scholarly journals The Role of the Sahara Low in Summertime Sahel Rainfall Variability and Change in the CMIP3 Models

2009 ◽  
Vol 22 (21) ◽  
pp. 5755-5771 ◽  
Author(s):  
M. Biasutti ◽  
A. H. Sobel ◽  
Suzana J. Camargo
Keyword(s):  
North Atlantic ◽  
Rainfall Variability ◽  
Coupled Model ◽  
First Century ◽  
African Region ◽  
Low Level ◽  
The North ◽  
Sahel Rainfall ◽  
Intercomparison Project

Abstract Projections for twenty-first-century changes in summertime Sahel precipitation differ greatly across models in the third Coupled Model Intercomparison Project (CMIP3) dataset and cannot be explained solely in terms of discrepancies in the projected anomalies in global SST. This study shows that an index describing the low-level circulation in the North Atlantic–African region, namely, the strength of the low-level Saharan low, correlates with Sahel rainfall in all models and at the time scales of both interannual and interdecadal natural variability and of the forced centennial trend. An analysis of Sahel interannual variability provides evidence that variations in the Sahara low can be a cause, not just a consequence, of variations in Sahel rainfall and suggests that a better understanding of the sources of model discrepancy in Sahel rainfall predictions might be gained from an analysis of the mechanisms influencing changes in the Sahara low.

scholarly journals The Multidecadal Atlantic SST—Sahel Rainfall Teleconnection in CMIP5 Simulations

2014 ◽  
Vol 27 (2) ◽  
pp. 784-806 ◽  
Author(s):  
Elinor R. Martin ◽  
Chris Thorncroft ◽  
Ben B. B. Booth
Keyword(s):  
North Atlantic ◽  
Rainfall Variability ◽  
Coupled Model ◽  
Multidecadal Variability ◽  
The North ◽  
Sst Variability ◽  
Tropical North Atlantic ◽  
Sahel Rainfall ◽  
Intercomparison Project ◽  
The Indian Ocean

Abstract This study uses models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) to evaluate and investigate Sahel rainfall multidecadal variability and teleconnections with global sea surface temperatures (SSTs). Multidecadal variability is lower than observed in all historical simulations evaluated. Focus is on teleconnections with North Atlantic SST [Atlantic multidecadal variability (AMV)] as it is more successfully simulated than the Indian Ocean teleconnection. To investigate why some models successfully simulated this teleconnection and others did not, despite having similarly large AMV, two groups of models were selected. Models with large AMV were highlighted as good (or poor) by their ability to simulate relatively high (low) Sahel multidecadal variability and have significant (not significant) correlation between multidecadal Sahel rainfall and an AMV index. Poor models fail to capture the teleconnection between the AMV and Sahel rainfall because the spatial distribution of SST multidecadal variability across the North Atlantic is incorrect. A lack of SST signal in the tropical North Atlantic and Mediterranean reduces the interhemispheric SST gradient and, through circulation changes, the rainfall variability in the Sahel. This pattern was also evident in the control simulations, where SST and Sahel rainfall variability were significantly weaker than historical simulations. Errors in SST variability were suggested to result from a combination of weak wind–evaporation–SST feedbacks, poorly simulated cloud amounts and feedbacks in the stratocumulus regions of the eastern Atlantic, dust–SST–rainfall feedbacks, and sulfate aerosol interactions with clouds. By understanding the deficits and successes of CMIP5 historical simulations, future projections and decadal hindcasts can be examined with additional confidence.

scholarly journals Atlantic Meridional Overturning Circulation (AMOC) in CMIP5 Models: RCP and Historical Simulations

2013 ◽  
Vol 26 (18) ◽  
pp. 7187-7197 ◽  
Author(s):  
Wei Cheng ◽  
John C. H. Chiang ◽  
Dongxiao Zhang
Keyword(s):  
North Atlantic ◽  
Coupled Model ◽  
Meridional Overturning Circulation ◽  
First Century ◽  
Model Intercomparison ◽  
The North ◽  
Intercomparison Project ◽  
Meridional Overturning ◽  
The North Atlantic ◽  
Twenty First Century

