Brazilian Ocean-Climate programs Seasonal Climate Prediction at CPTEC/INPE
P. Nobre, INPE, Brazil

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Ocean-atmosphere interactions over the tropical Atlantic: Interannual climate variability over the tropical Atlantic is dominated by anomalous meridional migrations of the intertropical convergence zone (ITCZ). It is shown that modulation of ITCZ migrations are related to modulations of meridional gradients of anomalous SST over the tropical Atlantic. Also, it is shown that rainfall anomalies that affect Nordeste (Northeast Brazil) are large scale phenomenon, encompassing the whole equatorial Atlantic and eastern Amazon region. Observational evidence supports the conjecture that atmospheric dynamics, linked to the occurrence of teleconnnection patterns originating from the equatorial central Pacific modulate the formation of anomalous SST patterns over northern tropical Atlantic. It is suggested that an ocean-atmosphere observing system over the tropical Atlantic must go beyond the equatorial band to be useful for seasonal rainfall forecasting over Brazil.

Seasonal Climate forecasting at CPTEC: The numerical seasonal rainfall forecast experiment done at CPTEC for the March April May (MAM) 1995 rainy season over northeast Brazil (Nordeste) is described. The model used is COLA/CPTEC's AGCM (T62 L28). Four member ensembles with varying initial conditions are used to obtain the seasonal forecasts. For each initial condition the AGCM is integrated for six months for both climatological and forecasted SSTs. Persisted SST anomalies are used to simulate forecasted SSTs. The runs which used persisted December 1994 SST anomalies (while ENSO conditions still dominated over the equatorial Pacific), forecasted MAM negative rainfall anomalies over Nordeste, in disagreement with the observed positive anomalies. The next runs, which used January, February, and March persisted SST anomalies respectively, showed progressively better forecasts, as the monthly SST fields approached more and more the actual MAM SST. The differences between the December and January forecasts (with the latter showing closer-to-observed values), are attributed in large part to the more favorable SST conditions over the southern tropical Atlantic in January, since not much change occurred over the equatorial Pacific during that period. These results highlight the importance of forecasting tropical Atlantic SST for the seasonal rainfall numerical predictions over the Nordeste, the equatorial Atlantic, and the Amazon regions. A March 1995 persisted SST anomaly run generated MAM rainfall forecast that resembled closely the observed rainfall distribution (Figure 5). It is concluded that atmospheric general circulation modeling is capable of predicting seasonal rainfall anomalies over Nordeste, provided accurate SST fields are prescribed. For the December 1994 March 1995 period, persisting SST anomalies was shown to be a poor method of forecasting SSTs over the tropical Atlantic and equatorial Pacific.

• Recent studies indicate that although tropical and extra-tropical SSTA variability in the Indian Ocean is largely correlated to the Pacific, Atlantic SSTA fields (Figure 6) exhibit largely independent variance modes (Kawamura, 1994; Tourre and White, 1995). On the other hand, ENSO-induced intensification and subsequent relaxation of the Western Equatorial Atlantic (WEA) zonal wind stresses may generate a strong subsurface signal which causes the flattening of the Atlantic thermocline a few months later (Delecluse et al., 1994). However, amplitude and phases of the observed signal are not explained by the OGCM simulation. Although linear equatorial ocean dynamics seem to partly explain the evolution of the eastern tropical SST fields, the phase relationships between SST, mixed layer depth and thermocline depth are space-time dependent (Houghton, 1991). This is due to the fact that in the southwestern tropical Atlantic, heat fluxes are generally dominated by horizontal advection and wind stress, which requires the routine observation of the complex patterns of thin (100 km across) surface and subsurface currents (Molinari, 1982) for a long period of time before a realistic coupled model can be developed.
• Most variability in the tropical basin is known to be equatorial wave driven by WEA winds (e.g., Carton and Huang, 1993), but low-resolution models cannot reproduce the observed SSTA anomaly field (Servain et al., 1994). This is certainly due to the fact that only high-resolution models (Schott and Boning, 1991) can partly reproduce the fine structure of observed currents and countercurrents in the WEA, which modify the advective heat transport field and the genesis of the SSTA field.

