Stronger super typhoons in a warmer world

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Tuesday, 4 February 2014: 4:30 PM
Room C101 (The Georgia World Congress Center )
Nam-Young Kang, Florida State University, Tallahassee, FL

Tropical cyclones (TCs) continue to inflict serious impacts on national economies and welfare, but how they are responding to global warming has not been fully clarified. Past studies are limited to separate analysis of observables such as frequency and intensity. Here those observables in tandem provide orthogonal axes for an integrated framework that allows us to project global sea-surface temperature (SST) and El Niņo variations onto a complete range of TC climate in the western North Pacific, the most prolific of the TC regions accounting for over a third of all TCs worldwide.

The analysisl framework proves that the out-of-phase relationship between TC frequency and intensity, is strongly linked with global SST, while the in-phase relationship with El Nino. The framework shows global SST has an influence on TC climate that is orthogonal to El Nino's influence. It also clearly shows why attempts to link SST with observed TC frequency and intensity have not been successful. By regarding the El Niņo effect as TC energy, the influence of global SST on TC climate is a regulator of this energy that is interpreted as the efficiency of intensity.

We note that positive and negative factors on TC activity are activated at the same time when global SST increases. To see the climate equilibrium between TC climate and its environemtn, we think of the two factors such as SST and sea level pressure (SLP), for example. Correlations of regional SST with global SST show favorable conditions for both frequency and intensity in TC basins overall except the eastern North Pacific. On the other hand, correlations of regional SLP with global SST variation show anomalous high values in the western North Pacific, which is noticeably different from anomalously low values across the North Atlantic. The anomalous atmospheric subsidence in the western North Pacific discourages TC intensification and genesis. Fewer but stronger TCs in the western North Pacific are interpreted as a climate equilibrium that occurs under global warming through regional changes in SST and atmospheric ubsidence. This implies that the influence of the synthesized environment works in opposite directions for TC frequency and TC intensity when global SST varies. Thus when global SST increases, fewer but stronger TCs result and vice versa. Global warming is an indicator of the gap between the variations of normalized TC frequency and intensity, that we define as the efficiency of intensity.

The upper 10% of the strongest TCs in the western North Pacific are investigated through the same process. The same climate connection with global warming appear in the strongest portion of tropical cyclones in the western North Pacific. The warming seas are providing additional energy to produce more extreme TCs but this is happening at the expense of typhoon frequency in the western North Pacfic. When the activity variation is removed from intensity variation, the annual threshold for the 10% subset appears to be increasing over the super typhoon threshold. It is clarified that super typhoons are getting stronger at the expense of the occurrences in this warming world. Results imply that record breaking typhoon intensities and destructiveness are likely under continued global warming regardless of the increase of tropical cyclone energy.

The novel framework is applicable to a broad range of geophysical phenomenon having frequency and magnitude statistics.