scholarly journals The implications of initial model drift for decadal climate predictability using EC-Earth

2016 ◽  
Author(s):  
Andreas Sterl
Keyword(s):  
Climate Model ◽  
North Atlantic Ocean ◽  
Initial Conditions ◽  
Deep Convection ◽  
Heat Content ◽  
The North ◽  
Atmospheric Noise ◽  
Large Heat ◽  
Decadal Climate Predictability ◽  
Decadal Climate

Abstract. The large heat capacity of the ocean as compared to the atmosphere provides a memory in the climate system that might have the potential for skilful climate predictions a few years ahead. However, experiments so far have only found limited predictability after accounting for the deterministic forcing signal provided by increased greenhouse gas concentrations. One of the problems is the drift that occurs when the model moves away from the initial conditions towards its own climate. This drift is often larger than the decadal signal to be predicted. In this paper we describe the drift occurring in the North Atlantic Ocean in the EC-Earth climate model and relate it to the lack of decadal predictability in that region. While this drift may be resolution dependent and disappear in higher resolution models, we identify a second reason for the low predictability. A subsurface heat content anomaly can only influence de atmosphere if (deep) convection couples it to the surface, but the occurrence of deep convection events is random and probably mainly determined by unpredictable atmospheric noise.

scholarly journals Initializing Decadal Climate Predictions with the GECCO Oceanic Synthesis: Effects on the North Atlantic

2009 ◽  
Vol 22 (14) ◽  
pp. 3926-3938 ◽  
Author(s):  
Holger Pohlmann ◽  
Johann H. Jungclaus ◽  
Armin Köhl ◽  
Detlef Stammer ◽  
Jochem Marotzke
Keyword(s):  
North Atlantic ◽  
Climate Model ◽  
Initial Conditions ◽  
Coupled Model ◽  
Meridional Overturning Circulation ◽  
Coupling Scheme ◽  
Max Planck ◽  
The North ◽  
The North Atlantic ◽  
Decadal Climate

Abstract This study aims at improving the forecast skill of climate predictions through the use of ocean synthesis data for initial conditions of a coupled climate model. For this purpose, the coupled model of the Max Planck Institute (MPI) for Meteorology, which consists of the atmosphere model ECHAM5 and the MPI Ocean Model (MPI-OM), is initialized with oceanic synthesis fields available from the German contribution to Estimating the Circulation and Climate of the Ocean (GECCO) project. The use of an anomaly coupling scheme during the initialization avoids the main problems with drift in the climate predictions. Thus, the coupled model is continuously forced to follow the density anomalies of the GECCO synthesis over the period 1952–2001. Hindcast experiments are initialized from this experiment at constant intervals. The results show predictive skill through the initialization up to the decadal time scale, particularly over the North Atlantic. Viewed over the time scales analyzed here (annual, 5-yr, and 10-yr mean), greater skill for the North Atlantic sea surface temperature (SST) is obtained in the hindcast experiments than in either a damped persistence or trend forecast. The Atlantic meridional overturning circulation hindcast closely follows that of the GECCO oceanic synthesis. Hindcasts of global-mean temperature do not obtain greater skill than either damped persistence or a trend forecast, owing to the SST errors in the GECCO synthesis, outside the North Atlantic. An ensemble of forecast experiments is subsequently performed over the period 2002–11. North Atlantic SST from the forecast experiment agrees well with observations until the year 2007, and it is higher than if simulated without the oceanic initialization (averaged over the forecast period). The results confirm that both the initial and the boundary conditions must be accounted for in decadal climate predictions.

