Southern Hemisphere Westerly Wind Control over the Ocean's Thermohaline Circulation

2009 ◽  
Vol 22 (5) ◽  
pp. 1277-1286 ◽  
Author(s):  
Willem P. Sijp ◽  
Matthew H. England
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Wind Stress ◽  
North Pacific ◽  
Thermohaline Circulation ◽  
Meridional Overturning Circulation ◽  
Wind Stress Curl ◽  
The North ◽  
Stress Maximum ◽  
The North Pacific

Abstract The effect of the position of the Southern Hemisphere subpolar westerly winds (SWWs) on the thermohaline circulation (THC) of the World Ocean is examined. The latitudes of zero wind stress curl position exert a strong control on the distribution of overturning between basins in the Northern Hemisphere. A southward wind shift results in a stronger Atlantic THC and enhanced stratification in the North Pacific, whereas a northward wind shift leads to a significantly reduced Atlantic THC and the development of vigorous sinking (up to 1500-m depth) in the North Pacific. In other words, the Atlantic dominance of the meridional overturning circulation depends on the position of the zero wind stress curl over the Southern Ocean in the experiments. This position has a direct influence on the surface salinity contrast between the Pacific and the Atlantic, which is then further amplified by changes in the distribution of Northern Hemisphere sinking between these basins. The results show that the northward location of the SWW stress maximum inferred for the last glacial period may have contributed to significantly reduced North Atlantic Deep Water formation during this period, and perhaps an enhanced and deeper North Pacific THC. Also, a more poleward location of the SWW stress maximum in the current warming climate may entail stronger salinity stratification of the North Pacific.

Variability of the wind stress curl over the North Pacific: Implications for the oceanic response

1991 ◽  
Vol 96 (C10) ◽  
pp. 18361 ◽  
Author(s):  
Alan D. Chave ◽  
Douglas S. Luther ◽  
Jean H. Filloux
Keyword(s):  
Wind Stress ◽  
North Pacific ◽  
Wind Stress Curl ◽  
The North ◽  
Oceanic Response ◽  
The North Pacific

scholarly journals ENSO-correlated fluctuations in ocean bottom pressure and wind-stress curl in the North Pacific

Ocean Science ◽  
2011 ◽  
Vol 7 (5) ◽  
pp. 685-692 ◽  
Author(s):  
D. P. Chambers
Keyword(s):  
Wind Stress ◽  
North Pacific ◽  
Low Frequency ◽  
Ocean Model ◽  
Ocean Bottom ◽  
Bottom Pressure ◽  
Wind Stress Curl ◽  
Ocean Bottom Pressure ◽  
The North ◽  
The North Pacific

Abstract. We examine the output of an ocean model forced by ECMWF winds to study the theoretical relationship between wind-induced changes in ocean bottom pressure in the North Pacific between 1992 until 2010 and ENSO. Our analysis indicates that while there are significant fluctuations correlated with some El Niño and La Niña events, the correlation is still relatively low. Moreover, the ENSO-correlated variability explains only 50 % of the non-seasonal, low-frequency variance. There are significant residual fluctuations in both wind-stress curl and ocean bottom pressure in the region with periods of 4-years and longer. One such fluctuation began in late 2002 and has been observed by the Gravity Recovery and Climate Experiment (GRACE). Even after accounting for possible ENSO-correlated variations, there is a significant trend in ocean bottom pressure in the region, equivalent to 0.7 ± 0.3 cm yr−1 of sea level from January 2003 until December 2008, which is confirmed with steric-corrected altimetry. Although this low-frequency fluctuation does not appear in the ocean model, we show that ECMWF winds have a significantly reduced trend that is inconsistent with satellite observations over the same time period, and so it appears that the difference is due to a forcing error in the model and not an intrinsic error.

scholarly journals Response of the Midlatitude Jets, and of Their Variability, to Increased Greenhouse Gases in the CMIP5 Models

