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1.
Although tornadoes are microscale meteorological features, their occurrence is linked to the larger synoptic-scale environment. Most conceptual models of synoptic situations that give rise to tornadoes are based on conditions prevalent in the Great Plains of the United States. However, tornadoes develop in many different synoptic environments, particularly when they form beyond the boundaries of “Tornado Alley.” Tornado occurrences in the state of Virginia are identified from 1951 through 1992. Using upper air data for the nearest site and observation time, a synoptic classification is produced via application of principal components analysis and cluster analysis. The five resulting synoptic classes each exhibit distinctive thermodynamic and flow conditions that serve as air-mass paradigms for tornado occurrence in Virginia. The groups include thermodynamic/northwest flow air masses, a mixed thermodynamic/dynamic category, a polar front jet situation, cool season midlatitude cyclone events, and Great Plains type tornadic air masses. A sixth type, tornadoes spawned by tropical systems, is defined separately. A variety of indices have been developed by forecasters to provide information about the likelihood of severe weather and tornadic activity. The lifted index, K-index, Showalter index, SWEAT, Totals index, and a wind shear index are calculated for each tornado event. Analysis of variance indicates that most of these indices are statistically different between synoptic classes. These results suggest that the synoptic-scale mechanisms responsible for tornado occurrence in the mid-Atlantic states are quite variable. Enhanced predictive capability could be gained by considering the prevailing synoptic conditions associated with individual storms. [Key words: synoptic climatology, tornadoes, Virginia, classification, severe weather.] 相似文献
2.
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.] 相似文献
3.
Andrew C. Comrie 《The Professional geographer》1996,48(3):237-251
The potential exists for widespread air quality problems in the U.S.-Mexico borderlands. Climate and weather are major factors governing the behavior of air pollution, and thus there is a need for greater understanding of border-region air pollution climatology. This paper presents a synoptic climatology of the 850 mb atmospheric circulation for the U.S.-Mexico border region, and an accompanying analysis of relationships between synoptic conditions and ground-level ozone. The synoptic methodology employs high-pass filtering to enable comparisons of all seasons, and it uses modified multiple k means clustering to identify six characteristic circulation patterns. The climatology succinctly summarizes important spatial and temporal complexities of border region circulation, including various pressure configurations, the seasonality of those patterns, and associated weather conditions across the region. These results are linked with ozone data for four border-region cities, and the subsequent findings highlight systematic seasonal and region-wide variations in ozone pollution corresponding to patterns of controlling climatic factors. Three high-ozone scenarios are identified, each of which selectively affects a different area or time of year. 相似文献
4.
Unseasonable floods are floods that occur in the season of lowest flood frequency, or dry season. Such floods pose a unique problem to flood planners and forecasters, yet little research has investigated the physical processes associated with unseasonable floods. The purpose of this study is to construct a synoptic climatology of extreme unseasonable floods for the southeastern United States. Results indicate that the types of storms creating unseasonable floods are location specific, with four unique regions across the study area: Carolina (tropical storms/hurricanes), Georgia Coastal Plain (Gulf depressions), Gulf-Atlantic (frontal), and Tennessee (frontal with upper-air enhancement). The precipitation created by these storms is low to moderate, rarely exceeding the 10-year 24-hour storm total. The precipitation levels suggest that a combination of meteorological conditions and land-surface conditions create the extreme events. A statistical analysis indicates that high soil-moisture levels combine with the moderate rains to produce extreme unseasonable floods. [Key words: unseasonable floods, synoptic climatology, land-surface conditions, southeastern United States.] 相似文献
5.
本文包括以下内容:(1)从气候概念的历史源流、感性基础、气候与天气的关系及气候与地理的关系、气候形成过程五个方面论述了人类对气候认识的发展情况。(2)把现代气候的概念总结为:统计气候学、天气气候学、地理气候学和动力气候学四个方面。(3)在批判流行多年的鲁宾施晋和特洛兹多夫气候定义的基础上提出气候的新定义,即气候是宏观的大气物理过程。(4)明确指出气候学不是地理学的部门学科,它们在科学分类中是并列的。 相似文献
6.
