Persistent Snow Research Articles

Landsat-based snow persistence map for northwest Alaska

Landsat imagery for northwest Alaska from 1 February to 31 August, 1985–2011 was used to map snow persistence at high spatial resolution. We analyzed 11,645 scenes covering 505,800km2, including five Arctic National Park units and the range of the Western Arctic caribou herd (85 Landsat path/rows). A cloud mask was created using the Landsat Ecosystem Disturbance Adaptive Processing System (LEDAPS). Terrain shadows were calculated from ASTER G-DEM2 and solar incidence angle. The presence of snow cover was determined using separate Snowmap algorithms for non-shadowed and shadowed pixels. Resulting snow cover data were reformatted into 562 30×30km tiles, with an average sample size per pixel of 216 cloud-free observations. A binary classification tree was used to successfully determine the day of the year that best marked the change from snow to snow-free conditions for 99.8% of the study area. An internal consistency check evaluating the occurrence of snow-free data earlier than that day or snow data later than that day, showed that 98.7% of the land pixels were consistently classified ≥90% of the time. Comparison with MODIS end of snow season data showed an average difference of 4.2days. The snow persistence map was strongly correlated with the few SNOTEL stations in the study area (r2=0.856). Broadly, most snowmelt over the study area occurs from late April through early June, with timing delayed farther north and at higher elevations. Many local-scale snow patterns are evident in the detailed, 30-m product. The snow persistence map was co-registered to Landsat land cover mapping, creating a powerful, publicly available resource for ecosystem and land use analyses (https://irma.nps.gov/App/Reference/Profile/2203863).

Evaluating biases in simulated snow albedo feedback in two generations of climate models

AbstractThis study presents a comprehensive evaluation of snow albedo feedback (SAF) in two generations of climate models (Coupled Model Intercomparison Project versions 3 (CMIP3) and 5 (CMIP5)). A comparison of the models is performed against a multiobservation‐based reference data set (mOBS) derived from the seasonal cycle of albedo, snow cover, and temperature. The observed total SAF shows low uncertainty and is generally well simulated by the CMIP3 and CMIP5 ensemble mean, except for a low (high) bias over the Arctic (northern boreal forest). Most CMIP5 models overestimate the snow cover component of SAF (SNC) and underestimate the temperature sensitivity component (TEM). The high bias in SNC is due to simulated snow albedos 4–5% brighter than observed driving unrealistically large albedo contrasts. However, overall representation of surface albedo—and mean climate—has improved, as fewer CMIP5 models exhibit large cold temperature, or high snow, biases. The low bias in TEM is related to overly persistent snow albedo during spring, particularly over southern Eurasia and North America. There is large observational uncertainty in the reference data set mOBS that is traced primarily to the different snow cover products, with a secondary contribution from the albedo products and a small contribution from the temperature products. The conclusion is that the model mean tends to simulate the multiobservation mean very closely; however, this masks considerable spread in both models and observations. There is clear motivation for producing improved submonthly snow cover products for the purpose of model evaluation.

Microhabitat use by mountain pygmy‐possum (Burramys parvus): Implications for the conservation of small mammals in alpine environments

AbstractThe Australian alpine region harbours a wide range of species, many of which are endemic and of high conservation value. Among these species, the endangered mountain pygmy‐possum, Burramys parvus, is of particular interest because this specialized marsupial is highly sensitive to extreme temperatures. The selection of microhabitats by B. parvus is a critical but poorly understood element of its biological characteristics. To understand the microhabitat preferences of B. parvus, we performed detailed investigations of the thermal properties of alpine boulder fields. The selection of a preferred microclimate was demonstrated by comparing temperatures and environmental conditions in preferred and non‐preferred boulder fields. The variability of the daily temperature depended on the depth at which measurements were made within the boulder fields. Temperatures were more stable as depth increased. The results suggest that B. parvus prefers to occupy deep boulder fields at high elevations with good rock structure (small rock and cavity size with multiple layers) and long snow duration because these boulder fields can provide a favourable microclimate. At 1 m depth, the maximum temperatures in the hottest part of the year were 1.27°C cooler in preferred compared to non‐preferred boulder fields. In the coldest part of the year, immediately following the melting of persistent snow cover, the minimum temperatures at a depth of 1 m were 1.67°C warmer in preferred compared to non‐preferred boulder fields. On average, the snow duration was 27 days greater in the boulder fields preferred by B. parvus than in non‐preferred boulder fields. Our results emphasize the value of boulder field microhabitats as thermal refuges for small mammals in rocky habitats within alpine environments in the light of continuing habitat loss and climate change.

