2. SCIENCE AND ENGINEERING UPDATES

2.1 WOCE Heavy Weather Tests and Recommend Drifter Design

Sixteen drifters of various design were released along 145 °W,between 47 and 45 °N, and 12 were recovered in early May 1990 off the coast of Washington for engineering evaluations. Also, three drifters were fitted with VMCMs and deployed for a 40-hour period near 50 °N, 145 °W, to acquire drogue slip calibration data in high wind conditions. Fig. 1 displays the trajectories of the drifters. The results of the engineering evaluations, briefly, were (also see Sybrandy and Niiler, 1991):

figure 1. Trajectories of 16 surface drifters deployed as part of the WOCE Heavy Weather Drifter Test for the time period October, 1989 through February, 1990.

The engineering data gathered from this experiment was incorporated into the the recommended design specifications of the WOCE/TOGA drifter. A report, entitled "WOCE/TOGA Lagrangian Drifter Construction Manual" has been published (Sybrandy and Niiler,1991).

2.2 Update of the Drifter Slip model

The model for the least-square regression of slip as a function of drag area ratio, R, wind velocity V and velocity difference across the drogue DV has been updated from the formula published in SVP-4. Data from slip measurements from the WOCE Heavy Weather Drifter Tests has been included in this analyses and a vector regression has been made. The new results do not differ significantly from those obtained separately from the downwind and crosswind analyses,as expressed in the equation below:

where W (m/s) is the downwind velocity, D (cm/s) is the velocity difference across drogue, R is the drag area ratio,and both a (m/s) and b are constants.

2.3 Preliminary Pressure Tests

Part of the work ongoing at the GDC is the adaptation of atmospheric pressure measuring capabilities to the standard SVP drifter. The first prototype port and sensor systems have been attached to a standard drifter and used in field tests off San Diego. These tests were quite successful. The next phase will involve long-term performance testing of a large number of drifters. To this end, a joint experiment is being undertaken between the GDC and other international scientific agencies to deploy between 15 and 20 pressure-equipped drifters in late 1991 off the coasts of California, southern England, France, Australia, and South Africa. As many as possible of these drifters will be recovered 6 months later for post calibration of the pressure sensors. The detailed proposal letter, including figures showing pressure port design and field data from the preliminary trials, is included as an appendix to this document.

2.4 DBCP and New GTS Processing Chain

An essential component of SVP is its interaction with the international meteorological community, particularly through the development and deployment of pressure-equipped drifters but also through the distribution of Sea Surface Temperature (SST) data. Although SVP goals require careful and lengthy post processing of drifter data, meteorological agencies have needs for atmospheric pressure and SST data in real time, which is accomplished by distribution through the Global Telecommunications System (GTS). At present,the distribution of drifter data collected by the ARGOS system to GTS requires users to provide calibration functions for converting from data counts to physical units. The conversion is then done by Service Argos just before distribution of data to GTS and principal investigators. Under some circumstances, such as those that use non-linear calibration functions, it may be impossible for a principal investigator to retrieve original data if the chosen calibration function is found later to have been in error. To date, calibration functions used by SVP for SST data have been reversible but it is important to change the way data is distributed to GTS in order to allow for more complicated functions in the future.

The World Meteorological Organization's Drifting Buoy Cooperation Panel (DBCP) is charged with maximizing the amount of data distributed to meteorological agencies through GTS. The Panel, through the efforts of its technical coordinator, is working to assist Service Argos in the implementation of a new GTS processing chain that will work in parallel with the existing data stream and, therefore,allow principal investigators to receive original data counts at the same time as physical data values are distributed to GTS. An early proposal for updating the GTS processing chain was discussed at the second meeting of the SVP Planning Committee (SVP-2, 1990). The final version was presented to the fourth meeting by the technical coordinator of the DBCP, Etienne Charpentier. It is expected to be approved by the DBCP in October, 1991 and implemented by Service Argos over the following year.

2.5 Survival Statistics

The success of engineering improvements resulting from the WOCE Heavy Weather Test, and other efforts to extend drifter lifetimes,can now be assessed from existing data. Of particular usefulness are the results from the pilot TOGA Pan Pacific Experiment, which has been active in the equatorial Pacific Ocean since 1988. Several drogue designs, including Ministars, TRISTARS, and Holey-socks,and many different lots have been used for this global experiment. The overall average half-life for drifters deployed during TOGA Pan Pacific is 220 days. However, that average reflects a range of performance based on incremental improvements made since the beginning of the experiment. Drifters with carroted tethers and improved drogue attachments (recommendations that arose from the Heavy Weather Test results) were not deployed until August of 1990. By July 1991, approximately 70 of the modified instruments will have been launched. The first 10 drifters built according to the complete WOCE/TOGA Lagrangian Drifter Manual instructions were completed in fall 1990 and deployed in early 1991. Examination of drifter survivability in fig. 2 shows a definite improvement in drifter life. After roughly 160 days, the percentage of instruments still functioning ranges from 40% for some Ministars (of all TOGAdrifters, certain lots of Ministars had the worst performance)to 100% for the latest instruments, built according to the recommendations in the construction manual. Lots of drifters that were refitted to include some of the recommended improvements fall in the middle of the performance range with between 55% and 90% surviving after 160 days. These results are extremely encouraging and show that the design modifications adopted have improved the drifter's survivability.

