第72回 ESCセミナー
Impacts of Regional Mixing on Circulations in the Subtropical and Tropical Pacific Ocean
- 日時
- 2013年5月29日(水) 11:00-12:00
- 場所
- 横浜研究所 シミュレータ研究棟1階 会議室
- 講演者
- 古恵 亮
(IPRC, University of Hawai’i at Manoa) - 使用言語
- 英語
要旨
We investigate the sensitivity of solutions to an eddy-permitting ocean general circulation model (OGCM) to regional changes in vertical diffusion at large spatial and temporal scales. Specifically, we increase the background part of the vertical diffusion coefficient, κ, within spatially distinct subregions of the subtropical and tropical Pacific, assess the impacts of those changes, and diagnose the processes that account for them. Each solution is integrated for 20 years.
The temperature anomaly, δT, can be largely explained as a response to ∂(δT)/∂t = δκ ∂2(T0)/∂z2 for the initial 1–2 years, where δκ is the κ increment and T0 is the temperature field of the control run. Salinity and density anomalies are similarly explained. This equation qualitatively explains the density increase (decrease) above (below) the main pycnocline in the first few years. This dynamical signal associated with density anomaly propagates westward as Rossby waves, equatorward along the western boundary, eastward along the equator, poleward along the eastern boundary, and then into the interior. The equilibrium state reflects this classical pathway of Kelvin and Rossby waves. This dynamical signal, however, tends to be much weaker outside the latitude band of the forcing region than within it. In contrast, the “spiciness” anomaly (temperature anomaly on isopycnal surface), being a passive tracer, can be advected to regions where the dynamical signal is weak. This contrast between dynamical and spiciness anomalies is most dramatic for the negative spiciness anomalies that are generated in the subtropics and advected to the equator, reducing temperature in the equatorial pycnocline, whereas density anomaly is negligible there. Similar contrast between dynamical and spiciness anomalies is important to explain the response of the equatorial pycnocline to κ enhancement just off the equator.
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