About POAMA Forecasts

The POAMA System

POAMA stands for Predictive Ocean Atmosphere Model for Australia. POAMA is a climate model system used for seasonal to interannual predictions. It consists of coupled ocean-atmosphere general circulation models along with sophisticated data assimilation and land-surface initialisation systems. POAMA was developed jointly by the Bureau of Meteorology and CSIRO Marine Research and is under continual development. POAMA forecasts of the state of El Niño - Southern Oscillation (ENSO) are issued daily by the National Climate Centre. Full details of the POAMA system and many trial products can be found on the official POAMA site.

POAMA forecasts

Each day a new POAMA forecast is performed. The ocean, atmosphere and land surface are initialised with the most up-to-date observations. The POAMA model is then run to simulate the ocean and atmosphere conditions of the next nine months. Each daily forecast therefore differs slightly in the initial state of the climate system. The variability of the results among forecasts gives an indication of the uncertainty in the future evolution of the climate system. When many individual forecasts are considered together they are said to comprise an ensemble and the spread in the conditions they forecast can be used to quantify the probability distribution of future conditions.

Generally the outlooks given on these pages are based on an ensemble of the 30 most recent POAMA forecasts. The start dates of each of these 30 forecasts are one day apart.

ENSO forecasts

The National Climate Centre (NCC) uses the NINO3 index to monitor the state of ENSO. An El Niño (warm) event is considered to occur when the NINO3 index exceeds +0.8°C, which is about one standard deviation. Similarly a La Niña (cold) event occurs when NINO3 is less that −0.8°C. POAMA forecasts of NINO3 are given out to eight months ahead to monitor the possible evolution of ENSO conditions. Similar forecasts of both NINO3.4 and NINO4 are also shown to monitor the details of possible future ENSO conditions.

Two types of plots are used to show POAMA forecasts of NINO indices: "plumes" showing an ensemble of individual forecasts of the index for the next eight months, and frequency distributions among the ensemble of the indices for each month in the forecast period.

Indian Ocean Dipole forecasts

Another region of SST variability that impacts on Australian climate is the Indian Ocean. One mode of variability that appears to affect Australian rainfall, particularly the south east of the country, is the Indian Ocean Dipole (IOD). The IOD referred to here is defined by an index that is the difference between SST in the western (50°-70°E, 10°S-10°N) and eastern (90°-110°E, 10°-0°S) tropical Indian Oceans. A positive IOD occurs when the western basin is warmer than average and the eastern basin is cool and hence the IOD index is positive. These regions were proposed in a paper by Saji et al. (1999)¹ on the Indian Ocean Dipole that showed a modulation in Australian seasonal rainfall with IOD positive and negative years. The influence of some modes of Indian Ocean SST variability on Australian climate is explicitly included in the model that produces the statistical Seasonal Climate Outlooks.

As with the NINO indices, POAMA forecasts of the IOD are given as averages of the monthly IOD index, plumes of the spread and frequency distributions of positive/neutral/negative IOD out to nine months for the ensemble of the 30 most recent forecasts. A positive IOD is defined here if the index is greater than +0.4°C, a negative IOD if the index is less than −0.4°C. The standard deviation of the monthly-mean IOD index averages about 0.4°C.

¹ Saji N.H., B.N. Goswami, P.N. Vinayachandran, T. Yamagata, 1999: A dipole mode in the tropical Indian Ocean. Nature, 401, 360-363.

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