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Atmospheric Circulation Patterns (atmospheric + circulation_pattern)

Distribution by Scientific Domains

Engineering	14%

Selected Abstracts

Effects of atmospheric circulation on ice conditions in the southern Baltic coastal lagoons

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2001
Józef Piotr Girjatowicz
Abstract Relationships between atmospheric circulation patterns and ice conditions in the southern Baltic coastal lagoons were explored. Ice data consisted of number of ice days (L) and duration of ice season (S) in the Szczecin Lagoon (off Karnin), the Puck Bay (off Puck) and the Vistula Lagoon (off Krasnoflotskoye) from 1950/1951 to 1989/1990. Atmospheric circulation patterns for the period studied were extracted from Lity,ski's ,Calendar of atmospheric circulation types' developed at the Institute of Meteorology and Water Management (IMWM). A circulation pattern was identified by three numerical parameters: the zonal circulation index, the meridional circulation index, both pertaining to a zone delimited by coordinates 40,60°N, 0,35°E, and the surface pressure index for Warsaw. The number of days with individual atmospheric circulation patterns occurring from October to March was calculated. Subsequently, the selected patterns were combined by wind direction sectors and several month-long periods that most closely correlated with ice conditions. The highest linear correlation coefficients (r>0.8) were obtained for the relationship between the number of days with winds from the east from December to February and December to March and the winter number of ice days (L). Somewhat higher were multiple correlation coefficients with winds from the east and west as circulation type predictors. Slightly lower correlation coefficients for the sectors and circulation periods mentioned were obtained for the duration of the ice season (S), although some of the coefficients were significant even at the probability level of ,=0.01. Higher correlation coefficients were obtained for correlations involving ,cold' circulation patterns (sector NE+E+SE winds) and ice conditions than for those involving ,warm' patterns (sector SW+W+NW). Copyright © 2001 Royal Meteorological Society [source]

Evidence for Changing Flood Risk in New England Since the Late 20th Century,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2009
Mathias J. Collins
Abstract:, Long-term flow records for watersheds with minimal human influence have shown trends in recent decades toward increasing streamflow at regional and national scales, especially for low flow quantiles like the annual minimum and annual median flows. Trends for high flow quantiles are less clear, despite recent research showing increased precipitation in the conterminous United States over the last century that has been brought about primarily by an increased frequency and intensity of events in the upper 10th percentile of the daily precipitation distribution , particularly in the Northeast. This study investigates trends in 28 long-term annual flood series for New England watersheds with dominantly natural streamflow. The flood series are an average of 75 years in length and are continuous through 2006. Twenty-five series show upward trends via the nonparametric Mann-Kendall test, 40% (10) of which are statistically significant (p < 0.1). Moreover, an average standardized departures series for 23 of the study gages indicates that increasing flood magnitudes in New England occurred as a step change around 1970. The timing of this is broadly synchronous with a phase change in the low frequency variability of the North Atlantic Oscillation, a prominent upper atmospheric circulation pattern that is known to effect climate variability along the United States east coast. Identifiable hydroclimatic shifts should be considered when the affected flow records are used for flood frequency analyses. Special treatment of the flood series can improve the analyses and provide better estimates of flood magnitudes and frequencies under the prevailing hydroclimatic condition. [source]

A Bayesian hierarchical model for local precipitation by downscaling large-scale atmospheric circulation patterns

ENVIRONMETRICS, Issue 7 2006
Jorge M. Mendes
Abstract Precipitation over the Western part of Iberian Peninsula is known to be related to the large-scale sea level pressure field and thus to advection of humidity into this area. The major problem is to downscale this synoptic atmospheric information to local daily precipitation patterns. One way to handle this problem is by weather-state models, where, based on the pressure field, each day is classified into a weather state and precipitation is then modeled within each weather state via multivariate distributions. In this paper, we propose a spatiotemporal Bayesian hierarchical model for precipitation. Basic objective and novelty of the paper is to capture and model the essential spatiotemporal relationships that exist between large-scale sea level pressure field and local daily precipitation. A specific local spatial ordering that mimics the essential large-scale patterns is used in the likelihood. The model is then applied to a network of rain gauge stations in the river Tagus valley. The inference is then carried out using appropriate MCMC methods. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Analysis of snow cover variability and change in Québec, 1948,2005

