Snowfall Periods Research Articles

A contrastive analysis on the causes of two regional snowstorm processes influenced by the southern branch trough in Hunan in early 2022

AbstractIn early 2022, there were four low‐temperature weather processes with rain and snow in Hunan Province, China. Two processes occurred on January 28–29 (referred to as the “0128” process) and February 6–7 (referred to as the “0206” process), and they have overlapping areas of heavy snowfall and high intensity of short‐term snowfall. Multi‐source observation data and the National Centers for Environmental Prediction (NCEP) reanalysis data are used to analyze the characteristics of circulation background and mesoscale. In addition, the causes of heavy snowfall processes under the influence of the southern branch trough are discussed based on the dual‐polarization radar products at Changsha station. The results show that two processes are characterized by the rapid phase transformation of rain and snow, concentrated snowfall periods, and heavy snowfall at night. The short‐term snowfall intensity of the “0206” process is greater than that of the “0128” process. The high‐latitude blocking high of the “0206” process is stronger than that of the “0128” process, and the water vapor transport of the southerly jet in low levels in the “0206” process is also stronger. The organized development of cold cloud clusters from the meso‐β scale to the meso‐α scale indicates that the snowfall intensifies, and the maximum blackbody temperature gradient corresponds well to the center of heavy snowfall. The propagation that is similar to the train effect is an important reason for the heavy snowfall process. The vertical variation of the ZH and the bright band of dual‐polarization parameters can determine the phase transformation between rain and snow. When the ZH and ZDR bright bands are 1–3 km away from the ground, the phase state is rain if the ZH near the ground is greater than 0 dBZ and the CC is close to 1; the phase state is the rain‐snow mixed phase if the CC is less than 0.95. When the bottom of the ZH bright band decreases, the CC/ZDR bright band disappears, the near‐surface CC is greater than 0.99 and the ZDR is less than 1 dB, the rain turns to snow. Compared with the “0128” process, the characteristics of the bright ring during the rainfall period of the “0206” process are more obvious, the precipitation intensity judged from the larger ZH and KDP is larger, and the phase transformation is faster due to more significant cooling effect caused by precipitation.

Characteristics of Lake-Effect Precipitation over the Black River Valley and Western Adirondack Mountains

Abstract Potential factors affecting the inland penetration and orographic modulation of lake-effect precipitation east of Lake Ontario include the environmental (lake, land, and atmospheric) conditions, mode of the lake-effect system, and orographic processes associated with flow across the downstream Tug Hill Plateau (herein Tug Hill), Black River valley, and Adirondack Mountains (herein Adirondacks). In this study we use data from the KTYX WSR-88D, ERA5 reanalysis, New York State Mesonet, and Ontario Winter Lake-effect Systems (OWLeS) field campaign to examine how these factors influence lake-effect characteristics with emphasis on the region downstream of Tug Hill. During an eight-cool-season (16 November–15 April) study period (2012/13–2019/20), total radar-estimated precipitation during lake-effect periods increased gradually from Lake Ontario to upper Tug Hill and decreased abruptly where the Tug Hill escarpment drops into the Black River valley. The axis of maximum precipitation shifted poleward across the northern Black River valley and into the northwestern Adirondacks. In the western Adirondacks, the heaviest lake-effect snowfall periods featured strong, near-zonal boundary layer flow, a deep boundary layer, and a single precipitation band aligned along the long-lake axis. Airborne profiling radar observations collected during OWLeS IOP10 revealed precipitation enhancement over Tug Hill, spillover and shadowing in the Black River valley where a resonant lee wave was present, and precipitation invigoration over the western Adirondacks. These results illustrate the orographic modulation of inland-penetrating lake-effect systems downstream of Lake Ontario and the factors favoring heavy snowfall over the western Adirondacks. Significance Statement Inland penetrating lake-effect storms east of Lake Ontario affect remote rural communities, enable a regional winter-sports economy, and contribute to a snowpack that contributes to runoff and flooding during thaws and rain-on-snow events. In this study we illustrate how the region’s three major geographic features—Tug Hill, the Black River valley, and the western Adirondacks—affect the characteristics of lake-effect precipitation, describe the factors contributing to heavy snowfall over the western Adirondacks, and provide an examples of terrain effects in a lake-effect storm observed with a specially instrumented research aircraft.

