To be cited as: Sy, A. and J. Ulrich (1989) North Atlantic Ship of Opportunity XBT Programme 1988 - Data Report - Wissensch. Techn. Ber. DHI, 1989-2, 79 pp. --------------------------------------------------------------------------- North Atlantic Ship of Opportunity XBT Programme 1988 Nordatlantisches XBT-Frachtschiffs-Programm 1988 - Data Report - Alexander Sy and Juergen Ulrich No. 1/89 Abstract ======== This report presents the temperature data acquired within the framework of the DHI's Ship of Opportunity Programme in 1988 between Europe and North America (IGOSS line A9 or WOCE line AX3, respectively). Beginning in May 1988, the XBT measurements were carried out during 8 voyages from CMS "Koeln Atlantic" of Hapag-Lloyd AG, Hamburg. The objectives of this programme, methods of measurements, flow and processing of data are described. The results are presented in terms of Tables, track plots, and profile plots and section plots of temperature. A scientific interpretation is not included and will be given elsewhere. Zusammenfassung =============== Dieser Bericht praesentiert die Temperaturdaten der im Rahmen eines Ship-of-Opportunity Programms des DHI aus dem Jahre 1988 zwischen Europa und Nordamerika durchgefhrten Messungen (IGOSS Linie A9 bzw. WOCE Linie AX3). Die XBT-Messungen wurden von Bord des CMS "Koeln Atlantic" der Hapag-Lloyd AG, Hamburg, ab Mai 1988 auf 8 Reisen durchgefhrt. Die Ziele des Programms, die Meáme- thode sowie der Fluss und die Aufbereitung der Daten wird be- schrieben und die Ergebnisse in Form von Tabellen, Stationskar- ten sowie Profilen und Schnitten der Temperatur dargestellt. Eine wissenschaftliche Interpretation beinhaltet der Bericht nicht, sie wird an anderer Stelle erfolgen. Introduction ============ This data report presents the temperature field in terms of profiles and section plots across the North Atlantic between the English Channel and the Grand Banks in 1988. Owing to the kind support of the shipping company Hapag-Lloyd AG in Hamburg, F.R.G., and the willing co-operation of the crew of CMS "Koeln Atlantic", the measurements have been carried out since May 1988, using expendable bathythermographs (XBT) launched from the bridge wing during the ship's bi-weekly passages of the North Atlantic. The objectives of this Ship of Opportunity Programme (SOOP) are: 1. To collect and distribute temperature data in near real- time for IGOSS. 2. To be prepared for high density measurements in the 1990 ongoing World Ocean Circulation Experiment (WOCE). 3. To obtain statistical information for the specific analysis of variable features in the North Atlantic. The Integrated Global Ocean Services System (IGOSS) co-sponsored by the Intergovernmental Oceanographic Commission (IOC) of UN- ESCO and the World Meteorological Organization (WMO) is a world- wide system for rapid collection, exchange and analysis of ocea- nographic data, and the timely preparation and dissemination of ocean products and services. Since the establishment of this programme in 1972, data have been collected by merchant and research vessels and distributed in near real-time (i.e. within 30 days after measurement) via the Global Telecommunication System (GTS) of WMO, and are thus placed at the worldwide scien- tific community's disposal. As a Federal German Governmental Authority the DHI has participated in this programme from the very first. Within the framework of the IGOSS network the new line A9 was announced in 1987 by DHI (IOC, 1987). Usually IGOSS lines are characterized by low density sampling (/\t = 6 hours) and are not suitable from an eddy resolving point of view. Obviously, low density XBT measurements established under operational aspects, are of limited scientific value (Sy, 1987a). This can be specifically concluded from the analysis of the French-German SOOP line between Europe and Brazil (Emery et al., 1987). For selected lines the high density sampling mode is a require- ment of WOCE, the field phase of which will start in 1990. Wit- hin WOCE, a Voluntary Observing