An Investigation of the Influence of Cyclonic Airstreams on Midwestern Snowfall

Although previous climatological studies have investigated the relationship between cyclone frequency and trajectory and regional weather, analyses of structural airflow features and precipitation have been confined to meteorological case studies. In the following paper, the influence of Colorado cyclone airstreams on Midwestern snowfall is investigated using isentropic streamline maps for five cold season months. Results indicate that Colorado cyclones account for a minor percentage of Midwestern snowfall events and amounts. When snowfall is induced by Colorado cyclogenesis, diffluence and instability in the cold sector portions of the cyclone are the dominant lifting mechanisms.     

CLIMATOLOGY OF SURFACE CYCLONE TRAJECTORY AND INTENSITY FOR HEAVY-SNOW EVENTS AT THREE MIDWESTERN STATIONS

In this paper, we assess interstorm cyclone variations in intensity and motion for heavy-snow events at three north-central U.S. stations: Minneapolis, Madison, and Indianapolis. Daily data for the period from 1966 to 1996 were used to select the 157 storm events. Heavy-snow cyclone track location (latitude and longitude) and intensity (central pressure) means and standard deviations are calculated for each station and related to snowfall magnitude. The most northwesterly of the three stations, Minneapolis, had the largest median heavy-snowfall total and also the largest standard deviation in heavy-snowfall amount. Statistical analysis of surface cyclone parameters reveals significant interstation differences in storm trajectory and intensity measures for all cyclones and cyclogenesis group subsets. Chi-square tests suggest that the distribution of storms by month and cyclogenesis type is significantly nonrandom for all stations. Summary findings indicate that Midwestern heavy-snow events are dominated by southern Great Plains cyclones and that storms from secondary cyclogenic regions contribute to significant differences at the three selected locations. [Key words: cyclones, snowfall, Midwest.]     

Estimating Climate-Change Impacts on Colorado Plateau Snowpack Using Downscaling Methods

This study develops observed climate-based downscaling transfer functions that are used with general circulation model (GCM) output to assess potential global-change impacts on Upper Colorado Plateau, USA, water resources. Daily automated snow water equivalent stations are used with 700 mb atmospheric circulation to determine empirical transfer functions. Downscaling methodologies using multiple regression and neural networks are evaluated, with the neural network results explaining approximately 70%of the daily snowfall variance. The neural network-based transfer functions are used with the GENESIS GCM to simulate snowfall characteristics in both a 1xCO₂ and a 2xCO₂ climate. While the total precipitation simulated by the 2xCO₂ analysis remains nearly the same as today, less will fall as snow; specifically, snow water equivalence shows significant reduction (except in the Green River Basin) as the snow season is reduced by 58 days on average.     

CLIMATOLOGICAL CLASSIFICATION OF SEVERE WIND-DRIVEN RAIN EVENTS AFFECTING THE SOUTHERN UNITED STATES

This paper follows recent studies of wind-driven rain (WDR), and statistically defines a “severe” WDR event. The research suggests a classification for severe WDR events by association with larger-scale weather systems. The study incorporates data for the period 1971 to 1995 and, from these data, the analysis reveals that severe WDR events are confined mainly to the southern United States and occur most frequently in the cold and transition seasons. Extratropical cyclones are the most common synoptic-scale weather systems associated with severe WDR events. Extratropical cyclones originating in three areas accounted for more than 70 percent of the severe events in the study. The cyclone types are referred to as Colorado Lows (CLs), Gulf Lows (GLs), and Texas Lows (TLs). The attendant synoptic-scale conditions of cyclones that produced severe WDR events differ significantly from extratropical cyclones originating in similar areas but not producing severe events. Key differences between the two cyclone populations are the cyclone track trajectories and the low and midlevel synoptic environments promoting cyclone intensification. [Key words: wind-driven rain (WDR), synoptic climatology, extratropical cyclones, United States.]     

