Reply #83: "Madden-Julian Oscillation"

[jbnow]

I read these and I still can't tell you just what it is, but this is what is says

This is the general description
http://www-das.uwyo.edu/~geerts/cwx/notes/chap12/mjo.html
<snip>
Structure of a Madden-Julian wave
Within the center of suppressed convection, clear skies associated with a stronger-than-normal trade wind inversion allow more shortwave radiation to reach the ocean surface (Figure 2), causing a slight SST increase as the wave travels eastward (3). The Trade winds too are stronger than normal, explaining enhanced evaporation from the sea surface.

Easterly winds (and the evaporation rate) weaken near the western edge of the suppressed convection region, and this leads to low-level moisture convergence. This triggers deep convection, leading to the other half of the OLR oscillation, i.e. the region of enhanced convection.

This is how it affects the US
http://www.cpc.ncep.noaa.gov/products/intraseasonal/intraseasonal_faq.html
<snip>
What are the impacts of intraseasonal oscillations on the U.S.? When do they occur?

The strongest impacts of intraseasonal variability on the U.S. occur during the winter months over the western U.S. During the winter this region receives the bulk of its annual precipitation. Storms in this region can last for several days or more and are often accompanied by persistent atmospheric circulation features. Of particular concern are the extreme precipitation events which are linked to flooding. There is strong evidence for a linkage between weather and climate in this region from studies that have related the El Niño-Southern Oscillation (ENSO) to regional precipitation variability. From these studies it is known that extreme precipitation events can occur at all phases of the El Niño-Southern Oscillation (ENSO) cycle, but the largest fraction of these events occur during La Niña episodes and during ENSO-neutral winters.