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Tropical Africa and the North Atlantic Ocean are significantly influenced by African easterly waves (AEWs), which play a fundamental role in tropical rainfall and cyclogenesis in that region. The dynamics of AEWs can be described in a potential vorticity (PV) framework. The important impact of latent heat release by cloud processes is captured in this framework by the diabatic generation of PV anomalies. This paper introduces an innovative approach for the identification and tracking of PV structures within AEWs. By employing AEW tracking and computing the wave phase of each point within the AEW domain using a Hilbert transform, we are able to effectively identify and collect 3-D PV structures associated with specific AEWs. To facilitate a climatological analysis, performed here over the months of June to October from 2002 to 2022, these structures are subsequently characterized by low-dimensional descriptors, including their location, intensity, and orientation. Our climatological analysis reveals the seasonal evolution and the structural attributes of PV anomalies within AEWs over the study domain. PV feature locations closely align with the African easterly jet's latitudinal shift during the summer season. Analysis of the mean pressure level of the 3-D PV structures shows a remarkable shift during their life cycle, indicating deep moist convection characteristics over land and more shallow convection characteristics over the ocean. On average, PV features identified within AEW troughs tilt downshear over land and equatorward over the ocean. The trough-centered analysis reveals distinct differences between satellite-estimated and model-predicted rainfall. Agreement between the results of a more traditional composite analysis and our new feature analysis provides confidence in our feature approach as a novel diagnostic tool. The feature framework provides a low-dimensional representation of the PV structure of AEWs, which facilitates future statistical analyses of the relation of this structure to, for example, tropical cyclogenesis or the predictability of tropical rainfall. [ABSTRACT FROM AUTHOR]

From a passive satellite remote sensing point of view, the richest set of information on aerosol properties can be obtained from instruments that measure both intensity and polarization of backscattered sunlight at multiple wavelengths and multiple viewing angles for one ground pixel. However, it is challenging to exploit this information at a global scale because complex algorithms are needed with many fit parameters (aerosol and land/ocean reflection), based on online radiative transfer models. So far, two such algorithms have demonstrated this capability at a global scale: the Generalized Retrieval of Atmosphere and Surface Properties (GRASP) algorithm and the Remote sensing of Trace gas and Aerosol Products (RemoTAP) algorithm. In this paper, we present a detailed comparison of the most recent versions of RemoTAP and GRASP. We evaluate both algorithms for synthetic observations, for real PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Science coupled with Observations from a Lidar) observations against AERONET (Aerosol Robotic Network) for common pixels, and for global PARASOL retrievals for the year 2008. For the aerosol optical depth (AOD) over land, both algorithms show a root mean square error (RMSE) of 0.10 (at 550 nm). For single scattering albedo (SSA), both algorithms show a good performance in terms of RMSE (0.04), but RemoTAP has a smaller bias (0.002) compared to GRASP (0.021). For the Ångström exponent (AE), GRASP has a smaller RMSE (0.367) than RemoTAP (0.387), mainly caused by a small overestimate of AE at low values (large particles). Over ocean both algorithms perform very well. For AOD, RemoTAP has an RMSE of 0.057 and GRASP an even smaller RMSE of 0.047. For AE, the RMSEs of RemoTAP and GRASP are 0.285 and 0.224, respectively. Based on the AERONET comparison, we conclude that both algorithms show very similar overall performance, where both algorithms have stronger and weaker points. For the global data products, we find a root mean square difference (RMSD) between RemoTAP and GRASP AOD of 0.12 and 0.038 over land and ocean, respectively. The largest differences occur over the biomass burning region in equatorial Africa. The global mean values are virtually unbiased with respect to each other. For AE the RMSD between RemoTAP and GRASP is 0.33 over land and 0.23 over ocean. For SSA, we find much better agreement over land (bias = - 0.01, RMSD = 0.043 for retrievals with AOD > 0.2) than over ocean (bias = 0.053, RMSD = 0.074). As expected, the differences increase towards low AOD, over both land and ocean. We also compared the GRASP and RemoTAP AOD and AE products against MODIS. For AOD over land, the agreement of either GRASP or RemoTAP with MODIS is worse than the agreement between the two PARASOL algorithms themselves. Over ocean, the agreement is very similar among the three products for AOD. For AE, the agreement between GRASP and RemoTAP is much better than the agreement of both products with MODIS. The agreement of the latest product versions with each other and with AERONET improved significantly compared to the previous version of the global products of GRASP and RemoTAP. The results demonstrate that the dedicated effort in algorithm development for multi-angle polarimetric (MAP) aerosol retrievals still leads to substantial improvement of the resulting aerosol products, and this is still an ongoing process. [ABSTRACT FROM AUTHOR]