HYDROLOGICAL PROCESSES, Issue 14 2010
Ross D. Brown
Abstract The spatial and temporal characteristics of annual maximum snow water equivalent (SWEmax) and fall and spring snow cover duration (SCD) were analysed over Québec and adjacent area for snow seasons 1948/1949,2004/2005 using reconstructed daily snow depth and SWE. Snow cover variability in Québec was found to be significantly correlated with most of the major atmospheric circulation patterns affecting the climate of eastern North America but the influence was characterized by strong multidecadal-scale variability. The strongest and most consistent relationship was observed between the Pacific Decadal Oscillation (PDO) and fall SCD variability over western Québec. El Niño-Southern Oscillation (ENSO) was found to have a limited impact on Québec snow cover. Evidence was found for a shift in circulation over the study region around 1980 associated with an abrupt increase in sea level pressure (SLP) and decreases in winter precipitation, snow depth and SWE over much of southern Québec, as well as changes in the atmospheric patterns with significant links to snow cover variability. Trend analysis of the reconstructed snow cover over 1948,2005 provided evidence of a clear north,south gradient in SWEmax and spring SCD with significant local decreases over southern Québec and significant local increases over north-central Québec. The increase in SWEmax over northern Québec is consistent with proxy data (lake levels, tree growth forms, permafrost temperatures), with hemispheric-wide trends of increasing precipitation over higher latitudes, and with projections of global climate models (GCMs). Copyright © 2010 Her Majesty the Queen in right of Canada. Published by John Wiley & Sons. Ltd [source]

Changes in hot days and heat waves in China during 1961,2007

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2010
Ting Ding
Abstract Based on the daily maximum temperature (DMT) records at 512 stations during 1961,2007, the geographical patterns and temporal variations of hot days (HDs) and heat waves (HWs, including those persisting for 3,5 days and longer) over mainland China were studied. The HD (and hence HW) was defined in two ways, one by an absolute criterion, DMT > 35 °C, as applied in the nationwide meteorological agencies and another in a relative sense, DMT > the 90th percentile threshold of a local daily temperature distribution around the day. Two centers of high frequencies (over 5 days per year) of the absolute HDs during June,September were found in the regions of Xinjiang and the mid-lower reaches of the Yangtze River. The highest frequencies of the absolute HWs were about 1.5 times per year in the Xinjiang region and to the south of the mid-lower reaches of the Yangtze River. The frequencies of the relative HWs were about 1,1.5 times per year in most of China. The HDs and HWs increased significantly during the studied period in most of China, especially over the southeastern coast and northern China (by over 4 days per decade for relative HDs and 0.4 times per decade for relative HWs), but decreased significantly at some stations in the lower reaches of the Yellow River. Over most of China except northwestern China, the frequency of HDs was high during the 1960s,1970s, low in the 1980s, and high afterwards, with strong interannual variations. A remarkable increasing trend of HDs occurred after the 1990s in all regions. The changes in HDs and HWs were closely related to those in rain days and atmospheric circulation patterns at the interannual and interdecadal scales. Copyright © 2009 Royal Meteorological Society [source]

Synoptic forcing of precipitation in the Mackenzie and Yukon River basins

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2010
Elizabeth N. Cassano
Abstract The relationship between near-surface atmospheric circulation, as characterized by sea level pressure patterns, and precipitation in the Mackenzie and Yukon River basins is presented. A synoptic climatology of sea level pressure patterns based on daily sea level pressure anomalies from the ERA40 reanalysis dataset was created using the method of self-organizing maps. This objective analysis identified all major near-surface atmospheric circulation patterns in the region and illustrated the change in dominant circulation patterns throughout the seasons, with strong Aleutian low patterns dominant in the winter and patterns characterized by low pressure over land areas and the Beaufort/Chukchi Seas in the summer. These synoptic patterns were then related to daily precipitation in the Mackenzie and Yukon River basins. The largest daily precipitation values, for both the Mackenzie and Yukon basins, were associated with patterns that occur most frequently in the summer, likely associated with increased frequency of cyclones and convective events that occur over land in that season. During winter, the largest positive precipitation anomalies were along the coastal mountain range in southeastern Alaska associated with Aleutian lows bringing warm, moist flow from the south resulting in upslope flow on the windward side of these mountains. These patterns were responsible for many of the large precipitation events in the winter in the Mackenzie basin. The largest precipitation events in the winter in the Yukon basin occurred with patterns that have a low pressure centre to the southwest of the basin. This synoptic pattern results in southerly flow advecting moisture into the basin to the west of the higher topography which bounds much of the southern boundary of the Yukon watershed. Copyright © 2009 Royal Meteorological Society [source]

Statistical downscaling model based on canonical correlation analysis for winter extreme precipitation events in the Emilia-Romagna region

