Correcting the Multi-model Ensemble Tropical Pacific SST Warming Pattern

The mid-Piacenzian or mid-Pliocene warm period (mPWP, 3.264 &#8211; 3.025 Ma) is the most recent geological period to see atmospheric CO&#173;2 levels similar to the present-day values (~400 ppm). Some proxy reconstructions for the mPWP show reduced zonal SST gradients in the tropical Pacific Ocean, possibly indicating an El Ni&#241;o-like mean state in the mid-Pliocene. However, past modelling studies do not show the same results. Efforts to understand mPWP climate dynamics have led to the Pliocene Model Intercomparison Project (PlioMIP). Results from the first phase (PlioMIP1) showed clear El Ni&#241;o variability (albeit significantly reduced) and did not show the greatly reduced time-mean zonal SST gradient suggested by some of the proxies.In this work, we study ENSO variability in the PlioMIP2 ensemble, which consists of additional global coupled climate models and updated boundary conditions compared to PlioMIP1. We quantify ENSO amplitude, period and spatial structure as well as the tropical Pacific annual mean state in a mid-Pliocene and pre-industrial reference simulation. Results show a reduced El Ni&#241;o amplitude in the model- ensemble mean, with 11 out of 13 individual models showing such a reduction. Furthermore, the spectral power of this variability considerably decreases in the 3&#8211;7-year band and shifts to higher frequencies compared to pre-industrial. The spatial structure of the dominant EOF shows no particular change in the patterns of tropical Pacific variability in the model-ensemble mean, compared to the pre-industrial. Further analyses that will be presented include the correlation of the zonal SST gradient with the El Ni&#241;o amplitude, investigation of shift in El Ni&#241;o flavour, and a discussion of the coupled feedbacks at play in the mid-Pliocene tropical Pacific Ocean.

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Amplified tropical Pacific rainfall variability related to background SST warming

Climate Dynamics ◽

10.1007/s00382-020-05119-3 ◽

2020 ◽

Vol 54 (3-4) ◽

pp. 2387-2402 ◽

Cited By ~ 1

Author(s):

Ning Sun ◽

Tianjun Zhou ◽

Xiaolong Chen ◽

Hirokazu Endo ◽

Akio Kitoh ◽

...

Keyword(s):

Rainfall Variability ◽

Tropical Pacific ◽

Sst Warming

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Sources of Uncertainty in the Tropical Pacific Warming Pattern under Global Warming Projected by Coupled Ocean-Atmosphere Models

10.1007/978-981-32-9844-6 ◽

2020 ◽

Author(s):

Jun Ying

Keyword(s):

Global Warming ◽

Tropical Pacific ◽

Sources Of Uncertainty ◽

Warming Pattern ◽

Ocean Atmosphere ◽

The Tropical Pacific

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The Role of Regional SST Warming Variations in the Drying of Meso-America in Future Climate Projections*

Journal of Climate ◽

10.1175/2010jcli3536.1 ◽

2011 ◽

Vol 24 (7) ◽

pp. 2003-2016 ◽

Cited By ~ 55

Author(s):

Sara A. Rauscher ◽

Fred Kucharski ◽

David B. Enfield

Keyword(s):