Synoptic-scale environments favorable for producing derechos in the cool season (September through February) are examined with the goal of providing useful techniques for identifying commonalities within derecho activity corridors. Fourteen derechos were identified from two activity corridors located in the southeastern United States and Atlantic seaboard regions between 1986 and 1995. The synoptic environment at the initiation and midpoint of each derecho was then evaluated using surface, upper-air, and the NCAR/NCEP reanalysis data sets. Models are provided in order to illustrate the synoptic-scale environment and to assist meteorologists in recognizing conditions favorable for cool-season derecho formation. Marginal instability and strong synoptic-scale forcing characterized the environments of events in both corridors. The overall synoptic patterns associated with cool-season derecho-producing mesoscale convective systems (DMCSs) resembled environments found with cool-season tornado episodes. Recognition of key elements in this environment could lead to improvements in cool-season severe weather prediction. [Key words: derecho, windstorm, mesoscale convective system (MCS), synoptic climatology, southeast United States.] 相似文献
7.
Barry D. Keim 《自然地理学》2013,34(4):313-328
This paper examines the synoptic climatology and seasonality of heavy rainfall across the southeastern United States. Frontal systems (particularly cold fronts) were found to be the dominant mechanism that induces heavy rainfall across the study area, but tropical disturbances and air-mass storms also contribute, especially at the more coastal locations. Annual regimes were found to vary dramatically from one site to another, and seven of the eight sites investigated exhibited statistically significant seasonality. Generally, peaks in heavy rainfall are bimodal in the western portion of the region, occurring in the transitional seasons. The central portion of the region peaks in late winter and spring, whereas the area east of the Appalachians (including Florida) has summer peaks. This spatial pattern is likely related to patterns of mid-tropospheric air flow and positions of the Bermuda High in summer, and the seasonality of cyclogenesis in North America. [Key words: synoptic climatology, seasonality, heavy rainfall, storms, southeastern United States.] 相似文献
8.
中国暴雨区划初步研究 总被引：3，自引：0，他引：3
本文根据近三十年水文站和气象站实测和调查24h最大暴雨均值和极值,将中国暴雨进行了初步区划。分区原则是:综合考虑暴雨强度及其分布特点、发生季节、暴雨天气系统以及地理诸因素(包括地形、拔海高度和海陆性质)。首先采用天气气候学方法对全国暴雨进行初步划分;然后,根据全国气象站25年汛期(5—9月)雨量和年雨量资料,算出各区域面雨量指标,以某区面雨量指标为变量,分别对其周围各站雨量求相关,如果相关系数通过显著性水平α=0.05,即将该站划归为同一暴雨气候区,否则,划归另一气候区。 最后将全国分为十个暴雨气候区和四个副区,并简述了各区暴雨洪水成因及特征。 相似文献
9.
Daniel J. Leathers 《自然地理学》2013,34(2):171-190
This study documents the spatial and temporal characteristics of northeast United States tornadoes and the synoptic patterns associated with their development. Daily 1200 UTC surface pressure, 500 mb height and 850 mb temperature data are used in a compositing analysis to indicate the general conditions on tornado-producing days during four quasi-seasonal periods. Temporally, two-thirds of all northeast tornadoes occur between the hours of 1800 UTC and 0000 UTC. Annually, greater than 75% occur during the four-month period from May through August. During the period of study (1950 through 1986) the region had an average of 30 tornado occurrences per year. Spatially, three preferred areas of tornadic development are identified across the northeast region. These areas include western and southeastern Pennsylvania and north-central Massachusetts. The general synoptic patterns associated with tornadic events in the northeast United States remain consistent throughout the year. The composite analyses indicate that the presence of a strong surface low pressure system moving through the Great Lakes, coupled with significant upper-level divergence associated with a vigorous shortwave feature and a cold frontal boundary, are the synoptic features most common during the initiation of tornadic storms in this region. [Key words: synoptic climatology, tornadoes, northeastern United States.] 相似文献
10.
Johnathan W. Sugg Christopher M. Fuhrmann L. Baker Perry Dorothy K. Hall Charles E. Konrad II 《自然地理学》2017,38(2):105-123
AbstractSnowfall 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. 相似文献
11.
A synoptic climatology of warm season heavy rainfall is developed from patterns of 850 mb thermal advection over the Appalachian region. Heavy rain events are categorized according to the position and orientation of a warm air advection (WAA) ridge, a feature found in nearly two-thirds of the events. Numerous study events occur within the conditionally unstable region of the WAA ridge. In fact, numerous occurrences of heavy rainfall are tied to a superpositioning of a WAA and air mass instability ridge in the vicinity or upstream of the heavy rain area. 相似文献
12.
