Role of temporal resolution of meteorological inputs for process‐based snow modelling

Accurate snow accumulation and melt simulations are crucial for understanding and predicting hydrological dynamics in mountainous settings. As snow models require temporally varying meteorological inputs, time resolution of these inputs is likely to play an important role on the model accuracy. Because meteorological data at a fine temporal resolution (~1 hr) are generally not available in many snow‐dominated settings, it is important to evaluate the role of meteorological inputs temporal resolution on the performance of process‐based snow models. The objective of this work is to assess the loss in model accuracy with temporal resolution of meteorological inputs, for a range of climatic conditions and topographic elevations. To this end, a process‐based snow model was run using 1‐, 3‐, and 6‐hourly inputs for wet, average, and dry years over Boise River Basin (6,963 km²), which spans rain dominated (≤1,400 m), rain–snow transition (>1,400 and ≤1,900 m), snow dominated below tree line (>1,900 and ≤2,400 m), and above tree line (>2,400 m) elevations. The results show that sensitivity of the model accuracy to the inputs time step generally decreases with increasing elevation from rain dominated to snow dominated above tree line. Using longer than hourly inputs causes substantial underestimation of snow cover area (SCA) and snow water equivalent (SWE) in rain‐dominated and rain–snow transition elevations, due to the precipitation phase mischaracterization. In snow‐dominated elevations, the melt rate is underestimated due to errors in estimation of net snow cover energy input. In addition, the errors in SCA and SWE estimates generally decrease toward years with low snow mass, that is, dry years. The results indicate significant increases in errors in estimates of SCA and SWE as the temporal resolution of meteorological inputs becomes coarser than an hour. However, use of 3‐hourly inputs can provide accurate estimates at snow‐dominated elevations. The study underscores the need to record meteorological variables at an hourly time step for accurate process‐based snow modelling.     

Linking hydrological variations at local scales to regional climate teleconnection patterns

Climate patterns over preceding years affect seasonal water and moisture conditions. The linkage between regional climate and local hydrology is challenging due to scale differences, both spatially and temporally. In this study, variance, correlation, and singular spectrum analyses were conducted to identify multiple hydroclimatic phases during which climate teleconnection patterns were related to hydrology of a small headwater basin in Idaho, USA. Combined field observations and simulations from a physically based hydrological model were used for this purpose. Results showed statistically significant relations between climate teleconnection patterns and hydrological fluxes in the basin, and climate indices explained up to 58% of hydrological variations. Antarctic Oscillation (AAO), North Atlantic Oscillation (NAO), and Pacific North America (PNA) patterns affected mountain hydrology, in that order, by decreasing annual runoff and rain on snow (ROS) runoff by 43% and 26% during a positive phase of NAO and 25% and 9% during a positive phase of PNA. AAO showed a significant association with the rainfall-to-precipitation ratio and explained 49% of its interannual variation. The runoff response was affected by the phase of climate variability indices and the legacy of past atmospheric conditions. Specifically, a switch in the phase of the teleconnection patterns of NAO and PNA caused a transition from wet to dry conditions in the basin. Positive AAO showed no relation with peak snow water equivalent and ROS runoff in the same year, but AAO in the preceding year explained 24 and 25% (p < 0.05) of their variations, suggesting that the past atmospheric patterns are equally important as the present conditions in affecting local hydrology. Areas sheltered from the wind and acted as a source for snow transport showed the lowest (40% below normal) ROS runoff generation, which was associated with positive NAO that explained 33% (p < 0.01) of its variation. The findings of this research highlighted the importance of hydroclimatic phases and multiple year variations that must be considered in hydrological forecasts, climate projections, and water resources planning.     

Estimation of the energy used to melt snow in the Tien Shan mountains and Japanese Islands

The heat needed to melt snow over the Tien Shan mountains and Japanese Islands for 10-day period (TDP) was estimated. Melting curves and a map of snowmelt duration were obtained through the long-term data from 79 stations in the Tien Shan mountains and 20 stations in the Japanese Islands. At high elevations in the mountains, about 40% of the snow melts during penultimate 10 days of snow cover. In the Japanese Islands, about 80% of the snow melts during the last 20 days of snow cover. Over the mountains, 0.13×10⁴ MJ m² year⁻¹ is needed to melt snow in the northern and western Tien Shan where maximum snow accumulation occurred. The volume of air cooled 10 °C by snowmelt amounted to 4.4×10⁶ km³ year⁻¹ over the Tien Shan mountains and 3×10⁶ km³ year⁻¹ over the Japanese Islands. The most significant impact of snowmelt on air temperature was observed at an elevation of 2500 m in the western and northern Tien Shan. Air that was cooled 10 °C could reach an elevation of 2.1 km day⁻¹. Over the Japanese Islands, energy losses from snowmelt amounted to 0.26×10¹⁴ MJ year⁻¹ and the maximum occurred over Honshu Island. The heat loss from snowmelt in the Tien Shan mountains and Japanese Islands amounted to about 2/3 of heat loss in the Eurasian continental plains.     

Statistical probability distribution of snow depth at the model sub‐grid cell spatial scale

Comprehensive snow depth data, collected using georadar and hand probing, were used for statistical analyses of snow depths inside 1 km grid cells. The sub‐grid cell spatial scale was 100 m. Statistical distribution functions were found to have varying parameters, and an attempt was made to connect these statistical parameters to different terrain variables. The results showed that the two parameters mean and standard deviation of snow depth were significantly related to the sub‐grid terrain characteristics. Linear regression models could explain up to 50% of the variation for both of the snowcover parameters mentioned. Copyright © 2004 John Wiley & Sons, Ltd.     

