MJO in Jan.: KATL day by day temp. anom.'s by phase since 1975

[GaWx]

 I just completed an analysis of the temp. anomalies for KATL for Jan. 1975-2014 for each of MJO phases 6-8 (amplitude >1):

 

6: 114 total days: MB: 23; B: 14; N: 22; A: 18; MA: 37; AVG: +222/114 = +1.9
7: 131 total days: MB: 26; B: 24; N: 29; A: 22; MA: 30; AVG: +36/131 = +0.3
8: 115 total days: MB: 26; B: 24; N: 24; A: 14; MA: 27; AVG: +24/115 = +0.2

 

MB/MA -8-/+8+; B/A: -7 to -3/+7 to +3; N: -2 to +2

 

Though phase 6 looks ok, I had expected phases 7 and 8 to average cooler than near normal.

 

 I now feel the need to do the other five phases ASAP and I may end up also doing the COD afterward. I really want to find the true colder than normal MJO phases for January!

[dsaur]

Well, if you consider much below to be indicative of what everyone seems to think causes snow, then it appears the phase doesn't matter Of the ones above....give or take up to 19 extra days.   My guess is most of our frozen occurs with it about normal, or a bit below.  Certainly not during much below outbreaks.  But I have been wrong before...and I'm sure you'll quickly correct me if I am again, lol.  T

[Webberweather53]

 I just completed an analysis of the temp. anomalies for KATL for Jan. 1975-2014 for each of MJO phases 6-8 (amplitude >1):

 

Phase 6: 117 total days: MB: 24; B: 15; N: 22; A: 19; MA: 37; AVG: +229/117 = +2.0

Phase 7: 129 total days: MB: 26; B: 24; N: 29; A: 22; MA: 28; AVG: +6/129 = 0.0

Phase 8: 110 total days: MB: 25; B: 22; N: 22; A: 13; MA: 28; AVG: +49/110 = +0.4

 

MB/MA -8-/+8+; B/A: -7 to -3/+7 to +3; N: -2 to +2

 

Though phase 6 looks ok, I had expected phases 7 and 8 to average cooler than near normal.

 

 I now feel the need to do the other five phases ASAP and I may end up also doing the COD afterward. I really want to find the true colder than normal MJO phases for January!

 

I would strongly suggest stratifying by ENSO phase, sure the sample size will shrink, but ENSO plays a huge role on how the atmosphere modifies the intraseasonal signals imparted by the MJO

[GaWx]

I would strongly suggest stratifying by ENSO phase, sure the sample size will shrink, but ENSO plays a huge role on how the atmosphere modifies the intraseasonal signals imparted by the MJO

 

 Webber,

 I will probably look at stratifying by ENSO phase later. In the meantime, I want to continue to look at each MJO phase unstratified because supposedly each phase overall has certain tendencies temperaturewise (i.e., regardless of ENSO) as the 500 mb maps for Jan phases 6-8 of Allan's that you posted suggest. I'm quite surprised that phase 8 has averaged near normal at KATL in Jan. when considering the solid +PNA shown for phase 8 in Allan's map. Can you explain this? The only thing I can think of is that I considered only amp. >1. Then again, why would those in phase 8 with amp <1 be so much colder than phase 8 with amp >1? That sould be counterintuitive to me.

[GaWx]

Well, if you consider much below to be indicative of what everyone seems to think causes snow, then it appears the phase doesn't matter Of the ones above....give or take up to 19 extra days.   My guess is most of our frozen occurs with it about normal, or a bit below.  Certainly not during much below outbreaks.  But I have been wrong before...and I'm sure you'll quickly correct me if I am again, lol.  T

 

Tony,

 I'd say that most of ATL's wintry precip. occurs with that day's avg. temp. much below or below normal.

