首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Recognized for years as a major environmental disruption, El Niño generated intense public interest in 1982–1983. During its last occurrence, this phenomenon, which develops in the tropical Pacific and usually affects rimlands of the Pacific basin, exceeded its boundaries and its effects were transmitted to continental North America, Europe, Africa and East Asia. Notwithstanding its vast areal extent, the interest of geographers in El Niño events, past and recent, has been comparatively less than that demonstrated by natural scientists and ecologists: little has been accomplished to place these climatic-ecological crises within global perspective. Lessons from El Niño include the acknowledgement of new concepts of climatic transitivity, ocean dynamics and energy exchanges that must find a place within the conceptual wealth of geography if this science intends to keep up with the rapid progress of other geosciences.  相似文献   

2.
There has been an enhanced focus on Atlantic tropical cyclone climatologies with the significant cyclones of the past decade and the associated loss of life and property. This study examines the geographic location of cyclone tracks and their relationship to El Niño-Southern Oscillation (ENSO). The average annual cyclone track latitude and longitude correlate positively with hurricane-season El Niño indices, indicating that during El Niño conditions, tropical cyclone tracks are shifted northward and eastward. June–November indices explain 11–22% and 3–11% of the variance in cyclone track latitude and longitude, respectively. Examination of the strongest and weakest El Niño years yields similar results. Higher sea level pressure over North America, a slight contraction of the Bermuda High, and a slight decrease in 500 mb heights during El Niño years helps to explain the observed northward and eastward movement of tropical cyclone tracks during El Niño years. Additionally, weaker easterly and stronger southerly winds on the western side of the North Atlantic Basin exist during El Niño years. Although future tropical cyclone track projection is beyond the scope of this research, these results may provide insight into forecast improvement and ultimately better responses for coastal communities.  相似文献   

3.
《自然地理学》2013,34(6):427-448
The goal of this study was to develop a 50-yr. statistical climatology of snowfall occurrences using data from a dense network of cooperative station observations covering northwest and central Missouri, and these records were provided by the Missouri Climate Center. This included a study of the long-term trends and interannual variability in snowfall occurrence as related to sea surface temperature variations in the Pacific Ocean basin associated with the El Niño and Southern Oscillation (ENSO) and the North Pacific Oscillation (NPO). These trends and variations were then related to four synoptic-scale flow regimes that produce these snowfalls in the Midwest. The results demonstrate that during the snowfall season (Oct-April) the northwest Missouri region can expect about eight snowfall events which produce ≥3 in. (>7.5 cm) of accumulation. While no significant long-term trend in overall snowfall occurrence was found, a decrease in the number of extreme events (≥10 in., >25 cm) was noted. Also, fewer snowfall events were found during El Niño years, while more heavy snowfall events occurred during "neutral" years, and these results could be related to synoptic-scale variability. A closer examination of the results demonstrated that El Niño/La Niña related variability in snowfall occurrence was superimposed on longer-term NPO-related variability.  相似文献   

4.
《自然地理学》2013,34(1):76-96
Regions based on seasonal precipitation variability for Hawaii are determined using a principal components analysis applied to 124 stations for the period 1971-2000. Nine regions are delineated and are consistent with known precipitation patterns; leeward and windward stations are in separate regions on all islands. Within each region, the relationship between precipitation and the El Niño-Southern Oscillation (ENSO) is examined using a correlation analysis with the Southern Oscillation Index (SOI), and the Niño 3.4 and Niño 1+2 indices. Precipitation is most frequently correlated with ENSO in the different regions using SOI and Niño 3.4. Using several nonparametric statistical tests, it is determined that while average precipitation received in Hawaii during El Niño events is significantly different from average precipitation (1971-2000) and from precipitation received during La Niña events, the relationship between precipitation and individual ENSO events within regions is rarely significant. Finally, during El Niño or La Niña events, average precipitation receipt across the regions co-varies during winter and summer under concurrent conditions and a one-season lag. Synoptic patterns are examined and indicate a deviation from average conditions during ENSO events that affects subsidence and precipitation patterns.  相似文献   

