Persistent Snow Research Articles

The effect of snow cover on lemming population cycles in the Canadian High Arctic

Rising temperatures and changes in the precipitation regime will have a strong impact on the quality of the snow cover in the Arctic. A snow cover of good quality protecting lemmings from cold temperatures and predators is thought to be an important factor for maintaining the cyclic dynamic of their populations in the tundra. We examined if the characteristics of annual fluctuations (amplitude and shape of phases) in brown lemming (Lemmus trimucronatus) density could be determined by snow depth, snow density, sub-nivean temperature and persistence of snow. Using an 18-year time series of brown lemming abundance on Bylot Island in the Canadian Arctic, we tested if snow variables could explain the residual variation between the observed lemming density and the one predicted by models where cyclicity had been accounted for. Our analysis provides support for the hypothesis that snow cover can affect the amplitude and possibly also the periodicity of lemming population cycles in the High Arctic. Summer abundance of brown lemmings was higher following winters with a deep snow cover and a low-density snow pack near the ground but was unaffected by the date of establishment or melting and duration of the snow cover. Two snow variables showed a temporal trend; mean winter snow depth tended to increase and date of establishment of the hiemal threshold occurred earlier over time. These temporal trends, which should be favourable to lemmings, may explain why healthy population cycles have apparently been maintained at our study site contrary to other Arctic sites.

Energy and Mass Balance of Forni Glacier (Stelvio National Park, Italian Alps) from a Four-Year Meteorological Data Record

Since 26 September 2005 an Automatic Weather Station (AWS1 Forni) has been running on the ablation area of the largest Italian valley glacier, Forni, in the Ortles–Cevedale Group. A 4-year record (from 1 October 2005 to 30 September 2009) of air temperature, relative humidity, wind speed and direction, incoming and outgoing radiative fluxes, air pressure, liquid precipitation, and snow depth is considered. The meteorological data are analyzed to describe glacier surface conditions, to calculate the energy balance, and to evaluate the ice ablation amount. Snow accumulation was measured, thus permitting the estimation of the glacier point mass balance.An annual average amount of melt of −5.4 ± 0.021 m w.e. was calculated and an annual average amount of accumulation of +0.7 ± 0.006 m w.e. was measured at the AWS site. The annual average amount of mass balance was −4.7 ± 0.023 m w.e.Our analyses show that surface conditions during summer and fall seasons are important in regulating glacier albedo and then mass balance. In particular, snow cover presence, due to a longer persistence of spring snow, summer snowfalls and earlier fall solid precipitation, drives the duration of the ice melt period.

Sensitivity analysis of temperature‐index melt simulations to near‐surface lapse rates and degree‐day factors at Vestari‐Hagafellsjökull, Langjökull, Iceland

AbstractThe performance of temperature‐index melt models is particularly affected by the choice of near‐surface lapse rate used to determine the sum of positive daily temperatures at different elevations, and by the choice of factor used to relate this sum to the rate of melting. Data from the Langjökull ice cap are used in this study to quantify the influence of lapse‐rate and degree‐day factor variation on temperature‐index melt simulations. The lapse rate was significantly lower during summer than in spring or autumn, as a result of diabatic cooling, reducing boundary‐layer sensitivity to free‐air temperature change. The summer lapse rate was also significantly lower than the saturated adiabatic lapse rate. A sensitivity of approximately 600 mm water equivalent (w.e.) cumulative June–August melt per 0.1 °C 100 m–1 change in lapse rate was found across a 500‐m altitude range. The sensitivity to a 1‐mm w.e. °C–1 day–1 change in degree‐day factors varied more: from approximately 500 mm w.e. cumulative summer melt at low elevation to approximately 200 mm w.e. at high elevation, reflecting the decline in melt rates associated with the greater persistence of snow with increasing altitude. The determination of a degree‐day factor for snow is complicated by the densification of the ageing snowpack, but the application of a parameterization for near‐surface density on the basis of albedo helped account for the development of snow water equivalence. Lapse rate was parameterized as a function of standardized anomalies in 750 hPa reanalysis temperature and significantly improved the simulation of cumulative summer melt compared with models applying the saturated adiabatic lapse rate. Copyright © 2012 John Wiley & Sons, Ltd.

