaging hail events. This analysis makes use of a unique insurance dataset, comprising building‐scale exposure and claim data over a multi‐year period. Overall, damaging hailstorms occur on an average of 26 and 32 days per year in the Brisbane and Sydney regions, respectively. The actual cities of Brisbane and Sydney both experience about five damaging hailstorms annually. In both regions, the highest hail frequencies occur along the coastal slopes of the Great Dividing Range, with more localised maxima highlighting the potential role of mesoscale circulations in storm initiation and intensification. For Brisbane, the seasonal cycle shows a pronounced peak in December, while in Sydney hail frequencies are high throughout the warm season (November–March). This difference reflects the distinct seasonal cycles of convective instability in the two regions. Consistent with previous studies, the combination of CAPE and deep‐layer shear is found to provide reasonable discrimination of environments conducive to severe hailstorms.
Using ground‐based radar observations, atmospheric soundings, and a unique insurance dataset, we investigate the climatology of damaging hailstorms in two domains centred on the major Australian cities of Brisbane and Sydney. The figure shows the annual frequency of damaging hail in the two domains on a 10 × 10 km2 grid.
As lightning-detection records lengthen and the efficiency of severe weather reporting increases, more accurate climatologies of convective hazards can be constructed. In this study we aggregate ...flashes from the National Lightning Detection Network (NLDN) and Arrival Time Difference long-range lightning detection network (ATDnet) with severe weather reports from the European Severe Weather Database (ESWD) and Storm Prediction Center (SPC) Storm Data on a common grid of 0.25° and 1-h steps. Each year approximately 75–200 thunderstorm hours occur over the southwestern, central, and eastern United States, with a peak over Florida (200–250 h). The activity over the majority of Europe ranges from 15 to 100 h, with peaks over Italy and mountains (Pyrenees, Alps, Carpathians, Dinaric Alps; 100–150 h). The highest convective activity over continental Europe occurs during summer and over the Mediterranean during autumn. The United States peak for tornadoes and large hail reports is in spring, preceding the maximum of lightning and severe wind reports by 1–2 months. Convective hazards occur typically in the late afternoon, with the exception of the Midwest and Great Plains, where mesoscale convective systems shift the peak lightning threat to the night. The severe wind threat is delayed by 1–2 h compared to hail and tornadoes. The fraction of nocturnal lightning over land ranges from 15% to 30% with the lowest values observed over Florida and mountains (∼10%). Wintertime lightning shares the highest fraction of severe weather. Compared to Europe, extreme events are considerably more frequent over the United States, with maximum activity over the Great Plains. However, the threat over Europe should not be underestimated, as severe weather outbreaks with damaging winds, very large hail, and significant tornadoes occasionally occur over densely populated areas.
The effect of anthropogenically enhanced greenhouse gas concentrations on the frequency and intensity of hail depends on a range of physical processes and scales. These include the environmental ...support of the hailgenerating convective storms and the frequency of their initiation, the storm volume over which hail growth is promoted, and the depth of the lower atmosphere conducive to melting. Here, we use high-resolution (convection permitting) dynamical downscaling to simultaneously account for these effects. We find broad geographical areas of increases in the frequency of large hail (≥35-mm diameter) over the United States, during all four seasons. Increases in very large hail (≥50-mm diameter) are mostly confined to the central United States, during boreal spring and summer. And, although increases in moderate hail (≥20-mm diameter) are also found throughout the year, decreases occur over much of the eastern United States in summer. Such decreases result from a projected decrease in convective-storm frequency. Overall, these results suggest that the annual U.S. hail season may begin earlier in the year, be lengthened by more than a week, and exhibit more interannual variability in the future.
Five different criteria that estimate hail signatures from single-polarization radar data are statistically evaluated over a 15-year period by categorical verification against loss data provided by a ...building insurance company. The criteria consider different levels or thresholds of radar reflectivity, some of them complemented by estimates of the 0°C level or cloud top temperature. Applied to reflectivity data from a single C-band radar in southwest Germany, it is found that all criteria are able to reproduce most of the past damage-causing hail events. However, the criteria substantially overestimate hail occurrence by up to 80%, mainly due to the verification process using damage data. Best results in terms of highest Heidke Skill Score HSS or Critical Success Index CSI are obtained for the Hail Detection Algorithm (HDA) and the Probability of Severe Hail (POSH). Radar-derived hail probability shows a high spatial variability with a maximum on the lee side of the Black Forest mountains and a minimum in the broad Rhine valley.
•Hail signals were estimated from 3D radar reflectivity over a 15-year period.•The Hail Detection Algorithm (HAD) and the Probability of Severe Hail (POSH) exhibit the highest prediction skill.•The Waldvogel criteria can be substantially improved with adjusted thresholds.•The spatial variability of the estimated hail signals is related to the orography.
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