scholarly journals Implications of Winter NAO Flavors on Present and Future European Climate

Climate ◽  
2020 ◽  
Vol 8 (1) ◽  
pp. 13 ◽  
Author(s):  
Efi Rousi ◽  
Henning W. Rust ◽  
Uwe Ulbrich ◽  
Christina Anagnostopoulou
Keyword(s):  
Clustering Algorithm ◽  
Self Organizing Maps ◽  
The North ◽  
Temperature And Precipitation ◽  
European Climate ◽  
Precipitation Anomalies ◽  
Temporal And Spatial ◽  
Azores High ◽  
Temporal And Spatial Characteristics ◽  
The North Atlantic Oscillation

The North Atlantic Oscillation (NAO), a basic variability mode in the Northern Hemisphere, undergoes changes in its temporal and spatial characteristics, with significant implications on European climate. In this paper, different NAO flavors are distinguished for winter in simulations of a Coupled Atmosphere-Ocean GCM, using Self-Organizing Maps, a topology preserving clustering algorithm. These flavors refer to various sub-forms of the NAO pattern, reflecting the range of positions occupied by its action centers, the Icelandic Low and the Azores High. After having defined the NAO flavors, composites of winter temperature and precipitation over Europe are created for each one of them. The results reveal significant differences between NAO flavors in terms of their effects on the European climate. Generally, the eastwardly shifted NAO patterns induce a stronger than average influence on European temperatures. In contrast, the effects of NAO flavors on European precipitation anomalies are less coherent, with various areas responding differently. These results confirm that not only the temporal, but also the spatial variability of NAO is important in regulating European climate.

scholarly journals Trends in compound extremes of air temperature and precipitation in Eastern Europe

2021 ◽  
Author(s):  
Elena Vyshkvarkova ◽  
Olga Sukhonos
Keyword(s):  
Eastern Europe ◽  
North Atlantic Oscillation ◽  
Air Temperature ◽  
North Atlantic ◽  
Large Scale ◽  
The North ◽  
Temperature And Precipitation ◽  
Atmosphere System ◽  
Daily Data ◽  
The North Atlantic Oscillation

Abstract The spatial distribution of compound extremes of air temperature and precipitation was studied over the territory of Eastern Europe for the period 1950–2018 during winter and spring. Using daily data on air temperature and precipitation, we calculated the frequency and trends of the four indices – cold/dry, cold/wet, warm/dry and warm/wet. Also, we studying the connection between these indices and large-scale processes in the ocean-atmosphere system such as North Atlantic Oscillation, East Atlantic Oscillation and Scandinavian Oscillation. The results have shown that positive trends in the region are typical of the combinations with the temperatures above the 75th percentile, i.e., the warm extremes in winter and spring. Negative trends were obtained for the cold extremes. Statistically significant increase in the number of days with warm extremes was observed in the northern parts of the region in winter and spring. The analysis of the impacts of the large-scale processes in oceans-atmosphere system showed that the North Atlantic Oscillation index has a strong positive and statistically significant correlation with the warm indices of compound extremes in the northern part of Eastern Europe in winter, while the Scandinavian Oscillation shows the opposite picture.

scholarly journals Flow-dependent and dynamical systems analyses of predictability of the Pacific-North American summertime circulation

2021 ◽  
Author(s):  
Ebrahim Nabizadeh ◽  
Sandro Lubis ◽  
Pedram Hassanzadeh
Keyword(s):  
Dynamical Systems ◽  
North American ◽  
Initial Conditions ◽  
Weather Prediction ◽  
Self Organizing Map ◽  
Near Surface ◽  
Pacific North American ◽  
The North ◽  
Temperature And Precipitation ◽  
Precipitation Anomalies

