scholarly journals NAO predictability from external forcing in the late 20th century

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Jeremy M. Klavans ◽  
Mark A. Cane ◽  
Amy C. Clement ◽  
Lisa N. Murphy
Keyword(s):  
North Atlantic ◽  
Radiative Forcing ◽  
Climate Models ◽  
North Atlantic Ocean ◽  
Signal To Noise Ratio ◽  
Prediction System ◽  
Signal To Noise ◽  
Late 20Th Century ◽  
The North ◽  
Predictive Skill

AbstractThe North Atlantic Oscillation (NAO) is predictable in climate models at near-decadal timescales. Predictive skill derives from ocean initialization, which can capture variability internal to the climate system, and from external radiative forcing. Herein, we show that predictive skill for the NAO in a very large uninitialized multi-model ensemble is commensurate with previously reported skill from a state-of-the-art initialized prediction system. The uninitialized ensemble and initialized prediction system produce similar levels of skill for northern European precipitation and North Atlantic SSTs. Identifying these predictable components becomes possible in a very large ensemble, confirming the erroneously low signal-to-noise ratio previously identified in both initialized and uninitialized climate models. Though the results here imply that external radiative forcing is a major source of predictive skill for the NAO, they also indicate that ocean initialization may be important for particular NAO events (the mid-1990s strong positive NAO), and, as previously suggested, in certain ocean regions such as the subpolar North Atlantic ocean. Overall, we suggest that improving climate models’ response to external radiative forcing may help resolve the known signal-to-noise error in climate models.

scholarly journals Volcanic impact on the Atlantic Ocean over the last millennium

2011 ◽  
Vol 7 (4) ◽  
pp. 1439-1455 ◽  
Author(s):  
J. Mignot ◽  
M. Khodri ◽  
C. Frankignoul ◽  
J. Servonnat
Keyword(s):  
Atlantic Ocean ◽  
Radiative Forcing ◽  
Climate Models ◽  
North Atlantic Ocean ◽  
Thermal Response ◽  
Volcanic Eruptions ◽  
Total Solar Irradiance ◽  
Meridional Overturning Circulation ◽  
Oceanic Circulation ◽  
The North

Abstract. The oceanic response to volcanic eruptions over the last 1000 years is investigated with a focus on the North Atlantic Ocean, using a fully coupled AOGCM forced by a realistic time series of volcanic eruptions, total solar irradiance (TSI) and atmospheric greenhouse gases concentration. The model simulates little response to TSI variations but a strong and long-lasting thermal and dynamical oceanic adjustment to volcanic forcing, which is shown to be a function of the time period of the volcanic eruptions. The thermal response consists of a fast tropical cooling due to the radiative forcing by the volcanic eruptions, followed by a penetration of this cooling in the subtropical ocean interior one to five years after the eruption, and propagation of the anomalies toward the high latitudes. The oceanic circulation first adjusts rapidly to low latitude anomalous wind stress induced by the strong cooling. The Atlantic Meridional Overturning Circulation (AMOC) shows a significant intensification 5 to 10 years after the eruptions of the period post-1400 A.D., in response to anomalous atmospheric momentum forcing, and a slight weakening in the following decade. In response to the stronger eruptions occurring between 1100 and 1300, the AMOC shows no intensification and a stronger reduction after 10 years. This study thus stresses the diversity of AMOC response to volcanic eruptions in climate models and discusses possible explanations.

scholarly journals Improving Climate Change Detection through Optimal Seasonal Averaging: The Case of the North Atlantic Jet and European Precipitation

2015 ◽  
Vol 28 (16) ◽  
pp. 6381-6397 ◽  
Author(s):  
Giuseppe Zappa ◽  
Brian J. Hoskins ◽  
Theodore G. Shepherd
Keyword(s):  
Climate Change ◽  
North Atlantic ◽  
Signal To Noise Ratio ◽  
Lower Latitude ◽  
Cmip5 Models ◽  
Signal To Noise ◽  
The North ◽  
The North Atlantic ◽  
Noise Ratio ◽  
North Atlantic Jet