Geochemical Markers of Stagnant Zones in an Urban Heat Island

The paper presents data acquired by a comparative study of the vertical variability in the chemical composition and ratios of aerosol subdisperse fractions in snow layers chronologically correlated with the stratigraphically significant snowfall periods. These data highlight features of the concentrating of trace elements at reactive (geochemical) barriers in the snow profile. The ratio of three geochemically close groups of elements, such as siderophile, sulfophile, and lithophile elements, were found out to vary relatively little from one snow layer to another in the growing snow cover. Trajectory analysis of the transfer of air masses to which stratigraphically significant snowfalls were related to the observation site provides no evidence that the identified geochemical phenomenon can be explained by that the winter aerosol field that was formed above an urban area with different trajectories of air masses can be somehow inherited in the snow layers of the growing snow cover and thus affect the vertical distributions of trace elements. Evidence indicates that that the ratios of assemblages of trace elements in the discrete snow layers, which remain stable with the growth of the snow mass, can be employed as geochemical markers of stagnant zones in an urban heat island, and the method of geochemical sampling of a snow cover in its discrete layers at a rare network of urban meteorological observation sites is an efficient additional tool for studying microscale atmospheric processes and recovering information on characteristics of the transfer of pollutants in a spatially limited urban area.

Физические свойства снежного покрова и механизм формирования геохимических барьеров в снежной толще

The results of vertical variability comparative studies of the chemical snow layers composition, chronologically linked to the stratigraphically significant snowfall periods, have been presented. The features of the impurity elements concentration on geochemical barriers in the snow mass have been shown. The formation mechanism in the seasonal snow cover has been discussed.

Simulation of Daily Snow Depth Data in China Based on the NEX-GDDP

In this study, a backpropagation artificial neural network snow simulation model (BPANNSIM) is built using data collected from the National Climate Reference Station to obtain simulation data of China’s future daily snow depth in terms of representative concentration pathways (RCP4.5 and RCP8.5). The input layer of the BPANNSIM comprises the current day’s maximum temperature, minimum temperature, snow depth, and precipitation data, and the target layer comprises snow depth data of the following day. The model is trained and validated based on data from the National Climate Reference Station over a baseline period of 1986–2005. Validation results show that the temporal correlations of the observed and the model iterative simulated values are 0.94 for monthly cumulative snow cover duration and 0.88 for monthly cumulative snow depth. Subsequently, future daily snow depth data (2016–2065) are retrieved from the NEX-GDPP dataset (Washington, DC/USA: the National Aeronautics and Space Administration(NASA)Earth Exchange/Global Daily Downscaled Projections data), revealing that the simulation data error is highly correlated with that of the input data; thus, a validation method for gridded meteorological data is proposed to verify the accuracy of gridded meteorological data within snowfall periods and the reasonability of hydrothermal coupling for gridded meteorological data.

Development of a statistical model to assess the climate conditions in the ventilation layer of double pitched roofs

For the proper simulation of hygrothermal processes in roof constructions with ventilation layers the knowledge of climate conditions within the ventilation layer is requisite. In this work a model for the assessment of temperature and air humidity has been developed using multiple regression analysis. Therefore, the climate conditions inside the ventilation layers of differently covered and oriented roofs have been monitored for one year. Relevant outside climate parameters for the calculation of ventilation layer climates have been identified. The comparison between measured and calculated values indicated an adequate accuracy of the developed model with limitations for the use in snow fall periods.

Interception of sulfate deposition from a closed canopy to a forest gap edge canopy in a subalpine dragon spruce plantation

Reducing the threats of sulfate ion (SO42−) deposition to terrestrial ecosystems is a great challenge. The canopy interception effect on SO42− deposition has been well documented, but the interception efficiency of the gap edge remains unknown. Therefore, a subalpine dragon spruce (Picea asperata) plantation was evaluated in the upper reaches of the Yangtze River. The dynamics of the SO42− concentration in the throughfall were investigated from the gap edge to the closed canopy during the rainfall and snowfall periods from August 2015 to July 2016. The annual input of SO42− totaled 2.56 kg/ha through rainfall and 0.69 kg/ha through snowfall. The total annual net interception fluxes (NIFs) of SO42− at the gap edge and in the closed canopy were 1.48 kg/ha and 0.66 kg/ha, respectively, and the net interception ratios (NIRs) accounted for 45.40% and 20.25%, respectively. The NIF and the NIR of SO42− at the gap edge were higher than those in the closed canopy. Therefore, the results suggested that a significant amount of SO42− deposition was intercepted by the tree canopy in the subalpine plantation, with more SO42− deposition at the gap edge than in the closed canopy, which is beneficial for improving the water quality in the upper reaches of the Yangtze River via forest management.

