Summary of findings for using high frequency radar in physical oceanographic and ecological studies 

FINAL TECHNICAL SUMMARY 

STUDY TITLE: “Application of High Frequency Radar for Surface Current Observations on

South-Central California Coast” 

REPORT TITLE: Summary of findings for using high frequency radar in physical 

oceanographic and ecological studies

CONTRACT NUMBER: 14-35-0001-30758 

SPONSORING OCS REGION: Pacific

APPLICABLE PLANNING AREA: Southern California

FISCAL YEARS OF PROJECT FUNDING: FY96, FY97, FY98, FY99 

COMPLETION DATE OF THE REPORT: 15 March 2001 

COSTS: FY 96 - $25,000, FY 97 - $91,246, FY 98 - $133,844, FY 99 - $51,727 

CUMULATIVE PROJECT COST: $301,817 

PROJECT MANAGER: Russell J. Schmitt

AFFILIATION: University of California, Santa Barbara

ADDRESS: Coastal Research Center, Marine Science Institute, University of California, Santa

Barbara, CA 93106

PRINCIPAL INVESTIGATORS: Libe Washburn, Professor, Institute for Computational 

Earth System Science, Dept. of Geography, University of California, Santa Barbara, CA 93106-

3060, email: washburn@icess.ucsb.edu; Steven Gaines, Professor, Dept. of Ecology, Evolution, 

and Marine Biology, Biology, California, Santa Barbara, CA 93106, email: 

gaines@lifesci.ucsb.edu 

1. BACKGROUND: 

1.1 High frequency radars for ocean current measurement 

Since the first observations of the Doppler spectrum of sea echo by [Crombie, 1955], high 

frequency (HF) radars have become a common technology for studying coastal circulation 

processes. Despite the increased use of HF radar, several issues remain about their performance

in measuring ocean surface currents. For example, the radars' ability to correctly place current

vectors on the sea surface, in less-than-ideal deployment situations, remains to be determined.

The factors affecting the accuracy and precision of HF radar measurements of surface currents 

are still not well understood, but in this research we made progress on these issues. 

Coastal HF radars for measuring ocean surface currents are divided into two types based on 

the method used to determine bearing to a sector on the ocean's surface: beam forming radars, 

such as the Ocean Surface Current Radar (OSCR), and direction finding radars, such as the 

Coastal Ocean Dynamics Application Radar (CODAR), the system used in our study. Beam

forming is accomplished by electronically steering a linear phased array of receive antennas to a 

sector of ocean surface. Direction finding of the CODAR system uses three receive antenna 

elements and a variant of the Multiple Signal Classification (MUSIC) algorithm [Schmidt, 1986] 

to determine bearing. Further discussion of the CODAR system can be found in [Paduan and 

1 
Final Technical Summary – Washburn and Gaines 

Rosenfeld, 1996], [Barrick and Lipa, 1997] and [Barrick and Lipa, 1999]. The beam forming 

method is discussed by [Graber et al., 1997], [Shay et al., 1998], and [Vesecky et al., 1998]. 

In 1997 with funding MMS and the W.M. Keck Foundation we began deploying an array of

five HF radars along the California coast in conjunction with a large coastal circulation study 

conducted by the Center for Coastal Studies at the Scripps Institution of Oceanography 

(CCS/SIO), which included an array of 9 current meter moorings (also MMS funded). We

obtained nearly 2 years of overlapping data from the Santa Barbara Channel and Santa Maria 

Basin that provided the opportunity to investigate the performance of HF radars over a range of 

conditions and deployment situations. We also used surface circulation data from the radars to 

address a number of research questions important to coastal marine ecology. 

1.2 Use of high frequency radar in ecological studies in the Santa Barbara Channel and 

Santa Maria Basin. 

We used a 3-year record of surface currents obtained by an array of HF radars to examine the 

surface circulation near Pt. Conception, California. We focused on aspects of the circulation 

important to larval transport and retention. In particular, we examined the role of a persistent

cyclonic eddy in the western Santa Barbara Channel. Evidence for larval retention within the

eddy came from mid-water trawling surveys for juvenile and late-stage larval fishes in June 

1998, 1999, and 2000. The trawling surveys were conducted by Mary M. Nishimoto of the 

Marine Science Institute at UCSB (MSI/UCSB) and were funded by the Biological Research 

Division (BRD) at no cost to this project. 

