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The South American Monsoon System Summary July 2008-June 2009

The South American Monsoon System Summary July 2008-June 2009. Update prepared by Climate Prediction Center / NCEP June 2009. For more information, visit: http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/American_Monsoons. Outline. Onset phase Mature phase Decay phase

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The South American Monsoon System Summary July 2008-June 2009

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  1. The South American Monsoon System SummaryJuly 2008-June 2009 Update prepared by Climate Prediction Center / NCEP June 2009 For more information, visit:http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/American_Monsoons

  2. Outline • Onset phase • Mature phase • Decay phase • Long-Term Departures from Average • Summary

  3. Precipitation Climatology ONSET DATES

  4. Precipitation Departures: Onset Phase (Sep-Nov 2008) During September-November 2008 rainfall was below average over most of South America, with rainfall deficits exceeding 210 mm in portions of the southern Amazon, southwestern Brazil, northern Colombia and portions of Venezuela. Much above-average rainfall was observed over southern Colombia, and portions of southern Brazil.

  5. Tropical Pacific and Atlantic SST Anomalies (Sep-Nov 2008) During September–November 2008, equatorial SSTs were below average from just west of the date line (180°) to the west coast of South America. In the Atlantic, SSTs were above average from northern South America to the west African coast.

  6. Precipitation Departures: Mature Phase (Dec 08-Feb 09) During December 2008-February 2009 rainfall was below average over most of Brazil and Argentina (red oval), with rainfall deficits greater than 270 mm in many areas. Much above-average rainfall was observed over the northern and northwestern Amazon basin.

  7. Tropical Pacific and Atlantic SST Anomalies (Dec08-Feb09) During December 2008–February 2009, equatorial SSTs were below average from just west of the date line (180°) to the west coast of South America, with largest negative anomalies evident in the central Pacific. This pattern is consistent with La Niña conditions. Over the Atlantic SSTs were below average near the west African coast and above average near the equator and along the coast of Angola.

  8. Precipitation Climatology END DATES

  9. Precipitation Departures: Decay Phase (Mar-May 09) During March-May 2009 rainfall was below average over northern South America, southwestern and southern Brazil, Paraguay, eastern Argentina and portions of Uruguay. Deficits greater than 270 mm were observed over portions of northern South America and northeastern Argentina. Much above-average rainfall was observed over the eastern Amazon basin and northeastern Brazil.

  10. Tropical Pacific and Atlantic SST Anomalies (Mar-May 2009) During March-May 2009, equatorial SSTs were near average in the Pacific Ocean, as La Niña conditions weakened. Over the Atlantic, SSTs were below average north of the equator from the mouth of the Amazon eastward to the west African coast and above average south of the equator from Northeast Brazil eastward to the coast of Angola. This dipole pattern of anomalous SSTs often accompanies heavy rainfall over Northeast Brazil, as was observed during this period.

  11. Atlantic Dipole Pattern Low-level westerly wind anomalies are consistent with positive SST anomalies along the equator and a southward shift in the ITCZ and heavy rainfall in Northeast Brazil. Suppressed convection Enhanced convection Atlantic Dipole

  12. Time 200-hPa Velocity Potential Anomalies (5°S-5°N) Positive anomalies (brown shading) indicate unfavorable conditions for precipitation Negative anomalies (green shading) indicate favorable conditions for precipitation • From mid-March to early May, eastward propagating velocity potential anomalies indicated moderate-to-strong MJO activity. • The active phase of the MJO was in the South American sector (phase 8) during the end of March and again in the beginning of May, contributing to excessive rainfall and flooding over northeastern Brazil during those periods. Longitude

  13. BP Rainfall over northeastern Brazil (MAM) • Rainfall totals over northeast Brazil during 11 March-6 June 2009 were above-average (surpluses of 210-600 mm). Note the increased rainfall at the end of March and again at the beginning of May, associated with the convectively active phase of the MJO.

  14. Precipitation Departures: July 2008-June 2009 During 1 July 2008-10 June 2009 rainfall was below average over southwestern and southern Brazil, most of Paraguay, eastern Argentina and Uruguay. Above-average rainfall was observed over the northern Amazon basin and northeastern Brazil. NOTE: The number of station data over Colombia and Venezuela is very limited, so the large deficits in rainfall over those regions may not be real.

  15. Precipitation Anomaly Patterns during La Niña Episodes over Brazil 2008-2009 The pattern of anomalous precipitation over Brazil for the water year (July 2008-June 2009, figure above) is consistent with the La-Nina composite.Wetter than average to the north and drier than average to the south. From Silva et al., 2007

  16. Summary • The rainy season onset (SON) was delayed over the southern Amazon, central and southeastern Brazil. This resulted in large rainfall deficits (greater than 150 mm) in many areas during September-November 2008. • During the mature phase of the monsoon (DJF) rainfall was below average over central and southern Brazil and most of Argentina, and above average over the northern Amazon Basin, which are features consistent with La-Nina conditions in the tropical Pacific. • During the decay phase of the rainy season (MAM), much above-average rainfall was observed over northeastern Brazil, consistent with La Niña conditions in the tropical Pacific and the Atlantic SST dipole pattern, which contributed to an intensification and southward displacement of the Atlantic Intertropical Convergence Zone (ITCZ). Another factor contributing to the rainfall anomalies in Northeast Brazil during MAM was the active Madden-Julian Oscillation (MJO). • In general, the pattern of rainfall departures for the water year (July 2008-June 2009) is similar to the composite for La Niña episodes.

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