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The text provides a detailed overview of the weather events that occurred in September and October 2024 across various regions in the United States. It highlights extreme weather conditions such as hurricanes, heatwaves, droughts, wildfires, and record-breaking temperatures and precipitation levels. The devastating impacts of hurricanes Helene and Milton, along with the historical context of these events, are discussed. Additionally, the text includes information on the weather patterns in Alaska during the same period, emphasizing significant storms, coastal flooding, and snowfall events. [Extracted from the article]

This article provides an analysis of the factors driving long-term change in the characteristics of the ice regime of the Northern Caspian Sea using satellite and in situ observation. It assesses the climatic shifts, comparing the linear trend and step change models. We link the stepwise shift in temperatures in the 1980s with the changes in the forms of atmospheric circulation. The decrease in the sum of negative temperatures impacts the length and intensity of winters with the 18–27-day reduction in the freeze period, leading to a shorter period of ice cover and reduced ice thickness by 20–28 cm. [ABSTRACT FROM AUTHOR]

The changing climate could expand northwards in Europe the autumn sowing of cool-season grain legumes to take advantage of milder winters and to escape the increasing risk of terminal drought. Greater frost tolerance is a key breeding target because sudden frosts following mild-temperature periods may produce high winter mortality of insufficiently acclimated plants. The increasing year-to-year climate variation hinders the field-based selection for frost tolerance. This study focused on pea and white lupin with the objectives of (i) optimizing an easy-to-build, high-throughput phenotyping platform for frost tolerance assessment with respect to optimal freezing temperatures, and (ii) verifying the consistency of genotype plant mortality responses across platform and field conditions. The platform was a 13.6 m2 freezing chamber with programmable temperature in the range of −15°C to 25°C. The study included 11 genotypes per species with substantial variation for field-based winter plant survival. Plant seedlings were evaluated under four freezing temperature treatments, i.e., −7°C, −9°C, −11°C, and −13°C, after a 15-day acclimation period at 4°C. Genotype plant mortality and lethal temperature corresponding to 50% mortality (LT50) were assessed at the end of a regrowth period, whereas biomass injury was observed through a 10-level visual score based on the amount of necrosis and mortality after recovery and regrowth. On average, pea displayed higher frost tolerance than white lupin (mean LT50 of −12.8 versus −11.0°C). The genotype LT50 values ranged from −11.6°C to −14.5°C for pea and from −10.0°C to −12.0°C for lupin. The freezing temperature that maximized the genotype mortality variation was −13°C for pea and −11°C for lupin. The genotype mortality at these temperatures exhibited high correlations with LT50 values (0.91 for pea and 0.94 for lupin) and the biomass injury score (0.98 for pea and 0.97 for lupin). The frost tolerance responses in the platform showed a good consistency with the field-based winter survival of the genotypes. Our study indicates the reliability of genotype frost tolerance assessment under artificial conditions for two cool-season grain legumes, offering a platform that could be valuable for crop improvement as well as for genomics and ecophysiological research. [ABSTRACT FROM AUTHOR]

The article "An enthalpy-based model for the physics of ice-crystal icing" in the Journal of Fluid Mechanics introduces a new enthalpy-based model for studying ice-crystal icing in aircraft engines. The model considers mixed-phase accretion layers, providing a more accurate representation of the physical conditions in ice-crystal icing. It compares favorably to existing models, showing thicker icing and water layers due to mixed-phase features. The text discusses non-dimensional parameters, asymptotic solutions, and numerical simulations, emphasizing the need for further research on complex icing scenarios in aviation. [Extracted from the article]

