Modellierung des gekoppelten Systems Ozean-Atmosphaere in den Tropen

SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Special Analysis Centre (SAC) in WOCE Final report

The emphasis was on two topics. Firstly, the assimilation of satellite data into ocean models was continued and, secondly, a compiler was developed permitting the automatic construction of the adjoint of a Fortran program. In both fields, publications in internationally renowned specialized magazines are being prepared. (orig.)Available from TIB Hannover: F96B566+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

On the interpretation of climate change in the tropical Pacific

Analysis of sea surface temperature (SST) observations of the last 150 years reveals strong changes in the tropical Pacific climate system during the most recent decades. These changes can be best described as a slow variation of the mean state of the tropical Pacific. The superimposed interannual variability associated with the El Nino/southern oscillation (ENSO) phenomenon does not exhibit any significant changes. However, the change in the mean state is ''El Nino-like'', with many aspects observed during present-day El Nino events. Thus, the change in the mean state biasses the SSTs in the tropical Pacific towards the warm side, which explains the stronger and more frequent El Ninos observed during the recent decades. (orig.)19 refs.Available from TIB Hannover: RR 1347(306) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Tropical Pacific/Atlantic Ocean interactions at multi-decadal time scales

Analysis of sea surface temperature (SST) observations suggests a pan-oceanic interaction between the tropical Pacific and the Atlantic Ocean at multidecadal time scales, such that periods of anomalously high SSTs in the eastern tropical Pacific are followed by a basinwide SST dipole in the Atlantic Ocean with a time delay of a few decades. The SST anomaly structure in the Atlantic Ocean is reminscent of variations in the North Atlantic thermohaline circulation. The two ocean basins are linked through an ''atmospheric bridge'' involving anomalous fresh water fluxes. Based on the observational findings, the Atlantic thermohaline circulation may strengthen during the next decades in response to the strong decades-long increase in eastern tropical Pacific SST, which will have strong impacts on the climates of North America and Europe through changes in the north Atlantic oscillation (NAO). (orig.)21 refs.Available from TIB Hannover: RR 1347(305) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

On North Pacific climate variability

The climate variability in the North Pacific is re-investigated by using the latest Hadley Centre SST analysis covering the period 1870-1998 and other observational datasets. The main result of this study is that the North Pacific decadal and multi-decadal variability on time scales from 10-50 years evolves independently of the variations in the tropical Pacific, so that this kind of variability must be regarded as internal to the North Pacific. (orig.)Available from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Vorhersagbarkeit dekadischer Klimaschwankungen ueber dem Nordatlantik und Europa Abschlussbericht

Three kinds of investigations were carried out: (1) Uncoupled simulations using the ECHAM atmosphere model; (2) Analysis of a coupled simulation using the ECHAM/LSG model; (3) Predictability studies using the ECHAM/LSG mode. It was found that at least the thermohaline circulation can be predicted for several years ahead, ranging from a few years to twenty years. The results for the ocean surface temperature and atmospheric data are less promising. Predictions appear to be possible only in certain cases and only a few years ahead.Es wurden drei Arten von Studien durchgefuehrt: (1) Ungekoppelte Simulationen mit den ECHAM Atmosphaerenmodell, (2) Analyse einer gekoppelten Simulation mit dem ECHAM/LSG Modell und (3.) Vorhersagbarkeitsstudien mit dem ECHAM/LSG Modell. Die Resultate zeigen, dass zumindest die Veraenderungen der thermohalinien Zirkulation einige Jahre im voraus prognostiziert werden kann. Die Vorhersagezeitraeume schwanken dabei von einigen Jahren bis zu zwanzig Jahren. Die Resultate fuer die Meeresoberflaechentemperatur und atmosphaerische Groessen sind weniger vielversprechend. Diese scheinen nur in bestimmten Faellen einige wenige Jahre im voraus vorhersagbar zu sein. (orig.)SIGLEAvailable from TIB Hannover: DtF QN1(99,45) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman

