Geoscience Reference
In-Depth Information
8
(a
) India (15°N-30°N, 60°E-120°E)
6
4
2
8
(b
) West Africa (5°N-15°N, 20°W-30°E)
6
4
2
8
(c
) Amazon Basin (15°S-0°, 60°E-30°E)
6
4
2
8
(d
) East Africa (0°-5°N, 35°E-45°E)
6
4
2
8
(e
) Tropical North Paci
c (0°-10°N, 120°W-240°W)
6
4
2
Jan.
Feb. ar. pr. ay
June
July
Aug.
Sept. ct. ov. ec.
Figure 3.1 Annual precipitation climatology (mm/day) for various low-latitude regions.
To form a
composite,
the phases of numerous MJO observations are aligned
to define a typical anomaly
(Fig. 3.2)
. The MJO begins with the development
of strong convection and positive precipitation anomalies in the western In-
dian Ocean. The anomalies are associated with low surface pressures, converg-
ing low-level winds, and diverging upper-level winds (top panel). At the same
time, the western Pacific is dry. About 2 weeks later (second panel), the positive
precipitation anomaly has moved to the eastern Indian Ocean, and 2 weeks
after that (third panel) the western Pacific receives anomalously high rainfall.
The wet and dry anomalies continue to propagate eastward at about 5-10 m/s,
dissipating in the central Pacific where the surface waters are cooler. In some
cases the oscillation is reinvigorated and becomes apparent again in the tropical