A key goal of the Paris Agreement (PA) is to reach net-zero greenhouse gas (GHG) emissions by 2050 globally, which requires mitigation efforts from all countries. Africa's rapidly growing population and gross domestic product (GDP) make this continent important for GHG emission trends. In this paper, we study the emissions of carbon dioxide (CO 2), methane (CH 4) and nitrous oxide (N 2 O) in Africa over 3 decades (1990–2018). We compare bottom-up (BU) approaches, including United Nations Convention Framework on Climate Change (UNFCCC) national inventories, FAO, PRIMAP-hist, process-based ecosystem models for CO 2 fluxes in the land use, land use change and forestry (LULUCF) sector and global atmospheric inversions. For inversions, we applied different methods to separate anthropogenic CH 4 emissions. The BU inventories show that, over the decade 2010–2018, fewer than 10 countries represented more than 75 % of African fossil CO 2 emissions. With a mean of 1373 Mt CO 2 yr -1 , total African fossil CO 2 emissions over 2010–2018 represent only 4 % of global fossil emissions. However, these emissions grew by +34% from 1990–1999 to 2000–2009 and by +31% from 2000–2009 to 2010–2018, which represents more than a doubling in 30 years. This growth rate is more than 2 times faster than the global growth rate of fossil CO 2 emissions. The anthropogenic emissions of CH 4 grew by 5 % from 1990–1999 to 2000–2009 and by 14.8 % from 2000–2009 to 2010–2018. The N 2 O emissions grew by 19.5 % from 1990–1999 to 2000–2009 and by 20.8 % from 2000–2009 to 2010–2018. When using the mean of the estimates from UNFCCC reports (including the land use sector) with corrections from outliers, Africa was a mean source of greenhouse gases of 262221863239 Mt CO 2 eq. yr -1 from all BU estimates (the subscript and superscript indicate min–max range uncertainties) and of +263717615873 Mt CO 2 eq. yr -1 from top-down (TD) methods during their overlap period from 2001 to 2017. Although the mean values are consistent, the range of TD estimates is larger than the one of the BU estimates, indicating that sparse atmospheric observations and transport model errors do not allow us to use inversions to reduce the uncertainty in BU estimates. The main source of uncertainty comes from CO 2 fluxes in the LULUCF sector, for which the spread across inversions is larger than 50 %, especially in central Africa. Moreover, estimates from national UNFCCC communications differ widely depending on whether the large sinks in a few countries are corrected to more plausible values using more recent national sources following the methodology of Grassi et al. (2022). The medians of CH 4 emissions from inversions based on satellite retrievals and surface station networks are consistent with each other within 2 % at the continental scale. The inversion ensemble also provides consistent estimates of anthropogenic CH 4 emissions with BU inventories such as PRIMAP-hist. For N 2 O, inversions systematically show higher emissions than inventories, on average about 4.5 times more than PRIMAP-hist, either because natural N 2 O sources cannot be separated accurately from anthropogenic ones in inversions or because BU estimates ignore indirect emissions and underestimate emission factors. Future improvements can be expected thanks to a denser network of monitoring atmospheric concentrations. This study helps to introduce methods to enhance the scope of use of various published datasets and allows us to compute budgets thanks to recombinations of those data products. Our results allow us to understand uncertainty and trends in emissions and removals in a region of the world where few observations exist and where most inventories are based on default IPCC guideline values. The results can therefore serve as a support tool for the Global Stocktake (GST) of the Paris Agreement. The referenced datasets related to the figures are available at 10.5281/zenodo.7347077 (Mostefaoui et al., 2022). [ABSTRACT FROM AUTHOR]

The extensive terrestrial ecosystems of tropical Africa are a significant store of carbon, and play a key but uncertain role in the atmospheric budgets of carbon dioxide and methane. As ground-based observations in the tropics are scarce compared with other parts of the world, recent studies have instead made use of satellite observations assimilated into atmospheric chemistry and transport models to conclude that methane emissions from this geographical region have increased since 2010 as a result of increased wetland extent, accounting for up to a third of global methane growth, and that the tropical Africa region dominates net carbon emission across the tropics. These studies rely critically on the accuracy of satellite datasets such as those from OCO-2, GOSAT, and Sentinel-5P TROPOMI, along with results from atmospheric transport models, over a geographical region where there are few independent data to test the robustness of published results. In this paper we present the first ground-based observations of greenhouse gas column concentrations over East Africa, obtained using a portable Bruker EM27/SUN FTIR spectrometer during a deployment covering the first few months of 2020 in Jinja, Uganda. We operated the instrument near-autonomously by way of an automated weatherproof enclosure, and observed total atmospheric column concentrations of the greenhouse gases carbon dioxide and methane, as well as carbon monoxide, a useful proxy for emissions from incomplete combustion processes in the region. We discuss the performance of the combined enclosure and spectrometer system that we deployed in Jinja to obtain this data, and show comparisons of our ground-based observations with satellite datasets from OCO-2 and OCO-3 for carbon dioxide, and Sentinel-5P TROPOMI for methane and carbon monoxide, whilst also comparing our results with concentration data from the GEOS-Chem and CAMS atmospheric inversions that provide a means of increasing spatial and temporal coverage where satellite data are not available. For our measurement period, we find statistically significant differences at the 95% confidence level between the EM27/SUN and OCO-2 XCO2 (OCO-2 lower by a mean of 1.20ppm, standard deviation 1.05ppm), and between the EM27/SUN and Sentinel-5P XCO (Sentinel-5P lower by a mean of 3.68ppb, standard deviation 7.00ppb), whilst we found that the differ-ences between the EM27/SUN and OCO-3 XCO2 (OCO-3 lower by a mean of 1.15ppm, standard deviation 1.61ppm), and between the EM27/SUN and Sentinel-5P XCH4 (Sentinel-5P lower by a mean of 8.33ppb, standard deviation 10.5ppb), were not statistically significant. With regards to the model comparisons, we also see statistically significant differences between the EM27/SUN and a global GEOS-Chem inversion for XCO2 (GEOS-Chem lower by a mean of 0.35ppm, standard deviation 1.08ppm), between the EM27/SUN and a high-resolution GEOS-Chem inversion for XCH4 (GEOS-Chem lower by a mean of 3.80ppb, standard deviation 12.5ppb), and between the EM27/SUN and CAMS global analysis XCO (CAMS lower by a mean of 11.7ppb, standard deviation 8.94ppb). Our results demonstrate the value of ground-based observations of total column concentrations, and show that the combined EM27/SUN and enclosure system employed would be suitable for acquisition of the longer-term observations needed to rigorously evaluate satellite observations and model calculations over tropical Africa. [ABSTRACT FROM AUTHOR]