Statistical assessments of the lifetime of the SST-measuring capabilities of SVP drifters (not pictured in this report) typically show longer lifetimes than the velocity-measuring capabilities discussed above. This is true even after recent improvements in the mechanical drogue connections,. although the very latest deployments show drogue lifetimes approaching those of the SST or the transmitters themselves. GDC will continue to monitor the success of the latest engineering changes and watch for additional ways to increase the longevity of the entire system if necessary.

figure 2. Fraction of deployed drifters with good transmitters and good drogues as a function of time after deployment for a variety of designs and lots, including TRISTAR drifters deployed in 1989 (l),Ministar drifters deployed in 1988-1990 (x), AOML A5-type Holey-sock drifters deployed in 1988-1990 (t),AOML A6 & A7-type Holey-sock drifters deployed in the latter half of 1990 (r), Holey-sock drifters deployed for the Tropical Instability Wave Experiment in fall 1990 (o), Holey-sock drifters refitted with carroting at the GDC and deployed in fall 1990 (+), and the latest SVP-standard Holey-sock drifters deployed in 1991 (*). Note the improved lifetimes for later-deployed instruments, particularly for the latest SVP-standard design.

2.6 Diffusivity Biases in TOGA Drifter Data

When Lagrangian particle displacement data is used to construct an estimate of an average velocity in a specific size bin, such an estimate can have a bias because the density of drifters is not uniform in adjacent bins. This bias is due to the tendency of particles to leave high density areas more frequently simply due to random motion, giving an appearance of a "mean motion" in the direction of decreasing density (array bias). A separate but related bias can result due to inhomogeneities in Eddy Kinetic Energy (EKE) called EKE or diffusivity bias. These biases have been described recently by Davis (1991). The large amount of drifter data that is now available from the tropical Pacific as a result of the TOGA Pan Pacific Drift Experiment (the pilot study for SVP) has made it possible to assess the impact of these biases using actual data. This has now been done for the eastern tropical Pacific by Pierre Poulain working with Don Hansen and the SVP Data Assembly Center (DAC). The entire EPOCS/NORPAX/TOGA drifter data set from 1979-1990 has been utilized to construct an unbiased northward velocity field as a function of Latitude, averaged over 90-180 ° W Longitude band. The results are based on drogued data. The number of six-hourly observations available in the eastern tropical Pacific are shown in fig. 3. The dramatic impact of the TOGA program is obvious in the figure. A plot of all trajectories in the region is shown in fig. 4. The concentration of drifter-derived velocity observations is non-uniform, which is most obviously portrayed in the figure by the relatively high density of trajectories along 5 °N. Diffusivity, or EKE, estimates from this data set also vary with latitude.

The theoretical effect of array bias, as given by Davis (1991),is:  -Kdy[ln(C(y))],where K is the meridional diffusivity and C is the drifter density. This expression is difficult to evaluate because of the large errors associated with the determination of K. Alternatively,the effect of array bias on the meridional velocities can be illustrated by comparing those velocity averages computed using all available data and those computed by randomly subsampling the data set with the constraint of uniform concentration. The results in the eastern tropical Pacific are shown in fig. 5, which presents the zonally-averaged meridional velocity as a function of latitude for both the regular method (using all available data) and the corrected method (subsampling to obtain a uniform concentration). The greatest errors due to array bias are 1-2 cm/sec and they occur north and south of the latitude band of extremely high concentration at 5 °N.

An example of the diffusivity bias, resulting from nonuniformity in EKE (or diffusivity), is presented in fig. 6, which shows the mean zonally-averaged meridional velocity and velocity variance as a function of latitude computed using three finite difference schemes: backward, centered, and forward differences of 0.5-day interpolated drifter positions. Results show the greatest spread between forward and backward differences of approximately 1 cm/sec for the regions north and south of the latitude band of high concentrations at 5 °N. To lowest order, the bias is proportional to the meridional gradient of meridional variance, which can be seen by comparing the spread between results obtained using different finite differencing schemes with the slope of the variance curves. The results clearly show that drifter velocities should be estimated using centered differences of position in order to avoid diffusivity biases, which can account for 10-15% of the northward velocity and result in a 20% biased estimate of horizontal divergence (not shown here).

figure 3. Number of drifter observations versus time for the eastern tropical Pacific based on drogued data only from 1979 to 1990. Bin size used is 30 days and time step used is 6 hours.

figure 4. Drifter trajectories in the eastern tropical Pacific from drogued instruments for the time period from 1979 to 1990.

figure 5. Zonally-averaged meridional velocity in the eastern tropical Pacific determined from drifter observations using all available data (regular) and using a subsample designed to give uniform data coverage (corrected).

figure 6. Zonally-averaged meridional velocity in the eastern tropical Pacific (V) and its variance (VV) determined from drifter observations using forward (solid), backward (dotted), and centered(dash-dotted) differences of 0.5-day position data. Differences between the curves provide a measure of diffusivity bias, which is seen to be proportional to the meridional gradient of meridional velocity variance.