During the 1998 survey, a series of midwater trawls were conducted in and around the eddy, 

finding extremely high concentrations of fishes in its center. During the 1999 and 2000 surveys,

high concentrations of fishes were not found and the eddy circulation was not consistently 

observed. Time series of relative vorticity computed from the HF radar show that the cyclonic 

circulation was less persistent in 1999 compared with 1998 when it was relatively stable. 

Analysis of surface circulation data from 2000 suggests temporal variability similar to 1999

and work on the 2000 biological data is continuing (BRD and UC Sea Grant funded). Patterns 

of surface currents filtered with a pass band of 7 – 28 days revealed small eddies propagating

through the western Santa Barbara Channel which appear to be linked to the stability of the 

larger cyclonic eddy. Horizontal scales of the eddies are of order 20 km and they propagate 

westward at about 7 km/day. In 1998 the small eddies began propagating through the region in 

late June, after the larval development period (approximately March through June). In 1999 the 

propagation began earlier, in mid-May. Analysis of 2000 data is not yet complete, but the onset 

of eddy propagation in 2000 appears similar to 1999. We hypothesize that the effectiveness of 

the eddy as a larval retention mechanism is linked to the stability of the eddy and the onset of the 

smaller propagating eddies. 

We also investigated relationships between settlement patterns of intertidal invertebrates (e.g. 

crabs, barnacles, limpets, etc.) and evolving patterns of coastal circulation. This analysis is 

continuing, but some patterns between settlement patterns and coastal circulation have emerged. 

For example, the typical pattern of offshore surface flow around Pt. Conception is consistent

with the fact that the Point is a northern range limit for several species. 

2 
Summary of findings for using high frequency radar in physical oceanographic and ecological studies 

2.0 OBJECTIVES: 

An overall objective our project was to evaluate the performance and feasibility of using high 

frequency radar systems to measure evolving patterns of surface currents in the waters off the 

south-central coast (SCC) of California. The study area encompassed the western Santa Barbara 

Channel and the Santa Maria Basin. 

Specific goals were to: 

1. To deploy HF radars at three sites along the between Pt. Conception and Pt. Buchon 

along the south-central coast of California. 

2. To compare HF radar-derived surface currents with other, independent measures of 

surface currents such as in situ current meters. 

3. To operate the HF radar systems continuously and obtain time series of sufficient length 

such that the important dynamic processes were resolved spatially and temporally. 

4. To compare HF radar-derived surface currents with the spatial and temporal patterns of 

nearshore plankton distributions, with a specific focus on the movement of larval stages 

of coastal invertebrates and fishes. 

All of these goals were accomplished during the project. 

3.0 DESCRIPTION AND RESULTS: 

3.1 HF radar deployments and evaluation. 

As discussed above an array of five HF radars were deployed in the Santa Barbara Channel 

over the course of the project. Three of the radars remain in operation; the other two radars were 

on loan (at no cost to the project) from NOAA's Environmental Science and Technology 

Laboratory in Boulder Colorado and had to be returned in February 2001. The coverage area of 

the HF radar array included eight moorings deployed in the western Santa Barbara Channel and 

Santa Maria Basin by CCS/SIO (open circles, Figure 1). The CCS/SIO moorings carried vector 

measuring current meters [Weller and Davis, 1980] at 5 and 45 meters depth providing hourly 

averages of current velocity. We used the 5 m data for comparison with the surface HF radar 

data. 

An additional mooring was deployed by UCSB investigators near the center of the Santa 

Barbara Channel from 20 May 1998 to 12 October 1999. The UCSB mooring carried an upward 

looking 1200 kHz acoustic Doppler current profiler (ADCP; manufactured by R.D. Instruments, 

San Diego CA) at 15 meters depth. The ADCP measured currents over 0.5 m depth increments 

(bins) to within 3-4 meters of the sea surface, every 20 minutes. These data were subsequently 

averaged into 1 hr blocks. Time series from occasional deployments of an electromagnetic 

current meter (model S4; manufactured by InterOcean, San Diego, CA) at 5 m depth on the 

UCSB mooring agreed closely with ADCP currents at 5 m. We compared HF radar time series 

with the time series from the ADCP bin nominally at 4 m depth. This was the shallowest depth 

consistently free from contamination due to surface reflections. 

