The North Pacific Gyre Oscillation and East Asian summer precipitation

Abstract This study investigates the features of atmospheric circulation and moisture transport associated with two modes of decadal variability in the North Pacific: the Pacific decadal oscillation (PDO) and the North Pacific Gyre Oscillation (NPGO), with emphasis on the multiscale water vapor transport and atmospheric river (AR) over the North Pacific region. During the positive phase of PDO, the geopotential height anomaly at 500-hPa exhibits a Pacific–North American-like pattern. During the positive phase of NPGO, the geopotential height anomaly at 500 hPa features a dipole pattern with a negative anomaly north of 40°N and a positive anomaly south of 40°N over the North Pacific. Associated with the positive PDO phase, the ocean-to-land moisture transport is enhanced between 25° and 35°N and reduced over the northeastern Pacific (25°–62°N, 180°–110°W) for the time-mean integrated vapor transport (IVT). The synoptic poleward transport is suppressed north of 40°N and enhanced south of 40°N. In the positive NPGO phase, the zonal moisture transport is intensified south of 20°N and between 40° and 50°N for the time-mean IVT and weakened over the west coast of North America for the low-frequency (10–100 days) IVT. The synoptic poleward transport is suppressed south of 30°N. The eastern part of the North Pacific AR belt moves southward during positive PDO as the entire North Pacific AR belt shifts slightly northward during positive NPGO. An investigation of AR anomalies during a period over which the PDO and NPGO coexist demonstrates that the AR frequency over the North American western coastal regions is significantly influenced by the conjunction of the PDO and NPGO modes.

Download Full-text

North Pacific Gyre Oscillation Synchronizes Climate Fluctuations in the Eastern and Western Boundary Systems*

Journal of Climate ◽

10.1175/2009jcli2848.1 ◽

2009 ◽

Vol 22 (19) ◽

pp. 5163-5174 ◽

Cited By ~ 98

Author(s):

Lina I. Ceballos ◽

Emanuele Di Lorenzo ◽

Carlos D. Hoyos ◽

Niklas Schneider ◽

Bunmei Taguchi

Keyword(s):

North Pacific ◽

Dominant Mode ◽

Subtropical Gyre ◽

Western Boundary ◽

North Pacific Subtropical Gyre ◽

Climate Fluctuations ◽

The North ◽

North Pacific Gyre Oscillation ◽

North Pacific Gyre ◽

The North Pacific

Abstract Recent studies have identified the North Pacific Gyre Oscillation (NPGO) as a mode of climate variability that is linked to previously unexplained fluctuations of salinity, nutrient, and chlorophyll in the northeast Pacific. The NPGO reflects changes in strength of the central and eastern branches of the subtropical gyre and is driven by the atmosphere through the North Pacific Oscillation (NPO), the second dominant mode of sea level pressure variability in the North Pacific. It is shown that Rossby wave dynamics excited by the NPO propagate the NPGO signature in the sea surface height (SSH) field from the central North Pacific into the Kuroshio–Oyashio Extension (KOE), and trigger changes in the strength of the KOE with a lag of 2–3 yr. This suggests that the NPGO index can be used to track changes in the entire northern branch of the North Pacific subtropical gyre. These results also provide a physical mechanism to explain coherent decadal climate variations and ecosystem changes between the North Pacific eastern and western boundaries.

Download Full-text

The North Pacific Gyre Oscillation and Mechanisms of Its Decadal Variability in CMIP5 Models

Journal of Climate ◽

10.1175/jcli-d-17-0344.1 ◽

2018 ◽

Vol 31 (6) ◽

pp. 2487-2509 ◽

Cited By ~ 1

Author(s):

Daling Li Yi ◽

Bolan Gan ◽

Lixin Wu ◽

Arthur J. Miller

Keyword(s):

