Subseasonal deterministic prediction skill of low-level geopotential height affecting southern Africa

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  • 1 South African Weather Service, Pretoria, South Africa
  • 2 Department of Geography, Geoinformatics and Meteorology, University of Pretoria, Pretoria, South Africa
  • 3 Global Change Institute, University of the Witwatersrand, Johannesburg, South Africa
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Abstract

The NCEP CFSv2 and ECMWF hindcasts are used to explore the deterministic subseasonal predictability of the 850 hPa circulation of a large domain over the Atlantic and Indian Oceans that is relevant to the weather and climate of the southern African region. For NCEP CFSv2, twelve years of hindcasts, starting on 1 January 1999 and initialized daily for four ensemble members up to 31 December 2010 are verified against ERA-Interim reanalysis data. For ECMWF, 20 years of hindcasts (1995-2014), initialized once a month for all the months of the year are employed in a parallel analysis to investigate the predictability of the 850 hPa circulation. The ensemble mean for 7-day moving averages are used to assess the prediction skill for all the start dates in each month of the year, with a focus on the start dates in each month that are representative of the week 3 and 4 hindcasts. The correlation between the anomaly patterns over the study domain shows skill over persistence up into the week 3 hindcasts for some months. The spatial distribution of the correlation between the anomaly patterns show skill over persistence to notably reduce over the domain by week 3. A prominent area where prediction skill survives the longest, occur over central South America and the adjacent Atlantic Ocean.

Corresponding author: Christien J. Engelbrecht, email: christien.engelbrecht@weathersa.co.za

Abstract

The NCEP CFSv2 and ECMWF hindcasts are used to explore the deterministic subseasonal predictability of the 850 hPa circulation of a large domain over the Atlantic and Indian Oceans that is relevant to the weather and climate of the southern African region. For NCEP CFSv2, twelve years of hindcasts, starting on 1 January 1999 and initialized daily for four ensemble members up to 31 December 2010 are verified against ERA-Interim reanalysis data. For ECMWF, 20 years of hindcasts (1995-2014), initialized once a month for all the months of the year are employed in a parallel analysis to investigate the predictability of the 850 hPa circulation. The ensemble mean for 7-day moving averages are used to assess the prediction skill for all the start dates in each month of the year, with a focus on the start dates in each month that are representative of the week 3 and 4 hindcasts. The correlation between the anomaly patterns over the study domain shows skill over persistence up into the week 3 hindcasts for some months. The spatial distribution of the correlation between the anomaly patterns show skill over persistence to notably reduce over the domain by week 3. A prominent area where prediction skill survives the longest, occur over central South America and the adjacent Atlantic Ocean.

Corresponding author: Christien J. Engelbrecht, email: christien.engelbrecht@weathersa.co.za
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