scholarly journals Dominant Modes of Moisture Flux Anomalies over North America

2005 ◽  
Vol 6 (2) ◽  
pp. 194-209 ◽  
Author(s):  
Francina Dominguez ◽  
Praveen Kumar
Keyword(s):  
United States ◽  
North America ◽  
Atmospheric Circulation ◽  
Moisture Flux ◽  
Eof Analysis ◽  
Anomaly Field ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Complex Eof ◽  
Precipitation Events

Abstract This study investigates the principal modes of seasonal moisture flux transport over North America, analyzing their possible dependence on large-scale atmospheric circulation patterns. It uses 23 yr (1979–2001) of 6-hourly data from the NCEP–NCAR reanalysis I project. Complex empirical orthogonal function (complex-EOF) analysis is implemented on the vertically integrated and seasonally averaged moisture flux, to identify the dominant modes. For every season, the characteristic spatial pattern of the two most dominant modes is compared to the geopotential height anomaly field and precipitation anomaly field using correlation analysis. The two dominant winter modes capture the variability in the moisture flux field associated with extreme precipitation events over the western coast of the United States. The first winter mode captures 52% of the variability of the season and is related to the strong ENSO events of 1982/83 and 1997/98 (El Niño) and 1989 (La Niña). The second winter mode captures anomalous high moisture flux over the southwest related to the east Pacific teleconnection pattern. The intense moisture transport associated with high-precipitation events in the central United States (including the 1993 flood) is captured by summer mode 1, while the second mode of the summer season captures the moisture flux variability related to the 1983 and 1988 droughts. The results show that these summer flood and drought events are characterized by very different moisture flux anomalies and are not the positive and negative phases of a given mode. The use of complex-EOF analysis captures extreme hydrologic events as characteristic modes of interannual variability and allows a better understanding of the atmospheric circulation patterns associated with these events.

scholarly journals Avalanche extremes and atmospheric circulation patterns

2001 ◽  
Vol 32 ◽  
pp. 135-140 ◽  
Author(s):  
K.W. Birkeland ◽  
C. J. Mock ◽  
J. J. Shinker
Keyword(s):  
United States ◽  
Atmospheric Circulation ◽  
Snow Water Equivalent ◽  
Hazard Index ◽  
Western United States ◽  
Atmospheric Circulation Patterns ◽  
Avalanche Hazard ◽  
Circulation Patterns ◽  
Jackson Hole ◽  
Exact Position

AbstractAvalanche forecasters can better anticipate avalanche extremes if they understand the relationships between those extremes and atmospheric circulation patterns. We investigated the relationship between extreme avalanche days and atmospheric circulation patterns at four sites in the western United States: Bridger Bowl, Montana; Jackson Hole, Wyoming; Alta, Utah; and Taos, New Mexico. For each site, we calculated a daily avalanche hazard index based on the number and size of avalanches, and we defined abnormal avalanche events as the top 10% of days with recorded avalanche activity. We assessed the influence of different variables on avalanche extremes, and found that high snow water equivalent and high snowfall correspond most closely to days of high avalanche hazard. Composite-anomaly maps of 500 hPa heights during those avalanche extremes clearly illustrate that spatial patterns of anomalous troughing prevail, though the exact position of the troughing varies between sites. These patterns can be explained by the topography of the western United States, and the low-elevation pathways for moisture that exist to the west of each of the sites. The methods developed for this research can be applied to other sites with long-term climate and avalanche databases to further our understanding of the spatial distribution of atmospheric patterns associated with extreme avalanche days.

scholarly journals Characteristics of Observed Atmospheric Circulation Patterns Associated with Temperature Extremes over North America

2012 ◽  
Vol 25 (20) ◽  
pp. 7266-7281 ◽  
Author(s):  
Paul C. Loikith ◽  
Anthony J. Broccoli
Keyword(s):  
North America ◽  
Atmospheric Circulation ◽  
Large Scale ◽  
Climate Models ◽  
Extreme Temperature ◽  
Future Climate Change ◽  
Temperature Extremes ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Patterns And Processes

Abstract Motivated by a desire to understand the physical mechanisms involved in future anthropogenic changes in extreme temperature events, the key atmospheric circulation patterns associated with extreme daily temperatures over North America in the current climate are identified. The findings show that warm extremes at most locations are associated with positive 500-hPa geopotential height and sea level pressure anomalies just downstream with negative anomalies farther upstream. The orientation, physical characteristics, and spatial scale of these circulation patterns vary based on latitude, season, and proximity to important geographic features (i.e., mountains, coastlines). The anomaly patterns associated with extreme cold events tend to be similar to, but opposite in sign of, those associated with extreme warm events, especially within the westerlies, and tend to scale with temperature in the same locations. Circulation patterns aloft are more coherent across the continent than those at the surface where local surface features influence the occurrence of and patterns associated with extreme temperature days. Temperature extremes may be more sensitive to small shifts in circulation at locations where temperature is strongly influenced by mountains or large water bodies, or at the margins of important large-scale circulation patterns making such locations more susceptible to nonlinear responses to future climate change. The identification of these patterns and processes will allow for a thorough evaluation of the ability of climate models to realistically simulate extreme temperatures and their future trends.