Citrus spp. trees are not fully dormant during the winter months in the northern hemisphere; therefore, they are susceptible to sporadic freeze events of various magnitudes that could decline tree productivity or be lethal. In Feb 2021, winter storm Uri produced freezing air temperatures for nearly 72 hours, which created several degrees of injuries to citrus orchards in southern Texas. Producers in the area implemented combinations of multiple horticultural practices aimed at remediating injuries from the cold spell to stimulate root and tree recovery. However, there is a gap in our understanding of how practices such as compost application (CA) combined with varying rates of nitrogen (N) might facilitate tree recovery. Therefore, we conducted a 2-year field experiment using two CAs as soil amendments in combination with three N rates (112, 168, and 224 kg·ha21 N) to evaluate fruit yield and internal quality, root growth, and recovery of 'Rio Red' grapefruits (Citrus ×paradisi Macf.) and 'Marrs' sweet oranges (Citrus sinensis). The yields of both crops exhibited modest improvement with CA in 2022; however, it was nonsignificant. Moreover, CA elicited more beneficial effects than N rates alone when rehabilitating trees and improving fruit internal quality after freezing events. Grapefruit brix was 4% higher in fruits harvested from trees treated with compost, and grapefruit roots exhibited a twofold dry weight increment with CA. Sweet oranges from trees in the CA treatment had 22% lower acidity compared with that of untreated trees. Overall, our results indicate that citrus producers in southern Texas and other subtropical citrus-producing regions might facilitate the rehabilitation of tree injuries attributed to mild to moderate freeze events with moderate financial gains with the timely application of compost, which enhanced tree fitness and ameliorated fruit productivity declines during subsequent harvests. [ABSTRACT FROM AUTHOR]

The frost heave failure mechanism of fractured rock mass is a complicated problem faced by engineering construction in cold area. In this study, low temperature frost heave test and post-freezing uniaxial compression test on sandstone samples with a water-filled flaw were carried out. The frost heave cracking mode, frost heave pressure, frost heave cracking criterion and the effect of frost heave-induced cracks on post-freezing uniaxial compression failure behavior under different flaw inclination angles (0 ~ 90°) and freezing temperatures (–10~–40 °C) were investigated. Frost heave cracks initiate and extend along the coplanar direction of flaws. The frost heave damage degree decreases with the increase of flaw inclination angle. As the freezing temperature drops, the flaw cracking length first increases greatly, and then decreases, reaching the maximum at − 15 °C. The evolution of frost heave pressure can be divided into six stages: pre-freeze stage, rapid increase stage, rapid decrease stage, stable stage, slight rebound stage and dissipation stage. The peak frost heave pressure first increases and then decreases with the increase of flaw inclination angle, and reaches the maximum at 60°, and increases as the freezing temperature drops. Formulas for calculating the critical stress intensity factor KIC for flaw frost heave cracking are provided, considering flaw inclination angle or freezing temperature. When the flaw is within a certain range of inclination angles (45 ~ 75°), cracks under uniaxial compression will extend from the frost heave-induced cracks. [ABSTRACT FROM AUTHOR]

Temperate winters are getting warmer, the length of the growing season is increasing and mid‐winter fluctuations of warm and freezing temperatures are more frequent. Although typically winter dormant, some herbaceous perennials can maintain or grow green leaves during the winter and more species may do so as winters become warmer. For wintergreen leaves to provide an advantage, they must be able to photosynthesize during the warm spells but also withstand freezing temperatures and fluctuations between the two conditions. To understand the leaf traits of wintergreen herbs, we studied three widely distributed perennial species: Bellis perennis, Plantago lanceolata and Trifolium repens. For contrast between winter and growing season leaves, we measured three common leaf economic traits (LDMC, SLA and leaf N content). To assess freezing tolerance, we measured the ice nucleation temperature and LT50 after frost exposure in winter leaves. To confirm photosynthetic ability, we measured photosynthetic efficiency (Fv/Fm value) in winter and late spring. Additionally, we surveyed the green and dead leaf coverage for herbaceous species in a lawn community from winter to early summer (four surveys in total). We used our observations to determine phenological categories and compared them to historical observations of wintergreenness. All three species had denser leaves with lower nitrogen content in winter than in the growing season and relatively high tolerance of freezing temperatures (average of −8°C ice nucleation temperature and −15°C LT50). Both winter and growing season leaves were capable of photosynthesis, but the efficiency was greater for growing season leaves. In the community survey, a majority of the plant species had green leaves in winter, and many were without dead winter leaves. Many wintergreen herbs had previously been labelled ‘summer green’. With these initial investigations into the traits and phenology of wintergreen herbs, we confirm that wintergreen leaves have different traits from typical growing season leaves and are capable of both photosynthesis and freezing tolerance. Wintergreen herbs have a broad range of phenological strategies and differ from observations 20 years ago. In many temperate regions, winter is becoming a new growing season and thus should be included in phenological studies. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Fluvial sediment dynamics in mountain rivers are changing rapidly in a degrading cryosphere, raising the potential for erosive rainfall and runoff and detrimental effects on downstream areas. Hence, we need to understand better what characterises and drives episodic pulses of water and suspended solids in rivers. Here, we infer different types of such sediment-discharge events from 959 automatically detected events based on 16 metrics derived from 15 min time series of streamflow and suspended sediment concentrations from Vent–Rofental in the high Ötztal Alps, Austria. We use principal component analysis to extract uncorrelated event characteristics and cluster event types with a Gaussian mixture model. We interpret the thus inferred event types with catchment metrics describing antecedent conditions, hydrometeorological forcing, and fraction of catchment area with freezing temperatures and snow cover. We find event magnitude, hysteresis, and event shape complexity to be the main factors characterising the overall event regime. The most important characteristics distinguishing the event types are suspended sediment and streamflow magnitude and complexity of the hydro- and sedigraphs. Sediment-discharge hysteresis is less relevant for discerning event types. We derive four event types that we attribute to (1) compound rainfall–melt extremes, (2) glacier and seasonal snowmelt, (3) freeze–thaw-modulated snowmelt and precipitation events, and (4) late-season glacier melt. Glacier and snowmelt events driven by warm conditions and high insolation were the most frequent and contributed some 40 % to annual suspended sediment yield on average; compound rainfall–melt extremes were the rarest but contributed the second-highest proportion (26 %). Our approach represents a reproducible method for objectively estimating the variety of event-scale suspended sediment transport conditions in mountain rivers, which can provide insights into the contribution of different drivers to annual sediment yields in current and future regimes. Our findings highlight the importance of both meltwater and rainfall–runoff as drivers of high-magnitude suspended sediment fluxes in mountain rivers. [ABSTRACT FROM AUTHOR]

