dud: ' NPS 68-88-002 NAVAL POSTGRADUATE SCHOOL Monterey, California THESIS CHANGES IN THE CALIFORNIA CURRENT SYSTEM OBSERVED OFF NORTHERN CALIFORNIA DURING JULY-AUGUST 1986 by Michael E. Beasley December 1987 Thesis Advisor M.L. Batteen Approved for public release; distribution is unlimited Prepared for: Chief of Naval Research 800 N. Quincy St. Arlington, VA 22217-5000 T238692 NAVAL POSTGRADUATE SCHOOL Monterey, California Rear Admiral R. C. Austin K. T. Marshall Superintendent Acting Provost This thesis was prepared in conjunction with research sponsored by the Naval Postgraduate School Research Foundation. Reproduction of all or part of this report is authorized. Released by: UNCLASSIFIED skuwitv rrgj : •C: REPORT DOCUMENTATION PAGE ;a REPO-T SiC'jH.-v UASS'F.CA* ON UNCLASSIFIED 'O RESTRICTIVE MARKINGS 2a SECuRiTy C-ASS.f ;CATiON AuTmQR.TY 2D DEC-ASS'FiCATiON DOWNGRADING SCHEDULE 3 Distribution availability of report Approved for public release; Distribution i*. unl irni ted . & performing organization REPORT NUMBER^) NPS 68-88-002 5 MONITORING ORGANIZATION REPORT NuMSER(S) 6a NAME 0^ PERFORMING ORGANIZATION Naval Postgraduate School 6o OF^CE SYMBOi. (If JDDiicab'e) 68 7a wAME OF MONITORING ORGANIZATION Naval Postgraduate School 6c. ADDRESS vGty Srare. and ZIP Code) Monterey, California 93943-5000 'o ADDRESS (C/ry. State, and ZIP Code) Naval Postgraduate School Research Foundatioi Naval Postgraduate bcnooi Kesearc Monterey, California 93 94 3-5000 8a NAVE 0= =-wN0:.\G- SPONSOR. NG ORGANIZATION NPS Research Foundation 8d OFFICE SYMBOL (if applicable) 9 PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER N0001487WR4E011 8c ADDRESS (Cry. State, and ZIP Coae) Naval Postgraduate School Monterey, California 93943-5000 'C SOURCE OF =:.AOAG \UM = E=S PROGRAM ELEMENT NO 61153N PROJECT NO RR014-01 TASK NO 10P-011 WORK UNIT "CCESSiON NO TiTLF (include Security Classification) Changes in the California Current System Observed Off Northern California During Julv-Ausust 1986 12 °ERSONAi_ Au'riOR(S) Beaslev. Michael E. in conjunction with M, L. Batteen and C. N. K. Mooers. 13a TYPE OF RE=ORT Master's Thesis 3d t me covered ==om -o 1C DATE OF REPORT ( Year, Month, Day) December 1987 15 PAGE COUNT 72 16 SUPPLEMENTARY NOTATION 17 COSAT. CODES F'ELD GROUP SUB-GROUP '8 SUBJECT TERMS (Conrmue on reverse if necessary and identity oy Dlock numoer) California Current System description - 1986, Upwelling. CCS jets 19 ABSTRACT {Continue on reverse it necessary and identity Dy block numoer) Changes in the flow pattern of the California Current Svstem (CCS) in a relatively short time period ( *- one week) are investigated. the offshore flow pattern changed orientation from southwestward to southward and a cool filament seen previously was no longer discernible. The nearshore flow pattern changed from a predominantly southward to a northward flow. The chanaes occurred between'two OPTOMA cruises conducted in the summer of 1986. Two possible causes are investigated for these chanaes : 1) a change in the poleward undercurrent of the CCS, and 2) a cnanae in the coastal winds. Analysis of cross-sections of the poleward undercurrent indicate that it remained subsurface throughout the cruises. Analysis of wind data indicate that southward winds were the dominant wind pattern throuahout the first cruise. Wind data from a moored buoy off Point Arena indicate northward winds (i.e., wind reversals) following the first cruise, which could be associated with the changes in the flow patterns of the CCS. 20 DISTRIBUTION 'AVAILABILITY OF A8STRACT ED UNCLASSiE'ED/UNLlMITED □ SAME AS RPT fj QTlC USERS 122a NAME OF RESPONS'BlE INDIVIDUAL M. L. Batteen DO FORM 1473. 84 mar 21 ABSTRACT SECURITY CLASSIFICATION UNCLASSIFIED 22b TELEPHONE {include Area Code) (408) 646-3265 UC OFFICE SYMBOL 68 Bv 83 APR edition may oe usea untn exnaustea All other editions are oosoiete SECURITY CLASSIFICATION OF THIS PAGE O U.S. CtfCnmiM PniMint o"ic« nli-40614. 