Tropical Africa and the North Atlantic Ocean are significantly influenced by African Easterly Waves (AEWs), which play a fundamental role in tropical rainfall and cyclogenesis in that region. The dynamics of AEWs can be described in a PV framework and redistribution of PV by latent heat release links PV to the important cloud and rain processes within the waves. This paper introduces an innovative approach for a comprehensive identification and tracking of potential vorticity (PV) structures within AEWs. By employing AEW tracking and computing the wave phase of each point within the AEW domain using a Hilbert transform, we are able to effectively identify and collect 3-D PV structures associated with specific AEWs. To facilitate a climatological analysis, these structures are subsequently characterized by low-dimensional descriptors, including spatial information, intensity, and geometric approximations. A climatological analysis reveals the seasonal evolution and the structural attributes of PV anomalies within AEWs over the study domain. PV feature locations closely align with the African Easterly Jet's latitudinal shift during the summer season. Analysis of the mean pressure level of the 3-D PV structures shows a remarkable shift during their life-cycle, indicating deep moist convection characteristics over land, and more shallow convection characteristics over the ocean. Both, composite data centered around identified AEW troughs and statistical analysis of main axes agree on an downshear tilt of the PV feature over land, and a tilt to the south over the ocean. The trough-centered analysis reveals distinct differences between satellite-estimated and model-predicted rainfall. The agreement between the results of the composite analysis and the feature analysis provides confidence in our feature approach as a novel diagnostic tool. The low-dimensional representation of PV features enables the research on further statistical analyses, for example the relationship of these features with tropical cyclogenesis or as predictor for rainfall in the tropics. [ABSTRACT FROM AUTHOR]

From a passive satellite remote sensing point-of-view, the richest set of information on aerosol properties can be obtained from instruments that measure both intensity and polarization of back- scattered sun light at multiple wavelengths and multiple viewing angles for one ground pixel. However, it is challenging to exploit this information at a global scale because complex algorithms are needed with many fit parameters (aerosol and land/ocean reflection), based on online radiative transfer 5 models. So far, two of such algorithms have demonstrated capability at a global scale: the Generalized Retrieval of Atmosphere and Surface Properties (GRASP) algorithm and the Remote Sensing of Trace gas and Aerosol Products (RemoTAP) algorithm. In this paper, we present a detailed comparison of the most recent versions of RemoTAP and GRASP. We evaluate both algorithms for synthetic observations, for real PARASOL observations against AERONET for common pixels, and for global PARASOL retrievals for the year 2008. Both RemoTAP and GRASP show good agreement against AERONET. For the Aerosol 10 Optical Depth (AOD) over land, both algorithms show a Root Mean Square Error (RMSE) of 0.10 (at 550 nm). For Single Scattering Albedo (SSA), both algorithms show a good performance in terms of RMSE ( 0.04) but RemoTAP has a smaller bias (0.002) compared to GRASP (0.021). For Angstrom Exponent (AE), GRASP has a smaller RMSE (0.367) than RemoTAP (0.387), mainly caused by a small overestimate of AE at low values (large particles). Over ocean both algorithms perform very well. For AOD, RemoTAP has an RMSE of 0.057 and GRASP an even smaller RMSE of 0.047. For AE, the RMSE 15 of RemoTAP and GRASP are 0.285 and 0.224, respectively. Based on the AERONET comparison, we conclude that both algorithms show very similar overall performance, where both algorithms have stronger and weaker points. For the global data products, we find a Root Mean Square Difference (RMSD) between RemoTAP and GRASP AOD of 0.12 and 0.038 over land and ocean, respectively. The largest differences occur over the biomass burning region in equatorial Africa. The global mean values are virtually unbiased with respect to each other. For AE the RMSD between RemoTAP and GRASP is 0.33 20 over land and 0.23 over ocean. For SSA, we find good agreement over land (RMSD=0.043) for retrievals with AOD > 0.2. Over ocean the agreement is poor with a bias of 0.053 (where RemoTAP retrieves higher SSA) and an RMSD of 0.074. As expected, the differences increase towards low AOD, both over land and ocean. We also compared the GRASP and RemoTAP AOD and AE products against MODIS. For AOD over land, the agreement of either GRASP or RemoTAP with MODIS is worse than the agreement between the 2 PARASOL algorithms themselves. Over ocean, the agreement is very similar among 25 the 3 products for AOD. For AE, the agreement between GRASP and RemoTAP is much better than the agreement of both products with MODIS. Overall, the good agreement between RemoTAP and GRASP, and between the individual algorithms with AERONET, demonstrates high fidelity of both data products for PARASOL. The agreement of the latest product versions with each other and with AERONET improved significantly compared to the previous version of the global products of GRASP and RemoTAP. The results demonstrate that dedicated effort on algorithm development for MAP aerosol retrievals still leads 30 to substantial improvement of the resulting aerosol products and this is still an ongoing process. [ABSTRACT FROM AUTHOR]