Abstract The Atlantic meridional overturning circulation (AMOC) simulated by 10 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) for the historical (1850–2005) and future climate is examined. The historical simulations of the AMOC mean state are more closely matched to observations than those of phase 3 of the Coupled Model Intercomparison Project (CMIP3). Similarly to CMIP3, all models predict a weakening of the AMOC in the twenty-first century, though the degree of weakening varies considerably among the models. Under the representative concentration pathway 4.5 (RCP4.5) scenario, the weakening by year 2100 is 5%–40% of the individual model's historical mean state; under RCP8.5, the weakening increases to 15%–60% over the same period. RCP4.5 leads to the stabilization of the AMOC in the second half of the twenty-first century and a slower (then weakening rate) but steady recovery thereafter, while RCP8.5 gives rise to a continuous weakening of the AMOC throughout the twenty-first century. In the CMIP5 historical simulations, all but one model exhibit a weak downward trend [ranging from −0.1 to −1.8 Sverdrup (Sv) century−1; 1 Sv ≡ 106 m3 s−1] over the twentieth century. Additionally, the multimodel ensemble–mean AMOC exhibits multidecadal variability with a ~60-yr periodicity and a peak-to-peak amplitude of ~1 Sv; all individual models project consistently onto this multidecadal mode. This multidecadal variability is significantly correlated with similar variations in the net surface shortwave radiative flux in the North Atlantic and with surface freshwater flux variations in the subpolar latitudes. Potential drivers for the twentieth-century multimodel AMOC variability, including external climate forcing and the North Atlantic Oscillation (NAO), and the implication of these results on the North Atlantic SST variability are discussed.

scholarly journals SST Forcings and Sahel Rainfall Variability in Simulations of the Twentieth and Twenty-First Centuries

2008 ◽  
Vol 21 (14) ◽  
pp. 3471-3486 ◽  
Author(s):  
M. Biasutti ◽  
I. M. Held ◽  
A. H. Sobel ◽  
A. Giannini
Keyword(s):  
Twentieth Century ◽  
Rainfall Variability ◽  
Coupled Model ◽  
First Century ◽  
Coupled Models ◽  
Sahel Rainfall ◽  
Intercomparison Project ◽  
Rainfall Anomalies ◽  
Twenty First Century ◽  
Tropical Sea

Abstract The outlook for Sahel precipitation in coupled simulations of the twenty-first century is very uncertain, with different models disagreeing even on the sign of the trends. Such disagreement is especially surprising in light of the robust response of the same coupled models to the twentieth-century forcings. This study presents a statistical analysis of the preindustrial, twentieth-century and twenty-first-century A1B scenario simulations in the latest Coupled Model Intercomparison Project 3 (CMIP3) dataset; it shows that the relationship that links Sahel rainfall anomalies to tropical sea surface temperature (SST) anomalies at interannual time scales in observations is reproduced by most models, independently of the change in the basic state as the world warms. The same SST–Sahel relationship can be used to predict the simulated twentieth-century changes in Sahel rainfall from each model’s simulation of changes in Indo-Pacific SST and Atlantic SST meridional gradient, although the prediction overestimates the simulated trends. Conversely, such a relationship does not explain the rainfall trend in the twenty-first century in a majority of models. These results are consistent with there being, in most models, a substantial direct positive effect of atmospheric greenhouse gases on Sahel rainfall, not mediated through SST.

scholarly journals Potential Large-Scale Forcing Mechanisms Driving Enhanced North Atlantic Tropical Cyclone Activity since the Mid-1990s

2018 ◽  
Vol 31 (4) ◽  
pp. 1377-1397 ◽  
Author(s):  
Haikun Zhao ◽  
Xingyi Duan ◽  
G. B. Raga ◽  
Fengpeng Sun
Keyword(s):  
Tropical Cyclone ◽  
North Atlantic ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Low Level ◽  
The North ◽  
Recent Increase ◽  
Forcing Mechanisms ◽  
Interdecadal Changes

A significant increase of tropical cyclone (TC) frequency is observed over the North Atlantic (NATL) basin during the recent decades (1995–2014). In this study, the changes in large-scale controls of the NATL TC activity are compared between two periods, one before and one since 1995, when a regime change is observed. The results herein suggest that the significantly enhanced NATL TC frequency is related mainly to the combined effect of changes in the magnitudes of large-scale atmospheric and oceanic factors and their association with TC frequency. Interdecadal changes in the role of vertical wind shear and local sea surface temperatures (SSTs) over the NATL appear to be two important contributors to the recent increase of NATL TC frequency. Low-level vorticity plays a relatively weak role in the recent increase of TC frequency. These changes in the role of large-scale factors largely depend on interdecadal changes of tropical SST anomalies (SSTAs). Enhanced low-level westerlies to the east of the positive SSTAs have been observed over the tropical Atlantic since 1995, with a pattern nearly opposite to that seen before 1995. Moreover, the large-scale contributors to the NATL TC frequency increase since 1995 are likely related to both local and remote SSTAs. Quantification of the impacts of local and remote SSTAs on the increase of TC frequency over the NATL basin and the physical mechanisms require numerical simulations and further observational analyses.

scholarly journals Response of global evaporation to major climate modes in historical and future Coupled Model Intercomparison Project Phase 5 simulations

