Abstract
A dry February rainfall signal in southeastern Brazil is shown to be a robust, repeatable feature of climatology. This February depression or minimum in climatological rain curves has an amplitude of about 30% of the seasonal mean and coincides with a poleward excursion of tropical barotropic easterlies to about 25°S in austral midsummer. Momentum budget decomposition indicates that stationary eddy momentum flux [u*υ*] near 150 hPa in Australian longitudes is a main sink in that latitude belt's zonal momentum budget. A physical linkage among these phenomena is suggested by statistically significant interannual correlations among February anomalies of southeastern Brazil rainfall, zonal-mean zonal wind, and indices of the Australian monsoon. To test a causality hypothesis that the sharply peaked Australian region monsoon drives the sharp climatological dry signal over Brazil, an observation-inspired tropospheric heating signal near Australia is added to the temperature equation of the full-physics Community Atmosphere Model. Results indicate the near linearity of the global subtropical responses for the modest (roughly 1 and 2 K day-1) magnitudes and scales of imposed heating. Consistent with the hypothesis, this imposed heating robustly causes easterly changes to subtropical, barotropic, zonal-mean momentum, a westward displacement of the mean synoptic-scale pattern in the western Atlantic (the western edge of the subtropical high), and reduced rainfall in southeastern Brazil. These results are closely analogous to the previous findings on a related boreal summer subtropical signal.
Original language | English (US) |
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Pages (from-to) | 7529-7546 |
Number of pages | 18 |
Journal | Journal of Climate |
Volume | 29 |
Issue number | 20 |
DOIs | |
State | Published - 2016 |
Keywords
- Anticyclones
- Atmospheric circulation
- Barotropic flows
- Monsoons
- South Atlantic convergence zone
- Subtropics
ASJC Scopus subject areas
- Atmospheric Science