A key goal of the Paris Agreement (PA) is to reach net-zero Greenhouse Gasses (GHG) emissions by 2050 globally, which requires mitigation efforts from all countries. Africa's rapidly growing population and GDP makes this continent important for GHG emission trends. In this paper, we study the emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in Africa over three decades (1990-2018). We compare bottom-up approaches including UNFCCC national inventories, FAO, PRIMAP-hist, process-based ecosystem models for CO2 fluxes in the Land Use, Land Use Change and Forestry (LULUCF) sector, and global atmospheric inversions. Our database is available from Zenodo at: https://doi.org/10.5281/zenodo.7347077 (Mostefaoui et al., 2022). For inversions, we applied different methods to separate anthropogenic CH4 emissions. The bottom-up (BU) inventories show that over the decade 2010-2018, less than ten countries represented more than 75% of African fossil CO2 emissions. With a mean of 1373 MtCO2 yr-1, total African fossil CO2 emissions over 2010-2018 represent only 4% of global fossil emissions. Yet, these emissions grew by +34% from 1990-1999 to 2000-2009 and by +31% over 2000-2009 to 2010-2018, more than doubling in 30 years. This growth rate is more than twice faster than the global growth rate of fossil CO2 emissions. The anthropogenic emissions of CH4 grew by 5% from 1990-1999 to 2000-2009 and by 14.8% from 2000-2009 to 2010-2018. The N2O emissions grew by 19.5% from 1990-1999 to 2000-2009; and by 20.8% from 2000-2009 to 2010-2018. When using the mean of estimates from UNFCCC reports (including the land use sector), with corrections from outliers, Africa was a mean source of greenhouse gasses of +2622 $%&' ($() MtCO2e yr-1 from all bottom-up estimates (sub- and superscript indicating min-max range uncertainties), and of +2637%,'% -&,(MtCO2e yr-1 from top-down methods, during their overlap period from 2001 to 2017. Although the mean values are consistent, the range of top-down estimates is larger than the one of bottom up, indicating that sparse atmospheric observations and transport model errors do not allow us to use inversions to reduce the uncertainty of bottom-up estimates. A main source of uncertainty comes from CO2 fluxes in the land-use sector (LULUCF) for which the spread across inversions is larger than 50%, especially in Central Africa. Moreover, estimates from national UNFCCC communications differ widely depending on whether the large sinks in a few countries are corrected to more plausible values using more recent national sources following the methodology of Grassi et al. (2022) The median of CH4 emissions from inversions based on satellite retrievals and in situ surface networks are consistent with each other within 2% at continental scale. The inversion ensemble also provides consistent estimates of anthropogenic CH4 emissions with bottom-up inventories such as PRIMAP-hist. For N2O, inversions systematically show higher emissions than inventories, on average about 4.5 times more than PRIMAP-hist, either because natural N2O sources cannot be separated accurately from anthropogenic ones in inversions, or because bottom-up estimates ignore indirect emissions and under-estimate emission factors. Future improvements can be expected thanks to a denser network for monitoring atmospheric concentrations. This study helps to introduce methods to enhance the scope of use of various published datasets and allows to compute budgets thanks to recombinations those data products. Our results allow to understand uncertainty and trends of emissions and removals in a region of the world where few observations exist and most inventories are based on default IPCC guidelines values. The results can therefore serve as a support tool for the Global Stocktake (GST) of the Paris Agreement. The referenced datasets related to figures are available at: https://doi.org/10.5281/zenodo.7347077 (Mostefaoui et al., 2022). [ABSTRACT FROM AUTHOR]

Deforestation is associated with a decrease in slope stability through the alteration of hydrological and geotechnical conditions. As such, deforestation increases landslide activity over short, decadal timescales. However, over longer timescales (0.1–10 Myr) the location and timing of landsliding is controlled by the interaction between uplift and fluvial incision. Yet, the interaction between (human-induced) deforestation and landscape evolution has hitherto not been explicitly considered. We address this issue in the North Tanganyika–Kivu rift region (East African Rift). In recent decades, the regional population has grown exponentially, and the associated expansion of cultivated and urban land has resulted in widespread deforestation. In the past 11 Myr, active continental rifting and tectonic processes have forged two parallel mountainous rift shoulders that are continuously rejuvenated (i.e., actively incised) through knickpoint retreat, enforcing topographic steepening. In order to link deforestation and rejuvenation to landslide erosion, we compiled an inventory of nearly 8000 recent shallow landslides in © Google Earth imagery from 2000–2019. To accurately calculate landslide erosion rates, we developed a new methodology to remediate inventory biases linked to the spatial and temporal inconsistency of this satellite imagery. Moreover, to account for the impact of rock strength on both landslide occurrence and knickpoint retreat, we limit our analysis to rock types with threshold angles of 24–28 ∘. Rejuvenated landscapes were defined as the areas draining towards Lake Kivu or Lake Tanganyika and downstream of retreating knickpoints. We find that shallow landslide erosion rates in these rejuvenated landscapes are roughly 40 % higher than in the surrounding relict landscapes. In contrast, we find that slope exerts a stronger control on landslide erosion in relict landscapes. These two results are reconciled by the observation that landslide erosion generally increases with slope gradient and that the relief is on average steeper in rejuvenated landscapes. The weaker effect of slope steepness on landslide erosion rates in the rejuvenated landscapes could be the result of three factors: the absence of earthquake-induced landslide events in our landslide inventory, a thinner regolith mantle, and a drier climate. More frequent extreme rainfall events in the relict landscapes, and the presence of a thicker regolith, may explain a stronger landslide response to deforestation compared to rejuvenated landscapes. Overall, deforestation initiates a landslide peak that lasts approximately 15 years and increases landslide erosion by a factor 2 to 8. Eventually, landslide erosion in deforested land falls back to a level similar to that observed under forest conditions, most likely due to the depletion of the most unstable regolith. Landslides are not only more abundant in rejuvenated landscapes but are also smaller in size, which may again be a consequence of a thinner regolith mantle and/or seismic activity that fractures the bedrock and reduces the minimal critical area for slope failure. With this paper, we highlight the importance of considering the geomorphological context when studying the impact of recent land use changes on landslide activity. [ABSTRACT FROM AUTHOR]

The Nonhydrostatic ICosahedral Atmospheric Model (NICAM), a global model with an icosahedral grid system, has been under development for nearly two decades. This paper describes NICAM16-S, the latest stable version of NICAM (NICAM.16), modified for the Coupled Model Intercomparison Project Phase 6, High Resolution Model Intercomparison Project (HighResMIP). Major updates of NICAM.12, a previous version used for climate simulations, included updates of the cloud microphysics scheme and land surface model, introduction of natural and anthropogenic aerosols and a subgrid-scale orographic gravity wave drag scheme, and improvement of the coupling between the cloud microphysics and the radiation schemes. External forcings were updated to follow the protocol of the HighResMIP. A series of short-term sensitivity experiments were performed to determine and understand the impacts of these various model updates on the simulated mean states. The NICAM16-S simulations demonstrated improvements in the ice water content, high cloud amount, surface air temperature over the Arctic region, location and strength of zonal mean subtropical jet, and shortwave radiation over Africa and South Asia. Some long-standing biases, such as the double intertropical convergence zone and smaller low cloud amount, still exist or are even worse in some cases, suggesting further necessity for understanding their mechanisms, upgrading schemes and parameter settings, and enhancing horizontal and vertical resolutions. [ABSTRACT FROM AUTHOR]

