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 characterized 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 22 July 2014
Third typhoon in northwest Pacific Ocean this month
Typhoon Matmo (Henry) formed over the Philippine Sea on 17 July and reached typhoon strength (average winds greater than 118 km/h) on 19 July, becoming the third typhoon in the northwest Pacific this month. Typhoon Neoguri (Florita) made landfall over southern Japan on 10 July and Typhoon Rammasun (Glenda) made landfall over both the Philippines and China within the past week. On average, 3.9 tropical storms (sustained winds greater than 64 km/h) including 2.5 typhoons form over the north-western Pacific in July (based on Joint Typhoon Warning Centre climatology from 1959-2012). Sea surface temperatures (SSTs) in the northwest Pacific Ocean are currently greater than 28°C, which provides an ideal environment for tropical cyclones to form.
The variability of the South-East Asian monsoon, including the formation of tropical cyclones, is usually influenced by the Madden-Julian oscillation (MJO). However, the MJO has been weak and at times indiscernible over the past five weeks and therefore is unlikely to have been a significant contributor to the recent typhoon activity. Most model forecast of the MJO predict it will remain weak for the next 10 to 14 days with only one model forecasting a strong MJO signal over the west Pacific this week.
See the Bureau's MJO Monitoring for more information on location and tracking of the MJO.
Indian Ocean Dipole event possible in 2014
The Indian Ocean is currently showing a negative Indian Ocean Dipole(IOD) like pattern, with warmer than normal SSTs in the east near the equator and cooler than normal SSTs in the tropical west. This pattern has been in place since mid-June. The Bureau's IOD index reflects this observed SST pattern and is currently below -0.4°C; if values of below -0.4°C; persist until early August, 2014 will be considered a negative IOD year. However, most climate models indicate the IOD index will return to neutral levels over the coming months. Only one model suggests a negative IOD event will develop fully.
Under favourable weather conditions tropical moisture from a warm Indian Ocean can be pulled over continental Australia producing bands of cloud over northwest and central Australia. The negative IOD like pattern in the Indian Ocean may have contributed to the above-average rainfall experienced in southeast Australia during June and over the Kimberley and Pilbara in July. It is also possible that the negative IOD pattern in the Indian Ocean has contributed to this season's weaker than usual southeast Indian monsoon.
El Niño remains on hold
Warming of the tropical Pacific Ocean over the past several months has primed the climate system for an El Niño in 2014. However, a general lack of atmospheric response over the last month has resulted in some cooling of the tropical Pacific Ocean. The majority of climate models surveyed by the Bureau still suggest El Niño remains likely for late 2014; however, most have eased their predicted strength. If an El Niño were to occur, it is increasingly unlikely to be a strong event.
The ENSO Tracker is currently at El Niño ALERT stage.
Next update expected by 29 July 2014| Product Code IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
Product Code: IDCKGEWWOO