A Recent Reversal in the Poleward Shift of Western North Pacific Tropical Cyclones

What is it about?

Tropical cyclones (TCs) account for the majority of natural catastrophic losses in the developed world and are the second leading cause (next to floods) of death and injury among natural disasters affecting developing countries. The challenges for climate detection and attribution research with regard to TCs are to determine whether an observed change in TC activity exceeds the natural variability and to attribute significant changes to anthropogenic forcing (e.g., greenhouse gases or aerosols). Recent studies have indicated that the TCs over the western North Pacific (WNP) systematically migrated poleward, which is plausibly linked to the expansion of the tropics associated with anthropogenic forcing. However, utilizing our new measurement, we find that the poleward migration of WNP TCs reversed direction during the recent warming slowing-down period (after ~1999). We thus propose a new mechanism associated with the regional pattern of SST change, which is characterized by a relatively warm or cold SST pool in the region (20°-40°N, 140°-160°E). Compared with the previous theory based on anthropogenic forcing and well-known dominant modes of variability, the new mechanism provides a more convincing explanation for the migration of WNP TCs since 1980, especially for the recent warming slowing-down period.

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Why is it important?

Recent studies have revealed a global, poleward migration trend of tropical cyclones (TCs) in terms of annual-averaged latitude of lifetime maximum intensity under the global warming. The TCs in the western North Pacific (WNP) make the largest contribution to this trend. One existing hypothesis is that there is a linkage between poleward migration of TCs and anthropogenic forcing. Here, we introduce a new measurement, the lifetime-averaged latitude weighted by TC destructive potential, to detect the meridional migration of the WNP TCs, which is more reliable and meaningful as it considers not only past data uncertainty but also public concerns. Our results show that the trend of WNP TC migration reversed during the recent warming slowing-down period (after ~1999). Different from the existing hypothesis, it is the change of regional pattern of sea surface temperature (SST) that contributes greatly to the meridional migration of WNP TCs.

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