QBO Relationship to Atlantic Tropical Activity

[OKpowdah]

I talked about messing around with this before. I have defined a QBO phase space which relates much better to the true stage of the oscillation.

 

Here I've related the phase to Atlantic ACE, filtered by climatology. Notice the two very distinct peaks ... one around -90 (easterly QBO max) and one around +90 (westerly QBO max)

 

So Atlantic tropical activity may have a strong link to the QBO. Up until now, correlations have only been calculated using the QBO index ... which return very weak results due to these two peaks in opposite stages of the oscillations. This is an excellent display of why this measure of the QBO is much better / more useful

 

[wxmeddler]

Holy correlation Batman! Great work Sam!

[am19psu]

This is great work, Sam. Are you going to write a paper on it?

[icebreaker5221]

Wow, very nice find!  I agree with Adam, you should write this up. 

 

Have you looked into any other basins yet?

[andyhb]

Good stuff here, definitely grounds for a paper.

[turtlehurricane]

One thing to be careful of is the fact that most of the time we're either in an easterly or westerly QBO phase, with the least amount of time spent in transition, so most of the ACE will occur during an easterly or westerly phase just by default. I fear the graph is just showing the sinusoidal nature of the QBO itself, unless you accounted for that somehow.

 

The difference in height between the peaks is interesting though, you have proven once again that the westerly phase is more favorable than the easterly phase, as detailed in Gray 1984.

[OKpowdah]

One thing to be careful of is the fact that most of the time we're either in an easterly or westerly QBO phase, with the least amount of time spent in transition, so most of the ACE will occur during an easterly or westerly phase just by default. I fear the graph is just showing the sinusoidal nature of the QBO itself, unless you accounted for that somehow.

 

The difference in height between the peaks is interesting though, you have proven once again that the westerly phase is more favorable than the easterly phase, as detailed in Gray 1984.

 

Great point. The way I defined the phases eliminates this characteristic of the oscillation ... It's not just calculated by the derivative of the QBO sine wave. It incorporates the 50mb wind to quantify the shear between QBO regimes which has the same "residence time" as the QBO stages themselves.

 

So the phases I use have much more even residence time. And then finally I did account for the minor differences that remained by applying a weighting.

 

I should mention I also filtered out variations due to the AMO. It didn't result in any changes in the distribution though.

 

I was expecting the distribution to lean more toward the westerly QBO stage. There's excellent support based on this relationship I found to the tropopause pressure. By the thermal wind balance, during the westerly QBO stage (+90 phase) the stratosphere is warmer over the equator and cold just off the equator, leading to a higher tropopause which would support deeper convection. 

 

The peak in the easterly QBO regime was more of a surprise. Something to look into some more.

 

Thanks everyone! I'm working on it alongside my masters/PhD thesis right now. There's some extra funding floating around that I could use to support this project on the side too. We'll see

[turtlehurricane]

So by weighting you mean you actually divided the ACE in each bin by the number of years in each bin? You want the average ACE for each bin to prevent biasing the results towards the phases that occurred more frequently. BTW, the QBO shear follows the same sinusoidal pattern as the QBO index itself.

 

And yup, calculating the shear is the way to go. I did the same thing for a class project, used the 30 mb - 50 mb wind shear as an index, since it's directly related to the secondary circulation associated with the thermal anomaly according to the thermal wind law. I also found an easterly QBO to be favorable (but not as favorable as your graph implies), I think it has something to do with rising motion along the equatorial tropopause during the easterly QBO, leading to higher tropopause heights and deeper convection.

[OKpowdah]

So by weighting you mean you actually divided the ACE in each bin by the number of years in each bin? You want the average ACE for each bin to prevent biasing the results towards the phases that occurred more frequently. BTW, the QBO shear follows the same sinusoidal pattern as the QBO index itself.

 

And yup, calculating the shear is the way to go. I did the same thing for a class project, used the 30 mb - 50 mb wind shear as an index, since it's directly related to the secondary circulation associated with the thermal anomaly according to the thermal wind law. I also found an easterly QBO to be favorable (but not as favorable as your graph implies), I think it has something to do with rising motion along the equatorial tropopause during the easterly QBO, leading to higher tropopause heights and deeper convection.

 

Essentially, yes. It's a little more involved than that. I apply a barnes-like interpolation to the monthly data, and use the weight that is produced from that calculation as a representation of the residence time of a certain phase.

