Evolution of Western Hemisphere Circulation in MJO
In this study by Naoko Sakaeda and Paul Roundy from the Dept. of Atmospheric and Environmental Sciences, the dynamics of Western Hemisphere circulation evolution in the Madden-Julian Oscillation (MJO) are explored. The research focuses on analyzing composite MJO events, utilizing the Western Hemisphere Zonal Wind Index (WHZI) and Zonal Momentum Budget methodology to study the impact of MJO phases on zonal winds and circulation patterns. The study uses data from Wind data from CFS Reanalysis, Interpolated Outgoing Longwave Radiation (OLR) as a proxy for tropical convection, and covers the period from 1980 to 2010. Various stages of the methodology are detailed, including the selection of MJO events based on amplitude thresholds and wind direction, as well as the zonal momentum budget analysis at 200 hPa. The findings provide insights into the zonal wind behavior and atmospheric circulation patterns in the Western Hemisphere under the influence of the MJO.
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Presentation Transcript
The Dynamics of Western Hemisphere Circulation Evolution in the MJO Naoko Sakaeda and Paul Roundy Dept. Atmospheric and Environmental Sciences
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
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
Methodology: MJO Events Select MJO Phase 1 events with amplitude greater than or equal to 0.5 during DJF WHZI<0: Easterly Wind Events MJO WHZI>0: Westerly Wind Events MJO
Methodology: Zonal Momentum Budget u = + + v u g fv X t x
Methodology: Zonal Momentum Budget At 200 hPa: 10 S-5 N, 110 W-80 W
10S-5N, 110W-80W Averaged Budget Terms: 200 hPa Time Lag (Days) Kelvin wave in Shallow Water System u = g t x
Methodology: Zonal Momentum Budget Time linear decomposition of zonal momentum equation u = u u u + = u * u ' u * v u v u v t + + v u g fv X * u t x + ' : Background State (Seasonal Cycle + Periods longer than 100 days) : Intraseasonal Timescale (20-100 days) : Transient Timescale (Periods shorter than 20 days) * u + * * * * ' ' * u v u g fv x
10S-5N, 110W-80W Averaged Budget Terms 200 hPa -u* u acts to maintain and amplify but it is offset by the pressure gradient force x * x
10S-5N, 110W-80W Averaged Budget Terms 200 hPa
10S-5N, 130W-100W Averaged Budget Terms, 100 hPa
10S-5N, 130W-100W Averaged Budget Terms, 100 hPa
10S-5N, 110W-80W Averaged Budget Terms 2 2 1 1 * u u = , * * C u v u 2 2 t t u u u = 2 * * * * * u u v u x y p Shading: Variance of 200hPa Intraseasonal Zonal Wind Black contour: Zonal Convergence of 200hPa Background Zonal Wind (2 x 106 s-1 interval)
10S-10N Averaged Longitude-Pressure Cross Sections Shading: intraseasonal zonal wind anomaly Black contour: intraseasonal geopotential height anomaly at 2 m interval
Eastward and Westward-Moving OLR, 100hPa Wind, and Geopotential Height Anomalies R A R A R A R A
Summary Upper-tropospheric intraseasonal wind over the Western Hemisphere cannot simply be explained as a free Kelvin wave generated by MJO convection H H Suppressed MJO Kelvin Kelvin MJO H H