2013 ◽  
Vol 26 (18) ◽  
pp. 7117-7135 ◽  
Author(s):  
Elizabeth A. Barnes ◽  
Lorenzo Polvani
Keyword(s):  
Climate Change ◽  
Greenhouse Gases ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
North Atlantic ◽  
North Pacific ◽  
Cmip5 Models ◽  
The North ◽  
The North Atlantic ◽  
The North Pacific

Abstract This work documents how the midlatitude, eddy-driven jets respond to climate change using model output from phase 5 of the Coupled Model Intercomparison Project (CMIP5). The authors consider separately the North Atlantic, the North Pacific, and the Southern Hemisphere jets. The analysis is not limited to annual-mean changes in the latitude and speed of the jets, but also explores how the variability of each jet changes with increased greenhouse gases. All jets are found to migrate poleward with climate change: the Southern Hemisphere jet shifts poleward by 2° of latitude between the historical period and the end of the twenty-first century in the representative concentration pathway 8.5 (RCP8.5) scenario, whereas both Northern Hemisphere jets shift by only 1°. In addition, the speed of the Southern Hemisphere jet is found to increase markedly (by 1.2 m s−1 between 850 and 700 hPa), while the speed remains nearly constant for both jets in the Northern Hemisphere. More importantly, it is found that the patterns of jet variability are a strong function of the jet position in all three sectors of the globe, and as the jets shift poleward the patterns of variability change. Specifically, for the Southern Hemisphere and the North Atlantic jets, the variability becomes less of a north–south wobbling and more of a pulsing (i.e., variation in jet speed). In contrast, for the North Pacific jet, the variability becomes less of a pulsing and more of a north–south wobbling. These different responses can be understood in terms of Rossby wave breaking, allowing the authors to explain most of the projected jet changes within a single dynamical framework.

scholarly journals ENSO-correlated fluctuations in ocean bottom pressure and wind-stress curl in the North Pacific

2011 ◽  
Vol 8 (4) ◽  
pp. 1631-1655
Author(s):  
D. P. Chambers
Keyword(s):  
Wind Stress ◽  
North Pacific ◽  
Low Frequency ◽  
Satellite Observations ◽  
Ocean Bottom ◽  
Bottom Pressure ◽  
Wind Stress Curl ◽  
Ocean Bottom Pressure ◽  
The North ◽  
The North Pacific

Abstract. We examine the magnitude of ENSO-correlated variations in wind-stress curl and ocean bottom pressure in the North Pacific between 1992 until 2010, using satellite observations and model output. Our analysis indicates that while there are significant fluctuations correlated with some El Niño and La Niña events, the correlation is still relatively low. Moreover, the ENSO-correlated variability explains only 50 % of the non-seasonal, low-frequency variance. There are significant residual fluctuations in both wind-stress curl and ocean bottom pressure in the region with periods of 4-years and longer. One such fluctuation began in late 2002 and has been observed by the Gravity Recovery and Climate Experiment (GRACE). Even after accounting for ENSO variations, there is a significant trend in ocean bottom pressure in the region, equivalent to 0.7 ± 0.3 cm yr−1 of sea level from January 2003 until December 2008, which is confirmed with steric-corrected altimetry. Although this low-frequency fluctuation does not appear in an ocean model, we show that the winds used to force the model have a significantly reduced trend that is inconsistent with satellite observations over the same time period.

Generation of Annual Rossby Waves in the North Pacific by the Wind Stress Curl

1986 ◽  
Vol 16 (7) ◽  
pp. 1179-1189 ◽  
Author(s):  
Patrick F. Cummins ◽  
Lawrence A. Mysak ◽  
Kevin Hamilton
Keyword(s):  
Wind Stress ◽  
North Pacific ◽  
Rossby Waves ◽  
Wind Stress Curl ◽  
The North ◽  
The North Pacific

scholarly journals Interdecadal Baroclinic Sea Level Changes in the North Pacific Based on Historical Ocean Hydrographic Observations

