MJO Questions

[Alpha5]

I understand the basics of the MJO.....you have convection over certain areas of the tropics which consequently alters some of the north american telleconnections and alters the weather here in the US. I understand how a nina usually kills convection over some areas and consequently, the MJO is affected by the ENSO.

That being said, I have a few questions.

1) Could someone post a map that shows what geographic areas correspond to the specific MJO regions

2) How specifically does convection in lower latitudes affect north american weather

Thanks

[kylemacr]

You are correct that the MJO is essentially a blob, or "envelope" of convection that circumnavigates the Equator. A well-known paper in 2004 by Matt Wheeler and Harry Hendon from the Australian Bureau of Meteorology came up with a fancy and now often used method of tracking the MJO. Their approach splits the MJO into 8 phases which begin over Africa and move eastward.

Here's a look at the phase space, which labels the geographic areas of each phase... this is recent as of today, by the way.

Note that right now, the blue line ends in Phase 3, which implies that the MJO is somewhere over the Indian Ocean, entering the Maritime Continent area. The circle corresponds to an MJO amplitude of 1. Anything less than 1 (inside circle) is often considered to be "inactive", but this is a rather arbitrary distinction, there's nothing very special about the value of "1".

As the MJO propagates around the Equator, it generates Rossby wave trains. This is mainly due to the diabatic heating and latent heat release from the convection (see the Latent Heat thread earlier in this forum). Under normal conditions (especially during Northern Hemisphere winter) there is a fairly strong jet stream over the CPAC. The convection from the MJO creates an anticyclone (high) just to the NW of maximum convection (famous result known as the Gill or Matsuno-Gill model). This anticyclonic flow can enhance the jet, which has strong implications for midlatitude weather. Below, I've attached a map showing the average jet location during DJF over many years. You can imagine that changing this jet can have strong implications on the midlatitude weather. Also, if you enhance the jet, you will affect teleconnections such as the AO, which is really just a measure of the strength of the polar jet.

As far as the MJO and ENSO, it's very possible that the MJO is an important component of ENSO. In a neutral ENSO state, the warmest water is in the Central Pacific (CPAC). The MJO, which has strong westerly winds associated with it, can provide what are called "westerly wind bursts" (WWBs). These WWBs enact stress on the ocean surface which may, in a sense, move the warm water east. Even more important is that these WWBs are a likely cause of oceanic Kelvin waves which have been associated with ENSO. If warm water from the CPAC moves east, the SST anomalies will be positive (warm water in an area where the isn't usually warm water) and that's the common signature of El Nino.

Hopefully this helps a bit! This was mostly a steam of consciousness, so please let me know if I don't make much sense.

By the way, a superb paper summarizing the MJO is found here http://metofis.rsmas...ions/MJOrev.pdf by Chidong Zhang from U. Miami.

Here's a real map that shows the phases geographically instead of in a phase space. The shaded areas are OLR anomalies, and cold colors represent active convection (active MJO).

[Alpha5]

Wow, very very informative post. Thank you for explaining that to me.

It seems that each MJO phase is really concentrated near the Indian Ocean, I always though that the phases extended around the world...guess not.

thanks again

[Metsfan]

Can someone explain why we need a phase 8 of the MJO

[am19psu]

Can someone explain why we need a phase 8 of the MJO

Short explanation: Phase 8 teleconnects to a ridge over the Rockies, which given the usual wavelengths, provides a storm track up the Eastern Seaboard and enhances the chances of a major EC snowstorm.

[QVectorman]

Found these a few months ago in my search for more info on the MJO

This page is a nice real time view to follow the MJO and other equatorial waves.

http://www.atmos.alb...olr_global.html

A snap shot of it's maps

[kylemacr]

Also, part of the reason we have a Phase 8 is simply because of how the analysis is set up. The MJO signal (at least its convection signal) is weakens a lot when it gets over the East Pacific. Sometimes the circulation signal continues over South America and the Atlantic.

But, the Wheeler Hendon phase space uses information about the convection and zonal winds at low (850 mb) and upper (200 mb) winds to create that diagram you see. If the circulation component of the signal is strong over the EPAC/Atlantic, it will still show up in the phase space. The results of their EOF analysis gives 2 principal components which must be orthogonal to each other and therefore they *must* create a circular phase space... there is no way that the results of the analysis can *not* go in a circle. Therefore, there has to be a Phase 8.

