Yan Xue, Wayne Higgins and Vernon Kousky Climate Prediction Center, NCEP/NWS
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Transcript of Yan Xue, Wayne Higgins and Vernon Kousky Climate Prediction Center, NCEP/NWS
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Influences of the Madden Julian Oscillation on Temperature and Precipitation in North America
During Weak/Neutral ENSO NH Winters
Yan Xue, Wayne Higgins and Vernon Kousky
Climate Prediction Center, NCEP/NWS
for the 27th Annual Climate Diagnostics and Prediction Workshop held in Fairfax, Virginia on October 21-25, 2002
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Review• The MJO has a strong influence on the atmospheric
circulation in the tropics and subtropics
Madden and Julian 1971; Weichmann et al. 1985; Lau and Chan 1985; Knutson and Weickmann 1987; Kiladis and Weickmann 1992; Kayano and Kousky 1999
• The MJO has some influence on the midlatitudes
( e.g. precipitation events along the west coast of U.S.)
Mo and Higgins 1998; Higgins et al. 2000
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Approach• Ten MJO indices are used to describe the eastward
propagation of the MJO– Real time monitoring– Composite – Extreme event frequency anomaly
• Composites are keyed to the convectively active phase of each MJO index– Atmospheric circulation– Temperature – Precipitation
• Extreme heavy precipitation (>75th percentile), extreme warm (>90th percentile) and cold (<10th percentile) surface air temperature
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Data• Pentad data from NCEP/NCAR reanalysis
– 200-hPa CHI, PSI, u, v.– 500-hPa Z– 2.5o latitude/longitude, 1958 – present
• Pentad Outgoing Longwave Radiation– 2.5o latitude/longitude, 1979 – present
• Pentad global surface air temperature (personal communication with Ping-Ping Xie)– 2.5o latitude/longitude, 1978 – present
• GPCP global pentad precipitation analysis– 2.5o latitude/longitude, 1979 – present
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MJO Indices• Band-passed (25-87 day) pentad 200-hPa velocity
potential (CHI)
• Extended empirical orthogonal function (EEOF) analysis of the filtered CHI– Extended winter (November – April)
– ENSO-neutral and weak ENSO winters (1979-2000)
– 30oS – 30oN, Ten time-lagged patterns
• Projection of the filtered CHI onto the ten patterns of the first EEOF
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INDEX 1 (80OE)
INDEX 2 (100OE)
INDEX 3 (120OE)
INDEX 4 (140OE)
INDEX 5 (160OE)
INDEX 6 (120OW)
INDEX 7 (40OW)
INDEX 8 (10OW)
INDEX 9 (20OE)
INDEX 10 (70OE)
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INDEX 9 10 1 2 3 4 5 6 7 8
LON 20OE 70OE 80OE 100OE 120OE 140OE 160OE 120OW 40OW 10OW
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December 2001
June 2001
Depth 20OC Anom
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Composite Methodology• MJO Index > 0.8 sigma (standard deviation)
– Using multiple pentads around the peaks
(3-4 pentads for strong MJOs / 1-2 pentads for weak MJOs)
• Composite is done with unfiltered data but the climatological mean for 1979-1995 was first removed and then the winter season (Dec-Apr) mean are removed.
• Two-tailed student’s t test (95% significance)
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Composite Members• Index 1: 80 pentads (29 MJO cases)• Index 2: 72 pentads (27 MJO cases) • Index 3: 71 pentads (25 MJO cases)• Index 4: 70 pentads (26 MJO cases)• Index 5: 75 pentads (26 MJO cases)• Index 6: 78 pentads (28 MJO cases)• Index 7: 79 pentads (27 MJO cases)• Index 8: 75 pentads (27 MJO cases)• Index 9: 67 pentads (25 MJO cases)• Index 10: 83 pentads (29 MJO cases)
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Seasonality of MJODec Jan Feb Mar Apr Dec-Apr
Index 1 4 5 6 8 6 29
Index 2 3 5 5 7 7 27
Index 3 3 4 5 5 8 25
Index 4 3 3 6 7 7 26
Index 5 4 4 4 6 8 26
Index 6 2 6 5 8 7 28
Index 7 2 4 4 9 8 27
Index 8 3 4 3 9 8 27
Index 9 3 4 4 10 4 25
Index 10 4 6 5 8 6 29
All Indices 31 45 47 77 69 269
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OLR
cint = 4 w/m2
20 W/m2
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200-hPa Zonal Wind
cint = 2 m/s
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Precipitation
cint = 0.2 mm/day
Shading is percentage departure relative to the climatology
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500-hPa Height
cint = 10 m
60 m
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Surface Air Temperature
cint = 0.5OC
-1OC+1OC
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Extreme Frequency Anomaly• Base pentads are composed of all the pentads in the
neutral/weak ENSO winters (Dec-Apr) with the MJO pentads excluded.
• For each MJO index, compute the percentage of the MJO pentads with pentad amounts greater than the base pentads’ percentile (Pmjo).
• For each MJO index, compute the frequency anomaly in percent of expected number of extreme events:
Panom = (Pmin/(1- –
percent for base pentadsPercent for mjo pentads
Gershunov and Barnett 1998, J. Climate
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Extreme Warm (> base 90th percentile) Surface Air Temperature Frequency Anomaly (cint=20%)
Base 90th percentile distribution
-80%
+80%
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Extreme Cold (< base 10th percentile) Surface Air Temperature Frequency Anomaly (cint=20%)
Base 10th percentile distribution
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Extreme Heavy (> base 75th percentile) Precipitation Frequency Anomaly (cint=20%)
Base 75th percentile distribution
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Summary
• Ten MJO indices were calculated as projections of pentad 200-hPa velocity potential onto ten time-lagged patterns of the first EEOF.
• Keying on the convectively active phases of the ten MJO indices, ten composites of the MJO events during ENSO-neutral and weak ENSO winters were constructed for various fields.
• Significant MJO-related influences on both means and extreme events of surface air temperature and precipitation in the North America are found.