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  • 1
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    In:  [Poster] In: Ocean Sciences Meeting 2018, 11.-16.02.2018, Portland, Oregon, USA .
    Publication Date: 2019-01-07
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 2
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    In:  [Poster] In: SPARC General Assembly 2018, 01.-05.10.2018, Kyoto, Japan .
    Publication Date: 2019-01-07
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 3
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    In:  [Talk] In: DRAKKAR 2018 Annual Workshop, 22.-24.01.2018, Grenoble, France .
    Publication Date: 2018-11-22
    Description: We discuss the development of a new coupled climate model at GEOMAR, capable of resolving the mesoscale. The ocean component is a ORCA05 NEMO configuration with regional refinements in e.g. the tropical Atlantic (INALT), Southern Ocean (ORION), or North Atlantic (VIKING) where the horizontal resolution is 10 km or finer. The atmosphere component is OpenIFS which can be run at T511 (39 km), T1023 (20 km) or T2047 (10 km) resolution. A climate model that resolves the mesoscale can capture oceanic eddies and tropical storms, and thus be used to understand how these phenomena respond to global warming. Latest results include experiments using NEMO ocean and ECHAM atmosphere, as well as atmosphere-only experiments with OpenIFS to understand the impact of horizontal resolution in the atmosphere. We report on the latest results and discuss the challenges and goals of future model development
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 4
    Publication Date: 2019-01-10
    Description: ENSO atmospheric feedbacks are strongly underestimated in state-of-the-art climate models (Bellenger et al. 2014)⁠. Therefore we investigate in a perturbed atmospheric physics ensemble with the Kiel Climate Model (KCM) and in CMIP5 models how ENSO atmospheric feedbacks depend on the mean state of the tropical Pacific. Additionally, uncoupled simulations are conducted with the atmospheric component of the KCM to obtain further insight into the mean state dependence. It is found that the strengths of the positive zonal wind feedback µ and the negative heat flux feedback α are both strongly linearly related equatorial sea surface temperature (SST) bias, while at least in the KCM differences in model physics seem to be less important (Bayr et al. 2017)⁠. In observations, strong zonal wind and heat flux feedbacks are caused by a convective response in the western central equatorial Pacific (Niño4 region), resulting from an eastward (westward) shift of the rising branch of the Walker Circulation (WC) during El Niño (La Niña). Climate models with a La Niña-like mean state, i.e. an equatorial SST cold bias in the Niño4 region (a common problem in many state-of-the-art climate models), simulate a too westward located rising branch of the WC (by up to 30°) and only a weak convective response. Thus, the position of the WC determines the strength of both the wind and heat flux feedback, which also explains why biases in these two feedbacks partly compensate in many climate models. Furthermore, a too eastward position of the WC leads to a fundamental change in ENSO dynamics, as ocean-atmosphere coupling shifts from a predominantly wind-driven to a more solar radiation-driven mode. On the other hand, enhanced atmospheric feedbacks lead to a substantial improvement of the non-linearity of ENSO. Differences in the mean state SST are suggested to be a major source of ENSO diversity in current climate models. References: Bayr, T., M. Latif, D. Dommenget, C. Wengel, J. Harlaß, and W. Park, 2017: Mean-State Dependence of ENSO Atmospheric Feedbacks in Climate Models. Clim. Dyn., doi:10.1007/s00382-017-3799-2. Bellenger, H., E. Guilyardi, J. Leloup, M. Lengaigne, and J. Vialard, 2014: ENSO representation in climate models: From CMIP3 to CMIP5. Clim. Dyn., 42, 1999–2018, doi:10.1007/s00382-013-1783-z.
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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  • 5
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    In:  [Talk] In: GSA Annual Meeting 2017, 22.10.-25.10.2017, Seattle, Washington, USA .
    Publication Date: 2019-01-11
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 6
    Publication Date: 2019-01-10
    Description: ENSO atmospheric feedbacks are strongly underestimated in state-of-the-art climate models (Bellenger et al. 2014)⁠. Therefore we investigate in a perturbed atmospheric physics ensemble with the Kiel Climate Model (KCM) and in CMIP5 models how ENSO atmospheric feedbacks depend on the mean state of the tropical Pacific. Additionally, uncoupled simulations are conducted with the atmospheric component of the KCM to obtain further insight into the mean state dependence. It is found that the strengths of the positive zonal wind feedback µ and the negative heat flux feedback α are both strongly linearly related equatorial sea surface temperature (SST) bias, while at least in the KCM differences in model physics seem to be less important (Bayr et al. 2017)⁠. In observations, strong zonal wind and heat flux feedbacks are caused by a convective response in the western central equatorial Pacific (Niño4 region), resulting from an eastward (westward) shift of the rising branch of the Walker Circulation (WC) during El Niño (La Niña). Climate models with a La Niña-like mean state, i.e. an equatorial SST cold bias in the Niño4 region (a common problem in many state-of-the-art climate models), simulate a too westward located rising branch of the WC (by up to 30°) and only a weak convective response. Thus, the position of the WC determines the strength of both the wind and heat flux feedback, which also explains why biases in these two feedbacks partly compensate in many climate models. Furthermore, a too eastward position of the WC leads to a fundamental change in ENSO dynamics, as ocean-atmosphere coupling shifts from a predominantly wind-driven to a more solar radiation-driven mode. On the other hand, enhanced atmospheric feedbacks lead to a substantial improvement of the non-linearity of ENSO. Differences in the mean state SST are suggested to be a major source of ENSO diversity in current climate models. References: Bayr, T., M. Latif, D. Dommenget, C. Wengel, J. Harlaß, and W. Park, 2017: Mean-State Dependence of ENSO Atmospheric Feedbacks in Climate Models. Clim. Dyn., doi:10.1007/s00382-017-3799-2. Bellenger, H., E. Guilyardi, J. Leloup, M. Lengaigne, and J. Vialard, 2014: ENSO representation in climate models: From CMIP3 to CMIP5. Clim. Dyn., 42, 1999–2018, doi:10.1007/s00382-013-1783-z.
