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OLR standard deviation

THE SACZ PERSISTENCE, FORM INTENSITY, INTRASEASONAL TO INTERANNUAL VARIATIONS AND IMPACTS ON EXTREME PRECIPITATION EVENTS

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OLR standard deviation

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  1. THE SACZ PERSISTENCE, FORM INTENSITY, INTRASEASONAL TO INTERANNUAL VARIATIONS AND IMPACTS ON EXTREME PRECIPITATION EVENTS Leila M. V. Carvalho1,21IAG, University of São Paulo, BrazilCharles Jones2ICESS- University of California, Santa BarbaraBrant LiebmannNOAA-CIRES, Climate Diagnostic Center, Boulder, CO

  2. OLR standard deviation The South Atlantic Convergence Zone (SACZ)

  3. OBJETIVES: • Objectively identify the SACZ INTENSITY, PERSISTENCE AND FORM (OCEANIC vs CONTINENTAL) using daily OLR data. • Investigate the relationships between intraseasonal variations (10-90 days) and the SACZ spatial and temporal characteristics. • Discuss the implication of the SACZ characteristics to the occurrence of daily extreme precipitation over Brazil. • Examine the role of the MJO activity in modulating the SACZ persistence. • Investigate the SACZ interannual variations, relationships with ENSO phases and implications to daily extreme precipitation over Brazil.

  4. METHODOLOGY • * Determination of the SACZ Characteristics • Contiguous regions of OLR  200W m-2 are identified in daily data (OLR200) (DJF 1979/1980 - 1999/2000) • Three regions are defined to search for patterns of convective activity: AMAZON, COASTAL and OCEAN. All selected OLR200 intercepted the COASTAL area. • FACTOR ANALYSIS for discrimination of events according to the intensity (weak or intense) and form (oceanic or continental) of deep convection in the SACZ.Input SPATIAL PROPERTIES OF OLR200. *Carvalho, LMV, C. Jones and B. Liebmann, 2002: Extreme precipitation events in southeastern South America and large-scale convective patterns in the South Atlantic Convergence Zone, J. Climate, 2377-2394.

  5. EXAMPLE OF OLR200 PROPERTIES Eccentricity: Minor axis/major axis Fraction AMAZON Fraction COASTAL • Total Area • Internal Variance • Minimum OLR • Fraction of Min OLR Fraction OCEAN MASCOTTE Algorithm: Carvalho and Jones (2001): J. Appl. Meteor. 1683-1701

  6. CONTINENTAL: Fact 2>0 Intensity Form INTENSE : Fact 1 <0 N=1750 (DJF) WEAK : Fact 1 >0 OCEANIC: Fact 2<0

  7. SACZ CATEGORIES • INTENSE : Factor-1  25th quartile • WEAK :Factor-1  75th quartile • OCEANIC : Factor-2  25th quartile • CONTINENTAL :Factor-1  75th quartile • PERSISTENCE: sequence of days in a given category • SACZ AND INTRASEASONAL ACTIVITY • composites of OLR, low-level (850hPa) winds and geopotential height (200hPa) from filtered data (10-90 days). • MJO ACTIVITY • EOF analysis ofOLR anomalies (10-90 days) (DJF) • Selection of events PC1 (PC2)  1 ( -1) DJF standard deviation

  8. OLR Daily Anomalies (W m-2) Intense SACZ OLR Daily Anomalies (W m-2) Weak SACZ OLR Daily Anomalies (W m-2) Oceanic SACZ OLR Daily Anomalies (W m-2) Continental SACZ Figure 3

  9. SACZ Composites 10-90 days anomalies westerlies easterlies

  10. Carvalho, L. M. V., C. Jones, and M. A. F. Silva Dias, 2002: Intraseasonal large-scale circulations and mesoscale convective activity in Tropical South America during the TRMM-LBA campaign. J. Geoph. Res. (in Press). Jones, C. , and L. M. V. Carvalho, 2002: Active and break phases in the South American Monsoon System. J. Climate, 15, 905-914.

  11. TIME-INTERVAL BETWEEN PERSISTENT EVENTS Outliers : data point values  1.5 times the interquartile range. Extremes: data point values  3.0 times the interquartile range.

  12. INTERANNUAL VARIABILITY Extracted from CPC achieves

  13. MJO ACTIVITY

  14. THE MJO ACTIVITY AND SACZ PERSISTENT CATEGORIES

  15. Frequency of extremes : SACZ Intense Frequency of extremes : SACZ Weak Frequency  5% (in green). Frequency  15% (yellow) DJF 95th percentile (mm/day) Frequency of extremes : SACZ Oceanic Frequency of extremes: SACZ Continental

  16. PC2 <0 PC2>0 PC1 <0 PC1>0

  17. CONCLUSIONS: SACZ and intraseasonal variations • The proposed methodology objectively characterizes the SACZ intensity and spatial properties. • There is evidence of a mid-latitude wave train modulating continental/oceanic SACZ categories • Persistence of SACZ categories have similar distribution. • The median time interval between persistent categories is similar and equal to 6 days, although more variability is observed for intense SACZ. • The ratio frequency of intense/weak SACZ with persistence ≥ 3 days increases during La Nina years, the opposite occurring during El Nino and Neutral years. • The spatial distribution of extreme precipitation events (≥ 95th percentile) varies with SACZ categories • MJO occurrences seem to modulate intense SACZ persistence  • MJO have an important role for the occurrence of extreme precipitation over central-east and northeast Brazil.Importance of monitoring MJO activity to improve rainfall predictability in the South America Monsoon System.

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