How the Tropics Induce Major Pattern Changes in the Midlatitudes

[CoastalWx]

Qvector, where did that chart come from? Is that chart specific for one season?

[QVectorman]

Qvector, where did that chart come from? Is that chart specific for one season?

http://www.nature.com/nature/journal/v455/n7212/fig_tab/nature07286_F3.html

He doesn't say, at least what I could read. Wes has pretty much the same chart in the -NAO thread from a month ago. But I believe this is not specific for one season.

[CoastalWx]

http://www.nature.co...re07286_F3.html

He doesn't say, at least what I could read. Wes has pretty much the same chart in the -NAO thread from a month ago. But I believe this is not specific for one season.

Ok cool. The reason why I ask, is because different seasons have different wavelengths which may affect how the hemispheric pattern looks. It's still a good chart though. Thanks for posting.

[QVectorman]

Yea, that's why I actually prefer composites done by individual months. I would be interested to see if there is a difference in composites if you break them down into Nino/nina episodes.

[phil882]

Time to bump this thread... The MJO is still quite alive and kicking... while also having some rather substancial impacts on the forecast. I want to elaborate further that sometimes the MJO signal is masked if you merely look at OLR alone, and how the much relied on plots of RMM can sometimes be misleading.

First lets look at the current CPC RMM plots for the MJO.

So great we just got into phase one with a significant amplitude, which is typically a configuration that favors cold in the Eastern United States and has a significance of about 50% along the east coast. However, this plot makes it look like the MJO has weakened with a lesser amplitude as compared to last week. With respect to the OLR this may be true, but lets look at another RMM plot that substitutes 200 hPa velocity potential as opposed to OLR

Wow big difference right? Notice how much stronger the MJO's amplitude was in phases 8 and 1, and now the MJO has already progressed into phase 2! Much of this contribution can be attributed to using the 200 hPa velocity potential as opposed to the OLR

So thats great and all, but what is the significance. Well as it turns out, the Central and East Pacific are very cold SST wise, which tends to suppress convection. Despite this, the MJO signal in the upper levels of the atmosphere, in particular using 200 hPa zonal winds and 200 hPa Velocity Potential have continued to show robust propagation of the MJO. For instance here are the 200 hPa zonal winds from 5S to 5N.

The diagram above illustrates that there is still plenty of divergence occurring at the 200 hPa level. This divergence would still aid in the ridge building process given that divergence aloft supports rising motion through the column of the atmosphere, despite the lack of convection. Thus, you would expect to see some enhanced ridging response in the mid-latitudes.

Interestingly, we don't see these same ridge anomalies in the low latitudes near the equator. It appears over the next 5-7 days there will also feature a series of cutoff 500 hPa lows that will sit and spin near Hawaii. As mid-latitude storm systems parade across the Pacific, this upper level low will as a bump in the road, forcing anti-cyclonic wave breaking. As this occurs, the subtropical ridge in the East Pacific will become displaced further north than usual, which results in the height anomalies you can see above. There is actually a lot more going on than just that, and I think I'm going to make a new thread that is highlighting the ridge building occurring over the East Pacific, because it has direct ramifications on what happens with the potential east coast snowstorm coming this weekend. Stay tuned folks!

[DaculaWeather]

Good stuff Phil! Thanks!

[WestMichigan]

Great read, keep up the informative posts.