scholarly journals Seasonal Prediction of North Atlantic Accumulated Cyclone Energy and Major Hurricane Activity

2019 ◽  
Vol 34 (1) ◽  
pp. 221-232 ◽  
Author(s):  
Kyle Davis ◽  
Xubin Zeng
Keyword(s):  
North Atlantic ◽  
Seasonal Prediction ◽  
Absolute Error ◽  
Atlantic Multidecadal Oscillation ◽  
Active Season ◽  
The North ◽  
Major Hurricane ◽  
Multivariate Enso Index ◽  
Atlantic Multidecadal Oscillation Index ◽  
The North Atlantic

Abstract Building upon our previous seasonal hurricane prediction model, here we develop two statistical models to predict the number of major hurricanes (MHs) and accumulated cyclone energy (ACE) in the North Atlantic basin using monthly data from March to May for an early June forecast. The input data include zonal pseudo–wind stress to the 3/2 power, sea surface temperature in the North Atlantic, and, depending on the magnitude of the Atlantic multidecadal oscillation index, the multivariate ENSO index. From 1968 to 2017, these models have a mean absolute error of 0.96 storms for MHs and 30 units for ACE. When tested over an independent period from 1958 to 1967, the models show a 22% improvement for MHs and 16% for ACE over a no-skill metric based on a 5-yr running average. Both the MH and ACE results show consistent improvements over those produced by three other centers using statistical–dynamical hybrid models and a 5-yr running average prediction over the period 2000–17 for MHs (2003–17 for ACE) in a simulated real-time prediction. These improvements vary from 25% to 37% for MHs and from 15% to 37% for ACE. While most forecasting centers called for a slightly above-average hurricane season in May/June 2017, our models predicted in June 2017 a very active season, in much better agreement with observations.

scholarly journals Climate impacts on multidecadal <i>p</i>CO<sub>2</sub> variability in the North Atlantic: 1948–2009

2015 ◽  
Vol 12 (17) ◽  
pp. 15223-15244
Author(s):  
M. L. Breeden ◽  
G. A. McKinley
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Dissolved Inorganic Carbon ◽  
Atlantic Multidecadal Oscillation ◽  
Climate Impacts ◽  
Co2 Uptake ◽  
Subpolar Gyre ◽  
The North ◽  
The North Atlantic

Abstract. The North Atlantic is the most intense region of ocean CO2 uptake. Here, we investigate multidecadal timescale variability of the partial pressure CO2 (pCO2) that is due to the natural carbon cycle using a regional model forced with realistic climate and pre-industrial atmospheric pCO2 for 1948–2009. Large-scale patterns of natural pCO2 variability are primarily associated with basin-averaged sea surface temperature (SST) that, in turn, is composed of two parts: the Atlantic Multidecadal Oscillation (AMO) and a long-term positive SST trend. The North Atlantic Oscillation (NAO) drives a secondary mode of variability. For the primary mode, positive AMO and the SST trend modify pCO2 with different mechanisms and spatial patterns. Warming with the positive AMO increases subpolar gyre pCO2, but there is also a significant reduction of dissolved inorganic carbon (DIC) due primarily to reduced vertical mixing. The net impact of positive AMO is to reduce pCO2 in the subpolar gyre. Through direct impacts on SST, the net impacts of positive AMO is to increase pCO2 in the subtropical gyre. From 1980 to present, long-term SST warming has amplified AMO impacts on pCO2.