Subpolar Gyre – AMOC – Atmosphere Interactions on Multidecadal Timescales in a Version of the Kiel Climate Model

2021 ◽  
Author(s):  
Jing Sun ◽  
Mojib Latif ◽  
Wonsun Park
Keyword(s):  
North Atlantic ◽  
Climate Model ◽  
Deep Convection ◽  
Meridional Overturning Circulation ◽  
Subpolar Gyre ◽  
Surface Salinity ◽  
The North ◽  
Ocean Coupling ◽  
Meridional Overturning ◽  
The North Atlantic

<p>There is a controversy about the nature of multidecadal climate variability in the North Atlantic (NA) region, concerning the roles of ocean circulation and atmosphere-ocean coupling. Here we describe NA multidecadal variability from a version of the Kiel Climate Model, in which both subpolar gyre (SPG)-Atlantic Meridional Overturning Circulation (AMOC) and atmosphere-ocean coupling are essential. The oceanic barotropic streamfuntions, meridional overturning streamfunctions, and sea level pressure are jointly analyzed to derive the leading mode of Atlantic variability. This mode accounting for about 23.7 % of the total combined variance is oscillatory with an irregular periodicity of 25-50 years and an e-folding time of about a decade. SPG and AMOC mutually influence each other and together provide the delayed negative feedback necessary for maintaining the oscillation. An anomalously strong SPG, for example, drives higher surface salinity and density in the NA’s sinking region. In response, oceanic deep convection and AMOC intensify, which, with a time delay of about a decade, reduces SPG strength by enhancing upper-ocean heat content. The weaker gyre circulation leads to lower surface salinity and density in the sinking region, which eventually reduces deep convection and AMOC strength. There is a positive ocean-atmosphere feedback between the sea surface temperature and low-level atmospheric circulation over the Southern Greenland area, with related wind stress changes reinforcing SPG changes, thereby maintaining the (damped) multidecadal oscillation against dissipation. Stochastic surface heat-flux forcing associated with the North Atlantic Oscillation drives the eigenmode.</p>

scholarly journals Dissolved iron in the North Atlantic Ocean and Labrador Sea along the GEOVIDE section (GEOTRACES section GA01)

2018 ◽  
Author(s):  
Manon Tonnard ◽  
Hélène Planquette ◽  
Andrew R. Bowie ◽  
Pier van der Merwe ◽  
Morgane Gallinari ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
Sea Water ◽  
North Atlantic Ocean ◽  
Deep Convection ◽  
Labrador Sea ◽  
Intermediate Water ◽  
The North ◽  
Irminger Sea ◽  
The North Atlantic

Abstract. Dissolved Fe (DFe) samples from the GEOVIDE voyage (GEOTRACES GA01, May–June 2014) in the North Atlantic Ocean were analysed using a SeaFAST-picoTM coupled to an Element XR HR-ICP-MS and provided interesting insights on the Fe sources in this area. Overall, DFe concentrations ranged from 0.09 ± 0.01 nmol L−1 to 7.8 ± 0.5 nmol L−1. Elevated DFe concentrations were observed above the Iberian, Greenland and Newfoundland Margins likely due to riverine inputs from the Tagus River, meteoric water inputs and sedimentary inputs. Air-sea interactions were suspected to be responsible for the increase in DFe concentrations within subsurface waters of the Irminger Sea due to deep convection occurring the previous winter, that provided iron-to-nitrate ratios sufficient to sustain phytoplankton growth. Increasing DFe concentrations along the flow path of the Labrador Sea Water were attributed to sedimentary inputs from the Newfoundland Margin. Bottom waters from the Irminger Sea displayed high DFe concentrations likely due to the dissolution of Fe-rich particles from the Denmark Strait Overflow Water and the Polar Intermediate Water. Finally, the nepheloid layers were found to act as either a source or a sink of DFe depending on the nature of particles.

scholarly journals The HadCM3 contribution to PlioMIP phase 2

2019 ◽  
Vol 15 (5) ◽  
pp. 1691-1713 ◽  
Author(s):  
Stephen J. Hunter ◽  
Alan M. Haywood ◽  
Aisling M. Dolan ◽  
Julia C. Tindall
Keyword(s):  
Land Surface ◽  
Climate Model ◽  
Deep Convection ◽  
Surface Air Temperature ◽  
Meridional Overturning Circulation ◽  
Mean Annual Precipitation ◽  
Phase 2 ◽  
The North ◽  
Orbital Configuration ◽  
Hadley Centre