3 
Final Technical Summary – Washburn and Gaines 

Figure 1. Locations of HF radars in the Santa Barbara Channel and Santa Maria Basin are indicated with

triangles: FBK is Fallback-22 near Pt. Sal, ARG is Pt. Arguello, PTC is Pt. Conception, RFG is Refugio Beach, 

and COP is Coal Oil Point. Circular sectors show nominal ranges of 42 km. Circles indicate locations of moored 

current meters used for comparison with HF radar currents. Naming convention of current meters is discussed in 

the text. Semi-circles show the extent of HF radar coverage. Bathymetric contours are plotted at 50, 100, 200,

300, 500, and 600 m. The inset shows the study site on the California coast.

We based our study of HF radar performance on comparisons of the radial component of 

currents observed by the radars with radial components observed by conventional current meters. 

We focused primarily on the radial current component rather than total velocity vectors because 

we wanted to evaluate the performance of individual radars. Calculation of total velocity vectors 

combines measurements of two or more radars and thus, makes evaluation of individual radars 

more difficult. 

To compare radial current vectors (radials) from a HF radar site VHF with those at a particular 

mooring, we computed the radial component of moored current velocity Vm, 

Vm = V • im (1) 

where • is the dot product, V is the mooring current velocity, and im is the unit vector pointing 

from the mooring toward the HF radar site. This procedure was repeated at each mooring for all 

radars having the mooring within range. A total of 18 paired mooring-HF radar time series were 

available with maximum record lengths exceeding one year. 

To examine performance of individual HF radars, we computed various statistics for each 

pair of HF radar and mooring time series. The square of the correlation coefficient (r2

) was 

computed between Vm and VHF for the sector containing the mooring, and for sectors 

surrounding the mooring. Typically, a single HF sector entirely contained the mooring watch 

circle (50 m to 300 m in radius depending on water depth for the CCS moorings; 750 m for the 

ADCP mooring). We interpret the value of r2

 as an overall measure of similarity between the 

4 
Summary of findings for using high frequency radar in physical oceanographic and ecological studies 

time series. Slopes and offsets of regression lines computed between Vm and VHF indicate 

systematic differences between the time series. Power spectra and squared coherence spectra of 

Vm and VHF compare the time series across a range of frequencies. 

The results of the comparisons between the HF radars and moored current meters are 

summarized in a paper (attached to this report), "Evaluating radial component current 

measurements from CODAR high frequency radars and moored in situ current meters", that has 

been submitted for publication [Emery et al., 2001]. 

3.2 HF radar in ecological studies of larval transport and advection 

In spring 1998, we observed a persistent cyclonic eddy in the western Santa Barbara Channel 

for several weeks preceding the annual midwater trawling survey conducted by Mary M. 

Nishimoto of the Marine Science Institute at UCSB (at no cost to this project) in June of that 

year. The feature was evident in surface current maps generated by HF radar (Figure 2A) and 

sea surface temperature (SST) imagery from satellite AVHRR (Figure 2B). The persistence of 

the eddy suggested the possibility that abundance patterns of pelagic juvenile fishes may be 

related in some way to this flow feature. Accordingly, several midwater trawls were conducted 

in the eddy and surrounding waters to test this conjecture. 

5 

120.8 120.6 120.4 120.2 120.0 119.8 119.6

A

Longitude

PC R

COP

Vorticity (x10-4 s-1)

Latitude

-1.0 -0.5 0 0.5 1.0

34.0

34.2

34.4

34.6 PA

B

Sea surface temperature (C)

Point Arguello

Point Purisima

Point Mugu

Santa Barbara

Californ

Point Conception ia

Figure 2. (A) Spatial pattern of surface currents at 1900 GMT on 2 June 1998 showing a strong cyclonic eddy in the western

anta Barbara Channel. Surface currents were mapped with HF radars at Coal Oil Point (COP), Refugio (R), and Point

onception (PC). Scale for current speed is at lower left. Circle (radius=3 km) at lower left is the area over which current 

vectors are averaged. (B) The cyclonic eddy is visualized by curving temperatures features wrapping around the eddy in the 

satellite sea surface temperature image at 0152 GMT on 3 June 1998. 