Mechanisms involved in the supercooling of plant tissues as a means of low temperature survival are still not fully understood. We investigated properties that may promote supercooling in overwintering sweet cherry (Prunus avium) flower buds.We conducted experiments on sweet cherry flower buds using differential thermal analysis (DTA) and observed locations of ice formation in the bud structure. We also used anatomical development and water‐soluble dye uptake throughout the overwintering period to identify changes that correlate with gain and loss of supercooling capacity.Our results revealed barriers to ice propagation are likely unique to each primordium, as inferred from exotherms produced from buds subjected to DTA, although multiple primordia may freeze simultaneously. Ice is accommodated between the bud scales and within the bud axis; however, full expression of supercooling was not dependent on the presence of scales. Anatomical and DTA studies revealed a correlation between vascular differentiation in primordia and loss of supercooling in the spring; these observations were at a higher temporal resolution than previously described for Prunus. Furthermore, disturbing tissues subtending the primordia interfered with typical patterns of supercooling, indicated more erratic and numerous exotherms produced during DTA.In summary, sweet cherry flower buds undergo extra‐organ freezing. In winter, a barrier to ice propagation in the region directly subtending primordia protects the flower from freezing damage, but in the spring xylem differentiation in primordia provides a conduit for ice propagation that compromises supercooling. [ABSTRACT FROM AUTHOR]

Wheat is a crucial staple worldwide, serving both human and animal needs. In Iran, where climate conditions vary widely, wheat farming faces significant challenges, especially in areas facing freezing winters and unfavorable temperatures during reproductive stages. Unfortunately, existing models often fail to account these extreme and specific climate conditions, leading to inaccurate predictions, notably in cold areas. To address this issue, wheat dryland farming (WDF) model was evaluated in predicting dryland winter wheat yields in five distinct areas including Shahrekord, Borujen, Koohrang, Farsan, Lordegan, and Ardal in Chahar‐Mahal and Bakhtiari province, Iran. The results showed that changes in precipitation and temperature significantly impacted dryland wheat production. While higher precipitation generally associates with higher yields, this relationship is not always straightforward due to factors like unfavorable precipitation patterns and types (i.e., rainfall or snow). Likewise, unfavorable temperatures, particularly during crucial growth stages and winter freezes, pose significant challenges to wheat growth and yield modeling. The WDF model's performance was evaluated across various temperature conditions in the study area, and it was more accurate in regions with certain minimum and maximum temperature values above thresholds. However, the model performance was poor in colder areas, where freezing temperatures were occurred in winter duration (Shahrekord, Borujen, Koohrang, and Farsan). In order to improve the model's accuracy, a correction factor based on the minimum and maximum air temperatures was incorporated in the model. The findings emphasized the importance of considering both precipitation and temperature dynamics when modeling winter wheat yields, especially in regions with diverse climates. By refining models like WDF, agricultural planners can better forecast the yield fluctuations and address the impacts of climate variability on food security in Iran and similar regions worldwide. [ABSTRACT FROM AUTHOR]