Evidence for sea-level change during and around Marine Isotopic Stage 5e (ca. 125 ka) in southern Africa derives from a wide variety of geomorphic and sedimentological sea-level indicators, supported in the past 2 decades by absolute chronological control. In addition to these proxies, data provided by both terrestrial (dune sediments and archaeological remains) and marine (lagoonal and nearshore littoral sediments) limiting points provide broad constraints on sea level. Here, we review publications describing these data points. Using the framework of the World Atlas of Last Interglacial Shorelines, we insert in a standardized database all the elements needed to assess former paleo relative sea level, and the chronological constraints associated with them (including uncertainties). Overall, we reviewed 69 studies, from which we extracted 35 sea-level indicators and 25 limiting points. As far as age attribution is concerned, early dating of molluscs and whole-rock beachrock samples using U-Series allowed ating of several sea-level indicators during the 1980s but the more widespread application of Optically Stimulated Luminescence dating since 2004 has yielded many more (and more accurate) dates from several sites. This has helped resolve the nature and timing of MIS5e shorelines and has the potential to further elucidate the apparent presence of two or more sea-level peaks at several South African sites during this interval. The standardized sea-level database presented in this paper is the first of its kind for this region. Future research should be directed to improve the stratigraphic description of LIG shorelines and to obtain better dating, high-accuracy elevation measurements with better palaeo-RSL interpretation. [ABSTRACT FROM AUTHOR]

NICAM, a nonhydrostatic global atmospheric model with an icosahedral grid system, has been developed for nearly two decades. This paper describes NICAM16-S, the latest stable version of NICAM (NICAM.16) modified for Coupled Model Intercomparison Project Phase 6 (CMIP6). Major updates from NICAM.12, a previous version used for climate simulations, include updates of a cloud microphysics scheme and a land model, an introduction of natural and anthropogenic aerosols and a subgrid-scale orographic gravity wave drag, and improvement of coupling between cloud microphysics and radiation schemes. External forcings were updated to follow a protocol of CMIP6 High Resolution Model Intercomparison Project (HighResMIP). A series of short-term sensitivity experiments were performed to check and understand impacts of the model updates on the simulated mean states. Improvements in the ice water content, the high cloud amounts, the surface air temperature over the Arctic region, the location and the strength of zonal mean subtropical jet, and shortwave radiation over the Africa and the South Asia were found in the NICAM16-S simulations. Some long-standing biases such as the double intertropical convergence zone and smaller low cloud amounts still exist or even worsen in some cases, suggesting further necessity for understanding their mechanisms and upgrading schemes and/or their parameter settings as well as for enhancing horizontal and vertical resolutions. [ABSTRACT FROM AUTHOR]

Rate of change of TEC (ROT) and its index (ROTI) are considered a good proxy to characterize the occurrence of ionospheric plasma irregularities like those observed after sunset at low latitudes. SBASs (satellite-based augmentation systems) are civil aviation systems that provide wide-area or regional improvement to single-frequency satellite navigation using GNSS (Global Navigation Satellite System) constellations. Plasma irregularities in the path of the GNSS signal after sunset cause severe phase fluctuations and loss of locks of the signals in GNSS receiver at low-latitude regions. ROTI is used in this paper to characterize plasma density ionospheric irregularities in central-western Africa under nominal and disturbed conditions and identified some days of irregularity inhibition. A specific low-latitude algorithm is used to emulate potential possible SBAS message using real GNSS data in the western African low-latitude region. The performance of a possible SBAS operation in the region under different ionospheric conditions is analysed. These conditions include effects of geomagnetic disturbed periods when SBAS performance appears to be enhanced due to ionospheric irregularity inhibition. The results of this paper could contribute to a feasibility assessment of a European Geostationary Navigation Overlay System-based SBAS in the sub-Saharan African region. [ABSTRACT FROM AUTHOR]

The retrieval of geophysical parameters is increasingly dependent on synergistic use of satellite instruments. More sophisticated parameters can be retrieved and the accuracy of retrievals can be increased when more information is combined. In this paper, a synergistic application of OMI/Aura and MODIS/Aqua Level 1B reflectances is described, enabling the retrieval of the aerosol direct radiative effect (DRE) over clouds using the differential aerosol absorption (DAA) technique. This technique was first developed for reflectances from SCIAMACHY/Envisat, which had the unique capability of measuring contiguous radiances from the ultraviolet (UV) at 240 nm to 1750 nm in the shortwave-infrared (SWIR), at a moderate spectral resolution of 0.2–1.5 nm. However, the spatial resolution and global coverage of SCIAMACHY was limited, and Envisat stopped delivering data in 2012. In order to continue the DRE data retrieval, reflectances from OMI and MODIS, flying in formation, were combined from the UV to the SWIR. This resulted in reflectances at a limited but sufficient spectral resolution, available at the OMI pixel grid, which have a much higher spatial resolution and coverage than SCIAMACHY. The combined reflectance spectra allow the retrieval of cloud microphysical parameters in the SWIR, and the subsequent retrieval of aerosol DRE over cloud scenes using the DAA technique. The new aerosol DRE over clouds dataset from OMI/MODIS is compared to the SCIAMACHY dataset for the period 2006–2009, showing a very high correlation. The average aerosol DRE over clouds in August 2006 was 31.5 Wm−2 with a standard deviation of 16 Wm−2. The maximum daily averaged DRE from OMI/MODIS in August 2006 was 75.6 ± 13 Wm−2. Over the Atlantic Ocean, the OMI/MODIS DRE dataset is related to AOT measurements over Ascension Island in 2016, showing the transport of smoke all the way from its source region in Africa over the Atlantic to Ascension and beyond. [ABSTRACT FROM AUTHOR]

