Post on 05-Jan-2016
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THE SACZ PERSISTENCE, FORM INTENSITY, INTRASEASONAL TO INTERANNUAL VARIATIONS
AND IMPACTS ON EXTREME PRECIPITATION EVENTS
Leila M. V. CarvalhoLeila M. V. Carvalho1,21,2
11IAG, University of São Paulo, BrazilIAG, University of São Paulo, Brazil
Charles JonesCharles Jones 22ICESS- University of California, Santa BarbaraICESS- University of California, Santa Barbara
Brant LiebmannBrant LiebmannNOAA-CIRES, Climate Diagnostic Center, Boulder, CONOAA-CIRES, Climate Diagnostic Center, Boulder, CO
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OLR standard deviation
The South Atlantic Convergence Zone (SACZ)
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OBJETIVES: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.
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* Determination of the SACZ Characteristics* 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.
METHODOLOGY
*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.
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Eccentricity:Minor axis/major axis
• Total Area
• Internal Variance
• Minimum OLR
• Fraction of Min OLR
Fraction AMAZON
Fraction COASTAL
Fraction OCEAN
EXAMPLE OF OLR200 PROPERTIES
MASCOTTE Algorithm:Carvalho and Jones (2001): J. Appl. Meteor. 1683-1701
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INTENSE : Fact 1 <0
WEAK : Fact 1 >0
CONTINENTAL:Fact 2>0
OCEANIC: Fact 2<0
Variable Fact-1 Fact-2
AREA -.82 .03
Ecc .01 .77
OLRmin .89 -.06
%OLRmin .87 -.01
VarOLR -.70 .04
% Coastal .82 .07
% Amazon -.57 .42
% Ocean .00 -.83Eigenvalues 3.73 1.48%Variance 47 19
Intensity Form
N=1750 (DJF)
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MJO ACTIVITY
EOF analysis of OLR anomalies (10-90 days) (DJF) Selection of events PC1 (PC2) 1 ( -1) DJF standard deviation
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).
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OLR Daily Anomalies (W m-2) Intense SACZ
OLR Daily Anomalies (W m-2) Oceanic SACZ
OLR Daily Anomalies (W m-2) Weak SACZ
OLR Daily Anomalies (W m-2) Continental SACZ
Figure 3
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SACZ Composites 10-90 days anomalies
westerlies
easterlies
10Carvalho, 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.
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0
510
15
2025
30
3540
45
2 3 4 5 6 7 8 9 10 More
Persistence (days)
Fre
qu
en
cy
(%
)
INTENSE WEAK
Total : 97 INTENSE 106 WEAK
05
101520
253035
4045
2 3 4 5 6 7 8 9 10 More
Persistence (days)
Fre
qu
en
cy
(%
)
OCEANIC CONTINENTAL
Total : 108 OCEANIC 106 CONTINENTAL
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PERSISTENCE GREATER OR EQUAL 3 DAYS
Median 25%-75% Non-Outlier Min-Max Outliers ExtremesINTENSE
WEAKOCEAN
CONTINENT
-5
0
5
10
15
20
25
30
35
40
45IN
TE
RV
AL
BE
TW
EE
N E
VE
NT
S (
DA
YS
)
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.
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Onset of the episode: persistence >= 3 days
3946
6154
0
10
20
30
40
50
60
70
intense w eak
Re
lati
ve
fre
qu
en
cy
(%
)
OCEANIC
CONTINENTAL
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Persistence >= 3 days
0
1
2
3
4
5
6
7
79
81
83
85
87
89
91
93
95
97
99
DJF season
INTENSE WEAK
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INTERANNUAL VARIABILITY
23
1922
32
13
29
0
5
10
15
20
25
30
35
El Nino La Nina Neutral
Nu
mb
er
of
ev
en
ts
INTENSE
WEAK
Persistence >= 3 days
5 years
9 years7 years
Extracted from CPC achieves
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MJO ACTIVITY
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0
10
20
30
40
50
60
>=2 >=3 >=4 >=5
Persistence threshold (days)
Fre
qu
en
cy
(%
)
PC2-
PC1-
OTHERS
PC2+
PC1+
OCEANIC
0
10
20
30
40
50
60
>=2 >=3 >=4 >=5
Persistence threshold (days)
Fre
qu
en
cy
(%
)
PC2-
PC1-
OTHERS
PC2+
PC1+
INTENSE
0
10
20
30
40
50
60
>=2 >=3 >=4 >=5
Persistence threshold (days)
Fre
qu
en
cy
(%
)
PC2-
PC1-
OTHERS
PC2+
PC1+
WEAK
0
10
20
30
40
50
60
>=2 >=3 >=4 >=5
Persistence threshold (days)
Fre
qu
en
cy
(%
)
PC2-
PC1-
OTHERS
PC2+
PC1+
CONTINENTAL
THE MJO ACTIVITY AND SACZ PERSISTENT CATEGORIES
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Frequency of extremes : SACZ Intense
Frequency of extremes: SACZ Continental
DJF 95th percentile (mm/day)
Frequency of extremes : SACZ Weak
Frequency of extremes : SACZ Oceanic
Frequency 5%(in green). Frequency
15% (yellow)
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PC2 <0
PC1 <0
PC2>0
PC1>0
20
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CONCLUSIONS: SACZ and intraseasonal variationsCONCLUSIONS: 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..