Importance of Stratospheric Polar Vortex Events for Seasonal Predictability of Sea Level Pressure over the North Atlantic and Europe

2020 ◽  
Author(s):  
Johanna Baehr ◽  
Simon Wett ◽  
Mikhail Dobrynin ◽  
Daniela Domeisen
Keyword(s):  
Sea Level ◽  
North Atlantic ◽  
Polar Vortex ◽  
Seasonal Prediction ◽  
Prediction System ◽  
Seasonal Predictability ◽  
Stratospheric Polar Vortex ◽  
Sea Level Pressure ◽  
The North ◽  
The North Atlantic

&lt;p&gt;The downward influence of the stratosphere on the troposphere can be significant during boreal winter when the polar vortex is most variable, when major circulation changes in&amp;#160;the stratosphere can impact the tropospheric flow. These strong and weak vortex events, the latter also referred to as Sudden Stratospheric Warmings (SSWs), are capable of influencing&amp;#160;the tropospheric circulation down to the sea level on timescales from weeks to months. Thus, the occurrence of stratospheric polar vortex events influences the seasonal predictability of&amp;#160;sea level pressure (SLP), which is, over the Atlantic sector, strongly linked to the North Atlantic oscillation (NAO).&lt;br&gt;We analyze the influence of the polar vortex on the seasonal predictability of SLP in a seasonal prediction system based on the mixed resolution configuration of the coupled Max-Planck-Institute Earth System Model (MPI-ESM), where we investigate a 30 member ensemble hindcast simulation covering 1982 -2016. Since the state of the polar vortex is predictable only a few weeks or even days ahead, the&amp;#160;seasonal prediction system cannot exactly predict the day of occurrence of stratospheric events. However, making use of the large number of stratospheric polar vortex events in the&amp;#160;ensemble hindcast simulation, we present a statistical analysis of the influence of a correct or incorrect prediction of the stratospheric vortex state on the seasonal predictability of SLP&amp;#160;over the North Atlantic and Europe.&lt;/p&gt;

scholarly journals Influence of the North Atlantic SST Variability on the Atmospheric Circulation during the Twentieth Century

2015 ◽  
Vol 28 (4) ◽  
pp. 1396-1416 ◽  
Author(s):  
Guillaume Gastineau ◽  
Claude Frankignoul
Keyword(s):  
Twentieth Century ◽  
North Atlantic ◽  
Lower Troposphere ◽  
Atlantic Multidecadal Oscillation ◽  
Early Winter ◽  
Tropical Forcing ◽  
The North ◽  
Sst Variability ◽  
Sst Anomaly ◽  
The North Atlantic

Abstract The ocean–atmosphere coupling in the North Atlantic is investigated during the twentieth century using maximum covariance analysis of sea surface temperature (SST) and 500-hPa geopotential height analyses and performing regressions on dynamical diagnostics such as Eady growth rate, wave activity flux, and velocity potential. The North Atlantic Oscillation (NAO) generates the so-called SST anomaly tripole. A rather similar SST anomaly tripole, with the subpolar anomaly displaced to the east and a more contracted subtropical anomaly, which is referred to as the North Atlantic horseshoe pattern, in turn influences the atmosphere. In the fall and early winter, the response is NAO like and primarily results from subpolar forcing centered over the Labrador Sea and off Newfoundland. In summer, the largest atmospheric response to SST resembles the east Atlantic pattern and results from a combination of subpolar and tropical forcing. To emphasize the interannual to multidecadal variability, the same analysis is repeated after low-pass filtering. The SST influence is dominated by the Atlantic multidecadal oscillation (AMO), which also has a horseshoe shape, but with larger amplitude in the subpolar basin. A warm AMO phase leads to an atmospheric warming limited to the lower troposphere in summer, while it leads to a negative phase of the NAO in winter. The winter influence of the AMO is suggested to be primarily forced by the Atlantic SSTs in the northern subtropics. Such influence of the AMO is found in winter instead of early winter because the winter SST anomalies have a larger persistence, presumably because of SST reemergence.

