Lynch Daniel R.

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Lynch
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Daniel R.
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  • Article
    Model simulations of the Bay of Fundy Gyre : 2. Hindcasts for 2005–2007 reveal interannual variability in retentiveness
    (American Geophysical Union, 2009-09-03) Aretxabaleta, Alfredo L. ; McGillicuddy, Dennis J. ; Smith, Keston W. ; Manning, James P. ; Lynch, Daniel R.
    A persistent gyre at the mouth of the Bay of Fundy results from a combination of tidal rectification and buoyancy forcing. Here we assess recent interannual variability in the strength of the gyre using data assimilative model simulations. Realistic hindcast representations of the gyre are considered during cruises in 2005, 2006, and 2007. Assimilation of shipboard and moored acoustic Doppler current profiler velocities is used to improve the skill of the simulations, as quantified by comparison with nonassimilated drifter trajectories. Our hindcasts suggest a weakening of the gyre system during May 2005. Retention of simulated passive particles in the gyre during that period was highly reduced. A recovery of the dense water pool in the deep part of the basin by June 2006 resulted in a return to particle retention characteristics similar to climatology. Retention estimates reached a maximum during May 2007 (subsurface) and June–July 2007 (near surface). Interannual variability in the strength of the gyre was primarily modulated by the stratification of the dense water pool inside the Grand Manan Basin. These changes in stratification were associated with mixing conditions the preceding fall–winter and/or advectively driven modification of water mass properties.
  • Article
    Data assimilative hindcast of the Gulf of Maine coastal circulation
    (American Geophysical Union, 2005-10-12) He, Ruoying ; McGillicuddy, Dennis J. ; Lynch, Daniel R. ; Smith, Keston W. ; Stock, Charles A. ; Manning, James P.
    A data assimilative model hindcast of the Gulf of Maine (GOM) coastal circulation during an 11 day field survey in early summer 2003 is presented. In situ observations include surface winds, coastal sea levels, and shelf hydrography as well as moored and shipboard acoustic Doppler D current profiler (ADCP) currents. The hindcast system consists of both forward and inverse models. The forward model is a three-dimensional, nonlinear finite element ocean circulation model, and the inverse models are its linearized frequency domain and time domain counterparts. The model hindcast assimilates both coastal sea levels and ADCP current measurements via the inversion for the unknown sea level open boundary conditions. Model skill is evaluated by the divergence of the observed and modeled drifter trajectories. A mean drifter divergence rate (1.78 km d−1) is found, demonstrating the utility of the inverse data assimilation modeling system in the coastal ocean setting. Model hindcast also reveals complicated hydrodynamic structures and synoptic variability in the GOM coastal circulation and their influences on coastal water material property transport. The complex bottom bathymetric setting offshore of Penobscot and Casco bays is shown to be able to generate local upwelling and downwelling that may be important in local plankton dynamics.