Reconstructing winter climate anomalies in the  Euro-Atlantic sector using circulation patterns

Abstract. The efficacy of Euro-Atlantic circulation regimes for estimating wintertime climate anomalies (precipitation and surface temperature) over Europe is assessed. A comparison of seasonal climate reconstructions from two different regime frameworks (cluster analysis of the low-level zonal flow, and traditional blocking indices) is presented and contrasted with seasonal reconstructions using the North Atlantic Oscillation (NAO) index. The reconstructions are quantitatively evaluated using correlations and the coefficient of efficiency, accounting for misfit in phase and amplitude. The skill of the various classifications in reconstructing seasonal anomalies depends on the variable and region of interest. The jet and blocking regimes are found to capture more spatial structure in seasonal precipitation anomalies over Europe than the NAO, with the jet framework showing generally better skill relative to the blocking indices. The reconstructions of temperature anomalies have lower skill than those for precipitation, with the best results for temperature obtained by the NAO for high-latitude and by the blocking framework for southern Europe. All methods underestimate the magnitude of seasonal anomalies due to the large variability in precipitation and temperature within each classification pattern.

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Reconstructing winter climate anomalies in the Euro-Atlantic sector using circulation patterns

10.5194/wcd-2021-6 ◽

2021 ◽

Author(s):

Erica Madonna ◽

David S. Battisti ◽

Camille Li ◽

Rachel H. White

Keyword(s):

Zonal Flow ◽

Winter Climate ◽

Atlantic Sector ◽

Climate Anomalies ◽

The North ◽

Nao Index ◽

Climate Reconstructions ◽

Circulation Patterns ◽

Precipitation Anomalies ◽

The North Atlantic Oscillation

Abstract. The efficacy of Euro-Atlantic circulation regimes for estimating wintertime climate anomalies (precipitation and surface temperature) over Europe is assessed. A comparison of seasonal climate reconstructions from two different regime frameworks (cluster analysis of the low-level zonal flow, and traditional blocking indices) is presented and contrasted with seasonal reconstructions using the North Atlantic Oscillation (NAO) index. The reconstructions are quantitatively evaluated using correlations and the coefficient of efficiency, accounting for misfit in phase and amplitude. While all methods show skill in reproducing wintertime precipitation and temperature variability, they underestimate the magnitude of seasonal anomalies by a factor of two. The regimes are found to capture more spatial structure in seasonal precipitation anomalies over Europe than the NAO, with the jet framework showing generally better skill relative to the blocking indices. The reconstructions of temperature anomalies have lower skill than those for precipitation, with the best results for temperature obtained by the NAO for high-latitude and by the blocking framework for southern Europe.

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Towards a better assessment of the historical climate of Extremadura region (SW Spain)

10.5194/egusphere-egu2020-5149 ◽

2020 ◽

Author(s):

José Manuel Vaquero ◽

María Cruz Gallego ◽

Víctor M. S. Carrasco ◽

Nieves Bravo-Paredes ◽

María Ángeles Obregón ◽

...

Keyword(s):