Cuban stalagmite suggests relationship between Caribbean precipitation and the Atlantic Multidecadal Oscillation during the past 1.3 ka

The Holocene ◽  
2012 ◽  
Vol 22 (12) ◽  
pp. 1405-1412 ◽  
Author(s):  
Claudia Fensterer ◽  
Denis Scholz ◽  
Dirk Hoffmann ◽  
Christoph Spötl ◽  
Jesús M Pajón ◽  
...  
Keyword(s):  
North Atlantic ◽  
Little Ice Age ◽  
Rainfall Intensity ◽  
Thermohaline Circulation ◽  
Atlantic Multidecadal Oscillation ◽  
Ice Age ◽  
The Past ◽  
The North ◽  
Southward Shift ◽  
The North Atlantic

Here we present the first high-resolution δ18O record of a stalagmite from western Cuba. The record reflects precipitation variability in the northwestern Caribbean during the last 1.3 ka and exhibits a correlation to the Atlantic Multidecadal Oscillation (AMO). This suggests a relationship between Caribbean rainfall intensity and North Atlantic sea-surface temperature (SST) anomalies. A potential mechanism for this relationship may be the strength of the Thermohaline Circulation (THC). For a weaker THC, lower SSTs in the North Atlantic possibly lead to a southward shift of the Intertropical Convergence Zone and drier conditions in Cuba. Thus, this Cuban stalagmite records drier conditions during cold phases in the North Atlantic such as the ‘Little Ice Age’. This study contributes to the understanding of teleconnections between North Atlantic SSTs and northern Caribbean climate variability during the past 1.3 ka.

scholarly journals Aerosol-forced multidecadal variations across all ocean basins in models and observations since 1920

2020 ◽  
Vol 6 (29) ◽  
pp. eabb0425 ◽  
Author(s):  
Minhua Qin ◽  
Aiguo Dai ◽  
Wenjian Hua
Keyword(s):  
North Atlantic ◽  
Atlantic Multidecadal Oscillation ◽  
Anthropogenic Aerosols ◽  
Surface Solar Radiation ◽  
The North ◽  
Aerosol Forcing ◽  
New Finding ◽  
The North Atlantic ◽  
Earth’S Climate ◽  
Aerosol Effects

Earth’s climate fluctuates considerably on decadal-multidecadal time scales, often causing large damages to our society and environment. These fluctuations usually result from internal dynamics, and many studies have linked them to internal climate modes in the North Atlantic and Pacific oceans. Here, we show that variations in volcanic and anthropogenic aerosols have caused in-phase, multidecadal SST variations since 1920 across all ocean basins. These forced variations resemble the Atlantic Multidecadal Oscillation (AMO) in time. Unlike the North Atlantic, where indirect and direct aerosol effects on surface solar radiation drive the multidecadal SST variations, over the tropical central and western Pacific atmospheric circulation response to aerosol forcing plays an important role, whereas aerosol-induced radiation change is small. Our new finding implies that AMO-like climate variations in Eurasia, North America, and other regions may be partly caused by the aerosol forcing, rather than being originated from the North Atlantic SST variations as previously thought.

scholarly journals A Hemispheric Mechanism for the Atlantic Multidecadal Oscillation

2007 ◽  
Vol 20 (11) ◽  
pp. 2706-2719 ◽  
Author(s):  
Mihai Dima ◽  
Gerrit Lohmann
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
North Pacific ◽  
Thermohaline Circulation ◽  
Atlantic Multidecadal Oscillation ◽  
Sea Surface ◽  
The North ◽  
Sea Surface Temperature Anomalies ◽  
The North Atlantic ◽  
The North Pacific

Abstract The physical processes associated with the ∼70-yr period climate mode, known as the Atlantic multidecadal oscillation (AMO), are examined. Based on analyses of observational data, a deterministic mechanism relying on atmosphere–ocean–sea ice interactions is proposed for the AMO. Variations in the thermohaline circulation are reflected as uniform sea surface temperature anomalies in the North Atlantic. These anomalies are associated with a hemispheric wavenumber-1 sea level pressure (SLP) structure in the atmosphere that is amplified through atmosphere–ocean interactions in the North Pacific. The SLP pattern and its associated wind field affect the sea ice export through Fram Strait, the freshwater balance in the northern North Atlantic, and consequently the strength of the large-scale ocean circulation. It generates sea surface temperature anomalies with opposite signs in the North Atlantic and completes a negative feedback. The authors find that the time scale of the cycle is associated with the thermohaline circulation adjustment to freshwater forcing, the SST response to it, the oceanic adjustment in the North Pacific, and the sea ice response to the wind forcing. Finally, it is argued that the Great Salinity Anomaly in the late 1960s and 1970s is part of AMO.

