Sun Yunfang

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Last Name
Sun
First Name
Yunfang
ORCID
0000-0001-6656-2581

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Article

Effects of interannual environmental variability on the transport-retention dynamics in haddock Melanogrammus aeglefinus larvae on Georges Bank

2013-07-30 , Boucher, Jason M. , Chen, Changsheng , Sun, Yunfang , Beardsley, Robert C.

Georges Bank is a region of high biological productivity characterized by a well-defined clockwise tidal rectified circulation gyre. Fluctuations in the year-class strength of haddock Melanogrammus aeglefinus on Georges Bank have been attributed to mortality during the highly vulnerable larval stages. While predation and starvation greatly impact on survival, advection to unfavorable regions may result in greatly reduced numbers of individuals. For successful self-recruitment to occur, individuals must remain within the shoal region of Georges Bank until settlement. An individual-based model (IBM) was utilized to estimate the retention of haddock eggs and larvae on Georges Bank annually for 1995 through 2009. The IBM was driven by the Finite-Volume Community Ocean Model (FVCOM) for the Gulf of Maine domain. Biological components of haddock larvae were omitted to restrict analyses to the impact of circulation on passive transport. Inflow over the Scotian Shelf and tidal interaction patterns were identified as the major drivers of variability in interannual transport-retention dynamics. The simulations indicated that retention rates were highest in 2000 and 2003, and lowest in 1997. The above-average retention in 2000 and 2003 with anomalously large recruitment only in 2003 indicates that high retention appears to be necessary but not sufficient to explain large recruitment events of haddock on Georges Bank.

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Article

Impact of current-wave interaction on storm surge simulation : a case study for Hurricane Bob

2013-05-30 , Sun, Yunfang , Chen, Changsheng , Beardsley, Robert C. , Xu, Qichun , Qi, Jianhua , Lin, Huichan

Hurricane Bob moved up the U.S. east coast and crossed over southern New England and the Gulf of Maine [with peak marine winds up to 54 m/s (100 mph)] on 19–20 August 1991, causing significant damage along the coast and shelf. A 3-D fully wave-current-coupled finite-volume community ocean model system was developed and applied to simulate and examine the coastal ocean responses to Hurricane Bob. Results from process study-oriented experiments showed that the impact of wave-current interaction on surge elevation varied in space and time, more significant over the shelf than inside the inner bays. While sea level change along the coast was mainly driven by the water flux controlled by barotropic dynamics and the vertically integrated highest water transports were essentially the same for cases with and without water stratification, the hurricane-induced wave-current interaction could generate strong vertical current shear in the stratified areas, leading to a strong offshore transport near the bottom and vertical turbulent mixing over the continental shelf. Stratification could also result in a significant difference of water currents around islands where the water is not vertically well mixed.

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Preprint

Surface circulation in Block Island Sound and adjacent coastal and shelf regions : a FVCOM-CODAR comparison

2016-02-29 , Sun, Yunfang , Chen, Changsheng , Beardsley, Robert C. , Ullman, Dave , Butman, Bradford , Lin, Huichan

CODAR-derived surface currents in Block Island Sound over the period of June 2000 through September 2008 were compared to currents computed using the Northeast Coastal Ocean Forecast System (NECOFS). The measurement uncertainty of CODAR-derived currents, estimated using statistics of a screened nine-year time series of hourly-averaged flow field, ranged from 3-7 cm/s in speed and 4°-14° in direction. The CODAR-derived and model-computed kinetic energy spectrum densities were in good agreement at subtidal frequencies, but the NECOFS-derived currents were larger by about 28% at semi-diurnal and diurnal tidal frequencies. The short-term (hourly to daily) current variability was dominated by the semidiurnal tides (predominantly the M2 tide), which on average accounted for ~87% of the total kinetic energy. The diurnal tidal and subtidal variability accounted for ~4% and ~9% of the total kinetic energy, respectively. The monthly-averaged difference between the CODAR-derived and model-computed velocities over the study area was 6 cm/s or less in speed and 28° or less in direction over the study period. An EOF analysis for the low-frequency vertically-averaged model current field showed that the water transport in the Block Island Sound region was dominated by modes 1 and 2, which accounted for 89% and 7% of the total variance, respectively. Mode 1 represented a relatively stationary spatial and temporal flow pattern with a magnitude that varied with season. Mode 2 was characterized mainly by a secondary cross-shelf flow and a relatively strong along-shelf flow. Process-oriented model experiments indicated that the relatively stationary flow pattern found in mode 1 was a result of tidal rectification and its magnitude changed with seasonal stratification. Correlation analysis between the flow and wind stress suggested that the cross-shelf water transport and its temporal variability in mode 2 were highly correlated to the surface wind forcing. The mode 2 derived onshore and offshore water transport, and was consistent with wind-driven Ekman theory. The along-shelf water transport over the outer shelf, where a large portion of the water flowed from upstream Nantucket Shoals, was not highly correlated to the surface wind stress.

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Article

Tidal dynamics in the Gulf of Maine and New England Shelf : an application of FVCOM

2011-12-10 , Chen, Changsheng , Huang, Haosheng , Beardsley, Robert C. , Xu, Qichun , Limeburner, Richard , Cowles, Geoffrey W. , Sun, Yunfang , Qi, Jianhua , Lin, Huichan

The unstructured-grid, Finite-Volume Community Ocean Model (FVCOM) was used to simulate the tides in the Gulf of Maine (GoM) and New England Shelf (NES) for homogeneous and summer stratified conditions. FVCOM captures the near-resonant nature of the semidiurnal tide and energy flux in the GoM and the complex dynamics governing the tide in the NES. Stratification has limited impact on tidal elevation, but can significantly modify the tidal current profile. Internal tides are energetic in the stratified regions over steep bottom topography, but their contribution to the total tidal energy flux is only significant over the northeast flank of Georges Bank. The model suggests that the tidal flushing-induced eddy east of Monomoy Island is the dynamic basis for the locally observed phase lead of the M2 tide. The southward propagating tidal wave east of Cape Cod encounters the northeastward propagating tidal wave from the NES south of Nantucket Island, forming a zone of minimum sea level along a southeast-oriented line from Nantucket Island. These two waves are characterized by linear dynamics in which bottom friction and advection are negligible in the momentum balance, but their superposition leads to a strong nonlinear current interaction and large bottom stress in the zone of lowest sea elevation.

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