Meteorological Data ◽

Main Task ◽

Winter Climate ◽

Historical Climate ◽

The North ◽

Nao Index ◽

Dry Conditions ◽

Good Proxy ◽

The North Atlantic Oscillation ◽

The Impact

Our efforts to a better understanding of the historical climate of the region of Extremadura (interior of the SW Iberia) have been directed in two main aspects. First, we have tried to recover all the meteorological data of the pre-instrumental period. Second, we have been working on the localization and analysis of proxy data, including &#8220;pro-pluvia&#8221; rogation ceremonies and a chronology of catastrophic floods in this region.The recovery of historical meteorological data from libraries and archives and the subsequent digitization to obtain readable-machine version has been a main task in our research. Meteorological data from different sources (manuscripts, books, newspapers, etc.) and eight different locations in Extremadura have been recovered and digitized. The oldest data were read in 1824 (Fern&#225;ndez-Fern&#225;ndez et al., 2014). Other important meteorological series can be highlighted as the actinometric measurements in C&#225;ceres for the period 1913-1920 (Bravo-Paredes et al., 2019).&#8220;Pro-pluvia&#8221; rogations were celebrated during dry conditions to ask God for rain. In our case, 35 &#8220;pro-pluvia&#8221; rogations were retrieved for the period 1824-1931 from different locations in Extremadura. The winter climate of this region is strongly dominated by the North Atlantic Oscillation (NAO) and, therefore, these pro-pluvia rogations were associated to the NAO index to analyze this relationship. The results of our analysis show that the rogation ceremonies in Extremadura can be considered a good proxy for the NAO index. Also, it is important to know the magnitude and the impact of the catastrophic floods occurred in Extremadura. In total, 40 floods occurred in Badajoz were recovered from different documentary sources for the period 1545-1989.All these research efforts will allow for a better understanding of the past climate in the region of Extremadura, where such studies have been very scarce.ReferencesBravo-Paredes, N. et al. (2019) &#8220;Analysis of actinometric measurements under different sky conditions in C&#225;ceres (Spain) for the period 1913-1920&#8221; Tellus B 71, 1663597. DOI: 10.1080/16000889.2019.1663597Fern&#225;ndez-Fern&#225;ndez, M.I. et al. (2014) "The climate of Zafra from 1750 to 1840: History and description of weather observations" Climatic Change 126, 107&#8211;118. (doi: 10.1007/s10584-014-1201-5)

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Decadal Relationship between European Blocking and the North Atlantic Oscillation during 1978–2011. Part I: Atlantic Conditions

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-14-0039.1 ◽

2015 ◽

Vol 72 (3) ◽

pp. 1152-1173 ◽

Cited By ~ 17

Author(s):

Dehai Luo ◽

Yao Yao ◽

Aiguo Dai

Keyword(s):

North Atlantic Oscillation ◽

North Atlantic ◽

Western Europe ◽

Storm Track ◽

Western Atlantic ◽

Atlantic Sector ◽

The North ◽

Nao Index ◽

The North Atlantic ◽

The North Atlantic Oscillation

Abstract Both the positive and negative phases of the North Atlantic Oscillation (NAO+ and NAO−, respectively) and atmospheric blocking in the Euro-Atlantic sector reflect synoptic variability over the region and thus are intrinsically linked. This study examines their relationship from a decadal change perspective. Since the winter-mean NAO index is defined as a time average of instantaneous NAO indices over the whole winter, it is unclear how the activity of European blocking (EB) events can be related to the variation of the positive mean NAO index. Here, this question is examined by dividing the winter period 1978–2011 into two decadal epochs: 1978–94 (P1) with an increasing and high NAO index and 1995–2011 (P2) with a decreasing and low NAO index. Using atmospheric reanalysis data, it is shown that there are more intense and persistent EB events in eastern Europe during P1 than during P2, while the opposite is true for western Europe. It is further shown that there are more NAO+ (NAO−) events during P1 (P2). The EB events associated with NAO+ events extend more eastward and are associated with stronger Atlantic mean zonal wind and weaker western Atlantic storm track during P1 than during P2, but EB events associated with NAO− events increase in western Europe under opposite Atlantic conditions during P2. Thus, the increase in the number of individual NAO+ (NAO−) events results in more EB events in eastern (western) Europe during P1 (P2). The EB change is also associated with the increased frequency of NAO− to NAO+ (NAO+ to NAO−) transition events.

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Tropospheric Rossby Wave Breaking and the NAO/NAM

Journal of the Atmospheric Sciences ◽

10.1175/2008jas2632.1 ◽

2008 ◽

Vol 65 (9) ◽

pp. 2861-2876 ◽

Cited By ~ 108

Author(s):

Courtenay Strong ◽

Gudrun Magnusdottir

Keyword(s):