 

Exactly, the QBO shear follows the same sinusoidal pattern as the QBO, which means that by incorporating it, I was able to develop a 2D phase space with more evenly-weighted phases, as the residence time of the shear antinodes balances the residence time of the absolute QBO antinodes.

 

The I have with the easterly QBO, is that while the thermal wind balance dictates a raised tropopause over the equator, the trop is lowered just off the equator (over the MDR) ...which is conveniently confirmed with this method. One possibility that I found is a zonally overturning circulation related to the phase (i.e. modulating the MJO), that happens to be supportive of upper level divergence over the Atlantic in the easterly phase. Will be interesting to examine other basins.

[OKpowdah]

As a follow up to this, that helps remove any uncertainty people may have about the relative frequency of each phase, here's a contingency table for each of these phases and the categories of monthly ACE during ASO, below (<33%), normal (33%-67%), and above (>67%).

 

This is pretty convincing for me and pretty exciting to see!!

 

[OKpowdah]

Wanted to throw this plot up here also. 

 

This is upper level (.21 sigma) velocity potential by MQI phase and longitude. 

 

Very strong signal, and interestingly a longitudinal progression between phases 90 and 210. Also, notice that a divergent regime (albeit weak) moves into the Atlantic around phase 270 ... in theory would support some increase in tropical activity, and be at least some support for that max in the easterly phase of the QBO.

 

[OKpowdah]

Same plot for OLR near the equator ... there is some signal of a relationship to ENSO that I'm trying to pull out. Tough to be confident because of the overlap in the QBO and ENSO frequency power spectra.

 

[HM]

Sam, awesome stuff! The 330-60 signal for Central Pacific divergence at 0.21 sigma level and -OLR anomalies suggests a possible ENSO connection for sure. This would essentially be the time the easterly shear stress was in the process of reaching and peaking in the lower stratosphere, correct?

 

Makes sense....

 

Obviously not the only factor but shows the signal well.

[OKpowdah]

Sam, awesome stuff! The 330-60 signal for Central Pacific divergence at 0.21 sigma level and -OLR anomalies suggests a possible ENSO connection for sure. This would essentially be the time the easterly shear stress was in the process of reaching and peaking in the lower stratosphere, correct?

 

Makes sense....

 

Obviously not the only factor but shows the signal well.

 

Thanks man! Yeah the 330-60 phase is right around the easterly shear peaking in the lower stratosphere.

 

Definitely stuff I want to explore more. Some signal there for sure.

[OKpowdah]

Just slapped this one together. It's TC density in the Atlantic from 1979 to the present (simply based on 6 hourly obs interpolated to a one degree grid using Barnes weighting). The first frame is all TCs ... the frames after that have each TC ob weighted by the particular MQI phase weight for that month.

 

I plan to compare the phases more effectively by scaling them based on all TCs. And also weight by intensity .. All coming soon..

 

[OKpowdah]

Here is the TC density standardized anomaly. Can notice some distinct predominant track regimes by phase

 

[Ground Scouring]

Here is the TC density standardized anomaly. Can notice some distinct predominant track regimes by phase

Given the expected phase 60 this year, the MQI chart suggests that this phase features one of the greatest concentrations of tracks at sea. That would suggest, on the whole, a rather "fishy" year again, aside from an increased Gulf threat. The southern two-thirds of FL have not had a high concentration of intense landfalls since the mid-1960s, excluding 1992, 2004, and 2005.

[Ground Scouring]

Andrea seems to have followed one of the MQI clusters for Phase 60 rather...well. Let's see how the rest of the year's tracks compare to the Phase-60 storm clusters.

 

[andyhb]

Given the expected phase 60 this year, the MQI chart suggests that this phase features one of the greatest concentrations of tracks at sea. That would suggest, on the whole, a rather "fishy" year again, aside from an increased Gulf threat. The southern two-thirds of FL have not had a high concentration of intense landfalls since the mid-1960s, excluding 1992, 2004, and 2005.

 

It also has a decent clustering in the MDR/Caribbean as well, which would potentially suggest a few long-tracked cyclones may be favored, as well as more home grown potential.

[Ground Scouring]

It also has a decent in the MDR/Caribbean as well, which would potentially suggest a few long-tracked cyclones may be favored, as well as more home grown potential.

By the way, check out the overlay that I posted above...Andrea's track seems to be an interesting coincidence in light of the MQI chart for this season, which is in Phase 60.

 

A question for Sam: what were the years which you used to compile your Phase-60 MQI chart? In other words, which Atlantic seasons were also in Phase 60?