Sedimentary geochemistry of core PG1351 from Lake El’gygytgyn—a sensitive record of climate variability in the East Siberian Arctic during the past three glacial–interglacial cycles

The ca. 13 m long sediment core PG1351, recovered in 1998 from the central part of Lake El’gygytgyn, NE Siberia, was investigated for lithostratigraphy, water content, dry bulk density (DBD), total organic carbon (TOC), total nitrogen (TN), total sulphur (TS) and biogenic silica (opal) contents, and for TOC stable isotope ratios (δ¹³C_TOC). The event stratigraphy recorded in major differences in sediment composition match variations in regional summer insolation, thus confirming a new age model for this core, which suggests that it spans the last 250 ka BP. Four depositional units of contrasting lithological and biogeochemical composition have been distinguished, reflecting past environmental conditions associated with relatively warm, peak warm, cold and dry, and cold but more moist climate modes. A relatively warm climate, resulting in complete summer melt of the lake ice cover and seasonal mixing of the water column, prevailed during the Holocene and Marine Isotope Stages (MIS) 3, 5.1, 5.3, 6.1, 6.3, 6.5, 7.1–7.3, 7.5, 8.1 and 8.3. MIS 5.5 (Eemian) was characterized by significantly enhanced aquatic primary production and organic matter supply from the catchment, indicating peak warm conditions. During MIS 2, 5.2, 5.4, 6.2 and 6.4 the climate was cold and dry, leading to perennial lake ice cover, little regional snowfall, and a stagnant water body. A cold but more moist climate during MIS 4, 6.6, 7.4, 8.2 and 8.4 is thought to have produced more snow cover on␣the perennial ice, strongly reducing light penetration and biogenic primary production in␣the lake. While the cold–warm pattern during␣the past three glacial–interglacial cycles is probably controlled by changes in regional summer insolation, differences in the intensity of the warm phases and in the degree of aridity (changing snowfall) during cold phases likely were due to changes in atmospheric circulation patterns. This is the seventh in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and its catchment in NE Russia. JulieBrigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue.     

Estimating Climate-Change Impacts on Colorado Plateau Snowpack Using Downscaling Methods

This study develops observed climate-based downscaling transfer functions that are used with general circulation model (GCM) output to assess potential global-change impacts on Upper Colorado Plateau, USA, water resources. Daily automated snow water equivalent stations are used with 700 mb atmospheric circulation to determine empirical transfer functions. Downscaling methodologies using multiple regression and neural networks are evaluated, with the neural network results explaining approximately 70%of the daily snowfall variance. The neural network-based transfer functions are used with the GENESIS GCM to simulate snowfall characteristics in both a 1xCO₂ and a 2xCO₂ climate. While the total precipitation simulated by the 2xCO₂ analysis remains nearly the same as today, less will fall as snow; specifically, snow water equivalence shows significant reduction (except in the Green River Basin) as the snow season is reduced by 58 days on average.     

The structure and behavior of the arctic cyclone in summer analyzed by the JRA-25/JCDAS data

In this study, three-dimensional structures and the life-time behavior of arctic cyclones are investigated as case studies, using reanalysis data of JRA-25 and JCDAS. In recent years, arctic region has undergone drastic warming in conjunction with the reduced sea ice concentration in summer. The rapid reduction of the sea ice concentration is explained, to some extent, by a pressure dipole of the arctic cyclone and Beaufort high over the Arctic Ocean. This paper presents some case studies for the structure of the arctic cyclone.It is found by the analysis of this study that the arctic cyclone indicates many differences in structure and behavior compared with the mid-latitude cyclone. The arctic cyclones move rather randomly in direction over the Arctic Ocean. The arctic cyclone has a barotropic structure in the vertical from the surface to the stratosphere. The arctic cyclone detected at the sea level pressure is connected with the polar vortex at the 500 hPa level and above. Importantly, the arctic cyclone has a cold core in the troposphere and a warm core around the 200 hPa level. The mechanism of the formation is discussed based on the analyzed structure of the arctic cyclones.     

Sub-regional snow cover distribution across the southern Appalachian Mountains

Abstract

Snowfall in the Southern Appalachian Mountain region of the eastern US is characterized by much spatiotemporal variability. Annual snowfall totals vary by up to 75 cm, and variations in snowfall intensity can lead to large differences in the local snowfall distribution. Research has shown that the synoptic pattern associated with the snowfall strongly influences the regional-scale distribution of snow cover. However, topographic variability results in locally complex snow cover patterns that are not well understood or documented. In this study, we characterize the snow covered area (SCA) and fractional snow cover associated with different synoptic patterns in 14 individual sub-regions. We analyze 63 snow events using Moderate-resolution Imaging Spectroradiometer standard snow cover products to ascertain both qualitative and quantitative differences in snow cover across sub-regions. Among sub-regions, there is significant variation in the snow cover pattern from individual synoptic classes. Furthermore, the percent SCA follows the regional snowfall climatology, and sub-regions with the highest elevations and northerly latitudes exhibit the greatest variability. Results of the sub-regional analysis provide valuable guidance to forecasters by contributing a deeper understanding of local snow cover patterns and their relationship to synoptic-scale circulation features.     