Forecast skills of numerical weather prediction (NWP) models and intrinsic predictability can be flow-dependent, e.g., different amongweather regimes. Here, we have examined the predictability of distinct Pacific-North American weather regimes in June-September. Fourweather regimes are identified using a self-organizing map analysis of daily 500-hPa geopotential height anomalies, and are shown to havedistinct and coherent links to near-surface temperature and precipitation anomalies over the North American continent. The 4 to 14-dayforecast skills of these 4 regimes are quantified for the ECMWF and the NCEP models (from the TIGGE project) and the Global EnsembleForecast System (GEFS). Based on anomaly correlation coefficient, persistence, and transition frequency, the highest forecast skills areconsistently found for regime 3 (Arctic high). In general, the least skillful forecasts are for regime 1 (Pacific trough). The instantaneous localdimension and persistence of each regime are computed using a dynamical systems-based analysis. The local dimension and persistenceare indicators of intrinsic predictability. This analysis robustly shows that regime 3 has the highest intrinsic predictability. The analysisalso suggests that overall, regime 1 has the lowest intrinsic predictability. These findings are consistent with the high (low) forecast skillsof NWP models for regime 3 (regime 1). Weather regime 1 is associated with above-normal temperature and precipitation anomalies overwestern North America and around the Gulf of Mexico region, indicating potentially important implications for the poor predictability ofthis regime. The dynamical systems analysis suggests that better estimates of initial conditions might improve the forecasts of this regime.

scholarly journals Seasonal Climate Trends, the North Atlantic Oscillation, and Salamander Abundance in the Southern Appalachian Mountain Region

2010 ◽  
Vol 49 (8) ◽  
pp. 1597-1603 ◽  
Author(s):  
Robert J. Warren ◽  
Mark A. Bradford
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
The North ◽  
Temperature And Precipitation ◽  
Southern Appalachian ◽  
Southern Appalachian Mountain ◽  
The North Atlantic ◽  
The North Atlantic Oscillation ◽  
Precipitation Trends

Abstract The North Atlantic Oscillation (NAO) is a large-scale climate teleconnection that coincides with worldwide changes in weather. Its impacts have been documented at large scales, particularly in Europe, but not as much at regional scales. Furthermore, despite documented impacts on ecological dynamics in Europe, the NAO’s influence on North American biota has been somewhat overlooked. This paper examines long-term temperature and precipitation trends in the southern Appalachian Mountain region—a region well known for its biotic diversity, particularly in salamander species—and examines the connections between these trends and NAO cycles. To connect the NAO phase shifts with southern Appalachian ecology, trends in stream salamander abundance are also examined as a function of the NAO index. The results reported here indicate no substantial long-term warming or precipitation trends in the southern Appalachians and suggest a strong relationship between cool season (November–April) temperature and precipitation and the NAO. More importantly, trends in stream salamander abundance are best explained by variation in the NAO as salamanders are most plentiful during the warmer, wetter phases.

scholarly journals The Interannual Variability of Tropical Cyclones

2007 ◽  
Vol 135 (10) ◽  
pp. 3587-3598 ◽  
Author(s):  
William M. Frank ◽  
George S. Young
Keyword(s):  
Tropical Cyclone ◽  
Interannual Variability ◽  
Tropical Cyclones ◽  
Large Scale ◽  
Storm Activity ◽  
Modes Of Variability ◽  
The North ◽  
Temporal And Spatial ◽  
Using Data ◽  
The North Atlantic Oscillation

Abstract This paper examines the interannual variability of tropical cyclones in each of the earth’s cyclone basins using data from 1985 to 2003. The data are first analyzed using a Monte Carlo technique to investigate the long-standing myth that the global number of tropical cyclones is less variable than would be expected from examination of the variability in each basin. This belief is found to be false. Variations in the global number of all tropical cyclones are indistinguishable from those that would be expected if each basin was examined independently of the others. Furthermore, the global number of the most intense storms (Saffir–Simpson categories 4–5) is actually more variable than would be expected because of an observed tendency for storm activity to be correlated between basins, and this raises important questions as to how and why these correlations arise. Interbasin correlations and factor analysis of patterns of tropical cyclone activity reveal that there are several significant modes of variability. The largest three factors together explain about 70% of the variance, and each of these factors shows significant correlation with ENSO, the North Atlantic Oscillation (NAO), or both, with ENSO producing the largest effects. The results suggest that patterns of tropical cyclone variability are strongly affected by large-scale modes of interannual variability. The temporal and spatial variations in storm activity are quite different for weaker tropical cyclones (tropical storm through category 2 strength) than for stronger storms (categories 3–5). The stronger storms tend to show stronger interbasin correlations and stronger relationships to ENSO and the NAO than do the weaker storms. This suggests that the factors that control tropical cyclone formation differ in important ways from those that ultimately determine storm intensity.

scholarly journals Weather regime dependence of extreme value statistics for summer temperature and precipitation