At the beginning of the trawling survey on 2 June 1998 the surface circulation (upper 1 m) in 

the Channel was strongly cyclonic, as determined by HF radar. The flow in the western Channel 

was dominated by an eddy centered at 120.1 W, 34.3 N with a diameter of about 30 km and 

maximum azimuthal currents of about 0.4 m s-1 (Figure 2A). The rotation of the eddy, quantified 

by its relative vorticity, ranged from 0.2 f (rotation period of ~ 9 days) on the periphery to about 

0.7 f (rotation period of ~3 days) in the center, where f is the Coriolis parameter. Strong rotary 

flow in the eddy was also indicated by alternating warm and cool streaks wrapped around the 

eddy as revealed by sea surface temperature (SST) imagery (Figure 2B). Time series of surface 

currents obtained from the HF radars showed that the eddy persisted throughout the juvenile fish 

survey. 

S

C

5 
Final Technical Summary – Washburn and Gaines 

The eddy circulation was not merely a surface flow, but extended to at least 200 m depth. 

The spatial pattern of dynamic height φ, determined from CTD casts during the trawling survey, 

had a minimum in the core of the eddy, consistent with the strong cyclonic circulation revealed 

by the HF radars (Figure 3A). Assuming a level of no motion at 200 dbar (~200 m depth), the 

sea surface (0 dbar) was lower in the center by about 0.05 m compared with surrounding waters. 

We defined the eddy center by φ<0.32 m.

2-15 JUNE 1998

Potential

Temp. (C)

Geostrophic

Velocity (ms-1)

Purisima (2)

Arguello (3) West Entrance (5)

West edge (3)

Eddy (9)

East edge (5)

East Channel (4)

Mugu (5)

Mean no. haul -1 (+1 SE)

0

2000

4000

0

4000

8000

0

400

800

0

2000

4000

Northern lampfish

California smoothtongue

Rockfishes

Pacific hake

.32

.38

.38 .34

A

B

C

Figure 3. A) Distribution of dynamic height in the western Santa Barbara Channel during trawling surveys in 1998. B) Vertical

sections of temperature and geostrophic velocity along bold line in panel A. C) Abundance of 5 fish taxa in the region. High

concentrations of fishes were found in the center of the eddy. In panel A, P indicates Purisima, A is Arguello, W is west channel,

+ signs are east and west edges, E is east Channel N is north Channel, and M is Mugu. 

120.5 120.0 Longitude

180

160

140

120

100

80

60

40

20

702701700301302 303802

0

Depth (m)

Station code

120.5 120.0

Isolines of potential temperature T along an east-west section across the eddy showed the 

effects of the earth’s rotation by rising sharply in the eddy center (Figure 3B). The 10°C 

isotherm rose about 80 m in the center; similar deflections were also apparent for salinity and 

density. Horizontal density gradients in the eddy supported vertical shear in horizontal currents; 

the speed of these geostrophic currents changes by about 0.2 m s-1 over the 200 m measurement 

interval. Currents across the section show southward flow at depth west of the center and 

northward flow to the east, consistent with deep cyclonic flow (Figure 3B). Deflections of the 

deepest isolines indicated the cyclonic circulation of the eddy extended below 200 m. 

Figure 3. (A) Distribution of dynamic height in the western Santa Barbara Channel during trawling surveys in

1998. (B) Vertical sections of temperature and geostrophic velocity along bold line in panel A. (C)

Abundance of 5 fish taxa in the region. High concentrations of fishes were found in the center of the eddy. In

panel A, P indicates Purisima, A is Arguello, W. is west Channel, + signs are east and west edges, E is east 

Channel, N is north Channel, and M is Mugu.. 

During the two weeks of sampling, 2-15 June, net hauls were conducted in the eddy and 

surrounding waters to look for possible influences on juvenile fish abundance. In post-cruise 

analysis, hauls were grouped into seven geographic areas, including the eddy center that was 

defined by φ < 0.32 m. The abundance of each of the five dominant taxa was greatest in the 

eddy center (Figure3C). The fishes were patchily distributed, and occasional large catches 

6 
Summary of findings for using high frequency radar in physical oceanographic and ecological studies 

occurred at the southwest and northeast edges of the eddy and at the west entrance of the 

Channel. Catches of rockfishes (Sebastes spp.) and Pacific hake (Merluccius productus), two 

abundant taxa represented by late-stage larvae and pelagic juveniles, were 39 to 1.1x104

 haul-1 in

the center compared with north of the Channel and in the east Channel where catches were 

typically less than 100 haul-1. Mesopelagic fishes California smoothtongue (Leuroglossus 

stilbius), northern lampfish (Stenobrachius leucopsarus), and Mexican lampfish (Triphoturus 

mexicanus), represented by juveniles and adults, exhibited similarly high abundance and possible 

entrainment in the eddy center. 