Northern Hemisphere ◽

Rossby Wave ◽

Wave Breaking ◽

Time Lag ◽

Zonal Flow ◽

Sea Level Pressure ◽

Rossby Wave Breaking ◽

The North ◽

Nao Index ◽

The North Atlantic Oscillation

Abstract Objective analysis of several hundred thousand anticyclonic and cyclonic breaking Rossby waves is performed for the Northern Hemisphere (NH) winters of 1958–2006. A winter climatology of both anticyclonic and cyclonic Rossby wave breaking (RWB) frequency and size (zonal extent) is presented for the 350-K isentropic surface over the NH, and the spatial distribution of RWB is shown to agree with theoretical ideas of RWB in shear flow. Composites of the two types of RWB reveal their characteristic sea level pressure anomalies, upper- and lower-tropospheric velocity fields, and forcing of the upper-tropospheric zonal flow. It is shown how these signatures project onto the centers of action and force the velocity patterns associated with the North Atlantic Oscillation (NAO) and Northern Hemisphere annular mode (NAM). Previous studies have presented evidence that anticyclonic (cyclonic) breaking leads to the positive (negative) polarity of the NAO, and this relationship is confirmed for RWB over the midlatitudes centered near 50°N. However, an opposite and statistically significant relationship, in which cyclonic RWB forces the positive NAO and anticyclonic RWB forces the negative NAO, is shown over regions 20° to the north and south, centered at 70° and 30°N, respectively. On a winter mean basis, the frequency of RWB over objectively defined regions covering 12% of the area of the NH accounts for 95% of the NAO index and 92% of the NAM index. A 6-hourly analysis of all the winters indicates that RWB over the objectively defined regions affects the NAO/NAM without a time lag. Details of the objective wave-breaking analysis method are provided in the appendix.

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Regionally improved seasonal forecast of precipitation through Best estimation of winter NAO

Advances in Science and Research ◽

10.5194/asr-16-165-2019 ◽

2019 ◽

Vol 16 ◽

pp. 165-174

Author(s):

Eroteida Sánchez-García ◽

José Voces-Aboy ◽

Beatriz Navascués ◽

Ernesto Rodríguez-Camino

Keyword(s):

Iberian Peninsula ◽

A Priori Estimates ◽

A Priori ◽

Region Of Interest ◽

Winter Precipitation ◽

The North ◽

Nao Index ◽

Priori Estimates ◽

The North Atlantic Oscillation ◽

Linear Unbiased Estimate

Abstract. We describe a methodology for ensemble member's weighting of operational seasonal forecasting systems (SFS) based on an enhanced prediction of a climate driver strongly affecting meteorological parameters over a certain region. We have applied it to the North Atlantic Oscillation (NAO) influence on the Iberian Peninsula winter precipitation. The first step in the proposed approach is to find the best estimation of winter NAO. Skill and error characteristics of forecasted winter NAO index by different Copernicus SFS are analysed in this study. Based on these results, a bias correction scheme is proposed and implemented for the ECMWF System 5 ensemble mean of NAO index, and then a modified NAO index pdf based on Gaussian errors is formulated. Finally, we apply the statistical estimation theory to achieve the Best linear unbiased estimate of winter NAO index and its uncertainty. For this purpose, two a priori estimates are used: the bias corrected NAO index Gaussian pdf from ECMWF System 5, and a skilful winter NAO index prediction based on teleconnection with snow cover advance with normal distributed errors. The second step of the proposed methodology is to employ the enhanced NAO index pdf estimates for ensemble member's weighting of a SFS based on a single dynamical model. The new NAO pdfs obtained in this work have been used to improve the skill of the ECMWF System 5 to predict both NAO index and precipitation over the Iberian Peninsula. We show the improvement of NAO prediction, and of winter precipitation forecasts over our region of interest, when members are weighted with the bias corrected NAO index Gaussian pdf based on ECMWF System 5 compared with the usual approach based on equiprobability of ensemble members. Forecast skill is further enhanced if the Best NAO index pdf based on an optimal combination of the two a priori NAO index estimates is used for ensemble member's weighting.

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Intermittency of Arctic-midlatitude teleconnections: the stratospheric pathway between autumn sea ice and the winter NAO

10.5194/egusphere-egu2020-7905 ◽

2020 ◽

Author(s):

Peter Yu Feng Siew ◽

Camille Li ◽

Stefan Sobolowski ◽

Martin King

Keyword(s):