5.
《自然地理学》2013,34(3):196-211
It has been suggested by some that warm El Niño Southern Oscillation (ENSO) events have become stronger and more frequent as a result of global warming. This study aims to investigate whether there is any evidence for changes in the behavior of the ENSO phenomenon that may be attributed to global warming. Cluster analysis is carried out to group warm and cold events by various characteristics using the U.K. Climatic Research Unit air-temperature anomaly data set for the period 1856-1999. Analysis of the resulting groups of events and their relation to global temperature changes gives rise to various conclusions. First, the cold (La Niña) phase of the ENSO phenomenon has been more stable in the period of study than the warm (El Niño) one. Second, average strength warm events seem to be more frequent immediately preceding and during periods of steep global temperature rise, supporting the idea (Hunt, 1999) that more frequent El Niños are a short-term response in ocean-atmosphere coupling to rising global temperature.  相似文献   

6.
Wildfires have long been an important environmental concern in Florida. Recent wildfires along the urban-rural interface of large cities in Florida have pointed to the need for an increased understanding of the physical and biological mechanisms that govern wildfire occurrence. Increased awareness of the relationships between global climate changes occurring in the tropics and their teleconnections outside the tropics dictate a reevaluation of the role of phenomena such as El Niño-Southern Oscillation on the risk of wildfire. One simple way of illustrating the relationship between ENSO and wildfire occurrence is the use of an Analysis of Variance (ANOVA) on wildfire data that has been categorized according to ENSO status (El Niño, La Niña, and neutral years). This research shows that a statistically significant relationship exists between ENSO conditions and annual wildfire occurrence in Florida when ENSO conditions are treated as a potential precursor to wildfire conditions. In particular, a statistically significant relationship exists between both acreage burned and average fire size, when the data are separated into El Niño and La Niña categories according to the previous year's ENSO status. This supports the idea that the climate from previous years has a measurable effect upon fire statistics in the years following the climate measurements, and that it may be possible to create a regional fire prediction model that incorporates ENSO information. [Key words: wildfire, natural hazards, ANOVA, Florida, ENSO.]  相似文献   

7.
西南地区冬季气温和降水的时空变化   总被引:2,自引:0,他引:2  
In recent years,the socio-economic impacts of winter extreme climate events have underscored the importance of winter climate anomalies in Southwest China (SWC).The spatio-temporal variability of surface air temperature (SAT) and precipitation in SWC and their possible causes have been investigated in this paper based on observational data from 1961 to 2010.The results indicate that SAT anomalies in SWC have two dominate modes,one is homogenous,and the other a zonal dipole.The former is caused by the anomalies of East Asian winter monsoon;the latter arises from the anomalies of both subtropical west Pacific high and regional cold air in lower troposphere.The most dominant mode of precipitation anomalies in SWC is homogenous and it has a high correlation with northern hemisphere annular mode (NAM,AO).Neither NAM nor ENSO has significant impacts on SAT in SWC.The anomalies of NAM are associated with the anomalies of tropical circulations,and there-fore precipitation over the SWC.When NAM is in positive (negative) phase,the winter pre-cipitation is more (less) than normal in SWC.Winter precipitation increase over the whole SWC is associated with the El Nino.However,during La Nina winter,the pattern is not uni-form.There is an increase in precipitation over the central parts and a decrease in western and eastern parts of SWC.The severe drought in SWC in winter 2010 is more likely caused by anomalies of NAM,not El Nino.  相似文献   