The striking observation motivated us to repeat the survey in 1999 and 2000. Results from

the 1999 and 2000 surveys were characterized by very different larger-than-channel scale and 

mesoscale oceanographic conditions and catch distributions. Physical conditions in the Channel 

in June 1999 were much different than June 1998; perhaps the biggest difference was the 

stronger winds in 1999 associated with La Niña conditions.

Circulation in the Channel was highly variable in 1999 compared to the stable cyclonic eddy 

flow pattern observed in 1998. In 1999, temperature-salinity distributions changed rapidly as 

indicated by repeated sampling in the western Channel (Figure 4A). During the first leg of 

sampling, 6-21 June 1999, dynamic height was low in the Channel north of the San MiguelSanta Rosa Islands passage and corresponded with a cyclonic eddy feature observed by HF radar 

at the time of sampling. The gradient in dynamic height across the feature was similar to that in 

1998. Dynamic height at 5 m depth (5 dbar) assuming a level of no motion at 200dbar was lower 

in the center by about 0.05 m compared with surrounding waters. We defined the center as φ < 

0.34 m. Re-sampling during 24 June-1 July (leg 2) revealed that dynamic height increased in that 

area, and a low dynamic height feature with φ < 0.34 m as its center was observed west of the 

Channel entrance (Figure 4A). The area to the west of the Channel was beyond HF radar 

coverage and was not sampled during leg 1. 

The flow field in the few months preceding and during the 1999 survey was characterized by 

propagating trains of eddies with alternating cyclones (rotating clockwise) and anti-cyclones 

(rotating counterclockwise) along with increased flow from the east entrance through the 

Channel. These eddies were discussed in presentations at the 2000 AGU meeting in San 

Francisco by Beckenbach and Washburn and by Washburn et al.). Coherence of the spatial 

distributions of the dynamic height from legs 1 and 2 and HF radar data suggested that we 

sampled twice an eddy that propagated westward from within the Channel to the western 

entrance. The importance of these eddies is one of the focuses of our ongoing research. 

Abundance of the dominant fish taxa and their spatial distributions differed substantially 

between 1998 and 1999. Catch abundance in 1999 was lower by an order of magnitude 

compared to 1998). The five taxa comprised 98% and 96% of the mean total catch in 1998 and 

1999, respectively. Rockfishes were the fifth most abundant taxa in 1998. In 1999, sanddabs 

(Citharichthys spp.) and northern anchovy (Engraulis mordax) were slightly more abundant than 

rockfishes. 

We grouped the 1999 trawling stations by φ and geographic area as we did with the 1998 

samples. Furthermore, we divided the 1999 samples into two sampling periods (Figure 4B). In 

contrast to 1998, late-larval stage and pelagic juvenile rockfishes and Pacific hake were more 

7 
Final Technical Summary – Washburn and Gaines 

-121.0 -120.8 -120.6 -120.4 -120.2 -120.0 -119.8 -119.6 -119.4 -119.2 -119.0

33.8

34.0

34.2

34.4

34.6

34.8

-121.0 -120.8 -120.6 -120.4 -120.2 -120.0 -119.8 -119.6 -119.4 -119.2 -119.0

33.8

34.0

34.2

34.4

34.6

34.8

6-21 JUNE 1999

Cruises 2-8

24 JUNE - 1 JULY 1999

Cruises 9-11

n=3 4 16 2 12 4

Rockfishes

No. per haul (+/- SE)

0

2

4

6

8

10

Pacific hake

0

200

400

600

800

1000

Northern lampfish

0

20

40

60

80

100

120

140

Calif. smoothtongue

Area

Purisima

Center

Chan_leg1

West_low

Chan_leg2

Mugu

0

200

400

600

800

1000

n=3 4 16 2 12 4

Leg 1:

.32 .38

.36

.36

.32

.38 .40

A B

Figure 4.

