Other studies have attributed these changes to post-condensation isotopic exchange between falling rain and ambient vapor 3, 10 or re-evaporation of falling precipitation 9 at the edge of TCs or the uptake of isotopically enriched moisture from nearby warm surface ocean waters 4.Ī few studies have examined high-frequency variability in TC rainfall during individual storm events and have observed large swings in the isotopic composition of precipitation on hourly timescales 4, 11. One process suggested to account for the isotopic change is the effect of higher vertical rainout efficiency associated with higher and thicker clouds near the eyewall 2, 3. What causes this spatial isotopic pattern remains a subject of debate. A consistent observation in many studies of TCs is that there is a systematic depletion of heavy isotopes in rainfall radially inward towards the center of the storm, with exceptionally negative delta values only occurring in areas close to the eyewall 2, 3, 8, 9. And while a number of studies over the past few decades have tried to characterize how rainwater stable isotopes change during TCs, and to identify hurricane events in proxy records, there remain questions about the mechanisms driving these changes and whether they are large enough to be recorded in even annually-resolved proxy records.įor example, previous studies have observed that rainwater isotopic values from TCs are spatiotemporally heterogeneous. However, recent studies of modern rainfall from Central America have demonstrated that anomalously positive stable isotope values in tropical precipitation can occur under a variety of conditions, complicating the interpretation of isotope-based TC reconstructions 4, 7. The exceptionally depleted isotopic signatures of TCs provide a potentially valuable indicator of past storm activity that may be recorded in high-resolution archives of climate (e.g., speleothems, tree rings, corals, etc.) 5, 6. Tropical cyclones (TCs) are known to produce precipitation with extremely negative stable isotopic delta values (i.e., δ 18O and δ 2H) compared with other tropical rainfall sources 1, 2, 3, 4. ![]() Isotope-enabled climate modeling suggests that it may be possible to identify the signature of tropical cyclones from annually resolved isotopic proxy records, but will depend on the size of the storm and the proximity of the site to the core of the storm system. These appear to be controlled by microphysical processes associated with the passage of spiral rainbands over the sampling locations. Superimposed on these gradual changes are abrupt isotopic shifts with exceptionally low deuterium excess values. Rainfall δ 18O trend towards more negative values as a result of Rayleigh distillation of precipitation-generating airmasses as they travel towards the center of the storm. Here we studied the isotopic composition of rainfall at sites across central Texas during Hurricane Harvey (2017) to better understand these processes. Tropical cyclones produce rainfall with extremely negative isotope values (δ 18O and δ 2H), but the controls on isotopic fractionation during tropical cyclones are poorly understood.
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