Perhaps the best way to think of it is like this. The Wheeler Hendon phase space shows MJO space. MJO space is, more or less, Africa to the end of the East Pacific. We take MJO space and try to assign it real geographic significance. Because "MJO space" ends in the EPAC the circular motion connects to the beginning of MJO space (Africa) and when translated to Earth space, it looks like EPAC connects to Africa.

Does that maybe make any sense?

[PottercountyWXobserver]

What phases 1-8 are the best for big storms east of the Mississippi and what phases are the worst ie Torch weather. I guess what I'm asking is a ranking

A 8?

B

C

D

E

F

G

H

I'm assuming phase 8 is the best but then rank from greatest to least if you can. Also can other phenomenons over power the MJO signals? And what site can I go to that has the MJO predictions?

[am19psu]

What phases 1-8 are the best for big storms east of the Mississippi and what phases are the worst ie Torch weather. I guess what I'm asking is a ranking

I'm assuming phase 8 is the best but then rank from greatest to least if you can. Also can other phenomenons over power the MJO signals? And what site can I go to that has the MJO predictions?

I'm assuming you mean for winter, since the response changes based on the season (due to the changing wavelengths of planetary waves)?

7-8-1 are the best for ridging on/near the West Coast, which allows troughs to amplify in the in the Eastern half. 3-4-5-6 are the torchy phases, as they tend to produce troughing in the west and ridging in the east.

Lots of other things can over power the MJO signals when the MJO is weak. I'd argue it is the single biggest forcer of the mid-latitude weather when the amplitude is high, though.

http://www.cpc.ncep....k/MJO/mjo.shtml

[famartin]

Also, part of the reason we have a Phase 8 is simply because of how the analysis is set up. The MJO signal (at least its convection signal) is weakens a lot when it gets over the East Pacific. Sometimes the circulation signal continues over South America and the Atlantic.

But, the Wheeler Hendon phase space uses information about the convection and zonal winds at low (850 mb) and upper (200 mb) winds to create that diagram you see. If the circulation component of the signal is strong over the EPAC/Atlantic, it will still show up in the phase space. The results of their EOF analysis gives 2 principal components which must be orthogonal to each other and therefore they *must* create a circular phase space... there is no way that the results of the analysis can *not* go in a circle. Therefore, there has to be a Phase 8.

Perhaps the best way to think of it is like this. The Wheeler Hendon phase space shows MJO space. MJO space is, more or less, Africa to the end of the East Pacific. We take MJO space and try to assign it real geographic significance. Because "MJO space" ends in the EPAC the circular motion connects to the beginning of MJO space (Africa) and when translated to Earth space, it looks like EPAC connects to Africa.

Does that maybe make any sense?

I think his question flew under you. IOW, he wanted to know "why we need a phase 8 to get snowstorms". I say "under" because obviously you know way more about this than I do.

[kylemacr]

I think his question flew under you. IOW, he wanted to know "why we need a phase 8 to get snowstorms". I say "under" because obviously you know way more about this than I do.

oh, wow, oops! my bad!

[usedtobe]

Also, part of the reason we have a Phase 8 is simply because of how the analysis is set up. The MJO signal (at least its convection signal) is weakens a lot when it gets over the East Pacific. Sometimes the circulation signal continues over South America and the Atlantic.

But, the Wheeler Hendon phase space uses information about the convection and zonal winds at low (850 mb) and upper (200 mb) winds to create that diagram you see. If the circulation component of the signal is strong over the EPAC/Atlantic, it will still show up in the phase space. The results of their EOF analysis gives 2 principal components which must be orthogonal to each other and therefore they *must* create a circular phase space... there is no way that the results of the analysis can *not* go in a circle. Therefore, there has to be a Phase 8.

Perhaps the best way to think of it is like this. The Wheeler Hendon phase space shows MJO space. MJO space is, more or less, Africa to the end of the East Pacific. We take MJO space and try to assign it real geographic significance. Because "MJO space" ends in the EPAC the circular motion connects to the beginning of MJO space (Africa) and when translated to Earth space, it looks like EPAC connects to Africa.

Does that maybe make any sense?

I'd extend your answer a little that when the convection gets to phase 8 and the signal on the wheeler diagram moves into phases 1 and 2, you tend to have a greater chance to have the NAO to go negative. At least that's always been my limited take on the subject.

Intraseasonal interaction between the Madden–Julian Oscillation and the North Atlantic Oscillation

Christophe Cassou¹

1. CNRS-Cerfacs, Global Change and Climate Modelling project, 42 Avenue G. Coriolis, 31057 Toulouse, France
   

Correspondence to: Christophe Cassou¹ Correspondence and requests for materials should be addressed to C.C. (Email: [email protected]).