North Atlantic ◽

Coupled Model ◽

Tropical Pacific ◽

Future Climate ◽

Ensemble Average ◽

Subtropical High ◽

Future Climate Change ◽

Eastern Tropical Pacific ◽

Enso Events ◽

Sst Warming

Abstract This paper addresses several hypotheses designed to explain why AOGCM simulations of future climate in the third phase of the Coupled Model Intercomparison Project (CMIP3) feature an intensified reduction of precipitation over the Meso-America (MA) region. While the drying is consistent with an amplification of the subtropical high pressure cells and an equatorward contraction of convective regions due to the “upped ante” for convection in a warmer atmosphere, the physical mechanisms behind the intensity and robustness of the MA drying signal have not been fully explored. Regional variations in sea surface temperature (SST) warming may play a role. First, SSTs over the tropical North Atlantic (TNA) do not warm as much as the surrounding ocean. The troposphere senses a TNA that is cooler than the tropical Pacific, potentially exciting a Gill-type response, increasing the strength of the North Atlantic subtropical high. Second, the warm ENSO-like state simulated in the eastern tropical Pacific could decrease precipitation over MA, as warm ENSO events are associated with drying over MA. The authors use the International Centre for Theoretical Physics (ICTP) AGCM to investigate the effects of these regional SST warming variations on the projected drying over MA. First, the change of SSTs [Special Report on Emissions Scenarios (SRES) A1B’s Twentieth-Century Climate in Coupled Model (A1B-20C)] in the ensemble average of the CMIP3 models is applied to determine if the ICTP AGCM can replicate the future drying. Then the effects of 1) removing the reduced warming over the TNA, 2) removing the warm ENSO-event-like pattern in the eastern tropical Pacific, and 3) applying uniform SST warming throughout the tropics are tested. The ICTP AGCM can reproduce the general pattern and amount of precipitation over MA. Simulations in which the CMIP3 A1B-20C ensemble-average SSTs are added to climatological SSTs show drying of more than 20% over the MA region, similar to the CMIP3 ensemble average. Replacing the relatively cooler SSTs over the TNA excites a Gill response consistent with an off-equatorial heating anomaly, showing that the TNA relative cooling is responsible for about 16% (31%) of the drying in late spring (early summer). The warm ENSO-like SST pattern over the eastern Pacific also affects precipitation over the MA region, with changes of 19% and 31% in March–June (MMJ) and June–August (JJA), respectively. This work highlights the importance of understanding even robust signals in the CMIP3 future scenario simulations, and should aid in the design and analysis of future climate change studies over the region.

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Cloud–Radiation Feedback as a Leading Source of Uncertainty in the Tropical Pacific SST Warming Pattern in CMIP5 Models

Journal of Climate ◽

10.1175/jcli-d-15-0796.1 ◽

2016 ◽

Vol 29 (10) ◽

pp. 3867-3881 ◽

Cited By ~ 22

Author(s):

Jun Ying ◽

Ping Huang

Keyword(s):

Heat Budget ◽

Tropical Pacific ◽

Eastern Pacific ◽

Shortwave Radiation ◽

Cmip5 Models ◽

Central Pacific ◽

Surface Warming ◽

Sst Warming ◽

Radiation Feedback ◽

The Tropical Pacific

Abstract The role of the intermodel spread of cloud–radiation feedback in the uncertainty in the tropical Pacific SST warming (TPSW) pattern under global warming is investigated based on the historical and RCP8.5 runs from 32 models participating in CMIP5. The large intermodel discrepancies in cloud–radiation feedback contribute 24% of the intermodel uncertainty in the TPSW pattern over the central Pacific. The mechanism by which the cloud–radiation feedback influences the TPSW pattern is revealed based on an analysis of the surface heat budget. A relatively weak negative cloud–radiation feedback over the central Pacific cannot suppress the surface warming as greatly as in the multimodel ensemble and thus induces a warm SST deviation over the central Pacific, producing a low-level convergence that suppresses (enhances) the evaporative cooling and zonal cold advection in the western (eastern) Pacific. With these processes, the original positive SST deviation over the central Pacific will move westward to the western and central Pacific, with a negative SST deviation in the eastern Pacific. Compared with the observed cloud–radiation feedback from six sets of reanalysis and satellite-observed data, the negative cloud–radiation feedback in the models is underestimated in general. It implies that the TPSW pattern should be closer to an El Niño–like pattern based on the concept of observational constraint. However, the observed cloud–radiation feedback from the various datasets also demonstrates large discrepancies in magnitude. Therefore, the authors suggest that more effort should be made to improve the precision of shortwave radiation observations and the description of cloud–radiation feedback in models for a more reliable projection of the TPSW pattern in future.

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