Leaderboard - 33andrain Jump to content

Leaderboard


Popular Content

Showing content with the highest reputation on 10/16/2018 in all areas

  1. 8 points
    YET ANOTHER ENSO SETBACK - EXPECT RENEWED ATLANTIC ACTIVITY DURING FINAL WEEK OF OCTOBER Those of us that monitor SSTs will know only too well how quickly they can change. We know that there is a strong relationship between ENSO phases and the impact on hurricane activity. +ve movements in ENSO SST anomalies (whether neutral, Nino-like or a full El Nino) depress Atlantic activity and enhance EPAC activity. -ve movements in ENSO SST anomalies (whether neutral, Nina-like or a full La Nina) enhance Atlantic activity and depress EPAC activity. The 2018 hurricane season has been remarkable for the almost perfect responses to quite small ENSO changes with a 10 to 14 day time lag. I have been reporting on this all season and, so far, not one SST change has failed to deliver a strong response. Last Saturday I posted on this thread wondering whether Michael had marked the end of significant Atlantic activity stating that we were running out of time for another ENSO setback and the time lagged response. Well, we have a significant shift! Most of the recent talk (posts and tweets) on various "33" threads has been that the final push towards El Nino was well underway. Malcolm @Blessed Weather did an excellent ENSO update only yesterday on the Teleconnections thread. This was based on last week's NOAA and other data and recent predictions from the likes of ECMWF. SST anomalies "had" been rising strongly in all 4 ENSO regions (with just a small down turn showing up at the end in the more volatile Nino 1+2 EPAC region). Last night the latest NOAA weekly report was published. Even these reports are based on data from a few days earlier - up to around October 12th at the latest. You can just see a hint of a down turn at the very end with Nino 4 leveling off and falling SSTs in the other regions. This chart (also from NOAA) only goes up to October 10th but the signs of at least a temporary setback were starting to show their hand. Note the colder waters from the south and south east starting to erode warmer waters further north and not just in the far east. This anomaly chart looked a lot warmer just a few days ago with SSTs rising strongly in the tropics and also in some mid latitudes but this does not show the recent changes. This shows the 7 day changes and as the down turn only really got underway 3 to 4 days ago, these are really significant. Not just pale blues but some dark colours starting to show their hand. Moving from west to east, Nino 4 has dropped by around 0.4c since Oct 12th. Nino 3.4 (used as the crude yardstick as the main ENSO indicator) was still rising until Oct 13th but has started to fall back since then. Nino 3 has been falling for 6 days. Nino 1+2 has been much more volatile as it's exposed to the battle between the Nino trying to set up and the much colder waters from the south drifting up on the ocean currents and driven by the still largely -ve (but weakening as we move towards the S Hem summer) SPO. It looks like Nino 1+2 will be -ve later today. Now, some of you might well be thinking, has Bring Back 1962-63 lost the plot? How can he be defying all the general evidence? Well I am not! Even this setback might prove to be temporary and the upward trend might resume in just a few days. Several members have actually suggested that despite the apparent progress towards a weak El Nino that there were still short term hurdles to cross. Tams @Tamara produced an excellent comprehensive post on Sunday on the "Winter Countdown" thread. This showed that the key drivers and indicators for shorter term pattern changes (up to 2 to 3 weeks ahead) of relative AAM (atmospheric angular momentum) and the GWO (global wind oscillation) were not yet supportive of Nino conditions and that at least a temporary more Nina-like phase was indicated. Then Tams as well as Tom @Isotherm, Zac @Snowy Hibbo and several others stated that there was still a lack of atmosphere/ocean coupling. Although I'm still learning about this crucial specialist field of AAM, GWO and the torques, I know enough to realise that we ignore these indicators at our peril. So, this is at least another stall in the progress towards El Nino conditions and "may" delay its development further towards winter. The implications of this latest setback may well have a strong impact on hurricane activity within 10 days or so. The lull in the Atlantic is likely to continue for another week or so. The development that formed in the Caribbean is crossing Central Am and producing high rainfall and storms there and its remnants will move out "westwards" into the EPAC. Meanwhile, the EPAC is really active again and we may well see 2 or 3 more named storms before the lower ENSO SST anomalies dampen things down again later next week. For those wanting to see a final burst of Atlantic activity, here's some more good news. As I and several others (including Steve @Superstorm93 and @CCB!) mentioned in the early development stages of Michael, the CAG (Central American Gyre) was a key factor