Atlantic Warm-Pool Variability in the IPCC AR4 CGCM Simulations

2012 ◽  
Vol 25 (16) ◽  
pp. 5612-5628 ◽  
Author(s):  
Hailong Liu ◽  
Chunzai Wang ◽  
Sang-Ki Lee ◽  
David Enfield
Keyword(s):  
Twentieth Century ◽  
Decadal Variability ◽  
Local Heating ◽  
Warm Pool ◽  
Shortwave Radiation ◽  
Coupled Models ◽  
Area Index ◽  
Low Level ◽  
Atlantic Warm Pool ◽  
Sst Bias

Abstract This study investigates Atlantic warm pool (AWP) variability in the twentieth century and preindustrial simulations of coupled GCMs submitted to the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). In the twentieth-century simulations, most coupled models show very weak AWP variability, represented by an AWP area index, because of the cold SST bias in the AWP. Among the IPCC models, a higher AWP SST index corresponds to increased net downward shortwave radiation and decreased low-level cloud fraction during the AWP peak season. This suggests that the cold SST bias in the AWP region is at least partly caused by an excessive amount of simulated low-level cloud, which blocks shortwave radiation from reaching the sea surface. AWP natural variability is examined in preindustrial simulations. Spectral analysis reveals that only multidecadal band variability of the AWP is significant in observations. All models successfully capture the multidecadal band, but they show that interannual and/or decadal variability is also significant. On the multidecadal time scale, the global SST difference pattern between large AWP years and small AWP years resembles the geographic pattern of the AMO for most coupled models. Observational analysis indicates that both positive ENSO phase and negative NAO phase in winter correspond to reduced trade winds in the AWP region. The westerly anomalies induced by positive ENSO and negative NAO lead to local heating and warm SST from March to May and February to April, respectively. This behavior as a known feature of anomalous AWP growth is well captured by only five models.

Atlantic Warm Pool Variability in the CMIP5 Simulations

2013 ◽  
Vol 26 (15) ◽  
pp. 5315-5336 ◽  
Author(s):  
Hailong Liu ◽  
Chunzai Wang ◽  
Sang-Ki Lee ◽  
David Enfield
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Warm Pool ◽  
Ocean Model ◽  
Radiation Balance ◽  
Area Index ◽  
Climate System Model ◽  
Atlantic Warm Pool ◽  
Sst Bias ◽  
High Level

Abstract This study investigates Atlantic warm pool (AWP) variability in the historical run of 19 coupled general circulation models (CGCMs) submitted to phase 5 of the Coupled Model Intercomparison Project (CMIP5). As with the CGCMs in phase 3 (CMIP3), most models suffer from the cold SST bias in the AWP region and also show very weak AWP variability as represented by the AWP area index. However, for the seasonal cycle the AWP SST bias of model ensemble and model sensitivities are decreased compared with CMIP3, indicating that the CGCMs are improved. The origin of the cold SST bias in the AWP region remains unknown, but among the CGCMs in CMIP5 excess (insufficient) high-level cloud simulation decreases (enhances) the cold SST bias in the AWP region through the warming effect of the high-level cloud radiative forcing. Thus, the AWP SST bias in CMIP5 is more modulated by an erroneous radiation balance due to misrepresentation of high-level clouds rather than low-level clouds as in CMIP3. AWP variability is assessed as in the authors' previous study in the aspects of spectral analysis, interannual variability, multidecadal variability, and comparison of the remote connections with ENSO and the North Atlantic Oscillation (NAO) against observations. In observations the maximum influences of the NAO and ENSO on the AWP take place in boreal spring. For some CGCMs these influences erroneously last to late summer. The effect of this overestimated remote forcing can be seen in the variability statistics as shown in the rotated EOF patterns from the models. It is concluded that the NCAR Community Climate System Model, version 4 (CCSM4), the Goddard Institute for Space Studies (GISS) Model E, version 2, coupled with the Hybrid Coordinate Ocean Model (HYCOM) ocean model (GISS-E2H), and the GISS Model E, version 2, coupled with the Russell ocean model (GISS-E2R) are the best three models of CMIP5 in simulating AWP variability.

scholarly journals The Rainfall Annual Cycle Bias over East Africa in CMIP5 Coupled Climate Models