Formation and persistence of snow instabilityassociated with precipitationinduced weak layer that caused Mumeizawa avalanche accident

2009年1月25日に八方尾根無名沢においてスノーボーダー1名が重傷を負う雪崩事故が発生した．破断面における観測結果と周辺の積雪・雪崩に関する記録，同時期に広域で行った積雪観測データ等を基に雪崩発生の原因となった積雪不安定性とその形成過程および空間的な分布について検討した．雪崩の原因となった積雪不安定性をもたらしたのは厚さ約40cmの新雪-しまり雪によって構成されたスラブと雲粒の付着のない大型の板状結晶からなる厚さ2cmの降雪結晶弱層の組み合わせから成る積雪構造であった．弱層は22〜23日にかけての低気圧に伴う降雪によって広域に形成されたが，弱層形成後に晴れ間があり日射の影響を受ける斜面では弱層の強度が増加した．また，スラブは冬型降雪によって形成されており日本海側に限定されて形成された．このため，この不安定性は日本海側山岳地の高標高域で，尚且つ日射の影響を受けにくい斜面に限定的に存在したと推定された．また，他の弱層の観測事例から得られたデータも合わせて検討したところ，大型で雲粒の付着のない板状結晶によって形成された層においては，他の新雪層よりも長期間脆弱な状態が持続すると考えられた．

Spatio-Temporal Change of Snow Cover and Its Response to Climate over the Tibetan Plateau Based on an Improved Daily Cloud-Free Snow Cover Product

Using new, daily cloud-free snow-cover products, this study examines snow cover dynamics and their response to climate change. The results demonstrate that the daily cloud-free snow-cover products not only posses the advantages of the AMSR-E (unaffected by weather conditions) and MODIS (relatively higher resolution) products, but are also characterized by high snow and overall classification accuracies (~85% and ~98%, respectively), substantially greater than those of the existing daily snow-cover products for all sky conditions and very similar to, or even slightly greater than, those of the daily MODIS products for clear-sky conditions. Using the snow-cover products, we analyzed the snow cover dynamics over the Tibetan Plateau and determined that the maximum number of snow-covered days (SCD) in a year followed a decreasing tendency from 2003 to 2010, with a decrease in snow-covered area (SCA) equivalent to 55.3% of the total Tibetan Plateau area. There is also a slightly increasing tendency in the maximum snow cover area (SCA), and a slightly decreasing tendency in the persistent snow cover area (i.e., pixels of SCD > 350 days) was observed for the 8-year period, which was characterized by increases in temperature (0.09 °C/year) and in precipitation (0.26 mm/year). This suggests that, on the Tibetan Plateau, changes in temperature and precipitation exert a considerable influence on the regional SCD and SCA, as well as the distribution of persistent snow cover.

Spatio-Temporal Change of Snow Cover and Its Response to Climate over the Tibetan Plateau Based on an Improved Daily Cloud-Free Snow Cover Product

Using new, daily cloud-free snow-cover products, this study examines snow cover dynamics and their response to climate change. The results demonstrate that the daily cloud-free snow-cover products not only posses the advantages of the AMSR-E (unaffected by weather conditions) and MODIS (relatively higher resolution) products, but are also characterized by high snow and overall classification accuracies (~85% and ~98%, respectively), substantially greater than those of the existing daily snow-cover products for all sky conditions and very similar to, or even slightly greater than, those of the daily MODIS products for clear-sky conditions. Using the snow-cover products, we analyzed the snow cover dynamics over the Tibetan Plateau and determined that the maximum number of snow-covered days (SCD) in a year followed a decreasing tendency from 2003 to 2010, with a decrease in snow-covered area (SCA) equivalent to 55.3% of the total Tibetan Plateau area. There is also a slightly increasing tendency in the maximum snow cover area (SCA), and a slightly decreasing tendency in the persistent snow cover area (i.e., pixels of SCD > 350 days) was observed for the 8-year period, which was characterized by increases in temperature (0.09 °C/year) and in precipitation (0.26 mm/year). This suggests that, on the Tibetan Plateau, changes in temperature and precipitation exert a considerable influence on the regional SCD and SCA, as well as the distribution of persistent snow cover.

