Strengthening of the Pacific Equatorial Undercurrent in the SODA Reanalysis: Mechanisms, Ocean Dynamics, and Implications
Several recent studies utilizing global climate models predict that the Pacific Equatorial Undercurrent (EUC) will strengthen over the twenty-first century. Here, historical changes in the tropical Pacific are investigated using the Simple Ocean Data Assimilation (SODA) reanalysis toward understandi...
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| Format: | Article |
| Language: | en_US |
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American Meteorological Society
2014
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| Online Access: | http://hdl.handle.net/1721.1/91276 |
| _version_ | 1811074446982643712 |
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| author | Karnauskas, Kristopher B. Drenkard, Elizabeth Joan |
| author2 | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences |
| author_facet | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Karnauskas, Kristopher B. Drenkard, Elizabeth Joan |
| author_sort | Karnauskas, Kristopher B. |
| collection | MIT |
| description | Several recent studies utilizing global climate models predict that the Pacific Equatorial Undercurrent (EUC) will strengthen over the twenty-first century. Here, historical changes in the tropical Pacific are investigated using the Simple Ocean Data Assimilation (SODA) reanalysis toward understanding the dynamics and mechanisms that may dictate such a change. Although SODA does not assimilate velocity observations, the seasonal-to-interannual variability of the EUC estimated by SODA corresponds well with moored observations over a ~20-yr common period. Long-term trends in SODA indicate that the EUC core velocity has increased by 16% century[superscript −1] and as much as 47% century[superscript −1] at fixed locations since the mid-1800s. Diagnosis of the zonal momentum budget in the equatorial Pacific reveals two distinct seasonal mechanisms that explain the EUC strengthening. The first is characterized by strengthening of the western Pacific trade winds and hence oceanic zonal pressure gradient during boreal spring. The second entails weakening of eastern Pacific trade winds during boreal summer, which weakens the surface current and reduces EUC deceleration through vertical friction. EUC strengthening has important ecological implications as upwelling affects the thermal and biogeochemical environment. Furthermore, given the potential large-scale influence of EUC strength and depth on the heat budget in the eastern Pacific, the seasonal strengthening of the EUC may help reconcile paradoxical observations of Walker circulation slowdown and zonal SST gradient strengthening. Such a process would represent a new dynamical “thermostat” on CO[subscript 2]-forced warming of the tropical Pacific Ocean, emphasizing the importance of ocean dynamics and seasonality in understanding climate change projections. |
| first_indexed | 2024-09-23T09:49:34Z |
| format | Article |
| id | mit-1721.1/91276 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T09:49:34Z |
| publishDate | 2014 |
| publisher | American Meteorological Society |
| record_format | dspace |
| spelling | mit-1721.1/912762022-09-30T17:03:16Z Strengthening of the Pacific Equatorial Undercurrent in the SODA Reanalysis: Mechanisms, Ocean Dynamics, and Implications Karnauskas, Kristopher B. Drenkard, Elizabeth Joan Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Woods Hole Oceanographic Institution Drenkard, Elizabeth Joan Several recent studies utilizing global climate models predict that the Pacific Equatorial Undercurrent (EUC) will strengthen over the twenty-first century. Here, historical changes in the tropical Pacific are investigated using the Simple Ocean Data Assimilation (SODA) reanalysis toward understanding the dynamics and mechanisms that may dictate such a change. Although SODA does not assimilate velocity observations, the seasonal-to-interannual variability of the EUC estimated by SODA corresponds well with moored observations over a ~20-yr common period. Long-term trends in SODA indicate that the EUC core velocity has increased by 16% century[superscript −1] and as much as 47% century[superscript −1] at fixed locations since the mid-1800s. Diagnosis of the zonal momentum budget in the equatorial Pacific reveals two distinct seasonal mechanisms that explain the EUC strengthening. The first is characterized by strengthening of the western Pacific trade winds and hence oceanic zonal pressure gradient during boreal spring. The second entails weakening of eastern Pacific trade winds during boreal summer, which weakens the surface current and reduces EUC deceleration through vertical friction. EUC strengthening has important ecological implications as upwelling affects the thermal and biogeochemical environment. Furthermore, given the potential large-scale influence of EUC strength and depth on the heat budget in the eastern Pacific, the seasonal strengthening of the EUC may help reconcile paradoxical observations of Walker circulation slowdown and zonal SST gradient strengthening. Such a process would represent a new dynamical “thermostat” on CO[subscript 2]-forced warming of the tropical Pacific Ocean, emphasizing the importance of ocean dynamics and seasonality in understanding climate change projections. National Science Foundation (U.S.) (Grant OCE-1031971) National Science Foundation (U.S.) (Grant OCE-1233282) 2014-11-04T13:20:25Z 2014-11-04T13:20:25Z 2014-03 2013-12 Article http://purl.org/eprint/type/JournalArticle 0894-8755 1520-0442 http://hdl.handle.net/1721.1/91276 Drenkard, Elizabeth J., and Kristopher B. Karnauskas. “Strengthening of the Pacific Equatorial Undercurrent in the SODA Reanalysis: Mechanisms, Ocean Dynamics, and Implications.” J. Climate 27, no. 6 (March 2014): 2405–2416. © American Meteorological Society en_US http://dx.doi.org/10.1175/JCLI-D-13-00359.1 Journal of Climate Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf American Meteorological Society American Meteorological Society |
| spellingShingle | Karnauskas, Kristopher B. Drenkard, Elizabeth Joan Strengthening of the Pacific Equatorial Undercurrent in the SODA Reanalysis: Mechanisms, Ocean Dynamics, and Implications |
| title | Strengthening of the Pacific Equatorial Undercurrent in the SODA Reanalysis: Mechanisms, Ocean Dynamics, and Implications |
| title_full | Strengthening of the Pacific Equatorial Undercurrent in the SODA Reanalysis: Mechanisms, Ocean Dynamics, and Implications |
| title_fullStr | Strengthening of the Pacific Equatorial Undercurrent in the SODA Reanalysis: Mechanisms, Ocean Dynamics, and Implications |
| title_full_unstemmed | Strengthening of the Pacific Equatorial Undercurrent in the SODA Reanalysis: Mechanisms, Ocean Dynamics, and Implications |
| title_short | Strengthening of the Pacific Equatorial Undercurrent in the SODA Reanalysis: Mechanisms, Ocean Dynamics, and Implications |
| title_sort | strengthening of the pacific equatorial undercurrent in the soda reanalysis mechanisms ocean dynamics and implications |
| url | http://hdl.handle.net/1721.1/91276 |
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