1 Approved for public release; distribution is unlimited. Changes in the California Current System observed off Northern California during July-August 1986 by Michael E. Beasley Lieutenant, United States Navy B.S., Auburn University, 1979 Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN METEOROLOGY AND OCEANOGRAPHY from the NAVAL POSTGRADUATE SCHOOL December 1987 ABSTRACT Changes in the flow pattern of the California Current System (CCS) in a relatively short time period (~ one week) are investigated. The offshore flow pattern changed orientation from southwestward to southward and a cool filament seen previously was no longer discernible. The nearshore flow pattern changed from a predominantly southward to a northward flow. The changes occurred between two OPTOMA cruises conducted in the summer of 1986. Two possible causes are investigated for these changes: 1) a change in the poleward undercurrent of the CCS, and 2) a change in the coastal winds. Analysis of cross-sections of the poleward undercurrent indicate that it remained subsurface throughout the cruises. Analysis of wind data indicate that southward winds were the dominant wind pattern throughout the first cruise. Wind data from a moored buoy off Point Arena indicate northward winds (i.e., wind reversals) following the first cruise, which could be associated with the changes in the flow patterns of the CCS. #5 TABLE OF CONTENTS I. INTRODUCTION .8 A. OBJECTIVES 8 B. STUDY AREA 8 C. BACKGROUND 9 1. Historical Notes on Atmospheric Forcing and the CCS 9 2. Previous Data Collections in the CCS 10 II. DATA ACQUISITION AND DESCRIPTION 12 A. DATA ACQUISITION 12 1. OPTOMA Cruise Data 12 2. Other Data Acquired 14 B. THE OBJECTIVE ANALYSIS TECHNIQUE 21 III. RESULTS 22 A. SATELLITE IMAGERY 22 B. WIND DATA 22 C. ANALYSIS OF HYDROGRAPHIC DATA 29 1. OPTOMA 21 29 2. OPTOMA 22 46 3. Coastal Flow 61 IV. CONCLUSIONS AND RECOMMENDATIONS 64 A. CONCLUSIONS 64 B. RECOMMENDATIONS 64 LIST OF REFERENCES 67 INITIAL DISTRIBUTION LIST 69 DUDLEY K] y LIST OF FIGURES 1.1 OPTOMA NOCAL and CENCAL subdomains and the CODE domain. Isobaths are shown in meters 10 2.1 Ship track for OPTOMA 21 from Wittmann et ai, 1987 13 2.2 OPTOMA 21 sea surface temperature field. The contour interval is 0.5°C 14 2.3 Ship track for OPTOMA 22 from Ciandro et at., 1986 15 2.4 OPTOMA 22 Sea surface temperature field The contour interval is 0.5°C 17 2.5 Relative positions of NDBC 14 (shown by the circle) and of the Bakun upwelling index (shown by the square) 18 2.6 Buoy winds at 39.2°N, 124.0°W during the OPTOMA cruises 19 2.7 The Bakun Upwelling Index for the period 1 March through 28 August, 1986 20 NOAA-9 satellite IR image, 18 June, 1986 23 NOAA-9 satellite IR image, 14 July, 1986 24 NOAA-9 satellite IR image, 16 July, 1986 25 NOAA-9 satellite IR image, 17 July, 1986 26 NOAA-9 satellite IR image, 29 July, 1986 27 NOAA-9 satellite IR image, 30 July, 1986 28 3.1 3.2 3.3 .3.4 3.5 3.6 3.7 Poleward winds following the OPTOMA 21 cruise 12Z 22 July, 1986. Arrow denotes NDBC 14 3q 3.8 Cessation of poleward winds immediately following the OPTOMA 21 cruise, 06Z 23 July, 1986 31 3.9 Start of poleward winds prior to OPTOMA 22 cruise 18Z 24 Julv 1986 32 3.10 Cessation of poleward winds prior to OPTOMA 22 cruise 00Z 27 July, 1986 , 33 3.11 Start of poleward winds during the OPTOMA 22 cruise 12Z 28 Julv 1986 34 3.12 OPTOMA 21 (A) Surface dynamic topography and (B) Surface geostrophic currents 36 3.13 OPTOMA 21 (A) 50 m depth dynamic topography and (B) 50 m depth geostrophic currents 37 3.14 OPTOMA 21 (A) 100 m Dynamic Height Topography and (B) 100 m geostrophic currents 38 3.15 OPTOMA 21 (A) 150 m dynamic topography and (B) 150 m geostrophic currents 40 3.16 OPTOMA 21 (A) 200 m dynamic topography and (B) 200 m geostrophic currents 41 3.17 OPTOMA 21 (A) 250 m dynamic topography and (B) 250 m geostrophic currents 42 3.18 OPTOMA 21 nearshore temperature- salinity diagram 43 3.19 OPTOMA 21 offshore temperature-salinity diagram 44 3.20 Survey stations for OPTOMA 21 (from Wittmann et al., 1987) and the two vertical cross sections 45 3.21 OPTOMA 21 vertical cross sections along the jet (A) Temperature and (B) Salinity 47 3.22 OPTOMA 21 vertical cross sections across the jet (A) Temperature and (B) Salinity 48 3.23 OPTOMA 22 (A) Surface dynamic topography and (B) Surface geostrophic currents 50 3.24 OPTOMA 22 (A) 50 m dynamic topography and (B) 50 m geostrophic currents 51 3.25 OPTOMA 22 (A) 100 m dynamic topography and (B) 100 m geostrophic currents 53 3.26 OPTOMA 22 (A) 150 m dynamic topography and (B) 150 m geostrophic currents 54 3.27 OPTOMA 22 (A) 200 m dynamic topography and (B) 200 m geostrophic currents 55 3.28 OPTOMA 22 (A) 250 m dynamic topography and (B) 250 m geostrophic currents 56 3.29 OPTOMA 22 offshore temperature-salinity diagram 57 3.30 OPTOMA 22 stations and the vertical cross sections (from Ciandro et al., 1986) 58 3.31 OPTOMA 22 temperature vertical cross section at E-F 59 3.32 OPTOMA 22 temperature vertical cross section at G-H 60 3.33 OPTOMA 22 temperature vertical cross section at I -J 62 3.34 OPTOMA 22 temperature vertical cross section at K-L 63 ACKNOWLEDGEMENTS The professional guidance, patience, and support of my advisor, Dr. Mary L. Batteen and second reader Dr. Christopher N.K. Mooers, have been an essential and invaluable part of this thesis. Dr. Mooers