Interactions between wind-blown snow redistribution and melt ponds in a coupled ocean–sea ice model

Introducing a parameterization of the interactions between wind-driven snow depth changes and melt pond evolution allows us to improve large scale models. In this paper we have implemented an explicit melt pond scheme and, for the first time, a wind dependant snow redistribution model and new snow thermophysics into a coupled ocean–sea ice model.The comparison of long-term mean statistics of melt pond fractions against observations demonstrates realistic melt pond cover on average over Arctic sea ice, but a clear underestimation of the pond coverage on the multi-year ice (MYI) of the western Arctic Ocean. The latter shortcoming originates from the concealing effect of persistent snow on forming ponds, impeding their growth. Analyzing a second simulation with intensified snow drift enables the identification of two distinct modes of sensitivity in the melt pond formation process. First, the larger proportion of wind-transported snow that is lost in leads directly curtails the late spring snow volume on sea ice and facilitates the early development of melt ponds on MYI. In contrast, a combination of higher air temperatures and thinner snow prior to the onset of melting sometimes make the snow cover switch to a regime where it melts entirely and rapidly. In the latter situation, seemingly more frequent on first-year ice (FYI), a smaller snow volume directly relates to a reduced melt pond cover.Notwithstanding, changes in snow and water accumulation on seasonal sea ice is naturally limited, which lessens the impacts of wind-blown snow redistribution on FYI, as compared to those on MYI. At the basin scale, the overall increased melt pond cover results in decreased ice volume via the ice-albedo feedback in summer, which is experienced almost exclusively by MYI.

Non‐growing‐season soil respiration is controlled by freezing and thawing processes in the summer monsoon‐dominated Tibetan alpine grassland

AbstractThe Tibetan alpine grasslands, sharing many features with arctic tundra ecosystems, have a unique non‐growing‐season climate that is usually dry and without persistent snow cover. Pronounced winter warming recently observed in this ecosystem may significantly alter the non‐growing‐season carbon cycle processes such as soil respiration (Rs), but detailed measurements to assess the patterns, drivers of, and potential feedbacks on Rs have not been made yet. We conducted a 4 year study on Rs using a unique Rs measuring system, composed of an automated soil CO2 flux sampling system and a custom‐made container, to facilitate measurements in this extreme environment. We found that in the nongrowing season, (1) cumulative Rs was 82–89 g C m−2, accounting for 11.8–13.2% of the annual total Rs; (2) surface soil freezing controlled the diurnal pattern of Rs and bulk soil freezing induced lower reference respiration rate (R0) and temperature sensitivity (Q10) than those in the growing season (0.40–0.53 versus 0.84–1.32 µmol CO2 m−2 s−1 for R0 and 2.5–2.9 versus 2.9–5.6 for Q10); and (3) the intraannual variation in cumulative Rs was controlled by accumulated surface soil temperature. We found that in the summer monsoon‐dominated Tibetan alpine grassland, surface soil freezing, bulk soil freezing, and accumulated surface soil temperature are the day‐, season‐, and year‐scale drivers of the non‐growing‐season Rs, respectively. Our results suggest that warmer winters can trigger carbon loss from this ecosystem because of higher Q10 of thawed than frozen soils.