Ship (VOS) programme will be established with the aid of commercial ships on scheduled tracks in order to estimate the statistics of the thermal field in the upper kilometre (WOCE IPO, 1988). The IGOSS line A9 corresponds to the WOCE line AX3. The DHI intends to participate actively in WOCE. The purpose of the past and ongoing high density XBT measurements is to collect specific experience and to determine the requirements needed for the WOCE hot phase. In that context the data presented here are the result of a DHI pilot study preparing the real WOCE field phase, which explains the recognizable changes in the sampling strategy. The third objective deals with the statistical analysis of spe- cific regional features in the North Atlantic. That is, the variability in space and time of (a) the thermal front between Labrador Current and North Atlan- tic Current (Horne and Petrie, 1988); (b) the eddy, meander and branching activity (Fig. 1) as well as persistent patterns of the North Atlantic Current (Sy, 1987b, 1988; Fahrbach and Wegner, 1987; Antonov and Grois- man, 1988); (c) the winter mixing in the eastern North Atlantic as a source of the subarctic mode water transformation (McCartney and Talley, 1982; Robinson et al., 1979; Meincke, 1986). Instrumentation, measurements and data flow =========================================== The Federal German container vessel "Koeln Atlantic" (callsign DAKE) was placed at our disposal as a measuring platform by Hapag-Lloyd AG (Fig. 2). The size of the vessel is 39 000 GRT (2600 TEU), the length is 240 m, and the speed is 21.5 knots but eventually depends upon the ship's schedule. On regular schedule in the North Atlantic service between Europe and the US East Coast and Canada the duration of a round trip is 28 days. Port of Call in Germany is Bremerhaven, where the vessel is met regu- larly by DHI personnel. The data acquisition system on board CMS "Koeln Atlantic" is a SEAS-II unit (Shipboard Environmental Data Acquisition System). It is a complete hardware/software system for semi-automatic acquisition of ocean temperature and meteorological data, which consists of Sippican hand-held XBT launcher, Bathy Systems SA- 810 controller, HP-85B desktop computer, Synergetics satellite transmitter, and 1/4 helix antenna (Figs. 3 and 7). The XBT probe contains a thermistor in its nose (Fig. 4). The electrical connection between the probe and the SEAS controller is made when the canister containing the probe is placed within the launcher. While the ship is underway, the observer drops the probe by pulling the retaining pin. The thin two conductor si- gnal wire dereels from the probe as it descends vertically through the water and, simultaneously, wire dereels from the spool within the canister, thus compensating the ship's move- ment. The XBT system uses seawater ground and, after water im- pact, the circuit is complete and temperatures - in terms of thermistor resistances - are telemetered to the shipboard sy- stem. The controller samples the data with 10 Hz and converts the resistance to voltage. The voltage versus time information is transmitted in real-time to the computer which generates a real-time plot of ocean temperature versus depth on the screen. Data acquisiton ends when the XBT probe exceeds maximum depth depending upon the ship's speed (Fig. 5), and the wire breaks, or the operator terminates the data cycle. Then the data are saved automatically on a cartridge tape for later scientific analysis. Optionally, as a next step - and for operational purposes only - significant points of the temperature profile (inflection points) are calculated by searching for changes in vertical gradients of temperature (Fig. 6). The inflection points and a preamble containing time, date, ship's position, and ship call sign is concatenated to construct a BATHY (JJXX) message according to WMO-FM63 code (WMO, 1984) which is then transferred into the data buffer of the satellite transmitter (data collecting platform). Periodically, at schedu- led times, the