Abstract The detection of anthropogenic climate change can be improved by recognizing the seasonality in the climate change response. This is demonstrated for the North Atlantic jet [zonal wind at 850 hPa (U850)] and European precipitation responses projected by the climate models from phase 5 of CMIP (CMIP5). The U850 future response is characterized by a marked seasonality: an eastward extension of the North Atlantic jet into Europe in November–April and a poleward shift in May–October. Under the RCP8.5 scenario, the multimodel mean response in U850 in these two extended seasonal means emerges by 2035–40 for the lower-latitude features and by 2050–70 for the higher-latitude features, relative to the 1960–90 climate. This is 5–15 years earlier than when evaluated in the traditional meteorological seasons (December–February and June–August), and it results from an increase in the signal-to-noise ratio associated with the spatial coherence of the response within the extended seasons. The annual mean response lacks important information on the seasonality of the response without improving the signal-to-noise ratio. The same two extended seasons are demonstrated to capture the seasonality of the European precipitation response to climate change and to anticipate its emergence by 10–20 years. Furthermore, some of the regional responses (such as the Mediterranean precipitation decline and the U850 response in North Africa in the extended winter) are projected to emerge by 2020–25, according to the models with a strong response. Therefore, observations might soon be useful to test aspects of the atmospheric circulation response predicted by some of the CMIP5 models.

scholarly journals Jet Latitude Regimes and the Predictability of the North Atlantic Oscillation

2020 ◽  
Author(s):  
Kristian Strommen
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Prediction Models ◽  
Signal To Noise Ratio ◽  
Weather Prediction ◽  
Signal To Noise ◽  
The North ◽  
The North Atlantic ◽  
Noise Ratio ◽  
The North Atlantic Oscillation

<pre>In recent years, numerical weather prediction models have begun to show notable levels of skill at predicting the <br />average winter North Atlantic Oscillation (NAO) when initialised one month ahead. At the same time, these model <br />predictions exhibit unusually low signal-to-noise ratios, in what has been dubbed a `signal-to-noise paradox'. <br />We analyse both the skill and signal-to-noise ratio of the Integrated Forecast System (IFS), the European Center for <br />Medium-range Weather Forecasts (ECMWF) model, in an ensemble hindcast experiment. Specifically, we examine the <br />contribution to both from the regime dynamics of the North Atlantic eddy-driven jet. This is done by constructing a <br />statistical model which captures the predictability inherent to to the trimodal jet latitude system, and fitting its <br />parameters to reanalysis and IFS data. Predictability in this regime system is driven by interannual variations in the <br />persistence of the jet latitude regimes, which determine the preferred state of the jet. We show that the IFS has <br />skill at predicting such variations in persistence: because the position of the jet strongly influences the NAO, this <br />automatically generates skill at predicting the NAO. We show that all of the skill the IFS has at predicting the <br />winter NAO over the period 1980-2010 can be attributed to its skill at predicting regime persistence in this way. <br />Similarly, the tendency of the IFS to underestimate regime persistence can account for the low signal-to-noise ratio, <br />giving a possible explanation for the signal-to-noise paradox. Finally, we examine how external forcing drives <br />variability in jet persistence, as well as highlight the role played by transient baroclinic eddy feedbacks to <br />modulate regime persistence.</pre>

scholarly journals Temperature domination of AMOC weakening due to freshwater hosing in two GCMs

2019 ◽  
Vol 54 (1-2) ◽  
pp. 273-286 ◽  
Author(s):  
Rosalind K. Haskins ◽  
Kevin I. C. Oliver ◽  
Laura C. Jackson ◽  
Richard A. Wood ◽  
Sybren S. Drijfhout
Keyword(s):  
North Atlantic ◽  
Climate Models ◽  
North Atlantic Ocean ◽  
Global Climate ◽  
Mixed Layer Depth ◽  
Global Climate Models ◽  
Meridional Overturning Circulation ◽  
Ice Melt ◽  
The North ◽  
The North Atlantic

