Madden-Julian Oscillation (MJO)
The Madden-Julian Oscillation (MJO) is the major fluctuation in tropical weather on weekly to monthly timescales. The MJO can be characterised as an eastward moving 'pulse' of cloud and rainfall near the equator that typically recurs every 30 to 60 days.
MJO phase diagram
*Note: There is missing satellite observations from 16/3/1978 to 31/12/1978.
The MJO phase diagram illustrates the progression of the MJO through different phases, which generally coincide with locations along the equator around the globe. RMM1 and RMM2 are mathematical methods that combine cloud amount and winds at upper and lower levels of the atmosphere to provide a measure of the strength and location of the MJO. When the index is within the centre circle the MJO is considered weak, meaning it is difficult to discern using the RMM methods. Outside of this circle the index is stronger and will usually move in an anti-clockwise direction as the MJO moves from west to east. For convenience, we define 8 different MJO phases in this diagram.
Average weekly rainfall probabilities
These maps show average weekly rainfall probabilities and expected 850 hPa (approximately 1.5 km above sea level) wind anomalies for each of the 8 MJO phases. Green and blue shading indicates higher than normal rainfall would be expected, while red and orange shading indicates lower than normal rainfall would be expected. The direction and length of the arrows indicate the direction and strength of the wind anomaly. The darker the arrow, the more reliable the information is. The relationship of the MJO with Australian rainfall and winds changes with the season (which can be selected at the top).
Average outgoing longwave radiation (OLR)
Outgoing longwave radiation (OLR) is often used as a way to identify tall, thick, convective rain clouds. These maps show the difference from expected cloudiness based on the position of the MJO. The violet and blue shading indicates higher than normal, active or enhanced tropical weather, while orange shading indicates lower than normal cloud or suppressed conditions. The direction and length of the arrows indicate the direction and strength of the wind anomaly. The darker the arrow, the more reliable the information is. The relationship of the MJO with tropical weather patterns changes with the season (which can be selected above the maps).
Global maps of outgoing longwave radiation (OLR)
Global maps of outgoing longwave radiation (OLR) highlight regions experiencing more or less cloudiness. The top panel is the total OLR in Watts per square metre (W/m²) and the bottom panel is the anomaly (current minus the 1979-1998 climate average), in W/m². In the bottom panel, negative values (blue shading) represent above normal cloudiness while positive values (brown shading) represent below normal cloudiness.
The graphs linked to this map show the OLRs for the different regions within the Darwin RSMC area. The horizontal dashed line represents what is normal for that time of year (based on the 1979 to 1998 period). The coloured curve is the 3-day moving average OLR in W/m². Below normal OLR indicates cloudier than normal conditions in this particular area, and is shown in blue shading. Above normal OLR indicates less cloudy conditions and is shown in yellow shading.
Postscript: Coral Sea Dateline Fiji Guam & Marianas Indochina Malyasia & Indonesia Micronesia Nauru & Tuvalu New Guinea Northern Australia Philippines Solomon Island Southern India & Sri Lanka Vanuatu
Daily averaged OLR anomalies
Westerly wind anomalies
Time-longitude plots of daily averaged OLR anomalies (left) and 850 hPa (approximately 1.5 km above sea level) westerly wind anomalies (right) are useful for indicating the movement of the MJO.
How to read the Time-Longitude plots
The vertical axis represents time with the most distant past on the top and becoming more recent as you move down the chart. The Horizontal axis represents longitude.
Eastward movement of a strong MJO event would be seen as a diagonal line of violet (downward from left to right) in the OLR diagram, and a corresponding diagonal line of purple in the wind diagram. These diagonal lines would most likely fall between 60°E and 150°E and they would be repeated nearly every 1 to 2 months.
Weekly Tropical Climate Note
Issued on Tuesday 26 August 2014
Over the past week, tropical activity has been focussed over the central equatorial Indian Ocean and the tropical central and eastern Pacific Ocean. Warmer than normal sea surface temperatures have been fuelling two tropical storms in the eastern equatorial Pacific Ocean, hurricane Marie and tropical storm Karina. The activity over the Indian Ocean has been present for almost three weeks now, and may be related to a relatively weak Madden–Julian Oscillation (MJO) event that has been analysed in the region over this period.
Most climate models predict the MJO signal over the Indian Ocean will weaken in the coming days, and hence is not likely to influence tropical weather. However, one model indicates the MJO will maintain strength while moving slowly eastwards across the tropical Indian Ocean over the coming week. If the MJO maintains strength it is possible that it will act to enhance tropical activity in the eastern Indian Ocean and then South–East Asia towards the end of the week. Tropical activity is often suppressed over the northwest Pacific when there is an MJO signal over the Indian Ocean.
See the Bureau's MJO Monitoring for more information on location and tracking of the MJO.
ENSO and Indian Ocean Dipole
While the tropical Pacific Ocean temperatures remain at neutral levels, there is still a chance of an El Niño in 2014. The latestNINO3.4NINO3.4 sea surface temperature anomaly is +0.3 °C. The latest 30–day Southern Oscillation Index (SOI) value up to 24 August is −9.3.
A negativeIndian Ocean Dipole (IOD) pattern remains in place over the tropical Indian Ocean. The latest value of the IOD index is −0.5 °C. A negative IOD pattern typically brings wetter conditions to inland and southern Australia during winter and spring, but its influence usually ends before summer begins. Model forecasts expect this negative IOD event to decay within the next month.
See the Bureau of Meteorology's ENSO Wrap up for official El Niño information including computer model projections.
Next update expected by 2 September 2014| Product Code IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
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