8.
This study explores the main factors controlling sediment and water discharge in the Santiago and Pánuco Rivers, the two largest rivers of central Mexico. Both Santiago and Pánuco Rivers are sourced in the Central Plateau of Mexico and flow in an opposite direction. Santiago River flows over a tectonically active margin draining to the Pacific Ocean, and Pánuco River flows into the passive margin of the Gulf of Mexico. Mean annual and monthly values of suspended sediment load and water discharge spanning around 50 years were used to evaluate sediment load and water discharge in these two rivers. Our findings indicated that Santiago River delivers to the ocean around 45% more sediment than Pánuco River. However, we found that Santiago River has about half the water discharge of Pánuco River. The high river gradient along Santiago River is likely to enhance the net erosion and sediment transport capacity. Water discharge at Pánuco Basin is higher than in Santiago Basin because the annual rainfall is higher for the former. The difference in sediment and water discharge for both rivers are also related to El Niño Southern Oscillation events. Our results indicated that water discharge in Santiago River increases during El Niño and La Niña events. In contrast, Pánuco River is mostly affected by La Niña events.  相似文献   

9.
The influence of climate associated with El Niño/Southern Oscillation (ENSO) events on tree growth in the central Colorado Front Range is investigated through the analysis of two high altitude tree-ring chronologies. Dendrochronological techniques are used to determine if ENSO-related climatic effects are detectable in tree-ring width patterns in the central Colorado Front Range. The form of the tree-growth response is identified and the variability of the influence of these events on tree growth over time is investigated. Results indicate that tree growth in this area does respond to ENSO events, but the response varies with species and type of event. El Niño-influenced climate tends to result in larger tree rings the year of or year following the event, while La Niña-influenced climate tends to result in smaller rings the year after the event, reflecting spring moisture conditions. Trees have a more consistent response to La Niña events, but El Niño events seem to have a greater effect on extremes in growth. The relationship between the Southern Oscillation Index (SOI) and tree growth has varied over time, probably because of the fact that ENSO events, characterized by the SOI, vary in magnitude and amplitude. [Key words: ENSO, dendrochronology, Colorado Front Range.]  相似文献   

10.
The Gulf of Mexico experiences significant changes in the distribution of daily precipitation totals that are linked to the El Niño–Southern Oscillation (ENSO). This research uses geospatial techniques to examine distribution patterns of ENSO-related precipitation. Kolmogorov–Smirnov test results comparing daily rainfall distributions for El Niño and La Niña are mapped at a 1° × 1° latitude/longitude resolution, and hotspot analysis using local Moran's I is performed to identify spatial clustering. Results indicate that ENSO-forced spatial and temporal variation in daily precipitation distributions influence large areas of the Gulf of Mexico region from August through January.  相似文献   

11.
This study examines the variability of the duration and frequency of Santa Ana winds due to El Niño over a thirty‐three‐year period. Daily Weather Maps and NCEP/NCAR Reanalysis were used to study large‐scale upper‐level and surface circulation patterns during wind events. A Student's t‐test was used to determine statistically significant changes in the winds during March of El Niño winters. A significant decrease in the duration and frequency of wind events was found in March during El Niño. This can be attributed to the decrease in strength and frequency of the Great Basin high pressure and the increase in wintertime cyclones in southern California.  相似文献   

12.
Pollen collected from snow samples on the Quelccaya Ice Cap in 2000 and 2001 reveals significant interannual variability in pollen assemblage, concentration, and provenance. Samples from 2000, a La Niña year, contain high pollen concentrations and resemble samples from the Andean forests (Yungas) to the east. Samples from 2001, an El Niño year, contain fewer pollen and resemble those from the Altiplano. We suggest that varying wind patterns under different El Niño/Southern Oscillation (ENSO) conditions may affect the processes of pollen transport over the Altiplano and on the ice cap, although confounding variables such as flowering phenology and sublimation should also be considered  相似文献   

13.
An analysis of the atmospheric water balance over the Southern Hemisphere is conducted for the time period June 1980 through May 1984 that includes the 1982–1983 El Niño event. Notable spatial and temporal variations are evident in the moisture flux divergence fields, in the mean meridional transport of water vapor, and in the moisture content of portions of the tropical atmosphere that are attributable to the 1982–1983 ENSO event. Estimates of the net gain/loss of atmospheric water are provided for 10° latitude belts; although the magnitudes of the differences between evaporation and precipitation fall within the range of previous estimates, they are most probably underestimated. [Key words: atmospheric water balance, El Niño, hydrologic cycle, southern hemisphere, water vapor flux.]  相似文献   