Abstract Anthropogenic climate change is projected to lead to a weakening of the Atlantic meridional overturning circulation (AMOC). One of the mechanisms contributing to this is ice melt leading to a freshening of the North Atlantic Ocean. We use two global climate models to investigate the role of temperature and salinity in the weakening of the AMOC resulting from freshwater forcing. This study finds that freshwater hosing reduces the strength of the AMOC, but in some situations it is not through reduced density from freshening, but a reduction in density from subsurface warming. When the freshwater is mixed down it directly reduces the density of the North Atlantic, weakening the strength of the AMOC. As the AMOC weakens, the mixed layer depth reduces and surface properties are less effectively mixed down. A buoyant surface cap forms, blocking atmospheric fluxes. This leads to the development of a warm anomaly beneath the surface cap, which becomes the primary driver of AMOC weakening. We found that the mean North Atlantic salinity anomaly can be used as a proxy for AMOC weakening because it describes the extent of this surface cap.

Potential Changes of the North Atlantic Wind and Wave Climate and Occurrence of Rogue Waves

2016 ◽  
Author(s):  
Elzbieta M. Bitner-Gregersen
Keyword(s):  
Climate Change ◽  
21St Century ◽  
North Atlantic ◽  
Radiative Forcing ◽  
Climate Models ◽  
Rogue Waves ◽  
The Past ◽  
The North ◽  
The North Atlantic ◽  
Wave Conditions

The present study investigates potential changes of wind and wave conditions in one North Atlantic location in the 21st century. The Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) uses four scenarios for future greenhouse gas concentrations in the atmosphere called Representative Concentration Pathways (RCP). Two of these scenarios with radiative forcing of 4.5 and 8.5 W/m2 by the end of the 21st century have been selected to project wind and wave conditions in the North Atlantic. The third generation (3G) wave model WAM, forced by winds obtained from GFDL-CM3, EC-Earth, HADGEM2, IPS-CM5A-MR, MRI-GCGCM3 and MIROC5 climate models, has been used to project waves for these two scenarios for the historical period 1971–2000 and the future period 2071–2100. Long-term probabilistic description of wind and waves is provided and deviations between the past and future wind and wave conditions are demonstrated, given attention to the projections obtained by use of the GFDL-CM3 and EC-Earth climate models. Changes in extreme wind and waves are shown and uncertainties associated with climate change projections discussed. Occurrence of rogue-prone crossing sea states which may trigger generation of rogue waves in the past and future climate is also investigated.

Revealing mechanisms of change in the Atlantic Meridional Overturning Circulation under global heating

2021 ◽  
Author(s):  
Maike Sonnewald ◽  
Redouane Lguensat ◽  
Venkatramani Balaji
Keyword(s):  
North Atlantic ◽  
Gulf Stream ◽  
North Atlantic Ocean ◽  
Meridional Overturning Circulation ◽  
The North ◽  
Predictive Skill ◽  
Meridional Overturning ◽  
And Storage ◽  
Global Heating ◽  
Atlantic Current

<p>The North Atlantic ocean is key to climate through its role in heat transport and storage, but the response of the circulation’s drivers to a changing climate is poorly constrained. The transparent machine learning method Tracking global Heating with Ocean Regimes (THOR) identifies drivers of circulation with minimal input: depth, dynamic sea level and wind stress. Beyond a black box approach, THOR's predictive skill is transparent. A dataset is created with features engineered and labeled by an explicitly interpretable equation transform and k-means application. A multilayer perceptron is then trained, explaining its skill using relevance maps and theory. THOR reveals a weakened circulation with abrupt CO<sub>2</sub> quadrupling, due to a shift in deep water formation areas and locations of the Gulf Stream and Trans Atlantic Current transporting heat northward. If CO<sub>2</sub> is increased 1% yearly, similar but transient patterns emerge. THOR could accelerate model analysis and facilitate process oriented intercomparisons.</p>

scholarly journals A Predictable AMO-Like Pattern in the GFDL Fully Coupled Ensemble Initialization and Decadal Forecasting System

