The Dynamics of Western Hemisphere Circulation Evolution in the MJO Naoko Sakaeda and Paul Roundy...
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![Page 1: The Dynamics of Western Hemisphere Circulation Evolution in the MJO Naoko Sakaeda and Paul Roundy Dept. Atmospheric and Environmental Sciences.](https://reader036.fdocuments.net/reader036/viewer/2022062322/5697bfca1a28abf838ca97a5/html5/thumbnails/1.jpg)
The Dynamics of Western Hemisphere Circulation
Evolution in the MJO
Naoko Sakaeda and Paul Roundy
Dept. Atmospheric and Environmental Sciences
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From Roundy (2014, J. Atmos. Sci)
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From Roundy (2014, J. Atmos. Sci)
![Page 4: The Dynamics of Western Hemisphere Circulation Evolution in the MJO Naoko Sakaeda and Paul Roundy Dept. Atmospheric and Environmental Sciences.](https://reader036.fdocuments.net/reader036/viewer/2022062322/5697bfca1a28abf838ca97a5/html5/thumbnails/4.jpg)
Data
• Wind data from CFS Reanalysis data (Saha et al. 2010)
• Interpolated Outgoing Longwave Radiation (OLR) as proxy for tropical convection (Liebmann and Smith 1996)
• Period: 1980-2010 DJF
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Methodology: Composite MJO Events
• MJO Index: Derived similarly to RMM except using 20-100days filtered OLR only
• The Western Hemisphere Zonal Wind Index (WHZI): 20-100 days 200hPa zonal wind averaged 2.5°N to 2.5°S and 140°W to 40°W
WHZI MJO
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MJO
MJO
Methodology: MJO Events
• Select MJO Phase 1 events with amplitude greater than or equal to 0.5 during DJF
• WHZI<0: Easterly Wind Events
• WHZI>0: Westerly Wind Events
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Methodology: Zonal Momentum Budget
Xfvx
guvt
u
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Methodology: Zonal Momentum Budget
At 200 hPa: 10°S-5°N, 110°W-80°W
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10°S-5°N, 110°W-80°W Averaged Budget Terms: 200 hPa
xg
t
u
Kelvin wave in
Shallow Water System
Time Lag (Days)
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Methodology: Zonal Momentum Budget
• Time linear decomposition of zonal momentum equation
Xfvx
guvt
u
'* uuuu : Background State (Seasonal Cycle + Periods longer than 100 days)
: Intraseasonal Timescale (20-100 days)
: Transient Timescale (Periods shorter than 20 days)
u*u'u
**
''*****
fvx
guvuvuvuvt
u
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10°S-5°N, 110°W-80°W Averaged Budget Terms 200 hPa
acts to maintain and amplify but it is offset by the pressure gradient force
x
*
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10°S-5°N, 110°W-80°W Averaged Budget Terms 200 hPa
![Page 13: The Dynamics of Western Hemisphere Circulation Evolution in the MJO Naoko Sakaeda and Paul Roundy Dept. Atmospheric and Environmental Sciences.](https://reader036.fdocuments.net/reader036/viewer/2022062322/5697bfca1a28abf838ca97a5/html5/thumbnails/13.jpg)
10°S-5°N, 130°W-100°W Averaged Budget Terms, 100 hPa
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10°S-5°N, 130°W-100°W Averaged Budget Terms, 100 hPa
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10°S-5°N, 110°W-80°W Averaged Budget Terms
p
uωu
y
uvu
x
uu
uvut
u
t
uC
*****
***
2
1,
2
1
2
22
Shading: Variance of 200hPa Intraseasonal Zonal WindBlack contour: Zonal Convergence of 200hPa Background Zonal Wind (2 x 106 s-1 interval)
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10°S-10°N Averaged Longitude-Pressure Cross Sections
Shading: intraseasonal zonal wind anomalyBlack contour: intraseasonal geopotential height anomaly at 2 m interval
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Eastward and Westward-Moving OLR, 100hPa Wind, and Geopotential Height Anomalies
R
R
R
R
A
A
A
A
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Summary
• Upper-tropospheric intraseasonal wind over the Western Hemisphere cannot simply be explained as a “free” Kelvin wave generated by MJO convection
MJO
H
HKelvin KelvinSuppressed
MJO
H
H
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Additional Figures