2015 ◽  
Vol 28 (24) ◽  
pp. 9789-9802 ◽  
Author(s):  
Wenchang Yang ◽  
Richard Seager ◽  
Mark A. Cane ◽  
Bradfield Lyon
Keyword(s):  
East Africa ◽  
Annual Cycle ◽  
Climate Models ◽  
Western Indian Ocean ◽  
Shortwave Radiation ◽  
Coupled Models ◽  
Near Surface ◽  
Historical Simulation ◽  
Sst Bias ◽  
Short Rains

Abstract East Africa has two rainy seasons: the long rains [March–May (MAM)] and the short rains [October–December (OND)]. Most CMIP3/5 coupled models overestimate the short rains while underestimating the long rains. In this study, the East African rainfall bias is investigated by comparing the coupled historical simulations from CMIP5 to the corresponding SST-forced AMIP simulations. Much of the investigation is focused on the MRI-CGCM3 model, which successfully reproduces the observed rainfall annual cycle in East Africa in the AMIP experiment but its coupled historical simulation has a similar but stronger bias as the coupled multimodel mean. The historical–AMIP monthly climatology rainfall bias in East Africa can be explained by the bias in the convective instability (CI), which is dominated by the near-surface moisture static energy (MSE) and ultimately by the MSE’s moisture component. The near-surface MSE bias is modulated by the sea surface temperature (SST) over the western Indian Ocean. The warm SST bias in OND can be explained by both insufficient ocean dynamical cooling and latent flux, while the insufficient shortwave radiation and excess latent heat flux mainly contribute to the cool SST bias in MAM.

Evaluation of twentieth-century Atlantic Warm Pool simulations in historical CMIP5 runs

2012 ◽  
Vol 41 (9-10) ◽  
pp. 2375-2391 ◽  
Author(s):  
Michael E. Kozar ◽  
Vasubandhu Misra
Keyword(s):  
Twentieth Century ◽  
Warm Pool ◽  
Atlantic Warm Pool

scholarly journals Response of Freshwater Flux and Sea Surface Salinity to Variability of the Atlantic Warm Pool

2013 ◽  
Vol 26 (4) ◽  
pp. 1249-1267 ◽  
Author(s):  
Chunzai Wang ◽  
Liping Zhang ◽  
Sang-Ki Lee
Keyword(s):  
Central America ◽  
North Atlantic ◽  
Warm Pool ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Freshwater Flux ◽  
Surface Salinity ◽  
Atlantic Warm Pool ◽  
Mean Circulation ◽  
Circulation Dynamics

Abstract The response of freshwater flux and sea surface salinity (SSS) to the Atlantic warm pool (AWP) variations from seasonal to multidecadal time scales is investigated by using various reanalysis products and observations. All of the datasets show a consistent response for all time scales: A large (small) AWP is associated with a local freshwater gain (loss) to the ocean, less (more) moisture transport across Central America, and a local low (high) SSS. The moisture budget analysis demonstrates that the freshwater change is dominated by the atmospheric mean circulation dynamics, while the effect of thermodynamics is of secondary importance. Further decomposition points out that the contribution of the mean circulation dynamics primarily arises from its divergent part, which mainly reflects the wind divergent change in the low level as a result of SST change. In association with a large (small) AWP, warmer (colder) than normal SST over the tropical North Atlantic can induce anomalous low-level convergence (divergence), which favors anomalous ascent (decent) and thus generates more (less) precipitation. On the other hand, a large (small) AWP weakens (strengthens) the trade wind and its associated westward moisture transport to the eastern North Pacific across Central America, which also favors more (less) moisture residing in the Atlantic and hence more (less) precipitation. The results imply that variability of freshwater flux and ocean salinity in the North Atlantic associated with the AWP may have the potential to affect the Atlantic meridional overturning circulation.

scholarly journals Investigating the Causes of Increased Twentieth-Century Fall Precipitation over the Southeastern United States

2018 ◽  
Vol 32 (2) ◽  
pp. 575-590 ◽  
Author(s):  
Daniel A. Bishop ◽  
A. Park Williams ◽  
Richard Seager ◽  
Arlene M. Fiore ◽  
Benjamin I. Cook ◽  
...  
Keyword(s):  
United States ◽  
Twentieth Century ◽  
Gulf Of Mexico ◽  
Specific Humidity ◽  
Precipitation Trend ◽  
Eastern United States ◽  
Atmospheric Models ◽  
Coupled Models ◽  
Fully Coupled ◽  
Precipitation Trends