13.
Brent Yarnal 《The Professional geographer》1985,37(2):197-203
Multiple regression is often complicated by collinearity of the predictor variables. This study demonstrates the use of ridge regression as a method for determining those correlated variables which must be eliminated from an analysis and for maximizing the amount of information gained from a set of correlated predictors. The model is reviewed and a case study, based on an objective synoptic climatology of the Pacific Northwest coast, is presented in which the technique is applied to a correlated set of climatological predictors. One highly collinear variable is identified and discarded while the effect of moderate collinearity in the remaining predictors is lessened and explained variance is optimized by ridge regression. 相似文献
14.
Annual floods in New England (USA) and Atlantic Canada: synoptic climatology and generating mechanisms 总被引：1，自引：1，他引：0
Mathias J. Collins Johnathan P. Kirk Joshua Pettit Arthur T. DeGaetano M. Sam McCown Thomas C. Peterson 《自然地理学》2014,35(3):195-219
New England and Atlantic Canada are characterized by mixed flood regimes that reflect different storm types, antecedent land surface conditions, and flood seasonality. Mixed flood regimes are known to complicate flood risk analyses, yet the synoptic climatology and precipitation mechanisms that generate annual floods in this region have not been described in detail. We analyzed a set of long-term annual flood records at climate-sensitive stream gauges across the region and classified the synoptic climatology of each annual flood, quantitatively describing the precipitation mechanisms, and characterize flood seasonality. We find that annual floods here are dominantly generated by Great Lakes-sourced storms and Coastal lows, known locally as ‘nor’easters.’ Great Lakes storms tend to be associated with lower magnitude annual floods (<75th percentile) and Coastal lows are more clearly associated with higher magnitude events (>75th percentile). Tropical cyclones account for few of all annual floods, including extreme events, despite causing some of the region’s largest and most destructive floods. Late winter/early spring is when the greatest number of annual floods occur region wide, and rainfall is the dominant flood-producing mechanism. Rainfall in combination with snowmelt is also important. Both mechanisms are expected to be impacted by projected regional climate change. We find little evidence for associations between flood-producing synoptic storm types or precipitation mechanisms and large-scale atmospheric circulation indices or time periods, despite upward trends in New England annual flood magnitudes. To more completely investigate such associations, partial duration flood series that include more floods than just the largest of each year, and their associated synoptic climatologies and precipitation mechanisms, should be analyzed. 相似文献
15.
Brent Yarnal Robert G. Crane Andrew M. Carleton Laurence S. Kalkstein 《The Professional geographer》1987,39(4):465-473
Greater emphasis is being placed on large-scale (synoptic and dynamic) climatology in geography. Concurrently, climatological research as a whole has evolved to view climate as a complex, integrated and interactive global system. In this context, we review new directions in large-scale climate studies in geography. We conclude that no matter at which climatic scale geographers are working, the new challenge is to integrate their research and teaching activities into a more holistic, global-systems approach while maintaining and improving their traditional strengths. 相似文献
16.
Gebeyehu Taye Jean Poesen Bas Van Wesemael Matthias Vanmaercke Daniel Teka Jozef Deckers 《自然地理学》2013,34(3):236-259
April lightning production in Richmond County, Georgia, from 1995 to 2003 is considered with regard to the associated risk to golfers and spectators at the Master's Golf Tournament and courses throughout the county. An examination of the April lightning climatology of Georgia, focusing on Richmond County, reveals a minimum in lightning activity during the time of the tournament (the first full week of April). A discriminant analysis of Richmond County lightning production utilizes several meteorological variables in order to discern between three categories of April lightning days: little or no lightning activity, minimal lightning activity, and high lightning activity. The analysis distinguishes relatively well between the categories with only 13.5% of the events misclassified. A composite regional analysis of the three lightning categories illustrates the environmental differences between these events. Although the little or no lightning and high lightning categories are somewhat similar environmentally, the intensity of features separates these events and allows for interpretation. The statistical and synoptic analyses together emphasize the importance of low-level instability and frontal proximity and intensity in enhancing lightning production in thunderstorms during April in and surrounding Richmond County. A multitude of meteorological conditions can lead to thunderstorm development. Localized studies of these environments, especially during times of major outdoor sporting events, are needed to help mitigate the risk associated with lightning. 相似文献
17.