We present a mathematical model that considers the formation of an ice layer with expansion in a container with a moving boundary. The displacement represents the strain of the tank when the solidifying water expands. The results show that the ice and liquid fractions inside the tank depend on the spring constant and dimensions of the tank. If the spring constant tends to infinity, the ice and liquid fractions are those corresponding to an isochoric process. For each temperature, there is a threshold value of the spring constant, below which all the contents of the tank become ice and above which a smaller fraction does so. The threshold value of the spring constant relates to the degree to which water expands as it freezes. Structural design of a tank shows that the process departs from isochoric. Keeping the process completely isochoric requires oversizing the tank with corresponding increases in manufacturing costs and transportation weight. • We model formation of ice in a self pressurizing elastic tank for freezing temperatures. • The model calculates ice fraction as a function of freezing temperature and elastic constant. • The solution includes as a special case the isochoric freezing process. • The model determines the modified spring constant below which all the water becomes ice. • Structural design of a spherical tank shows the process may depart from the isochoric case. [ABSTRACT FROM AUTHOR]

In modern construction, one of the most important factors in the execution of contracts is time. Standard procedures for assessing the frost resistance or concrete are usually very time‐consuming and can take up to 40 days. The current paper is experimentally and practically oriented. It presents an alternative testing method, based on air void network, that allows to assess the frost resistance of concrete within just a few days of taking the samples. X‐ray micro‐CT scans were introduced to obtain the quantitative and qualitative 3D information about the air void microstructure taking into account total air content: A (%), pores of the size below 300 μm in diameter content: A300 (%), specific surface of air voids: α (mm−1) and spacing factor: L (mm) to predict the freeze/thaw durability. To verify the assumptions of the frost resistance method, based on the analysis of pore microstructure, tests of freeze/thaw resistance in accordance with Polish supplement to European Standard were carried out. Presented research revealed that the appropriate microstructure of air pores, in particular, content of micropores with the diameter less than 0.3 mm: A300 combined with a spacing factor: L (mm) can constitute a reliable basis for determining concrete freeze/thaw durability. Thus, the method proposed in the current paper can be effectively used for fast and trustworthy determination of the air‐entrained concrete durability in a short time and without any special preparation of the tested sample that allows immediate preventive or repair actions to be taken if required. [ABSTRACT FROM AUTHOR]

Freeze tolerance is a complex agronomic trait that is difficult to evaluate in the field because of year‐to‐year variation in weather. Discovering plant characteristics closely related to freeze tolerance would enable more effective selection for this important trait. To explore possible physiological mechanisms and search for useful characteristics related to freeze tolerance in winter barley, we conducted field and growth chamber experiments with seven freeze‐tolerant and seven freeze‐susceptible genotypes that exhibited contrasting winter survival in preliminary field screenings. In a 2‐year field experiment, malondialdehyde, proline and water‐soluble carbohydrate concentrations were measured during cold acclimation and deacclimation to investigate differences in osmoregulation and membrane stability between freeze‐tolerant and freeze‐sensitive genotypes. All parameters varied by sampling year, and significant differences between freeze tolerance groups were found mainly during cold deacclimation in the spring. In growth chamber experiments, the size of xylem vessels and stomates was measured with and without cold acclimation. Freeze‐tolerant genotypes had smaller xylem vessels and stomates than freeze‐sensitive genotypes with and without cold acclimation, and small stomatal length was associated with a small xylem vessel area. Thus, it may be possible to improve freeze tolerance in winter barley by selecting smaller xylem and stomate cells. This study also validated germplasms of winter barley with differential freeze tolerance for future projects on breeding for improving winter hardiness and on plant physiology and genetics in response to freezing stress. [ABSTRACT FROM AUTHOR]