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2008
A. Busuioc
Abstract Optimum statistical downscaling models for three winter precipitation indices in the Emilia-Romagna region, especially related to extreme events, were investigated. For this purpose, the indices referring to the number of events exceeding the long-term 90 percentile of rainy days, simple daily intensity and maximum number of consecutive dry days were calculated as spatial averages over homogeneous sub-regions identified by the cluster analysis. The statistical downscaling model (SDM) based on the canonical correlation analysis (CCA) was used as downscaling procedure. The CCA was also used to understand the large-/regional-scale mechanisms controlling precipitation variability across the analysed area, especially with respect to extreme events. The dynamic (mean sea-level pressure-SLP) and thermodynamic (potential instability-,Q and specific humidity-SH) variables were considered as predictors (either individually or together). The large-scale SLP can be considered a good predictor for all sub-regions in the dry index case and for two sub-regions in the case of the other two indices, showing the importance of dynamical forcing in these cases. Potential instability is the best predictor for the highest mountain region in the case of heavy rainfall frequency, when it can be considered as a single predictor. The combination of dynamic and thermodynamic predictors improves the SDM's skill for all sub-regions in the dry index case and for some sub-regions in the simple daily intensity index case. The selected SDMs are stable in time only in terms of correlation coefficient for all sub-regions for which they are skilful and only for some sub-regions in terms of explained variance. The reasons are linked to the changes in the atmospheric circulation patterns influencing the local rainfall variability in Emilia-Romagna as well as the differences in temporal variability over some sub-regions and sub-intervals. It was concluded that the average skill over an ensemble of the most skilful and stable SDMs for each region/sub-interval gives more consistent results. Copyright © 2007 Royal Meteorological Society [source]

The influence of atmospheric circulation at different spatial scales on winter drought variability through a semi-arid climatic gradient in Northeast Spain

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2006
Sergio M. Vicente-Serrano
Abstract This paper analyses the spatial and temporal variability of winter droughts in a semi-arid geographic gradient in Northeast Spain, from the Pyrenees in the north to the Mediterranean coastland in the south. Droughts that occurred between 1952 and 1999 were analysed by means of the Standardised Precipitation Index (SPI). The influence of the weather-type frequency and of the general North Atlantic atmospheric circulation patterns was analysed. The results indicate that winter droughts show an important spatial variability in the study area, differentiating three well-defined patterns. These correspond to the Pyrenees, the centre of the Ebro Valley, and the Mediterranean coastland. General negative trends in winter SPI have been found, which are indicative of the increase in winter drought conditions in the study area. Nevertheless, important spatial differences have also been recorded. Dominant north,south gradients in the influence of weather types are shown. Moreover, the negative trends in winter-SPI values agree with the negative trend in the frequency of the weather types prone to cause precipitation, such as the C, SW and W weather types and the increase in the frequency of A weather types. Nevertheless, in the Mediterranean coastland, the positive trend in SPI values agrees with the increase in the frequency of weather types of the east (E, SE), which are prone to cause precipitation in this area. Interannual variations in the frequency of the different weather types have been highly determined by different general atmospheric circulation patterns, mainly the North Atlantic Oscillation (NAO). Nevertheless, the correlation between the time series of weather-type frequency and the winter SPI is higher than that found between the SPI and the NAO. Thus, although the interannual NAO variability explains a high percentage of the interannual differences in the frequency of different weather types, it is not sufficient to explain the spatial and temporal variability of droughts, which respond better to atmospheric variability at more detailed (synoptic) spatial scales. Copyright © 2006 Royal Meteorological Society. [source]

Influence of seasonal pressure patterns on temporal variability of vegetation activity in Central Siberia

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 3 2006
Sergio M. Vicente-Serrano
Abstract This paper analyses the spatial distribution of the inter-annual variability of vegetation activity in central Siberia and its relationship with atmospheric circulation variability. We used NOAA-AVHRR NDVI series from Pathfinder Land Data Set at 1° of spatial resolution, and we calculated the annual vegetation activity in each pixel (aNDVI) from 1982 to 2001. Principal component analysis (PCA) was used to determine the general spatial patterns of inter-annual variability of vegetation activity. We identified three main modes, which explain more than 50% of the total variance, each corresponding to a large region. By means of surface pressure grids, we analysed the main patterns of the seasonal atmospheric circulation in the study area: its variability was summarised by means of a few circulation modes and the patterns differ significantly between winter, spring and summer. However, a pattern with a North,South dipole structure represents the general spatial pattern of atmospheric circulation. We investigated the effect of seasonal atmospheric circulation patterns on the inter-annual variation of vegetation activity. In general, the strongest relationships between the atmospheric circulation variability, climate and the aNDVI variability were found in areas where the climatic characteristics are more limiting for the vegetation development, such as the northern regions. This may be explained by the fact that in these areas the variability of atmospheric circulation modes determines summer temperatures, which have a direct impact on vegetation activity. Copyright © 2006 Royal Meteorological Society. [source]

