Climate Model Summary

Climate Model Summary Archive: August 2014

Models ease their El Niño outlook for spring

Despite significant warming in the tropical Pacific Ocean in the first half 2014, the ocean and atmosphere have largely failed to reinforce each other, and hence cooling has occurred in recent months. Similarly, most international climate models have eased their outlooks for El Niño in 2014, with four models not reaching El Niño thresholds until the austral summer of 2014/15, while the remaining models stay neutral.

El Niño is often, but not always, associated with below-average rainfall during the second half of the year across large parts of southern and inland eastern Australia. Daytime temperatures also tend to be above average over southern Australia.

The Indian Ocean Dipole (IOD) has been below −0.4 °C (the negative IOD threshold) since mid-June, which means 2014 is now considered a negative IOD year. Model outlooks suggest this negative IOD event to decay within the next month, and return to neutral. A negative IOD pattern typically brings wetter conditions to inland southern Australia during winter and spring.

NINO3.4 outlook

The latest NINO3.4 forecasts (initialised in August) indicate the tropical Pacific Ocean is most likely to continue warming over the coming months, but remain within neutral values to the end of 2014. Four of the models indicate sea surface temperatures in the central tropical Pacific will exceed El Niño thresholds by January 2015.

The most recent NINO3.4 value is +0.2 °C for the week ending 17 August 2014. Sustained NINO3.4 values above +0.8 °C indicate El Niño conditions.

Indian Ocean Dipole (IOD) outlook

The Indian Ocean Dipole (IOD) has been below −0.4 °C (the negative IOD threshold) since mid-June, which means 2014 is now considered a negative IOD year. The latest weekly index value (to 17 August 2014) is –0.6 °C, with model outlooks indicating that the tropical Indian Ocean should return to neutral values within the next month. A negative IOD pattern typically brings wetter conditions to inland and southern Australia during winter and spring.

The following graph shows the average forecast value of the IOD index for each international model surveyed for the selected calendar month. If the majority of models are approaching or exceeding the blue dashed line, then there is an increased risk of a negative IOD event. If the majority of models are approaching or exceeding the red dashed line, then there is an increased risk of a positive IOD event.

Predictive Ocean Atmosphere Model for Australia (POAMA)

POAMA, run at the Bureau of Meteorology, generates an eight-monthly forecast on the first day of each month. The most recent model run (started in August) predicts NINO3.4 is likely to remain well within neutral bounds throughout the forecast period. The following forecast values (at the top of the table) are for the ensemble mean.

POAMA archive data is available here.

ENSO Dials

The arrows on the dials below indicate the combined average ofmonthly NINO3.4 outlooks from a survey of international global climate models. Note that the individual model runs vary around the average.

ENSO dial month+1 ENSO dial month+3 ENSO dial month+5

NINO3.4 outlook bar-graphs

The following graphs shows the average forecast value of NINO3.4 for each international model surveyed for the selected calendar month. If the bars on the graph are approaching or exceeding the blue dashed line, there is an increased risk of La Niña. Similarly, if the bars on the graph are approaching or exceeding the red dashed line, there is an increased chance of El Niño.

NINO3.4 bar graph month+1 NINO3.4 bar graph month+3 NINO3.4 bar graph month+5

IOD outlook bar-graphs

The following graph shows the average forecast value of the IOD index for each international model surveyed for the selected calendar month. If the majority of models are approaching or exceeding the blue dashed line, then there is an increased risk of a negative IOD event. If the majority of models are approaching or exceeding the red dashed line, then there is an increased risk of a positive IOD event.

IOD bar graph month+1 IOD bar graph month+3 IOD bar graph month+5

Past climate model summaries