Dynamics of snow ablation in a small Alpine catchment observed by repeated terrestrial laser scans

AbstractThe spatio‐temporal distribution of snow in a catchment during ablation reflects changes in the total amount of snow water equivalent and is thus a key parameter for the estimation of melt water run‐off. This study explores possible rules behind the spatial variability of snow depth during the ablation season in a small Alpine catchment with complex topography. The snow depth observations are based on more than 160 000 terrestrial laser scanner data points with a spatial resolution of 1 m, which were obtained from 11 scanning campaigns of two consecutive ablation seasons.The analysis suggests that for estimating cumulative snow melt dynamics from the catchment investigated, assessing the initial snow distribution prior to the melt season is more important than addressing spatial differences in the melt behaviour. Snow volume and snow‐covered area could be predicted well using a conceptual melt model assuming spatially uniform melt rates. However, accurate results were only obtained if the model was initialized with a pre‐melt snow distribution that reflected measured mean and standard deviation. Using stratified melt rates on the other hand did not improve the model results. At least for sites with similar meteorological and topographical conditions, the model approach presented here comprises an efficient way to estimate snow depletion dynamics, especially if persistent snow accumulation pattern between years facilitate the characterization of the initial snow distribution prior to the melt. Copyright © 2011 John Wiley & Sons, Ltd.

Graminan breakdown by fructan exohydrolase induced in winter wheat inoculated with snow mold

Fructan structures vary widely among plant species. Graminan-type fructans, extensions of sucrose through β-(2,6)-linked fructosyl units with branches of β-(2,1)-linked fructosyl units, accumulate in tissues of winter wheat ( Triticum aestivum) during cold hardening and are metabolized under persistent snow cover. Snow molds such as Typhula ishikariensis and Microdochium nivale opportunistically infect wheat under snow cover. Snow mold-resistant wheat cultivars tend to heavily accumulate and slowly metabolize water-soluble carbohydrates including graminans in comparison with snow mold-susceptible cultivars. We observed time-dependent changes in the amounts of water-soluble carbohydrates in snow mold-inoculated wheat tissues, and accumulated fructan levels significantly decreased as a result of snow mold inoculation and incubation under snow cover, especially in a snow mold-susceptible wheat cultivar. Three candidates for fructan exohydrolase (FEH) cDNAs with high homology to cell wall invertases were isolated from wheat leaf tissues inoculated with snow mold and incubated under snow cover. The substrate specificity of enzymes encoded by the isolated clones was analyzed by recombinant proteins expressed in Pichia pastoris. The recombinant protein (Wfh-sm3m) encoded by one ( Wfh-sm3) of the isolated clones preferentially degraded 6-kestotriose and possessed minor hydrolase activity to 1-kestotriose and 1,1-kestotetraose. Moreover, Wfh-sm3m hydrolyzed almost all graminans that accumulated in hardened wheat tissues. Wfh-sm3 transcripts increased in wheat leaf tissues inoculated with snow mold and incubated under snow cover. These results suggest that Wfh-sm3 encodes a 6-FEH with minor 1-FEH activity and is associated with degradation of fructans in wheat leaf tissues during inoculation and incubation under snow cover.

Persistence in intra‐annual snow depth distribution: 1. Measurements and topographic control

Terrestrial and airborne laser scanning (TLS and ALS) techniques have only recently developed to the point where they allow wide‐area measurements of snow distribution in varying terrain. In this paper we present multiple TLS measurements showing the snow depth development for a series of precipitation events. We observe that the pattern of maximum accumulation is similar for the two years presented here (correlation up to r = 0.97). Storms arriving from the northwest show persistent snow depth distributions and contribute most to the final accumulation pattern. Snow depth patterns of maximum accumulation for the two years are more similar than the distribution created by any two pairs of individual storms. Based on the strong link between accumulation patterns and terrain, we investigated the ability of a model based on terrain and wind direction to predict accumulation patterns. This approach of Winstral et al. (2002), which describes wind exposure and shelter, was able to predict the general accumulation pattern over scales of slopes but failed to match observed variance. Furthermore, a high sensitivity to the local wind direction was demonstrated. We suggest that Winstral et al.'s model could form a useful tool for application from hydrology and avalanche risk assessment to glaciology.

