Circulation, Moisture, and Precipitation Relationships along the South Pacific Convergence Zone in Reanalyses and CMIP5 Models

Abstract One theorized control on the position of the South Pacific convergence zone (SPCZ) is the amount of low-level inflow from the relatively dry southeastern Pacific basin. Building on an analysis of observed SPCZ region synoptic-scale variability by Lintner and Neelin, composite analysis is performed here on two reanalysis products as well as output from 17 models in phase 5 of the Coupled Model Intercomparison Project (CMIP5). Using low-level zonal wind as a compositing index, it is shown that the CMIP5 ensemble mean, as well as many of the individual models, captures patterns of wind, specific humidity, and precipitation anomalies resembling those obtained for reanalysis fields between weak- and strong-inflow phases. Lead–lag analysis of both the reanalyses and models is used to develop a conceptual model for the formation of each composite phase. This analysis indicates that an equatorward-displaced Southern Hemisphere storm track and an eastward-displaced equatorial eastern Pacific westerly (wind) duct are features of the weak-inflow phase although, as indicated by additional composite analyses based on these features, each appears to account weakly for the details of the low-level inflow composite anomalies. Despite the presence of well-known biases in the CMIP5 simulations of the SPCZ region climate, the models appear to have some fidelity in simulating synoptic-scale relationships between low-level winds, moisture, and precipitation, consistent with observations and simple theoretical understanding of interactions of dry air inflow with deep convection.

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Millennial-scale precipitation variability over Easter Island (South Pacific) during MIS 3: inter-hemispheric teleconnections with North Atlantic abrupt cold events

Climate of the Past Discussions ◽

10.5194/cpd-11-1407-2015 ◽

2015 ◽

Vol 11 (2) ◽

pp. 1407-1435 ◽

Cited By ~ 2

Author(s):

O. Margalef ◽

I. Cacho ◽

S. Pla-Rabes ◽

N. Cañellas-Boltà ◽

J. J. Pueyo ◽

...

Keyword(s):

Southern Hemisphere ◽

North Atlantic ◽

Storm Track ◽

South Pacific ◽

Easter Island ◽

South Pacific Convergence Zone ◽

Convergence Zone ◽

The South ◽

Mis 3 ◽

Millennial Scale

Abstract. Marine Isotope Stage 3 (MIS 3, 59.4–27.8 kyr BP) is characterized by the occurrence of rapid millennial-scale climate oscillations known as Dansgaard–Oeschger cycles (DO) and by abrupt cooling events in the North Atlantic known as Heinrich events. Although both the timing and dynamics of these events have been broadly explored in North Atlantic records, the response of the tropical and subtropical latitudes to these rapid climatic excursions, particularly in the Southern Hemisphere, still remains unclear. The Rano Aroi peat record (Easter Island, 27° S) provides a unique opportunity to understand atmospheric and oceanic changes in the South Pacific during these DO cycles because of its singular location, which is influenced by the South Pacific Anticyclone (SPA), the Southern Westerlies (SW), and the Intertropical Convergence Zone (ITCZ) linked to the South Pacific Convergence Zone (SPCZ). The Rano Aroi sequence records 6 major events of enhanced precipitation between 38 and 65 kyr BP. These events are compared with other hydrological records from the tropical and subtropical band supporting a coherent regional picture, with the dominance of humid conditions in Southern Hemisphere tropical band during Heinrich Stadials (HS) 5, 5a and 6 and other Stadials while dry conditions prevailed in the Northern tropics. This antiphased hydrological pattern between hemispheres has been attributed to ITCZ migration, which in turn might be associated with an eastward expansion of the SPCZ storm track, leading to an increased intensity of cyclogenic storms reaching Easter Island. Low Pacific Sea Surface Temperature (SST) gradients across the Equator were coincident with the here-defined Rano Aroi humid events and consistent with a reorganization of Southern Pacific atmospheric and oceanic circulation also at higher latitudes during Heinrich and Dansgaard–Oeschger stadials.

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The Role of Tropical–Extratropical Interaction and Synoptic Variability in Maintaining the South Pacific Convergence Zone in CMIP5 Models

Journal of Climate ◽

10.1175/jcli-d-14-00527.1 ◽

2015 ◽

Vol 28 (8) ◽

pp. 3353-3374 ◽

Cited By ~ 14

Author(s):

Matthew J. Niznik ◽

Benjamin R. Lintner ◽

Adrian J. Matthews ◽

Matthew J. Widlansky

Keyword(s):

Climate Models ◽

Coupled Model ◽

South Pacific ◽

South Pacific Convergence Zone ◽

Cmip5 Models ◽

Convective Heating ◽

Convergence Zone ◽

The South ◽

Synoptic Variability ◽

Background State

Abstract The South Pacific convergence zone (SPCZ) is simulated as too zonal a feature in the current generation of climate models, including those in phase 5 of the Coupled Model Intercomparison Project (CMIP5). This zonal bias induces errors in tropical convective heating, with subsequent effects on global circulation. The SPCZ structure, particularly in the subtropics, is governed by the tropical–extratropical interaction between transient synoptic systems and the mean background state. In this study, analysis of synoptic variability in the simulated subtropical SPCZ reveals that the basic mechanism of tropical–extratropical interaction is generally well simulated, with storms approaching the SPCZ along comparable trajectories to observations. However, there is a broad spread in mean precipitation and its variability across the CMIP5 ensemble. Intermodel spread appears to relate to a biased background state in which the synoptic waves propagate. In particular, the region of mean negative zonal stretching deformation or “storm graveyard” in the upper troposphere is displaced in CMIP5 models to the northeast of its position in reanalysis data, albeit with pronounced (≈25°) intermodel longitudinal spread. Precipitation along the eastern edge of the SPCZ shifts in accordance with a storm graveyard shift, and in general models with stronger storm graveyards show higher precipitation variability. Building on prior SPCZ research, it is suggested that SPCZs simulated by CMIP5 models are not simply too zonal; rather, in models the subtropical SPCZ manifests a diagonal tilt similar to observations while SST biases force an overly zonal tropical SPCZ, resulting in a more discontinuous SPCZ than observed.

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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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