The climatology of winter cyclones crossing the western Great Lakes was investigated. Data concerning storm strength, place of origin, and surface and 500 mb level synoptic characteristics were obtained from the months of October through February, 1955–1976, for 469 cyclones. November cyclones had the lowest mean pressure and strongest pressure gradient of the 5 months examined, but cyclonic frequencies were greatest in December and January. In all months, cyclones originating in the southwestern United States were significantly deeper than storms of northern origins, and these cyclones crossed the western Lakes most frequently in November. In November, cyclogenesis in the southwest was related to departures of the observed flow from the mean monthly mid-tropospheric circulation with trough development over the west. Yearly variations in the number of severe November cyclones were related to differences of mean monthly 500 mb flow. 相似文献
18.
Cary J. Mock 《自然地理学》2013,34(3):165-187
The avalanche hazard in the United States is most severe in the continental zone of Colorado, where property damage and deaths exceed those in any other state. The continental zone is normally characterized by a shallow snowpack, faceted crystal growth, and relatively fewer avalanches as compared to the coastal and intermountain zones farther west. This study illustrates that variations in the avalanche character in the continental zone may, at times, resemble some less continental characteristics that are found farther west as a result of anomalous atmospheric circulation patterns. Results from cluster analyses show that some sites in the southern portion of the continental zone generally represent a less continental character. Anomalies of 500-mb heights explain the variability of avalanche climates for selected sites, particularly for Berthoud Pass, within the continental zone. Negative heights over the southwestern United States during early winter correspond with less continental conditions, but the zone of negative heights tends to shift westward over the eastern Pacific Ocean during February and March. However, generalizations of how synoptic patterns govern avalanche climate variations also vary between different locations as a result of smaller-scale climatic controls that operate over the region. [Key words: avalanche climatology, continental zone, 500-mb heights, Rocky Mountains.] 相似文献
19.
Comparisons are made between thunderstorm data collected from a lightning detector network and from conventional climatic stations for the province of Manitoba, Canada. The greater resolution in time and space of lightning detector (direction finder) data makes it a valuable source of thunderstorm information and lends itself to some important applications. Data were collected for the forest fire season of 1985 using a network of 7 lightning direction finders distributed throughout the province. Some 67,912 cloud-to-ground lightning strikes were recorded by time and location during 122 thunderstorm days. July was the most active month with 27,260 strikes over 28 days. Two regions of the province had the greatest concentration of lightning strikes, indicating some influence by topography and position of large lakes. Case studies are presented of the most active lightning storms of 1985 and 1986. These storms are exclusively frontal storms, with most having similar synoptic weather patterns to those of large hailstorms and tornadoes in Manitoba. Relationships between meteorological parameters and lightning strike distribution are presented. These relationships may prove useful in the suppression of lightning-caused forest fires, especially in remote areas of the province. [Key words: lightning, thunderstorm, synoptic climatology, natural hazards, fire prevention.] 相似文献
20.
Thomas B. Williams 《自然地理学》2013,34(1):35-49
Field observations of temperature, humidity, and wind conditions were taken during mesoscale lake breeze, synoptic-aided lake breeze, and synoptic-scale lake effect situations in Milwaukee, Wisconsin. Measurements were made along two east-west transect routes to document Lake Michigan's cooling impact. Lake breezes are characterized by significant changes in weather parameters: a sharp drop in temperature, a rise in dew point, an increase in relative humidity, and a shift from offshore to onshore winds. Temperature contrasts between lakefront and inland envirionments exceed 5°C. Lake cooling is confined to a coastal zone extending 8.0 km inland. Synoptic-aided lake breezes combine mesoscale lake breeze formation with the added influence of developing synoptic onshore winds. These situations are characterized by earlier time of occurrence, greater inland movement, and reduce land-lake thermal contrasts. Synoptic lake effect is produced by steady prevailing onshore winds from the northeast or east under the control of the large-scale pressure pattern. The greatest degree of lake cooling occurs under synoptic lake effect conditions, with widespread impact extending well inland. Maximum temperature differences between nearshore and inland locations exist in spring, the season of greatest land-lake thermal contrast. [Key Words: Lake effect, lake breeze, mesoscale climatology, Lake Michigan.] 相似文献