Top of page

Abstract

Bridging the traditional gap between the spatio-temporal scales of weather and climate is a significant challenge facing the atmospheric community. In particular, progress in both medium-range and seasonal-to-interannual climate prediction relies on our understanding of recurrent weather patterns and the identification of specific causes responsible for their favoured occurrence, persistence or transition. Within this framework, I here present evidence that the main climate intra-seasonal oscillation in the tropics—the Madden–Julian Oscillation^{1, 2} (MJO)—controls part of the distribution and sequences of the four daily weather regimes defined over the North Atlantic–European region in winter³. North Atlantic Oscillation⁴ (NAO) regimes are the most affected, allowing for medium-range predictability of their phase far exceeding the limit of around one week that is usually quoted. The tropical–extratropical lagged relationship is asymmetrical. Positive NAO events mostly respond to a mid-latitude low-frequency wave train initiated by the MJO in the western–central tropical Pacific and propagating eastwards. Precursors for negative NAO events are found in the eastern tropical Pacific–western Atlantic, leading to changes along the North Atlantic storm track. Wave-breaking diagnostics tend to support the MJO preconditioning and the role of transient eddies in setting the phase of the NAO. I present a simple statistical model to quantitatively assess the potential predictability of the daily NAO index or the sign of the NAO regimes when they occur. Forecasts are successful in ~70 per cent of the cases based on the knowledge of the previous ~12-day MJO phase used as a predictor. This promising skill could be of importance considering the tight link⁴ between weather regimes and both mean conditions and the chances of extreme events occurring over Europe. These findings are useful for further stressing the need to better simulate and forecast the tropical coupled ocean–atmosphere dynamics, which is a source of medium-to-long range predictability and is the Achilles’ heel of the current seamless prediction suites^{5, 6, 7}.

http://www.nature.com/nature/journal/v455/n7212/full/nature07286.html

[winterymix]

Simple questions for meteorologists here;

1. for this particular La Nina dominated season, will the Wheeler & Hendon chart repeated walk itself toward the

center during phases 7 and 8 and balloon outward from the center for phases 3 through 7?

2. Will the number of days to complete a full cycle tend to remain about the same throughout a single entire (NH) winter?

[usedtobe]

Simple questions for meteorologists here;

1. for this particular La Nina dominated season, will the Wheeler & Hendon chart repeated walk itself toward the

center during phases 7 and 8 and balloon outward from the center for phases 3 through 7?

2. Will the number of days to complete a full cycle tend to remain about the same throughout a single entire (NH) winter?

The MJO varies signficantly based on the ENSO signal. It is most active during enso neutral year and when the la nina or el nino is weak. When either is strong, the enso signal often overwhelms the MJO convection.

[Alpha5]

Bumping this for another question.

Looking at the charts off Raleighwx's site, here is the phase 8 H5 composite map.

Now, a map posted earlier shows that phase 8 corresponds to enhanced convection over the dateline. How does this create such an anomalous area of lower heights over the Aleutians?

Thanks

[usedtobe]

There are two threads discussion what you asked.

and this

one

[Alpha5]

There are two threads discussion what you asked.

http://www.americanw...e-midlatitudes/ and this

one

http://www.americanw...on/page__st__35

Thanks Wes, much appreciated.

[frostfern]

Wow, very very informative post. Thank you for explaining that to me.

It seems that each MJO phase is really concentrated near the Indian Ocean, I always though that the phases extended around the world...guess not.

thanks again

I think it's important to point out that the WH MJO phases do not correspond to equally spaced locations around the globe. This is because the WH phase is built from the projection of the current pattern onto two primary "orthogonal" modes based on something called "principle component analysis". In simpler terms it's determined based on some statistical massaging and the location labels can be misleading.

A related issue is the fact that the MJO is not a purely linear phenomenon. The high precipitation anomalies tend to initiate over Africa or the eastern Indian Ocean and progress slowly eastward across Indonesia into the Western Pacific. It isn't necessarily a smooth motion either as it tends to move east in lurches accompanied by bursts of anomalous westerly wind directly over or just to either side (north/south) of the equator. Then the anomaly tends to speed up and become much less distinct over the Eastern Pacific and Atlantic basins. The bottom line is the WH phase doesn't capture all the complexities of the MJO.