Insight into the formation of secondary inorganic aerosol based on high-time-resolution data during haze episodes and snowfall periods in Zhengzhou, China

Episodic haze is frequently observed in Zhengzhou, China. Such haze typically contains secondary inorganic aerosols. In this paper, we explore the formation mechanisms of sulfate, nitrate, and ammonium (SNA) in Zhengzhou from January 3 to 25, 2018 based on the results of a series of online instruments and a size-segregated filter sampler. Our results document the remarkable contributions of SNA to winter haze episodes in Zhengzhou, where they account for about 50% of PM2.5 mass concentration. SNA were mainly concentrated in droplet-mode particles, which increased remarkably with the aggravation of the haze episode. In addition, KNO3 and NaNO3 were formed in droplet-mode particles and coarse-mode particles respectively with increasing PM2.5 concentration. The atmosphere during the observation period was ammonia-rich, and the aerosol was acidic under high PM2.5 concentration. Homogeneous reactions dominated the formation of nitrate. HONO photolysis played a more important role in the origin of OH radicals when O3 decreased during haze episode. Under high relative humidity (RH), nitrate formation was influenced by heterogeneous hydrolysis reactions of N2O5. Sulfates were mainly formed through aqueous-phase reactions, especially when the RH was higher than 60%. Under these conditions, there were amounts of liquid water content existed in aerosols. Finally, we observed enhanced conversion of SO2 and NO2 during snowfall periods. This effect may be attributable to the higher RH and O3 levels despite the unfavorable effects of wet deposition and low concentrations of gaseous precursors.

Public health vulnerability to wintertime weather: time-series regression and episode analyses of national mortality and morbidity databases to inform the Cold Weather Plan for England

ObjectivesTo inform development of Public Health England's Cold Weather Plan (CWP) by characterizing pre-existing relationships between wintertime weather and mortality and morbidity outcomes, and identification of groups most at risk. Study designTime-series regression analysis and episode analysis of daily mortality, emergency hospital admissions, and accident and emergency visits for each region of England. MethodsSeasonally-adjusted Poisson regression models estimating the percent change in daily health events per 1 °C fall in temperature or during individual episodes of extreme weather. ResultsAdverse cold effects were observed in all regions, with the North East, North West and London having the greatest risk of cold-related mortality. Nationally, there was a 3.44% (95% CI: 3.01, 3.87) increase in all-cause deaths and 0.78% (95% CI: 0.53, 1.04) increase in all-cause emergency admissions for every 1 °C drop in temperature below identified thresholds. The very elderly and people with COPD were most at risk from low temperatures. A&E visits for fractures were elevated during heavy snowfall periods, with adults (16–64 years) being the most sensitive age-group. Since even moderately cold days are associated with adverse health effects, by far the greatest health burdens of cold weather fell outside of the alert periods currently used in the CWP. ConclusionsOur findings indicate that levels 0 (‘year round planning’) and 1 (‘winter preparedness and action’) are crucial components of the CWP in comparison to the alerts. Those most vulnerable during winter may vary depending on the type of weather conditions being experienced. Recommendations are made for the CWP.

A hydrological approach to estimating daily glacier ablation

Reduced meltwater discharge owing to glacier retreat can have severe impacts on downstream water users. To assess these impacts, it is essential to differentiate between water from glacier melt and other sources. We propose a method for doing this on a daily time scale by applying a mixing law to electrical conductivity and proglacial discharge measurements. Daily ablation is then estimated by applying a recession law to the glacier melt component. Testing this method on summer hydrology and meteorology measurements from the Baounet Glacier (France) taken over six consecutive years (2008–2013) allowed us to reconstruct daily ablation during the ablation period. Mean ablation rates ranged from 20 to 30 mm·day−1. Air temperature measurements showed that periods of low ablation during the summer were linked to cooler days and snowfall periods. Comparisons for three consecutive summers showed that the ablation rates obtained by summing calculated daily ablation were statistically similar to the rates recorded by ablation stakes.