[Webberweather53]

 Webber,

 I will probably look at stratifying by ENSO phase later. In the meantime, I want to continue to look at each MJO phase unstratified because supposedly each phase overall has certain tendencies temperaturewise (i.e., regardless of ENSO) as the 500 mb maps for Jan phases 6-8 of Allan's that you posted suggest. I'm quite surprised that phase 8 has averaged near normal at KATL in Jan. when considering the solid +PNA shown for phase 8 in Allan's map. Can you explain this? The only thing I can think of is that I considered only amp. >1. Then again, why would those in phase 8 with amp <1 be so much colder than phase 8 with amp >1? That sould be counterintuitive to me.

 

 

Interesting... Well, I think it just has to do w/ the fact that not every MJO event in January leads to the same results, & this is a huge reason why further stratification is often a viable option to weed out years (especially la Ninas) where we don't observe nearly the amount of downstream pattern amplification in the northeastern Pacific, and it's also why the actual temperature anomalies associated w/ the MJO are relatively small, because of the vast amount of internal variance that's a result of varying modification by the extratropics & other background forcing on the effects from the MJO. Additionally, I should mention that the RMM MJO index you've analyzed is susceptible to missing out on many central Pacific & Western Hemisphere MJO events because of it's incorporation of Outgoing Longwave Radiation (OLR) into it's EOFs, which often withholds the RMM index into the naturally wetter eastern hemisphere where SSTs associated w/ the Indian-West Pacific Warmpool are sufficient to promote latent heat processes & especially convection which (not only is a determinant of the MJO's propagation & phase speed), but it is exactly what the OLR  relies upon to track the MJO... This is a primary reason why Mike Ventrice et al created the VPM (Velocity Potential MJO) Index for monitoring the MJO, to capture these central Pacific & western hemisphere MJO events that RMM may often completely miss because it incorporates OLR, and the VPM index w/ it's utilization of 200mb Velocity Potential generally experiences more MJO events in general (i.e. less time within the COD), w/ notably higher MJO amplitude. The available dataset w/ VPM is shorter than RMM (for now at least, Dr. Ventrice is working on extending it back to at least the length of RMM), but here's the daily data from April 30 1989 to Sep 30 2012...

http://www.atmos.albany.edu/student/ventrice/documents/VPM_dates.txt

 

I will be very interested to see a direct comparison between the RMM & VPM datasets from the winter of 1989-90 through 2011-12...

[Webberweather53]

 Webber,

 I will probably look at stratifying by ENSO phase later. In the meantime, I want to continue to look at each MJO phase unstratified because supposedly each phase overall has certain tendencies temperaturewise (i.e., regardless of ENSO) as the 500 mb maps for Jan phases 6-8 of Allan's that you posted suggest. I'm quite surprised that phase 8 has averaged near normal at KATL in Jan. when considering the solid +PNA shown for phase 8 in Allan's map. Can you explain this? The only thing I can think of is that I considered only amp. >1. Then again, why would those in phase 8 with amp <1 be so much colder than phase 8 with amp >1? That sould be counterintuitive to me.

 

 

Your observed trend in temperatures is confirmed by Allan Huffman's composites...

 

All days Phase 8

 

Phase 8 w/ amplitude

 

increased phase 8 amplitude in RMM composites show an eastward shift in the Aleutian low that's due to more vigorous Pacific Jet extension, this induces more of an El Nino-ish look to the pattern that alters the source region for cold air in such an MJO event ,and allows a bit more Pacific air to infiltrate into the pattern, but in analyzing the RAH past events & MJO, MJO phase 7 & 8 with amplitude (especially January phase 7) is more favorable for producing wintry weather here in NC... In fact Pacific & western hemisphere MJO phases (phase 6, 7, 8, & 1) w/ amplitude are much better for wintry weather vs Indian Ocean & Maritime Continent Phases...

 

You also see similar trends w/ NE US cyclones w/ pressures below 995mb, Pacific & western hemisphere & even MJO phase 2 are favorable, Maritime Continent, not so much...

[WXinCanton]

Interesting stuff Larry, appreciate the work!!