Beach erosion due to large storms critically affects coastal vulnerability, but is challenging to monitor and quantify. Attributing erosion to a specific storm requires a reliable counterfactual scenario: hypothetical beach conditions, absent the storm. Calibrating models to construct counterfactuals requires numerous observations that are rarely available. Storm paths are unpredictable, making long‐term instrumentation of specific beaches costly. Optical remote sensing is hampered by persistent cloud cover. We use Sentinel‐1 satellite radar imagery to monitor shoreline changes through clouds and propose regression discontinuity as a strategy to estimate the causal effect of large storms on beach erosion. Applied to 75 beaches across Puerto Rico, the approach detects shoreline changes with a root‐mean‐square error comparable to the resolution of the imagery. Hurricane Maria caused an erosion of 3 to 5 m along its path, up to 40 m at particular beaches. Results reveal strong local disparities that are consistent with simulated nearshore hydrodynamic conditions.
The relationship between eastward propagating convective equatorial signals (CES) along the Equatorial Indian Ocean (EIO) and the northward propagating Monsoon Intraseasonal Oscillations (MISOs) in the Bay of Bengal (BOB) was studied using observational datasets acquired during the 2018 and 2019 MISO-BOB field campaigns. Convective envelopes of MISOs originating from just south of the BOB were associated with both strong and weak eastward CES (average speed ~ 6.4 m/s). Strong CES contributed to ~ 20% of the precipitation budget of BOB, and they spurred northward propagating convective signals that matched the canonical speed of MISOs (1-2 m/s). In contrast, weak CES signals contributed to ~ 14% of the BOB precipitation budget, and they dissipated without significant northward propagation. Eastward propagating Intraseasonal Oscillations (ISOs; period 30-60 days) and Convectively Coupled Kelvin Waves (CCKWs; period 4-15 days) accounted for most precipitation variability across the EIO during the 2019 boreal summer as compared to that of 2018. An agreement could be noted between high moisture content in the mid-troposphere and the active phases of CCKWs and ISOs for two observational locations in the BOB. Basin-scale thermodynamic conditions prior to the arrival of strong/weak CES revealed warmer/cooler SSTs. Flux measurements aboard a research vessel suggest that the evolution of MISOs associated with strong CES are signified by local enhanced air-sea interactions, in particular the supply of local moisture and sensible heat, which could enhance deep convection and further moisten the upper troposphere.
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