in that. The CAG weakened and shifted further south but is still there. That's why the latest development is moving west on its northern flank. There is a strong suggestion that the CAG will drift back northwards again, bringing the south westerly monsoon type winds across Central Am again and into the north west Caribbean and GoM. One almost essential ingredient is for the MJO to be in phases 8, 1 or 2 at good amplitude - I posted and reviewed an excellent paper on this on here about 3 weeks ago. For Michael we saw the MJO in phases 8 and 1 at decent amp. Since then is moved through phase 2 and is about to weaken and enter the COD (circle of death). However, the models (such as GEFS above) predict it to quickly re-emerge into phase 8 and on into phase 1 at even higher amp than the last cycle. This is during the last week of October and into early November - precisely at the time that the Atlantic is set to become more active again! Now, a word of caution. The SSTs may recover again very quickly, reducing the window to just a few days. The CAG may not shift back northwards and week 2 MJO forecasts are notoriously unreliable. SSTs in the GoM have already recovered since Michael churned up the surface layers (see below). Even if all the conditions become highly conducive again, developments, especially into named storms and hurricanes are still by no means certain. Given the highly unusual nature of the 2018 Atlantic hurricane season, I would not be at all surprised to see one or two more very late season storms. Plenty to monitor for the next 2 to 3 weeks from now onwards. David
  2. 7 points
    Actually, after seeing the record breaking August value of 2.40 (using CPC's dataset going back to 1948), its September value still was high coming in at the 1.78 and the streak hit record territory given the stretch its been + since post SSWE this past winter/spring. I decided to take the 7 highest +NAO readings in Oct and then rolled them over towards subsequent DJF. Coincidentally, 6 out of the 7 years were +ENSO (didn't even know until I cross checked), and as you can see, the dipole had seen a complete flip. So, I suppose a Oct +NAO reading may have some type of statistical + correlation with the upcoming winter period, but of course there are other types of catalyst influences at play each year. Still, found it to be interesting nonetheless!
  3. 7 points
    Hey, I know I'm not too active on this site, I'm more of a listener than someone who likes to talk especially with all of the talent you guys have on here, but here is my winter outlook. Now it's a little simplified so that most people can understand what I'm saying, but I do make my opinions heard. Please give me constructive criticism as well.
  4. 6 points
    Many times when folks discuss the QBO, they are referring to 30mb. However, it is best to view the QBO across the full stratosphere from high up at 10mb, down to 100mb, as seen on the Free University of Berlin QBO chart below. When I was first learning about the QBO, this chart helped me more than anything else to understand the progression of the QBO. It's an oscillation that progresses in a largely predictable manner (sans the odd case of 15-16), so it's highly likely that the QBO at 30mb will continue to move toward zero, and then progress positive thru winter. In fact, if you were to average the daily sounding that is launched from Singapore, the QBO at 30mb for the first 15 days of October is right around zero. This is the transition from negative to positive QBO at 30mb....but that's only at 30mb. The QBO lower in the stratosphere at 50mb will likely remain negative at least through the first half of winter. At any rate, on the chart, the gray shaded areas are the +QBO and the white areas are the -QBO. With that in mind, you can move along thru the calendar and see how the QBO makes a steady progression with the alternating negative and positive phases. "0" on the chart is the zero line transition between the negative and positive QBO. "10" in the gray shaded areas is the +QBO value of +10. "-10" in the white areas is the -QBO value of -10. "-30" in the white areas is the -QBO value of -30. This link also gives you a good visual of the QBO progression in tabular form (once again, this is monthly averaged QBO data from the daily Singapore sounding) - http://www.geo.fu-berlin.de/met/ag/strat/produkte/qbo/singapore.dat
  5. 4 points
    Scandi blocking in late November, could be a good December. But it is a Euro weekly run. Maybe time to start talking sub-seasonal? Might bring one of the old hand forecasted GWO maps in tomorrow if I have time.
  6. 4 points
    TBH I think the weakest link in the chain is the NAO. My thoughts on the NP domain have firmed up, my thoughts on the NAO domain are pretty intent on a weak -NAO. I reckon this winter will be driven from the -EPO domain up into the Arctic, and blocking in the Laptev-Barents-Kara Sea. I was reading a musing from @snow_cohen earlier, about a deep Aleutian low and Barents-Kara High coupling to send energy and momentum flux to the Arctic to help a potential SSW. Another thing to stay on top of during this winter.
