Lecture No:  Madden-Julian Oscillation (MJO)

1.     Definition: An equatorial traveling pattern of anomalous rainfall or other weather

        features (strong wind, outgoing long-wave radiation, and air pressure,etc.) from

        west to east.

(1).   The MJO is characterized by an eastward progression of large regions of both

         enhanced and suppressed tropical rainfall, observed mainly over the

         Indian Ocean  and Pacific Ocean.

(2).   The anomalous rainfall is usually first evident over the western Indian Ocean,

         and remains evident as it propagates over the very warm ocean waters of the

         western and central tropical Pacific.

(3).   This pattern of tropical rainfall then generally becomes very nondescript as

         it moves over the cooler ocean waters of the eastern Pacific but reappears

         over the tropical Atlantic and Indian Ocean.

(4).   The wet phase of enhanced convection and precipitation is followed by a dry

         phase where convection is suppressed at a given location. Each cycle lasts

         approximately 30-60 days (intraseasonal oscillation). ENSO is an

         interannual oscillation (year-to-year variability)

2.     Relationship between MJO and ENSO

(1).   Although MJO is an intraseasonal variation it shows interannual variablity.

         (2).   In the Pacific, strong MJO activity is often observed 6 - 12

                  months prior to the peaks of El Niņo episodes (1997-98), while weak MJO

                  activity is typically associated with La Niņa years (1996-97 active MJO vs

                  1997-98 El Nino).

3.      MJO effect on the US weather

        (1).   The strongest impacts of intraseasonal variability (MJO) on the United States                        

                 occur during the winter months (rainy season) over the western U.S.   

        (2).   It is known that extreme precipitation events (floods) can occur at all phases of             

                 the ENSO cycle, but the largest fraction of these events occur during La Niņa                      

                 episodes and during ENSO-neutral winters.

        (3).   During La Niņa episodes much of the Pacific Northwest (Washington,

             Oregon, and Northern California) experiences increased storminess,

             increased precipitation and more overall days with  measurable

             Precipitation.

        (4).   Strong MJO activity is often observed during weak La Niņa years or during                  

                 ENSO-neutral years, while weak or absent MJO activity is typically                           

                  associated with strong El Niņo episodes.

        (5).   A recent example is the winter of 1996-97, which featured heavy flooding in                         

                 California and in the Pacific Northwest (estimated damage costs of $2.0-3.0                         

                 billion at the time of the event) and a very active MJO. Such winters are also                         

                 characterized by relatively small sea surface temperature anomalies (SSTA) in               

                 the tropical Pacific compared to stronger warm and cold episodes. In these                  

                 winters there is a stronger linkage between the MJO events and extreme west                       

                 coast precipitation events.

        (7).   Pineapple Express (a MJO event)

                 A.     A significant amount of the deep tropical moisture traverses the                          

                    Hawaiian Islands on its way towards western North America.

             B.    Evolution of a pineapple express leading to a heavy west coast                           

                    precipitation event (see figure)

4.     Wintertime blocking activity over the North Pacific and western North America

        (1).   Definition of blocking activity

                 Atmospheric circulation features (High, Low, ridge, or trough) that persist             

             near the same location for several days or more.

       (2).  MJO is a contributor to blocking activity.

5.    Tropical storm development

       (1).  The strongest tropical cyclones tend to develop when the MJO favors                  

             enhanced precipitation.

       (2).  As the MJO progresses eastward, the favored region for tropical cyclone               

             activity also shifts eastward from the western Pacific to the eastern Pacific          

             and finally to the Atlantic basin.

       (3).  The MJO is one of many factors that contribute to the development of                 

             tropical cyclones. For example, it is well known that SSTs must be                       

             sufficiently warm and vertical wind shear must be sufficiently weak for                  

             tropical disturbances to form and persist.

 6.   Summer monsoon

        (1).   During the Northern Hemisphere summer season the MJO-related effects               

             on the Indian summer monsoon are well documented.

       (2).  MJO-related effects on the North American summer monsoon also occur,               

             though they are relatively weaker.

       (3).  the relative influences of ENSO and the MJO on the summer precipitation              

             regime of North America are not well understood.

7.      MJO indice

        The MJO analyses are often displayed in time-longitude format so as to                

       reveal the propagation, amplitude and location of the MJO-related features.

       (1). Outgoing Longwave Radiation, which is a satellite-derived measure of                   

             tropical convection and rainfall.

       (2).  Velocity potential, which is a derived quantity that isolates the divergent                

             component of the wind at upper levels of the atmosphere.

       (3).  Upper-level and lower-level wind anomalies.

       (4).  500-hPa height anomalies to represent the atmospheric responses in                      

             midlatitudes.

Please click on the following URL for details (optional)

http://www.wrh.noaa.gov/lox/nino.php

http://www.cpc.ncep.noaa.gov/products/intraseasonal/intraseasonal_faq.html

http://en.wikipedia.org/wiki/Madden-Julian_oscillation

http://envam1.env.uea.ac.uk/mjo.html (animation)

http://www.icess.ucsb.edu/asr/mjo_forecasts.htm

http://www.icess.ucsb.edu/asr/MJO_current_run.htm

http://meted.ucar.edu/climate/mjo/ (original MJO video)