Analytic Relationship Between Walker Circulation Strength and Precipitation
Abstract
Using a Kuo-Eliassen -type equation for the Walker circulation streamfunction in a linear Boussinesq fluid, we find analytic solutions for the circulation strength (mass transport) as a function of convective cloud depth, the amount of convective heating, and the zonal extent of the convecting region. In the present climate, the analytic solution indicates that the circulation strength is mainly dependent on the zonal width of the convection, and less sensitive to the depth of the clouds. Through increasing convective heating power (in W/m^2) comes a stronger circulation. These results are qualitatively consistent with three-dimensional (non-linear) model simulations. More importantly, the analytic solutions well explain much of the observed seasonal and interannual (El Niño) variability in the Pacific-Indian Ocean Walker circulation. The seasonal cycle of convective heating power (as measured by precipitation, in W/m^2) over the Indian Ocean-Western Pacific region can explain up to 90% of the variability in the Walker circulation strength (outside of the Asian winter monsoon season, which impacts the counter-clockwise (western) cell). A reduction in the zonal extent of the convection corresponds to a stronger circulation. Similarly, the stronger circulation during La Niña is also associated with more intense convective heating and shorter zonal scale (as compared to El Niño).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A21T2781I
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 3319 General circulation;
- ATMOSPHERIC PROCESSES;
- 3337 Global climate models;
- ATMOSPHERIC PROCESSES;
- 3373 Tropical dynamics;
- ATMOSPHERIC PROCESSES