Abstract Much of the eastern United States experienced increased precipitation over the twentieth century. Characterizing these trends and their causes is critical for assessing future hydroclimate risks. Here, U.S. precipitation trends are analyzed for 1895–2016, revealing that fall precipitation in the southeastern region north of the Gulf of Mexico (SE-Gulf) increased by nearly 40%, primarily increasing after the mid-1900s. Because fall is the climatological dry season in the SE-Gulf and precipitation in other seasons changed insignificantly, the seasonal precipitation cycle diminished substantially. The increase in SE-Gulf fall precipitation was caused by increased southerly moisture transport from the Gulf of Mexico, which was almost entirely driven by stronger winds associated with enhanced anticyclonic circulation west of the North Atlantic subtropical high (NASH) and not by increases in specific humidity. Atmospheric models forced by observed SSTs and fully coupled models forced by historical anthropogenic forcing do not robustly simulate twentieth-century fall wetting in the SE-Gulf. SST-forced atmospheric models do simulate an intensified anticyclonic low-level circulation around the NASH, but the modeled intensification occurred farther west than observed. CMIP5 analyses suggest an increased likelihood of positive SE-Gulf fall precipitation trends given historical and future GHG forcing. Nevertheless, individual model simulations (both SST forced and fully coupled) only very rarely produce the observed magnitude of the SE-Gulf fall precipitation trend. Further research into model representation of the western ridge of the fall NASH is needed, which will help us to better predict whether twentieth-century increases in SE-Gulf fall precipitation will persist into the future.

scholarly journals The North Pacific blob acts to increase the predictability of the Atlantic warm pool

2021 ◽  
Author(s):  
Yusen Liu ◽  
Cheng Sun ◽  
Fred Kucharski ◽  
Jianping Li ◽  
Chunzai Wang ◽  
...  
Keyword(s):  
North Pacific ◽  
Warm Pool ◽  
The North ◽  
Atlantic Warm Pool ◽  
The North Pacific

Long-term predictability of winter teleconnection indices and their relationship to seasonal temperature extremes in Europe

2021 ◽  
Author(s):  
Nina Schuhen ◽  
Nathalie Schaller ◽  
Hannah C. Bloomfield ◽  
David J. Brayshaw ◽  
Jana Sillmann ◽  
...  
Keyword(s):  
Twentieth Century ◽  
Surface Temperature ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Decadal Variability ◽  
Environmental Research ◽  
Seasonal Temperature ◽  
East Atlantic ◽  
Teleconnection Patterns

<p>European winter weather is dominated by several low-frequency teleconnection patterns, the main ones being the North Atlantic Oscillation (NAO), East Atlantic, East Atlantic/Western Russia and Scandinavian patterns. Through predicting these patterns, skillful forecasts of weather parameters like surface temperature can be generated, which in turn are used in a variety of applications (e.g., predictions of energy demand). A previous study (Weisheimer et.al., 2017) found that the NAO was subject to decadal variability during the twentieth century, affecting its long-term predictability. During recent decades, predictions for the NAO index have shown considerable skill, but this is likely to change during future periods of reduced predictability.</p><p>We analyze the century-long ERA-20C reanalysis and ASF-20C seasonal hindcast datasets to find if the other main teleconnection patterns also experience fluctuations in predictability, with potential implications for future skill and development of seasonal forecasting models. By linking the teleconnections to extreme cold and heat wave indices (Russo et al., 2015), we highlight the impact of these large-scale patterns on seasonal surface temperature in Europe during two periods of interest in the middle and end of the century. Our study shows that even though the predictability of the teleconnection patterns themselves fluctuates on a decadal scale, the links to winter surface temperatures are not significantly affected. However, the ability of the seasonal hindcasts to reproduce these patterns is quite limited.</p><p> </p><p>References:</p><p>Russo, S., Sillmann, J., & Fischer, E. M. (2015). Top ten European heatwaves since 1950 and their occurrence in the coming decades. Environmental Research Letters, 10(12), 124003. doi: 10.1088/1748-9326/10/12/124003</p><p>Weisheimer, A., Schaller, N., O’Reilly, C., MacLeod, D. A., & Palmer, T. (2017). Atmospheric seasonal forecasts of the twentieth century:  multi-decadal variability in predictive skill of the winter North Atlantic Oscillation (NAO) and their potential value for extreme event attribution. Quarterly Journal of the Royal Meteorological Society, 143(703), 917-926. doi: 10.1002/qj.29</p>

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