Bibliography - Whit G Anderson
- Gnanadesikan, Anand, K A Emanuel, Gabriel A Vecchi, Whit G Anderson, and Robert W Hallberg, in press: How ocean color can steer Pacific tropical cyclones. Geophysical Research Letters. 7/10.
[ Abstract ]Because ocean color alters the absorption of sunlight, it can produce
changes in sea surface temperatures with further impacts on atmospheric
circulation. These changes can project onto fields previously recognized
to alter the distribution of tropical cyclones. If the North Pacific
subtropical gyre contained no absorbing and scattering materials, the
result would be to reduce subtropical cyclone activity in the
subtropical Northwest Pacific by 2/3, while concentrating cyclone tracks
along the equator. Predicting tropical cyclone activity using coupled
models may thus require consideration of the details of how heat moves
into the upper thermocline as well as biogeochemical cycling.
- Anderson, Whit G., Anand Gnanadesikan, and Andrew T Wittenberg, August 2009: Regional impacts of ocean color on tropical Pacific variability. Ocean Science, 5(3), 313-327.
[ Abstract PDF ]The role of the penetration length scale of shortwave radiation into the surface ocean and its impact on tropical Pacific variability is investigated with a fully coupled ocean, atmosphere, land and ice model. Previous work has shown that removal of all ocean color results in a system that tends strongly towards an El Niño state. Results from a suite of surface chlorophyll perturbation experiments show that the mean state and variability of the tropical Pacific is highly sensitive to the concentration and distribution of ocean chlorophyll. Setting the near-oligotrophic regions to contain optically pure water warms the mean state and suppresses variability in the western tropical Pacific. Doing the same above the shadow zones of the tropical Pacific also warms the mean state but enhances the variability. It is shown that increasing penetration can both deepen the pycnocline (which tends to damp El Niño) while shifting the mean circulation so that the wind response to temperature changes is altered. Depending on what region is involved this change in the wind stress can either strengthen or weaken ENSO variability.
- Gnanadesikan, Anand, and Whit G Anderson, February 2009: Ocean water clarity and the ocean general circulation in a coupled climate model. Journal of Physical Oceanography, 39(2), 314-332.
[ Abstract PDF ]Ocean water clarity affects the
distribution of shortwave heating in the water column. In a one-dimensional
time-mean sense, increased clarity would be expected to cool the surface and
heat subsurface depths as shortwave radiation penetrates deeper into the
water column. However, wind-driven upwelling, boundary currents, and the
seasonal cycle of mixing can bring water heated at depth back to the
surface. This warms the equator and cools the subtropics throughout the year
while reducing the amplitude of the seasonal cycle of temperature in polar
regions. This paper examines how these changes propagate through the climate
system in a coupled model with an isopycnal ocean component focusing on the
different impacts associated with removing shading from different regions.
Increasing shortwave penetration along the equator causes warming to the
south of the equator. Increasing it in the relatively clear gyres off the
equator causes the Hadley cells to strengthen and the subtropical gyres to
shift equatorward. Increasing shortwave penetration in the less clear
regions overlying the oxygen minimum zones causes the cold tongue to warm
and the Walker circulation to weaken. Increasing shortwave penetration in
the high-latitude Southern Ocean causes an increase in the formation of mode
water from subtropical water. The results suggest that more attention be
paid to the processes distributing heat below the mixed layer.
- Anderson, Whit G., Anand Gnanadesikan, Robert W Hallberg, John P Dunne, and Bonita L Samuels, June 2007: Impact of ocean color on the maintenance of the Pacific Cold Tongue. Geophysical Research Letters, 34, L11609, doi:10.1029/2007GL030100.
[ Abstract ]The impact of the penetration length scale of shortwave radiation into the surface ocean is investigated with a fully coupled ocean, atmosphere, land and ice model. Oceanic shortwave radiation penetration is assumed to depend on the chlorophyll concentration. As chlorophyll concentrations increase the distribution of shortwave heating becomes shallower. This change in heat distribution impacts mixed-layer depth. This study shows that removing all chlorophyll from the ocean results in a system that tends strongly towards an El Niño state—suggesting that chlorophyll is implicated in maintenance of the Pacific cold tongue. The regions most responsible for this response are located off-equator and correspond to the oligotrophic gyres. Results from a suite of surface chlorophyll perturbation experiments suggest a potential positive feedback between chlorophyll concentration and a non-local coupled response in the fully coupled ocean-atmosphere system.
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