scholarly journals Multiple Changepoint Detection via Genetic Algorithms

2012 ◽  
Vol 25 (2) ◽  
pp. 674-686 ◽  
Author(s):  
Shanghong Li ◽  
Robert Lund
Keyword(s):  
Time Series ◽  
Genetic Algorithms ◽  
North Atlantic ◽  
Minimum Description Length ◽  
Correlated Data ◽  
Reference Station ◽  
Objective Functions ◽  
The North ◽  
Climate Time Series ◽  
Climatic Time Series

Abstract This paper studies genetic algorithms as a means of estimating the number of changepoints and their locations in a climatic time series. Such methods bypass classic subsegmentation algorithms, which sometimes yield suboptimal conclusions. Minimum description length techniques are introduced. These techniques require optimizing an objective function over all possible changepoint numbers and location times. The general objective functions allow for correlated data, reference station aspects, and/or nonnormal marginal distributions, all common features of climate time series. As an exhaustive evaluation of all changepoint configurations is not possible, the optimization is accomplished via a genetic algorithm that randomly walks through a subset of good models in an intelligent manner. The methods are applied in the analysis of 173 yr of annual precipitation measurements from New Bedford, Massachusetts, and the North Atlantic basin tropical cyclone record.

scholarly journals Dynamic wavelet correlation analysis for multivariate climate time series

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Josué M. Polanco-Martínez ◽  
Javier Fernández-Macho ◽  
Martín Medina-Elizalde
Keyword(s):  
Time Series ◽  
Tropical Cyclone ◽  
North Atlantic ◽  
Large Scale ◽  
Southern Oscillation ◽  
Atlantic Multidecadal Oscillation ◽  
Last Millennium ◽  
Climate Data ◽  
The North ◽  
Climate Time Series

AbstractThe wavelet local multiple correlation (WLMC) is introduced for the first time in the study of climate dynamics inferred from multivariate climate time series. To exemplify the use of WLMC with real climate data, we analyse Last Millennium (LM) relationships among several large-scale reconstructed climate variables characterizing North Atlantic: i.e. sea surface temperatures (SST) from the tropical cyclone main developmental region (MDR), the El Niño-Southern Oscillation (ENSO), the North Atlantic Multidecadal Oscillation (AMO), and tropical cyclone counts (TC). We examine the former three large-scale variables because they are known to influence North Atlantic tropical cyclone activity and because their underlying drivers are still under investigation. WLMC results obtained for these multivariate climate time series suggest that: (1) MDRSST and AMO show the highest correlation with each other and with respect to the TC record over the last millennium, and: (2) MDRSST is the dominant climate variable that explains TC temporal variability. WLMC results confirm that this method is able to capture the most fundamental information contained in multivariate climate time series and is suitable to investigate correlation among climate time series in a multivariate context.

scholarly journals The 14C Age of the Icelandic Vedde Ash: Implications for Younger Dryas Marine Reservoir Age Corrections

Radiocarbon ◽  
1995 ◽  
Vol 37 (1) ◽  
pp. 53-62 ◽  
Author(s):  
W. E. N. Austin ◽  
Edouard Bard ◽  
J. B. Hunt ◽  
Dick Kroon ◽  
J. D. Peacock
Keyword(s):  
Time Series ◽  
Surface Water ◽  
North Atlantic ◽  
Younger Dryas ◽  
The North ◽  
14C Age ◽  
Climatic Event ◽  
The North Atlantic ◽  
Climatic Time Series ◽  
Reservoir Age

Increased marine 14C reservoir ages from the surface water of the North Atlantic are documented for the Younger Dryas period. We use terrestrial and marine AMS 14C dates from the time of deposition of the Icelandic Vedde Ash to examine the marine 14C reservoir age. This changed from its modem North Atlantic value of ca. 400 yr to ca. 700 yr during the Younger Dryas climatic event. The increased marine reservoir age has implications for both comparing climatic time series dated by 14C and understanding palaeoceanographic changes that generated the increase.

