Ocean color affects tropical cyclone formation

From the AGU:

The color of the ocean can alter the frequency of tropical cyclones, according to a recent study. The absorption of sunlight is affected by the concentration of chlorophyll, with the Sun’s heat penetrating deeper in clear, low-chlorophyll waters. In ocean gyres, this heat can get carried away, so that lower concentrations of chlorophyll are associated with colder surface waters. Ocean surface temperatures can affect atmospheric circulation patterns, and thus the formation of cyclones and other weather patterns.

Gnanadesikan et al. use a coupled climate model to study how chlorophyll levels could affect tropical cyclones. They simulate the formation rate of cyclones in the subtropical North Pacific under scenarios with current chlorophyll levels, with half of current chlorophyll levels, and with no chlorophyll. They find that reducing chlorophyll focused the paths of cyclones along the equator. Eliminating all chlorophyll would reduce tropical cyclone activity poleward of 15 degrees North latitude by two thirds.

Although a no-chlorophyll scenario is extreme, the researchers note other research suggesting that 1960s chlorophyll levels in the Pacific were about 50 percent lower than at present. As tropical cyclone activity has increased since that time, they suggest that ocean color could be a factor that should be taken into account in explaining and predicting such changes.

See 13 August press release at: http://www.agu.org/news/press/pr_archives/2010/2010-25.shtml

Title: How ocean color can steer Pacific tropical cyclones

Authors: Anand Gnanadesikan: Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, New Jersey, USA;

Kerry Emanuel:Department of Earth, Atmosphere and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA;

Gabriel A. Vecchi, Whit G. Anderson, and Robert Hallberg: Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, New Jersey, USA.

Source: Geophysical Research Letters, doi:10.1029/2010GL044514, 2010 http://dx.doi.org/10.1029/2010GL044514