Microwave Radiometers
- PDF / 2,621,454 Bytes
- 60 Pages / 595.276 x 790.866 pts Page_size
- 14 Downloads / 176 Views
MADDEN-JULIAN OSCILLATION (MJO) Baijun Tian and Duane Waliser Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
Synonyms 30–60 day oscillation; 40–50 day oscillation; Intraseasonal oscillation (ISO); Intraseasonal variability (ISV) Definition The MJO is a planetary-scale quasiperiodic oscillation of atmospheric wind and convective cloudiness anomalies that moves slowly eastward along the equator mainly over the tropical Indian and Pacific Oceans with a timescale on the order of 30–60 days. Introduction In 1971, Roland Madden and Paul Julian stumbled across a 40–50 day oscillation when analyzing the zonal (east– west) wind data from rawinsondes at Kanton Island (3 S, 172 W) over the equatorial western Pacific. Until the early 1980s, little attention was paid to this oscillation, which later became known as the MJO. Since the 1982– 1983 El Niño event, low-frequency variations in the tropics, both on intra-annual (less than a year) and interannual (more than a year) timescales, have received much more attention, and the number of MJO-related publications grew rapidly. The MJO turned out to be the dominant form of the intraseasonal (30–90 day) variability in the tropical atmosphere and has many important influences on the global weather and climate system. The MJO is a naturally occurring mode of variability of the tropical ocean–atmosphere system. It is characterized by an eastward propagation of large regions of both
enhanced and suppressed tropical convection, cloudiness and rainfall near the equator mainly over the tropical Indian and Pacific Oceans, and associated large-scale atmospheric circulation (wind) anomalies over the whole globe. The anomalous cloudiness or rainfall usually first emerges over the equatorial western Indian Ocean and intensifies and remains evident as it propagates eastward over the warm ocean waters of the equatorial eastern Indian Ocean and western Pacific, the so-called IndoPacific warm pool. This pattern of anomalous cloudiness and rainfall then generally weakens and disappears as it moves over the cooler ocean waters of the equatorial eastern Pacific, the so-called equatorial cold tongue. Along with this eastward-propagating pattern of equatorial cloudiness and rainfall anomalies, there also exist eastward moving distinct baroclinic patterns of lower- and upper-level atmospheric circulation anomalies in the tropics and subtropics. The circulation anomalies extend around the globe and are not confined to the eastern hemisphere as opposed to the cloudiness and rainfall anomalies. When the MJO moves eastward, it modulates the background cloud, rainfall, and circulation in the tropical Indian and Pacific Oceans on timescales shorter than a season but longer than a couple of weeks. The length of a typical MJO cycle is approximately 30–60 days but normally 40–50 days. Thus, the MJO is also known as the 30–60 day oscillation, 40–50 day oscillation, intraseasonal oscillation (ISO), or intraseasonal variability (ISV) after its typical timescale. A complete MJ
Data Loading...
