charles jones and leila m. v. carvalho university of california santa barbara
DESCRIPTION
Changes in the Activity of the Madden-Julian Oscillation during 1958-2004. Charles Jones and Leila M. V. Carvalho University of California Santa Barbara. Extensively studied over the years but no comprehensive theory Behavior on time scales longer than interannual is unknown. Case to Case. - PowerPoint PPT PresentationTRANSCRIPT
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Charles Jones and Leila M. V. CarvalhoCharles Jones and Leila M. V. Carvalho
University of California Santa BarbaraUniversity of California Santa Barbara
Changes in the Activity of the Madden-Julian Changes in the Activity of the Madden-Julian
Oscillation during 1958-2004Oscillation during 1958-2004
Case to Case
Seasonal Variations
Interannual Variations
Long-term Behavior
Time scales
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Extensively studied over the years but no comprehensive theory
Behavior on time scales longer than interannual is unknown
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This Study
Are there linear trends in the activity of the MJO? (intensity
& number of events)
Does the MJO exhibit regimes of high and low activity?
Are there significant seasonal differences in the activity of
the MJO on time scales longer than interannual?
Note: MJO refers to summer and winter events
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Identification of MJO events
• NCEP/NCAR U200, U850 (1958-2004) 20-100 day anomalies
• OLR (1979-2004) 20-100 day anomaliesEOF analysis
• Summer domain: south Asian monsoon (Lawrence and Webster 2001) • Winter domain: Equatorial region (Kessler 2001)
Summer Winter
1979-2004 EOF (OLR)Covariance matrix PC1, PC2 (~20%) RPC1, RPC2 (~43%)
1958-2004 combined EOF (U200, U850)
Correlation matrixPC1, PC2 (~19%) PC1, PC2 (~40%)
• Event: amplitude PC1 exceeds 1 sigma
within 20 days PC2 exceeds 1 sigma
• Events registered at pentads in which PC1 exceed 1 sigma
• 1958-2004: 158 events (75 in summer; 83 in winter) (U200,U8500)
• 1979-2004: 90 events (49 summer; 41 winter)(OLR)
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• 158 events (1958-2004) identified with CEOF (U200, U850) (correlation matrix)
• Each bar represents an event registered at peak in PC1
• Amplitude is the variance (15S-15N; all longitudes) of eastward wavenumbers 1-6 20-100 day anomalies (Hendon et al. 1999)
MJO Events more frequent in some years than in other periods
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MJO Occurrences (1958-2004)
Low-Frequency diagram
• Consider XT, T=1, 3431 pentads, XT=1 event, XT= 0 no event
Does the MJO exhibit regimes of high and low activity?
• Define moving window SK and compute percentage of MJO events in SK: PK,T = MK,T / N where MK,T is number of events and N total number of events
• Similar for summer: PSK,T = MSK,T / NS where MSK,T is number of summer events and NS total number of summer events
• Similar for winter: PWK,T = MWK,T / NW where MWK,T is number of winter events and NW total number of winter events
• SK odd number and varied from smallest (1 pentad) to largest possible (3431 pentads)
SK
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0
1
2
3
1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 97 101 105 109 113 117
SK
Hypothetical Case: events evenly spaced in time
Low-frequency diagram
Cone of Influence
Cone
of In
fluen
ce
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Winter & Summer
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Mean MJO Low-frequency Variability
Overall
Summer
Winter
Mean PK,T
Mean PSK,T
Mean PWK,T
SK = 145 to 657 (1.98 to 9 years)
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Are regime changes different than random occurrences?
Monte Carlo simulations
Summer
• XT, XT=1 summer event, XT= 0 no event
• Randomize seasons 999 times
• Each batch:
• compute LF diagram
• mean RSK,T (SK =145 to 657 (1.98 to 9 years)
• correlation PSK,T and RSK,T
• Frequency distribution of correlation > Cr
• Same for winter
1% of time series with random events correlated with observed at 0.7 or higher (~50% or more of the observed variance in the mean LF MJO variability)
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Summary and Conclusions
o MJO exhibits substantial changes in regimes longer than interannual
o Two regimes of high activity (1974-1978, 1988-1992), and low activity (1981-1986).
o Markedly different changes in summer and winter activity
o Summer: increased from early 1960’s to mid 1970’s and decreased steadily until the 1990’s
o Winter: more regular changes with peaks in 1967, 1976 and 1989 and lows in 1971, 1983 and 1997.
o Changes in summer and winter MJO activity are statistically different from random occurrences
o There are positive linear trends in (1958-2004): o U200 amplitudes of summer and winter MJO events
o Number of summer MJO events
o Linear trends are not higher than random occurrences (5% level)
o Trends in U200 amplitudes of the MJO are consistent between EOF metric (this study) and equatorial zonal mean intraseasonal index (Slingo et. 1999)
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EOF - OLR
Summer Winter
i Separation
(i - i+1) Error
% Variance Separation
(i - i+1) Error
% Variance (Rotated)
1 8636.43 8746.24 12.14 1525.29 1676.03 25.19 2 5710.03 6253.12 8.68 1833.43 1216.14 18.28 3 4560.94 4604.78 6.39 799.96 663.34 9.97 4 1226.12 3288.15 4.56 498.32 422.14 6.35 5 458.06 2934.19 4.07 39.27 271.89 4.09 6 2309.30 2801.97 3.89 79.68 260.05 3.91 7 669.48 2135.33 2.96 110.98 236.03 3.55 8 483.40 1942.07 2.70 44.72 202.56 3.05 9 608.06 1802.52 2.50 49.36 189.08 2.84
10 530.11 1626.99 2.26 135.12 174.20 2.62
CEOF - U200 U850
Summer Winter
i Separation
(i - i+1) Error
% Variance Separation
(i - i+1) Error
% Variance
1 29.89 38.60 10.29 9.32 13.21 21.27 2 32.27 32.15 8.57 31.94 11.20 18.03 3 24.22 25.19 6.72 2.74 4.31 6.94 4 13.41 19.97 5.32 2.19 3.72 5.99 5 6.58 17.08 4.55 1.61 3.25 5.23 6 11.62 15.66 4.17 3.12 2.90 4.67 7 4.97 13.15 3.51 0.59 2.23 3.59 8 4.14 12.08 3.22 0.60 2.10 3.38 9 6.24 11.19 2.98 2.00 1.97 3.18
10 0.98 9.84 2.62 0.88 1.54 2.48
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Interannual variations in the MJO; NCEP/NCAR 1958-1997
Zonal mean of U 200hPa (10°S - 10°N)
20-100 day anomalies; square and apply 100 day smoothing
40-yr integration of HadAM2a model driven with observed SST reproduced general trends in “MJO activity”
Index contains up to 40% unrelated MJO variability (Hendon et al. 1999)
Slingo et al. (1999) Intraseasonal Index (QJRMS)
No-sat Sat
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Are MJO events becoming more intense?
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Is the MJO becoming more frequent?
Summer y = 0.0222x + 1.0629
0
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58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 00 02 04
Nu
mb
er o
f E
ven
ts
Winter y = 0.0071x + 1.6377
0
1
2
3
4
5
58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 00 02 04
Nu
mb
er o
f E
ven
ts
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