2.7 Coastal Transition Zone

The Coastal Transition Zone Experiment (CTZ) was designed to study the intense cold-water filaments observed off the west coast of North America. Drifter measurements were a crucial part of the experiment itself and drifter performance in the experiment played an important role in the development of the standard SVP drifter. Analysis of drifter data from CTZ has been presented in several publications including Paduan and Niiler (1991) and Brink et.al. (1991). Most recently, Swensen et. al. (1991) used the position fixes and temperature readings from 56 TRISTAR-II mixed-layer drifters, in conjunction with AVHRR images, to provide a description of the mesoscale variability of the flows associated with cold-water filaments in the California Current System off Northern California in July 1988. fig. 7 presents an example of drifter trajectories combined with the AVHRR surface temperature data. After concentrating on the strong feature into which drifters were deployed, Swenson et. al. (1991) found that the northern, offshore temperature front of the filament was convergent and was closely associated with the core of a high-speed (> 100 cm/s) jet that had a broader spatial scale than the cold-water filament. Mesoscale features were observed to be related to all developments of the cold-water filament on a variety of time scales (1-30 days). In one well-observed feature, estimates of vertical velocity (w) based on a vorticity budget were ~20 m/day over an area of 150 km² and were associated with a gain of vorticity. Estimates of w based on a local heat budget following a drifter were about three times larger over an area of 60 km². These intense upwelling features were also places where horizontal stirring occurred.

figure 7. An AVHRR image from July 18, 1988 superimposed with three-day drifter tracks centered at the time of the image. Diamonds represent the earliest displayed position fix for each drifter. The insets are sections of the images for which a different grayscale map has been used to emphasize features that would otherwise be faint or masked. The inset corresponds to a section centered north of (A).

2.8 WEPOCS

Evidence for significant flow through the Indonesian Seas from the Pacific to the Indian Ocean was provided by 4 drogued surface drifters during May-September 1988. The four drifted southward from the Mindanao Current through the Makassar Strait from 1 °N to 5 °S along very similar paths (fig. 8) and with similar mean velocities of around 50 cm/sec. Two Japanese buoys drifted south during the last 3 weeks of May 1988 (H. Ishii, personal communication). Two WEPOCS buoys drifted south, one from 8-24 August and the other from 2-15 September 1988. Assuming the average width of the flow through is 100 km and the average depth is 200 m yields an estimated transport of 107 m³/sec. The drifters were several times faster than the mean southward velocity, 14 cm/sec, for the same region from historical ship drifts. The discrepancy could be due to the different spatial and temporal averages of the data sets; more drifters plus other measurements are needed to sort out this discrepancy.

figure 8. Trajectories of four surface drifters illustrating flow through the Makassar Strait.

2.9 Indian Ocean Exploratory Array Results (1985-1988)

Donald B. Olson and Robert Molinari analyzed data from an array of forty mixed-layer drifters deployed in the northern Indian Ocean from November 1985 to January 1987 (Molinari et al., 1990). The drifters were of two designs: the EPOCS/TOGA AOML drifter and a modified version of the CODE drifter (Davis, 1985) designed by H. White (currently referred to as a STOKES drifter). The array provided fairly dense coverage of the equatorial zone of the Indian Ocean through two monsoon periods. The coverage in the Somali Basin and Bay of Bengal was also adequate to quantify the nature of the interior flows and some statistics in the boundary currents. Results suggest an equatorial gyre system maintained in part by the alternate down welling system along the equator during the summer. This flow is closed by boundary flows along the Somali and Sumatran coasts and by counter currents on either side of the equator. The response of the system to the monsoon forcing involves rapid accelerations during the monsoon onsets associated with direct wind forcing of the surface layer. During the monsoon lulls in spring and fall there are also pronounced accelerations associated with the relaxation of the pressure gradients built up during the monsoon periods.

3. NATIONAL PLANS

3.1 Argentina

The participation of Argentina within WOCE is concentrated on supporting the hydrographic lines emanating from that country. Dr. Alberto Piola of Servicio de Hidrographia Naval is also interested in contributing to SVP. One form of contribution will be through deployment of SVP-supplied drifters from the WOCE sections in the south Atlantic beginning spring of 1992. There is also a request by the Argentinean Antarctic Service for 5-10 drifters per year to be placed in the Drake Passage and Weddel Sea beginning 1992 or 1993 and it is hoped that these drifters can be of SVP design, thus providing consistent measurements both outside the official domain of SVP and, possibly, within the domain of SVP should there be north-south exchange processes that move the drifters out of the Antarctic regions. Support for SVP from Argentina may be able to increase when pressure-equipped drifters are available to be released in the southern Atlantic off Argentina. There are also requests for support of SVP being forwarded to the newly-forming oceanographic institute in Argentina funded by international debt relief programs and overseen by the University of Miami (RSMAS).