Synoptic conditions of the occurrence of snow cover in central European lowlands

AbstractIn the central European lowlands, snowiness increases meridionally from the south to the north and latitudinally from the west to the east. Taking into account the spatial variability in the occurrence of snow cover, four regions of snow cover were distinguished using the principal component analysis (PCA). Furthermore, circulation patterns responsible for intense snowfalls and persistence of snow in each region were analysed. Composite maps of the sea level pressure (SLP) and 500‐hPa geopotential height means and anomalies were constructed for the days on which snow depth increased by ≥ 5 cm and for days on which the snow cover lasted for at least 3 days. Contour maps show negative anomalies of SLP and 500‐hPa heights over central Europe, associated with organized low‐pressure systems. The lows may differ in the intensity and localization, depending on the region. In the south‐western part of central Europe, heavy snowfalls usually appear as a result of cold‐air fronts in the colder parts of Mediterranean cyclones, the centres of which are often situated over the Italian Peninsula. Another typical location of cyclones or troughs of low pressure causing heavy snowfalls is the Baltic Sea region, where meteorological fronts appear quite frequently. Such a location of cyclonic systems causes snowfalls particularly frequently in the most snowy north‐western part of central Europe. The cyclonic activity over the continent that brings snowfalls is simultaneous to the weakening of Icelandic Low and significant positive SLP anomalies over the north Atlantic. The persistence of snow cover in the central European lowlands is possible under the positive anomalies of SLP over most of the continent, except for its south‐western part where weak negative anomalies are observed. At the same time, positive anomalies of 500‐hPa geopotential heights appear over the northern Atlantic and Scandinavia. Copyright © 2010 Royal Meteorological Society

Ecosystem Feedbacks to Climate Change in California: Development, Testing, and Analysis Using a Coupled Regional Atmosphere and Land Surface Model (WRF3–CLM3.5)

Abstract A regional atmosphere model [Weather Research and Forecasting model version 3 (WRF3)] and a land surface model [Community Land Model, version 3.5 (CLM3.5)] were coupled to study the interactions between the atmosphere and possible future California land-cover changes. The impact was evaluated on California’s climate of changes in natural vegetation under climate change and of intentional afforestation. The ability of WRF3 to simulate California’s climate was assessed by comparing simulations by WRF3–CLM3.5 and WRF3–Noah to observations from 1982 to 1991. Using WRF3–CLM3.5, the authors performed six 13-yr experiments using historical and future large-scale climate boundary conditions from the Geophysical Fluid Dynamics Laboratory Climate Model version 2.1 (GFDL CM2.1). The land-cover scenarios included historical and future natural vegetation from the Mapped Atmosphere-Plant-Soil System-Century 1 (MC1) dynamic vegetation model, in addition to a future 8-million-ha California afforestation scenario. Natural vegetation changes alone caused summer daily-mean 2-m air temperature changes of −0.7° to +1°C in regions without persistent snow cover, depending on the location and the type of vegetation change. Vegetation temperature changes were much larger than the 2-m air temperature changes because of the finescale spatial heterogeneity of the imposed vegetation change. Up to 30% of the magnitude of the summer daily-mean 2-m air temperature increase and 70% of the magnitude of the 1600 local time (LT) vegetation temperature increase projected under future climate change were attributable to the climate-driven shift in land cover. The authors projected that afforestation could cause local 0.2°–1.2°C reductions in summer daily-mean 2-m air temperature and 2.0°–3.7°C reductions in 1600 LT vegetation temperature for snow-free regions, primarily because of increased evapotranspiration. Because some of these temperature changes are of comparable magnitude to those projected under climate change this century, projections of climate and vegetation change in this region need to consider these climate–vegetation interactions.

