Impacts of Extratropical Weather Perturbations on Tropical Cyclone Activity: Idealized Sensitivity Experiments With a Regional Atmospheric Model Geophysical Research Letters

Extratropical weather perturbations have been linked to Atlantic tropical cyclones (TCs) activity in observations. However, modeling studies of the extratropical impact are scarce and disagree about its importance and climate implications. Using a nonhydrostatic regional atmospheric model, we explore the extratropical impact by artificially suppressing extratropical weather perturbations at the tropical-extratropical interface. Our 22-year simulations of August–October suggest that the extratropical suppression adds ~3.7 Atlantic TCs per season on average, although the response varies among individual years. The TC response mainly appears within 30–40°N, where tropical cyclogenesis frequency quadruples compared to control simulations. This increased cyclogenesis, accompanied by a strong increase of midtropospheric relative humidity, arises as the perturbation suppression reduces the extratropical interference of TC development. The suppression of extratropical perturbations is highly idealized but may suggest mechanisms by which extratropical atmospheric variability potentially influences TC activity in past or future altered climate states.