Oregon Chapter
American Meteorological Society

On April 21, 2011, 22 members attended this meeting, at the Stark Street Pizza House, Portland.  OR-AMS President Bobby Corser welcomed folks and gave the opening remarks, updates, and explained the proposed draft amendments to the chapter Bylaws.  Secretary Kyle Dittmer gave an election nomination update.  VP Steve Pierce gave a fast review of the weather extremes of recent – with record cold and precipitation events. (Opening Presentation: pps file; pfd file)

Chris explained that the MJO works on an intra-seasonal time frame and is characterized by changes in tropical wind, cloud cover, and rain.  A MJO event can move 5 - 15 m/sec and occurs 3-5 times per year.  Outgoing Longwave Radiation (OLR) is the current proxy for tropical rainfall and convection.  The MJO bridges the gap of short-term (1-30 days) to intermediate-seasonal (e.g., ENSO) to long-term decadal (e.g., solar variability). 

MJO dynamics: an event progresses eastward, in phases, and alternates in patterns of tropical rain, wind, and pressure.  The rain signal is strong over the Indian and western Pacific Oceans.  The circulation signals spans the Earth.  The lifecycle starts as rain in the Indian Ocean, on to New Guinea, then across the western, central, and eastern Pacific Ocean.  The rain alternates with dry periods during its eastern propagation.  Convection shows Sea-Surface Temperature (SST) changes, as the warm water helps in the eastward propagation.

MJO is most active in ENSO-neutral years and mostly absent in El Niño years.  A MJO event can affect tropical and mid-latitude weather and change in strength as it evolves.  We need daily monitoring to help with predictions.  Mathematical modeling troubles occur with tropical rain processes. 

MJO is best tracked by: OLR, 850-mb wind (convergence signal), 200-mb (divergence signal), and velocity potential (divergence signal).  The Wheeler-Hendron Diagram tracks enhanced convection with the computation based on OLR, 850-mb and 200-mb winds (RMM1, RMM2), and is plotted out as eight-phases (based on longitudinal position).  A counter-clockwise trace indicates eastward propagation.  The distance from the center is proportional to the strength.  There are 4-5 days per phases, with a 30-60 day life-span of a MJO event. 

Weather impacts: alternating periods of wet/dry weather, heavy west-coast rain, monsoon dynamics, ENSO, and tropical storm-track development.  MJO can modulate the intensity, timing, and duration of ENSO events.  Biggest impact is on the equatorial Pacific SSTs (as seen in the Kelvin waves).  Phases 6-8 show the initiation of El Niño.  Phases 3-5 show the initiation of La Niña.  Highest variability is shown in strong La Niña years.  MJO is most active in El Niño years.  MJO is much shorter in time than ENSO but can show ENSO-like circulation. 

Forecasting: MJO can give a 1-2 week lead time on mid-latitude circulation.  The prediction skill can go 2-3 weeks out.  The highest skill is when an event is already underway.  However, MJO event transitions are poorly modeled.  A forecast is comprised of a statistical and dynamic model.  Examples of good skill predictions: western USA heat wave of the summer 2006, Heavy rain event in December 2006, record Portland cold and snowfall of December 2008.

The latest MJO reference links:

MJO Monitoring

MJO Forecasts

Much Q&A followed.  We had a great time and good discussions.  Thanks, Chris!

Note-taker: Kyle Dittmer, 2009-2011 Oregon-AMS Secretary