Physiographic and climatic controls on snow cover persistence in the Sierra Nevada Mountains

AbstractThe persistence of snow cover across mountainous landscapes influences land‐atmosphere energy exchange, water availability, the partitioning of snowmelt into various hydrologic pathways, vegetation productivity, and fluxes of nutrients. Understanding the processes controlling snow cover persistence has been limited as relationships between physiography, climate, and snow persistence are nonlinear and difficult to characterize empirically. The work detailed herein uses 7 years of remotely sensed snow cover persistence observed from the Moderate Resolution Imaging Spectroradiometer over the Sierra Nevada Mountains as a dependent variable in binary regression tree models with a suite of independent variables comprised of both physiographic and climatic metrics. Annual snow cover persistence over 2001–2007 revealed significant inter‐annual variability, with domain‐average snow persistence values exceeding 4.01 (i.e. early April) in the wettest year of 2005 and reaching as low as 2.90 (i.e. late February) in the driest year of 2007. Regression tree models revealed that elevation was the most important explanatory variable regarding snow cover persistence, ranking first in the hierarchical models in 10 out of 13 watersheds. Precipitation (Feather and Owens River basins) and temperature (Kern River basin) were the first‐ranking variables in the remaining three watersheds. Second, the order variables of importance included vegetation, which ranked between 2nd and 5th in 10 of 13 watersheds, and slope, which ranked 4th and 5th in 12 of the 13 watersheds. Interestingly, solar radiation and aspect were of tertiary importance but were more influential in watersheds with north–south orientation (e.g. in the Feather, Mokelumne and Stanislaus watersheds). These results have implications for understanding the sensitivity of snow cover persistence to changes in climate as watersheds where elevation and/or temperature strongly influence snow cover persistence may be more sensitive to future warming. Further work is needed to identify associated ecosystem sensitivities to future changes in snow cover persistence. Copyright © 2014 John Wiley & Sons, Ltd.

A GIS-based method for defining snow zones: application to the western United States

This study maps the geographic extent of intermittent and seasonal snow cover in the western United States using thresholds of 2000–2010 average snow persistence derived from moderate resolution imaging spectroradiometer snow cover area data from 1 January to 3 July. Results show seasonal snow covers 13% of the region, and intermittent snow covers 25%. The lower elevation boundaries of intermittent and seasonal snow zones increase from north-west to south-east. Intermittent snow is primarily found where average winter land surface temperatures are above freezing, whereas seasonal snow is primarily where winter temperatures are below freezing. However, temperatures at the boundary between intermittent and seasonal snow exhibit high regional variability, with average winter seasonal snow zone temperatures above freezing in west coast mountain ranges. Snow cover extent at peak accumulation is most variable at the upper elevations of the intermittent snow zone, highlighting the sensitivity of this snow zone boundary to climate conditions.

Permafrost and snow monitoring at Rothera Point (Adelaide Island, Maritime Antarctica): Implications for rock weathering in cryotic conditions

In February 2009 a new permafrost borehole was installed close to the British Antarctic Survey Station at Rothera Point, Adelaide Island (67.57195°S 68.12068°W). The borehole is situated at 31masl on a granodiorite knob with scattered lichen cover. The spatial variability of snow cover and of ground surface temperature (GST) is characterised through the monitoring of snow depth on 5 stakes positioned around the borehole and with thermistors placed at three different rock surfaces (A, B and C). The borehole temperature is measured by 18 thermistors placed at different depths between 0.3 and 30m. Snow persistence is very variable both spatially and temporally with snow free days per year ranging from 13 and more than 300, and maximum snow depths varying between 0.03 and 1.42m. This variability is the main cause of high variability in GST, that ranged between −3.7 and −1.5°C. The net effect of the snow cover is a cooling of the surface. Mean annual GST, mean summer GST, and the degree days of thawing and the n-factor of thawing were always much lower at sensor A where snow persistence and depth were greater than in the other sensor locations. At sensor A the potential freeze–thaw events were negligible (0–3) and the thermal stress was at least 40% less than in the other sensor locations. The zero curtain effect at the rock surface occurred only at surface A, favouring chemical weathering over mechanical action. The active layer thickness (ALT) ranged between 0.76 and 1.40m. ALT was directly proportional to the mean air temperature in summer, and inversely proportional to the maximum snow depth in autumn. ALT temporal variability was greater than reported at other sites at similar latitude in the Northern Hemisphere, or with the similar mean annual air temperature in Maritime Antarctica, because vegetation and a soil organic horizon are absent at the study site. Zero annual amplitude in temperature was observed at about 16m depth, where the mean annual temperature is −3°C. Permafrost thickness was calculated to range between 112 and 157m, depending on the heat flow values adopted. The presence of sub-sea permafrost cannot be excluded considering the depth of the shelf around Rothera Point and its glacial history.

