Connecting Tropical Cyclones, Precursor Disturbances, and the ITCZ in Aquaplanet Simulations.
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| Title: | Connecting Tropical Cyclones, Precursor Disturbances, and the ITCZ in Aquaplanet Simulations. |
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| Authors: | Burnett, Adam C.1 (AUTHOR) acb18@stanford.edu, Sheshadri, Aditi1 (AUTHOR), Robinson, Thomas2 (AUTHOR), Lin, Pu2,3 (AUTHOR) |
| Source: | Journal of Advances in Modeling Earth Systems. Jul2025, Vol. 17 Issue 7, p1-16. 16p. |
| Subject Terms: | *Climate change, *Ecological disturbances, *Ocean temperature, *Rainstorms, Tropical cyclones, Intertropical convergence zone, Coriolis force |
| Abstract: | We investigate a scaling relationship between global tropical cyclone (TC) frequency and the latitude of the intertropical convergence zone (ITCZ) in simulations performed with a 50‐km‐resolution aquaplanet version of the Geophysical Fluid Dynamics Laboratory Atmosphere Model 4.0. The simulations use fixed, zonally symmetric sea surface temperature distributions, including some with uniform warming and cooling perturbations. We find that TC frequency per unit area is proportional to the Coriolis parameter at the ITCZ, following the same scaling introduced in a previous study. We hypothesize that TCs in these simulations originate as precursor disturbances at the ITCZ and intensify into TCs upon reaching sufficiently warm SSTs. We test this interpretation by tracking TC precursors, with different methods based on precipitation and vorticity, and comparing TC precursor frequency with TC frequency and ITCZ latitude. Both tracking methods show that precursors predominantly originate around the poleward edge of the ITCZ, consistent with our hypothesized TC genesis pathway. We also verify that most TC genesis events are immediately preceded by the occurrence of a precursor in the same area. However, precursor frequency is only weakly correlated with the Coriolis parameter at the ITCZ and precursor frequency. The correlation is stronger for vorticity‐based precursors than for precipitation‐based precursors. These mixed results provide partial, but not complete, support for our hypothesized interpretation. They also illustrate how results can depend on the choice of precursor tracking scheme, underlining a need for improved understanding of how best to define and track TC precursors. Plain Language Summary: It is unclear whether tropical cyclones, which include hurricanes and similar storms around the world, will occur more or less often due to climate change. We would like to understand what factors determine how often tropical cyclones occur. In this study, we examine the link between tropical cyclones and the intertropical convergence zone (ITCZ), which is a region of intense rainfall near the equator. In agreement with previous work, we find that more tropical cyclones occur when the ITCZ is farther from the equator, and that this relationship also holds in a variety of warmer and cooler climates. We also show that, consistent with our hypothesis, the ITCZ produces smaller storms that later become tropical cyclones. Like the number of tropical cyclones, the number of these smaller storms is higher when the ITCZ is farther from the equator, but this result differs depending on how these smaller storms are defined. Key Points: Tropical cyclone frequency scales with the Coriolis parameter at the intertropical convergence zone in warm and cool aquaplanet simulationsTracking precursor disturbances reveals a moderate correlation between the Coriolis parameter and precursor frequencyDifferent tracking methods and definitions of precursors yield different relationships with tropical cyclones and large‐scale climate [ABSTRACT FROM AUTHOR] |
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| Abstract: | We investigate a scaling relationship between global tropical cyclone (TC) frequency and the latitude of the intertropical convergence zone (ITCZ) in simulations performed with a 50‐km‐resolution aquaplanet version of the Geophysical Fluid Dynamics Laboratory Atmosphere Model 4.0. The simulations use fixed, zonally symmetric sea surface temperature distributions, including some with uniform warming and cooling perturbations. We find that TC frequency per unit area is proportional to the Coriolis parameter at the ITCZ, following the same scaling introduced in a previous study. We hypothesize that TCs in these simulations originate as precursor disturbances at the ITCZ and intensify into TCs upon reaching sufficiently warm SSTs. We test this interpretation by tracking TC precursors, with different methods based on precipitation and vorticity, and comparing TC precursor frequency with TC frequency and ITCZ latitude. Both tracking methods show that precursors predominantly originate around the poleward edge of the ITCZ, consistent with our hypothesized TC genesis pathway. We also verify that most TC genesis events are immediately preceded by the occurrence of a precursor in the same area. However, precursor frequency is only weakly correlated with the Coriolis parameter at the ITCZ and precursor frequency. The correlation is stronger for vorticity‐based precursors than for precipitation‐based precursors. These mixed results provide partial, but not complete, support for our hypothesized interpretation. They also illustrate how results can depend on the choice of precursor tracking scheme, underlining a need for improved understanding of how best to define and track TC precursors. Plain Language Summary: It is unclear whether tropical cyclones, which include hurricanes and similar storms around the world, will occur more or less often due to climate change. We would like to understand what factors determine how often tropical cyclones occur. In this study, we examine the link between tropical cyclones and the intertropical convergence zone (ITCZ), which is a region of intense rainfall near the equator. In agreement with previous work, we find that more tropical cyclones occur when the ITCZ is farther from the equator, and that this relationship also holds in a variety of warmer and cooler climates. We also show that, consistent with our hypothesis, the ITCZ produces smaller storms that later become tropical cyclones. Like the number of tropical cyclones, the number of these smaller storms is higher when the ITCZ is farther from the equator, but this result differs depending on how these smaller storms are defined. Key Points: Tropical cyclone frequency scales with the Coriolis parameter at the intertropical convergence zone in warm and cool aquaplanet simulationsTracking precursor disturbances reveals a moderate correlation between the Coriolis parameter and precursor frequencyDifferent tracking methods and definitions of precursors yield different relationships with tropical cyclones and large‐scale climate [ABSTRACT FROM AUTHOR] |
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| ISSN: | 19422466 |
| DOI: | 10.1029/2024MS004868 |