Sea Ice ◽

Causal Effect ◽

Signal To Noise Ratio ◽

Kara Sea ◽

Arctic Sea Ice ◽

Winter Climate ◽

The North ◽

Nao Index ◽

Ice Conditions ◽

The North Atlantic Oscillation

An observed relationship linking Arctic sea ice conditions in autumn to the North Atlantic Oscillation (NAO) index the following winter has potential relevance for seasonal predictions of European and North American climate. The physical pathway most often invoked to explain this particular teleconnection passes through the stratosphere. A Causal Effect Networks (CEN) approach is used to explore this stratospheric pathway between late autumn Barents-Kara sea ice and the February NAO, focusing on its seasonal evolution, timescale-dependence, and robustness. This pathway is statistically detectable in the satellite period, explaining 26% of the interannual variability in the February NAO. However, a bootstrap-resampling test reveals that the pathway is highly intermittent: the whole pathway emerges in only 15% of the bootstrapped samples. The intermittent nature of the pathway is consistent with the weak signal-to-noise ratio of the atmospheric response in the sea ice perturbation experiments, and suggests that a background state is important in determining whether the pathway is active. Higher frequency synoptic interactions between Barents-Kara sea ice and sea level pressure over Urals potentially interfere with the stratospheric pathway. Such interference likely reduces the potential for using the ice-NAO relationship for predicting midlatitude winter climate. This study helps quantify the robustness of linkages within the stratospheric pathway, and provides insight into which linkages are most subject to sampling issues within the relatively short observational record.

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A Regime View of the North Atlantic Oscillation and Its Response to Anthropogenic Forcing

Journal of Climate ◽

10.1175/2009jcli3087.1 ◽

2010 ◽

Vol 23 (6) ◽

pp. 1291-1307 ◽

Cited By ~ 90

Author(s):

Tim Woollings ◽

Abdel Hannachi ◽

Brian Hoskins ◽

Andrew Turner

Keyword(s):

North Atlantic Oscillation ◽

North Atlantic ◽

Anthropogenic Forcing ◽

The Third ◽

The North ◽

Nao Index ◽

Future Behavior ◽

Real Change ◽

The North Atlantic Oscillation

Abstract The distribution of the daily wintertime North Atlantic Oscillation (NAO) index in the 40-yr ECMWF Re-Analysis (ERA-40) is significantly negatively skewed. Dynamical and statistical analyses both suggest that this skewness reflects the presence of two distinct regimes—referred to as “Greenland blocking” and “subpolar jet.” Changes in both the relative occurrence and in the structure of the regimes are shown to contribute to the long-term NAO trend over the ERA-40 period. This is contrasted with the simulation of the NAO in 100-yr control and doubled CO2 integrations of the third climate configuration of the Met Office Unified Model (HadCM3). The model has clear deficiencies in its simulation of the NAO in the control run, so its predictions of future behavior must be treated with caution. However, the subpolar jet regime does become more dominant under anthropogenic forcing and, while this change is small it is clearly statistically significant and does represent a real change in the nature of NAO variability in the model.

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Dynamical analysis of a reduced model for the North Atlantic Oscillation

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0282.1 ◽

2021 ◽

Author(s):

Courtney Quinn ◽

Dylan Harries ◽

Terence J. O’Kane

Keyword(s):

North Atlantic Oscillation ◽

North Atlantic ◽

Growth Rates ◽

Time Dependent ◽

Unstable State ◽

Time Step ◽

Atlantic Sector ◽

The North ◽

The North Atlantic ◽

The North Atlantic Oscillation

AbstractThe dynamics of the North Atlantic Oscillation (NAO) are analyzed through a data-driven model obtained from atmospheric reanalysis data. We apply a regularized vector autoregressive clustering technique to identify recurrent and persistent states of atmospheric circulation patterns in the North Atlantic sector (110°W-0°E, 20°N-90°N). In order to analyze the dynamics associated with the resulting cluster-based models, we define a time-dependent linear delayed map with a switching sequence set a priori by the cluster affiliations at each time step. Using a method for computing the covariant Lyapunov vectors (CLVs) over various time windows, we produce sets of mixed singular vectors (for short windows) and approximate the asymptotic CLVs (for longer windows). The growth rates and alignment of the resulting time-dependent vectors are then analyzed. We find that the window chosen to compute the vectors acts as a filter on the dynamics. For short windows, the alignment and changes in growth rates are indicative of individual transitions between persistent states. For long windows, we observe an emergent annual signal manifest in the alignment of the CLVs characteristic of the observed seasonality in the NAO index. Analysis of the average finite-time dimension reveals the NAO− as the most unstable state relative to the NAO+, with persistent AR states largely stable. Our results agree with other recent theoretical and empirical studies that have shown blocking events to have less predictability than periods of enhanced zonal flow.

