Naoko Sakaeda and Paul Roundy Dept Atmospheric and Environmental Sciences From Roundy 2014 J Atmos Sci From Roundy 2014 J Atmos Sci Data Wind data from CFS Reanalysis data Saha ID: 489418
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Slide1
The Dynamics of Western Hemisphere Circulation Evolution in the MJO
Naoko Sakaeda and Paul RoundyDept. Atmospheric and Environmental SciencesSlide2
From Roundy (2014, J. Atmos.
Sci)Slide3
From Roundy (2014, J. Atmos.
Sci)Slide4
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 DJFSlide5
Methodology: Composite MJO Events
MJO Index: Derived similarly to RMM except using 20-100days filtered OLR onlyThe 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
MJOSlide6
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 EventsSlide7
Methodology:
Zonal Momentum BudgetSlide8
Methodology:
Zonal Momentum Budget
At 200
hPa
:
10
°S-5°N, 110°W-80°W Slide9
10°S-5°N, 110°W-80°W Averaged Budget Terms: 200
hPa
Kelvin wave in Shallow Water System
Time Lag (Days)Slide10
Methodology:
Zonal Momentum BudgetTime linear decomposition of zonal momentum equation
: Background State (Seasonal Cycle + Periods longer than 100 days)
: Intraseasonal Timescale (20-100 days)
: Transient Timescale (Periods shorter than 20 days)Slide11
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 forceSlide12
10°S-5°N, 110°W-80°W Averaged Budget Terms 200
hPaSlide13
10°S-5°N, 130°W-100
°W Averaged Budget Terms, 100 hPaSlide14
10°S-5°N,
130°W-100°W Averaged Budget Terms, 100 hPaSlide15
10°S-5°N, 110°W-80°W Averaged Budget Terms
Shading: Variance of 200hPa Intraseasonal Zonal Wind
Black contour: Zonal Convergence of 200hPa Background Zonal Wind (2 x 10
6
s
-1
interval)Slide16
10°S-10°N Averaged Longitude-Pressure Cross Sections
Shading: intraseasonal zonal wind anomaly
Black contour: intraseasonal geopotential height anomaly at 2 m intervalSlide17
Eastward and Westward-Moving OLR, 100hPa Wind, and Geopotential
Height Anomalies
R
R
R
R
A
A
A
ASlide18Slide19Slide20
Summary
Upper-tropospheric intraseasonal wind over the Western Hemisphere cannot simply be explained as a “free” Kelvin wave generated by MJO convection
MJO
H
H
Kelvin
Kelvin
Suppressed
MJO
H
HSlide21
Additional Figures