Snowmelt runoff and soil moisture dynamics on steep subalpine hillslopes

AbstractSnowmelt water supplies streamflow and growing season soil moisture in mountain regions, yet pathways of snowmelt water and their effects on moisture patterns are still largely unknown. This study examined how flow processes during snowmelt runoff affected spatial patterns of soil moisture on two steep sub‐alpine hillslope transects in Rocky Mountain National Park, CO, USA. The transects have northeast‐facing and east‐facing aspects, and both extend from high‐elevation bedrock outcrops down to streams in valley bottoms. Spatial patterns of both snow depth and near‐surface soil moisture were surveyed along these transects in the snowmelt and summer seasons of 2008–2010. To link these patterns to flow processes, soil moisture was measured continuously on both transects and compared with the timing of discharge in nearby streams. Results indicate that both slopes generated shallow lateral subsurface flow during snowmelt through near‐surface soil, colluvium and bedrock fractures. On the northeast‐facing transect, this shallow subsurface flow emerged through mid‐slope seepage zones, in some cases producing saturation overland flow, whereas the east‐facing slope had no seepage zones or overland flow. At the hillslope scale, earlier snowmelt timing on the east‐facing slope led to drier average soil moisture conditions than on the northeast‐facing slope, but within hillslopes, snow patterns had little relation to soil moisture patterns except in areas with persistent snow drifts. Results suggest that lateral flow and exfiltration processes are key controls on soil moisture spatial patterns in this steep sub‐alpine location. Copyright © 2014 John Wiley & Sons, Ltd.

Pseudo 3‐D P wave refraction seismic monitoring of permafrost in steep unstable bedrock

AbstractDegrading permafrost in steep rock walls can cause hazardous rock creep and rock slope failure. Spatial and temporal patterns of permafrost degradation that operate at the scale of instability are complex and poorly understood. For the first time, we used P wave seismic refraction tomography (SRT) to monitor the degradation of permafrost in steep rock walls. A 2.5‐D survey with five 80 m long parallel transects was installed across an unstable steep NE‐SW facing crestline in the Matter Valley, Switzerland. P wave velocity was calibrated in the laboratory for water‐saturated low‐porosity paragneiss samples between 20°C and −5°C and increases significantly along and perpendicular to the cleavage by 0.55–0.66 km/s (10–13%) and 2.4–2.7 km/s (>100%), respectively, when freezing. Seismic refraction is, thus, technically feasible to detect permafrost in low‐porosity rocks that constitute steep rock walls. Ray densities up to 100 and more delimit the boundary between unfrozen and frozen bedrock and facilitate accurate active layer positioning. SRT shows monthly (August and September 2006) and annual active layer dynamics (August 2006 and 2007) and reveals a contiguous permafrost body below the NE face with annual changes of active layer depth from 2 to 10 m. Large ice‐filled fractures, lateral onfreezing of glacierets, and a persistent snow cornice cause previously unreported permafrost patterns close to the surface and along the crestline which correspond to active seasonal rock displacements up to several mm/a. SRT provides a geometrically highly resolved subsurface monitoring of active layer dynamics in steep permafrost rocks at the scale of instability.

Anatomy of wintertime ozone associated with oil and natural gas extraction activity in Wyoming and Utah