Influence of snow cover distribution on soil temperature and nutrient dynamics in alpine pedoenvironments

In Alpine sites snow is present on the ground from six to eight months per year in relation to elevation and exposure. Water is therefore immobilized into the solid state for the greater part of the winter season and released to the ground in a short period during spring snowmelt. In these areas, snow distribution exercises a fundamental role in influencing soil temperature and nutrient dynamics, in particular of nitrogen, with great consequences on plant nutrition. The dormant vegetation period, the low temperatures and the persistent snow cover suggest that soil biological activity is only concentrated during summer. As a matter of fact, soils covered with a consistent snow cover are isolated from the air temperature and can not freeze during winter. A snowpack of sufficient thickness, accumulated early in winter, insulates the ground from the surrounding atmosphere maintaining soil temperature closed to 0 °C during the whole winter season. The elevation of the snow line and the shorter permanence of snow on the ground, as a result of global warming (IPCC, 1996, 2001), might reduce the insulation effect of the snowpack, exposing soils of the mountain belt to lower temperatures and to a greater frequency of freeze/thaw cycles, which might alter organic matter dynamics and soil nutrient availability. Such thermal stresses may determine the lysis of microbial cells and the consequent increase of nitrogen and carbon mineralization by the survived microorganisms. Moreover, the freeze/thaw cycles can determine the exposure of exchange surfaces not available before, with release of organic matter of non-microbial origin, which may become available to surviving microorganisms for respiration. The reduced or absent microbial immobilization may cause the accumulation of remarkable amounts of inorganic nitrogen in soil, potentially leachable during spring snowmelt, when plants have not still started the growing season. Changes of snow distribution in alpine sites can consequently have a great impact on the thermal regime and nutrient cycle of soils. The environmental implications have to be estimated for a long time, through specific studies that aim to evidence the indirect effects of climatic change on characteristics of alpine pedoenvironments.

Response of Colorado River runoff to dust radiative forcing in snow

The waters of the Colorado River serve 27 million people in seven states and two countries but are overallocated by more than 10% of the river's historical mean. Climate models project runoff losses of 7-20% from the basin in this century due to human-induced climate change. Recent work has shown however that by the late 1800s, decades prior to allocation of the river's runoff in the 1920s, a fivefold increase in dust loading from anthropogenically disturbed soils in the southwest United States was already decreasing snow albedo and shortening the duration of snow cover by several weeks. The degree to which this increase in radiative forcing by dust in snow has affected timing and magnitude of runoff from the Upper Colorado River Basin (UCRB) is unknown. Here we use the Variable Infiltration Capacity model with postdisturbance and predisturbance impacts of dust on albedo to estimate the impact on runoff from the UCRB across 1916-2003. We find that peak runoff at Lees Ferry, Arizona has occurred on average 3 wk earlier under heavier dust loading and that increases in evapotranspiration from earlier exposure of vegetation and soils decreases annual runoff by more than 1.0 billion cubic meters or ∼5% of the annual average. The potential to reduce dust loading through surface stabilization in the deserts and restore more persistent snow cover, slow runoff, and increase water resources in the UCRB may represent an important mitigation opportunity to reduce system management tensions and regional impacts of climate change.

Subcolony variation in phenology and breeding parameters in little auk Alle alle

In seabirds, variation in breeding phenology and success is often induced by macro- and mesoscale fluctuations in oceanographic conditions, which is recordable at the regional or colony scale. Variation in breeding parameters may also exist at the microscale—among discrete breeding aggregations and subcolonies. The aim of this study was to compare breeding phenology and parameters (hatching success, chick survival, chick body mass indices) among little auks (Alle alle) nesting in three subcolonies differing in their microtopographic and microclimatic features, situated in Magdalenefjorden (north-western Spitsbergen). The hatching phenology varied significantly among the subcolonies. This was probably due to the different duration of snow persistence in spring, as nests are occupied as soon as the snow cover melts sufficiently to allow access to them. The earliest hatching was recorded in the subcolony located on steep slopes at low altitude in the vicinity of the fjord, which favours early ice and snow melting in spring. Hatching success differed significantly among subcolonies, which could also have been due to the microclimatic features of the subcolonies. Hatching success was the lowest in the subcolony where birds started to breed while patchy snow was still persisting. Water from the melting snow could have flooded some of the nests. Alternatively, the low hatchability could have been caused by a higher frequency of less experienced breeders (e.g., first-time breeders) among the individuals nesting in this subcolony. Other breeding parameters (chick survival and growth) were generally similar in all the subcolonies.