2008 ◽  
Vol 15 (3) ◽  
pp. 365-378 ◽  
Author(s):  
P. Yiou ◽  
K. Goubanova ◽  
Z. X. Li ◽  
M. Nogaj
Keyword(s):  
North Atlantic ◽  
Clustering Algorithm ◽  
Value Theory ◽  
Extreme Value ◽  
Extreme Value Statistics ◽  
Climate Data ◽  
Atmospheric Variability ◽  
Weather Patterns ◽  
The North ◽  
Temperature And Precipitation

Abstract. Extreme Value Theory (EVT) is a useful tool to describe the statistical properties of extreme events. Its underlying assumptions include some form of temporal stationarity in the data. Previous studies have been able to treat long-term trends in datasets, to obtain the time dependence of EVT parameters in a parametric form. Since there is also a dependence of surface temperature and precipitation to weather patterns obtained from pressure data, we determine the EVT parameters of those meteorological variables over France conditional to the occurrence of North Atlantic weather patterns in the summer. We use a clustering algorithm on geopotential height data over the North Atlantic to obtain those patterns. This approach refines the straightforward application of EVT on climate data by allowing us to assess the role of atmospheric variability on temperature and precipitation extreme parameters. This study also investigates the statistical robustness of this relation. Our results show how weather regimes can modulate the different behavior of mean climate variables and their extremes. Such a modulation can be very different for the mean and extreme precipitation.

Peatland pines as climate indicators? A regional comparison of the climatic influence on Scots pine growth in Sweden

2002 ◽  
Vol 32 (8) ◽  
pp. 1400-1410 ◽  
Author(s):  
Hans W Linderholm ◽  
Anders Moberg ◽  
Håkan Grudd
Keyword(s):  
20Th Century ◽  
Scots Pine ◽  
Response Patterns ◽  
Growth Responses ◽  
Late 20Th Century ◽  
The North ◽  
Temperature And Precipitation ◽  
Climate Indicators ◽  
The North Atlantic Oscillation ◽  
Climatic Information

Six tree-ring chronologies from Sweden were analyzed to assess if Scots pine (Pinus sylvestris L.) growing on peatlands are useful as annually resolved climate indicators. Also, climate–growth relationships were compared with those of pines growing on nearby dry sites to evaluate if pines from both environments may be combined to yield climate information. While temperatures in spring and summer had positive influences on peatland pine growth, precipitation responses ranged from negative in the north to positive in the south. Climate – growth response patterns differed between peatland and neighboring dry sites, where climatic information in peatland pines was weaker. Added to the direct effect of growth-year climate, is the response of peatland pines to water table variations, a function of climate over several years, likely causing annual growth to reflect a synthesis of climate over a long period. Scots pine climate – growth responses, in both environments, changed throughout the 20th century, corresponding to changes in temperature and precipitation patterns in Sweden. Decreasing growth trends since the late 1970s may be a result of late 20th century change to a warmer and wetter climate, possibly related to a strengthening of the North Atlantic Oscillation (NAO) in recent decades.

scholarly journals North Atlantic midwinter storm track suppression and the European weather response in ERA5 reanalysis

2021 ◽  
Author(s):  
Estefania Montoya Duque ◽  
Frank Lunkeit ◽  
Richard Blender
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Storm Track ◽  
Reanalysis Data ◽  
Band Pass Filter ◽  
Pass Filter ◽  
The North ◽  
Temperature And Precipitation ◽  
Precipitation Increase ◽  
Precipitation Anomalies

AbstractIn this study, we analyse the influence of North Atlantic midwinter storm track suppressions on European synoptic temperature and precipitation anomalies to determine the large-scale conditions relevant for the so-called Christmas thaw. We diagnose this relation in daily ERA5 reanalysis data in the spatial resolution of 0.25∘ between 1979 and 2018. To access synoptic time scales, a 3–10-day band-pass filter is applied. An index for the suppression is defined by the upper tropospheric Eddy Kinetic Energy (EKE) anomalies in the North Atlantic. We define the strong jet stream years as the year exceeding the 75% of the winter seasonal values at 250 hPa. In winters with strong jet activity, the storm track suppression is found, in agreement with the barotropic governor mechanism. Composites of European surface temperature and precipitation for low index values reveal weakly warmer conditions during winter (DJF) in Central Europe and the British Isles and a distinct cooling in Northern Europe. In the 1-month interval during December 15 to January 15, the warming is more pronounced. The clearest signal is the precipitation increase with a magnitude of 1 mm/day in the Mediterranean region.

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