allowed me to participate in the OPTOMA 22 cruise, which led to this thesis. Dr. Batteen continually guided me along in this endeavor. Ms. Melissa Ciandro, currently at the Scripps Satellite Oceanography Facility, was invaluable due to her expertise in computer programming and satellite imagery. Much of the credit in the completion of this thesis is due to my wife and children, Cary, William, and Rebecca, who continually gave their time and loving support throughout. I. INTRODUCTION A. OBJECTIVES Recently, an oceanographic cruise was conducted in the waters off northern California that yielded unexpected results. OPTOMA 22, an oceanographic cruise, was conducted 27 July through 5 August, 1986. The purpose of the cruise was to define an offshore flowing jet mapped by OPTOMA 21, a cruise that ended seven days earlier. What was seen though, was a different dynamical structure than was expected. The offshore flowing jet of OPTOMA 21 was no longer present and the general flow was now oriented parallel to the coast instead of perpendicular to the coast. The nearshore flow pattern also changed from southward to northward. What happened over such a relatively small time scale to change the structure of the flow field? The primary objectives of this thesis are to describe the flow fields during both cruises and also systematically investigate what caused the changes in the flow fields off northern California seen in OPTOMA 22. Two possible reasons for these changes which could well be coupled are: 1) a significant decline or change in the winds favorable for upwelling; and 2) a change in the state of the poleward California Undercurrent. The organization of this paper is as follows. I will first present background information on the general features and discuss recent data acquired in surveys prior to OPTOMA 22 (from the CODE and OPTOMA programs). Next, I will describe the various types of data acquired and how they are used in my analysis (Chapter II). I will then show the results of the data analysis (Chapter III). Finally I will discuss my results, present conclusions and discuss very briefly some areas that might_be covered by future research (Chapter IV). B. STUDY AREA The study domain for OPTOMA 22, NOCAL, is the northern of two sub- domains of the Ocean Prediction Through Observations, Modeling and Analysis (OPTOMA) program and is located at about 37°N to 39°N, 124°W to 128°W (Figure 1.1). The domain is located south of the Mendocino Escarpment, is mostly offshore of the continental slope, and has an average water depth of ~ 3900 m. The region is well within the California Current System (CCS) regime, which is now known to be a complex eastern boundary current system consisting of eddies, jets and filaments (Mooers and Robinson, 1984). C. BACKGROUND 1 . Historical Notes on Atmospheric Forcing and the CCS a. Atmospheric Forcing The North Pacific High is the forcing mechanism for the equatorward California Current and upwelling along North America's west coast (Huyer,1983). In the summer, the high is at its most northwest position, centered at about 38 N, 150°W. Simultaneously, the extreme western United States develops a thermal low resulting from the very warm solar heated surface. This sets up an offshore pressure gradient marked by equatorward winds. These winds cause an offshore transport of water in the Ekman layer (Huyer, 1983). Superimposed on these equatorward winds are atmospheric fluctuations of 2 - 20 days which can lead to wind events or relaxations (Halliwell and Allen, 1987). b. The CCS As a result of this atmospheric forcing, a broad equatorward flowing surface California Current is set up as an eastern boundary current of the Pacific Ocean subtropical gyre. This is the major current in the CCS. The other currents in the CCS are: 1) the poleward flowing Southern California Countercurrent located south of Point Conception in the California Bight; 2) a poleward flowing Davidson Current located north of Point Conception during the fall and winter; and 3) a California Undercurrent, also known as the Poleward Undercurrent or PUC (Kosro, 1987), that flows poleward in the vicinity of the continental slope and shelf (Hickey, 1979). Rienecker et al. (1985) ascertain that a synoptic look at the CCS will differ markedly from the classical notion that the CCS should have a broad, slow and shallow dynamic structure consistent with eastern boundary currents (Hickey, 1979). Recent observations have shown that the CCS contains numerous mesoscale eddies, meandering jets and turbulent filaments (Mooers and Robinson, 1984; Bernstein et. al, 1977). 