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- Title
<sup>17</sup>O‐Excess in Tropical Cyclones Reflects Local Rain Re‐Evaporation More Than Moisture Source Conditions.
- Authors
Sun, Chijun; Shanahan, Timothy; He, Shaoneng; Bailey, Adriana; Nusbaumer, Jesse; Hu, Jun; Hillman, Aubrey; Ornouski, Erika; Warner, Jacob; DeLong, Kristine
- Abstract
17O‐excess is a relatively new water isotope parameter that could potentially provide useful information about the hydrological cycle. Previous works focusing on 17O‐excess in polar regions suggest that it primarily tracks moisture source relative humidity, but little is known about how to interpret 17O‐excess data in lower latitudes. Here we present quasi‐hourly triple oxygen isotope data of precipitation collected from two tropical cyclones in Texas and Louisiana in 2020 to understand the impacts of environmental and meteorological processes on the 17O‐excess of low‐to mid‐latitude precipitation. We find that at both hourly timescales and the event scale, 17O‐excess is strongly correlated to changes in on‐site rainfall intensity and relative humidity, which is consistent with the theory that the isotopic fractionation associated with rain re‐evaporation lowers the 17O‐excess of the remaining droplet. In addition, although evaporative conditions at the moisture source region may also influence 17O‐excess of water vapor transported to the precipitation site, their impacts are likely overprinted by the post‐condensation rain re‐evaporation processes. Our results thus suggest that 17O‐excess can be used as a proxy for local rather than source region evaporative conditions during tropical cyclones. Plain Language Summary: The stable isotopic composition of water can be used to track the hydrologic cycle. 17O‐excess measures the relative abundance of the two less abundant stable isotope species of oxygen (17O and 18O), and is known to contain unique information about how humid the air is where the water comes from. However, most of such observations were done in polar regions. In order to understand how to use 17O‐excess in (sub‐) tropical regions correctly, we collected rainwater from two tropical cyclone storms in the southern United States in 2020. We discovered that during these storms, it was actually the humidity at the site of precipitation, rather than where the water came from, that drove changes in 17O‐excess values of precipitation. This is because rainwater tends to evaporate back into the air when the local condition is drier, making 17O‐excess values lower. Our study suggests that 17O‐excess should be interpreted as local humidity instead of the humidity at the moisture source in (sub‐) tropical regions. Key Points: Intra‐event 17O‐excess data is reported for two tropical cyclonesRe‐evaporation is the dominant control on 17O‐excess variability in the tropical cyclones observed in this study17O‐excess may be used as a proxy for assessing rain re‐evaporation in low‐to mid‐latitudes
- Subjects
LOUISIANA; TEXAS; TROPICAL cyclones; RAINFALL; HYDROLOGIC cycle; HUMIDITY; WATER vapor transport; TROPICAL storms
- Publication
Journal of Geophysical Research. Atmospheres, 2024, Vol 129, Issue 6, p1
- ISSN
2169-897X
- Publication type
Article
- DOI
10.1029/2023JD039361