The ocean circulation is driven by a combination of winds and surface buoyancy fluxes. We run a number of experiments with varied surface forcings and look at the spatial variations in ocean circulation on short and long time-scales.
| Name of experiment | Description | Issues |
|---|---|---|
| Zero mean winds | Removing the time-mean winds and inputting only the temporal fluctuations. It is believed that the ocean gyres receive momentum input from the mean winds. A contradictory theory (refer Chris Bull's paper) also highlights the role of wind variability in determining the strength of western boundary currents in ocean gyres. | Should we alter the mean winds or mean wind stress for this experiment? The ACCESS-OM2 uses relative winds to estimate wind stress, which is the difference between absolute winds and ocean surface velocities. Removing mean winds wouldn't necessarily imply that all time fluctuations in wind stresses are removed. |
| Altering surface buoyancy forcing | In the past, our experiments focused on altering wind stress in ocean basins. However, winds affect a lot of ocean dynamics which could have an adverse effect on surface buoyancy forcing as well. Therefore, instead of changing the magnitude of wind stress, we change the magnitude of surface buoyancy forcing and study the resulting effect on ocean circulation. We can change (block/permit) the heat fluxes entering the ocean in various ways, like (i) Altering the bulk formulae, (ii) Changing KPP and (iii) Perturbing the SAT (Surface air temperature). | None so far |
| Altering wind stress magnitude | In the past, our experiments focused on either having or zeroing wind stress in ocean basins. In this run, instead of completely shutting down winds, we aim to strengthen/weaken winds by 20-30%. We can use the spatial mask already coded in ACCESS-OM2 for our purpose. | None so far |
| Manual tweaking of KPP depth | This experiment is in line with changing the surface buoyancy forcing to meet similar magnitudes as the control run. We expect to increase the KPP depth manually (by multiplying the depth with a factor greater than 1) to a resolved velocity shear parameterised no-stress run. | Manually changing the mixing layer depth is unphysical, and the numerical solution could blow up. |
| Winds adjusted in specific basins | In this series of experiments, we switch off (or modify) winds in particular basin(s). For eg: The ocean circulation in North Atlantic is a lot more dependent on the global ocean circulation than the North Pacific, as can be seen in all the experiments we have done so far (). By turning off winds in entire Hemispheres have consequences on global ocean circulation, which affects local circluation, like ocean gyes in these basins. By switching off winds in the North Pacific, we expect the basin to not affect (or be affected) by global circulation. | There is a North Pacific subtropical cell which is an outcome of wind stress, and leads to a net meridional heat transfer from the tropics to the poles. Absence of such a cell would lead to a feeback loop, where a lack of meridional heat transport would eventually lead to lesser heat input in the tropics. |
| Winds off in [50 S, 50 N] | Our previous experiments have failed to establish a correlation between gyre strength and surface buoyancy fluxes, partly because turning winds off reduces the buoyancy forcing (via a reduction in overturning circulation and meridional heat flux) too, which makes it virtually impossible to attribute changes in gyre circulation to a particular forcing. The formation of two water masses, the NADW and AABW, occur in the subpolar regions, and are crucial to the sustenance of global overturning circulation (Talley 2013). In this experiment, we remove (or weaken) winds only in the tropics and subtropics, but keep the surface forcing in the subpolar and polar regions similar to control run. We can therefore, expect that the NADW and AABW are formed and could potentially result in a similar overturning as the control run, which can lead to similar amounts of buoyancy fluxes entering the ocean. | The AABW upwells in the Indian and Pacific oceans to form the Indian/Pacific deep waters, which occurs through diapycnal mixing. This process is also crucial in completing overturning. |