The objective of this paper is to present a new data set of bias-corrected CMIP5 global climate models (GCMs) daily data over Africa. This dataset was obtained in using the Cumulative Distribution Function Transform (CDF-t) method, a method that has been applied on several regions and contexts but never on Africa. Here CDF-t is used over the period 1950–2099 combining historical runs and climate change scenarios on 6 variables, precipitation, mean near-surface air temperature, near-surface maximum air temperature, near-surface minimum air temperature, surface down-welling shortwave radiation, and wind speed, which are critical variables for agricultural purposes. Evaluation of the results is carried out over West Africa on a list of priority users-based metrics that was discussed and selected with stakeholders and on simulated yield using a crop model simulating maize growth. Bias-corrected GCMs data are compared with another available dataset of bias-corrected GCMs, and the impact of three different reference datasets on bias-corrections is also examined in details. CDF-t is very effective in removing the biases and in reducing the high inter-GCMs scattering. Differences with other bias-corrected GCMs data are mainly due to the differences between the reference datasets. This is particular true for surface down-welling shortwave radiation, which has impacts in terms of simulated maize yields. Projections of future yields over West Africa have quite different levels, depending on bias-correction method used, but they all show a similar relative decreasing trend over the 21st century. [ABSTRACT FROM AUTHOR]

Movements within early Gondwana dispersal are poorly constrained and there is uncertainty about the position and structural style of the continent-ocean transition and the timing and directions of the rifting and earliest seafloor spreading phases. In this paper, we present a combined structural interpretation of multichannel reflection seismic profiles from offshore northern Mozambique (East Africa), and the conjugate Riiser Larsen Sea (Antarctica). We find similar structural styles at the margins of both basins. At certain positions at the foot of the continental slope, the basement is intensely deformed and fractured, a structural style very untypical for rifted continental margins. Sediments overlying the deformation zone are deformed and reveal toplap and onlap geometries, implying a post-breakup deformation phase. We propose this unique deformation zone as tie-point for Gondwana reconstructions. Accordingly, we interpret the western flank of Gunnerus Ridge, Antarctica as a transform margin, similar to Davie Ridge, East Africa, implying that they are conjugate features. We consider it likely that a first phase of rifting and early seafloor spreading in NE-SW direction was subsequently replaced by a N-S directed transform deformation phase, overprinting the continent-ocean transition. This change of the spreading directions from NW-SE to N-S is suggested to have occurred by the Late Middle Jurassic, around magnetic anomaly M38n.2n (~ 164 Ma). We suggest that the second phase of deformation corresponds to the strike-slip movement of Madagascar and Antarctica and discuss implications for Gondwana breakup. [ABSTRACT FROM AUTHOR]

A resurrected interest in agriculture has brought in its wake growing interest in smallholders in the global South by scholars, companies, governments and development agencies alike. While non-governmental organisations and development agencies see the potential to reduce poverty, companies look upon smallholder agriculture as a widely untapped resource for the sourcing of crops and as a sales market for agricultural inputs. While the important role of large corporate buyers of agricultural produce as lead firms in value chains is often discussed and emphasised, the power of providers of technology and agricultural inputs is being rather neglected. In this paper, we analyse two case studies of technology and input providers in agricultural value chains and their role in smallholder inclusion with the aim of finding out how such companies impact the governance of the value chains. To do so we combine insights from the value chain literature with the concept of framing/overflowing. [ABSTRACT FROM AUTHOR]

This paper describes a computationally efficient framework for uncertainty studies in global and regional climate change. In this framework, the Massachusetts Institute of Technology (MIT) Integrated Global System Model (IGSM), an integrated assessment model that couples an Earth system model of intermediate complexity to a human activity model, is linked to the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM). Since the MIT IGSM-CAM framework (version 1.0) incorporates a human activity model, it is possible to analyze uncertainties in emissions resulting from both uncertainties in the underlying socio-economic characteristics of the economic model and in the choice of climate-related policies. Another major feature is the flexibility to vary key climate parameters controlling the climate system response to changes in greenhouse gases and aerosols concentrations, e.g., climate sensitivity, ocean heat uptake rate, and strength of the aerosol forcing. The IGSM-CAM is not only able to realistically simulate the present-day mean climate and the observed trends at the global and continental scale, but it also simulates ENSO variability with realistic time scales, seasonality and patterns of SST anomalies, albeit with stronger magnitudes than observed. The IGSM-CAM shares the same general strengths and limitations as the Coupled Model Intercomparison Project Phase 3 (CMIP3) models in simulating present-day annual mean surface temperature and precipitation. Over land, the IGSM-CAM shows similar biases to the NCAR Community Climate System Model (CCSM) version 3, which shares the same atmospheric model. This study also presents 21st century simulations based on two emissions scenarios (unconstrained scenario and stabilization scenario at 660 ppm CO2-equivalent) similar to, respectively, the Representative Concentration Pathways RCP8.5 and RCP4.5 scenarios, and three sets of climate parameters. Results of the simulations with the chosen climate parameters provide a good approximation for the median, and the 5th and 95th percentiles of the probability distribution of 21st century changes in global mean surface air temperature from previous work with the IGSM. Because the IGSM-CAM framework only considers one particular climate model, it cannot be used to assess the structural modeling uncertainty arising from differences in the parameterization suites of climate models. However, comparison of the IGSM-CAM projections with simulations of 31 CMIP5 models under the RCP4.5 and RCP8.5 scenarios show that the range of warming at the continental scale shows very good agreement between the two ensemble simulations, except over Antarctica, where the IGSM-CAM overestimates the warming. This demonstrates that by sampling the climate system response, the IGSM-CAM, even though it relies on one single climate model, can essentially reproduce the range of future continental warming simulated by more than 30 different models. Precipitation changes projected in the IGSM-CAM simulations and the CMIP5 multi-model ensemble both display a large uncertainty at the continental scale. The two ensemble simulations show good agreement over Asia and Europe. However, the ranges of precipitation changes do not overlap - but display similar size - over Africa and South America, two continents where models generally show little agreement in the sign of precipitation changes and where CCSM3 tends to be an outlier. Overall, the IGSM-CAM provides an efficient and consistent framework to explore the large uncertainty in future projections of global and regional climate change associated with uncertainty in the climate response and projected emissions. [ABSTRACT FROM AUTHOR]