Meridional Tripole Mode of Winter Precipitation over the Arctic and Continental North Africa–Eurasia

2021 ◽  
pp. 1
Author(s):  
Xiaolin Liu ◽  
Jianhua Lu ◽  
Yimin Liu ◽  
Guoxiong Wu
Keyword(s):  
Time Series ◽  
North Africa ◽  
North Atlantic ◽  
Hadley Cell ◽  
The Arctic ◽  
Positive Phase ◽  
The North ◽  
Ferrel Cell ◽  
The North Atlantic ◽  
Westerly Jets

AbstractWintertime precipitation is vital to the growth of glaciers in the northern hemisphere. We find a tripole mode of precipitation (PTM), with each pole of the mode extending zonally over the eastern hemisphere roughly between 30°W and 120°E, and the positive/negative/positive structure for its positive phase extending meridionally from the Arctic to the continental North Africa–Eurasia. The large-scale dynamics associated with the PTM is explored. The positive phase of the PTM is associated with the negative while eastward-shifted phase of the North Atlantic Oscillation (NAO) and a zonal band of positive SST anomaly in the tropics, together with a narrowed Hadley cell and weakened Ferrel cell. While being north-eastward tilted and separated from their North Africa-Eurasia counterpart in the climatological mean, the upper-tropospheric westerly jets over the east Pacific and north Atlantic become extending zonally and shifting southward and hence form a circumpolar subtropical jet as a whole by connecting with the westerly jets over the North Africa-Eurasia. The enhanced zonal winds over the north Atlantic promote more synoptic-scale transient eddies which are waveguided by the jet streams. The polar vortex weakens and cold air dips southward from the North Pole. Further diagnosis of the E-vectors suggests that transient eddies have a positive feedback on the weakening of Ferrel cell. Opposite features are associated with the negative phase of the PTM. The reconstructed time series using multiple linear regression on the NAO index and the tropical SST averaged over 20°S– 20°N, can explain 62.4% of the variance of the original the original precipitation time series.

scholarly journals Regional differences in modelled net production and shallow remineralization in the North Atlantic subtropical Gyre

2011 ◽  
Vol 8 (6) ◽  
pp. 12477-12519 ◽  
Author(s):  
B. Fernández-Castro ◽  
L. Anderson ◽  
E. Marañón ◽  
S. Neuer ◽  
B. Ausín ◽  
...  
Keyword(s):  
Time Series ◽  
North Atlantic ◽  
Regional Differences ◽  
Dissolved Inorganic Carbon ◽  
Net Production ◽  
Time Series Study ◽  
The North ◽  
European Station ◽  
Lateral Advection ◽  
Series Study

Abstract. We used 5-year concomitant data of tracers distribution from the BATS (Bermuda Time-series Study) and ESTOC (European Station for Time-Series in the Ocean, Canary Islands) sites to build a 1-D tracer model conservation including horizontal advection and compute net production and shallow remineralization rates at both sites. Net production rates computed below the mixed layer to 110 m from April to December for oxygen, dissolved inorganic carbon and nitrate at BATS (1.34 ± 0.79 mol O2 m−2, −1.73 ± 0.52 mol C m−2 and −125 ± 36 mmol N m−2) showed no statistically significant differences compared to ESTOC (1.03 ± 0.62 mol O2 m−2, −1.42 ± 0.30 mol C m−2 and −213 ± 56 mmol N m−2). Shallow remineralization rates between 110 and 250 m computed at ESTOC (−3.9 ± 1.0 mol O2 m−2, 1.53 ± 0.43 mol C m−2 and 38 ± 155 mmol N m−2) were statistically higher for oxygen compared to BATS (−1.81 ± 0.37 mol O2 m−2, 1.52 ± 0.30 mol C m−2 and 147 ± 43 mmol N m−2). Lateral advection, which was more significant at ESTOC, was responsible for the differences in estimated oxygen remineralization rates between both stations. Due to the relevance of the horizontal transport at ESTOC, we cannot assert that the differences in shallow remineralization rates computed for both stations can explain the observed descrepancies in the flux of sinking organic matter.

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

2012 ◽  
Vol 16 (5) ◽  
pp. 1389-1399 ◽  
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.

scholarly journals Comparison of in situ time-series of temperature with gridded sea surface temperature datasets in the North Atlantic

2009 ◽  
Vol 66 (7) ◽  
pp. 1467-1479 ◽  
Author(s):  
Sarah L. Hughes ◽  
N. Penny Holliday ◽  
Eugene Colbourne ◽  
Vladimir Ozhigin ◽  
Hedinn Valdimarsson ◽  
...  
Keyword(s):  
Time Series ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Atlantic ◽  
Sea Surface ◽  
The North ◽  
Spatial Coverage ◽  
The North Atlantic