41N 39N 37N 35N ka Cape Mendocino Son Francisco ■C^iallrMonttrt] >rro 123NV 126W 124W 122W 120W Figure 1.1 OPTOMA NOCAL and CENCAL subdomains and the CODE domain. Isobaths are shown in meters.. 10 2. Previous Data Collections in the CCS a. CALCOFI and CUE Programs In 1949 the California Cooperative Fisheries Investigations (CALCOFI) program was initiated. Its main goal was to study fisheries variability associated with interannual variability in the CCS. These large-scale, long-term studies were conducted south of San Francisco, primarily between Point Conception at 35 °N and Cabo San Lazaro at 25 °N (Reid et ai, 1958). About 1960, small scale studies of the coastal upwelling regime off Oregon were initiated (Huyer, 1983). Repeated sampling of a hydrographic section off Newport, Oregon was carried out, and in 1965 current meters were put in along the same section (Huyer, 1983). All of these upwelling study efforts culminated in the intensive Coastal Upwelling Experiments (CUE-I and CUE-II), which were carried out during the upwelling seasons (i.e., ~ March to September) of 1972 and 1973. b. Data Analysis of the CODE Program At the beginning of the OPTOMA program, the Coastal Ocean Dynamics Experiment (CODE) was finishing. It was conducted near the NOCAL domain (Figure 1.1) during the upwelling seasons of 1981 and 1982. The domain was in the area from Point Reyes (38 °N, 123°W) to Point Arena (39 °N, 123.7°W) with an offshore extent of ^50 km (Beardsley and Lentz, 1987; Zemba and Friehe, 1987). As seen in Figure 1.1, this area has a relatively straight coastline, simple and gradual bottom topography, and large wind stress fluctuations from winter to summer (Nelson, 1977). c. Previous OPTOMA Surveys Since 1982, the OPTOMA program has acquired observations in the NOCAL and CENCAL subdomains (see Figure 1.1). The cruises prior to OPTOMA 21 and OPTOMA 22, which were conducted during the summer, have documented upwelling, meandering jets, and mesoscale turbulent filaments (Rienecker et ai., 1985). These features seem to be typical features in the CCS occurring when equatorward winds dominate the atmospheric flow. 11 II. DATA ACQUISITION AND DESCRIPTION A. DATA ACQUISITION 1. OPTOMA Cruise Data Both OPTOMA 21 and 22 were part of a research program sponsored by the Office of Naval Research. The OPTOMA program was conceived to try to understand the mesoscale (fronts, eddies and jets) variability and dynamics of the CCS and to determine the scientific limits to practical mesoscale ocean forecasting. The general OPTOMA domain was off the California coast, with two subdomains being extensively sampled, NOCAL and CENCAL (Figure 1.1). The NOCAL subdomain was covered in both OPTOMA 21 and 22, with both coastal and offshore observations taken. OPTOMA 21 was conducted from 7 through 20 July, 1986. A primary purpose of this cruise was to make a quasi-synoptic CTD/XBT (conductivity- temperature-depth/expendable-bathythermograph) mapping of the synoptic/mesoscale variability in the NOCAL domain, placing special emphasis on the cool anomaly, meandering jet and eddy system that was present. Another purpose of the cruise was to carry out a multidisciplinary study of this eddy, jet and cool anomaly system (Mooers et ai, 1987; Mooers and Rienecker, 1987; Jones et ai, 1986; Stanton and Washburn, 1986; Washburn and Stanton, 1986; Flegal 1986; Bucklin, 1986). There was a total of 72 CTD casts and 122 XBT drops. The domain was about 150 x 250 km (Figure 2.1). The cruise consisted of a series of zig-zags, crossing a cool anomaly (see Figures 2.1 and 2.2) and then a leg into the jet near the completion of the cruise. OPTOMA 22 was conducted 27 July through 5 August, 1986, one week following the OPTOMA 2J cruise. Besides surveying the NOCAL domain off Point Arena, California, a specific purpose of the cruise was to help define how the cool anomaly/jet system tracked in OPTOMA 21 related to a larger-scale pattern. The cruise track, shown in Figure 2.3, sampled a domain approximately 240 km square centered about 280 km off the coast between Point Arena and Cape Mendocino. 177 XBT's were successfully dropped but due to winds and high seas only six CTD casts were made. The sea surface temperature (SST) field from OPTOMA 22 was oriented along the coast (Figure 2.4). A comparison of Figure 2.4 with Figure 2.2 shows that there is a noticeable change in the orientation of the SST fields. 12 Figure 2.1 Ship track for OPTOMA 21 from Wittmann et ai, 1987. 