3.2 Australia

The Australian participation in SVP is being led by Dr. George Cresswell of CSIRO in Hobart. He has ordered the construction of 10 drifters to be produced by a local manufacturer. The drifters will be built according to specifications in the WOCE/TOGA Lagrangian Drifter Construction Manual produced by the GDC except in regards to the surface float. The Australian drifters will have a short cylindrical surface float rather than the suggested spherical design. Deployments of the instruments will take place over the next year in the waters near southern Australia or the island of Tasmania and will be done with consultation of the GDC in order to coordinate with the overall coverage in the south Pacific.

There is also interest on the part of Dr. John Middleton of the University of New South Wales to procure and deploy drifters within SVP. At present, no WOCE-related experiments, other than those of Dr. Cresswell, have been funded but it is hoped that funds will be made available to release SVP-standard drifters in addition to the suite of larger meteorological drifters that are maintained by the Australian Bureau of Meteorology.

3.3 Brazil

SVP-related drifter work has been proposed in Brazil by Dr. Merritt Stevenson of the Instituto Nacional de Pesquisas Espaciais (INPE). The project will be funded by the Brazilian government and will be part of an integrated project called COROAS, which is made up of oceanographers from INPE and the Oceanographic Institute at USP. Available resources will fund 12-15 SVP drifters, including service ARGOS tracking costs. Separate from this WOCE-related project, there exists the possibility of funding additional drifter deployments as a component of the existing Joint US/Brazil Scientific Agreement. Deployments will take place in or around the Brazilian waters of the Atlantic and will be coordinated with the GDC.

3.4 Canada

Canadian efforts in SVP have begun in the northeast Pacific. Ten surface drifters were deployed in 1990. These were SVP-type drifters that contained some of the improvements suggested by the GDC such as carroting of the surface float to tether connections. The epoxy carroting was actually done by the engineer from the GDC on board a Canadian research vessel en route to the deployment locations. The retrofits have helped to make these 10 drifters very long lasting. After 200 days at sea, 9 out of 10 are working perfectly and the 10th instrument ran aground off the coast of British Columbia. The northeast Pacific program will continue in conjunction with deployments of deep-drogued drifters as described in SVP-3 (1991).

The Canadian Department of Fisheries and Oceans (DFO) is supporting drifter measurements off the Labrador coast. The scientific contact for this program is Jim Helbig. Plans are to deploy 25 drifters in the spring of 1991, 1992, and 1993. Some of the instruments are expected to enter the north Atlantic via the Labrador Current and contribute to SVP in that basin. The drifters being used for the first two years will have spar-type surface floats with a Holey-sock drogue centered at 20 m depth. The drag area ratio of those instruments is 43:1. It is possible that the program will use SVP-standard drifters in 1993 and beyond, if the program continues. The Canadian DFO is supplying battery life for six months only, but it encourages SVP to extend the battery life and tracking where possible.

3.5 France

The French plan to continue to support drifter measurements in the equatorial Pacific that contribute to SVP under the auspices of TOGA's Pan Pacific and COARE programs. Ten to twelve drifters will be deployed in 1991 by R/V Le Noroit along either 155 °W or 165 °W. Twenty drifters will be available in the following two years in support of COARE. Four cruises to 155 °W and 165 °W have been proposed for 1992 plus additional ship time for the COARE Intensive Observing Period. Lead scientists for the drifter measurements are Dr. Gilles Reverdin of Lamont-Doherty Geological Observatory and Dr. Yves du Penhoat of ORSTROM-Noumea. It is expected that all deployments will be coordinated with the GDC.

3.6 Japan

The drifter activities in Japan in support of SVP are essentially unchanged from those presented in SVP-3 (1991). Dr. Haroa Ishiiof the Hydrographic Office is the principal scientist involved with these measurements. Five to ten drifters per year are planned for deployment in the north Pacific and twenty drifters per year are planned for deployment in the equatorial Pacific in support of TOGA Pan Pacific. Instrument costs in Japan remain a limiting factor in the Japanese drifter program. Unit costs there are approximately $6000, almost twice the current price for drifters manufactured in the United States.

3.7 Korea

The drifter activities of Korea in support of SVP are unchanged from those presented in SVP-3 (1991). Dr. Heung-Jae Lie of the Korean Ocean Research & Development Institute (KORDI) has undertaken to build SVP-standard drifters in house using guidelines and assistance from the GDC, which included a visit by a KORDI senior engineer to the GDC. KORDI plans call for deployment of 5 drifters per year over the next 3 years in the Japan Sea. The first year's drifters have been constructed at KORDI and are scheduled for deployment in May, 1991. A request for 20 additional drifters has been made by Dr. Sangbok Hahn of the Department of Oceanography and Marine Resources' Fisheries Research & Development Agency.

3.8 Peru

Peru does not have resources available to purchase drifters in support of SVP. They will, however, continue to provide important assistance through ship support in the eastern equatorial Pacific. The Peruvian ships have been instrumental in deploying drifters for the Pan Pacific study. The lead scientist in Peru for SVP-related matters is Mr. Hector Soldi of the Director de Hidrografia.

