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1950s and 1960s to persistent dry conditions in the 1970s and 1980s is, in magnitude and spatial extent, unparalleled globally in the instrumental record ( Nicholson 2000 ; Hulme 2001 ; Trenberth et al. 2007 ; Greene et al. 2009 ). During the early 1970s, meteorologists posited that the drying was the result of local human activity in a positive feedback loop between poor land use practices, land degradation, and atmospheric response ( Charney 1975 ). Predating acid rain and global warming, the
1950s and 1960s to persistent dry conditions in the 1970s and 1980s is, in magnitude and spatial extent, unparalleled globally in the instrumental record ( Nicholson 2000 ; Hulme 2001 ; Trenberth et al. 2007 ; Greene et al. 2009 ). During the early 1970s, meteorologists posited that the drying was the result of local human activity in a positive feedback loop between poor land use practices, land degradation, and atmospheric response ( Charney 1975 ). Predating acid rain and global warming, the
repetition every 6 days, leading to ~1–6 days between measurements in any location ( Torres et al. 2012 ). Furthermore, soil moisture data are available from reanalyses and LDAS. LDAS has uncoupled land surface schemes that assimilate multiple observations using optimal interpolation and other techniques in near–real time. These merged products produce the best spatial coverage and temporal resolution but have drawbacks such as inaccurately accounting for the uncertainty of each product, unbalanced
repetition every 6 days, leading to ~1–6 days between measurements in any location ( Torres et al. 2012 ). Furthermore, soil moisture data are available from reanalyses and LDAS. LDAS has uncoupled land surface schemes that assimilate multiple observations using optimal interpolation and other techniques in near–real time. These merged products produce the best spatial coverage and temporal resolution but have drawbacks such as inaccurately accounting for the uncertainty of each product, unbalanced
in the above calculations have key advantages for this investigation. For the NARR data these strengths include the fine spatial (32 km) and temporal (3 h) resolutions, the direct assimilation of precipitation and radiances, and use of an improved land surface model (e.g., Berbery et al. 2003 ; Ek et al. 2003 ; Mitchell et al. 2004a , b ; Shafran et al. 2004 ). Inclusion of direct precipitation assimilation in the NARR—which is not part of global reanalysis systems—was intended to increase
in the above calculations have key advantages for this investigation. For the NARR data these strengths include the fine spatial (32 km) and temporal (3 h) resolutions, the direct assimilation of precipitation and radiances, and use of an improved land surface model (e.g., Berbery et al. 2003 ; Ek et al. 2003 ; Mitchell et al. 2004a , b ; Shafran et al. 2004 ). Inclusion of direct precipitation assimilation in the NARR—which is not part of global reanalysis systems—was intended to increase
) Merged Analysis of Precipitation (CMAP; Xie and Arkin 1997 ) and the Global Precipitation Climatology Project (GPCP; Xie et al. 2003 ) satellite datasets also were used. Both the CMAP and GPCP datasets blend rain gauge observations and satellite estimations. They are gridded in 2.5° latitude × 2.5° longitude boxes and are available from 1979 to the present. Over land areas, the CMAP and the GPCP datasets were shown to have similar major precipitation patterns (e.g., Xie and Arkin 1997 ; Yin, et
) Merged Analysis of Precipitation (CMAP; Xie and Arkin 1997 ) and the Global Precipitation Climatology Project (GPCP; Xie et al. 2003 ) satellite datasets also were used. Both the CMAP and GPCP datasets blend rain gauge observations and satellite estimations. They are gridded in 2.5° latitude × 2.5° longitude boxes and are available from 1979 to the present. Over land areas, the CMAP and the GPCP datasets were shown to have similar major precipitation patterns (e.g., Xie and Arkin 1997 ; Yin, et
years, the number of spaceborne instruments collecting data available to Earth scientists has grown (e.g., Ungar et al. 2003 ; Friedl et al. 2002 ; Tapley et al. 2004 ). It is now feasible, even routine, to access estimates of precipitation, potential evapotranspiration, land use, land cover, topography, soil moisture, and other variables collected from space in a timely fashion. Moreover, these datasets are often available for free regardless of geopolitical boundaries. Multiple studies have
years, the number of spaceborne instruments collecting data available to Earth scientists has grown (e.g., Ungar et al. 2003 ; Friedl et al. 2002 ; Tapley et al. 2004 ). It is now feasible, even routine, to access estimates of precipitation, potential evapotranspiration, land use, land cover, topography, soil moisture, and other variables collected from space in a timely fashion. Moreover, these datasets are often available for free regardless of geopolitical boundaries. Multiple studies have