Abstract Hughes, S. L., Holliday, N. P., Colbourne, E., Ozhigin, V., Valdimarsson, H., Østerhus, S., and Wiltshire, K. 2009. Comparison of in situ time-series of temperature with gridded sea surface temperature datasets in the North Atlantic. – ICES Journal of Marine Science, 66: 1467–1479. Analysis of the effects of climate variability and climate change on the marine ecosystem is difficult in regions where long-term observations of ocean temperature are sparse or unavailable. Gridded sea surface temperature (SST) products, based on a combination of satellite and in situ observations, can be used to examine variability and long-term trends because they provide better spatial coverage than the limited sets of long in situ time-series. SST data from three gridded products (Reynolds/NCEP OISST.v2., Reynolds ERSST.v3, and the Hadley Centre HadISST1) are compared with long time-series of in situ measurements from ICES standard sections in the North Atlantic and Nordic Seas. The variability and trends derived from the two data sources are examined, and the usefulness of the products as a proxy for subsurface conditions is discussed.

scholarly journals Assessing drought cycles in SPI time series using a Fourier analysis

2015 ◽  
Vol 15 (3) ◽  
pp. 571-585 ◽  
Author(s):  
E. E. Moreira ◽  
D. S. Martins ◽  
L. S. Pereira
Keyword(s):  
Time Series ◽  
Fourier Analysis ◽  
North Atlantic ◽  
Clustering Analysis ◽  
Standardized Precipitation Index ◽  
The North ◽  
Southern Portugal ◽  
Circulation Indices ◽  
The Common ◽  
The North Atlantic Oscillation

Abstract. In this study, drought in Portugal was assessed using 74 time series of Standardized Precipitation Index (SPI) with a 12-month timescale and 66 years length. A clustering analysis on the SPI Principal Components loadings was performed in order to find regions where SPI drought characteristics are similar. A Fourier analysis was then applied to the SPI time series considering one SPI value per year relative to every month. The analysis focused on the December SPI time series grouped in each of the three identified clusters to investigate the existence of cycles that could be related to the return periods of droughts. The most frequent significant cycles in each of the three clusters were identified and analysed for December and the other months. Results for December show that drought periodicities vary among the three clusters, pointing to a 6-year cycle across the country and a 9.4-year cycle in central and southern Portugal. Both these cycles likely show the influence of the North Atlantic Oscillation (NAO) on the occurrence and severity of droughts in Portugal. Relative to other months it was observed that cycles varied according to the common occurrence of precipitation: for the rainy months – November, December and January – cycles are similar to those for December; for the dry months – May to September – where the lack of precipitation masks the occurrence of drought, the dominant cycles are of short duration and cannot be related to the NAO or other large circulation indices to explain drought variability; for the transition months – February, March, April and October – 6-year and 3-year cycles were identified, the latter being more strongly apparent in central and southern Portugal. NAO influence is again identified relative to the 6-year cycles. The short cycles are apparently associated with positive SPI, thus with wetness, not drought. Overall, results confirm the importance of the NAO as a driving force for dry and wet periods.

scholarly journals Nonlinear time series models for the North Atlantic Oscillation

2020 ◽  
Vol 6 (2) ◽  
pp. 141-157
Author(s):  
Thomas Önskog ◽  
Christian L. E. Franzke ◽  
Abdel Hannachi
Keyword(s):  
Time Series ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Nonlinear Models ◽  
Weather Conditions ◽  
Dominant Mode ◽  
Statistical Properties ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract. The North Atlantic Oscillation (NAO) is the dominant mode of climate variability over the North Atlantic basin and has a significant impact on seasonal climate and surface weather conditions. This is the result of complex and nonlinear interactions between many spatio-temporal scales. Here, the authors study a number of linear and nonlinear models for a station-based time series of the daily winter NAO index. It is found that nonlinear autoregressive models, including both short and long lags, perform excellently in reproducing the characteristic statistical properties of the NAO, such as skewness and fat tails of the distribution, and the different timescales of the two phases. As a spin-off of the modelling procedure, we can deduce that the interannual dependence of the NAO mostly affects the positive phase, and that timescales of 1 to 3 weeks are more dominant for the negative phase. Furthermore, the statistical properties of the model make it useful for the generation of realistic climate noise.

scholarly journals Detecting quasi-oscillations in the monthly precipitation regimes of the Iberian Peninsula

2003 ◽  
Vol 21 (3) ◽  
pp. 819-832 ◽  
Author(s):  
L. Morala ◽  
A. Serrano ◽  
J. A. Garcia
Keyword(s):  
Time Series ◽  
High Pressure ◽  
Iberian Peninsula ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Singular Spectrum Analysis ◽  
Monthly Precipitation ◽  
The North ◽  
Precipitation Regimes ◽  
The North Atlantic