coded messages are automatically transmitted to METEOSAT and passed to the ground station operated by EUMETSAT, Darmstadt, F.R.G., and then via the Deutscher Wetterdienst (DWD) in Offenbach, F.R.G. in near real-time to the DHI (Fig. 7). Finally, the DHI enters the BATHY messages into the GTS of the World Weather Watch (WWW) to make the data available to users on a timely basis. For further information see McDowell and Dorson (1983). In addition to the transmission of ocean temperature data the SEAS unit aboard CMS "K”ln Atlantic" is also used for entry and transmission of weather data of six hourly interval observations. This has the advantage that weather data are transmitted to DWD even if the radio operator is off duty. As XBT probes Sippican "Deep Blue" only were launched. The spe- cification given by the manufacturer is as follows: Temperature: Range -2 øC to 35.5 øC Accuracy ñ 0.2 øC Resolution to 0.01 øC Depth: Range to 760 m Accuracy ñ 2 % of depth Resolution 65 cm Owing to the fact that the probes were deployed from the wing of the navigation bridge (height: 30 m) a depth accuracy influen- cing effect should be expected (Krause, 1986), however, its quality cannot be given. To date, no sea surface temperatures are measured independently aboard CMS "K”ln Atlantic" as a reference. Thus, for the WOCE field phase it is hoped to install a thermometer within the ship at the ship's side, equipped with a display on the navigation bridge. Furthermore, a vertical extension of measurements down to 1500 m is planned. Data processing =============== An overview of the data processing carried out with the XBT data stored on cartridge tapes is given in Fig. 8. It is a scheme for the main fraction of data. In this context, the filter coeffi- cients for the moving average application is only a guiding principle. For some single profiles of particularly bad quality the processing may differ under certain cicumstances. Thus e.g. profiles which are disturbed by heavy noise stronger filtering was carried out using q = 15 - 21 filter weights. Remarkable profiles are marked by special notes in the station lists. The final depth interval averaging with /\z = 1 m disregards the reduced statistical independency by the previous filtering. By compaction on 1 m steps, only a uniform standard for archived data is guaranteed. Whatever the further needs for scientific analysis may be, the relatively high nominal vertical resolution of the final data keeps the option for adjustments open, which is left to the investigator's discretion intentionally. The finally processed data are archived in the Deutsches Ozeano- graphisches Datenzentrum (DOD) which is operated by DHI. In case of need, in particular for WOCE, the data are placed at users' disposal, provided that the data originators gave their agree- ment. Special reservations are made concerning topics such as the statistical analysis, heat content, wintertime convection, and North Atlantic Current, which are the primary reason of this Ship of Opportunity Programme. Presentation of data ==================== An overview of the schedules of the 8 voyages of CMS "K”ln At- lantic" is summarized in Table 1, and the positions of all XBT drops are presented in Fig. 9. A presentation of all data is given separately in Tables, track plots, profile plots, and section plots assorted by voyages Acknowledgement =============== We thank Hapag-Lloyd AG, Hamburg, the owners of CMS "Koeln Atlantic", her masters Ldeking and Menck, and her mates Sell, Bergmann, Schtte, Wode, Frings, and Radloff for co-operating in this programme and carrying out the measurements skilfully. Ralf Berger and Jochen Weichert developed and improved the processing software according to our needs. Finally, we wish to express our hope to continue this Ship of Opportunity Programme, in co-opera- tion with Hapag-Lloyd AG and its highly motivated masters and officers, as long as possible to collect the data base needed to attain the above scientific objectives described. Hamburg, March 1989 