Atlantic Multidecadal Oscillation (AMO) and sea surface temperature in the Bay of Biscay and adjacent regions

2011 ◽  
Vol 92 (2) ◽  
pp. 213-234 ◽  
Author(s):  
Carlos Garcia-Soto ◽  
Robin D. Pingree
Keyword(s):  
North Atlantic ◽  
Atlantic Multidecadal Oscillation ◽  
Sea Surface ◽  
Bay Of Biscay ◽  
The North ◽  
Sst Variability ◽  
The North Atlantic ◽  
Climate Mode ◽  
Sst Anomalies

The sea surface temperature (SST) variability of the Bay of Biscay and adjacent regions (1854–2010) has been examined in relation to the evolution of the Atlantic Multidecadal Oscillation (AMO), a major climate mode. The AMO index explains ~25% of the interannual variability of the annual SST during the last 150 years, while different indices of the North Atlantic Oscillation (NAO) explain ≤1% of the long-term record. NAO is a high frequency climate mode while AMO can modulate low frequency changes. Sixty per cent of the AMO variability is contained in periods longer than a decade. The basin-scale influence of NAO on SST over specific years (1995 to 1998) is presented and the SST anomalies explained. The period analysed represents an abrupt change in NAO and the North Atlantic circulation state as shown with altimetry and SST data. Additional atmospheric climate data over a shorter ~60 year period (1950–2008) show the influence on the Bay of Biscay SST of the East Atlantic (EA) pattern and the Scandinavia (SCA) pattern. These atmospheric teleconnections explain respectively ~25% and ~20% of the SST variability. The winter SST in the shelf-break/slope or poleward current region is analysed in relation to AMO. The poleward current shows a trend towards increasing SSTs during the last three decades as a result of the combined positive phase of AMO and global warming. The seasonality of this winter warm flow in the Iberian region is related to the autumn/winter seasonality of south-westerly (SW) winds. The SW winds are strengthened along the European shelf-break by the development of low pressure conditions in the region to the north of the Azores and therefore a negative NAO. AMO overall modulates multidecadal changes (~60% of the AMO variance). The long-term time-series of SST and SST anomalies in the Bay of Biscay show AMO-like cycles with maxima near 1870 and 1950 and minima near 1900 and 1980 indicating a period of 60–80 years during the last century and a half. Similar AMO-like variability is found in the Russell cycle of the Western English Channel (1924–1972). AMO relates at least to four mesozooplankton components of the Russell cycle: the abundance of the chaetognaths Parasagitta elegans and Parasagitta setosa (AMO −), the amount of the species Calanus helgolandicus (AMO −), the amount of the larvae of decapod crustaceans (AMO −) and the number of pilchard eggs (Sardine pilchardus; AMO +). In addition to AMO, the decadal to multidecadal (D2M) variability in the number of sunspots is analysed for the last 300 years. Several periodicities and a multi-secular linear increase are presented. There are secular minima near 1710, 1810, 1910 and 2010. The long term variability (>11 years) of the solar sunspot activity explains ~50% of the variance of the SST of the Bay of Biscay with periods longer than 11 years. AMO is finally compared with the Pacific Decadal Oscillation, the leading principal component of North Pacific SST anomalies.

scholarly journals A New Statistical Model for Predicting Seasonal North Atlantic Hurricane Activity