North Pacific ◽

Time Scale ◽

Decadal Variability ◽

Low Frequency ◽

Coupled Model ◽

Cmip5 Models ◽

The North ◽

North Pacific Gyre Oscillation ◽

North Pacific Gyre ◽

The North Pacific

Based on the Simple Ocean Data Assimilation (SODA) product and 37 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) database, the North Pacific Gyre Oscillation (NPGO) and its decadal generation mechanisms are evaluated by studying the second leading modes of North Pacific sea surface height (SSH) and sea level pressure (SLP) as well as their dynamical connections. It is found that 17 out of 37 models can well simulate the spatial pattern and decadal time scales (10–30 yr) of the NPGO mode, which resembles the observation-based SODA results. Dynamical connections between the oceanic mode (NPGO) and the atmospheric mode [North Pacific Oscillation (NPO)] are strongly evident in both SODA and the 17 models. In particular, about 30%–40% of the variance of the NPGO variability, which generally exhibits a preferred time scale, can be explained by the NPO variability, which has no preferred time scale in most models. Two mechanisms of the decadal NPGO variability that had been proposed by previous studies are evaluated in SODA and the 17 models: 1) stochastic atmospheric forcing and oceanic spatial resonance and 2) low-frequency atmospheric teleconnections excited by the equatorial Pacific. Evaluation reveals that these two mechanisms are valid in SODA and two models (CNRM-CM5 and CNRM-CM5.2), whereas two models (CMCC-CM and CMCC-CMS) prefer the first mechanism and another two models (CMCC-CESM and IPSL-CM5B-LR) prefer the second mechanism. The other 11 models have no evident relations with the proposed two mechanisms, suggesting the need for a fundamental understanding of the decadal NPGO variability in the future.

Download Full-text

Understanding the Predictability of East Asian Summer Monsoon from the Reproduction of Land–Sea Thermal Contrast Change in AMIP-Type Simulation

Journal of Climate ◽

10.1175/2010jcli3546.1 ◽

2010 ◽

Vol 23 (22) ◽

pp. 6009-6026 ◽

Cited By ~ 64

Author(s):

Tianjun Zhou ◽

Liwei Zou

Keyword(s):

North Pacific ◽

Asian Summer Monsoon ◽

East Asian ◽

Monsoon Circulation ◽

Asian Continent ◽

Thermal Contrast ◽

The North ◽

Tropical Western Pacific ◽

Asian Summer ◽

The North Pacific

Abstract Previous studies on the predictability of East Asian summer monsoon circulation based on SST-constrained Atmospheric Model Intercomparison Project (AMIP)-type simulations show that this phenomenon is reproduced with lower skill than other monsoon patterns. The authors examine the reason in terms of the predictability of land–sea thermal contrast change. In the observation, a stronger monsoon circulation is dominated by a tropospheric warming over East Asian continent and a cooling over the tropical western Pacific and North Pacific, indicating an enhancement of the summertime “warmer land–colder ocean” mean state. The tropospheric cooling over the tropical western Pacific and North Pacific, and the tropospheric warming over East Asian continent are reproducible in AMIP-type simulations, although there are biases over both the North Pacific and East Asia. The tropospheric temperature responses in the model indicate a reasonable predictability of the meridional land–sea thermal contrast; the zonal land–sea thermal contrast change is also predictable but shows bias over the region north to 25°N in North Pacific. The reproducibility of the meridional thermal contrast is higher than that of the zonal thermal contrast. An examination of the predictability of two commonly used monsoon indices reveals far different skills. The index defined as zonal wind shear between 850 and 200 hPa averaged over East Asia is highly predictable. The skill comes from the predictability of the meridional land–sea thermal contrast. Although the zonal thermal contrast change is mostly predictable except for the biases over the North Pacific, the monsoon index defined as zonal sea level pressure (SLP) difference across the East Asian continent and the North Pacific is unpredictable. The low skill is related to the index definition, which attaches more importance to the land SLP change. The limitation of the index in measuring the land SLP change reduces the model skill. Although regional features of monsoon precipitation changes remain a challenge for current climate models, the predictable land–sea thermal contrast change sheds light on monsoon circulation prediction.

Download Full-text