Design and realization of the drawing software for snow/ice stratigraphic profile

1　IntroductionSnow/icestratigraphicprofileisoneofthetraditionalandimportantresearchfieldsinglaciology (Qin 1 995 ;Xie 1 988) .Thesnow pitprofilesareobserveddirectlyinthefield ,andthestratigraphicprofilesoficecoresaredelineatedandcompiledindetailat1∶1scalethroughnakedeyesinlow temperaturelaboratory .Themajorstratigraphicchar acteristicsobservedincludingcrystalgrainsize,structureofdepthhoar,lighttransmis sion,meltphenomena,windcrustetc.(ShojiandLangway 1 989) ,arenecessarytobedelineatedindia…     

Role of Ozone Deposition in the Occurrence of the Spring Maximum

Abstract

A hypothesis has been formulated on the basis of experimental data presented in this article. According to the hypothesis, occurrence of the spring surface ozone maximum at mid-latitudes results from a delay in snow-cover melt. The data were collected at ozone stations in Minsk (Belarus) and Preila (Lithuania). Because the measurements of surface ozone concentration are quite different, despite the close proximity of the stations, a conclusion can be drawn about the significant influence of meteorological parameters on measurements. In addition to a rather subjective and poorly defined parameter—time of snow melt—the difference between the average March temperature and a climatological mean may be treated as a criterion for the presence or absence of the spring ozone maximum.     

2015年1月大气环流和天气分析

2015年1月大气环流主要特征为：北半球极涡呈偶极型分布,中心气压均较常年偏低。欧亚中高纬环流呈三波型,以纬向环流为主;西太平洋副热带高压和南支槽的强度接近常年平均水平。1月全国平均气温为-3.1℃,较常年同期（-5.0℃）偏高1.9℃,为1961年以来同期最高。全国平均降水量14.4 mm,较常年同期(13.2 mm)偏多气候中心原数据为9.0,但计算为9.1,但分布极不均匀,西南地区、西北地区和华南南部降水偏多,而华北至江南一带则明显偏少,北京等地几乎无降水。月内仅在上旬出现了1次全国范围中等强度冷空气过程,而降水过程有5次。上旬后期,云南等地出现了创历史极值的强雨雪天气,气象干旱得到有效缓解。月末中东部地区出现入冬以来最大范围雨雪过程,贵州等地出现冻雨。中东部月内共出现3次大范围雾 霾天气。     

2013年湖北省两次降雪过程对比分析

利用常规观测资料、NCEP再分析资料、微波辐射计及多普勒雷达等资料对2013年2月7—8日干雪过程、2月18—19日湿雪过程,从水汽、不稳定、动力及温湿层结方面进行对比分析,得出如下结论：（1）2月7—8日的干雪过程水汽层次浅薄,水汽输送支仅为700 hPa弱西南气流;2月18—19日的湿雪过程水汽充沛,水汽输送支为700 hPa强西南急流和850 hPa 东南气流。（2）干雪过程低层冷平流强,层结稳定。湿雪过程低层暖平流强,冷暖交汇使大气不稳定度增加。（3）干雪过程中弱暖湿气流沿深厚冷空气垫爬升,动力辐合位于中高层,次级环流的形成减弱上升运动。湿雪过程中弱冷空气楔入到强暖湿气流底部,迫使其抬升,形成深厚上升运动区,次级环流的形成增强上升运动。（4）干雪过程整层温度<0℃,700 hPa出现冷性逆温层,-10℃层位于925 hPa附近,水汽密度、液态水含量、整层水汽含量较小;湿雪过程700 hPa出现暖性逆温层,-10℃层位于500 hPa附近,水汽密度、液态水含量、整层水汽含量较大。在上述研究的基础上给出了干、湿雪形成的三维物理模型,该模型从温湿（风）垂直层结上面体现出了干、湿雪形成的主要环境背景差异,对于干、湿雪预报具有一定的参考价值。     

Influence of canopy density on snow distribution in a temperate mountain range

We analyse spatial variability and different evolution patterns of snowpack in a mixed beech–fir stand in the central Pyrenees. Snow depth and density were surveyed weekly along six transects of contrasting forest cover during a complete accumulation and melting season; we also surveyed a sector unaffected by canopy cover. Forest density was measured using the sky view factor (SVF) obtained from digital hemispherical photographs. During periods of snow accumulation and melting, noticeable differences in snow depth and density were found between the open site and those areas covered by forest canopy. Principal component analysis provided valuable information in explaining these observations. The results indicate a high variability in snow accumulation within forest areas related to differences in canopy density. Maximum snow water equivalent (SWE) was reduced by more than 50% beneath dense canopies compared with clearings, and this difference increased during the melting period. We also found significant temporal variations: when melting began in sectors with low SVF, most of the snow had already thawed in areas with high SVF. However, specific conditions occasionally produced a different response of SWE to forest cover, with lower melting rates observed beneath dense canopies. The high values of correlation coefficients for SWE and SVF (r > 0·9) indicate the reliability of predicting the spatial distribution of SWE in forests when only a moderate number of observations are available. Digital hemispherical photographs provide an appropriate tool for this type of analysis, especially for zenith angles in the range 35–55 . Copyright © 2007 John Wiley & Sons, Ltd.