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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  • 7
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    PANGAEA
    In:  Supplement to: Song, Zhaoyang; Latif, Mojib; Park, Wonsun; Zhang, Yuming (2018): Influence of Model Bias on Simulating North Atlantic Sea Surface Temperature During the Mid-Pliocene. Paleoceanography and Paleoclimatology, https://doi.org/10.1029/2018PA003397
    Publication Date: 2019-04-30
    Description: Climate models generally underestimate the pronounced warming in the sea surface temperature (SST) over the North Atlantic during the mid-Pliocene that is suggested by proxy data. Here, we investigate the influence of the North Atlantic cold SST bias, which is observed in many climate models, on the simulation of mid-Pliocene surface climate in a series of simulations with the Kiel Climate Model. A surface freshwater-flux correction is applied over the North Atlantic, which considerably enhances simulation of North Atlantic Ocean circulation and SST under present-day conditions. Using reconstructed mid-Pliocene boundary conditions with closed Bering and Arctic Archipelago Straits, the corrected model depicts significantly reduced model-proxy SST discrepancy in comparison to the uncorrected model. A key factor in reducing the discrepancy is the stronger and more sensitive Atlantic Meridional Overturning Circulation and poleward heat transport. We conclude that simulations of mid-Pliocene surface climate over the North Atlantic can considerably benefit from alleviating model biases in this region.
    Type: Dataset
    Format: text/tab-separated-values, 20 data points
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  • 8
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    PANGAEA
    In:  Supplement to: Song, Zhaoyang; Latif, Mojib; Park, Wonsun (2017): Expanding Greenland Ice Sheet Enhances Sensitivity of Plio-Pleistocene Climate to Obliquity Forcing in the Kiel Climate Model. Geophysical Research Letters, https://doi.org/10.1002/2017GL074835
    Publication Date: 2019-04-30
    Description: Proxy data suggest that the Plio-Pleistocene transition from ~3.2 - 3.0 to 2.5 Ma featured the onset of Northern Hemisphere glaciation and enhanced climate variability on obliquity timescale. Here, we investigate the influence of the expanding Greenland ice sheet (GrIS) on the mean climate and obliquity-related variability. Special attention is given to the Atlantic Meridional Overturning Circulation (AMOC). A series of climate model simulations suggest that the expanding GrIS weakens the AMOC by ~1 Sv, which is mainly due to reduced heat loss of the Greenland-Iceland-Norwegian Sea. Moreover, the expanded GrIS amplifies the Hadley circulation response to obliquity forcing. This drives enhanced obliquity-forced variations in freshwater export from the tropical Atlantic and in turn variations of the AMOC that increase by about a factor. The stronger AMOC response to obliquity forcing in turn drives a stronger global-mean near-surface temperature response. We conclude that the AMOC response to obliquity forcing is important to understand the enhanced climate variability on obliquity timescale during the Plio-Pleistocene transition.
    Type: Dataset
    Format: text/tab-separated-values, 50 data points
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  • 9
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    PANGAEA
    In:  Supplement to: Zhang, Xiao; Prange, Matthias; Steph, Silke; Butzin, Martin; Krebs, Uta; Lunt, Daniel J; Nisancioglu, Kerim H; Park, Wonsun; Schmittner, Andreas; Schneider, Birgit; Schulz, Michael (2012): Changes in equatorial Pacific thermocline depth in response to Panamanian seaway closure: Insights from a multi-model study. Earth and Planetary Science Letters, 317-318, 76-84, https://doi.org/10.1016/j.epsl.2011.11.028
    Publication Date: 2019-04-30
    Description: The early Pliocene warm phase was characterized by high sea surface temperatures and a deep thermocline in the eastern equatorial Pacific. A new hypothesis suggests that the progressive closure of the Panamanian seaway contributed substantially to the termination of this zonally symmetric state in the equatorial Pacific. According to this hypothesis, intensification of the Atlantic meridional overturning circulation (AMOC) - induced by the closure of the gateway - was the principal cause of equatorial Pacific thermocline shoaling during the Pliocene. In this study, twelve Panama seaway sensitivity experiments from eight ocean/climate models of different complexity are analyzed to examine the effect of an open gateway on AMOC strength and thermocline depth. All models show an eastward Panamanian net throughflow, leading to a reduction in AMOC strength compared to the corresponding closed-Panama case. In those models that do not include a dynamic atmosphere, deepening of the equatorial Pacific thermocline appears to scale almost linearly with the throughflow-induced reduction in AMOC strength. Models with dynamic atmosphere do not follow this simple relation. There are indications that in four out of five models equatorial wind-stress anomalies amplify the tropical Pacific thermocline deepening. In summary, the models provide strong support for the hypothesized relationship between Panama closure and equatorial Pacific thermocline shoaling.
    Type: Dataset
    Format: text/tab-separated-values, 30 data points
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  • 10
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    In:  [Talk] In: DRAKKAR meeting, 20.-21.01, Grenoble, France .
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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