3.9 R.O.C.Taiwan

Prof. J.H. Hu of the National Taiwan Ocean University, Keelung is leading a group of R.O.C. Taiwan scientists in a 4-year program to deploy drifters at the formation area of the Kuroshio. His laboratory has built 28 drifters in 1991 and has begun the construction of 36 more drifters to be deployed in 1992. In a joint agreement with the GDC, the drifter construction costs are being carried by the National Taiwan Ocean University under GDC supervision and US/WOCE will pay for the Service Argos costs. The deployments will start in July, 1991. Dr.H.Ordonez, of the Phillipine National Committee of Marine Sciences, will aid in deployment of drifters off the coast of the Phillipine Island of Luzon.

3.10 U.S.A

The activities and organization of the U.S. SVP efforts is proceeding as described in earlier planning documents (e.g. SVP-3, 1991)with tasks split between the GDC and the DAC. The progress of the GDC during the past year has centered around three activities: 1) implementing the program in the Pacific Ocean, 2) planning for implementation within the Atlantic Ocean, and 3) addressing a series of technical improvements to the SVP Lagrangian Drifter designed to result in an increased half-life for the instrument and to add additional measuring capabilities. This latter category is addressed in detail in other sections of this report that deal with interpreting the results of the WOCE Heavy Weather Tests and implementing recommendations based on the results and with the adaptation of atmospheric pressure measuring capabilities to the SVP standard drifter. Other technical projects that were initiated this year, and that will continue in coming years, include testing of SEACAT salinity sensors and their adaptation to SVP drifters and development of air deployable capabilities for SVP drifters. Efforts of the DAC have centered, in general, on the mission to collect, quality-control, and disseminate SVP data and, in particularly, on the additional requirements imposed by the increasing numbers of drifters being deployed as SVP enters its first full field year.

3.11 U.S.S.R

Drifter hull construction is being carried out under the supervision of scientists at the Shirshov Institute of Oceanology in Moscow according to the agreement between the GDC and the Soviet scientists,which has been described in earlier documents. The project is overseen by Dr. Nikolay Maksimenko of the Shirshov Institute and A. Kharlamov for the Soviet-Swiss joint venture called MANVIC. The goal is to construct 50 drifter hulls per year in the Soviet Union at a cost below that in the United States. The instruments will be used in SVP. Electronic components, tracking services,and deployment guidance will be supplied by the GDC. In support of this program, members of the GDC traveled to the Soviet Union in October, 1990 for sea trials of the first Soviet-made drifters in the Black Sea. The field trials pointed out some preliminary problems with the drifter hulls as constructed, which have since been corrected. The next phase will be deployment of 6 Soviet-made drifters off California in late 1991 for further field tests. If successful, these tests will signal the start of drifter hull production in the Soviet Union in support of SVP.

4. RELATED AGENCY PROGRAMS

4.1 U.S. Minerals Management Service

MMS is interested in monitoring and modeling movement of oil and the construction of drifters that follow oil spill trajectories. In 1989 an intentional spill was done off Norway and others are planned for 1991. The most successful drifters in following the 1989 spill were specially-ballasted spherical fiberglass floats developed by the GDC for the WOCE/TOGA Lagrangian Drifter. MMS has adopted the WOCE/TOGA drifter design criteria of drag area ratios of 40 in specifying drifters for their field programs in the Gulf of Mexico and in the Florida Current. This MMS data can also be used by WOPCE/TOGA SVP scientists in the global description of surface circulation.

4.2 N.A.T.O. SACLANT Undersea Research Laboratory

Under the leadership of Dr. A. Warn-Varnas, SACLANTEN has begun a program of deploying WOCE/TOGA Lagrangian Drifters in the Greenland,Iceland and Norwegian Seas; 80 drifters will be released during 1991-1992 period. The objectives of this program are to quantify eddy activity, study wind-driven currents and heat advection,and provide a data set for verifying numerical models and AVHRR retrievals of SST.

4.3 U.S. Navy

The US Navy has a program of deploying 200 drifters each year from which SST and atmospheric pressure are measured. Under the leadership of R. Partridge, NAVOCEANCOM has issued requirements to upgrade these drifters to WOCE/TOGA SVP water following standards. U.S. Navy has considerable expertise in air deployments and will work together with the GDC to deploy WOCE/TOGA Lagrangian Drifters from Navy aircraft as a proof of concept.

4.4 U.S. Coast Guard

The U.S. Coast Guard (USCG) is supporting drifter studies to provide information critical in distress or lifeboat situations. They also have an interest, through their International Ice Patrol, in movements of sea ice and water in ice-filled regions. Drifter programs within USCG are being overseen by Art Allen and Don Murphy and are concentrated in the vicinity of the Labrador Sea. In the Pacific regions, USCG will be able to assist with Canadian drifter deployments in the northeast Pacific during regular Seattle to Kodiak transects.

