Abstract
Extra-tropical cyclones, such as 2012 Superstorm Sandy, pose a significant climatic threat to the northeastern United Sates, yet prediction of hydrologic and thermodynamic processes within such systems is complicated by their interaction with mid-latitude water patterns as they move poleward. Fortunately, the evolution of these systems is also recorded in the stable isotope ratios of storm-associated precipitation and water vapor, and isotopic analysis provides constraints on difficult-to-observe cyclone dynamics. During Superstorm Sandy, a unique crowdsourced approach enabled 685 precipitation samples to be obtained for oxygen and hydrogen isotopic analysis, constituting the largest isotopic sampling of a synoptic-scale system to date. Isotopically, these waters span an enormous range of values (21‰ for O, 160‰ for H) and exhibit strong spatiotemporal structure. Low isotope ratios occurred predominantly in the west and south quadrants of the storm, indicating robust isotopic distillation that tracked the intensity of the storm's warm core. Elevated values of deuterium-excess (25‰) were found primarily in the New England region after Sandy made landfall. Isotope mass balance calculations and Lagrangian back-trajectory analysis suggest that these samples reflect the moistening of dry continental air entrained from a mid-latitude trough. These results demonstrate the power of rapid-response isotope monitoring to elucidate the structure and dynamics of water cycling within synoptic-scale systems and improve our understanding of storm evolution, hydroclimatological impacts, and paleo-storm proxies.
Highlights
Addressing the challenge posed by extra-tropical cyclones requires a detailed understanding of how mid-latitidue weather patterns interact with the water and energy budgets of poleward moving storms [1,2]
Information about the hydrologic and thermodynamic processes of these large storms is recorded as distinct isotopic signatures in the waters of contemporary hurricanes [3,4,5,6,7,8,9,10] as well as in isotopic proxies found in the prehistoric record [11,12,13]
The stable isotope ratios of oxygen, d18O [%], and hydrogen, d2H [%], (d = Rsample/Rstd -1 where R = 2H/1H or 18O/16O) obtained from cyclonic precipitation are informative tools that can aid in untangling the dynamic evolution of extra-tropical systems
Summary
Addressing the challenge posed by extra-tropical cyclones requires a detailed understanding of how mid-latitidue weather patterns interact with the water and energy budgets of poleward moving storms [1,2]. The stable isotope ratios of oxygen, d18O [%], and hydrogen, d2H [%], (d = Rsample/Rstd -1 where R = 2H/1H or 18O/16O) obtained from cyclonic precipitation are informative tools that can aid in untangling the dynamic evolution of extra-tropical systems. Isotopic values well below the typical range of low and midlatitude precipitation were attributed to the increased longevity, size, and thickness of clouds within cyclonic systems. This rainout effect is known to arise because the progressive loss of moisture coupled with temperature dependent equilibrium fractionation drives heavier isotopes to preferentially rainout, and the remaining vapor becomes increasingly depleted in the heavy isotopes [14]
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