HIGH-DENSITY SPATIOTEMPORAL MONITORING OF WATER TRANSPORT IN HURRICANE SANDY USING STABLE ISOTOPES

Extra-tropical cyclones such as Sandy pose an increasingly serious challenge to a broad portion of the northeastern United States, and their evolution as they mix with mid-latitude weather systems merits further investigation. The large spatial and temporal scale of Sandy, coupled with early predictions of the storm track and extensive media coverage, allowed for a uniquely dense dataset of more then 600 precipitation samples to be collected and analyzed for oxygen and hydrogen stable isotopes. Stable isotope ratios have previously been used to diagnose modes of moisture addition, water transport, and precipitation formation within cyclones. We find that storm-associated waters span an enormous range of isotopic values (>21.4‰ for δ¹⁸O) and exhibit strong spatial and temporal structure. The most striking feature of the storm-water isotope distribution was a profound asymmetry of values about the eye of the storm that developed as Sandy made landfall late on October 29th and was sustained for ~48 hours. During this time low isotope ratios occurred only to the west and south quadrants of the storm and strong gradients in isotopic composition (up to 4.2‰/100km) existed in the vicinity of the storm center. We attribute this pattern to differences in moisture source and varying degrees of heavy-isotope distillation along transport paths feeding different parts of the storm. High values of deuterium-excess (>25‰) were found only in the New England portion of the storm and indicate the mixing of moisture derived from a pre-existing mid-latitude trough with evaporated ocean water. Isotopic analysis of moisture patterns within the storm is complimented by results from the Stochastic Time-Inverted Lagrangian Trajectory (STILT) model which constrain the origin and transport history of air parcels across the study domain. Back trajectory analysis from the STILT model confirm the terrestrial influence of the mid-latitude trough on precipitation in the outer rain-bands of the system occurring in the northeastern quadrant of the storm and demonstrate the utility of spatially explicit isotope monitoring to elucidate the structure and dynamics of water cycling within synoptic-scale systems as they transition from tropical to post-tropical events.