To date, 110 large, FGGE-style drifters have been deployed by USCG. Next year, plans are to shift to Holey-sock drifters that will be compatible with SVP. Deployment of 15-20 drifters per year are planned for the near future and GDC, or individual scientists, are encouraged to obtain resources to extend the battery life and tracking of these drifters so they can contribute to SVP in the north Atlantic. USCG has an interest in air-deployable versions of the drifter and plans to cooperate with efforts underway to develop that option. In order to evaluate the data from past FGGE-style drifters, Art Allen has undertaken field calibration studies for the FGGE-type window shade drogues at 50 m depth by placing current meters on the drogues. Preliminary results show very high slips of up to 50 cm/sec at the bottom of the drogue! The calibration studies will be continued in the coming year with a deployment of 3 shallow and 3 deep instrumented drogues.

4.5 NOAA/National Data Buoy Center

The National Data Buoy Center (NDBC) has a program of selection and calibration of inexpensive barometers for use in drifting buoys. This is of great interest to SVP program of barometer developments. The GDC will stay in close contact with Ron Kozak who is heading up this NDBC program.

5. OLD BUSINESS

5.1 Report of the GDC

The actions of the Global Drifter Center (GDC) over the past year focused on the following activities:

Procuring drifters for deployment in the Pacific Ocean and researching deployment options on various volunteer observing ships.

Evaluation of results from the WOCE Heavy Weather Tests as described in section 2.1 and incorporation of those results in the updated recommendation for SVP drifter design (Sybrandy and Niiler, 1991).

Assistance to international partners in the construction of SVP-quality drifters,which included trips to Taiwan and the Soviet Union by the developmental engineer of the GDC and a trip to the GDC by a senior engineer of the Korean Ocean Research and Development Institute.

Development and testing of a pressure port and atmospheric pressure sensors for use on SVP drifters, which included at-sea trials off San Diego and the distribution of the proposal for expanded at-sea trials to take place this next year (see Appendix).

Adaptation of SEACAT salinity sensors for use on SVP drifters, which will include at-sea trials off San Diego in June of this year.

Development of air-deployable capabilities for SVP drifters. Three drifters were sucessfully deployed southwest of Hawaii in the North Pacific from a US/NAVY aircraft in July 1991.

Monitoring and influencing the cost of satellite tracking through Service Argos, which included participation by the GDC manager at the annual meetings of the DBCP and the Argos Joint Tariff Agreement. Participation at the Argos Joint Tariff Agreement meeting led to a change in Service Argos accounting practices that now allows SVP to deploy drifters that transmit for 8 hours out of 24 hours at a rate of 1/3 the normal rate.

5.2 Report of the DAC

Actions of the Data Assembly Center over the past year were weighted toward the task of receiving drifter position and temperature data from all SVP-related instruments and processing that data for distribution to principal investigators and, ultimately, the data archival center at the Marine Environmental Data Service (MEDS), Canada. Areas that have been identified as requiring action or more information include the following:

Decisions as to if and where to apply changes to the temporal sampling scheme that take advantage of the new reduced-rate option of transmitting 8 hours out of 24 hours instead of the current method of transmitting 24 hours out of 72 hours.

Final Decisions about which temperature transfer functions to use for SVP drifters.

Compilation of transfer functions required for French Bodega drifters.

Interpretations of Japanese drogue-on sensor data for drifters manufactured by Toyocom.

Obtaining Pacific Ocean drifter data from Japanese principal investigators to eliminate a data gap that exists for October,1989.

6. NEW BUSINESS

6.1 Announcements of Opportunity

It is now an appropriate time to circulate announcements of opportunity, which will solicit proposals for analysis work using SVP drifter data. Existing funding for SVP does not include support for scientific analysis work. It is, therefore, important that advance planning begin immediately. Any announcement of opportunity should be widely distributed through major funding agencies in the U.S. and elsewhere and through WOCE and TOGA organizational bodies. Bruce Taft of the WOCE International Project Office agreed to write and circulate a draft letter for approval, which could then be distributed by consenting funding agencies and by the international and U.S. WOCE newsletters.

6.2 Atlantic Climate Change Program (ACCP) Drifters

In May, 1991 ACCP funded 12 drifters for deployment into the Atlantic Ocean with the objective of improving the SST and atmospheric pressure measurements in areas of scant ship traffic. The deployment plan will be decided upon in late January, 1992 at the ASLO\AUGG Ocean Sciences meeting in New Orleans.

6.3 Update of Data Sharing Protocol

SVP has worked to develop a reasonable and fair protocol for sharing of drifter data collected as part of the Program. The adopted protocol has been presented in previous reports (SVP-2, 1991;SVP-3, 1991). Further discussion of the details of data processing and distribution was conducted at this meeting. The protocol was amended to define an additional level of distribution. After 6 months from the time of collection, processed data should be available through DAC for distribution to general SVP participants, which includes any scientist that is specifically funded to do analysis work using SVP data. After two years from the time of collection, processed data should be available to the general public through MEDS.

6.4 Deployment Strategy for the Pacific Ocean

The GDC will continue to seed the equatorial Pacific ocean at the rate of 60 drifters per year and intends to maintain close cooperation with the other Pan Pacific Experiment participants. However, most of the efforts will be directed towards launching the southeast, northeast and northwest Pacific arrays whose sizes were set at 74, 47 and 11 drifters, respectively. Two thirds of this task will be accomplished by the end of 1991. Most of the deployments will be done by VOS ships (the GDC is presently searching for VOS lines in the south Pacific) as well as by research vessels. In particular, advantage will be taken of the WOCE hydrographic lines in the south Pacific which traverse areas rarely frequented by merchant vessels. Twenty three drifters have already been deployed off WOCE lines along 135 °W and 150 °W. Implementation of the Atlantic Ocean will become the primary focus of the GDC in conjunction with the ACCP (see section 6.2 above) as soon as the Pacific Ocean arrays are completed.