13 U ITt 4MLTSU n»ia nmumt i ,;f« Figure 2.2 OPTOMA 21 sea surface temperature field. The contour interval is 0.5 °C. The hydrographic data acquired from these two OPTOMA cruises will be utilized in running the objective analysis program (see section II. B) to obtain dynamic height and geostrophic current plots. For obtaining these plots, it is assumed that the data are quasi-synoptic (i.e., the dynamic structure was assumed to have not changed much over the period of sampling). 2. Other Data Acquired a. Satellite Imagery To provide real-time analysis and depiction of the jet and its movement, satellite images from Scripps Satellite Oceanography Facility (SSOF) were transmitted as soon as they were received to the ship through WWD, the radio station located at Scripps, via the facsimile (FAX). The infrared (IR) images used were advanced very high resolution radiometer (AVHRR) images from the NOAA-9 satellite. In contrast, 14 Figure 2.3 Ship track for OPTOMA 22 from Ciandro et ai, 1986. 15 IR images collected at SSOF during OPTOMA 22 were not sent directly to the ship since the ship was remapping the domain systematically instead of tracking the offshore flowing jet. These IR images, together with others from the NOAA-9 satellite, are used in Chapter III to show SST features in the CCS such as squirts, jets and meanders. b. Buoy Wind Data Wind data for the buoy NDBC 14, located at 39.2°N 124°W (Figure 2.5), were obtained from the National Weather Service in San Francisco, California. The data are recorded every hour and include wind direction and speed, wave information, air temperature and atmospheric pressure. A wind stick plot was made for the buoy time series at three hour intervals (Figure 2.6). c. Bakun Upwelling Index The Bakun upwelling indices (Bakun, 1973; Bakun, 1975; Bakun, 1986) are offshore Ekman transports computed from daily means of six-hourly synoptic surface atmospheric pressure fields from the Navy's Fleet Numerical Oceanography Center (FNOC) arranged on a 3° mesh length grid. To use this index, Bakun assumes that the offshore surface Ekman transport by the longshore component of the wind stress occurs on large enough spatial scales that it cannot be readily replaced by alongshore surface flow, but must be replaced by the upwelling of deeper waters. The Bakun Upwelling Index to be used in the data analysis is located at 39°N, 124°W and is ~ 100 km to the west of the buoy NDBC 14. The proximity of this location to NDBC 14 should allow a fairly close comparison of correlations of the buoy wind and upwelling index data to be made for the immediate area. In particular, by referring to the time series plot of the upwelling index (Figure 2.7) and comparing it with the wind stickplot (Figure 2.6), a wind relaxation or reversal and the associated cessation of upwelling may be inferred. Figure 2.7 shows the upwelling index for the period 1 March through 28 August, 1986. d. Synoptic Meteorology Charts North American Meteorology charts for the OPTOMA 21 and 22 cruise periods, obtained from the Meteorology Department at the Naval Postgraduate School, show the large-scale wind field for North America. These charts can be used to indicate if conditions are favorable for upwelling or for wind reversals/relaxations. By combining these synoptic charts with the stickplot data and the Bakun upwelling index, winds favorable for upwelling and relaxations/reversals can be readily identified for a broader picture of the wind field. 16 4l'N it H MM J7*M •••• MM lit « ID * 111 V Figure 2.4 OPTOMA 22 Sea surface temperature field. The contour interval is 0.5 C. 17 O NDBO 14 □ Bakun Upwelling Index ape Mendocino o o Co I o o l o o o *n I 8Uj||SD03 JO LU 001 J&d s/r1^ Figure 2.7 The Bakun Upwelling Index for the period 1 March through 2S August, 1986. 20 B. THE OBJECTIVE ANALYSIS TECHNIQUE The objective analysis technique was first developed by Gandin (1965), applied to oceanic data by Bretherton et al. (1976); the program used in OPTOMA is documented by Carter and Robinson (1981). The objective analysis program incorporates data that is irregular in time and/or space, and interpolates it objectively onto a regularly spaced grid. To do this, a correlation function must be defined. Carter and Robinson (1981) identified four specific parameters to determine the selection of observational data affecting an interpolation point. These parameters are: 1) a maximum temporal increment between observations, 2) a spatial radius of influential points, 3) a dominant phase speed, and 4) a maximum number of surrounding influential points. Obviously, it is best to use observational data closest to the interpolation point. By specifying a maximum range at which observational data may affect the interpolation point, usually determined by running a covariance program on the data, the problem of distant points influencing the interpolation can be solved. The objective analysis program used the hydrographic data acquired by the two OPTOMA cruises to produce dynamic height and geostrophic current charts at six depth levels: 0 m, 50 m, 100 m, 150 m, 200 m, and 250 m. The dynamic heights at all levels were referenced to 450 m, a typical OPTOMA reference depth. For XBT data, the program uses a mean salinity-temperature relationship for the region. Rienecker, et al. (1985) estimate an rms error of 4 dyn-cm for this technique. 