Abstract Winter maximum daily 8-hour average (MDA8) ozone concentrations in the Upper Green River Basin, Wyoming (UGRBWY) and the Uintah Basin, Utah (UBUT) have frequently exceeded 100 ppb in January, February and March, in the past few years. Such levels are well above the U.S. air quality standard of 75 ppb. In these two remote basins in the Rockies, local ozone precursor emissions result from intense oil and gas extraction activities that release methane, volatile organic compounds (VOCs), and nitrogen oxides (NOx) to the atmosphere. These emissions become trapped beneath a stable and shallow (∼50–200 m) boundary layer maintained in low wind conditions. Wintertime surface ozone formation conditions are more likely in the UBUT than in the UGRBWY as the topography of the UBUT is an enclosed basin whereas the UGRBWY is open on its southern perimeter thus allowing for more air turnover. With snow-covered ground, high ozone events regularly begin in mid-December and last into early March in the UBUT whereas they usually do not begin in earnest until about a month later in the UGRBWY and may persist until mid-March. Winters without snow cover and the accompanying cold pool meteorological conditions do not experience high ozone events in either basin. For nine years with ozone observations in the UGRBWY (2005–2013) and four in the UBUT (2010–2013), all years with adequate (≥6 inches) and persistent snow cover, experienced days with ozone values ≥75 ppb except in 2012 in the UGRBWY when persistent high wind (>5 m/s) conditions were prevalent. Year to year differences in the occurrences of high ozone episodes appear to be driven primarily by differing meteorological conditions rather than by variations in ozone precursor levels.

Long-term vegetation dynamic in the Northwestern Caucasus: which communities are more affected by upward shifts of plant species?

We studied long-term (25–31 years) dynamics of alpine communities at the Teberda Reserve, NW Caucasus, Russia, to test the following hypotheses: (1) lower altitude species increase and high altitude species decrease their abundance as a consequence of climate warming; (2) such changes in abundance are more significant in communities with short growth season (due to persistent snow cover) compared to exposed communities; (3) species with similar changes in abundance have similar functional traits. Four alpine communities with different positions in relief were considered in order of winter snow cover: alpine lichen heaths (ALH), Festuca varia grasslands (FVG), Geranium-Hedysarum meadows (GHM), and snowbed communities (SBC).

Overwintering potential of the stripe rust pathogen (Puccinia striiformis) in central Alberta

In central Alberta, stripe rust (Puccinia striiformis) of wheat and barley has become more prevalent and this disease is generally more severe on winter wheat than spring wheat. This study was carried out to determine the potential role of winter wheat in overwintering and transmission of inoculum to subsequent spring crops. Field plants of winter wheat, infected in the autumn, were sampled during January to May from 2008 to 2011 in central Alberta. The pathogen's viability was established using in vivo growth parameters and pathogen detection was determined using PCR. Approximately 4–20% of urediniospores sampled from pustules on winter wheat during January to March–April of each year were viable. Latent mycelia were intermittently observed on winter wheat sampled from January to May in each of 2008 and 2010. The fungus was detected using PCR intermittently from winter to early spring. Persistent snow cover was found to be critical for the survival of overwintering inoculum, as viable pustules and urediniospores rarely survived after snow melt. There was higher stripe rust severity in spring wheat or barley seeded near winter wheat compared with the same crops seeded near spring wheat, for all years of field testing. The epidemiological significance of overwintering inoculum is discussed in relation to stripe rust management in central Alberta.

Spatiotemporal index for analyzing controls on snow climatology: application in the Colorado Front Range

Mountain snowpacks are important water supplies that are susceptible to climate change, yet snow measurements are sparse relative to snowpack heterogeneity. We used remote sensing to derive a spatiotemporal index of snow climatology that reveals patterns in snow accumulation, persistence, and ablation. Then we examined how this index relates to climate, terrain, and vegetation. Analyses were based on Moderate Resolution Imaging Spectroradiometer eight-day snow cover from 2000 to 2010 for a mountain watershed in the Colorado Front Range, USA. The Snow Cover Index (SCI) was calculated as the fraction of years that were snow covered for each pixel. The proportion of SCI variability explained by independent variables was evaluated using regression analysis. Independent variables included elevation, northing, easting, slope, aspect, northness, solar radiation, precipitation, temperature, and vegetation cover. Elevation was the dominant control on SCI patterns, due to its influence on both temperature and precipitation. Grouping SCI values by elevation, we identified three distinct snow zones in the basin: persistent, transitional, and intermittent. The transitional snow zone represents an area that is sensitive to losing winter snowpack. The SCI can be applied to other basins or regions to identify dominant controls on snow cover patterns and areas sensitive to snow loss.