As global climate change intensifies, extreme weather events are becoming more frequent, with ice disasters posing an increasingly significant threat to the stable operation of power distribution networks. Particularly during power outages for de-icing, multiple power islands may form within a distribution area, increasing the complexity of grid operations. Existing research has not fully considered the comprehensive coordination of stable operation of these power islands and de-icing maintenance schedules. Therefore, for the potential multi-island operation of distribution networks caused by freezing disasters, this paper first establishes a dynamic island partitioning model based on distribution network reconfiguration technology. Secondly, based on the characteristics of the de-icing phase, a de-icing maintenance schedule model is established. Finally, dispatch optimization of the distribution network is coordinated with the line de-icing maintenance schedule. By adjusting the de-icing strategies and network structure, the aim is to minimize the risk of load loss. The relevant case analysis indicates that the collaborative optimization model established in this paper helps power distribution networks to reduce their economic losses when facing adverse weather conditions. [ABSTRACT FROM AUTHOR]

This study introduced the application of concepts and methods from extreme value theory (EVT) to estimate the probability that daily minimum temperatures exceed springtime critical temperature thresholds for Pinot noir buds and young shoots as a function of springtime phenology. The springtime frost risk estimates were computed spatially for Pinot noir throughout the Willamette Valley (WV) American Viticultural Area (AVA) using a gridded dataset of historical daily minimum surface air temperature data. EVT-based springtime frost risk maps can inform vineyard-management operations by identifying those locations throughout a wine region with a low risk for any cold injury where remedial action is likely not necessary when there is a forecasted frost event. Frost risk estimates were computed for 1991–2021 and 1991–2022 to examine a potentially changed risk profile for springtime frost events throughout the WV AVA due to the April 2022 advective frost event. The April 2022 advective frost event influenced the risk profile throughout the AVA such that an event of its magnitude is now modelled to occur more frequently. The EVT-based risk analysis can be readily updated each year as new data become available. While spatially varying budbreak calculations facilitated computation of the spring frost risk estimates, the EVT approach profiled in this study does not necessarily depend on potentially uncertain predetermined budbreak date estimates. Gridded maps of extreme daily minimum temperature exceedances, reclassified relative to the springtime phenology critical temperature thresholds for Pinot noir, were readily combined with a ripening potential map to identify optimal areas for vineyard site selection throughout the WV AVA. When simultaneously evaluating Pinot noir ripening potential with springtime frost risk using historical data, the limiting factor for vineyard site selection throughout the WV AVA was frost risk, not ripening potential. The study approach is also applicable for other winegrape-growing regions, assessments of winter freeze risk and summertime heatwaves, and with non-gridded observed temperature datasets. [ABSTRACT FROM AUTHOR]

(1) Background. At subzero temperatures, water crystallizes on ice nucleation agents. Researchers have identified ice-nucleating microbes (INMs) in insect digestive tracts that can raise the insect's supercooling point, causing freezing at higher temperatures but slower rates. For freeze-tolerant insects, such gut microbes should allow for slower freezing away from tissues and higher survival rates. For freeze-susceptible insects, however, such microbes could cause a fatal freeze at higher temperatures, and could possibly be used as biocontrol. (2) Methods. A first-ever scoping review was carried out of research on insect-associated INMs, from observational studies attempting to isolate these microbes, to experimental studies applying them and checking for increased mortality. (3) Results. Relatively few research groups have studied insect-associated INMs in any capacity. (4) Conclusions. Several authors hypothesized that such microbes are probably abundant, and their contribution to ice nucleation activity in insects is under-reported. Biocontrol assays using ice-nucleating microbes showed promise, but a risk to non-target organisms has been experimentally confirmed. Future surveys of insect–microbe interactions using molecular tools are likely to reveal new examples, if not new microbe species capable of ice nucleation. [ABSTRACT FROM AUTHOR]