Spatial Scale and Population Assignment Choices in Environmental Justice Analyses 1

Abstract

Environmental justice laws protect certain populations against discriminatory actions that may result from a myriad of enterprises, including transportation activities. Previous environmental equity studies examining the effects of transportation-engendered externalities have been criticized on several points, including (1) that the choice of a reference population for comparison to the criterion variable may influence the outcome of research results and (2) that the selection and use of inappropriate methodologies intended to identify and characterize populations may foreordain research outcomes. This article examines the potentially confounding effects of selected spatial scale and population assignment strategies as applied to a study of excessive noise levels at a large Midwestern airport, finding that reported outcomes can vary significantly as a function of methodological choices.     

Experienced Teacher Participation in Preservice Programs: A Model in Geography at the University of Northern Colorado

Abstract

This paper discusses a model program for preparing secondary geography teachers in the Department of Geography at the University of Northern Colorado. The key feature of the program is the presence of an outstanding secondary teacher in residence throughout the year who team-teaches the Teaching Methods in Geography and World Geography courses with geography faculty, modeling effective ways of teaching the subject. Students are paired with Colorado Geographic Alliance teacher-consultants in summer institutes and for student teaching. Analysis of formative evaluation data collected through the third year provides some measure of the program's success. Students have responded favorably to the use of a variety of teaching strategies, the opportunity to discuss with faculty why certain strategies are utilized, and how their own constructed lessons have worked in their student teaching. They have also reported that their understanding of geography has improved from taking the team-taught courses.     

新疆北部小时降雪特征及大暴雪天气影响系统研究

新疆北部是我国降雪高频区之一,随着全球变暖降雪量呈显著增加趋势,对新疆气候产生重要影响,由于观测资料限制对该区域小时降雪研究还未开展,影响降雪精细化预报和服务能力提升。因此,利用新疆天山山区及其以北（以下称“新疆北部”）2012年11月—2021年2月50个国家气象站小时降雪观测资料,分析了冷季（11月—翌年2月）小时降雪特征,并按日降雪量从高到低挑选30个大暴雪过程分析其小时降雪特征、影响系统及典型环流配置。结果表明：（1） 阿勒泰北部、塔城盆地、伊犁河谷为降雪小时数（SHN）高频区,可达200 h·a^-1以上;天山山区SHN高频区为海拔1800~2000 m的中山带,达127.3 h·a^-1,2000 m以上降雪很少。（2） 北疆和天山山区小时降雪量（R）≤1.0 mm·h^-1量级SHN占比分别为91.7%和91.9%,对降雪量贡献分别为70.7%和68.9%,R>1.0 mm·h^-1为小时极端降雪事件,对北疆和天山山区降雪量贡献分别为29.3%和31.1%。（3） 极端暴雪过程平均SHN为25.5 h,平均降雪量为30.7 mm,雪强约为1.2 mm·h^-1,大暴雪过程由长时间降雪导致,降雪持续时间是开展大暴雪研究和进行预报服务的关键点,造成大暴雪过程的影响系统主要有中亚长波槽、中亚低涡、乌拉尔山长波槽和西西伯利亚低涡（槽）,占比分别为30.0%、6.7%、13.3%和50.0%,中纬度长波槽（涡）和北方西西伯利亚低涡（槽）系统各为50.0%。     

冷锋型和蒙古气旋型沙尘天气过程典型个例对比分析

利用观测资料和NCEP再分析资料,对冷锋型和蒙古气旋型两类沙尘天气过程的典型个例进行对比分析。结果表明:斜压强迫在两类过程中均较为显著,冷锋型沙尘天气过程中,随高度降低高空槽明显加深;蒙古气旋型则在对流层低层（850 hPa）、中层（500 hPa）形成切断低压。冷锋型沙尘天气过程高空锋区位置较蒙古气旋型偏南,且南压更为明显;冷锋型沙尘天气过程沙尘天气区位置也较蒙古气旋型偏南,且主要向东南方向扩展。冷锋型地面高、低压强度对比明显大于蒙古气旋型,且地面风速与能见度的反相关性高于蒙古气旋型,锋后降温也较蒙古气旋型显著。冷锋型锋前上升运动中心位于700 hPa,锋后下沉运动中心位于600 hPa。蒙古气旋型气旋中心及其附近300 hPa以下均有强的上升运动。冷锋型锋面附近正涡度随高度增高而增大,蒙古气旋型气旋中心及其附近为正涡度。最后给出了冷锋型和蒙古气旋型沙尘天气过程的天气学概念模型。     