[OKpowdah]

By the way, check out the overlay that I posted above...Andrea's track seems to be an interesting coincidence in light of the MQI chart for this season, which is in Phase 60.

 

A question for Sam: what were the years which you used to compile your Phase-60 MQI chart? In other words, which Atlantic seasons were also in Phase 60?

 

Thanks for the overlay man. We got our first Gulf to SE coast rider of the year.

 

So all phases were using data from 1979 to the present (satellite era, and available data for stratospheric winds). Each month in this period is then weighted based on it's actual calculated phase (i.e. for phase 60, a month with a phase of 52.6 has a higher weight than a month with a phase of 31.9). Each TC data point in HURDAT then gets two weights applied: the Barnes interpolation to a 1 deg grid, and the phase weight.

 

I can tell you that there are 59 individual TCs that contribute some level of weight on the phase 60 map

[jordanwx]

Wanted to throw this plot up here also. 

 

This is upper level (.21 sigma) velocity potential by MQI phase and longitude. 

 

Very strong signal, and interestingly a longitudinal progression between phases 90 and 210. Also, notice that a divergent regime (albeit weak) moves into the Atlantic around phase 270 ... in theory would support some increase in tropical activity, and be at least some support for that max in the easterly phase of the QBO.

 

tropicvelpot.png

Could you restrict this domain to the Atlantic basin for us? Isn't really representative of conditions over the Atlantic when you are defining the region as the entire tropics (23.5S to 23.N).

 

Also, I see the peak for ACE is highest when we are centered on the westerly phase. However, if you were to integrate the area within say 45 degrees of each phase (e.g. -45 to -135 and +45 to +135) it appears that the easterly is actually more favorable overall. I know the QBO usually is in on one phase or the other during hurricane season, but is it directly on that phase (-90 or +90) throughout the entire season? I would think not. Which to me means that as a whole, the easterly, not the westerly, phase is more favorable. Or perhaps a better interpretation is neither phase is more favorable than the other, unless you are directly centered on the westerly phase.

 

 

Finally, on your blog you posted the image of TC count vs MQI phase. On that chart it appears the easterly phase is more favorable. Also, ACE>100kt is higher for the easterly phase. Sounds like the QBO has some regional effects though distinguishing those effects is not very easy. But, if I were to make some assumptions, it sounds like long track CV storms are more favorable during the westerly phase, Caribbean developments seem more likely in the easterly phase. This would explain the stronger storms in the easterly phase as well as the higher ACE during the westerly phase.

 

EDIT.

Few more questions, what time period (years) is used for this? What months are being used also (entire calendar year or just hurricane season)?

[Mike.Ventrice]

Hi guys,

 

I noticed we are currently in a transitional QBO phase- from easterlies to westerlies at 50 hPa. Any sort of teleconnection that is useful here? Last time this happened was late 2010!

 

[Ground Scouring]

Could you restrict this domain to the Atlantic basin for us? Isn't really representative of conditions over the Atlantic when you are defining the region as the entire tropics (23.5S to 23.N).

 

Also, I see the peak for ACE is highest when we are centered on the westerly phase. However, if you were to integrate the area within say 45 degrees of each phase (e.g. -45 to -135 and +45 to +135) it appears that the easterly is actually more favorable overall. I know the QBO usually is in on one phase or the other during hurricane season, but is it directly on that phase (-90 or +90) throughout the entire season? I would think not. Which to me means that as a whole, the easterly, not the westerly, phase is more favorable. Or perhaps a better interpretation is neither phase is more favorable than the other, unless you are directly centered on the westerly phase.

 

 

Finally, on your blog you posted the image of TC count vs MQI phase. On that chart it appears the easterly phase is more favorable. Also, ACE>100kt is higher for the easterly phase. Sounds like the QBO has some regional effects though distinguishing those effects is not very easy. But, if I were to make some assumptions, it sounds like long track CV storms are more favorable during the westerly phase, Caribbean developments seem more likely in the easterly phase. This would explain the stronger storms in the easterly phase as well as the higher ACE during the westerly phase.

 

EDIT.

Few more questions, what time period (years) is used for this? What months are being used also (entire calendar year or just hurricane season)?

Good questions...bump for Sam.

[OKpowdah]

Could you restrict this domain to the Atlantic basin for us? Isn't really representative of conditions over the Atlantic when you are defining the region as the entire tropics (23.5S to 23.N).