Ice-nucleating particles (INPs) are an essential class of aerosols found worldwide that have far-reaching but poorly quantified climate feedback mechanisms through interaction with clouds and impacts on precipitation. These particles can have highly variable physicochemical properties in the atmosphere, and it is crucial to continuously monitor their long-term concentration relative to total ambient aerosol populations at a wide variety of sites to comprehensively understand aerosol–cloud interactions in the atmosphere. Hence, our study applied an in situ forced expansion cooling device to measure ambient INP concentrations and test its automated continuous measurements at atmospheric observatories, where complementary aerosol instruments are heavily equipped. Using collocated aerosol size, number, and composition measurements from these sites, we analyzed the correlation between sources and abundance of INPs in different environments. Toward this aim, we have measured ground-level INP concentrations at two contrasting sites, one in the Southern Great Plains (SGP) region of the United States with a substantial terrestrially influenced aerosol population and one in the Eastern North Atlantic Ocean (ENA) region with a primarily marine-influenced aerosol population. These measurements examined INPs mainly formed through immersion freezing and were performed at a ≤ 12 min resolution and with a wide range of heterogeneous freezing temperatures (T s above - 31 °C) for at least 45 d at each site. The associated INP data analysis was conducted in a consistent manner. We also explored the additional offline characterization of ambient aerosol particle samples from both locations in comparison to in situ data. From our ENA data, on average, INP abundance ranges from ≈ 1 to ≈ 20 L -1 (- 30 °C ≤ T ≤ - 20 °C) during October–November 2020. Backward air mass trajectories reveal a strong marine influence at ENA with 75.7 % of air masses originating over the Atlantic Ocean and 96.6 % of air masses traveling over open water, but analysis of particle chemistry suggests an additional INP source besides maritime aerosols (e.g., sea spray aerosols) at ENA. In contrast, 90.8 % of air masses at the SGP location originated from the North American continent, and 96.1 % of the time, these air masses traveled over land. As a result, organic-rich SGP aerosols from terrestrial sources exhibited notably high INP abundance from ≈ 1 to ≈ 100 L -1 (- 30 °C ≤ T ≤ - 15 °C) during October–November 2019. The probability density function of aerosol surface area-scaled immersion freezing efficiency (ice nucleation active surface site density; ns) was assessed for selected freezing temperatures. While the INP concentrations measured at SGP are higher than those of ENA, the ns(T) values of SGP (≈ 10 5 to ≈ 10 7 m -2 for - 30 °C ≤ T ≤ - 15 °C) are reciprocally lower than ENA for approximately 2 orders of magnitude (≈ 10 7 to ≈ 10 9 m -2 for - 30 °C ≤ T ≤ - 15 °C). The observed difference in ns(T) mainly stems from varied available aerosol surface areas, Saer , from two sites (Saer,SGP > Saer,ENA). INP parameterizations were developed as a function of examined freezing temperatures from SGP and ENA for our study periods. [ABSTRACT FROM AUTHOR]

In this study, the qualitative changes in raw birch sap after freezing and thawing were determined. Ten-liter bottles and one-ton plastic containers with six replications were used for the freezing of birch sap and thawing of frozen sap. During and after the thawing, the physical and physical–chemical properties of the sap were measured. According to the results, as the ice melts, the concentration of acids and other soluble substances in the sap decreases, but changes in qualitative indicators indicate the beginning of fermentation processes through color changes and pH as the temperature of the melting sap becomes positive. As a result, to freeze raw sap in large-volume containers, it is necessary to develop fast thawing technology using auxiliary means—circulation, external energy sources, and mechanical ice crushing. [ABSTRACT FROM AUTHOR]

In May 2023, a major snowstorm occurred in Canaan Valley, West Virginia, dropping 20 inches of snow. This event was unusual because it contradicted global and local warming trends that typically decrease snowfall in warmer months. While some people use events like this to deny global warming, there is evidence that extreme weather events are increasing in frequency and intensity alongside overall warming. The Canaan Valley has a cold, humid-type climate, and its high elevation allows for more snowfall. The storm was well-forecasted, and weather watchers can analyze how forecasters handle such unusual events. [Extracted from the article]

Lower winter temperatures may negatively affect winter survival by preventing maximum cold acclimation before freezing temperatures. The process of cold acclimation requires adaptation to both light and low temperatures, depending on the duration of exposure. Accordingly, research is needed to identify strategies to promote cold acclimation and increase freezing tolerance. Therefore, this experiment was conducted to investigate whether a shorter or more extended preconditioning cold treatment can improve the cold hardiness of hollyhock and its threshold of winter hardiness. The results showed that both 14 (CP1) and 28 days of Cold Preconditioning (CP2) decreased electrolyte loss, increased the activity of SOD, CAT, and APX enzymes, inhibited accumulation of Hydrogen peroxide (H2O2), and delayed the increase of Malondialdehyde (MDA) content, while non-acclimated plants experienced a decrease in MDA. No difference was observed in antioxidant activity and photosynthetic parameters between CP1 and CP2. Although proline and water-soluble sugar contents were higher in plants subjected to 28 days of cold preconditioning than in those treated for 14 days, no significant difference was found in survival percentage. Low temperatures decreased photosynthetic parameters, while increasing leaf contents of Abscisic Acid (ABA) and phenolic. The results suggested that 14-day cold preconditioning could be used to increase cold tolerance for non-acclimated hollyhocks to grow in the field at -4°C. [ABSTRACT FROM AUTHOR]