14.
The southeastern United States, including Florida, has been identified as a region of homogeneous response to the El Niño/Southern Oscillation (ENSO) climatic anomaly, in which mean monthly precipitation and discharge during winter is above or below normal following the onset of the warm (El Niño) or cold (La Niña) phase of ENSO, respectively. However, this understanding of the response is expanded through a study of the effects of the ENSO phenomenon on the probability distributions of mean monthly streamflows of the Santa Fe river. The Santa Fe river basin is situated between one region, which experiences the greatest proportion of annual streamflow during winter, and another where the largest percentage of annual flow occurs during late summer. The basin experiences both winter and summer peaks in precipitation and (subsequent) streamflow and may therefore display responses to ENSO during each season. A two-parameter lognormal distribution is employed to model these streamflows during warm and cold phases of ENSO. Increases in both the mean and the variance detected during warm phase winters are compatible with previous observations. Increases in variance apparent during cold phase summers have not been previously identified. These results, which have considerable bearing upon predictions of high and low flow probabilities during the year, suggest that the response in streamflow is not spatially homogeneous across the state.  相似文献   

15.
Climate variability in the Pacific basin has been attributed to large‐scale oceanic‐atmospheric modulations (e.g. the El Niño‐Southern Oscillation (ENSO)) that dominate the weather of adjacent land areas. The Pacific Decadal Oscillation (PDO) and north Pacific index are thought to be indicators of modulations and events in the northeast Pacific. In this study we find that variations in the PDO are reflected in the terminus position of glaciers on Mt Baker, in the northern Cascade Range, Washington. The initiation of retreat and advance phases of six glaciers persisted for 20–30 years, which relate to PDO regime shifts. The result of this study agrees with previous studies that link glacier mass balance changes to local precipitation anomalies and processes in the Pacific. However, the use of mass balance changes and glacier terminus variation for identification of regime shifts in climate indices is complicated by the lack of standardized measuring techniques, differing response times of individual glaciers to changes in climate, geographic and morphometric factors, and the use of assorted climate indices with different domains and time‐scales in the Pacific for comparison.  相似文献   

16.

The southeastern United States, including Florida, has been identified as a region of homogeneous response to the El Niño/Southern Oscillation (ENSO) climatic anomaly, in which mean monthly precipitation and discharge during winter is above or below normal following the onset of the warm (El Niño) or cold (La Niña) phase of ENSO, respectively. However, this understanding of the response is expanded through a study of the effects of the ENSO phenomenon on the probability distributions of mean monthly streamflows of the Santa Fe river. The Santa Fe river basin is situated between one region, which experiences the greatest proportion of annual streamflow during winter, and another where the largest percentage of annual flow occurs during late summer. The basin experiences both winter and summer peaks in precipitation and (subsequent) streamflow and may therefore display responses to ENSO during each season. A two-parameter lognormal distribution is employed to model these streamflows during warm and cold phases of ENSO. Increases in both the mean and the variance detected during warm phase winters are compatible with previous observations. Increases in variance apparent during cold phase summers have not been previously identified. These results, which have considerable bearing upon predictions of high and low flow probabilities during the year, suggest that the response in streamflow is not spatially homogeneous across the state.  相似文献   

17.
Based on the long-term precipitation series with annual time resolution in the middle and lower reaches of the Yellow River and its four sub-regions during 1736-2000 reconstructed from the rainfall and snowfall archives of the Qing Dynasty, the precipitation cycles are analyzed by wavelet analysis and the possible climate forcings, which drive the precipitation changes, are explored. The results show that: the precipitation in the middle and lower reaches of the Yellow River has inter-annual and inter-decadal oscillations like 2-4a, quasi-22a and 70-80a. The 2-4a cycle is linked with El Nino events, and the precipitation is lower than normal year in the occurrence of the El Nino year or the next year; for the quasi-22a and the 70-80a cycles, Wolf Sun Spot Numbers and Pacific Decadal Oscillation (PDO) coincide with the two cycle signals. However, on a 70-80a time scale, the coincidence between solar activity and precipitation is identified before 1830, and strong (weak) solar activity is generally correlated to the dry (wet) periods; after 1830, the solar activity changes to 80-100a quasi-century long oscillation, and the adjusting action to the precipitation is becoming weaker and weaker; the coincidence between PDO and precipitation is shown in the whole time series. Moreover, in recent 100 years, PDO is becoming a pace-maker of the precipitation on the 70-80a time scale.  相似文献   