The bioclimatic envelope of the wolverine (Gulo gulo): do climatic constraints limit its geographic distribution?

We propose a fundamental geographic distribution for the wolverine ( Gulo gulo (L., 1758)) based on the hypothesis that the occurrence of wolverines is constrained by their obligate association with persistent spring snow cover for successful reproductive denning and by an upper limit of thermoneutrality. To investigate this hypothesis, we developed a composite of MODIS classified satellite images representing persistent snow cover from 24 April to 15 May, which encompasses the end of the wolverine’s reproductive denning period. To investigate the wolverine’s spatial relationship with average maximum August temperatures, we used interpolated temperature maps. We then compared and correlated these climatic factors with spatially referenced data on wolverine den sites and telemetry locations from North America and Fennoscandia, and our contemporary understanding of the wolverine’s circumboreal range. All 562 reproductive dens from Fennoscandia and North America occurred at sites with persistent spring snow cover. Ninety-five percent of summer and 86% of winter telemetry locations were concordant with spring snow coverage. Average maximum August temperature was a less effective predictor of wolverine presence, although wolverines preferred summer temperatures lower than those available. Reductions in spring snow cover associated with climatic warming will likely reduce the extent of wolverine habitat, with an associated loss of connectivity.

Re-evaluating the Relevance of Vegetation Trimlines in the Canadian Arctic as an Indicator of Little Ice Age Paleoenvironments

The origin of trimlines associated with the so-called “lichen-free” areas in the Canadian Arctic has been attributed both to perennial snowfield expansion during the Little Ice Age (LIA) and to seasonally persistent snow cover in more recent times. Because of the disparate hypotheses (ecological versus paleoclimatic) regarding the formation of these trimlines, their use as a paleoclimatic indicator has been abandoned for more than two decades. We re-examine this debate and the validity of the opposing hypotheses in the light of new regional mapping of trimlines across the Queen Elizabeth Islands (QEI). The ecological hypothesis—insufficient duration of the growing season resulting from seasonally persistent snow cover—fails to account for the poikilohydric nature of lichens and their ability to endure short growing seasons. It cannot adequately explain the existence of sharp trimlines or account for the occurrence of those trimlines on sparsely vegetated carbonate terrain. Furthermore, trimlines outlining the former extent of thin plateau ice caps are accordant with trimlines associated with former perennial snowfields, indicating that these trimlines record snow and ice expansion during the LIA rather than the seasonal persistence of more recent snow cover. We suggest that these features represent an important LIA climate indicator and should therefore be used for paleoclimatic reconstruction.

An Analysis of the Large-Scale Climate Anomalies Associated with the Snowstorms Affecting China in January 2008

Abstract Extraordinarily frequent and long-lasting snowstorms affected China in January 2008, causing above-normal precipitation, below-normal temperature, and severe icing conditions over central–southern China. These snowstorms were closely linked to the change in the Middle East jet stream (MEJS), which intensified and shifted southeastward. The change in MEJS was accompanied by southeastward shifts of the ridge and the trough over Europe and western Asia. The intensified MEJS also strengthened the trough embedded in the southern branch of the subtropical westerlies over the southern Tibetan Plateau, enhancing the water vapor transport from western Asia and the Bay of Bengal to China. In the meantime, the subtropical western Pacific high (SWPH) was stronger and its ridgeline was farther north than normal. The anomalous high slowed down the eastward propagation of weather systems to the Pacific and favored convergence of water vapor over central–southern China. The MEJS is usually strong when the Arctic Oscillation (AO) is positive and the SWPH is farther north than normal in La Niña winters. Compared to the SWPH and the Niño-3.4 sea surface temperature (SST), the MEJS and the AO exert stronger influences on the temperature and the precipitation over central–southern China, despite the fact that these possible impacting factors are not completely independent from each other. Although the La Niña event might contribute to the climate anomalies through its relation with the SWPH in January 2008, an analysis of historical events indicates that La Niña conditions alone can hardly cause severe and persistent snow conditions over central–southern China. In addition, compared to the Niño-3.4 SST and the SWPH, the conditions of December MEJS and AO exhibit stronger precursory signals of the variability of January temperature over central–southern China.