The maximum annual freeze depth (MFD) is a primary indicator of the thermal state of frozen ground, affecting ecosystems, hydrological processes, vegetation growth, infrastructure, and human activities in cold regions. It is thus important to quantify the past, present, and future spatial and temporal variability of MFD at the hemispheric scale. We develop a data‐driven MFD simulation method within a machine learning framework, integrating MFD observations from meteorological stations and several environmental predictors, to analyze past and future scenarios in the Northern Hemisphere (NH). Based on ERA5 reanalysis estimates and historical to future CMIP6 scenarios, the NH MFD averaged 133 cm (ERA5) and 131 cm (CMIP6) during 1981–2010, and will vary 81–112 cm during 2015–2100 depending on the emission scenario. During 1950–2013, MFD decreased by 0.37 cm/a (ERA5) versus 0.22 cm/a (CMIP6), and is projected to decrease 0.16–0.69 cm/a by 2100. During 1981–2010, MFD decreased by an average of 19.1% (ERA5) and 13.9% (CMIP6), with a net change of −17 cm (ERA5) and −13 cm (CMIP6). Depending on the emission scenario, MFD will decrease 11% (−12 cm) to 42% (−19 cm) between 2015 and 2099 relative to the 1981–2010. Warming, increased moisture, warmer cold seasons, warmer warm seasons, shallower snow depths, and increased vegetation cover all lead to a reduction in MFD. The results from this novel machine learning approach provide useful insights regarding the fate of future frozen ground changes. Plain Language Summary: Seasonally frozen ground covers approximately half of the exposed ground surface in the Northern Hemisphere and is found in areas of intense human activity. There, the moisture retention and occurrence of freezing and thawing significantly impact agricultural production and infrastructure. Maximum freeze depth is a key indicator of the status of seasonally frozen ground. We simulate and predict the spatial distribution of maximum freeze depth at the hemispheric scale and quantify the variability of maximum freeze depth over past and future periods. Depending on the choice of future emission scenario, average maximum freeze depth in the Northern Hemisphere will decrease by 11% (−12 cm) to 42% (−19 cm) between 2015 and 2099, relative to the base period (1981–2010). Key Points: A novel machine learning approach is used to calculate 250 years of maximum freeze depth for Northern Hemisphere seasonally frozen groundUnder the SSP5‐8.5 scenario, the maximum freeze depth in the Northern Hemisphere will decrease by 42% by 2099The maximum freeze depth decreases the most in the snow climate zone [ABSTRACT FROM AUTHOR]

The free tropospheric height of the 0 °C isotherm (H0), commonly referred to as the freezing level, denotes the lowest altitude within a specific location's atmosphere where the air temperature reaches 0 °C. This serves as an indicator for the transition between rain and snow, making it useful for monitoring and visualizing the altitude of freezing temperatures in the atmosphere. We study the spatial and temporal variability of H0 across Patagonia (41°–54° S) for the 1950–2021 period. Our results highlight the contrast around the Andes, manifested in lower/higher H0 on the western/eastern side, indicating the orographical influence on temperature vertical profiles on both sides of mountains. Our results indicate that the spatial mean value of the isotherm field in the region is 1691 meters above sea level (m.a.s.l). In terms of seasonal variability, H0 ranges from 585 m.a.s.l (winter) to 3480 m.a.s.l (summer). Moreover, the significant trends calculated over the period only show positive values in the area. This indicates an upward trend in the isotherm, averaging an increase of 8 to 61 meters per decade from 1959–2021, where the higher value is over northwestern Patagonia. Empirical orthogonal function (EOF) analysis was performed on isotherm anomalies. The first empirical orthogonal function (EOF) mode of H0 variability accounts for 84 % of the total variance, depicting a monopole structure centered in the northwest area. This mode exhibits a positive correlation with the spatial average H0 anomalies field, the Southern Annular Mode (SAM), temperature at 850 hPa in the Drake Passage, and sea surface temperature off the western coast of Patagonia; underscoring the significant role of these factors in influencing the vertical temperature profile within the region. [ABSTRACT FROM AUTHOR]