Abstract. We present the UK's input into the Pliocene Model Intercomparison Project phase 2 (PlioMIP2) using the Hadley Centre Climate Model version 3 (HadCM3). The 400 ppm CO2 Pliocene experiment has a mean annual surface air temperature that is 2.9 ∘C warmer than the pre-industrial and a polar amplification of between 1.7 and 2.2 times the global mean warming. The Pliocene Research Interpretation and Synoptic Mapping (PRISM4) enhanced Pliocene palaeogeography accounts for a warming of 1.4 ∘C, whilst the CO2 increase from 280 to 400 ppm leads to a further 1.5 ∘C of warming. Climate sensitivity is 3.5 ∘C for the pre-industrial and 2.9 ∘C for the Pliocene. Precipitation change between the pre-industrial and Pliocene is complex, with geographic and land surface changes primarily modifying the geographical extent of mean annual precipitation. Sea ice fraction and areal extent are reduced during the Pliocene, particularly in the Southern Hemisphere, although they persist through summer in both hemispheres. The Pliocene palaeogeography drives a more intense Pacific and Atlantic meridional overturning circulation (AMOC). This intensification of AMOC is coincident with more widespread deep convection in the North Atlantic. We conclude by examining additional sensitivity experiments and confirm that the choice of total solar insolation (1361 vs. 1365 Wm−2) and orbital configuration (modern vs. 3.205 Ma) does not significantly influence the anomaly-type analysis in use by the Pliocene community.

scholarly journals Investigating the impact of Lake Agassiz drainage routes on the 8.2 ka cold event with a climate model

2009 ◽  
Vol 5 (3) ◽  
pp. 471-480 ◽  
Author(s):  
Y.-X. Li ◽  
H. Renssen ◽  
A. P. Wiersma ◽  
T. E. Törnqvist
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
Climate Model ◽  
North Atlantic Ocean ◽  
Sensitivity Study ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Cold Event ◽  
The North ◽  
The Impact

Abstract. The 8.2 ka event is the most prominent abrupt climate change in the Holocene and is often believed to result from catastrophic drainage of proglacial lakes Agassiz and Ojibway (LAO) that routed through the Hudson Bay and the Labrador Sea into the North Atlantic Ocean, and perturbed Atlantic meridional overturning circulation (MOC). One key assumption of this triggering mechanism is that the LAO freshwater drainage was dispersed over the Labrador Sea. Recent data, however, show no evidence of lowered δ18O values, indicative of low salinity, from the open Labrador Sea around 8.2 ka. Instead, negative δ18O anomalies are found close to the east coast of North America, extending as far south as Cape Hatteras, North Carolina, suggesting that the freshwater drainage may have been confined to a long stretch of continental shelf before fully mixing with North Atlantic Ocean water. Here we conduct a sensitivity study that examines the effects of a southerly drainage route on the 8.2 ka event with the ECBilt-CLIO-VECODE model. Hosing experiments of four routing scenarios, where freshwater was introduced to the Labrador Sea in the northerly route and to three different locations along the southerly route, were performed to investigate the routing effects on model responses. The modeling results show that a southerly drainage route is possible but generally yields reduced climatic consequences in comparison to those of a northerly route. This finding implies that more freshwater would be required for a southerly route than for a northerly route to produce the same climate anomaly. The implicated large amount of LAO drainage for a southerly routing scenario is in line with a recent geophysical modelling study of gravitational effects on sea-level change associated with the 8.2 ka event, which suggests that the volume of drainage might be larger than previously estimated.

Transport of Excess Heat at 24.5°N

2020 ◽  
Author(s):  
Marie-José Messias ◽  
Herlé Mercier
Keyword(s):  
Heat Transport ◽  
North Atlantic Ocean ◽  
Heat Content ◽  
Global Ocean ◽  
Geochemical Tracers ◽  
Excess Heat ◽  
Future Evolution ◽  
The North ◽  
Source Regions ◽  
Geographic Origins