2015 ◽  
Vol 30 (3) ◽  
pp. 730-741 ◽  
Author(s):  
Kyle Davis ◽  
Xubin Zeng ◽  
Elizabeth A. Ritchie
Keyword(s):  
Statistical Model ◽  
North Atlantic ◽  
Decadal Variability ◽  
Poor Performance ◽  
Seasonal Prediction ◽  
Atlantic Multidecadal Oscillation ◽  
Hybrid Models ◽  
Colorado State University ◽  
Atlantic Hurricane ◽  
The North

Abstract Statistical, dynamical, and statistical–dynamical hybrid models have been developed in past decades for the seasonal prediction of North Atlantic hurricane numbers. These models’ prediction skills show considerable decadal variability, with particularly poor performance in the past few years. Here, environmental factors that affect hurricane activities are reevaluated to develop a new statistical model for seasonal prediction by 1 June of each year. The predictors include the April–May multivariate ENSO index (MEI) conditioned upon the Atlantic multidecadal oscillation (AMO) index, the power of the average zonal pseudo–wind stress across the North Atlantic in May, and the average March–May tropical Atlantic sea surface temperature. When compared to the actual number of hurricanes each year from 1950 to 2013, this model has a root-mean-square error (RMSE) of 1.91 with a correlation coefficient of 0.71. It shows a 39% improvement in RMSE over a no-skill metric (based on the 5-yr running mean of seasonal hurricane counts) for the period 2001–13. It also outperforms three statistical–dynamical hybrid models [CPC, Colorado State University (CSU), and Tropical Storm Risk (TSR)] by more than 25% for the same period. Furthermore, two approaches are developed to provide the uncertainty ranges around the predicted (deterministic) hurricane number per season that better encompass the range of uncertainty than does the standard method of adding/subtracting a standard deviation of the errors.

scholarly journals The Atlantic Multidecadal Oscillation Inferred from the Forced Climate Response in Coupled General Circulation Models

2009 ◽  
Vol 22 (7) ◽  
pp. 1610-1625 ◽  
Author(s):  
Jeff R. Knight
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Internal Variability ◽  
Atlantic Multidecadal Oscillation ◽  
Forced Response ◽  
Climate System ◽  
Climate Response ◽  
The North ◽  
Ensemble Mean ◽  
The North Atlantic

Abstract Instrumental sea surface temperature records in the North Atlantic Ocean are characterized by large multidecadal variability known as the Atlantic multidecadal oscillation (AMO). The lack of strong oscillatory forcing of the climate system at multidecadal time scales and the results of long unforced climate simulations have led to the widespread, although not ubiquitous, view that the AMO is an internal mode of climate variability. Here, a more objective examination of this hypothesis is performed using simulations with natural and anthropogenic forcings from the Coupled Model Intercomparison Project phase 3 (CMIP3) database. Ensemble means derived from these data allow an estimate of the response of models to forcings, as averaging leads to cancellation of the internal variability between ensemble members. In general, the means of individual model ensembles appear to be inconsistent with observed temperatures, although small ensemble sizes result in uncertainty in this conclusion. Combining the ensembles from different models creates a multimodel ensemble of sufficient size to allow for a good estimate of the forced response. This shows that the variability in observed North Atlantic temperatures possess a clearly distinct signature to the climate response expected from forcings. The reliability of this finding is confirmed by sampling those models with low decadal internal variability and by comparing simulated and observed trends. In contrast to the inconsistency with the ensemble mean, the observations are consistent with the spread of responses in the ensemble members, suggesting they can be accounted for by the combined effects of forcings and internal variability. In the most recent period, the results suggest that the North Atlantic is warming faster than expected, and that the AMO entered a positive phase in the 1990s. The differences found between observed and ensemble mean temperatures could arise through errors in the observational data, errors in the models’ response to forcings or in the forcings themselves, or as a result of genuine internal variability. Each of these possibilities is discussed, and it is concluded that internal variability within the natural climate system is the most likely origin of the differences. Finally, the estimate of internal variability obtained using the model-derived ensemble mean is proposed as a new way of defining the AMO, which has important advantages over previous definitions.

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