2020 ◽  
Vol 24 (3) ◽  
pp. 1131-1143 ◽  
Author(s):  
Thanh Le ◽  
Deg-Hyo Bae
Keyword(s):  
North Atlantic ◽  
Coupled Model ◽  
Climate Extremes ◽  
Early Warning Systems ◽  
Warning Systems ◽  
Model Intercomparison ◽  
Climate Modes ◽  
The North ◽  
Intercomparison Project ◽  
The North Atlantic

Abstract. Climate extremes, such as floods and droughts, might have severe economic and societal impacts. Given the high costs associated with these events, developing early-warning systems is of high priority. Evaporation, which is driven by around 50 % of solar energy absorbed at surface of the Earth, is an important indicator of the global water budget, monsoon precipitation, drought monitoring and the hydrological cycle. Here we investigate the response of global evaporation to main modes of interannual climate variability, including the Indian Ocean Dipole (IOD), the North Atlantic Oscillation (NAO) and the El Niño–Southern Oscillation (ENSO). These climate modes may have an influence on temperature, precipitation, soil moisture and wind speed and are likely to have impacts on global evaporation. We utilized data of historical simulations and RCP8.5 (representative concentration pathway) future simulations derived from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Our results indicate that ENSO is an important driver of evaporation for many regions, especially the tropical Pacific. The significant IOD influence on evaporation is limited in western tropical Indian Ocean, while NAO is more likely to have impacts on evaporation of the North Atlantic European areas. There is high agreement between models in simulating the effects of climate modes on evaporation of these regions. Land evaporation is found to be less sensitive to considered climate modes compared to oceanic evaporation. The spatial influence of major climate modes on global evaporation is slightly more significant for NAO and the IOD and slightly less significant for ENSO in the 1906–2000 period compared to the 2006–2100 period. This study allows us to obtain insight about the predictability of evaporation and hence, may improve the early-warning systems of climate extremes and water resource management.

scholarly journals Climate model configurations of the ECMWF Integrated Forecasting System (ECMWF-IFS cycle 43r1) for HighResMIP

2018 ◽  
Vol 11 (9) ◽  
pp. 3681-3712 ◽  
Author(s):  
Christopher D. Roberts ◽  
Retish Senan ◽  
Franco Molteni ◽  
Souhail Boussetta ◽  
Michael Mayer ◽  
...  
Keyword(s):  
North Atlantic ◽  
Climate Model ◽  
Coupled Model ◽  
Ocean Model ◽  
Model Resolution ◽  
Model Intercomparison ◽  
The North ◽  
Forecasting System ◽  
Intercomparison Project ◽  
The North Atlantic

Abstract. This paper presents atmosphere-only and coupled climate model configurations of the European Centre for Medium-Range Weather Forecasts Integrated Forecasting System (ECMWF-IFS) for different combinations of ocean and atmosphere resolution. These configurations are used to perform multi-decadal ensemble experiments following the protocols of the High Resolution Model Intercomparison Project (HighResMIP) and phase 6 of the Coupled Model Intercomparison Project (CMIP6). These experiments are used to evaluate the sensitivity of major biases in the atmosphere, ocean, and cryosphere to changes in atmosphere and ocean resolution. All configurations successfully reproduce the observed long-term trends in global mean surface temperature. Furthermore, following an adjustment to account for drift in the subsurface ocean, coupled configurations of ECMWF-IFS realistically reproduce observation-based estimates of ocean heat content change since 1950. Climatological surface biases in ECMWF-IFS are relatively insensitive to an increase in atmospheric resolution from  ∼ 50 to  ∼ 25 km. However, increasing the horizontal resolution of the atmosphere while maintaining the same vertical resolution enhances the magnitude of a cold bias in the lower stratosphere. In coupled configurations, there is a strong sensitivity to an increase in ocean model resolution from 1 to 0.25°. However, this sensitivity to ocean resolution takes many years to fully manifest and is less apparent in the first year of integration. This result has implications for the ECMWF coupled model development strategy that typically relies on the analysis of biases in short ( < 1 year) ensemble (re)forecast data sets. The impacts of increased ocean resolution are particularly evident in the North Atlantic and Arctic, where they are associated with an improved Atlantic meridional overturning circulation, increased meridional ocean heat transport, and more realistic sea-ice cover. In the tropical Pacific, increased ocean resolution is associated with improvements to the magnitude and asymmetry of El Niño–Southern Oscillation (ENSO) variability and better representation of non-linear sea surface temperature (SST)–radiation feedbacks during warm events. However, increased ocean model resolution also increases the magnitude of a warm bias in the Southern Ocean. Finally, there is tentative evidence that both ocean coupling and increased atmospheric resolution can improve teleconnections between tropical Pacific rainfall and geopotential height anomalies in the North Atlantic.

