Time-dependent asymmetry of phytoplankton bloom in the wake of tropical cyclones

We composited northern hemispheric SeaWIFS and MODIS data to study the time-dependent development of Chl-a in the wake of tropical cyclones (TCs) according to their observed tracks obtained from the IBTrACS data, from 1998-2014. The response is much stronger in the western Pacific than the Atlantic. At the early stage ~5 days after the passage of the TC, the Chl-a shows a rightward asymmetry, while the longer-term response ~10 days and after shows a shift towards leftward asymmetry. In order to understand this change, we studied the left-right asymmetry of the mixed-layer depth using the ARGO data, mixing using satellite wind, inertial current energy using surface drifters, cooling using GHRSST, and precipitation using the TRMM data. We also conducted coupled biophysical model experiments. The early response leading to the rightward asymmetry is caused by re-stratification by sub-mesosacle eddies on the right-side – due to the mechanism proposed by Huang and Oey [2015; JGR] - not by vertical mixing as has previously been assumed. The later leftward asymmetric Chl-a response after ~10days in the western North Pacific is caused by preferential stratification caused by enhanced precipitation on the left side as a result of preferential northeasterly wind shear.