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John G. Dwyer, Michela Biasutti, and Adam H. Sobel

( Fu and Wang 2004 ; Kitoh and Arakawa 1999 ). Despite this, given the observed SST and radiative forcings, AGCMs capture the annual precipitation anomalies over land and for the tropics overall, although there is some discrepancy over ocean ( Liu et al. 2012 ). Similar studies where the annual cycle of SST was modified or suppressed have been carried out to study the effect of SST on the Asian summer monsoon ( Shukla and Fennessy 1994 ), the equatorial Atlantic and Pacific ( Li and Philander 1997

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Thomas Engel, Andreas H. Fink, Peter Knippertz, Gregor Pante, and Jan Bliefernicht

–trough system, the former being located over Guinea and Sierra Leone. To the west of the trough, the 0600 UTC analysis shows enhanced lower-tropospheric wind shear of 10–20 m s −1 over northern Burkina Faso and westernmost Niger, but because of the early morning hours, CAPE is lower than 1000 J kg −1 ( Fig. 4b ). From this, we conclude that the convective invigoration must be related to synoptic forcing from the AEW that provided strong convergence and record amounts of moisture. Canonical squall lines

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Robert A. Clark III, Zachary L. Flamig, Humberto Vergara, Yang Hong, Jonathan J. Gourley, Daniel J. Mandl, Stuart Frye, Matthew Handy, and Maria Patterson

scales as part of the Global Hydrologic Prediction System ( Zhang et al. 2015 ). To this end, the model accepts precipitation forcing from the NASA Tropical Rainfall Measurement Mission 3B42V7 real-time (TRMM RT; Huffman et al. 2007 , 2010 ) and research products. More generally, gridded precipitation in the Environmental Systems Research Institute (ESRI) American Standard Code for Information Exchange (ASCII) or binary equivalent grid formats is also accepted. Later, CREST was used to forecast

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Kerry H. Cook and Edward K. Vizy

1. Introduction Precipitation distributions over tropical East Africa exhibit pronounced regional variations, and the seasonal cycle is complicated. In most regions there are two peak rainfall seasons that are nominally associated with solar-heating maxima in the equinox seasons, but topography, SST forcing, and teleconnections to the West African and Indian monsoon systems are among the other important factors influencing the timing and intensity of seasonal rainfall. The tropical East African

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Lisa Hannak, Peter Knippertz, Andreas H. Fink, Anke Kniffka, and Gregor Pante

; Paxian et al. 2016 ). Moreover, Marsham et al. (2013) and Birch et al. (2014) show that issues in the diurnal cycle of latent heating and cloud radiative forcing impact on the north–south pressure gradient and thus the northward advection of moisture from the south to the Sahel. One element of the WAM that has received relatively little attention so far is the extensive cover of low- and midlevel clouds over southern West Africa (SWA) during the peak summer monsoon from July to September (JAS

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Elinor R. Martin and Chris Thorncroft

AEW forcing; maintenance, including representation of the AEJ; and feedbacks with convection in the atmospheric component of the models. While Fig. 2 shows the biases in the multimodel ensemble mean, it is important to assess the spread of the models’ ability to simulate AEWs. This is illustrated by Taylor diagrams of the spatial distribution of JJAS EKE at 700 and 850 hPa over West Africa and the eastern Atlantic (dashed box in Fig. 1b ) in Fig. 3 . The reference dataset used is the

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Abdou L. Dieng, Saidou M. Sall, Laurence Eymard, Marion Leduc-Leballeur, and Alban Lazar

relatively cold waters (SST ranging between 25° and 26°C). Therefore, these unfavorable conditions could be responsible for the decay of the north-SLS in this zone. Although the south-SLS are evolving in better conditions (high humidity and greater SST), their mean trajectory suggests that they mainly propagate outside of the MDR, in the southern part, where the Coriolis force is less important. Thus, the absolute vorticity ( , where is the Coriolis parameter and is the relative vorticity) associated

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Rosalind Cornforth, Douglas J. Parker, Mariane Diop-Kane, Andreas H. Fink, Jean-Philippe Lafore, Arlene Laing, Ernest Afiesimama, Jim Caughey, Aida Diongue-Niang, Abdou Kassimou, Peter Lamb, Benjamin Lamptey, Zilore Mumba, Ifeanyi Nnodu, Jerome Omotosho, Steve Palmer, Patrick Parrish, Leon-Guy Razafindrakoto, Wassila Thiaw, Chris Thorncroft, and Adrian Tompkins

—coastal regions, central Africa, and the eastern Sahel as a source of intraseasonal variability affecting West Africa. Further study of the forcing by, and interactions with, midlatitude and equatorial waves, and the Indian monsoon. Extending research to other seasons, in particular, spring and the corresponding heat waves, and to the pre-onset of the monsoon. Coupling with the ocean, in particular, cold tongue development and its impact on the monsoon. More attention on radiation processes, clouds, and

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M. Issa Lélé, Lance M. Leslie, and Peter J. Lamb

Atlantic Ocean contributes the most to rainfall over western Sahel, whereas the Gulf of Guinea and the South Atlantic Ocean contribute the most over the central Sahel. Local evaporation is the second largest contributor to rainfall for both regions. Long et al. (2000) examine the large-scale forcing mechanisms in relation to initiation and maintenance of the Sahelian long-term drought. They analyzed rainfall, moisture flux, and vertical motion data and concluded that changes in the general circulation

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Mimi Stith, Alessandra Giannini, John del Corral, Susana Adamo, and Alex de Sherbinin

. , 2012 : Cereal yield response to conservation agriculture practices in drylands of West Africa: A quantitative synthesis . J. Arid Environ. , 78 , 13 – 25 , doi: 10.1016/j.jaridenv.2011.10.011 . Biasutti, M. , and Giannini A. , 2006 : Robust Sahel drying in response to late 20th century forcings . Geophys. Res. Lett. , 33 , L11706 , doi: 10.1029/2006GL026067 . Boserup, E. , 1965 : The Conditions of Agricultural Growth: The Economics of Agrarian Change under Population Pressure . Allen

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