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BOON research Projects > Oceanography

Seasonal Flow Patterns

Contact: John Largier Ph.D.

Silvia Piedracoba-Varela, Ph.D.

This work uses HF radar current analysis to determine typical surface flow patterns off Bodega Bay during the winter (Dec, Jan, Feb) of 2006/2007/2008. Surface trajectories show variable transport patterns depending on wind conditions (upwelling or relaxation) during the winter season. This research focuses on describing onshore/offshore and northward/southward transports and the onset, development and persistence of several structures (meanders). Also of interest is the relationship between currents and the most important winter season forcing factors (winds, continental runoff) as well as statistical differences between winter and summer seasons and the biological implications.

Figure 1. Mean surface currents

Flow Figure 1

Fig. 1. Mean surface currents for January 2006. Vectors indicate mean current at that grid point. Black arrow shows mean wind velocity for January 2006 at the NDBC 46013 buoy.

Figure 2. Median surface currents

Flow Figure 2

Fig. 2. Median surface currents for January 2006. Vectors indicate mean current at that grid point. Black arrow shows mean wind velocity for January 2006 at the NDBC 46013 buoy.

Figure 3. Three day average surface currents

Flow Figure 3

Fig. 3. 3-Day average surface currents from 7 January 2006. Vectors indicate mean current at that grid point. Black arrow shows mean wind velocity for 7 January 2006 at the NDBC 46013 buoy. The figure shows an offshore/southward flow off Bodega Bay very close to the coast under moderate northerly winds of 7 Jan’06. A clockwise eddy north of Point Reyes has developed. Note the interaction between onshore and offshore flows off Bodega Bay.

 

Figure 4. Four regions selected to calculate mean and median currents

Flow Figure 4

Fig. 4.  Four regions (northern/southern inshore and northern/southern onshore were defined to calculate the mean and median current (Fig. 5).

Figure 5. Mean and median along-shelf and cross-shelf currents and wind velocity

Flow Figure 5

Fig. 5. a. Along-shelf and cross-shelf wind velocity. b.1, b.2, b.3. Daily average cross-shelf current (Ux), daily average along-shelf current (Uy) and daily total current , V=(Ux2+Uy2)1/2 and c.1, c.2, c.3 median cross-shelf current, median along-shelf currents and median total current for one of each regions defined in Fig.4.

 

Figure 6. Monthly mean chlorophyl a concentration and SST

Flow Figure 6

Fig. 6. a) Monthly average chlorophyl a concentration  (log [Chla]) and b) number of days used per position (according to thee availability of satellite images) for January 2006. c) Monthly average sea surface temperature (SST) and d) number of days per position used for the average.

Each dot is a 2 km ratio grid average approx.

Satellite ocean color data and sea surface temperature is from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor via NOAA's West Coast Regional Node.