HAZE: Indian Ocean Dipole 2019 is approaching the 2015 level

According to the Indian Ocean Dipole Index published by BOM on 15 September 2019, the current level of Positive Indian Ocean Dipole is approaching the level of 2015. The wild fire in Indonesia in year 2015 was among the worst haze episode that affecting most of the ASEAN countries.

Based on the IOD Index released by BON, the current IOD Index already passed 1 degree Celcius and approaching the similar level of 2015. The highest record in 2015 is 1.17 degree Celcius. The highest record of 2019 is 1.08 degree Celcius. Until 15 September 2019, it is still recorded at the high level of 1.02 degree Celcius.

More worrying is the data from the BOM Climate Modelling where the projected peak of IOD will be reaching 1.6 degree Celcius by October 2019, which could mean the severe wild fire and haze episode could be worst than 2015 level.

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Indian Ocean Dipole outlooks

BOM, 17 September 2019

The Indian Ocean Dipole (IOD) remains positive, with the latest weekly index value to 15 September at +1.02 °C.

The overall pattern of sea surface temperatures has remained generally consistent with a positive IOD pattern since late May, with warmer than average sea surface temperatures in the central and western tropical Indian Ocean, and average to cooler than average waters in the eastern tropical Indian Ocean, to the north of Australia and south of Indonesia.

Typically, to be considered a positive IOD event, index values need to remain above the positive threshold (+0.4 °C) for at least eight weeks. The index value has been above the threshold in eight of the last nine weeks, and was also above the threshold from late May to mid-June.

All six international climate models surveyed by the Bureau indicate the IOD will remain positive into December. IOD events usually dissipate by early summer as the monsoon trough moves into the southern hemisphere, which changes the broadscale wind patterns over the IOD region and returns sea surface temperatures to near average. Models are indicating a slower break down of the IOD than usual, but it remains unlikely that the positive IOD influence will persist far into summer.

20190917.sstOutlooks_iod

Source: http://www.bom.gov.au/climate/enso/#tabs=Indian-Ocean

The Indian Ocean Dipole indices

Indian Ocean Dipole (IOD) events are driven by changes in the tropical Indian Ocean. Sustained changes in the difference between normal sea surface temperatures in the tropical western and eastern Indian Ocean are what characterise IOD events.

The IOD is commonly measured by an index (sometimes referred to as the Dipole Mode Index, or DMI) that is the difference between sea surface temperature (SST) anomalies in two regions of the tropical Indian Ocean (see map above):

  • IOD west: 50°E to 70°E and 10°S to 10°N
  • IOD east: 90°E to 110°E and 10°S to 0°S

A positive IOD period is characterised by cooler than average water in the tropical eastern Indian Ocean and warmer than average water in the tropical western Indian Ocean. Conversely, a negative IOD period is characterised by warmer than average water in the tropical eastern Indian Ocean and cooler than average water in the tropical western Indian Ocean.

For monitoring the IOD, Australian climatologists consider sustained values above +0.4 °C as typical of a positive IOD, and values below −0.4 °C as typical of a negative IOD.

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Figure 1 Regions used to monitor ENSO and IOD. The NINO regions are used to monitor ENSO, with NINO3 and NINO3.4 typically used to identify El Niño and La Niña events. The IOD index (or Dipole Mode Index, DMI) is used to identify IOD events, by taking the difference between the west and east poles. (Picture courtesy of BOM)

Source: http://www.bom.gov.au/climate/enso/indices/about.shtml