References ========== Antonov, D.I. and P.Y. Groisman (1988) Variation of Water Temperature below Active Layer in North Atlantic Ocean. Meteorologiya i Gidrologiya, 3, pp 57 - 63. Emery, J.W., W. Zenk, K. Huber, P. Rual and P. Nowlan (1987) Trends in Atlantic Equatorial Current Variability. Dt. Hy- drogr. Z., 40, pp 261 - 276. Fahrbach, E. and G. Wegner (1987) Observations of Persistent Pattern in the Temperature Field related to the North Atlantic Current. Dt. Hydrogr. Z., 40, pp 141 - 155. Horne, E. and B. Petrie (1988) Mean Position and Variability of the Sea Surface Temperature Front East of the Grand Banks. Atmosphere-Ocean, 26, pp 321 - 328. IOC (1987) Second Joint IOC-WMO Meeting for Implementation of IGOSS XBT Ship-of-Opportunity Programmes, IOC-WMO/IGOSS-XBT-II/3. Krause, G. (1986) In-situ instruments and measuring techniques. In: Landoldt- B”rnstein, New Series, Group V, 3, Oceanography, pp 134 - 232. McCartney, M.S. and L.D. Talley (1982) The Subpolar Mode Water of the North Atlantic Ocean. J. Phys. Oc., 12, pp 1169 - 1188. McDowell, S.E. and D.L. Dorson (1983) GOES Transmission of Ocean Temperature and Weather Data from a North Atlantic Ship-of-Opportunity. Presented at the 1983 Intern. Geoscience and Remote Sensing Symposium (IGARSS '83), 4 pp. Meincke, J. (1986) Convection in the oceanic waters west of Britain. Proc. Royal Soc. Edinburgh, 88B, pp 127 - 139. Robinson, M.K., R.A. Bauer and E.H. Schroeder (1979) Atlas of North Atlantic - Indian Ocean Monthly Mean Tempera- tures and Mean Salinities of the Surface Layer. Naval Ocea- nographic Office Reference Publ. 18. Sy, A. (1987a) National report on the Ship-of-Opportunity Programme of the Federal Republic of Germany. In: Complement of the Second Joint IOC-WMO Meeting for Implementation of IGOSS XBT Ship- of-Opportunity Programmes, IOC/INF-731, pp 8 - 12. Sy, A. (1987) Untersuchungen zum groáskaligen Feld der Zirkulation des Nordatlantiks im Bereich des Mittelatlantischen Rckens. Dt. Hydrogr. Z., Erg„nzungsheft 19, 123 pp. Sy, A. (1988) Investigation of large-scale circulation patterns in the central North Atlantic: the North Atlantic Current, the Azores Current, and the Mediterranean Water plume in the area of the Mid-Atlantic Ridge. Deep-Sea Res., 35, pp 383 - 413. WMO (1984) Manual on Codes, Vol. 1, WMO-No. 306 WOCE IPO (1988) World Ocean Circulation Experiment - Implementation Plan, Vol. 1 (WMO/TD No. 242) and 2 (WMO/TD No. 243). In the following, and sorted by voyage numbers, the measurements are presented in 1. Tables containing header information and remarks of each XBT drop, 2. track plots of each transect, 3. profile plots of final temperature data (the profiles beeing offset according the tick marks, the temperature at tick mark is 6 øC), 4. and section plots showing the vertical temperature field of each transect. The different numeration may give raise to some confusion. The complete XBT drop number consists of 6 digits as shown in the profile plots. The leading 2 digits denote the year of measure- ment, the next 3 digits give the XBT drop number ranging from 001 to 999, and the last digit marks the repetition if necessary. In the Tables and section plots the leading zero of the XBT drop number is omitted while in the track plots additionally the repetition digit is omitted. Figure Captions =============== Fig. 1: The North Atlantic current system (after Sy, 1988) and area covered by XBT drops of WOCE line AX3. Fig. 2: CMS "Koeln Atlantic" (Hapag-Lloyd photo) Fig. 3: The semi-automatic XBT data acquisition system SEAS-II (Bathy Systems Inc. photo) Fig. 4: Exploded view of an XBT (after Sippican Ocean Systems, Inc.) Fig. 5: The maximum depth as a function of ship's speed (after Sippican Ocean Systems, Inc.) Fig. 6: Sample XBT graph (expanded) with inflection points plotted (after McDowell and Dorson, 1983) Fig. 7: Hardware components of SEAS-II unit and near real-time data flow Fig. 8: Flow diagram for non-operational XBT data processing Fig. 9: Track plot of all XBT drops between 20.5.1988 and 5.1.1989