6.5 Selection of Planning Committee Members

The U.S. SVP Implementation Panel has been disbanded this year so that maximum effort can be placed into the International Planning Committee, which has always maintained a largely overlapping membership with U. S. Panel. Because of the increased duties, however, the WOCE International Project Office was asked to support one additional member on the Planning Committee. Four slots on the committee have been opened up this year due to members rotating off the committee. The meeting attendees, therefore, nominated a total of five people to serve as new members on the Planning Committee whose membership will become the following (* indicates new member): D Hansen, H. Ishii, W. Krauss, R. Partridge*, P. Niiler (chairman), A. Bianchi*, P. Richardson*, R. Wilson, D. Painting (ex-officio), Y. du Penhoat* and N. Maksimenko*.

6.6 GDC Manager Position

Dr. Jeffrey D. Paduan, who has been working part time, will be resigning as manager of the GDC as of June, 1991. The GDC, through the Scripps Institution of Oceanography, will advertise for a person with a technical background and some oceanography experience to take over these duties. The position will be full time reflecting the increasing organizational tasks involved with the implementation of the field portion of SVP. In June, 1991, Laurence Sombardier accepted the full time position of GDC manager.

6.7 Atmospheric Pressure Measurements

6.7.1 Overview and Timing of Workshop

In support of the adaptation of atmospheric pressure measurements to the SVP-standard drifter, there will be a workshop focusing on the unique aspects of making pressure measurements from small surface floats at sea. The workshop will be co-sponsored by the GDC and the DBCP. The agenda will include presentation and discussion of the results from the at-sea trials of the first 15-20 pressure drifters as described in section 2.3 and in the Appendix. The workshop will be combined with next year's meeting of SVP participants. Special invitations will be sent out to scientists and engineers with particular expertise in at-sea pressure measurements with the aim of addressing any shortcomings in the SVP pressure drifters identified in the sea trials.

6.7.2 DBCP Cooperation Booklet

In support of its efforts to adapt atmospheric pressure measuring capabilities to the standard drifter, SVP is asking international meteorological agencies to consider participating in the Program by becoming involved in the at-sea tests as described in the appendix and by sharing the costs of future upgrades to the drifters and their ARGOS tracking in order to provide the additional pressure measurements. An increased number of measurements important to both oceanographers and atmospheric scientists would be obtained under such a cooperative arrangement.

In order to make the opportunity to participate in SVP known to international meteorological agencies, the DBCP has produced a document entitled "Low-cost Meteorological Measurements from Data Sparse Ocean Areas" which it plans to distribute widely after the document is approved at the its annual meeting in October, 1991. The document presents a background of SVP and proposes a specific plan, including cost estimates, for agency support of pressure enhancements and additional ARGOS tracking time. The document was written by the technical coordinator of the DBCP with support from the chairmen and input from the GDC. Copies of the document will be available through the WOCE International Project Office once it is released.

6.8 Next Meeting

The most pressing issues for the next meeting of the Planning Committee will stem from the Program's progress in the Atlantic Ocean as part of the Atlantic Climate Change Program and from the progress of the at-sea tests of pressure drifters. The meeting attendees acknowledged the need for an Atlantic site that has both good facilities and is easily accessible from the U.S. and Europe for attendees of next year's Planning Committee meeting and joint pressure measurement workshop. The facilities of the Bermuda Biological Station on the Island of Bermuda were deemed to be ideally suited and tentative dates within the week of April 6th, 1991 were agreed upon.