Figure 4. A) Distribution of dynamic height in the western Santa Barbara Channel during trawling surveys of 1999. B) Distributions of fish taxa Fiduring 1999 surveys. gure 4. (A) Distribution of dynamic height in the western Santa Barbara Channel during trawling

surveys of 1999. (B) Distribut

abundant north of the Channel off Pt. Purisima than in the Channel, and their distributions did 

not show a relationship with dynamic height features in 1999. Northern lampfish and California 

smoothtongue, both represented by juvenile and adults, were more abundant in the western 

Channel during the first sampling period when it was occupied by a cyclonic eddy with a center 

of low dynamic height (“Low_leg 1”) than during the second sampling leg when the area is 

characterized by high dynamic height (“Chan_leg 2”). No consistent relationship between 

dynamic height areas and the spatial distribution of the dominant taxa in the Channel was 

observed in 1999. 

Leg 

1 2

Leg 2:

ions of fish taxa during 1999 surveys. 

Flows in the western Santa Barbara Channel and Santa Maria Basis were also compared with 

recruitment patterns of several invertebrate species. Recruitment was measured as part of the 

Partnership for Interdisciplinary Studies of the Coastal Ocean (PISCO) (at no cost to this project) 

along several sites on the south-central California coast including three in the HF radar coverage 

area (green squares, Figure 5). A typical regional flow pattern from summer 2000 shows strong 

equatorward and offshore flows outside the Channel consistent with prevailing upwelling 

favorable winds. The upwelling center around Points Conception and Arguello had mean 

offshore flows of about 10 cm/s when averaged over a six week period. The along shore 

distribution of settlement of 13 species showed a minimum at the recruitment site within this 

upwelling center (red arrow and bars in inset diagram of Figure 5). This suggests a strong link 

between settlement patterns of inter-tidal invertebrates and persistent coastal circulation features 

such as this upwelling center. We are continuing our investigation of links between settlement 

patterns and coastal circulation as part of PISCO. 

8 
Summary of findings for using high frequency radar in physical oceanographic and ecological studies 

Recruitment 1997-1999

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Paradise Cove

Port Hueneme

Ventura

Stearns

Ellwood

Gaviota

Boathouse

Avila

San Simeo

Av

n

erage number of settlers per

collector per sample interval

Elwood

Gaviota

Boathouse

Figure 5. Spatial mean currents in the Santa Barbara Channel and Santa Maria Basin during 6 June – 26 July, 2000. Inset shows inter-tidal

recruitment at several sites. Squares show recruitment sites within radar coverage area. Arrow in inset indicates low settlement in the upwelling

center between Points Conception and Arguello. Black circles and dots indicate HF radar sites.

poleward

4.0 SIGNIFICANT CONCLUSIONS: 

4.1 Radar performance 

Our investigation of the performance of HF radars for measuring surface currents supports 

the following conclusions: 

1. Radial currents obtained from the radars were significantly correlated with radial currents 

obtained from the moored current meters with r2

 in the range 0.39-0.77. Root-meansquare (rms) radial speed differences ranged from 7-19 cm s-1. A weak trend of 

increasing rms differences was found with increasing range. 

2. Significant coherence was found between current meter and radar-derived time series for 

frequencies below 2.2 cpd (11 hour period and longer). Power spectra showed similar 

magnitudes and slopes for frequencies below 2.2 cpd. 

3. A pointing error ∆θ ranging from –16o

 to19o was found for some of the radar sites where 

positive values indicate a clockwise error. ∆θ for a given radar was not constant, but 

varied with bearing. We speculate that ∆θ resulted from distortions of the receive antenna 

patterns in the near field. 

9 
Final Technical Summary – Washburn and Gaines 

4. We used a simple model of ∆θ versus bearing based on our observations to simulate 

errors in total velocity vectors computed from two radars. Using a uniform flow parallel 

to shore, ∆θ produced speed errors of up 15% and direction errors up to 9o in total 

velocity vectors We are working with colleagues at CODAR Ocean Sensors, Oregon 

State University, and the Naval Postgraduate School to correct these errors in processing 

algorithms for HF radar data. 

4.2 Application of HF radar to coastal circulation and marine ecology 

1. Persistent cyclonic circulation is a dominant flow pattern in the western Santa Barbara 

Channel consistent with results of [Dever et al., 1998; Harms and Winant, 1998; Winant 

et al., 1999]. 