Abstract. A spectral analysis of the time series corresponding to the main monthly precipitation regimes of the Iberian Peninsula was performed using two methods, the Multi-Taper Method and Monte Carlo Singular Spectrum Analysis. The Multi-Taper Method gave a preliminary view of the presence of signals in some of the time series. Monte Carlo Singular Spectrum Analysis discriminated between potential oscillations and noise. From the results of the two methods it is concluded that there exist three significant quasi-oscillations at the 95% level of confidence: a 5.0 year quasi-oscillation and a long-term trend in the Atlantic pattern of March, a 3.2 year quasi-oscillation in the Cantabrian pattern of January, and a 4.0 year quasi-oscillation in the Catalonian pattern of February. These quasi-oscillations might be related to climatic variations with similar periodicities over the North Atlantic Ocean. The possible simultaneity of high values of precipitation generated by the significant quasi-oscillations and high sea–level pressures was studied by means of composite maps. It was found that high values of precipitation generated by the oscillations of the Atlantic patterns of January and March exist simultaneously with a specific high pressure structure over the North Atlantic Ocean, that allow cyclonic perturbations to cross the Iberian Peninsula. During the non-wet years, this high pressure structure moves northwards, keeping the track of the low pressure centers to the north, far from the Iberian Peninsula. On the other hand, high values of precipitation generated by the oscillation of the Cantabrian pattern of January exist simultaneously with a high pressure structure over the Galicia region and the Cantabrian Sea, that allow a northerly flow over the region. Also, a positive trend in the NAO index for March has been found, starting in the sixties, which is not evident for other winter months. This trend agrees with the decreasing trend found in the March Atlantic pattern.Key words. Meteorology and atmospheric dynamics (climatology; precipitation) Oceanography: general (climate and interannual variability)

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

2011 ◽  
Vol 8 (6) ◽  
pp. 11233-11275
Author(s):  
P. De Vita ◽  
V. Allocca ◽  
F. Manna ◽  
S. Fabbrocino
Keyword(s):  
Time Series ◽  
Air Temperature ◽  
North Atlantic ◽  
Campania Region ◽  
The North ◽  
Nao Index ◽  
Groundwater Circulation ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract. Climate change is one of the issues most debated by the scientific community with a special focus to the combined effects of anthropogenic modifications of the atmosphere and the natural climatic cycles. Various scenarios have been formulated in order to forecast the global atmospheric circulation and consequently the variability of the global distribution of air temperature and rainfall. The effects of climate change have been analysed with respect to the risks of desertification, droughts and floods, remaining mainly limited to the atmospheric and surface components of the hydrologic cycle. Consequently the impact of the climate change on the recharge of regional aquifers and on the groundwater circulation is still a challenging topic especially in those areas whose aqueduct systems depend basically on springs or wells, such as the Campania region (Southern Italy). In order to analyse the long-term climatic variability and its influence on groundwater circulation, we analysed 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, in the period from 1921 to 2010, choosing 18 rain gauges and 9 air temperature stations among those with the most continuous functioning as well as arranged in a homogeneous spatial distribution. Moreover, for the same period, we gathered the time series of the winter NAO index (December to March mean) and of the discharges of the Sanità spring, belonging to an extended carbonate aquifer (Cervialto Mount) located in the central-eastern area of the Campania region, as well as of two other shorter time series of spring discharges. The hydrogeological features of this aquifer, its relevance due to the feeding of an important regional aqueduct system, as well as the unique availability of a long-lasting time series of spring discharges, allowed us to consider it as an ideal test site, representative of the other carbonate aquifers in the Campania region. The time series of regional normalised indexes of mean annual precipitation, mean annual air temperature and mean annual effective precipitation, as well as the time series of the normalised annual discharge index were calculated. Different methods were applied to analyse the time series: long-term trend analysis, through smoothing numerical techniques, cross-correlation and Fourier analysis. The investigation of the normalised indexes has highlighted long-term complex periodicities, strongly correlated with the winter NAO index. Moreover, we also found robust correlations among precipitation indexes and the annual discharge index, as well as between the latter and the NAO index itself. Although the effects of the North Atlantic Oscillation had already been proved on long-term precipitation and streamflow patterns of different European countries and Mediterranean areas, the results obtained appear original because they establish a link between a large-scale atmospheric cycle and the groundwater circulation of regional aquifers. Therefore, we demonstrated that the winter NAO index can be considered as an effective proxy to forecast the decadal variability of groundwater circulation in Mediterranean areas and in estimating critical scenarios for the feeding of aqueduct systems.

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