<p>Repeated hydrographic surveys have allowed for the monitoring of the 24.5°N trans-Atlantic transect of volume and heat transports  since the middle of the last century. However, identifying the geographic origins and the temporal characteristics of full depth ocean heat content (OHC) anomalies is still at the frontier of  global ocean warming research albeit it is critical to the  understanding of  the current warming of the ocean and its future evolution. To address this gap,  we  combine volume transports at 24.5°N  with an historical reconstruction of  excess heat, which we define as the heat gained across the section since the year 1850 to  present. The  reconstruction is based on  a maximum entropy approach  that links the  location and time of the last entry into the ocean of a series of transient and geochemical tracers to their full depth in situ measurements in the interior. Here, we apply it to tracers measured on the hydrographic sections at  24.5°N since 1992. This methodology is a step forward in exploring the coherence of the OHC distributions at 24.5°N over time with the variability of the SST in  the source regions and the role of the AMOC, all genuinely based on observations. We find that the AMOC ranges from 16 to 19 Sv, heat transport from 0.9 to 1.5 PW and excess heat transport from 19 to 31 TW. The excess heat is transported northward across 24.5°N thus reinforcing the warming of the North Atlantic Ocean.</p>

Transport into the upper troposphere-lower stratosphere over North America

2020 ◽  
Author(s):  
Xinyue Wang ◽  
William Randel ◽  
Yutian Wu
Keyword(s):  
Gulf Of Mexico ◽  
Large Scale ◽  
Lower Stratosphere ◽  
Climate Model ◽  
Deep Convection ◽  
Vertical Diffusion ◽  
Dynamical Mechanism ◽  
Upper Troposphere ◽  
The North ◽  
Budget Analysis

<p>We study fast transport of air from the surface into the North American upper troposphere-lower stratosphere (UTLS) during northern summer with a large ensemble of Boundary Impulse Response (BIR) idealized tracers. Specifically, we implement 90 pulse tracers at the Northern Hemisphere surface and release them during July and August months in the fully coupled Whole Atmosphere Community Climate Model (WACCM) version 5. We focus on the most efficient transport cases above southern U.S. (10°-40°N, 60°-140°W) at 100 hPa with modal ages fall below 10th percentile. We examine transport-related terms, including resolved dynamics computed inside model transport scheme and parameterized processes (vertical diffusion and convective parameterization), to pin down the dominant dynamical mechanism. Our results show during the fastest transport, air parcels enter ULTS directly above the Gulf of Mexico. The budget analysis indicates that strong deep convection over the Gulf of Mexico fast uplift the tracer into 200 hPa, and then is vertically advected into 100 hPa and circulated by the enhanced large-scale anticyclone. </p>

The Value of Initialization on Decadal Timescales: State-Dependent Predictability in the CESM Decadal Prediction Large Ensemble

2020 ◽  
Vol 33 (17) ◽  
pp. 7353-7370
Author(s):  
H. M. Christensen ◽  
J. Berner ◽  
S. Yeager
Keyword(s):  
Time Scale ◽  
Initial Conditions ◽  
Heat Content ◽  
Atlantic Multidecadal Oscillation ◽  
Forced Response ◽  
Climate Change Signal ◽  
Seasonal Forecasts ◽  
The North ◽  
State Dependent ◽  
Start Dates

AbstractInformation in decadal climate prediction arises from a well-initialized ocean state and from the predicted response to an external forcing. The length of time over which the initial conditions benefit the decadal forecast depends on the start date of the forecast. We characterize this state-dependent predictability for decadal forecasts of upper ocean heat content in the Community Earth System Model. We find regionally dependent initial condition predictability, with extended predictability generally observed in the extratropics. We also detect state-dependent predictability, with the year of loss of information from the initialization varying between start dates. The decadal forecasts in the North Atlantic show substantial information from the initial conditions beyond the 10-yr forecast window, and a high degree of state-dependent predictability. We find some evidence for state-dependent predictability in the ensemble spread in this region, similar to that seen in weather and subseasonal-to-seasonal forecasts. For some start dates, an increase of information with lead time is observed, for which the initialized forecasts predict a growing phase of the Atlantic multidecadal oscillation. Finally we consider the information in the forecast from the initial conditions relative to the forced response, and quantify the crossover time scale after which the forcing provides more information. We demonstrate that the climate change signal projects onto different patterns than the signal from the initial conditions. This means that even after the crossover time scale has been reached in a basin-averaged sense, the benefits of initialization can be felt locally on longer time scales.

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