 

Velocity potential is generally symmetric about the equator with the maximum amplitude in the tropics. How the velocity potential varies with time (phase) is mostly a function of longitude. The tropics latitude band is thus the best representation of its variability. It is representative of conditions over the Atlantic because of its symmetry.

 

 

Also, I see the peak for ACE is highest when we are centered on the westerly phase. However, if you were to integrate the area within say 45 degrees of each phase (e.g. -45 to -135 and +45 to +135) it appears that the easterly is actually more favorable overall. I know the QBO usually is in on one phase or the other during hurricane season, but is it directly on that phase (-90 or +90) throughout the entire season? I would think not. Which to me means that as a whole, the easterly, not the westerly, phase is more favorable. Or perhaps a better interpretation is neither phase is more favorable than the other, unless you are directly centered on the westerly phase.

 

1) For each particular phase, I used a weighting function that actually incorporates months +/-40 degrees from the phase of interest, so there's some representation of the "season" around a particular phase.

 

2) Since this calculation incorporates a range of months, it's not necessarily supposed to be a gauge for a complete hurricane season. It's an indication of the "bias" of TC activity for a given month.

 

I understand what you're saying though. Honestly, to tell you the truth, I don't care which is more active W/E, just that they are relative maxima.

 

 

 

Finally, on your blog you posted the image of TC count vs MQI phase. On that chart it appears the easterly phase is more favorable. Also, ACE>100kt is higher for the easterly phase. Sounds like the QBO has some regional effects though distinguishing those effects is not very easy. But, if I were to make some assumptions, it sounds like long track CV storms are more favorable during the westerly phase, Caribbean developments seem more likely in the easterly phase. This would explain the stronger storms in the easterly phase as well as the higher ACE during the westerly phase.

 

Not sure what you're asking, but the track density maps give an indication of predominant tracks fairly well. I have one with track trajectory vectors overlaid also. Just haven't gotten around to posting it.

 

 

Few more questions, what time period (years) is used for this? What months are being used also (entire calendar year or just hurricane season)?

 

1979-2012. For the TC activity by month, I used the months of the hurricane season. For the track density maps, I used all storms (ranged between 20 to 80 storms for each phase).

[jordanwx]

Velocity potential is generally symmetric about the equator with the maximum amplitude in the tropics. How the velocity potential varies with time (phase) is mostly a function of longitude. The tropics latitude band is thus the best representation of its variability. It is representative of conditions over the Atlantic because of its symmetry.

 

 

1) For each particular phase, I used a weighting function that actually incorporates months +/-40 degrees from the phase of interest, so there's some representation of the "season" around a particular phase.

 

2) Since this calculation incorporates a range of months, it's not necessarily supposed to be a gauge for a complete hurricane season. It's an indication of the "bias" of TC activity for a given month.

 

I understand what you're saying though. Honestly, to tell you the truth, I don't care which is more active W/E, just that they are relative maxima.

 

 

Not sure what you're asking, but the track density maps give an indication of predominant tracks fairly well. I have one with track trajectory vectors overlaid also. Just haven't gotten around to posting it.

 

 

1979-2012. For the TC activity by month, I used the months of the hurricane season. For the track density maps, I used all storms (ranged between 20 to 80 storms for each phase).

Thanks for the response.

 

So the phase is already being averaged by +/-40 degrees in those first charts at the top of ACE and storm count with MQI phase...westerly would have to be slightly more favorable then.

 

Also, please do post the track trajectory vectors plot too, would love to see that.

[OKpowdah]

Thanks for the response.

 

So the phase is already being averaged by +/-40 degrees in those first charts at the top of ACE and storm count with MQI phase...westerly would have to be slightly more favorable then.

 

Also, please do post the track trajectory vectors plot too, would love to see that.

 

Here's what the weight function looks like. Excuse the dark background: taken off a presentation I gave a few weeks ago.

 

 

Here is the track trajectory plot. ... I really need to get around to coding the vectors as white lol just lazy on my part

 

[jordanwx]

Here's what the weight function looks like. Excuse the dark background: taken off a presentation I gave a few weeks ago.

 

mqiweights.png

 

Here is the track trajectory plot. ... I really need to get around to coding the vectors as white lol just lazy on my part

 

tc3stanomtrack.gif

Awesome. Thanks

[OKpowdah]

Awesome work Mike! The only thing I would alter is instead of looking at the wind as a function of longitude, average them zonally and look at a function of latitude, maybe 20S-20N.

 

Anyway, cool stuff!

[OKpowdah]

Full EOFs using zonally averaged 10, 20, 30, 50, and 70mb level zonal wind.