祁连山区季节性积雪资源的气候分析*

本文采用1986年10月至1988年9月NOAA—9、10两颗卫星的AVHRR资料标准化后反演的积雪参量,对照祈连山区26个气象站1951—1988年逐日雪深、雪密度和积雪日数的资科,修正卫星反演的平均值。得到高分辨率多年平均雪深和雪盖频率的空间分布。从而估算出各流域平均雪储量,并与降雪量和春季融雪径流作对此分析。     

Reconstruction of a climate record for the past 140 kyr based on diatom valve flux data from Lake Biwa, Japan

To reconstruct the pattern of past climate change in central Japan during the last 140 kyr, total planktonic diatom valve concentrations (valves g^–1) and fluxes (valves cm^–2 year^–1) of total planktonic diatoms flux (PVF) and individual species were examined using a 140-m core taken from Lake Biwa, Shiga Prefecture. Most records had a sample resolution between approximately 150 and 300 yr. Based on characteristics of past and modern diatom responses to possible climate variables, we interpreted changes in Stephanodiscus suzukii flux (SVF) to reflect changes in phosphorus levels, which reflect, in turn, summer precipitation levels; changes in Aulacoseiva nipponica flux (AVF) reflect winter vertical lake-water mixing induced by winter temperatures and snowfall levels. Thus, changes in total planktonic diatom flux reflect a combination of summer precipitation, winter temperature, and snowfall values. During the 140–101 ka interval, changes in S. suzukii productivity at a millennial timescale may correspond to changes in summer rainfall in central Japan. The disappearance of A. nipponica during the same period could indicate weaker vertical mixing, possibly caused by increased temperatures and decreased snowfall levels in winter. During the 101–70 ka interval, the AVF record shows levels near or above those observed in present times, indicating that winter water temperatures fell within the optimal range for A. nipponica to prosper. Generally low AVF values during the 70–7 ka interval indicate weak winter vertical mixing and cold winters. The many intervals with low PVF values during the same period suggest decreased summer precipitation levels. Between 7 and 0 ka, PVF, SVF, and AVF records show levels near or above those of the present, suggesting winter temperatures favorable for A. nipponica growth, and snowfall and summer precipitation levels probably similar to or above those currently recorded.     

Decrease in snowfall/rainfall ratio in the Tibetan Plateau from 1961 to 2013

On the basis of two gridded datasets of daily precipitation and temperature with a spatial resolution of 0.5°×0.5°, and meteorological station data released by the National Meteorological Information Center (NMIC) during 1961–2013, the spatial and temporal variations of total amount of precipitation, amount of rainfall, amount of snowfall and snowfall/rainfall ratio (S/R) in the Tibetan Plateau (TP) are analyzed using Sen’s slope, the Mann–Kendall mutation test, Inverse Distance Weighting (IDW) and the Morlet wavelet. Total amount of precipitation and amount of rainfall generally show statistically significant increasing trends of 0.6 mm·a^–1 and 1.3 mm·a^–1, respectively, while amount of snowfall and S/R have significant decreasing trends of–0.6 mm·a^–1 and–0.5% a^–1, respectively. In most regions, due to significant increasing trends in total amount of precipitation and amount of rainfall, and significant decreasing trends in amount of snowfall, S/R shows a decreasing trend in the TP. Abrupt changes in total amount of precipitation, amount of rainfall, amount of snowfall and S/R are detected for 2005, 2004, 1996 and 1998, respectively. Total amount of precipitation, amount of rainfall, amount of snowfall and S/R are concentrated in cycles of approximately 5 years, 10 years, 16 years and 20 years, respectively. The trend magnitudes for total amount of precipitation and amount of rainfall all show decreasing-to-increasing trends with elevation, while amount of snowfall and S/R show decreasing trends.     

