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
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
(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
(1). The strongest impacts of intraseasonal
variability (MJO) on the United States
occur during the winter months
(rainy season) over the western
(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 (
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
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
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
(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
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)