7. LIST OF PARTICIPANTS

Name and Address	Voice Phone #	FAX #
John Thomas	(604) 664-9188	(604) 664-9195
Atmospheric Environmental Service, Pacific Region
700-1200 W 73rd Ave.
Vancouver, B. C. V6P6 6H9
CANADA
Allen, Mr. Art	(203) 441-2600	(203) 441-2792
USCG Research & Development Center
1082 Shennecossett Rd.
Groton, CT 06340-6096
Bruce Taft	(409) 845-1443	(409) 845-3923
WOCE International Project Office
c/o Institute of Oceanographic Sciences
Deacon Laboratory
Wormley, Godalming, Surrey GU8 5UB
UNITED KINGDOM
Charpentier, Etienne	(301) 925-4054	(301) 925-8995
Technical Coordinator
Drifting Buoy Cooperation Panel
c/o Service ARGOS Inc.
1801 McCormick Drive
Suite 10
Landover, MD 20785
Hansen, Donald	(305) 361-4340	(305) 361-4449
NOAA/AOML
4301 Rickenbacker Causeway
Miami, FL 33149
Hu, Jian-Hwa	(32) 622192 x815	(32) 620724
Department of Oceanography
National Taiwan Ocean University
Keelung, Taiwan 20224
REPUBLIC OF CHINA
Kozak, Ron	(601) 688-1711	(601) 688-3153
National Data Buoy Center
Stennis Space Center, MS 39529
Large, William G.	(303) 497-1364	(303) 497-1137
NCAR
P.O Box 3000
Boulder, CO 80307
Lie, Heung-Jae	(02)863-4770	(0345)82-6698
Physical Oceanography Lab.
Korea Ocean Research & Development Inst
Ansan P.O.Box 29
Seoul 425-600
SOUTH KOREA
Maksimenko, Nikolay A.	334-94-31	411968 OKEAN SU
P.P. Shirshov Institute of Oceanology
Krasikova 23
Moscow 117218
USSR
Murphy, Don		(203) 441-2792
USCG, International Ice Patrol
Avery Point
Groton, CT 06340
Niiler, Pearn P.	(619) 534-4100	(619) 534-1731
Scripps Institution of Oceanography
Code A-030, UCSD
La Jolla, CA 92093
Olson, Donald	(305) 361-4074	(305) 361-4622
RSMAS/MPO
4600 Rickenbacker Causeway
Miami, FL 33149
Paduan, Jeffrey D.	(619) 534-6027	(619) 534-1731
Scripps Institution of Oceanography
Code A-030, UCSD
La Jolla, CA 92093
Partridge, Ray	(601) 688-4322	(601) 688-5791
Commander, NAVOCEANCOM
Code N534
Stennis Space Center, MS 39529
Pazos, Mayra	(305) 361-4340	(305) 361-4449
NOAA/AOML
4301 Rickenbacker Causeway
Miami, FL 33149
Piola, Alberto R.		54 1 21-7797
Servicio de Hidrographia Naval
Avenida Montes de Oca 2124
1271 Buenos Aires
ARGENTINA
Poulain, Pierre-Marie	(305) 361-4165
CIMAS-RSMAS
4600 Rickenbacker Causeway
Miami, FL 33149
Price, Jim	703	(703) 787-1614 or 1010
Dept. of Interior
Minerals Management Service
381 Elden St.
Hernden, VA 22070
Reverdin, Gilles	(914) 359-2900	(914) 365-0718
Lamont-Doherty Geological Observatory
Palisades, NY 10964
Richardson, Philip	(508) 548-1400 x2546	457-2181
Woods Hole Oceanographic Institution
Woods Hole, MA 02543
Soldi, Mr. Hector		51 14 652995
Director de Hidrografia
Casilla Postal 80-Callao
PERU
Swenson, Mark	(619) 534-7153	(619) 534-7931
Scripps Institution of Oceanography
Mail Code A-030, UCSD
La Jolla, CA 93093
Warn-Varnas, Alex	39 187 540 111	39 187 524 600
SACLANT Undersea Research Center
APO New York 09019-5000
White, Mr. Hank
Technocean Inc.
2213 Caminito del Barco
Del Mar, CA 92014
Williams, Gary		(617) 332-9130
Clearwater Consultant
83 Grasmere Street
Newton, MA 02158

8. REFERENCES

Brink, K.H., R.C. Beardsley, P.P. Niiler, M.Abbott, A. Huyer, S. Ramp, T. Stanton, and D. Stuart, 1991: Statistical properties of near-surface flow in the California coastal transition zone. J. Geophys. Res., 96, 14693-14706.

Davis, R.E., 1985: Drifter observations of coastal surface currents during CODE: The statistical and dynamical views. J. Geophys. Res., 90, 4756-4772.

Davis, R.E., 1991: Observing the general circulation with floats, Deep-Sea Res., 38, S531-S571.

Molinari R.L., D. Olson, and G. Reverdin, 1990: Surface current distribution in the tropical Indian Ocean derived from compilations of surface buoy trajectories. J. Geophys.Res., 95, 7217-7238.

Niiler, P.P., R.E. Davis, and H.J. White, 1987: Water-following characteristics of a mixed layer drifter. Deep-Sea Res., 34, 1867-1881.

Paduan, J.D., and P.P. Niiler, 1991: A Lagrangian description of motion in northern California coastal transition filaments. J. Geophys. Res., 95, 18095-18109.

SVP-2, 1990: Surface Velocity Program, Report of the Second Meeting with Focus on the Atlantic Sector. WOCE Report No. 50/90. WOCE International Project Office, Wormley, 50 pp.

SVP-3, 1991: WOCE/TOGA Surface Velocity Programme Planning Committee, Report of the Third Meeting with Focus on the Pacific Sector. WOCE Report No. 65/91. WOCE International Project Office, Wormley, 50 pp.

Swenson, M.S, P.P. Niiler, K.H. Brink, and M.R. Abbot, 1991: Drifter observations of a cold filament off Point Arena, California in July 1988. J. Geophys. Res.,In Press.

Sybrandy, A.L., and P.P. Niiler, 1990: The WOCE/TOGA Lagrangian drifter construction manual. Scripps Institution of Oceanography, Univ. of California, San Diego, Ref 91/6, WOCE Report Number 63, 58 pp.