References:

Carton, J.A. and B.Huang, 1994: Warm events in the Tropical Atlantic. J. Phys. Oceanogr. 24, 888 903.

Delecluse, P., J. Servain, C. Levy, K. Arpe, and L. Bengtsson, 1994: On the connection between the 1984 Atlantic warm event and the 1982-1983 ENSO. Tellus, 46A, 448-464.

Houghton, R.W. 1991: The relationship of Sea Surface Temperature to thermocline depth at annual and interannual time scales in the tropical Atlantic ocean. J. Geophys. Res., 96(C8), 15:173 15:185.

Kawamura, R. 1994: A rotated EOF analysis of global sea surface temperature variability with interannual and interdecadal scales. J. Phys. Oceanogr., 24, 707-715.

Molinari, R. L. 1982: Observations of eastward currents in the tropical south Atlantic ocean: 1978 1980. J. Geophys. Res., 87(C12), 9707-9714.

Schott, F.A. and C.W. Boning, 1991: The WOCE model in the western Equatorial Atlantic: upper layer circulation. J. Geophys.Res., 96(C4), 6993-7004.

Servain, J.M., A. Morliere, C.S. Pereira, 1994: Simulated versus observed sea surface temperature in the tropical Atlantic Ocean. The Global Atm. Ocean Sys., 2, 1-20.

Tourre, Y.M. and W.B. White, 1995: ENSO signals in global upper ocean temperature. J. Phys. Oceanogr., 6, 1317-1332.

Vianna, M.L. and M. Kampel, 1995: A high resolution study of the dynamics of Atlantic SST fields. In: Proc. TOGA 95 International Scientific Conference, 2-7 April 1995, Melbourne, Australia (to appear as a WMO Publication).

Status of Brazilian Anchored and Drifting Buoys
M. Stevenson, INPE, Brazil
Due to a recognized need for instrumented buoys and drifters for use in experiments of interest to the national community, the oceanographic group at INPE has, over the past 10 years, developed and deployed various types of buoys. The first type of buoy to be designed and fabricated has a bi-conic shape. It is fabricated in fiberglass and has an effective displacement of about 250 kg. This buoy can handle up to 16 data channels (8 channels for each data transmission), can accommodate one of three types of sensor towers developed for the buoy and can be used in either the anchored (up to 1000 m depth) or drifting mode. The second type of buoy is the TOGA/WOCE standard low cost drifter (LCD). The Brazilian version of the LCDs have been built. As part of Project COROAS, the Brazilian contribution to SVP (surface velocity programme) of WOCE, 15 LCDs were deployed off SE Brazil during 1993 and 1994. The 16th LCD was launched in the Polar Front of the Antarctic Circumpolar Current in November 1993 and is still transmitting to this date (>660 days). Longevity data for our LCDs are based on the limited number of LCDs launched, but suggests that life expectancy for Brazilian LCDs is about the same as for users of these drifters from other countries. The third type of buoy (Figure 7) was developed with the financial and technical assistance of the University of Paraiba Valley (UniVap). The objective in developing this buoy is different from the other buoys. For Project SIMA (Integrated System for Environmental Monitoring) we use a system approach. SIMA consists of: a) a data acquisition and transmission subsystem; b) a data reception subsystem; and c) a data processing and modeling subsystem. The data acquisition and transmission subsystem consists of one or more toroidal buoys, each one being 2.3 m in diameter and with an tubular aluminum tower to support sensors, solar panels and UHF antenna, a payload consisting of an ARGOS compatible PCD connected to sensor interface boards and CPU processor and memory and batteries. Combined buoy and tower mass are about 750 kg; and the buoy's displacement provides about one ton of positive buoyancy in addition to the load produced by the anchoring of the buoy in up to several kms of water depth. Data are received in real time by the use of a compact VHF satellite receiver station connected to a microcomputer. Data reception is facilitated with the use of software written for this purpose. The data processing and modeling subsystem consists of a 486 microcomputer and uses two types of specially written software for the quality control data (data voids and spurious values) and the determination of certain data statistics, and a barotropic circulation model based on finite elements that may be adapted to a particular field situation. In practice, 20/8-bit channels are available to transmit environmental data and time of data acquisition. Data acquisition time is programmable, and presently set at one hour intervals. Data are stored in memory and transmitted from hourly time bins. Wind measurements are used to force the circulation model. Data processing and interpretation are facilitated by the use of user-friendly pulldown window software developed for this purpose. Status of