18.
Recent decades, particularly since the late 1970s, have witnessed a rapid retreat of glaciers in the tropical Andes. We compiled the changes in glacier surfaces along the eastern cordilleras of the tropical Andes of Peru and Bolivia since the early 1980s from the literature. Water levels from two Brazilian river basins in the Amazon basin (one (Madeira River) glacially fed by meltwater from the Andes and the other (Envira River) non‐glacially fed), were analysed for a 30‐year period between 1985?2014. Furthermore, precipitation data near these two basins were also analysed in order to understand the differential contributions of glacier melting and rainfall. Variations in the water levels from the glacially fed Madeira River showed that some years were associated with higher water levels even when the precipitation remained low during the corresponding season (May‐October). This observation was common when El Niño events occurred during the positive phase of Pacific Decadal Oscillation (PDO). Water levels in glacier‐fed Madeira River were slightly higher during the periods where El Niño and warm PDO co‐occurred. On the other hand, water levels in the Envira River were precipitation dependent; water levels were higher when the rainfall was high.  相似文献   

19.
During recent decades, more frequent flood-drought alternations have been seen in China as a result of global climate change and intensive human activities, which have significant implications on water and food security. To better identify the characteristics of flood-drought alternations, we proposed a modified dry-wet abrupt alternation index (DWAAI) and applied the new method in the middle and lower reaches of the Yangtze River Basin (YRB-ML) to analyze the long-term spatio-temporal characteristics of dry-wet abrupt alternation (DWAA) events based on the daily precipitation observations at 75 rainfall stations in summer from 1960 to 2015. We found that the DWAA events have been spreading in the study area with higher frequency and intensity since 1960. In particular, the DWAA events mainly occurred in May and June in the northwest of the YRB-ML, including Hanjiang River Basin, the middle reaches of the YRB, north of Dongting Lake and northwest of Poyang Lake. In addition, we also analyzed the impact of El Niño Southern Oscillation (ENSO) on DWAA events in the YRB-ML. The results showed that around 41.04% of DWAA events occurred during the declining stages of La Niña or within the subsequent 8 months after La Niña, which implies that La Niña events could be predictive signals of DWAA events. Besides, significant negative correlations have been found between the modified DWAAI values of all the rainfall stations and the sea surface temperature anomalies in the Nino3.4 region within the 6 months prior to the DWAA events, particularly for the Poyang Lake watershed and the middle reaches of the YRB. This study has significant implications on the flood and drought control and water resources management in the YRB-ML under the challenge of future climate change.  相似文献   

20.
《自然地理学》2013,34(6):465-475
Saguaro cacti establish periodically in cohorts during years that are climatically favorable. Determining the establishment year is complicated by age-height relationships that vary considerably from site to site and require extensive data collection. Estimations of age-height relationships for only a few locales have thus limited the ability of researchers to estimate age in other populations, and consequently to relate periods of regeneration to climate. We collected data for 254 saguaros in the arid western portion of the species' range and employed a recently developed site-specific technique for estimating saguaro age to reconstruct the population structure at this locale. Second, we used discriminant analysis to determine which climate variables best predict regeneration years. We found that above-average temperatures in November coupled with concurrent high soil moisture levels, conditions typically associated with El Niño years, are associated with years characterized by high regeneration. Accordingly, these results suggest that El Niño events may be related to years of favorable regeneration for saguaros.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号