El Niño has arrived in the tropical Pacific...
From the Australian Bureau of Meteorology:
El Niño in the tropical Pacific
Issued on 12 May 2015
The tropical Pacific is in the early stages of El Niño. Based upon model outlooks and current observations, the Bureau's ENSO Tracker has been raised to El Niño status.
El Niño–Southern Oscillation (ENSO) indicators have shown a steady trend towards El Niño levels since the start of the year. Sea surface temperatures in the tropical Pacific Ocean have exceeded El Niño thresholds for the past month, supported by warmer-than-average waters below the surface. Trade winds have remained consistently weaker than average since the start of the year, cloudiness at the Date Line has increased and the Southern Oscillation Index (SOI) has remained negative for several months. These indicators suggest the tropical Pacific Ocean and atmosphere have started to couple and reinforce each other, indicating El Niño is likely to persist in the coming months.
International climate models surveyed by the Bureau indicate that tropical Pacific Ocean temperatures are likely to remain above El Niño thresholds through the coming southern winter and at least into spring.
Sea Surface Temperature: Here are the changes in the sea surface temperature between 22 December 2014 and 10 May 2015. Click to enlarge as always.
|Sea Surface Temperature - 22 December 2014 to 10 May 2015 |
Source: Bureau of Meteorology
Sub-Surface Temperature: Here are the changes sub-surface between February 2015 and May 2015:
|Sub-Surface Temperature - February 2015 to 10 May 2015|
Source: Bureau of Meteorology
Southern Oscillation Index (SOI): Here is a chart of the 30 day moving SOI. The SOI is a measure of the As BoM states: "Sustained positive values of the SOI above +7 may indicate La Niña, while sustained negative values below −7 may indicate El Niño. Values of between about +7 and −7 generally indicate neutral conditions."
|30 day moving SOI. Source: Bureau of Meteorology|
BoM normally uses 0.8, not 0.7 - is this a climate change? :D
In case you're new to the subject, the SOI is calculated using the pressure differences between Tahiti and Darwin. It's long been used by BoM as an indicator of ENSO status. As stated on the BoM website:
Sustained negative values of the SOI below −8 often indicate El Niño episodes. These negative values are usually accompanied by sustained warming of the central and eastern tropical Pacific Ocean, a decrease in the strength of the Pacific Trade Winds, and a reduction in winter and spring rainfall over much of eastern Australia and the Top End.
POAMA Projections: Here are the projections for ENSO, from BoM's Predictive Ocean Atmosphere Model for Australia (POAMA). The chart below shows that we've only just crossed into El Niño territory. BoM measures El Niño differently to other weather bureaux:
|POAMA model projections for ENSO - Nino 3.4 Source: BoM|
- ABC news item about the BoM announcement
- Sydney Morning Herald item about the BoM announcement, with a video
- Bureau of Meteorology ENSO Wrap-Up (current)
- Bureau of Meteorology ENSO archives dating back to 2001
- Bureau of Meteorology - El Niño history going back to 1902-03
- NOAA ENSO Reports
- Gobbling up or Spitting Out Bob Tisdale's ENSO Leftovers at WUWT - a fairly detailed HotWhopper article about ENSO