FUNCEME's Programs (Present and Planned) in Climate Studies
C.A. Repelli and J.A. Torsani, FUNCEME, Brazil
The Political Northeast Region of Brazil is a densely populated region located approximately between 1° and 18°S and 35° and 47°W. In this region, three different rainfall regimes have been identified throughout the year. They represent annual precipitation amounts varying between 600 mm and 2000 mm.

The east part of the Northeast has its rainy season between May and August. In contrast, the characteristic regime of the southern part of the region has maximum precipitation in November/December. The Northern part of the Northeast (Nordeste) is known for its semi-arid climate with its rainy season concentrated between February and May, and very large interannual variability that can vary from 50% through 150% of the average.

Many authors have identified the relationship between precipitation over the Northeast and ENSO events; Atlantic Ocean sea surface temperature, trade winds, and sea level pressure; the position of the Intertropical Convergence Zone (ITCZ) over the Atlantic Ocean; cold fronts and other phenomena.

The Nordeste not only exhibits a high variability in the total amount of precipitation from year to year but also, a high spatial and temporal variability in the precipitation within its rainy season. This monthly variability is related to the different rainfall systems that cause precipitation over the region in the different months of the rainy season.

February and March is the period when the ITCZ over Tropical Atlantic Ocean reaches its southern most position, initializing what is called the principal' rainy season over Nordeste. The return of the ITCZ to its more northern position is what determines the end of the Nordeste principal rainy season. Some mechanisms of the ITCZ movement are related to the thermal conditions over either the Pacific or the Atlantic Basins. Recent work has shown that both oceans have influences on Nordeste precipitation during the different months of the rainy season. However, it seems that sea surface temperature (SST) anomalies in the Atlantic Ocean are more important than those in the Pacific in controlling the precipitation variability of the Nordeste.

The high interannual variability and the high spatial and temporal distribution of the precipitation have enormous impacts on the society and economy of the region generating population migration and high level of unemployment.

Different methodologies have been developed to forecast the Nordeste's rainy season and have been used during the last several years for operational purposes at the National Institute for Space Research-INPE in Sao Jose dos Campos - SP - Brazil and at the Ceara State Foundation for Meteorology and Water Resources (FUNCEME). Those methodologies are based on empirical atmospheric and oceanic parameters, on results from coupled models and on statistical models, developed specifically for forecasting Nordeste rainy season. The predictability of the quality of the rainy season has great importance for local agriculture and the water management of the region. The main users of the climate information generated by FUNCEME are farmers, civil defense, insurance companies, banks, press, water management company, and the agricultural secretariat, which has a special program for seed distribution.

As the Atlantic Basin is very important to the climate variability of the region, some projects related to it are under development at FUNCEME, e.g., a dynamical-stochastic model for monthly SST anomalies (in collaboration with a senior scientist from Hydro-meteorological Center of Moscow-Russia), Canonical Correlation Analysis model and SST retrieval by using NOAA/AVHRR data.

A new TAO array over the Atlantic Basin will improve the quality of observational data over the basin. It will also contribute to studies related to Nordeste climate variability as well as help validate SST retrievals from satellite imagery, with applications for climate monitoring, climate modeling and fishery activities.

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