| 1. |
- Gaetani, Marco, et al.
(author)
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Understanding the Mechanisms behind the Northward Extension of the West African Monsoon during the Mid-Holocene
- 2017
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In: Journal of Climate. - 0894-8755 .- 1520-0442. ; 30:19, s. 7621-7642
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Journal article (peer-reviewed)abstract
- Understanding the West African monsoon (WAM) dynamics in the mid-Holocene (MH) is a crucial issue in climate modeling, because numerical models typically fail to reproduce the extensive precipitation suggested by proxy evidence. This discrepancy may be largely due to the assumption of both unrealistic land surface cover and atmospheric aerosol concentration. In this study, the MH environment is simulated in numerical experiments by imposing extensive vegetation over the Sahara and the consequent reduction in airborne dust concentration. A dramatic increase in precipitation is simulated across the whole of West Africa, up to the Mediterranean coast. This precipitation response is in better agreement with proxy data, in comparison with the case in which only changes in orbital forcing are considered. Results show a substantial modification of the monsoonal circulation, characterized by an intensification of large-scale deep convection through the entire Sahara, and a weakening and northward shift (similar to 6.5 degrees) of the African easterly jet. The greening of the Sahara also leads to a substantial reduction in the African easterly wave activity and associated precipitation. The reorganization of the regional atmospheric circulation is driven by the vegetation effect on radiative forcing and associated heat fluxes, with the reduction in dust concentration to enhance this response. The results for the WAM in the MH present important implications for understanding future climate scenarios in the region and in teleconnected areas, in the context of projected wetter conditions in West Africa.
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| 2. |
- Hegen, Harald, et al.
(author)
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Diagnostic value of kappa free light chain index in patients with primary progressive multiple sclerosis - a multicentre study
- 2023
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In: FRONTIERS IN IMMUNOLOGY. - 1664-3224. ; 14
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Journal article (peer-reviewed)abstract
- BackgroundKappa free light chains (kappa-FLC) in the cerebrospinal fluid (CSF) are an emerging biomarker in multiple sclerosis (MS).ObjectiveTo investigate whether kappa-FLC index has similar diagnostic value in patients with primary progressive multiple sclerosis (PPMS) compared to oligoclonal bands (OCB).MethodsPatients with PPMS were recruited through 11 MS centres across 7 countries. kappa-FLC were measured by immunonephelometry/-turbidimetry. OCB were determined by isoelectric focusing and immunofixation.ResultsA total of 174 patients (mean age of 52 +/- 11 years, 51% males) were included. kappa-FLC index using a cut-off of 6.1 was positive in 161 (93%) and OCB in 153 (88%) patients.Conclusion kappa-FLC index shows similar diagnostic sensitivity than OCB in PPMS.
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| 3. |
- Messori, Gabriele, et al.
(author)
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On cold spells in North America and storminess in western Europe
- 2016
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 43:12, s. 6620-6628
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Journal article (peer-reviewed)abstract
- We discuss the dynamical and statistical links between cold extremes over eastern North America and storminess over western Europe, with a focus on the midlatitude jet stream, the North Atlantic Oscillation (NAO) and the Pacific-North American Pattern (PNA). The analysis is performed on the European Centre for Medium-Range Weather Forecasts 20th Century Reanalysis. The large-scale circulation associated with the cold spells corresponds to advection of cold air from the Arctic region into North America and to a very zonal and intense North Atlantic jet, shifted persistently south of its climatological location. These features of the Atlantic jet are conducive to destructive windstorms and intense precipitation over a large part of southern and continental Europe and the British Isles. The cold spells are preceded by a negative NAO and followed by a positive PNA; however, we interpret the associated circulation anomalies as being distinct from these standard modes of climate variability.
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| 4. |
- Messori, Gabriele, et al.
(author)
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The water cycle of the mid-Holocene West African monsoon : The role of vegetation and dust emission changes
- 2019
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In: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 39:4, s. 1927-1939
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Journal article (peer-reviewed)abstract
- During the mid-Holocene (6 kyr BP), West Africa experienced a much stronger and geographically extensive monsoon than in the present day. Changes in orbital forcing, vegetation and dust emissions from the Sahara have been identified as key factors driving this intensification. Here, we analyse how the timing, origin and convergence of moisture fluxes contributing to the monsoonal precipitation change under a range of scenarios: orbital forcing only; orbital and vegetation forcings (Green Sahara); orbital, vegetation and dust forcings (Green Sahara-reduced dust). We further compare our results to a range of reconstructions of mid-Holocene precipitation from palaeoclimate archives. In our simulations, the greening of the Sahara leads to a cyclonic water vapour flux anomaly over North Africa with an anomalous westerly flow bringing large amounts of moisture into the Sahel from the Atlantic Ocean. Changes in atmospheric dust under a vegetated Sahara shift the anomalous moisture advection pattern northwards, increasing both moisture convergence and precipitation recycling over the northern Sahel and Sahara and the associated precipitation during the boreal summer. During this season, under both the Green Sahara and Green Sahara-reduced dust scenarios, local recycling in the Saharan domain exceeds that of the Sahel. This points to local recycling as an important factor modulating vegetation-precipitation feedbacks and the impact of Saharan dust emissions. Our results also show that temperature and evapotranspiration over the Sahara in the mid-Holocene are close to Sahelian pre-industrial values. This suggests that pollen-based paleoclimate reconstructions of precipitation during the Green Sahara period are likely not biased by possible large evapotranspiration changes in the region.
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| 5. |
- Pausata, Francesco S. R., et al.
(author)
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The Greening of the Sahara : Past Changes and Future Implications
- 2020
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In: One Earth. - : ELSEVIER. - 2590-3330 .- 2590-3322. ; 2:3, s. 235-250
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Research review (peer-reviewed)abstract
- In the future, the Sahara and Sahelian regions could experience more rainfall than today as a result of climate change. Wetter periods, termed African humid periods, occurred in the past and witnessed a mesic landscape in place of today's hyperarid and semiarid environment. Such large past changes raise the question of whether the near future might hold in store similar environmental transformations, particularly in view of the growing human-induced climate, land-use, and land-cover changes. In the last decades, geoengineering initiatives (in the form of active re-greening projects of the Sahara and Sahel) have been proposed and could have significant effects on the climate of the region. Here, we synthesize the literature on past and projected changes in the hydroclimate of the Sahelian-Saharan region and the associated feedbacks. We further address the current state of knowledge concerning Saharan and Sahelian afforestation projects and their consequences. Our review underscores the importance of vegetation in land-atmosphere-ocean feedback processes and the far-field impacts of northern African ecosystem changes.
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