2015 ◽  
Vol 28 (11) ◽  
pp. 4585-4594 ◽  
Author(s):  
Tatsuo Suzuki ◽  
Masayoshi Ishii
Keyword(s):  
Sea Level ◽  
Wind Stress ◽  
North Pacific ◽  
Water Mass ◽  
Mass Density ◽  
Baroclinic Mode ◽  
Sea Level Changes ◽  
The North ◽  
Basin Scale ◽  
The North Pacific

Abstract Using historical ocean hydrographic observations, decadal to multidecadal sea level changes from 1951 to 2007 in the North Pacific were investigated focusing on vertical density structures. Hydrographically, the sea level changes could reflect the following: changes in the depth of the main pycnocline, density gradient changes across the pycnocline, and modification of the water mass density structure within the pycnocline. The first two processes are characterized as the first baroclinic mode. The changes in density stratification across the pycnocline are sufficiently small to maintain the vertical profile of the first baroclinic mode in this analysis period. Therefore, the first mode should represent mainly the dynamical response to the wind stress forcing. Meanwhile, changes in the composite of all modes of order greater than 1 (remaining baroclinic mode) can be attributed to water mass modifications above the pycnocline. The first baroclinic mode is associated with 40–60-yr fluctuations in the subtropical gyre and bidecadal fluctuations of the Kuroshio Extension (KE) in response to basin-scale wind stress changes. In addition to this, the remaining baroclinic mode exhibits strong variability around the recirculation region south of the KE and regions downstream of the KE, accompanied by 40–60-yr and bidecadal fluctuations, respectively. These fluctuations follow spinup/spindown of the subtropical gyre and meridional shifts of the KE shown in the first mode, respectively. A lag correlation analysis suggests that interdecadal sea level changes due to water mass density changes are a secondary consequence of changes in basin-scale wind stress forcing related to the ocean circulation changes associated with the first mode.

scholarly journals Source-receptor relationships between East Asian sulfur dioxide emissions and Northern Hemisphere sulfate concentrations

2008 ◽  
Vol 8 (2) ◽  
pp. 5537-5561 ◽  
Author(s):  
J. Liu ◽  
D. L. Mauzerall ◽  
L. W. Horowitz
Keyword(s):  
Northern Hemisphere ◽  
North Pacific ◽  
East Asian ◽  
Source Region ◽  
The United States ◽  
So2 Emissions ◽  
Aerosol Model ◽  
The North ◽  
The North Pacific ◽  
Sulfur Emissions

Abstract. We analyze the effect of varying East Asian (EA) sulfur emissions on sulfate concentrations in the Northern Hemisphere, using a global coupled oxidant-aerosol model (MOZART-2). We conduct a base and five sensitivity simulations, in which sulfur emissions from each continent are tagged, to establish the source-receptor (S-R) relationship between EA sulfur emissions and sulfate concentrations over source and downwind regions. We find that from west to east across the North Pacific, EA sulfate contributes approximately 80%–20% of sulfate at the surface, but at least 50% at 500 hPa. In addition, EA SO2 emissions account for approximately 30%–50% and 10%–20% of North American background sulfate over the western and eastern US, respectively. The contribution of EA sulfate to the western US at the surface is highest in MAM and JJA, but is lowest in DJF. Reducing EA SO2 emissions will significantly decrease the spatial extent of the EA sulfate influence over the North Pacific both at the surface and at 500 mb in all seasons, but the extent of influence is insensitive to emission increases, particularly in DJF and JJA. We find that EA sulfate concentrations over most downwind regions respond nearly linearly to changes in EA SO2 emissions, but sulfate concentrations over the EA source region increase more slowly than SO2 emissions, particularly at the surface and in winter, due to limited availability of oxidants (mostly H2O2). We find that similar estimates of the S-R relationship for trans-Pacific transport of EA sulfate would be obtained using either sensitivity or tagging techniques. Our findings suggest that future changes in EA sulfur emissions may cause little change in the sulfate induced health impact over downwind continents but SO2 emission reductions may significantly reduce the sulfate related climate cooling over the North Pacific and the United States.

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