2. Propagating trains of eddies occur in the western Santa Barbara Channel. The eddies 

have horizontal scales of order 15 km, current speeds of 0.1-0.2 m/s, and alternating 

relative vorticity of magnitudes comparable to the vertical component of the earth’s 

rotation rate. They propagate westward at ~7 km/day. Their high relative vorticity 

indicates that the eddies are not in simple geostrophic balance, but rotate rapidly enough 

to produce significant centripetal acceleration. We use the term "eddy" to describe the 

features, but they may be some type of wave such as a topographic Rossby wave. 

3. Animations of HF radar data show that surface currents respond rapidly to changes in 

local wind velocity, especially in the Santa Maria Basin. 

4. Very high concentrations of juvenile and late stage larval occur in the western Santa 

Barbara Channel under conditions of stable cyclonic flow 

5. Propagating eddies can prevent establishment of stable circulation patterns that might 

otherwise retain larvae. 

6. Coastal circulation features such as the upwelling center between Points Conception and 

Arguello limit settlement in the region due to strong persistent offshore advection driven 

by upwelling-favorable winds. 

5.0 STUDY PRODUCTS: 

Publications: 

Emery, B.M., L. Washburn, and J. Harlan, Evaluating CODAR high frequency radars for 

measuring surface currents: observations in the Santa Barbara Channel, Journal of 

Atmospheric and Oceanic Technology (manuscript submitted), 2001. 

Beckenbach, E.H. and L. Washburn, Propagating eddies in the Santa Barbara Channel, in 

preparation. 

Washburn, L. and S. Gaines. Summary of findings for using high frequency radar in physical 

oceanographic and ecological studies. MMS OCS Study 2001-056. Coastal Research 

Center, Marine Science Institute, University of California, Santa Barbara, California. 

MMS Cooperative Agreement Number 14-35-0001-30758. 32 pages. 

10 
Summary of findings for using high frequency radar in physical oceanographic and ecological studies 

Presentations: 

2000 Surface circulation near Pt. Conception, California: A mechanism for larval retention?, 

Washburn, L., M.M. Nishimoto, E.H. Beckenbach, and B.M. Emery, Fall Meeting, 

American Geophysical Union, San Francisco, 15-19 September. 

2000 Observations of propagating eddies in the Santa Barbara Channel, Beckenbach, E.H., L. 

Washburn, D. Salazar, and B.M. Emery, Fall Meeting, American Geophysical Union, 

San Francisco, 15-19 September. 

2000 Time series mapping of currents in the coastal ocean, Kosro, P.M., J.D. Paduan, and L. 

Washburn, Fall Meeting, American Geophysical Union, San Francisco, 15-19 September. 

2001 Surface circulation on the South-central coast: Mechanisms for larval transport and 

retention, seminar in the Dept. of Atmospheric Science, UCLA, 24 January. 

2001 Variability in mesoscale oceanographic processes corresponds to variability in the 

distribution and abundance of rockfish (Sebastes spp.) juveniles, Schroeder, D M , M.M. 

Nishimoto, and L. Washburn, American Society of Limnology and Oceanography, 

Albuquerque2001, Albuquerque, NM, 12-16 February. 

2001 The physical environment of the Santa Barbara Channel, seminar presented to volunteers 

of the Channel Islands National Marine Sanctuary", Chase Palm Park, 1 March. 

11 
Final Technical Summary – Washburn and Gaines 

6.0 REFERENCES: 

Barrick, D.E., and B.J. Lipa, Evolution of bearing determination in HF current mapping radars, 

Oceanography, 10 (2), 72-75, 1997. 

Barrick, D.E., and B.J. Lipa, Using antenna patterns to improve the quality of SeaSonde HF 

radar surface current maps, IEEE 6th Working Conference on Current Measurement, 

1999. 

Crombie, D.D., Doppler Spectrum of Sea Echo at 13.56 Mc/s, Nature, 175, 681-682, 1955. 

Dever, E.P., M.C. Henderschott, and C.D. Winant, Statistical Aspects of surface drifter 

observations of circulation in the Santa Barbara Channel, Journal of Geophysical 

Research, 103 (C11), 24,781-24,797, 1998. 

Emery, B.M., L. Washburn, and J. Harlan, Evaluating CODAR high frequency radars for 

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