January 22, 2007
Japan Agency for Marine-Earth Science and Technology

Succeeded to Observe Onset of Deep Cumulus Convection in Indian Ocean
~Remarkable advancement for elucidation of MJO~


Institute of Observational Research for Global Change (IORGC), Japan Agency for Marine-Earth Science and Technology (hereafter JAMSTEC; Mr. Yasuhiro Kato, President) succeeded to observe the onset of cloud clusters, which horizontal length could be up to several thousand kilometers, from various angles in chronological order, through intensive observation of atmosphere and ocean using Oceanographic Research Vessel MIRAI at the Indian Ocean. R/V MIRAI returned to its home port, Mutsu Institute for Oceanography (MIO), in Mutsu City, Aomori Prefecture on January 20th.


In tropical area, it is known that cloud cluster of several thousand kilometers scale develops with a local intraseasonal period of 30 to 60 days in the Indian Ocean and propagates slowly eastward at the speed of approximately 20 kilometers per hour. This phenomenon is called "Madden-Julian Oscillation (MJO)", named after the discoverers. It is said that MJO influences not only tropical climate but the occurence of El Nino and tropical cyclone, and it is the important phenomenon to understand the entire global climate variability. Over 30 years since its discovery, its large-scale structure and feature, and its influence to the climate are gradually elucidated, but its generating mechanism is not yet elucidated. One of the reasons is that the observation for this phenomenon had not been done in the Indian Ocean which is its generating area so that the in-situ data were very little. Therefore, this time, atmospheric and oceanographic observations were carried out at Maldives Islands and on R/V MIRAI located in the site sea area from the beginning of October to December 2006 (the cruise of R/V MIRAI was 71 days from October 4th to December 13th). This intensive observation is called MISMO project. MISMO is the acronym for "Mirai Indian Ocean cruise for the Study of the MJO-convection Onset".


(1)Observation by R/V MIRAI
Observation of atmospheric vertical structure and interaction between ocean and atmosphere at the site sea area
•Stationary observation (October 24th through November 25th) Atmospheric observation using Doppler radar and radiosonde Oceanographic observations using mooring buoy
•Cruise observation (November 28th through December 13th) The course is from Maldives to Singapore
(2)On land observation at Maldives Islands
In order to capture precipitation system and spatial structure of the environment for the onset of the convections in the MJO and to supplement the observation by R/V MIRAI, observation on Maldives Islands carried out using Doppler radar and radiosonde.

During the intensive observation period, we constructed the observation network of R/V MIRAI, Maldives Islands and buoy array to monitor the atmospheric and oceanic features associated with the onset of the MJO-convection (Fig. 1).


Cloud clusters growing at the site sea in the beginning of November extended east and west by several thousand kilometers around November 20th and started propagating eastward slowly.

R/V MIRAI could observe the onset of the cloud cluster during the stationary observation and could also observe its propagating eastward since the ship sailed the same direction fortunately.

The cloud clusters became so large, several thousand kilometers scale, that the whole picture was confirmed by the cloud images taken by satellite (Fig. 2). Some results of the observation are shown in Figs.3 and 4. The Indian Ocean is windy area as known for the monsoon, but just before the onset of deep cumulus convection, sometimes the ocean is so calm that the surface looks like a mirror and many clouds those top heights are 2 to 3 kilometers are formed (upper panel of Fig. 3). However, during the active phase of the MJO, the whole sky is covered with deep cloud and heavy precipitation are often observed as rain band (bottom panel of Fig. 3). This time, we could capture how cumulus propagate eastward (rainfall area and intensity are going to bigger), since the ship sailed the same direction of the cumulus movement (Fig. 4). From this observation, it is expected to be able to understand the cumulus feature, such as, even an each one exists only for hours, as an ensemble, it exists for days.

We could obtain detailed observation data of inside the cumulus. In particular, the observation period corresponded to the positive phase of the Indian Ocean Dipole mode (IOD) which is similar to El Nino in the Pacific Ocean. The observation was rarely conducted during the IOD event in the past. From that aspect, it can be said that these are very valuable data.

Future Plan

Conduct the further data analysis. At first, we will report this observation result as a preliminary report at the Blue Earth Symposium which is going to be held by JAMSTEC in March. And the special session of this observation is hastily-arranged in International Union of Geodesy and Geophysics (IUGG) General Assembly which will be held in June in Italy. Following these, this research report will be released promptly. It is pointed out that the MJO can trigger the onset and termination of the El Nino event, which causes a warm winter in Japan, and also affect to generation of tropical cyclone. Therefore the relation with those phenomena is going to be elucidated especially. Furthermore, the result will be used for the simulation of cumulus development and the prediction research by Earth Simulator.


(For the research)
Mr. Masanori Yoshizaki, e-mail: info-iorgc@jamstec.go.jp
Project Director, Ocean, Land and Atmosphere Interactions Integrated Research Project Institute of Observational Research for Global Change (IORGC)
Mr. Kunio Yoneyama, e-mail: info-iorgc@jamstec.go.jp
Research Scientist, Ocean, Land and Atmosphere Interactions Integrated Research Project, IORGC
Mr. Tatsunosuke Tsuzuku, e-mail: info-iorgc@jamstec.go.jp
Manager, Research Promotion Office, IORGC
(For Publication)
Mr. Shinji Oshima, e-mail: press@jamstec.go.jp
Manager, Planning Department Press Office JAMSTEC