Mechanisms of Mid-Holocene Precipitation Change in the South Pacific Convergence Zone

Abstract The variability of the South Pacific convergence zone (SPCZ) during the mid-Holocene is investigated using models archived in the Paleoclimate Modelling Intercomparison Project Phase II (PMIP2) database. Relative to preindustrial conditions, mid-Holocene top-of-atmosphere insolation was relatively lower during austral summer [December–February (DJF)], which is the season when the SPCZ is at its peak intensity. In response to this perturbation, the PMIP2 models simulate a displacement of the SPCZ to the southwest. This SPCZ shift is associated with a sea surface temperature (SST) dipole, with increased rainfall collocated with warm SST anomalies. Decomposing the DJF precipitation changes in terms of a diagnostic moisture budget indicates that the SPCZ shift is balanced to leading order by a change in the mean moisture convergence. Changes to the broad area of upper-level negative zonal stretching deformation, where transient eddies can become trapped and subsequently generate deep convection, support the notion that the SPCZ shift in the subtropics is tied to eddy forcing. Idealized experiments performed with an intermediate-level complexity model, the Quasi-Equilibrium Tropical Circulation Model (QTCM), suggest that the mid-Holocene change in rainfall in the SPCZ region as well as the equatorial Pacific is dominated by a change in the underlying SST. The tropical portion of the SPCZ is further remotely affected by the orbitally induced weakening of the Australian monsoon, even though this effect is weaker compared to the effect from SSTs.

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The Influence of South Pacific Convergence Zone Heating on the South Pacific Subtropical Anticyclone

Journal of Climate ◽

10.1175/jcli-d-20-0509.1 ◽

2021 ◽

pp. 1-38

Author(s):

Abdullah A. Fahad ◽

Natalie J. Burls ◽

Erik T. Swenson ◽

David M. Straus

Keyword(s):

Southern Hemisphere ◽

Wave Train ◽

Austral Summer ◽

South Pacific ◽

South Pacific Convergence Zone ◽

Convergence Zone ◽

The South ◽

Sea Level Pressure ◽

Subtropical Anticyclone ◽

South Indian

AbstractSubtropical anticyclones and midlatitude storm tracks are key components of the large-scale atmospheric circulation. Focusing on the southern hemisphere, the seasonality of the three dominant subtropical anticyclones, situated over the South Pacific, South Atlantic, and South Indian Ocean basins, has a large influence on local weather and climate within South America, Southern Africa, and Australia, respectively. Generally speaking, sea level pressure within the southern hemisphere subtropics reaches its seasonal maximum during the winter season when the southern hemisphere Hadley Cell is at its strongest. One exception to this is the seasonal evolution of the South Pacific subtropical anticyclone. While winter maxima are seen in the South Atlantic and South Indian subtropical anticyclones, the South Pacific subtropical anticyclone reaches its seasonal maximum during local spring with elevated values extending into summer. In this study, we investigate the hypothesis that the strength of the austral summer South Pacific subtropical anticyclone is largely due to heating over the South Pacific Convergence Zone. Using added cooling and heating atmospheric-general-circulation-model experiments to artificially change the strength of austral summer diabatic heating over the South Pacific Convergence Zone, our results show that increased heating, through increased upper-level divergence, triggers a Rossby wave train that extends into the Southern Hemisphere mid-latitudes. This propagating Rossby wave train creates a high-low sea level pressure pattern that projects onto the center of the South Pacific Subtropical Anticyclone to intensify its area and strength.

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The South Pacific Convergence Zone in three decades of satellite images

Journal of Geophysical Research Atmospheres ◽

10.1002/jgrd.50838 ◽

2013 ◽

Vol 118 (19) ◽

pp. 10,839-10,849 ◽

Cited By ~ 18

Author(s):

Colene Haffke ◽

Gudrun Magnusdottir

Keyword(s):

Satellite Images ◽

South Pacific ◽

South Pacific Convergence Zone ◽

Convergence Zone ◽

The South

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Impacts of Detoured Madden-Julian Oscillations on the South Pacific Convergence Zone

Journal of Climate ◽

10.1175/jcli-d-20-0444.1 ◽

2021 ◽

pp. 1-41

Author(s):

Lei Zhou ◽

Ruomei Ruan ◽

Raghu Murtugudde

Keyword(s):

Southern Hemisphere ◽

Rossby Waves ◽

South Pacific ◽

South Pacific Convergence Zone ◽

Boreal Winter ◽

Convergence Zone ◽

The South ◽

Maritime Continent ◽

Meridional Winds ◽

Southern Pacific Ocean

AbstractMadden-Julian Oscillations (MJOs) are a major component of tropical intraseasonal variabilities. There are two paths for MJOs across the Maritime Continent; one is a detoured route into the Southern Hemisphere and the other one is around the equator across the Maritime Continent. Here, it is shown that the detoured and non-detoured MJOs have significantly different impacts on the South Pacific convergence zone (SPCZ). The detoured MJOs trigger strong cross-equatorial meridional winds from the Northern Hemisphere into the Southern Hemisphere. The associated meridional moisture and energy transports due to the background states carried by the intraseasonal meridional winds are favorable for reinforcing the SPCZ. In contrast, the influences of non-detoured MJOs on either hemisphere or the meridional transports across the equator are much weaker. The detoured MJOs can extend their impacts to the surrounding regions by shedding Rossby waves. Due to different background vorticity during detoured MJOs in boreal winter, more ray paths of Rossby waves traverse the Maritime Continent connecting the southern Pacific Ocean and the eastern Indian Ocean, but far fewer Rossby wave paths traverse Australia. Further studies on such processes are expected to contribute to a better understanding of extreme climate and natural disasters on the rim of the southern Pacific and Indian Oceans.

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