MODIS/Terra observed snow cover over the Tibet Plateau: distribution, variation and possible connection with the East Asian Summer Monsoon (EASM)

Based on the snow cover fraction (SCF) data acquired from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the NASA Terra spacecraft from 2000–2006, statistical analyses are performed to explore the spatial and temporal distribution and variation of the snow cover over the Tibetan Plateau (TP). It is found that the snow persistence over the TP varies in different elevation ranges generally becomes longer with increases in the terrain elevation. In addition, the spatial distribution of the snow cover not only depends on the elevation but also varies with terrain features, such as aspect, slope, and curvature in the local areas. With 7-year observational data, seasonal and interannual variability of snow cover has been detected. There are slight decreasing trends in SFCs from 2000–2006. With MODIS satellite snow-cover fraction data and the National Centers for Environmental Predictions and U.S. Department of Energy NCEP/DOE reanalysis II dataset, the relationship between snow cover anomalies over the TP and the East Asian Summer Monsoon (EASM) is examined. Results indicate that the onset of the EASM is closely associated with snow cover anomalies in the spring. Specifically, a positive (negative) snow cover anomaly is followed by a later (earlier) onset of the EASM.

Fungal Endophyte Removal Does Not Reduce Cold Tolerance of Tall Fescue

Tall fescue [Schenodorus phoenix (Scop.) Holub.] has historically been of minor importance to livestock agriculture in cooler regions of the temperate zone. As its use in these regions expands, it becomes increasingly important to understand the effect of infection by its fungal endophyte (Neotyphodium coenophialum Morgan‐Jones and Gams) on agronomic fitness of tall fescue. Our objective was to determine the effect of endophyte infection status on forage yield and survival of tall fescue under field conditions in which freezing temperatures, combined with lack of persistent snow cover, constitute the most significant stress factor. In Experiment 1, we evaluated 427 half‐sib families of four tall fescue cultivars, half endophyte‐infected (E+) and half endophyte‐free (E−), for forage yield and survival. There was no effect of endophyte removal on either forage yield or survival, despite complete stand loss of one cultivar during two winters. In Experiment 2, we evaluated 640 clones of confirmed endophyte status, half E+ and half E−, for survival under two management regimes at four Wisconsin locations. Results were nearly identical to those for Experiment 1, with complete mortality in the unadapted cultivar and high survival rates in the three adapted cultivars, regardless of endophyte status, management, or location. In conclusion, we found no evidence that endophyte removal resulted in any disadvantage to tall fescue host‐plant survival under harsh winter conditions. In regions where freezing temperatures and desiccating winds provide the only or most important abiotic stress factor, removal of endophytic fungi do not appear to reduce fitness of their tall fescue host.

Role of predation and hunting on eastern cottontail mortality at Cape Cod National Seashore, Massachusetts

The degree that hunting may influence game populations depends on whether hunting mortality is additional to (additive) or replaces (compensatory) natural-caused mortalities. In response to limited information on the effects of exploitation on eastern cottontail ( Sylvilagus floridanus (J.A. Allen, 1890)) populations within Cape Cod National Seashore (CCNS), we initiated an investigation of cause-specific mortality using transmitter-equipped cottontails in hunted and nonhunted areas as a way to examine the additive versus compensatory aspect of hunting. Predation caused >70% of all deaths, whereas hunting caused 10% of deaths in the areas sampled. Survival rate was substantially lower among hunted sites (0.05) than at nonhunted sites (0.19) during the winter–spring of year 1, but there was no difference between hunted (0.33) and nonhunted (0.40) sites during year 2. Lower survival in year 1 was likely due to deep and persistent snow that increased vulnerability to predation and probably reduced the prospect for hunting mortalities to be compensated by reductions among other mortality factors. However, at least partial compensation apparently occurred during year 2 when winter weather was less severe. Cottontails at CCNS are near the northern edge of their geographic range and therefore may be ultimately limited by severe weather conditions. Compared with predation, we do not believe that the current levels and distributions of hunting influence cottontail populations at CCNS.

