Understanding the tropical system Madden-Julian Oscillation |27 April 2015
Seychellois to join US researchers to analyse data collected here
A Meteorological Services staff will join US researchers at the University of Notre Dame to help with the analysis of data collected in Seychelles in an attempt to better understand the tropical system Madden-Julian Oscillation (MJO) and what really initiates it.
Discovered by Roland Madden and Paul Julian in 1971, the MJO is the most important mode of weekly to monthly (sub-seasonal) variability across the tropics.
It can be described as a large-scale coupled convective and atmospheric circulation anomaly that slowly propagates eastward around the equatorial region within a period of 30-90 days at approximately 5 metres per second (m s-1). It affects weather in many parts of the world, but active convection is more prominent over the Indian and western Pacific Oceans where the sea surface temperature is warmer. The MJO has major influence on the active-break phases of the Indian and Australian monsoons. But little is known about its impact on rainfall in the Seychelles.
Last year, meteorologist Vincent Amelie did some studies to investigate whether there is any relationship between the MJO and the wet-season in Seychelles, and if there is, whether it is significant enough to be used to improve forecasting skills.
The study reveals that although there is no direct correlation between the daily MJO amplitude and daily rainfall; there is however an important relationship between the MJO phase and the rainfall probabilities. Generally, MJO is described in terms of phases, and there are eight phases. The study shows that when MJO is in phase six it has greater influences over Seychelles and increases the probability of daily rainfall, whereas phase seven has a stronger influence to increase the probability of consecutive days of rainfall above a threshold that can cause flooding.
On the other hand, MJO phase four has the greatest potential to reduce rainfall. The influence of MJO phases one, two, three, and five is not strong and consistent, whereas phase eight shows no major impact as expected. The results of this study has today helped in the development of a statistical forecasting technique which the local weather forecasters are now using to predict Seychelles’ rainfall on one-two week timescales, thus improving the weather warnings, particularly related to flooding, which is one of the common and major weather-related hazards during the wet season.
However, in spite of some of the suggestions given to explain the causes of the MJO influences on the rainfall, particularly in phases six and seven, further research is needed using other datasets. But this can only be achieved if MJO itself is better understood, because while scientists worldwide have studied the phenomenon and have been able to establish that it is an oscillation that repeats itself every 30 to 90 days, that it moves eastward around the equator at an average speed of 5 metres per second affecting the variability of rainfall in many parts of the tropical region and that it influences the development of other weather phenomena like the El Nino and tropical cyclone, many things about it remain unclear.
In fact it is based on an attempt to better understand this tropical system and what really initiates MJO that researchers from the University of Notre Dame, USA, spent almost two months in Seychelles recently collecting various datasets such as wind, humidity, clouds and other weather and climatic parameters using some sophisticated equipment which were deployed in the country and assembled at the international airport based radiosonde station.
Today, one month after the collection of data has completed and the researchers have returned to USA, the national meteorological services is proud to have partnered with the University of Notre Dame and a locally based non-governmental organisation – Better Life Foundation (BLF) – led by the chairman of the Seychelles Chamber of Commerce and Industries (SCCI) Marco Francis, to successfully implement this very useful scientific activity in Seychelles, a partnership which saw the signing of a memorandum of understanding (MoU) which allows the collaboration to continue beyond the completion of the field study where one of the Meteorological Services’ staff will have the opportunity to join the US team at the University of Notre Dame to help with the data analysis, a first for the Seychelles Meteorological Services.
Seychelles chosen for its geographical position
Seychelles was selected as the site for the study not only because of its geographical position in respect to the formation and tracking of the MJO, since it is believed that Seychelles is the region where most MJO activities start to develop, thus is a good spot for MJO tracking and monitoring.
The selection was also based on the good reputation of the Seychelles Meteorological Services among the international research institutions. This explains why since the first group of meteorological researchers came to Seychelles almost 15 years ago to conduct research activities the number of research programmes undertaken in the country by various international institutions has continued to increase. Just recently ‘Meteo France’, La Reunion, invited the Seychelles Met Services to take part in two regional studies.
One of these studies involve installation of a so-called Mini-SAOZ and a UV Kipp & Zonen radiometer in Seychelles which will be dedicated to the monitoring of the climatic evolution of UV radiation in the Indian Ocean together with similar measurements in Reunion and Madagascar.
The second one is a project called ReNovRisk-CYCLONES, which is about a FEDER programme dealing with the impacts of cyclones on small islands in the south-west Indian Ocean. Under this programme Seychelles could benefit with the installation of a Galileo-GPS station for the duration of the programme, for the measurement of the total quality of water in the atmospheric column. Seychelles will also benefit with some additional radiosondes or even in other domains associated with the programme. The Seychelles Meteorological Services have already confirmed its willingness to take part in both projects.
Back to the MJO, for Seychelles specifically, after all the hard work to collect the data it is expected that the results from the analysis will eventually provide further knowledge about MJO to allow local meteorologists to make better predictions and long-term forecasts which in turn will help policy makers to make informed decisions when dealing with the management of issues or resources that are directly affected by weather conditions. More information from this experiment can also allow the Seychelles Meteorological Services to undertake further studies to build on what is already known about MJO, and this can ultimately help with the improvement of the weather forecasting. A better understanding of the MJO will also go a long way in helping to distinguish the different climate variability causing extreme weather events in the country and help meteorologists to know when exactly it’s El Nino, when it’s MJO, when it’s climate change and so on.
As for the USA, although MJO does not directly affect them, the results of the study can help them better understand other weather systems which are linked with MJO. It is well known, for example, that MJO influences the development of El Nino which also affects many non-tropical countries. Therefore, being able to better understand MJO could therefore help to improve the forecast of El Nino.
MJO also modulates tropical cyclone or hurricane. Furthermore, MJO also provides a tough test to the knowledge of the relationship between the small-scale and large-scale weather systems thus provides additional information that will help to solve the more complex problems of MJO, particularly in relation to its representation in models.