Globale Modellierung in WOCE Schlussbericht

Most studies were made to determine the mean ocean circulation and its variability on time scales of decades, centuries, and millenniums. In addition, we continued the model and the model-development and -verification. Studies were carried out with the circulation models LSG and HOPE. Because of some budget cuts, we were not able to realise all objectives. In the following five studies performed within the project will be sketched briefly. The first and second study were made with the LSG-model and the following three investigations with the HOPE-model. Publications in international journals are in preparation or in press. (orig.)Es wurden vor allem Studien zur Bestimmung der mittleren Ozeanzirkulation und ihrer Variabilitaet auf Zeitskalen von Dekaden, Jahrhunderten und Jahrtausenden durchgefuehrt. Zusaetzlich wurde die Modellentwicklung bzw. Modellverifizierung weitergefuehrt. Studien wurden durchgefuehrt mit den beiden Zirkulationsmodellen LSG und HOPE. Allerdings konnten infolge der Streichungen nicht alle Ziele realisiert werden. Im folgenden werden kurz fuenf Arbeitsschwerpunkte skizziert. Die ersten beiden Studien wurden mit dem LSG, die letzten drei Studien mit dem HOPE Modell durchgefuehrt. Veroeffentlichungen in international renomierten Zeitschriften sind eingereicht oder in Vorbereitung. (orig.)Available from TIB Hannover: D.DT.F.QN1(17,33) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Modes of ocean variability in the tropical Pacific as derived from GEOSAT altimetry

Satellite-derived (GEOSAT) sea surface height anomalies for the period November 1986 to August 1989 were investigated in order to extract the dominant modes of climate variability in the tropical Pacific. Four modes are identified by applying the POP technique. The first mode has a time scale of about 3 months and can be identified with the first baroclinic equatorial Kelvin wave mode. The second mode has a time scale of about six months and describes the semi-annual cycle in tropical Pacific sea level. Equatorial wave propagation is also crucial for this mode. The third mode is the annual cycle which is dominated by Ekman dynamics. Wave propagation or reflection are found to be unimportant. The fourth mode is associated with the El Nino/Southern Oscillation (ENSO) phenomenon. The ENSO mode is found to be consistent with the 'delayed action oscillator' scenario. The results are substantiated by a companion analysis of the sea surface height variability simulated with an oceanic general circulation model (OGCM) forced by observed wind stresses for the period 1961 to 1989. The modal decomposition of the sea level variability is found to be similar to that derived from the GEOSAT data. The high consistency between the satellite and the model data indicates the high potential value of satellite altimetry for climate modeling and forecasting. (orig.)SIGLEAvailable from TIB Hannover: RR 1347(103) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

A new theory for tropical instability waves

Large-scale westward propagating waves, so-called ''Legeckis'' or ''tropical instability waves'', are a prominent feature of sea surface temperature images of the equatorial Pacific. Our analyses of satellite altimetry data and long-term moorings reveals that the Legeckis waves can be interpreted as a superposition of two distinct wave modes, a first equatorial Rossby wave and a Rossby-gravity wave. We present evidence that the energy sources for both waves are the mean currents. Our results imply that Legeckis waves can be explained within the framework of linear equatorial waves. (orig.)19 refs.Available from TIB Hannover: RR 1347(268) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

A cautionary note on the interpretation of EOFs

EOF and rotated EOF analyses are widely used tools in climate research. In recent years there have been several cases in which the EOF- or rotated EOF analyses were used to identify physical modes. These are the ''tropical Atlantic'' and the ''tropical Indian Ocean SST dipole'' modes and the different modes of the Northern Hemisphere winter surface air pressure variability. Here we would like to discus the problems in interpreting these statistically derived modes as physical modes. By constructing an artificial example we shall show that the patterns derived from EOF- or rotated EOF analysis can lead to misinterpretations. This study should be seen as a cautionary note to highlight the pitfalls which may occur when using the EOF or rotated EOF techniques. (orig.)14 refs.Available from TIB Hannover: RR 1347(309) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman