MJO_summary

MJO_summary - Authors: Jon Gottschalck, Vernon Kousky,...

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Authors: Jon Gottschalck, Vernon Kousky, Wayne Higgins, and Michelle L’Heureux Madden Julian Oscillation (MJO) I. Definition : The MJO is an intraseasonal fluctuation or “wave” occurring in the global tropics. The MJO is responsible for the majority of weather variability in these regions and results in variations in several important atmospheric and oceanic parameters which include both lower- and upper-level wind speed and direction, cloudiness, rainfall, sea surface temperature (SST), and ocean surface evaporation. The MJO is a naturally occurring component of our coupled ocean-atmosphere system and the typical length of the MJO cycle or wave is approximately 30-60 days (Madden and Julian, 1971, 1972; Madden and Julian, 1994; Zhang, 2005). II. Characteristics : The MJO is characterized by eastward propagation of regions of enhanced and suppressed tropical rainfall, primarily over the Indian and Pacific Oceans. The anomalous rainfall is often first evident over the Indian Ocean, and remains apparent as it propagates eastward over the very warm waters of the western and central tropical Pacific. Over the cooler ocean waters of the eastern Pacific, the pattern of tropical rainfall generally becomes nondescript, but often reappears over the tropical Atlantic and Africa. Along with these variations in tropical rainfall, there are distinct patterns of lower- and upper-level atmospheric circulation anomalies in the tropics and subtropics. These features extend around the globe and are not confined to the eastern hemisphere. Thus, they provide important information regarding the regions of ascending and descending motion associated with particular phases of the oscillation. Figure 1 illustrates an equatorial vertical cross section of the MJO showing the changes in cloudiness, rainfall, wind speed and direction, and SST as the MJO propagates eastward around the global tropics (Adapted from Madden and Julian, 1971; 1972). By combining many MJO events together into composites, we obtain an idealized representation of the three dimensional structure of the MJO (Figure 2; Rui and Wang, 1990). When convection is active in the Indian Ocean and Indonesia, anomalous easterlies (westerlies) exit the area of enhanced convection in the upper levels of the atmosphere and associated with anti-cyclonic gyres along and behind the area of enhanced convection. Conversely, cyclonic gyres exist behind areas of suppressed convection in both hemispheres. At low levels, anomalous easterlies (westerlies) are evident ahead (behind) the area of enhanced convection. The low level gyres are generally weaker than those at upper levels. As the dipole propagates toward the central Pacific, the lower and upper level circulation anomalies become less recognizable and coherent but remain an important component in redistributing mass around the global tropics. III. Monitoring the MJO
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This note was uploaded on 12/28/2011 for the course GEOG 133 taught by Professor Leila during the Fall '09 term at UCSB.

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MJO_summary - Authors: Jon Gottschalck, Vernon Kousky,...

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