2011년 강원 폭설과 GPS 가강수량의 상관성 분석

본 연구에서는 2011년 강원도 영동 지방의 폭설 기간 동안 GPS 위성 신호의 대류권 지연량 추정으로부터 대기 가강수량을 복원하였다. 폭설이 발생하는 기간 동안에 GPS 가강수량과 신적설 발생량과의 상관관계에 대한 분석을 실시하였다. 분석 결과, GPS를 이용하여 복원한 대류권에서의 가강수량 증가가 발생된 이후에 강설량이 증가하는 추세를 나타냈다. 또한 웨이블릿을 이용한 주기 분석에서는 본 연구기간에 한해서 GPS 가강수량의 주기가 포화수증기압의 주기와 유사한 것으로 검출되었다. GPS 가강수량의 감소와 이에 대응하는 신적설량의 증감은 두 연구 지역인 강릉과 울진에서 모두 다르게 증감하는 경향을 나타냈다. 폭설 기간 동안 GPS 가강수량과 포화수증기압의 상관 계수는 강설이 발생하지 않는 기간 동안의 결과와는 달리 양의 상관성을 갖는 것으로 나타났다. In this paper, the GPS precipitable water vapor was retrieved by estimating of GPS signal delay in the troposphere during the progress of heavy snowfall on the Gangwon Province, 2011. For this period, the time series analysis between GPS precipitable water vapor and fresh snow depth was accomplished. The time series and the comparison with the GPS precipitable water vapor and the fresh snow depth indicates that the temporal change of two variations is closely related to the progress of the heavy snowfall. Also, the periodicity of GPS precipitable water vapor using the wavelet transform method was showed a similar cycle of saturated water vapor pressure as the limitation of this study span. The result shows that the decrement of GPS precipitable water vapor was conflicted with the increment of fresh snow depth at two sites, Gangneung and Uljin. The correlation between the GPS precipitable water vapor and the saturated water vapor pressure for the event was showed a positive correlation, compare with the non-heavy snowfall periods.

Fluxes of nitrates between snow surfaces and the atmosphere in the European high Arctic

Abstract. Measurements of atmospheric and snow mixing ratios of nitrates and nitrites and their fluxes above the snow surface were made during two intensive campaigns during spring time 2001 at Ny-Ålesund, Svalbard as part of the EU project "`The NItrogen Cycle and Effects on the oxidation of atmospheric trace species at high latitudes" (NICE). At this coastal site close to the unseasonably unfrozen fjord, of the measured nitrogen species, only HNO3 showed a significant flux on to the snow surface; a mean deposition of -8.7 nmol h-1 m-2 was observed in late April / early May 2001. These fluxes may be due to the reaction of HNO3 with sea salt, and especially NaCl, or may be simply uptake of HNO3 by ice, which is alkaline because of the sea salt in our marine environment. During snowfall periods dry deposition of HNO3 may contribute up to 10% of the N budget in the snow; however, the main source for N is wet deposition in falling snow. The surface snow at Ny-Ålesund showed very complex stratigraphy; the NO3- mixing ratio in snow varied between 65 and 520 ng g-1, the total NO3- content of the snowpack was on the order of 2700 ng cm-2. In comparison the atmospheric boundary layer column showed a NO3- content of only 8 ng cm-2. The limited exchange, however, between the snow and the atmosphere was attributed to low mobility of NO3- in the observed snow. Contrary to other Arctic sites (i.e. Alert, Nunavut or Summit, Greenland) deposition of sea salt and crustal aerosols in this marine environment made the surface snow alkaline; snow NO3- was associated with heavier cations and was not readily available for physical exchange or photochemical reactions.

Winter 1999: a valuable test of the avalanche-hazard mapping procedure in Switzerland

AbstractIn Switzerland three large snowfall periods led to numerous large avalanche events, causing the deaths of 17 people, damage to about 1000 buildings and blockage of many important traffic systems. This situation was a valuable test of the avalanche-hazard mapping procedure developed in Switzerland since the last extreme avalanche winter in 1951. In most cases, the avalanches stopped within the avalanche-hazard zones. However, approximately 40 of about 1200 large avalanche events passed the limits of the existing hazard zones. The primary deficiency was underestimation of the hazard of powder-snow avalanches. The other reason the hazard-zone boundaries were passed was multiple avalanche events in a single track within a short time period. In addition, some fracture depths were larger than those used in avalanche-dynamics calculations. Therefore, the guideline assumptions for defining the fracture depths are questioned. Winter 1999 impressively underlined the danger of avalanches in mountainous regions. It emphasized the importance of avalanche-hazard mapping, showed the existing deficiencies and provided a large amount of field data that will help to improve our knowledge of avalanche dynamics.