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Coupled decadal variability of the North Atlantic Oscillation, regional rainfall and karst spring discharges in the Campania region (southern Italy)

Hydrology and Earth System Sciences ◽

10.5194/hess-16-1389-2012 ◽

2012 ◽

Vol 16 (5) ◽

pp. 1389-1399 ◽

Cited By ~ 21

Author(s):

P. De Vita ◽

V. Allocca ◽

F. Manna ◽

S. Fabbrocino

Keyword(s):

Time Series ◽

North Atlantic Oscillation ◽

Air Temperature ◽

North Atlantic ◽

Karst Spring ◽

The North ◽

Nao Index ◽

The North Atlantic ◽

The North Atlantic Oscillation

Abstract. Thus far, studies on climate change have focused mainly on the variability of the atmospheric and surface components of the hydrologic cycle, investigating the impact of this variability on the environment, especially with respect to the risks of desertification, droughts and floods. Conversely, the impacts of climate change on the recharge of aquifers and on the variability of groundwater flow have been less investigated, especially in Mediterranean karst areas whose water supply systems depend heavily upon groundwater exploitation. In this paper, long-term climatic variability and its influence on groundwater recharge were analysed by examining decadal patterns of precipitation, air temperature and spring discharges in the Campania region (southern Italy), coupled with the North Atlantic Oscillation (NAO). The time series of precipitation and air temperature were gathered over 90 yr, from 1921 to 2010, using 18 rain gauges and 9 air temperature stations with the most continuous functioning. The time series of the winter NAO index and of the discharges of 3 karst springs, selected from those feeding the major aqueducts systems, were collected for the same period. Regional normalised indexes of the precipitation, air temperature and karst spring discharges were calculated, and different methods were applied to analyse the related time series, including long-term trend analysis using smoothing numerical techniques, cross-correlation and Fourier analysis. The investigation of the normalised indexes highlighted the existence of long-term complex periodicities, from 2 to more than 30 yr, with differences in average values of up to approximately ±30% for precipitation and karst spring discharges, which were both strongly correlated with the winter NAO index. Although the effects of the North Atlantic Oscillation (NAO) had already been demonstrated in the long-term precipitation and streamflow patterns of different European countries and Mediterranean areas, the results of this study allow for the establishment of a link between a large-scale atmospheric cycle and the groundwater recharge of carbonate karst aquifers. Consequently, the winter NAO index could also be considered as a proxy to forecast the decadal variability of groundwater flow in Mediterranean karst areas.

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Heavy Rainfall and Landslide Event in January 1831 at the Pedregoso Mountains (Cabeza Del Buey, SW Spain)

Atmosphere ◽

10.3390/atmos11050544 ◽

2020 ◽

Vol 11 (5) ◽

pp. 544 ◽

Cited By ~ 1

Author(s):

Juan Pedro García-Garrido ◽

María Cruz Gallego ◽

Teodoro Palacios ◽

Ricardo M. Trigo ◽

José Manuel Vaquero

Keyword(s):

North Atlantic ◽

Large Scale ◽

Meteorological Data ◽

Triggering Mechanism ◽

Sw Spain ◽

The North ◽

Nao Index ◽

Landslide Event ◽

High Precipitation ◽

The North Atlantic Oscillation

In this work, a landslide event that took place on January 1831 at the Pedregoso Mountains, Cabeza del Buey, SW Spain, is described. This landslide had not been documented to date and was only described in the local press. This event involved an estimated amount of dislodged material in the order of 104 m3. The amount of meteorological data is very scarce as the event occurred before the setting up of the national meteorological service in Spain. However, data from the relatively near location of SW Iberia suggest that the landslide was preceded by a prolonged period of unusually high precipitation totals and that this intense wet period is compatible with the large-scale atmospheric configuration in the winter of 1829–1830. In fact, the North Atlantic Oscillation (NAO) index for that winter achieved one of the most negative values observed in the bicentennial period spanning 1821 to 2019. This multidisciplinary work represents the first attempt to report and describe the main triggering mechanism for an historical landslide in the Extremadura region that is similar to other great historical landslides which have already been documented for other locations in Spain.

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