Journal
JOURNAL OF THE ATMOSPHERIC SCIENCES
Volume 79, Issue 9, Pages 2453-2469Publisher
AMER METEOROLOGICAL SOC
DOI: 10.1175/JAS-D-21-0206.1
Keywords
Atmospheric circulation; Planetary waves; Stationary waves; Jets; Climate variability; Cool season
Categories
Funding
- Australian Research Council [1947282]
- Australian Government Research Training Program Scholarship
- CLEX/Australian Bureau of Meteorology PhD Top-up scholarship
- Regional and Global Model Analysis component of the Earth and Environmental System Modeling Program of the U.S. Department of Energy's Office of Biological and Environmental Research via National Science Foundation
- Australian government
- [CE170100023]
- Australian Research Council [CE170100023] Funding Source: Australian Research Council
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Stationary Rossby waves forced by the Indian Ocean dipole play a significant role in Southern Hemisphere weather and climate. The dynamics of these teleconnections are not fully understood, but recent studies suggest that these waves can overcome the negative beta* barrier and propagate into the extratropics of the Southern Hemisphere.
Stationary Rossby waves, forced by the Indian Ocean dipole (IOD), have an important role in Southern Hemisphere (SH) weather and climate, including promoting Australian drought and driving Antarctic sea ice variations. However, the dynamics of these teleconnections are not fully understood. During winter, the subtropical jet (STJ) should prohibit continuous propagation of a stationary Rossby wave into the SH extratropics due to the negative meridional gradient of absolute vorticity (beta*) on its poleward flank. The mechanisms that enable this teleconnection are investigated using observational and reanalysis datasets, a hierarchy of atmospheric model experiments and Rossby wave diagnostics. We conduct 90-member simulations using the Community Atmosphere Model, version 5, with an imposed local diabatic heating anomaly over the eastern Indian Ocean. We find an initial zonal propagation along the STJ waveguide, but after about 10 days, a poleward-arcing wave train appears in the extratropics that has the characteristics of the observed IOD teleconnection. Our results suggest that the Rossby wave can overcome the negative beta* barrier by (i) propagating directly poleward in the midtroposphere and thus avoiding this evanescent region in the upper troposphere, (ii) partly propagating directly through this barrier, and (iii) propagating around this barrier farther upstream to the west. A transient eddy feedback, previously postulated to be the key mechanism to allow the stationary Rossby wave to appear on the poleward side of the negative beta* region, reinforces the response but is not a requisite, which we confirm through comparison with a simplified linear model.
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