Range errors in global positioning system during ice cloud and snowfall periods

Results from a global positioning system (GPS) measurement campaign conducted during March 1989 on a baseline of 13.1415 km length show a relatively large discrepancy in the adjusted baseline height component during ice cloud and snowfall periods. These experimental observations have stimulated the development of a propagation-prediction model to investigate the performance of GPS carrier beat phase measurements during ice cloud (predominantly present above the freezing level) and snowfall precipitation periods. Theoretical results revealed that even for extremely high ice cloud volume concentrations and for snowfall rates up to 20 mm/h the estimated phase delay, if identical at the two receiver sites, has negligible effect on the recovery of the vector baseline components. However, due to the localized nature of many snow storms and the nonuniform spatial cover of ice clouds, the differential effects between two distant receiver sites can become important for precise relative GPS applications. Finally, the model demonstrates that a differential phase delay of about 4.6/spl deg/ at zenith which is to be expected under adverse storm conditions may explain the range of experimentally observed discrepancies in the relative baseline height component.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Oxygen isotopic composition of Central Sierra Nevada precipitation, I. Identification of ice-phase water capture regions in winter storms

Measurements of the stable isotopic ratios of oxygen and simultaneously observed ice crystal structure in freshly fallen snow, have been used to estimate the weighted mean altitudes of ice-phase precipitation formation in winter clouds over the Central Sierra Nevada. Observations of dominant, diffusionally grown ice-crystal habits were used to estimate relatively narrow ranges of temperatures of initial formation of the precipitation particles using the Nakaya (1954) ice-crystal classification techniques. The mean oxygen isotope ratio 18O/ 16O for each snow sample, together with local upper air soundings, were used to estimate ranges of temperature-altitude within the clouds where the precipitating particles had captured their ice-phase water. For this initial study, snow samples were collected each five (5) to ten (10) minutes during three snowfall periods on 27 January, 26 February and 28 February, 1983. For the 27 January case, the ice formation mechanism was predominantly vapor deposition and hence the narrow range of temperatures determined by the ice-crystal habits was directly relatable to the mean δ 18O value. The 26 and 28 February cases were more complicated because the solid-phase precipitation was formed by vapor deposition and by freezing of drops and droplets (which occurs without isotopic fractionation). In these cases, the oxygen isotopic composition of the snow reaching the ground was representative of solid phase precipitation which had formed at warmer temperatures than those corresponding to the primary ice-crystal habits alone. There was no apparent relationship between δ 18O values and surface temperature at the sampling site. If relationships between 18O/ 16O and temperature-altitude are established for this geograpic region for winter snowfall conditions, this crystal habit—isotopic composition technique can provide knowledge about the regions of the clouds in which the ice-phase precipitation is forming over the Central Sierra Nevada.

Rehydration response of nitrogenase activity and carbon fixation in terrestrial Nostoc commune from Stipa–Bouteloa grassland

The effects of wetting–drying cycles on patterns of carbon dioxide exchange and acetylene reduction were examined for colonies of the terrestrial cyanophyte Nostoc commune collected from a semiarid grassland site in southern Alberta, Canada. At 14 and 21 °C acetylene reduction takes ca. 14 h to resume maximal rates, although activity is detected within minutes of rehydration. Net photosynthesis reaches compensation minutes after rehydration and is maximal in under 80 min at 21 °C. No respiratory burst is evident, either for replicates previously dried rapidly (0.5 h) or slowly (5 h). In marked contrast, however, at 7 °C only minimal recovery of acetylene reduction is evident after 48 h diurnal treatment, while net photosynthesis requires a recovery time of 6 h. Again no respiratory burst is evident. After rehydration, the magnitude of acetylene reduction is strongly dependent on both the previous illumination level and temperature. The rapid decline in activity on transfer to darkness or on addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea can be moderated by increasing the duration of the previous light exposure or by incubation at lower temperature. This suggests the presence of substrate pools, the replenishment of which by photosynthesis allows oxidative phosphorylative support of nitrogenase activity in the dark. The extreme resistance of N. commune to desiccation and heat stress combined with its ability to resume metabolic activity within minutes of wetting should allow very effective utilization of small precipitation events during the summer months. The slower recovery of nitrogenase activity upon rehydration at lower temperatures may restrict winter field activity on rare occasions when thalli become dehydrated between snowfall periods.

Continuous Snowfall Replicator

A continuous snowfall replicator has been developed using the “roll-on” Formvar technique to apply a continuous strip of liquid Formvar to a 35-mm motion picture film base. Snow crystals which settle onto the moving strip are replicated upon Formvar hardening, producing a continuous sample. The replicas are viewed by either a 20× microfilm reader or a 50–100 × 35-mm projector. Computations are presented which give approximate crystal concentration figures (crystals cm−2) sampled with the instrument. Field tests during the Yellowstone Field Research Expedition #6, January 1966, produced continuous snow crystal concentration figures. Among the snowfall samples taken during the winter of 1965–66 near Climax, Colo., several recorded the change of crystal shapes, sizes, and concentrations through snowfall periods. Such information attests to the usefulness of continuous snowfall samples. The snow crystal replicas obtained with this instrument have significantly improved the Formvar replication technique.