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OLR standard deviation

Analyzing the SACZ intensity, persistence, form, and impact on extreme precipitation events in Brazil. Examining intraseasonal to interannual variations and MJO activity. Discussing methodology, categorization of SACZ, and conclusions from the study.

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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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