19 November 2014

Cyclone-Cyclone Interactions through the Ocean Pathway


Tropical cyclones are among the most destructive and widespread natural hazards in the tropics and subtropics, with considerable socio-economic impact and the potential to actively modulate climate. When over the ocean, a cyclone induces intense vertical mixing that entrains colder, deeper water into the relatively warm mixed layer. The resulting intense sea surface temperature cooling lasts several weeks and thus may influence a later cyclone passing over it. Using a 28-year analysis spanning the North Atlantic, eastern Pacific, and Northwest Pacific, a team of scientists led by Department of Energy researchers at Pacific Northwest National Laboratory systematically demonstrated that, on average, when tropical cyclones encounter lingering wakes, they experience sea surface temperatures that are ~0.25–0.5oC colder. Consequently, the intensification rates for cyclones that interact with wakes are ~0.4–0.7 m s-1 / 36 hr. lower than cyclones that do not pass over wakes, consistent with the maximum potential intensity theory. The probability for cyclones to encounter lingering wakes varies positively with cyclone frequency, is ~10% on average, and has been as high as 27%–37% in the past during busy cyclone seasons. These large interaction probabilities reduce the mean intensification rates for cyclones by 3%–6% on average and by ~12%–15% during the most active years. “Cyclone-cyclone interactions” occurring through the ocean pathway may therefore represent a mechanism through which tropical cyclones self-regulate their activity to an extent on intraseasonal time scales, with potential implications for future cyclone activities in a warmer climate.

Karthik Balguru
Pacific Northwest National Laboratory (PNNL)
Balguru, K, S Taraphdar, LR Leung, GR Foltz, and JA Knaff.  2014.  "Cyclone-Cyclone Interactions through the Ocean Pathway."  Geophysical Research Letters, doi:10.1002/2014GL061489.