Atlantic Forcing of Persistent Drought in West Africa

Shanahan, T. M.; Overpeck, Jonathan T.; Anchukaitis, Kevin J.; Beck, J. Warren; Cole, Julia E.; Dettman, David L.; Peck, John A.; Scholz, Christopher A.; King, J. W.

doi:10.1126/science.1166352

Cited by 344 publications

(256 citation statements)

References 39 publications

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“…These systems directly influence precipitation over Ethiopia (Nicholson and Grist 2003;Segele and Lamb 2005), and the impact of SSTA modes on Ethiopian precipitation is primarily driven by modifications to the abovementioned systems (e.g. Rowell 2003;Segele and Lamb 2005;Shanahan et al 2009;Ummenhofer et al 2009;Diro et al 2011a). Figure 5 summarizes the observed and modeled relationships among the three large-scale circulation systems and Ethiopian precipitation in the Kiremt season.…”

Section: Factors Contributing To Kiremt-season Precipitationmentioning

confidence: 99%

“…Likewise, the Indian Ocean Dipole (IOD) and Mediterranean Ocean sea surface temperatures affect EALLJ dynamics and moisture supply, respectively (Rowell 2003;Ummenhofer et al 2009). In addition, sea surface temperature anomalies (SSTAs) over the North Atlantic can influence the temporal and spatial variability of the NASH (Kushnir et al 2010) and mainly influence the low frequency variability of precipitation (Shanahan et al 2009). …”

Section: Introductionmentioning

confidence: 99%

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CMIP5 model simulations of Ethiopian Kiremt-season precipitation: current climate and future changes

Ballard

et al. 2015

Clim Dyn

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over central Highlands and northern Great Rift Valley in Ethiopia, but a decrease in precipitation over the southern part of the country. Such a dipole pattern is attributable to the intensification of the North Atlantic subtropical high (NASH) in a warmer climate, which influences Ethiopian Kiremt-season precipitation mainly by modulating atmospheric vertical motion. Diagnosis of the omega equation demonstrates that an intensified NASH increases (decreases) the advection of warm air and positive vorticity into the central Highlands and northern Great Rift Valley (southern part of the country), enhancing upward motion over the northern Rift Valley but decreasing elsewhere. Under the RCP 4.5 scenario, the high-resolution models project an intensification of the NASH by 15 (3 × 10 5 m 2 s −2 ) geopotential meters (stream function) at the 850-hPa level, contributing to the projected precipitation change over Ethiopia. The influence of the NASH on Kiremtseason precipitation becomes more evident in the future due to the offsetting effects of two other major circulation systems: the East African Low-level Jet (EALLJ) and the Tropical Easterly Jet (TEJ). The high-resolution models project a strengthening of the EALLJ, but a weakening of the TEJ. Future changes in the EALLJ and TEJ will drive this precipitation system in opposite directions, leading to small or no net changes in precipitation in Ethiopia.

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Section: Factors Contributing To Kiremt-season Precipitationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

CMIP5 model simulations of Ethiopian Kiremt-season precipitation: current climate and future changes

Ballard

et al. 2015

Clim Dyn

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“…H Sierra Nevada (California) Sequoia grove fire scar frequency (blue with circles; Swetnam 1993). I Ghana lake silicate concentration index (green with circles; Shanahan et al 2009). J Yucatan lake precipitation-evaporation (CaC; Hoddell et al 1995).…”

Section: Proxy Recordsmentioning

confidence: 99%

“…While these records are diverse with respect to interpretation, calibration, sensitivity and resolution, it is now possible to use the more complete proxy network presently in place to attempt qualitative interpretations of linked climate/circulation changes at larger spatial (hemispheric) scales. Some of these more recently available records show distinctive MCA-LIA changes in North Atlantic SSTs and sea ice (Sicre et al 2008a;Massé et al 2008), Meso-American/ Caribbean/Gulf of Mexico climate and oceanic conditions (Haug et al 2003;Lund et al 2006;Richey et al 2007), tropical African rainfall (Verschuren 2004;Verschuren et al 2000;Russel et al 2007;Shanahan et al 2009), and the Indian and East Asian monsoons (von Rad et al 1999;Sinha et al 2007;Zhang et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Support for global climate reorganization during the “Medieval Climate Anomaly”

et al. 2010

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Widely distributed proxy records indicate that the Medieval Climate Anomaly (MCA; *900-1350 AD) was characterized by coherent shifts in large-scale Northern Hemisphere atmospheric circulation patterns. Although cooler sea surface temperatures in the central and eastern equatorial Pacific can explain some aspects of medieval circulation changes, they are not sufficient to account for other notable features, including widespread aridity through the Eurasian sub-tropics, stronger winter westerlies across the North Atlantic and Western Europe, and shifts in monsoon rainfall patterns across Africa and South Asia. We present results from a full-physics coupled climate model showing that a slight warming of the tropical Indian and western Pacific Oceans relative to the other tropical ocean basins can induce a broad range of the medieval circulation and climate changes indicated by proxy data, including many of those not explained by a cooler tropical Pacific alone. Important aspects of the results resemble those from previous simulations examining the climatic response to the rapid Indian Ocean warming during the late twentieth century, and to results from climate warming simulations-especially in indicating an expansion of the Northern Hemisphere Hadley circulation. Notably, the pattern of tropical Indo-Pacific sea surface temperature (SST) change responsible for producing the proxy-model similarity in our results agrees well with MCA-LIA SST differences obtained in a recent proxy-based climate field reconstruction. Though much remains unclear, our results indicate that the MCA was characterized by an enhanced zonal Indo-Pacific SST gradient with resulting changes in Northern Hemisphere tropical and extra-tropical circulation patterns and hydroclimate regimes, linkages that may explain the coherent regional climate shifts indicated by proxy records from across the planet. The findings provide new perspectives on the nature and possible causes of the MCA-a remarkable, yet incompletely understood episode of Late Holocene climatic change.

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“…It also allows the reconstruction of main climate signals. The method is particularly efficient when combined with other techniques and has been widely used in paleoclimatic studies [7][8][9][10]. In this study, MTA [11][12][13] and WSA [14] are used to explore the spectral features of the relevant SSA components.…”

Section: Methodsmentioning

confidence: 99%

Decadal-scale variability of warm season temperature in Beijing over the past 2650 years

Dai

Zhang

2011

Chin. Sci. Bull.

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A continuous record of surface temperature for the past 2650 years was obtained in an earlier study from a Beijing stalagmite based on sedimentary layer counting and thickness measurements. Singular spectrum analysis, multi-taper and wavelet spectral analyses are used in this study to identify decadal-scale signals and their origins in this record. Besides long-term cycles of solar origin identified in earlier studies, this record contains cycles that dominate temperature with periods of 102-70, 66-50, 31, 25-22, 19, 15, 12 and 9 years. The 102-70, 25-22, 12 and 9 year cycles are attributable to solar variation, while the others are likely to be related to low-latitude ocean forcing. These results suggest that century-scale changes in the Beijing summer temperature over the past 2650 years are primarily controlled by solar variation, while ocean-atmospheric interactions play a prominent role in modulating decadal-scale variability.

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Atlantic Forcing of Persistent Drought in West Africa

Cited by 344 publications

References 39 publications

CMIP5 model simulations of Ethiopian Kiremt-season precipitation: current climate and future changes

CMIP5 model simulations of Ethiopian Kiremt-season precipitation: current climate and future changes

Support for global climate reorganization during the “Medieval Climate Anomaly”

Decadal-scale variability of warm season temperature in Beijing over the past 2650 years

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