This paper addresses various characteristic features associated with the hydration of the tropical upper troposphere and lower stratosphere (UTLS) in association with the boreal monsoonal convective activity occurring over three different tropical regions viz. Asian region, American region and African region. Analysis of water vapor mixing ratio (WVMR) data obtained from AURA MLS (v3.3), ISCCP D1 cloud top pressure data and outgoing long-wave radiation data (OLR) from NOAA reanalysis has brought out two significant results. Firstly, high altitude clouds and high WVMR regions are mostly associated with the low OLR region. Convection over Asian region is very deep and spread over a large geographical area as compared to African or American region. Magnitude of WVMR in the pressure range of 261.0-146.8 hPa is observed to be higher over the Asian region, whereas, close to the tropopause level (+ 100 hPa) it is comparable or more over the American region as compared to Asian and African regions. Secondly, the vertical ascent rate of water vapour obtained from AURA MLS data suggest that convection associated transport might have dominated up to 146.8-121.2 hPa in addition to slow large scale diabatic transport, which appears to be prominent above the pressure range of 100-82.5 hPa. Within the pressure levels of 121.2 to 82.5 hPa, the influence of convective transport appears to be gradually decreasing. However, there are other possible processes like ice sublimation or cirrus jumping which could contribute to the hydration of the tropical lower stratosphere. Present analysis has, thus, brought out the significance of convection in water vapour transport and distribution in the tropical UTLS. Another interesting feature which is observed is the anomalous increase in temperature during boreal winters (November-April) over all three convective regions. Such phenomenon is only observed within the pressure range of 100.0-261.0 hPa; however it is relatively weaker for levels >177.8 hPa. [ABSTRACT FROM AUTHOR]

The Paris Agreement of COP21 set a goal of holding global average temperature increases to below 2 °C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5 °C. This is particularly relevant for the African context where temperatures are likely to warm faster than the global average and where the magnitude of change will be regionally heterogeneous. Most studies that provide information over Africa under specific global warming levels have used data from global models, however global models poorly resolve local scale forcing (e.g. topography) nor the internal climate variability of a region. Although downscaling using regional climate models can address these issues, we found only one paper that had used downscaled data for GWL studies over Africa. During 2018 the CORDEX-Africa campaign investigated the impact of 1.5 and 2 degrees of global warming over many regions of sub-Saharan Africa and compiled the results for a special issue of nine papers in ERL. This paper reports on some of the key regional findings of the analysis of 25 CORDEX downscalings, including the impact of the extra 0.5 degrees of warming between 1.5 and 2 degrees on particular extremes and the differences noted between the driving GCMs and downscaled results. We also briefly discuss the impact of the papers in the IPCC SR15 and their contribution to the development of adaptation and mitigation policies. [ABSTRACT FROM AUTHOR]

Weather and climate services (WCS) are expected to improve the capacity of Africa's agricultural sector to manage the risks of climate variability and change. Despite this, a lack of evidence regarding WCS prevents a realistic analysis of whether services are delivering on their potential. This paper reviews 65 studies that have evaluated outcomes and/or impacts of agricultural WCS in Africa, highlighting areas that have received relatively more attention, as well as persistent gaps. While the evaluation of WCS outcomes is relatively straightforward, estimates of the number of people who access and use of these services are uneven (covering a small number of communities in 23 of 54 African countries) and highly variable (with access ranges from ~2-86%, depending on the service and the population). Meanwhile, 22 documents estimate the impact of WCS with respect to yields and/or income. Developed with a variety of methods, these estimates are also wide ranging (some users lose, while others experience up to 66% marginal gains) and illustrate how impact is conditioned on a number of characteristics of the service, the user, and the context in which both operate. This study uses lessons developed through this review to develop a "learning agenda," or evidence-building roadmap, to establish priorities that can guide future work to generate evidence that can improve the design, delivery, and impact of agricultural WCS in Africa. Priorities learning areas include: broadening our view of potential users and uses of WCS; filling of geographic and demographic gaps; and quantifying the extent to which "good practice" leads to improved outcomes and impacts. [ABSTRACT FROM AUTHOR]