21 III. RESULTS A. SATELLITE IMAGERY The IR image of 18 June, 1986 (Figure 3.1), well before either cruise, indicates the" complex structure of the coastal waters south of Point Arena. At the southern edge of the image a southwest oriented jet is seen, as well as what appears to be cold, newly upwelled water along the coast between Point Arena and Point Reyes. The IR images from 14, 16 and 17 July (Figures 3.2 - 3.4) reveal the jet that was tracked by the OPTOMA 21 cruise, conducted 7 - 20 July, 1986. The jet is located just south of Point Arena, with a southwestward orientation. The first three images show the jet advecting the cold upwelled water well out from the coast, with the jet boundaries being fairly well defined. Figure 2.2, the SST plot based on data for the whole cruise, reveals the same cool anomaly seen in the IR images. This cool anomaly is associated with the offshore flowing jet tracked by the OPTOMA 21 cruise. Following the 17 July image, cloud cover obscured the area for over a week so that the next good image of the area obtained was on 29 July (Figure 3.5). This was the first day of the OPTOMA 22 cruise. Although the coastal waters were obscured by low clouds or fog, it is apparent that the flow field has changed. No longer are offshore filaments or jets visible. Instead, a field of mixed water with the general flow parallel instead of perpendicular to the coast is seen. The next clear image was on 30 July (Figure 3.6). A band of clouds stretches from Point Reyes southwest, partially obscuring the flow field. Again though, the flow field is oriented along the coast instead of being perpendicular to the coast as seen in the earlier images (i.e., Figures 3.2 - 3.4). Also noted is the warm water adjacent to the coast south of Point Arena. No other images were obtained due to cloudy, overcast conditions until well after the OPTOMA 22 cruise had ended on 5 August. B. WIND DATA As can be seen in the velocity time series, commonly referred to as a stickplot diagram (Figure 2.6), the winds in the region are equatorward, or favorable for upwelling, throughout the OPTOMA 21 cruise. However, by July 22 (Julian day 203) a low pressure system had moved into the area off the California Coast. The cyclonic flow of this system reversed the winds so that they blew poleward instead of 22 Figure 3.1 NOAA-9 satellite IR image, 18 June, 1986. 23 gxx^£>>y-:.sragtfc-v _^y.y--::--':- *<■*<<< — ... .^. *•.;•.... ,.....y, n «i»—w m Figure 3.2 NOAA-9 satellite IR image, 14 July, 1986. 24 Figure 3.3 NOAA-9 satellite IR image, 16 July, 1986. 25 Figure 3.4 NOAA-9 satellite IR image, 17 July, 1986. 26 Figure 3.5 NOAA-9 satellite IR image, 29 July, 1986. 27 ■-.\v.-v-.v ••... ^T.v----.v :■>- ■ - ■ • :: r-yNWN?^ *>~ , ■. iMiiiir ifflfT°g*Ba Figure 3.6 NOAA-9 satellite IR image, 30 July, 1986. 28 equatorward, as observed at NDBC 14 (Figure 3.7). These poleward winds continued for almost 24 hours, which disrupted the surface water circulation of offshore flow and consequently broke up the upwelling. Comparing Figure 2.6 with the Bakun Upwelling Upwelling Index (Figure 2.7), the following correlations can be made. Following the OPTOMA 21 cruise, a decrease in the index, indicating less upwelling was occurring, is noted on Julian day 204 (July 22). As expected, there is a short time lag between the wind cessation/reversal and the dynamical ocean response. The winds are equatorward again on 23 July (Figure 2.6) in response to the 'normal' atmospheric situation with the North Pacific High and the southwestern United States thermal low (Figure 3.8 ). After slightly more than 24 hours of equatorward winds, another wind reversal occurred on 24 July, Julian day 205 (Figures 2.6 and 3.9). This wind reversal followed that of 22 July close enough that the Bakun Upwelling Index (Figure 2.7) did not indicate a significant increase in upwelling between the two poleward wind events. Figure 3.10 shows the equatorward winds at the beginning of the OPTOMA 22 cruise. Again equatorward winds dominated the atmospheric regime from 26-28 July (Figure 2.6). Then, on 28 July (Julian day 209), poleward winds (Figures 3.11 