2013 ◽  
Vol 26 (2) ◽  
pp. 650-661 ◽  
Author(s):  
Xiaosong Yang ◽  
Anthony Rosati ◽  
Shaoqing Zhang ◽  
Thomas L. Delworth ◽  
Rich G. Gudgel ◽  
...  
Keyword(s):  
North Atlantic ◽  
Radiative Forcing ◽  
Coupled Model ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Subpolar Gyre ◽  
Coupled Models ◽  
Significance Level ◽  
The North ◽  
Predictive Skill ◽  
The North Atlantic

Abstract The decadal predictability of sea surface temperature (SST) and 2-m air temperature (T2m) in the Geophysical Fluid Dynamics Laboratory (GFDL) decadal hindcasts, which are part of the Fifth Coupled Model Intercomparison Project experiments, has been investigated using an average predictability time (APT) analysis. Comparison of retrospective forecasts initialized using the GFDL Ensemble Coupled Data Assimilation system with uninitialized historical forcing simulations using the same model allows identification of the internal multidecadal pattern (IMP) for SST and T2m. The IMP of SST is characterized by an interhemisphere dipole, with warm anomalies centered in the North Atlantic subpolar gyre region and North Pacific subpolar gyre region, and cold anomalies centered in the Antarctic Circumpolar Current region. The IMP of T2m is characterized by a general bipolar seesaw, with warm anomalies centered in Greenland and cold anomalies centered in Antarctica. The retrospective prediction skill of the initialized system, verified against independent observational datasets, indicates that the IMP of SST may be predictable up to 4 (10) yr lead time at 95% (90%) significance level, and the IMP of T2m may be predictable up to 2 (10) yr at the 95% (90%) significance level. The initialization of multidecadal variations of northward oceanic heat transport in the North Atlantic significantly improves the predictive skill of the IMP. The dominant roles of oceanic internal dynamics in decadal prediction are further elucidated by fixed-forcing experiments in which radiative forcing is returned abruptly to 1961 values. These results point toward the possibility of meaningful decadal climate outlooks using dynamical coupled models if they are appropriately initialized from a sustained climate observing system.

scholarly journals Volcanic impact on the Atlantic ocean over the last millennium

2011 ◽  
Vol 7 (4) ◽  
pp. 2511-2554 ◽  
Author(s):  
J. Mignot ◽  
M. Khodri ◽  
C. Frankignoul ◽  
J. Servonnat
Keyword(s):  
Atlantic Ocean ◽  
Radiative Forcing ◽  
Climate Models ◽  
North Atlantic Ocean ◽  
Thermal Response ◽  
Volcanic Eruptions ◽  
Total Solar Irradiance ◽  
Meridional Overturning Circulation ◽  
Oceanic Circulation ◽  
The North

Abstract. The oceanic response to volcanic eruptions over the last 1000 years is investigated with a focus on the North Atlantic Ocean, using a fully coupled AOGCM forced by a realistic time series of volcanic eruptions, total solar irradiance (TSI) and atmospheric greenhouse gases concentration. The model simulates little response to TSI variations but a strong and long-lasting thermal and dynamical oceanic adjustment to volcanic forcing, which is shown to be a function of the time period of the volcanic eruptions, probably due to their different seasonality. The thermal response consists of a fast tropical cooling due to the radiative forcing by the volcanic eruptions, followed by a penetration of this cooling in the subtropical ocean interior one to five years after the eruption, and propagation of the anomalies toward the high latitudes. The oceanic circulation first adjusts rapidly to low latitude anomalous wind stress induced by the strong cooling. The Atlantic Meridional Overturning Circulation (AMOC) shows a significant intensification 5 to 10 years after the eruptions of the period post-1400 AD, in response to anomalous atmospheric momentum forcing, and a slight weakening in the following decade. In response to the stronger eruptions occurring between 1100 and 1300, the AMOC shows no intensification and a stronger reduction after 10 years. This study thus stresses the diversity of AMOC response to volcanic eruptions in climate models and tentatively points to an important role of the seasonality of the eruptions.

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