Due to changes in economics, technology, population, agriculture, and climate, there have been significant changes in terms of fires around the, and their impacts on air pollution, climate, and society. In specific, we are interested to know more about how these effects play out, from source to sink, on the atmospheric loadings and associated impacts of aerosols and some specific co-emitted trace gasses. Fires produce plumes of aerosols which are first lofted to a significant height, and then advected near and far to impact the larger atmosphere. We know from measurements that the absolute magnitude of smoke from fires is currently vastly underestimated. In this paper, we demonstrate a new database of emissions, formed in a uniform way, using 4 different remotely sensed measurements, coupled with three types of models. We then work to demonstrate what has worked well and why, as well as outline what still needs to be improved. We combine existing measurements of NO2 columns, AOD, CO, vertical distribution, with models at Global Scale, Mesoscale, and plume scale, into a single product. This product yields a spatially and temporally variable distribution of the emissions from global fires of aerosols and some trace gasses. Furthermore, we draw a set of relationships based on the physics and chemistry: making a connection from the emissions amounts and the heat tsources to the ultimate vertical structure and magnitude. The point is not only to be able to force a model to match the measurements, but to build a system through which we can mode deeply understand and constrain these relationships. This will slowly allow us to understand to the point where we can improve the model predictions analytically, as well as to perform massive uncertainty calculations. Given the changes occurring over the past decade, this is essential. We draw three conclusions. First, that the total underestimate of BC emissions is more than 40 percent to 70 percent of the present total global emissions, a more than doublig in magnitude. Second, that there are significant missing sources with a time scale from 3 to 6 weeks in duration, annually occurring in mountainous regions of Africa and Asia which are not present in existing databases. Thirdly, we demonstrate that a larger fraction of total emissions is lofted high up, and hence the impact on the atmosphere is larger than presently assumed. We make some initial conclusions in terms of these relationships over Africa, Southeast Asia, and the High Arctic, and show that they are different in each of these critical areas. We then try to explain a bit as to why this is the case, and build towards a more comprehensive and physically based relationship for future work. [ABSTRACT FROM AUTHOR]

Under the present environmental conditions, the Nile Valley acts as a 'natural' route between Africa and Eurasia, and is often considered as a corridor of dispersal out of and back into Africa in the past. This paper intends to address the role played by the Nile Valley at the end of the Pleistocene (25-15ka) in the context of modern human dispersals, from an archaeological perspective. Genetic studies based on both modern and ancient DNA indicate pre-Holocene dispersals 'back into Africa' as well as genetic interactions between modern humans across Africa and the Levant. During the Last Glacial, the lowering, or even desiccation of major eastern African lakes, including Lake Victoria, reduced the White Nile to a highly seasonal river, depriving the main Nile from its most important tributary. This had deep consequences, although still debated, on the behaviour of the main Nile and the landscape around the Nile Delta. Despite this shift to more arid conditions, there is abundant evidence for human occupation in the Egyptian Nile Valley and in the arid zone of the Southern Levant at this time. Here, we use lithic data to characterise human occupations in the Nile Valley and test for potential technical diffusion between the Nile Valley and the southern Levant. This study failed to highlight compelling evidence for contacts between the two regions at the end of the Pleistocene. Combining available geological, palaeoenvironmental, anthropological, genetic and archaeological data, we discuss problems encountered when trying to reconcile results from different fields, current limitations of the available data and research perspectives to further address the role of the Nile Valley as a corridor of dispersal or environmental refugium at the end of the Pleistocene. [ABSTRACT FROM AUTHOR]

As a result of the world-wide attention that global climate change is receiving, laudable attempts are made to increase the share of renewable energies in electricity production around the globe. In addition to climate change issue, the need for bringing electricity to millions of people who live in the least-developed parts of the world act as a stimulus to the development of renewable energy share of electricity generation. Despite all efforts, a considerable number of people in rural and remote areas of Africa are still striving to gain access to energy. This issue has been partly addressed by the introduction and development of off-the-grids (stand-alone power systems) using renewable energy sources, including wind. The key aim of this research is to study wind power as a source of electrification in Africa. Renewable energy supply is very vulnerable to hydro-climatic variability and extreme hydro-meteorological events, and wind energy is no exception. In particular, low wind speeds throughout Africa pose a real challenge to electricity generation from wind. Using hourly estimates of wind speed provided by ERA5 (the latest climate reanalysis produced by ECMWF), this paper evaluates spatial and temporal variability in daily wind power production across Africa, for a 18-year period (from 2000 to 2017), in terms of the capacity factor of wind (the average wind power generated each day divided by the rated peak power), and the minimum required wind speed for power production (useable wind speed). Furthermore, by calculating the low percentile values of daily capacity factors, we gain understanding of the ability of wind turbines to achieve a given level of service quality, and put an economic perspective on wind power production. [ABSTRACT FROM AUTHOR]

The Neogene and Quaternary are characterized by enormous changes in global climate and environments, including global cooling and the establishment of northern high-latitude glaciers. These changes reshaped global ecosystems, including the emergence of tropical dry forests and savannahs that are found in Africa today, which in turn may have influenced the evolution of humans and their ancestors. However, despite decades of research we lack long, continuous, well-resolved records of tropical climate, ecosystem changes, and surface processes necessary to understand their interactions and influences on evolutionary processes. Lake Tanganyika, Africa, contains the most continuous, long continental climate record from the mid-Miocene (∼10 Ma) to the present anywhere in the tropics and has long been recognized as a top-priority site for scientific drilling. The lake is surrounded by the Miombo woodlands, part of the largest dry tropical biome on Earth. Lake Tanganyika also harbors incredibly diverse endemic biota and an entirely unexplored deep microbial biosphere, and it provides textbook examples of rift segmentation, fault behavior, and associated surface processes. To evaluate the interdisciplinary scientific opportunities that an ICDP drilling program at Lake Tanganyika could offer, more than 70 scientists representing 12 countries and a variety of scientific disciplines met in Dar es Salaam, Tanzania, in June 2019. The team developed key research objectives in basin evolution, source-to-sink sedimentology, organismal evolution, geomicrobiology, paleoclimatology, paleolimnology, terrestrial paleoecology, paleoanthropology, and geochronology to be addressed through scientific drilling on Lake Tanganyika. They also identified drilling targets and strategies, logistical challenges, and education and capacity building programs to be carried out through the project. Participants concluded that a drilling program at Lake Tanganyika would produce the first continuous Miocene–present record from the tropics, transforming our understanding of global environmental change, the environmental context of human origins in Africa, and providing a detailed window into the dynamics, tempo and mode of biological diversification and adaptive radiations. [ABSTRACT FROM AUTHOR]