and 2.6) resulted in a corresponding decrease in the Bakun Upwelling Index (Figure 2.7). C. ANALYSIS OF HYDROGRAPHIC DATA 1. OPTOMA 21 a. Dynamic Topography and Geostrophic Current Analysis Figures 3.12 — 3.17 show the dynamic topography and geostrophic currents of the domain, produced by the objective analysis technique, for OPTOMA 21. The plots are at 50 m depth intervals and are relative to 450 m, a typical reference level for the OPTOMA program (Rienecker et a/., 1985). Each dynamic topography/geostrophic current plot pair are at the same depth. The OPTOMA 21 dynamic topography at the surface (Figure 3.12 a) shows the same general water structure as that shown by the hand contour analysis of the SST (see Figure 2.2), i.e., a cold water jet extending ~200 km southwest of Point Arena. On the dynamic topography map, the center of the jet can be seen at 37.5°N, 124. 8°W. This jet is most likely the result of cold water upwelled from the colder subsurface water, since the winds before and during the cruise were favorable for upwelling (Figure 2.6). Anticyclones are seen to the southwest and northwest of the topographic low. 29 Figure 3.7 Poleward winds following the OPTOMA 21 cruise 12Z 22 July, 19S6. Arrow denotes NDBC 14.. 30 Figure 3.8 Cessation of poleward winds immediately following the OPTOMA 21 cruise, 06Z 23 July, 1986. 31 Figure 3.9 Start of poleward winds prior to OPTOMA 22 cruise 18Z24July, 1986. 32 '7 37" 123 "S* tni! IS3 3» X 2lf 64S KO'«s -I f 8*r^l33 55019S ri-t /tf 69. S 'A ^ tSj ft • 9 7* Mia rJto«* i?Y SEWiiil/S« X-.M »S2*c\ 0a>i3i ~?4 / £K> , 088 !^20S * 59^.11 82, ■V Figure 3.10 Cessation of poleward winds prior to OPTOMA 22 cruise 00Z27July, 19S6. 33 Figure 3.11 Start of poleward winds during the OPTOMA 22 cruise 12Z28 July, 19S6. 34 The coastal currents have a maximum of ~25 cm/s, while the offshore currents reach a maximum of ~45 cm/s. There was a general equatorward geostrophic flow, both along the coast and offshore (Figure 3.12 b). The low (Figure 3.12 a) is part of a cyclonic current. The southwestward currents to the north of this low have a maximum of ~ 30 cm/s. At 50 m depth (Figure 3.13 a), the upwelled jet is still discernible. The shoreward side of the low was "pinched". The anticyclones appear to have moved slightly to the east, now being oriented further north and south of the low. The geostrophic currents (Figure 3.13 b) at this depth exhibit the same general flow characteristics and strengths as at the surface. However, the westward flow to the north of the low is less than at the surface, with maximum currents on the order of ~ 25 cm/s. At the 100 m depth (Figure 3.14 a) the 'pinching' of the upwelled jet is evident, with the low now represented by closed contours. This is accentuated by an anticyclonic eddy discernible near the eastward extent of the anticyclone southwest of the low, just west of San Francisco Bay. This is the deepest level that evidence of the jet can be seen. The geostrophic currents for this depth (Figure 3.14 b) are still generally southward. The currents are however, weaker with maxima of ~ 10 cm/s near the coast and ~25 cm/s in the southern portion of the main offshore flowing jet. Eddy-like structure is revealed by the current pattern. The eddy-like structure at this and deeper depths could well be artifacts of the objective analysis technique, since the objective analysis error fields (not shown) are greatest where the eddy-like structure is seen. A smaller domain size than used here for the objective analysis program could well reduce the error fields, since they are mainly a result of sparsely sampled data. The deeper levels, i.e., 150 m, 200 m and 250 m (Figures 3.15 a — 3.17 a), all show the intricate structure of eddies. There is no jet signature. An anticyclone is seen south of Point Arena. An anticyclone west of San Francisco Bay, first seen in the 100 m depth, is discernible. A low that was linked with the offshore jet in the upper layers is seen in the lower layers as a large cyclonic eddy. The anticyclone southwest of the low recedes to the west with depth. To the north is an anticyclonic eddy. The geostrophic currents of the deepest three depths (Figures 3.15 b — 3.17 b) clearly indicate an eddy structure and a lack of any generalized equatorward flow. 35 T W \ \> \ » pa Is Figure 3.12 OPTOMA 21 (A) Surface dynamic topography and (B) Surface geostrophic currents. 36 pa z z z o a CO "+ n CO Figure 3.13 OPTOMA 21 (A) 50 m depth dynamic topography and (B) 50 m depth geostrophic currents. 37 CQ z z z o a 00 T « « Figure 3.14 OPTOMA 21 (A) 100 m Dynamic Height Topography and (B) 100 m geostrophic currents. 