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Browsing by Author "Beraki, Asmerom F"

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Dynamical seasonal climate prediction using an ocean-atmosphere coupled climate model developed in partnership between South Africa and the IRI

Author: Beraki, Asmerom F ; De Witt, DG ; Landman, WA ; Olivier, C Date: Feb 2014 The recent increase in availability of high-performance computing (HPC) resources in South Africa allowed the development of an ocean–atmosphere coupled general circulation model (OAGCM). The ECHAM4.5-South African Weather Service (SAWS) ... Read more
ENSO forecasts in South Africa

Author: Landman, WA ; Beraki, Asmerom F Date: Nov 2015 The SST prediction systems currently being used at the Council for Scientific and Industrial Research (CSIR) and the South African Weather Service (SAWS) are presented. In particular, the skill of these systems to predict Niño3.4 SST and how ... Read more
The impact of different sea-surface temperature prediction scenarios on Southern African seasonal climate forecast skill

Author: Landman, WA ; Beraki, Asmerom F ; DeWitt, D Date: Dec 2009 Retro-active forecasts produced at a 1-month lead-time by the ECHAM4.5 AGCM are statistically downscaled to South African district rainfall totals for the austral mid-summer season of December to February. The AGCM is forced with SST forecasts ... Read more
Impact of lower stratospheric ozone on seasonal prediction systems

Author: Mathole, K ; Ndarana, T ; Beraki, Asmerom F ; Landman, WA Date: 2014 We conducted a comparison of trends in lower stratospheric temperatures and summer zonal wind fields based on 27 years of reanalysis data and output from hindcast simulations using a coupled ocean atmospheric general circulation model (OAGCM). ... Read more
Multi-model forecast skill for mid-summer rainfall over southern Africa

Author: Landman, WA ; Beraki, Asmerom F Date: Feb 2012 Southern African December-January-February (DJF) probabilistic rainfall forecast skill is assessed over a 22-year retroactive test period (1980/1981 to 2001/2002) by considering multi-model ensembles consisting of downscaled forecasts from ... Read more
Ocean-atmosphere coupled climate model development at SAWS: description and diagnosis

Author: Beraki, Asmerom F ; DeWitt, D ; Landman, WA ; Olivier, C Date: Sep 2011 This paper introduces the South African Weather Service's coupled ocean-atmosphere model. The paper also demonstrates the advances made in configuring an operational coupled ocean-atmosphere model in South Africa for seasonal forecast production. ... Read more
On the comparison between seasonal predictive skill of global circulation models: Coupled versus uncoupled

Author: Beraki, Asmerom F ; Landman, WA ; DeWitt, D Date: Nov 2015 The study compares one- and two-tiered forecasting systems as represented by the South African Weather Service Coupled Model and its atmosphere-only version. In this comparative framework, the main difference between these global climate ... Read more
Operational seasonal forecast system development in South Africa

Author: Landman, WA ; Beraki, Asmerom F Date: Sep 2011 The development of operational seasonal prediction as a science in South Africa is explained, as well as the current forecast systems and how they may further evolve. Read more
Predictability of the intra-seasonal rainfall characteristics variables over South Africa

Author: Phakula, S ; Landman, WA ; Beraki, Asmerom F Date: Sep 2015 Aspects of seasonal forecast skill of the SCM and ECHAM4.5 general circulation model (GCMs) are assessed over South Africa. The GCMs output is configured to predict low and high number of rainfall days at South African Weather Service stations ... Read more
Projected changes in tropical cyclones over the South West Indian Ocean under different extents of global

Author: Muthige, Mavhungu S ; Malherbe, Johan ; Engelbrecht, Francois A ; Grab, S ; Beraki, Asmerom F ; Maisha, Thizwilondi R ; Van der Merwe, Jacobus H Date: Apr 2018 The Paris Agreement achieved in December 2015 established that the signatory countries should pursue to hold the increase in global average temperature to below 2°C relative to the preindustrial period and to strive to limit the temperature ... Read more
Recent advances in operational seasonal forecasting in South Africa: Models, infrastructure and networks

Author: Landman, WA ; Beraki, Asmerom F Date: Nov 2011 The various institutions involved with seasonal forecast development and production are discussed. New modelling approaches and the establishment of infrastructures to improve forecast dissemination are discussed. Read more
River-flow predictions for the South African mid-summer using a coupled general circulation model

Author: Olivier, C ; Landman, WA ; Beraki, Asmerom F Date: Sep 2013 There are limited sources of streamflow data available in South Africa. These include simulated streamflow for catchments across South Africa and measured river-flow at specific rivers around the country. Given that a number of studies has ... Read more
The role of the southern annular mode in dynamical global coupled model

Author: Beraki, Asmerom F ; Landman, WA Date: Sep 2013 The interannual and decadal variability of the Southern Annual Mode (SAM) was examined in the ECHAM 4.5-MOM3-SA ocean-atmosphere coupled general circulation model (OAGCM). The analysis placed emphasis on the behavior of the SAM when its ... Read more
Seasonal rainfall prediction skill over South Africa: one- versus two-tiered forecasting systems

Author: Landman, WA ; Dewitt, D ; Lee, D-E ; Beraki, Asmerom F ; Lotter, D Date: Apr 2012 Forecast performance by coupled ocean–atmosphere or one-tiered models predicting seasonal rainfall totals over South Africa is compared with forecasts produced by computationally less demanding two-tiered systems where prescribed sea surface ... Read more
South African mid-summer seasonal rainfall prediction performance by a coupled ocean-atmosphere model

Author: Landman, WA ; DeWitt, D ; Beraki, Asmerom F Date: Jan 2011 Estimation of the evolution of SST anomalies, which are often relatively predictable, and subsequently employing them in atmospheric general circulation models (AGCMs), provides means of generating forecasts of seasonal-average weather (Graham ... Read more
South African seasonal rainfall prediction performance by a coupled ocean-atmosphere model

Author: Landman, WA ; DeWitt, D ; Lee, D-E ; Beraki, Asmerom F ; Lotter, D Date: Dec 2010 Evidence is presented that coupled ocean-atmosphere models can already outscore computationally less expensive atmospheric models. However, if the atmospheric models are forced with highly skillful SST predictions, they may still be a very ... Read more
Southern hemisphere climate variability as represented by an ocean-atmosphere coupled model

Author: Beraki, Asmerom F ; Landman, WA ; DeWitt, D Date: Sep 2012 Southern Hemisphere (SH) climate variability has been the focus of several researchers (e.g., Wallace and Hsu, 1983). According to these early studies, the SH is characterized by quasistationary oscillations and zonally propagating waves in ... Read more
SST prediction methodologies and verification considerations for dynamical mid-summer rainfall forecasts for South Africa

Author: Landman, WA ; Beraki, Asmerom F ; DeWitt, D ; Lötter, D Date: Oct 2014 Seasonal-to-interannual hindcasts (re-forecasts) for December-January-February (DJF) produced at a 1-month lead-time by the ECHAM4.5 atmospheric general circulation model (AGCM) are verified after calibrating model output to DJF rainfall at ... Read more
Supercomputing for weather and climate modelling: convenience or necessity

Author: Landman, WA ; Beraki, Asmerom F ; Engelbrecht, F ; Landman, S Date: Dec 2009 Weather and climate modelling require dedicated computer infrastructure in order to generate high-resolution, large ensemble, various models with different configurations, etc. in order to optimise operational forecasts and climate projections. ... Read more

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