Austral Summer Droughts and their Driving Mechanisms in Observations and Present-day Climate Simulations across Malawi

2021 ◽  
Author(s):  
Emmanuel Likoya ◽  
Cathryn Birch ◽  
Sarah Chapman ◽  
Andrew Dougill
Keyword(s):  
Atmospheric Circulation ◽  
Climate Models ◽  
Moisture Flux ◽  
Development Planning ◽  
Global Climate Models ◽  
Cmip5 Models ◽  
Atmospheric Circulation Patterns ◽  
Societal Relevance ◽  
Circulation Patterns ◽  
Moisture Fluxes

<p>The societal relevance of droughts in Africa underscores the need for improved understanding of the atmospheric processes that drive them. This study examined drought characteristics across Malawi, and the associated atmospheric circulation patterns, in observations, reanalysis and global climate models. Droughts were identified using the Standardised Precipitation and Evapotranspiration Index (SPEI) for the period 1965 to 2018. Atmospheric circulation patterns during droughts were examined and the main moisture fluxes into Malawi were identified. Despite differences in the frequency, and events being asynchronous at times, droughts exhibited characteristics that were statistically similar between northern and southern Malawi. Droughts in both regions were associated with anomalous circulation that typically worked to diminish moisture advection and thus convection. Differences in the structure of the anomalies were indicative of differences in mechanisms associated with droughts in the north and south of Malawi. Three main moisture flux pathways were identified, and categorized as northeasterly, southeasterly, and northwesterly, each with a unique correlation structure with precipitation and global SSTs. Positive and negative biases of varying magnitudes were noted for drought and rainfall characteristics across the range of CMIP5 models. Such biases can be attributed to biases in moisture fluxes whose variability was found to be a key driver of summer precipitation variability across Malawi. Despite biases in moisture fluxes and their influence on precipitation biases, the majority of models exhibited moisture flux-precipitation correlations consistent with observations and reanalysis. Results from the study highlight the extent to which climate models are reliable in simulating droughts and therefore of value in developing narratives of climate variability essential for long-term development planning.</p>

scholarly journals Investigating changes in atmospheric circulation patterns connected to extreme precipitation in Norway

2021 ◽  
Author(s):  
Karianne Ødemark ◽  
Malte Müller ◽  
Ole Einar Tveito ◽  
Cyril Palerme
Keyword(s):  
Atmospheric Circulation ◽  
Extreme Precipitation ◽  
Good Description ◽  
Construction Technique ◽  
Sea Ice Concentration ◽  
Data Set ◽  
Atmospheric Circulation Patterns ◽  
Extreme Precipitation Events ◽  
Circulation Patterns ◽  
Precipitation Events

<p>Extreme precipitation events that lead to excess surface water and flood are becoming an amplifying societal cost as a result of both the increasing precipitation amounts in recent years and urbanization. Knowledge about extreme precipitation events is important for the ability to predict them, but also to know how often they occur with various intensities in order to estimate design values for constructions and critical infrastructure. A good description of extreme precipitaton is a challenge since observation networks are often too sparse to describe the spatial structure of precipitation, and the highest amounts are most likely not captured by a precipitation gauge. For the study of extreme precipitation events by means of statistical analysis, long timesteries are required, which is a major challenge when using conventional or new observational data records.  Here, a data set constructed from the numerical seasonal prediction system at ECMWF, SEAS5, has been applied to evaluate mechanisms controlling extreme precipitation events. The construction technique gives the ability to increase the event sample size compared to conventional data sets. We analyze 3-day  maximum precipitation events in the September-October-November season for an area on the west coast of Norway, an area subject to the largest precipitation amounts in Europe. A principal component analysis of the 500 hPa geopotential anomaly has been performed to identify atmospheric circulation patterns related to the extreme precipitation events. We find that two of the EOFs are related to precipitation with high return values for the selected area. These two EOFs have a significant trend over the data period, but with opposing signs. We also investigate the connection between both sea surface temperature (SST) and sea-ice concentration in the Barents-Kara sea and the occurrence of extreme precipitation.</p>

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