Simulation of a persistent snow storm over southern China with a regional atmosphere-ocean coupled model

A regional atmosphere-ocean coupled model, RegCM3-POM, was developed by coupling the regional climate model (RegCM3) with the Princeton Ocean Model (POM). The performance of RegCM3-POM in simulating a persistent snow storm over southern China and the impact of the Madden-Julian oscillation (MJO) on this persistent snow storm were investigated. Compared with the stand-alone RegCM3, the coupled model performed better at reproducing the spatial-temporal evolution and intensity of the precipitation episodes. The power spectral analysis indicated that the coupled model successfully captured the dominant period between 30 and 60 days in the precipitation field, leading to a notable improvement in simulating the magnitude of intraseasonal precipitation variation, and further in enhancing the intensity of the simulated precipitation. These improvements were mainly due to the well-simulated low-frequency oscillation center and its eastward propagation characteristics in each MJO phase by RegCM3-POM, which improved the simulations of MJO-related low-frequency vertical motions, water vapor transport, and the deep inversion layer that can directly influence the precipitation event and that further improved the simulated MJO-precipitation relationship. Analysis of the phase relationship between convection and SST indicated that RegCM3-POM exhibits a near-quadrature relation between the simulated convection and SST anomalies, which was consistent with the observations. However, such a near-quadrature relation was not as significant when the stand-alone RegCM3 was used. This difference indicated that the inherent coupled feedback process between the ocean and atmosphere in RegCM3-POM played an important part in reproducing the features of the MJO that accompanied the snow storm.

Ecological tree line history and palaeoclimate – review of megafossil evidence from the Swedish Scandes

The postglacial tree line and climate history in the Swedish Scandes have been inferred from megafossil tree remains. Investigated species are mountain birch (Betula pubescens ssp. czerepanovii), Scots pine (Pinus sylvestris) and grey alder (Alnus incana). Betula and Pinus first appeared on early deglaciated nunataks during the Lateglacial. Their tree lines peaked between 9600 and 9000 cal. a BP, almost 600 m higher than present‐day elevations. This implies (adjusted for land uplift) that early Holocene summer temperatures may have been 2.3°C above modern ones. Elevational tree line retreat characterized the Holocene tree line evolution. For short periods, excursions from this trend have occurred. Between c. 12 000 and 10 000 cal. a BP, a pine‐dominated subalpine belt prevailed. A first major episode of descent occurred c. 8200 cal. a BP, possibly forced by cooling and an associated shift to a deeper and more persistent snow pack. Thereafter, the subalpine birch forest belt gradually evolved at the expense of the prior pine‐dominated tree line ecotone. A second episode of pine descent took place c. 4800 cal. a BP. Historical tree line positions are viewed in relation to early 21st century equivalents, and indicate that tree line elevations attained during the past century and in association with modern climate warming are highly unusual, but not unique, phenomena from the perspective of the past 4800 years. Prior to that, the pine tree line (and summer temperatures) was consistently higher than present, as it was also during the Roman and Medieval periods, c. 1900 and 1000 cal. a BP, respectively.

Soil radon in winter months under snowpack in Hokkaido, Japan

Soil radon (222Rn) has been monitored during winter months under cool-temperate deciduous stands of different surface geology in Tomakomai and in Sapporo, Hokkaido, Japan. Radon level was lower in Tomakomai of immature soil of porous volcanic ash emitted from an active volcano (Mt. Tarumae), compared with those in Sapporo of alluvial sediments. In Tomakomai, mean value of the 222Rn activity concentration was higher in winter (570 Bq m−3) than in summer (350 Bq m−3) at a depth of 1 m, which is consistent with the results in cold and dry winter reported in the literature. In contrast, soil radon decreasing with decreasing soil temperature from mid-September (5.0 kBq m−3) remained low (2.6 kBq m−3) under persistent snow in Sapporo, which had already been observed in the same location. Measurements of the activity concentrations of 222Rn in snow and in snow air as well as in soil air indicate that the small amount of 222Rn is released from the ground surface to the overlying snowpack with a 222Rn flux density of 0.4 mBq m−2 s−1 under thick snow cover in Sapporo.