The article provides a summary of the weather conditions in September and October 2023 in the United States. In September, there was late-season warmth in some regions, while others experienced cooler-than-normal conditions. Drought coverage increased, with extreme drought observed in several states. Hurricane Ophelia caused heavy rainfall and flooding along the Atlantic coast, and there were record-setting heatwaves in Texas. In October, there were significant weather events across the country, including snowfall, heavy rain, and record-setting temperatures. The article concludes with information about the overall temperature and precipitation rankings for October. [Extracted from the article]

The evolution of ice‐phase particles within precipitating clouds depends on the environmental properties of the cloud and on physical characteristics of the particles themselves, which can be modified by airflow over steep terrain. Through employing a unique Lagrangian particle‐based precipitation model, this study investigates the sensitivities in ice‐phase particle growth and transport due to variabilities in riming processes over an orographic barrier. This analysis is applied to two wintertime stratiform cyclones sampled by in situ aircraft over windward slopes during the Olympic Mountains Experiment. For both events, we simulate the ice‐phase particle evolution and trajectory within a two‐dimensional prescribed state representative of median observed cloud properties. Sensitivity simulations were constructed based on observed variabilities in supercooled liquid water (SLW) properties and its vertical extent above the melting level. Perturbations of SLW concentration equivalent to the 85th and 15th percentiles of observed values, which typically amounted to a change of less than 0.05 g m−3, resulted in respective increases or decreases in the ice‐phase contribution to surface precipitation mass by as much as 50% and horizontal particle trajectories differences exceeding 10 km. Similar sensitivities were found in response to varying the vertical extent of SLW above the melting level and to adjustments in mean SLW droplet size. The significant precipitation response to small variations in cloud properties principally arises from changing rates of rime mass accumulation and correspondingly, increases in particle fall speed. Considerations for the numerical representation of the riming process and its complex effects on precipitation are discussed. Plain Language Summary: Precipitating clouds produce rain and snow at varying rates depending on the properties of the cloud. At below freezing temperatures in clouds, it is common to have a mixed‐phase layer where ice crystals and liquid droplets, in a supercooled state, coexist. Collection of the supercooled liquid droplets on the ice crystals greatly affects the mass and fall speed of the ice crystals, thereby affecting where, and how much, precipitation reaches the surface. In this study, we use a numerical model to simulate the evolution of individual precipitating ice crystals and evaluate sensitivities to the concentration and distribution of supercooled liquid droplets in the cloud. Based on variabilities measured in clouds upstream of the Olympic Mountains, small changes in the concentration of supercooled liquid droplets, the size of the liquid droplets, or the depth of the mixed‐phase layer produces changes in rain rates of up to 50% and increases or decreases in the distance a particle travels by as much as 10 km. We discuss the implications of these significant sensitivities to the precipitation rate and fall characteristics. Key Points: Particle‐based models provide frameworks for simulating the evolution and trajectory of precipitating particles in stratiform winter stormsFor sufficiently deep mixed‐phase clouds, small variations in supercooled liquid water mass may alter precipitation rates by as much as 50%Particle trajectory is significantly modulated by mixed‐phase layer depth through cumulative adjustments in fall velocity during riming [ABSTRACT FROM AUTHOR]

Cold spells and severe weather may have detrimental effects in wild birds, but owing to the stochastic nature of these events, it is not always possible to measure their impacts. In January 2021, a strong snowstorm known as 'Filomena' affected Spain, mainly the region of Madrid (Central Spain), which was fully covered with snow and suffered freezing temperatures for a fortnight. Using bird surveys conducted in the winter-spring of 2020 and 2021 (before and after Filomena) at same locations, we addressed the possible impact of the cold spell in three widespread gamebirds: Wood Pigeon (Columba palumbus), Eurasian Magpie (Pica pica) and Red-legged Partridge (Alectoris rufa). No significant abundance differences were found between years for none of the species and hunting pressure was only significantly reduced for Partridges, hence this species may have been negatively affected by Filomena. Results suggest that in response to Filomena, Pigeons conducted partial migration in search of better conditions, while Magpies aggregated in certain areas of Madrid and Partridges endured the harsh conditions within their home ranges. Our results highlight the importance to alleviate negative impacts of extreme weather events in wild birds through management actions, especially for sedentary species. [ABSTRACT FROM AUTHOR]