38 The currents at these depth levels are weak, ranging from a maximum in the current field of ~ 15 cm/s at 150 m to a maximum of ~ 10 cm/s at the 250 m depth. At the 250 m depth two eddies are discernible which are cyclonic remnants of the low and the anticyclonic flow of the high off San Francisco Bay. In general, the winds were favorable for upwelling prior to and through the OPTOMA 21 cruise. This resulted in coastal upwelling with an offshore jet 'originating' from a locally intense upwelling region. This is consistent with the same type of upwelling pattern that Kosro and Huyer (1987) found during CODE when equatorward winds were dominant (primarily in 1981). b. T-S Diagrams Figures 3.18 and 3.19 show the OPTOMA 21 temperature-salinity (T-S) diagrams for nearshore and offshore CTD stations, respectively. A comparison of the diagrams shows that the upper layer temperatures from the offshore CTDs can be as much as 3 K higher (i.e., maximum of ~ 17°C vice that of ** 14 °C) than those from the nearshore CTDs. The salinities span a broader range (l%o compared to 0.5%o) for the offshore CTDs than for to the nearshore CTDs. At greater depths the same overall T-S relationship is depicted at both the nearshore and offshore CTD stations, but extend for greater depths for the offshore stations, as expected. c. Vertical Cross Sections of the Domain Two vertical cross sections from the OPTOMA 21 survey were drawn, one along the upwelled jet and one across the jet. These two sections are shown on the OPTOMA 21 survey station diagram, Figure 3.20. In the figure, transects are identified by letters. The cross sections were drawn from the XBT and CTD data. The sections are of temperature and salinity and are drawn to 750 m depth. The contour interval for the temperature cross section is 0.5 °C for temperatures less than 10 °C, and 1°C for temperatures greater than 10°C. The salinity cross section contour interval is 0.1%o for all salinities. The vertical cross section taken along the upwelled jet, A-B, is shown in Figure 3.21. The temperature cross section (Figure 3.21 a) reveals a broad upwelling of cool water with a general southward geostrophic flow (out of the page to the reader) down to ~250 m. Below ~200 m the isotherms are level or have a reverse tilt indicating a northward flow. However, near the coast at depths greater than ~ 150 m, the downward tilting of isotherms indicate warm water and a northward flow. 39 — — -*— ♦ — . t... — i . — j_ ; i ' • » • ♦ » . r . i * . \ * I « 6 « 4 1 ' - * , \ x • ' ♦ i * / ; • • - » * - - « • » . \ * • - • # * 1 4 t ,» ** \ k t , » ^ - , . 4 < 1 b \ \ « V \ i . »> » ■ « f f \ ^ i / t ; / \ ' \ ** / 0 \ \ 1 i / / / . t V \ \ \ k M -* P "" /^ / s* t I 1 k . « , *. ^_ * I s "'-;: \ - * i - - » - x* / ' * / ; i * \ * 1 t / t J* / r i f t ' 1 / * ' ' CQ * (J Figure 3.15 OPTOMA 21 (A) 150 m dynamic topography and (B) 150 m geostrophic currents. 40 \ -— \ i * % % \ h 9 • V \ \ 4 ^ \ 4 | » i / 4 1 | ff ff 1 4 a - \ « 9 * » \ » - - fc r f ft » 1 * * k « - » «, % ► - - # « m> s » 4 « « t 4 • \ \ / -. » * % - 4 f # X V I \ 1 4 * t t r . ^ « ■ - 1" -4» / 4 * V. \ - / / / . ^ « 9 * m 4 k 4 i "» ** /• / * 4 | * i 4 -* X* •* X» - t 4 » - ^* /* <* ' % 4 f « ^» •» /» 4 * t i | ♦ . >* x» . • 4- * 4 f . t / - • / t f / 4 * i i o o o O D i » 1 O O CO 2 o 2 2 W 2 CO 2 (0 n Figure 3.16 OPTOMA 21 (A) 200 m dynamic topography and (B) 200 m gcostrophic currents. 41 ' « — \ ■ 1 ' v ' ' ' • » • s ft, "• r * » - , , . ' * - - * . . . • « « • ' * ■ g , > • ' / ' * . • ..-''•.... * $ * ft o -"''-.,,« » * «*»» '■*■*»*» a ■ t p . o ''.,,....,. « f S CO Figure 3.17 OPTOMA 21 (A) 250 m dynamic topography and (B) 250 m geostrophic currents. 42 17 X f » •• •• 15 • * • • • — • • / / / « .ft .«* 13 - •* V • • t /_^ • • • 11 • • • •••■£»! 2 0) « • • • 1 ^ 3 9 • « * -*-> i (0 * * *mfll. • • Jh ^S « • 4 CD w&k • P. m k B 7 - n .<*> M E- » * ' N. N ~* - * ^ X *- - ^ ^ N, ^s. N. >» > X N. N» ■» N N N N "»> "» ^ >» N \ * * * \ \ < 1 • S *~ — ' CQ Figure 3.26 OPTOMA 22 (A) 150 m dynamic topography and (B) 150 m geostrophic currents. 54 . \\- s / 1 ; • O o -~~~ s / -"> • ■■•X***** - o . o * "*"-»-»x-»»* » V % , % % • * / ' * » » x -* \ ♦ # o o • ' * ' \ \ \ \ - t , - - <• •» * * v - - - - - , . ? "o , , . . - v * » - - s • — - . 9 E !° Figure 3.27 OPTOMA 22 (A) 200 m dynamic topography and (B) 200 m gcostrophic currents. 55 « Figure 3.2S OPTOMA 22 (A) 250 m dynamic topography and (B) 250 m geostrophic currents. 56 o (D 0) u -4-> *-. 0) £ 17 15 13 11 ♦* t ,• ,• • • • .V" • * • • • « •* * * f / V « / t t . • • « • • % • & • " ••• 7< i ■"'" • • • • * • \i •-" • • • * • vt • • • • • • • • % •••''' Jp <0 \v <\