1970—2018年秦岭南北冷季降雪量时空变化及其影响因素

基于72个气象站点逐日观测数据,对1970/1971—2018/2019年秦岭南北冷季（11月~次年5月）降水类型（降雪、降雨和雨夹雪）进行识别;重点关注降雪时空变化特征,探讨降雪与气温、湿球温度的响应关系;依据“夏季-秋季-冬季”Niño 3.4区海温异常状态,细化4种不同发展过程的厄尔尼诺-南方涛动（ENSO）事件,分析降雪异常与不同ENSO事件的对应关系。结果表明：① 相比气候平均态（1970—2000年）,1990—2018年,秦岭南坡（山地暖温带）降雪量下降了3.1 mm,基本与关中平原降雪量（17.1 mm）持平;② 空间趋势上,低海拔河谷地带降雪量以年代波动为主,山地高海拔地区为降雪下降区;③ 秦岭高山地区气温或湿球温度每升高1.0℃,降雪量分别下降23.1 mm和24.3 mm;从地带性角度分析,由北向南气温或湿球温度每升高1.0℃,秦岭南北降雪量分别下降3.0 mm和2.8 mm;④ 当厄尔尼诺/拉尼娜持续型发生时,关中平原降雪异常偏多;当拉尼娜发展型发生时,秦岭山地和大巴山区降雪异常偏少。当厄尔尼诺发展型发生时,秦岭南北降雪异常呈现“东西分异”,秦岭山地东部和关中平原为降雪异常偏少区。     

Contributors

Abstract

Jan Nijman, assistant professor and Knight Junior Fellow, University of Miami, Florida. Main research and teaching interests are in international relations, political geography, and development issues. Recipient of Nystrom Award 1991, Association of American Geographers, for doctoral dissertation “A Political Geography of U.S.-Soviet Relations, 1948–1988: The Value of a Spatial Perspective” (Department of Geography, University of Colorado at Boulder, 1990).     

Meteorological triggering scenarios of tree-ring-based snow avalanche occurrence on scree slopes in a maritime climate,Eastern Canada

ABSTRACT

Statistical relationships between weather conditions and the release of snow avalanches in the low-elevation coastal valleys of the northern Gaspé Peninsula are still poorly validated. As such, we explored climate–avalanche relationships through classification tree algorithms applied to tree-ring reconstructions of avalanche events. In order to assess the contribution of local factors on avalanche activity, avalanche regimes on east- and west-facing slopes were analyzed and compared. The results showed that avalanches on east-facing slopes appear to be primarily related to large cumulative snowfall in January, February, and March. On west-facing slopes, avalanches are mainly due to episodic snowfall and warming temperatures. However, both sides of the valleys showed the potential for the release of large avalanches in November and December, which is earlier than expected by the literature. Indeed, the weather variability at that time of the year (temperature oscillation around 0ºC) appears to favor the formation of an early, unstable snowpack and subsequent triggering of avalanches, such as the wet slab avalanche recorded by a time-lapse camera in November 2014. This camera provided a useful insight on the capacities of classification-tree models to link the yearly resolution of tree-ring data with weather triggers at different timescales.     

Development Of City Size Distributions For The Egyptian Urban System, 1897–1960 1

Two scenarios of CO₂-induced climatic change and projections of population and consumptive use of water to the year 2035 are utilized in a climate impact assessment of future water resources in the Great Lakes basin. When expressed as a streamflow/population index, results indicate a sharp decline of this index. Future index values are projected to be similar to those presently recorded for the Colorado River basin.     

乌鲁木齐典型暴雪天气机理及成因分析

利用常规地面、高空观测资料、NCEP/NCAR 1°×1°再分析和FY卫星资料,针对乌鲁木齐1990年以来的3场典型暴雪天气,从高低空环流和天气系统配置、不稳定条件、水汽、动力及黑体亮温（TBB）变化等方面综合对比分析暴雪成因。结果表明：（1） 3场暴雪均发生在欧洲高压脊东南衰退,推动西西伯利亚低槽东移南下,与中纬度短波槽结合的环流形势下,高低空系统呈“后倾槽”结构,乌鲁木齐处在925~600 hPa西北急流与600~200 hPa强西南急流叠置区,且天山山脉的地形强迫抬升有利于暴雪的维持和加强。（2） 暴雪前850~700 hPa均有东南风存在,微差平流作用有利于平流逆温生成和加强,使得能量不断积聚,后期冷空气进入,冷锋锋生,层结不稳定发展,为暴雪天气提供热力条件,东南风和平流逆温维持时间越长,储存能量越多,降雪越强。（3） 暴雪区存在西南和偏西2条水汽输送通道,中层水汽输送对乌鲁木齐暴雪至关重要,850~600 hPa存在较强的水汽辐合,且700 hPa最强。水汽输送、辐合强度及持续时间共同决定暴雪强度。（4） TBB与降雪强弱有一定的对应关系,TBB越低,云顶高度越高,中尺度云团发展越旺盛,降雪越强,降雪前TBB（云顶高度）的第一次迅速降低（升高）预示降雪开始,降雪过程中TBB降低对应降雪强度增强,且TBB降幅越大、低TBB值维持时间越长,降雪越强。