How the Madden-Julian Oscillation (MJO) index can be interpret?
Let's suppose I have got an MJO index value of 0.6 in a given day, what this does mean?
Does 0.6 represents a weak MJO?
Data from https://www.esrl.noaa.gov/psd/mjo/mjoindex/ Thanks
$\begingroup$
$\endgroup$
Add a comment
|
$\begingroup$
$\endgroup$
2
I prefer to use the BOM MJO index and the explanation provided over there -
When the index is within the centre circle the MJO is considered weak, meaning it is difficult to discern using the RMM methods. Outside of this circle the index is stronger and will usually move in an anti-clockwise direction as the MJO moves from west to east. For convenience, we define 8 different MJO phases in this diagram.
So in your case your signal value is 0.6 and that means it is fairly weak in amplitude as it is inside the circle. You also need to mention the phase of the MJO phase diagram. There are eight phases
Phase 1 & 8 - Western Hemisphere And Africa
Phase 2 & 3 - Indian Ocean
Phase 4 & 5 - Maritime Continent
Phase 6 & 7 - Western Pacific.
Currently the signal is a weak one as seen in this phase diagram MJO Phase diagram
When the MJO signal is strong it's amplitude will be greater than 1 and the contour line will be outside the circle. It should be noted that the MJO is an empircal index consisting of the 850 hPa winds, OLR and 200 hPa winds.
MJO passage through phase 6 and 7 is always of global interest as the impact can be of planetary scale. Usually El Ninos are preceded by Westerly Wind Bursts and the forcing factor can be a MJO passage through phase 6 and 7.
One can look at the raw data of the signal here - RMM Index text. This provides the amplitude of the signal as well as the phase of the MJO.
Another version of the same can be seen here - MJO RMM index
-
$\begingroup$ thank you. what if I will need the MJO monthly averages? can I just average the daily MJO amplitude within each month? and how can I assign an average value to the monthly phase? $\endgroup$ – aaaaa Apr 3 '19 at 15:37
-
1$\begingroup$ @aaaaa A climatological value of the MJO index only has meaning by counting the number of days it takes to come back to the same point. So monthly values may not be of significance. Because the number of days it takes to return to the same point varies you can track that rather than monthly averages. Take a look at this paper - journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-14-00744.1 $\endgroup$ – gansub Apr 3 '19 at 15:46