A preliminary inventory of rock glaciers at 30°S latitude, Cordillera Frontal of San Juan, Argentina

The Dry Andes of the Cordillera Frontal of San Juan (30°S latitude) is characterized by high relief with peaks up to 5000 m a.s.l. This geological province is mainly made up of a suite of Triassic to Miocene volcanic rocks. Modern ice glaciers are small and few in number, and persistent snow fields are similarly small and scattered. The predominant landforms in these areas have been shaped in a periglacial environment superimposed on an earlier glacial landscape. A preliminary inventory map of rock glaciers was constructed using optical remote sensing techniques, digital topographic analysis and aerial photograph data organized in a geographic information system (GIS). Over 140 rock glaciers have been identified: 90% are active or inactive and the rest are fossil. A total of 88 rock glaciers are considered active. The most common periglacial features recognized in the area are talus glaciers, and only 23% are tongue-shaped glaciers.

Synoptic conditions of snow occurrence in Budapest

Daily circulation patterns responsible for snow occurrence in Budapest were analysed. Three types of circulation patterns were distinguished, using a Principal Component Analysis and clustering technique, for days with snowfalls and snow cover persistence. Low pressure systems located over the Italian Peninsula (south-west of Budapest) are characteristic for days with snowfalls. Such lows coming from the west generate warm fronts and are a source of humidity necessary for the snowfalls. At the same time, higher pressure extends north or east of the Carpathian Basin and brings polar continental air masses and consequently low temperature. Snow persistence also requires temperature below zero. This condition is fulfilled at the airflow direction from the east (or south east) which brings frosty air from the interior of the continent. A winter high pressure system extending over the Carpathian Basin also generates low temperature, mainly due to the nocturnal radiation conditioned by a clear sky.

First report of dwarf bunt caused by Tilletia controversa in Latvia

In August 2006, an unreported bunt disease was observed on winter wheat (Triticum aestivum) ears and in grain samples collected from commercial fields in different geographical regions in Latvia. The visible symptoms on ear included glumes pushed apart laterally, giving them characteristic disheveled appearance. Sori were spherical, containing a blackish mass of teliospores surrounded by a thin grey-brown tegument. Consistency of teliospore mass was hard to pulverulent. Hardness of sori is a typical characteristic of dwarf bunt whereas T. tritici is normally pulverulent. The initial identification was made using light microscopy to compare teliospores with those of the morphologically similar species in Latvia –Tilletia tritici (syn. T. caries) (Priekule, 1997). Teliospores were yellow-brown, globose or subglobose, 19·6 ± 0·58 µm (16–24 µm) in diameter, reticulated. Exospores had relatively wide and deep polygonal meshes (areolae); areolae were irregular. The polygonal reticulations were 1·81 ± 0·04 µm (1–3 µm) deep. Sterile cells were fewer and smaller than the teliospores, globose, with smooth walls. These morphological characteristics are similar to those previously reported for T. controversa (Wilcoxson & Saari, 1996). Epifluorescence microscopy was used to confirm the identity as T. controversa (Stockwell & Trione, 1986). Teliospores of T. controversa appeared spherical when mounted in immersion oil and the reticulated wall layer fluoresced yellow-orange and appeared as spike-like protrusions when viewed at the median plane or appeared net-like when focused on the upper surface of the teliospores. The endospore wall layer fluoresced yellow and the cytoplasm was yellow-green in color. By contrast, mature teliospores of T. tritici collapse in immersion oil and the reticulated walls do not autofluoresce. The environmental conditions that favor dwarf bunt development (a long period with stable low temperatures and persistent snow cover in winter) occur only sporadically in Latvia. However, because of the longevity of teliospores in the soil, there is potential for localized agronomic and economic losses in winter wheat when these disease-conducive conditions occur. This is the first report of T. controversa on winter wheat in Latvia.