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

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

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

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

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

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)

INDEX 9 10 1 2 3 4 5 6 7 8

LON 20OE 70OE 80OE 100OE 120OE 140OE 160OE 120OW 40OW 10OW

December 2001

June 2001

Depth 20OC Anom

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)

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)

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

OLR

cint = 4 w/m2

20 W/m2

200-hPa Zonal Wind

cint = 2 m/s

Precipitation

cint = 0.2 mm/day

Shading is percentage departure relative to the climatology

500-hPa Height

cint = 10 m

60 m

Surface Air Temperature

cint = 0.5OC

-1OC+1OC

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

Extreme Warm (> base 90th percentile) Surface Air Temperature Frequency Anomaly (cint=20%)

Base 90th percentile distribution

-80%

+80%

Extreme Cold (< base 10th percentile) Surface Air Temperature Frequency Anomaly (cint=20%)

Base 10th percentile distribution

Extreme Heavy (> base 75th percentile) Precipitation Frequency Anomaly (cint=20%)

Base 75th percentile distribution

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.