track vortices tracking southward after leaving the coast and leading to TC genesis. A recent study by Skinner and Diffenbaugh (2014) investigating future projections of AEW activity using phase 5 of the Coupled Model Intercomparison Project (CMIP5) output showed a significant increase in JJAS EKE activity over land in the northern track. However, as discussed, this track is not currently as effective for TC development as the southern track. Errors in the representation of TCs, AEWs, and
track vortices tracking southward after leaving the coast and leading to TC genesis. A recent study by Skinner and Diffenbaugh (2014) investigating future projections of AEW activity using phase 5 of the Coupled Model Intercomparison Project (CMIP5) output showed a significant increase in JJAS EKE activity over land in the northern track. However, as discussed, this track is not currently as effective for TC development as the southern track. Errors in the representation of TCs, AEWs, and
simulations were run for at least 10 years, sufficiently long to characterize the annual cycle of precipitation. The only change we made in the perturbed simulations was to alter either the mean or the annual cycle of SST. Land temperatures were free to adjust on their own and the atmospheric chemical composition was the same between simulations. We use two methods to calculate the seasonal characteristics of temperature and precipitation. The first is to Fourier transform data to directly obtain the
simulations were run for at least 10 years, sufficiently long to characterize the annual cycle of precipitation. The only change we made in the perturbed simulations was to alter either the mean or the annual cycle of SST. Land temperatures were free to adjust on their own and the atmospheric chemical composition was the same between simulations. We use two methods to calculate the seasonal characteristics of temperature and precipitation. The first is to Fourier transform data to directly obtain the
. 2011 ). Using diagnostic relationships developed in those studies, several other investigations further assessed the predictability of Ethiopian Belg ( Diro et al. 2008 ) and Kiremt ( Gissila et al. 2004 ; Block and Rajagopalan 2007 ; Korecha and Barnston 2007 ; Jury 2013 ; Nicholson 2014 ) seasonal rainfall. The possible role of land surface conditions for African rainfall was noted first by Charney (1975) and has been investigated in many subsequent studies (e.g., Charney et al. 1977
. 2011 ). Using diagnostic relationships developed in those studies, several other investigations further assessed the predictability of Ethiopian Belg ( Diro et al. 2008 ) and Kiremt ( Gissila et al. 2004 ; Block and Rajagopalan 2007 ; Korecha and Barnston 2007 ; Jury 2013 ; Nicholson 2014 ) seasonal rainfall. The possible role of land surface conditions for African rainfall was noted first by Charney (1975) and has been investigated in many subsequent studies (e.g., Charney et al. 1977
African domain. Observed precipitation is used to characterize the diurnal cycle, and atmospheric reanalyses are used to explore the physical processes that control it. The current understanding of the diurnal cycle of rainfall over West Africa is reviewed in section 2 . Observational and reanalysis datasets used in this study are described in section 3 . Results are presented in section 4 , and conclusions are summarized in section 5 . To further advance our understanding of how the diurnal cycle
African domain. Observed precipitation is used to characterize the diurnal cycle, and atmospheric reanalyses are used to explore the physical processes that control it. The current understanding of the diurnal cycle of rainfall over West Africa is reviewed in section 2 . Observational and reanalysis datasets used in this study are described in section 3 . Results are presented in section 4 , and conclusions are summarized in section 5 . To further advance our understanding of how the diurnal cycle
-lead forecasts of seasonal precipitation in Africa using CCA . Wea. Forecasting , 11 , 506 – 520 , doi: 10.1175/1520-0434(1996)011<0506:LLFOSP>2.0.CO;2 . Cane , M. A. , G. Eshel , and R. W. Buckland , 1994 : Forecasting Zimbabwean maize yield using eastern equatorial Pacific sea surface temperature . Nature , 370 , 204 – 205 , doi: 10.1038/370204a0 . Chen , M. , P. Xie , J. Janowiak , and P. A. Arkin , 2002 : Global land precipitation: A 50-yr analysis based on gauge observations
-lead forecasts of seasonal precipitation in Africa using CCA . Wea. Forecasting , 11 , 506 – 520 , doi: 10.1175/1520-0434(1996)011<0506:LLFOSP>2.0.CO;2 . Cane , M. A. , G. Eshel , and R. W. Buckland , 1994 : Forecasting Zimbabwean maize yield using eastern equatorial Pacific sea surface temperature . Nature , 370 , 204 – 205 , doi: 10.1038/370204a0 . Chen , M. , P. Xie , J. Janowiak , and P. A. Arkin , 2002 : Global land precipitation: A 50-yr analysis based on gauge observations