scholarly journals Abrupt cooling over the North Atlantic in modern climate models

2017 ◽  
Vol 8 (1) ◽  
Author(s):  
Giovanni Sgubin ◽  
Didier Swingedouw ◽  
Sybren Drijfhout ◽  
Yannick Mary ◽  
Amine Bennabi
Keyword(s):  
North Atlantic ◽  
Climate Models ◽  
Coupled Model ◽  
Deep Ocean ◽  
Warming Trend ◽  
Necessary Condition ◽  
Adaptation Policy ◽  
The North ◽  
Intercomparison Project

Abstract Observations over the 20th century evidence no long-term warming in the subpolar North Atlantic (SPG). This region even experienced a rapid cooling around 1970, raising a debate over its potential reoccurrence. Here we assess the risk of future abrupt SPG cooling in 40 climate models from the fifth Coupled Model Intercomparison Project (CMIP5). Contrary to the long-term SPG warming trend evidenced by most of the models, 17.5% of the models (7/40) project a rapid SPG cooling, consistent with a collapse of the local deep-ocean convection. Uncertainty in projections is associated with the models’ varying capability in simulating the present-day SPG stratification, whose realistic reproduction appears a necessary condition for the onset of a convection collapse. This event occurs in 45.5% of the 11 models best able to simulate the observed SPG stratification. Thus, due to systematic model biases, the CMIP5 ensemble as a whole underestimates the chance of future abrupt SPG cooling, entailing crucial implications for observation and adaptation policy.

scholarly journals Implications of Ural Blocking for East Asian Winter Climate in CMIP5 GCMs. Part I: Biases in the Historical Scenario

2015 ◽  
Vol 28 (6) ◽  
pp. 2203-2216 ◽  
Author(s):  
Hoffman H. N. Cheung ◽  
Wen Zhou
Keyword(s):  
Time Scales ◽  
North Atlantic ◽  
East Asian ◽  
Coupled Model ◽  
Winter Climate ◽  
The North ◽  
Intercomparison Project ◽  
The North Atlantic ◽  
Mean Circulation

Abstract This study assesses the ability of the 25 GCMs from phase 5 of the Coupled Model Intercomparison Project (CMIP5) to simulate Ural blocking (UB) and its linkage with the East Asian winter climate [December–February (DJF)] in a historical run (1950/51–2004/05). A Ural blocking index (UBI) is defined as the DJF-mean blocking frequency over 45°–90°E for each winter. Regression analyses suggest that the long-term mean bias of UBI is caused by the long-term mean circulation bias over the North Atlantic. On seasonal time scales, the GCMs simulating a positive bias of UBI are associated with a stronger Atlantic jet stream, as well as stronger westerly momentum fluxes from the North Atlantic to Europe. On synoptic time scales, however, these GCMs tend to be associated with a weaker Siberian high and East Asian trough during the evolution of a UB event. Altogether, there is no apparent linkage between the long-term mean bias of UB and the East Asian winter climate. Further studies are needed to explore the teleconnection between UB and the East Asian winter climate in the GCMs.

scholarly journals THE (IR)RELEVANCE OF BIBLICAL SCHOLARSHIP? A CHALLENGE, AND AN OPPORTUNITY

Scriptura ◽  
2021 ◽  
Vol 120 (1) ◽  
Author(s):  
Benjamin D. Giffone
Keyword(s):  
North Atlantic ◽  
Qualitative Difference ◽  
Modern World ◽  
The Bible ◽  
Biblical Scholarship ◽  
The North ◽  
Scholarly Discourse ◽  
Biblical Education ◽  
Bible Reading

Has biblical scholarship become irrelevant to modern secular societies? Are the threats to the viability of biblical scholarship of the same nature as the threats to other areas of the humanities (history, philosophy, literature), or is there a qualitative difference? What about the role of technology in biblical research and biblical education? What is the future of the institutions of biblical scholarship such as universities, seminaries, journals, and academic presses? What is the role of biblical scholars in secular and post-secular societies, as contrasted with scholars in/from emerging communities? This essay argues that the problem of “validation” lies at the heart of biblical scholarship’s irrelevancy within the broader secularity of modern world and that this problem is even more evident in the scholarly discourse coming from regions like Eastern Europe and South Africa. However, the loss of authority of biblical scholarship more generally represents an opportunity for these communities. Rather than becoming enamoured of validation from the North Atlantic world, Bible-reading communities must cultivate their own forms of validation based in their unique histories with the Bible, and the affinities between their own histories/cultures and the cultures that produced the Old and New Testament texts.

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