Links between circulation and changes in the characteristics of Iberian rainfall

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2002
C. M. Goodess
Abstract Investigation of the links between atmospheric circulation patterns and rainfall is important for the understanding of climatic variability and for the development of empirical circulation-based downscaling methods. Here, spatial and temporal variations in circulation-rainfall relationships over the Iberian Peninsula during the period 1958,97 are explored using an automated circulation classification scheme and daily rainfall totals for 18 stations. Links between the circulation classification scheme and the North Atlantic oscillation (NAO) are also considered, as are the direct links between rainfall and the NAO. Trends in rainfall and circulation-type frequency are explored. A general tendency towards decreasing mean seasonal rainfall over the peninsula, with the exception of the southeastern Mediterranean coast, hides larger changes in wet day amount and rainfall probability. There is a tendency towards more, less-intensive rain days across much of Iberia, with a tendency towards more, more-intensive rain days along the southeastern Mediterranean coast, both of which are reflected in changes in rainfall amount quantiles. A preliminary analysis indicates that these changes may have occurred systematically across all circulation types. Comparison of the trends in rainfall and in circulation-type frequency suggests possible links. These links are supported by linear regression analyses using circulation-type frequencies as predictor variables and rainfall totals for winter months as the predictands. The selected predictor variables reflect the main circulation features influencing winter rainfall across the peninsula, i.e. the strong influence of Atlantic westerly and southwesterly airmasses over much of the peninsula, of northerly and northwesterly surface flow over northern/northwestern Spain and northern Portugal and the stronger effect of Mediterranean rather than Atlantic influences in southeastern Spain. The observed rainfall changes cannot, however, be explained by changes in circulation alone. Copyright © 2002 Royal Meteorological Society. [source]

Effects of atmospheric circulation on ice conditions in the southern Baltic coastal lagoons

Reconstruction of the North Atlantic Oscillation, 1429,1983

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2001
Mary F. Glueck
Abstract The North Atlantic Oscillation (NAO) is considered to be the dominant mode of winter atmospheric variability in the Northern Hemisphere (Barnston AG, Livezey RE. 1987. Classification, seasonality and persistence of low frequency atmospheric circulation patterns. Monthly Weather Review115: 1083,1126), especially in the North Atlantic region. A better understanding of its recent variability in the context of pre-instrumental period variations is critical for prediction purposes. A 555-year (1429,1983) multi-proxy reconstruction of the cool season NAO, calibrated against the Lisbon,Iceland (LISJHI) NAO, is presented. Predictor variables include tree-ring chronologies from Morocco and Finland, GISP2 ,18O annual series, and a GISP2 snow accumulation record. Although the reconstructed values are generally lower than the instrumental values during the calibration period (1863,1983), the final reconstruction does capture the low frequency of the instrumental NAO. The reconstruction compares favourably with existing shorter NAO reconstructions and with the instrumental NAO. The variability in the reconstructed NAO is also discussed within the context of lengthy regional climate records. Results suggest that the occurrence and length of the recent persistently high phase of the NAO are not unusual over the 555-year period of time, but that the magnitude of some of the instrumental values may, in fact, be unique. Copyright © 2001 Royal Meteorological Society [source]

Precipitation and atmospheric circulation patterns at mid-latitudes of Asia

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2001
Elena M. Aizen
Abstract Analyses of the coupling between large-scale atmospheric patterns and modifications of regional precipitation regimes at seasonal and annual time scales in different terrain of mid-latitudes in Asia, including western Siberia, Tien Shan and Pamir mountains, and plains of middle Asia and Japanese Islands, were examined based on data from 57 and 88 hydro-climatic stations with 100 and 60 year records, respectively. For the past 100 years, a positive trend in precipitation was revealed in western Siberia, northern regions of Tien Shan and Japanese Islands. North Atlantic Oscillation (NAO) and West Pacific Oscillation (WPO) indices have inverse associations, with average amount of precipitation in western Siberia and in mountains and plains of middle Asia, and positive correlation in central and western regions of Japanese Islands. The Pacific North American (PNA) index is positively correlated with annual precipitation over most of the Japanese Islands. Northern Asian (NA) positive anomalies lead to decrease in winter precipitation in the western and eastern regions of Japanese Islands. We did not find significant impact of PNA or NA on precipitation in middle Asia. We suggest that during the last century, impacts of the western jet stream increased in the northern regions of Tien Shan and Japanese Islands, and weakened in the eastern Japanese Islands. There is a suggestion that conditions are more favourable for precipitation development over continental regions of Asia when the Siberian High is positioned further to the east than further to the west. During dominant development of a zonal atmospheric pattern, the annual and seasonal precipitation decreased over most regions in continental Asia and central Japan. Copyright © 2001 Royal Meteorological Society [source]