  7. 3 points
    ENSO - October Update Here are some extracts from the latest NOAA report on ENSO developments over the last month. I'll start with the 'official' NOAA Climate Prediction Centre update and follow this with a look at the 'unofficial' Multivariate ENSO Index (MEI). For most charts used in this post I've included last month's Sept output and the Oct update for comparison. The official forecast of 70% - 75% chance of El Nino onset during winter 2018/19 is up from the Sept report saying a 65% - 70% chance. El Niño is favored to form in the next couple of months and continue through the Northern Hemisphere winter 2018-19 (70-75% chance). ENSO-neutral continued during September, but with increasingly more widespread regions of above-average sea surface temperatures (SSTs) across the equatorial Pacific Ocean. Over the last month, all four Niño index values increased, with the latest weekly values in each region near +0.7°C. Chart: Nino Regions SST Anomalies: Positive subsurface temperature anomalies (averaged across 180°-100°W) also increased during the last month..... Chart: Upper Ocean Temp Anomalies: ......due to the expansion and strengthening of above-average temperatures at depth across the equatorial Pacific. Chart: Sub-surface Temp Anomalies: Convection was increasingly suppressed over Indonesia and around the Date Line. Low-level westerly wind anomalies were evident over the western and east-central Pacific, with some of the strongest anomalies occurring over the eastern Pacific during the past week. Upper-level wind anomalies were easterly over the east-central Pacific. Overall, the oceanic and atmospheric conditions reflected ENSO-neutral, but with recent trends indicative of a developing El Niño. The majority of models in the IRI/CPC plume predict El Niño to form during the fall and continue through the winter. Chart: SST Anomaly Forecasts for ENSO 3.4: Link to NOAA ENSO page: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml MEI Update The MEI is produced by NOAA but is a separate team from that responsible for the 'official' forecast. The team attempts to monitor ENSO by basing MEI on the six main observed variables over the tropical Pacific. These six variables are: sea-level pressure, zonal and meridional components of the surface wind, sea surface temperature, and total cloudiness fraction of the sky. Their September report stated their believe that an El Nino would not develop in 2018. Below are a few headlines from their October report, and whilst not as bullish as the official NOAA forecast, it nevertheless agrees on a more positive last month for movement towards El Nino onset. They are still not going as far as saying that an El Nino will develop in 2018, but rather cage their wording that they now believe the chance is "over 50%" for onset in winter 2018/19. More details on the MEI webpage. With the MEI showing ENSO-neutral conditions, six key anomalies in the MEI component fields flag El Niño, a large increase compared to last month, while La Niña anomalies dropped to a still respectable three, so 'not everyone is on board'. Compared to last month, the updated (August-September) MEI rebounded dramatically by almost 0.4 standard deviations to +0.51, ending up right below the lowest El Niño ranking. While not a single season has reached El Niño conditions in 2018, this is about to change. Looking at the nearest 12 rankings (+6/-6) in this season, it is rather striking that the stronger cases all maintained El Niño status for at least a few months, while all weaker cases but 1992 remained stuck in ENSO-neutral conditions. This increases the odds to over 50% for 2018-19 to reach and maintain at least weak El Niño in the next few months. Link to MEI page: https://www.esrl.noaa.gov/psd/enso/mei/
  8. 2 points
    I actually think February will be the best month. I dont think the QBO will be strongly positive, maybe weak which couls be offset easily
  9. 2 points
    Yesterday's Euro Weeklies feature the Berents-Kara ridge beginning in mid November.
  10. 2 points
  11. 2 points
    2002 and 2009 had a negative QBO heading into the winter...it looks like 2018 will be heading into winter with a positive QBO...I like the sound of 2002 and 2009 but will the QBO derail or enhance this winter...
  12. 2 points
    Basin wine Ninos are not the kiss of death. I don't want to focus on one thing here , but that nino in 2010 had similar low solar. No 2 seasons are alike , but right now I dont see anything glaring that worries me. I guess something could show up by early December and shatter this. So I will leave it alone for the time being.
  13. 2 points
    WHY DO I LOVE FEB SO MUCH ? I like a blend of 02/03 09/10 14/15 WSI
  14. 1 point
    Links Section In This Post, below the intro. I have been recently asked to start a thread, to talk about weather teleconnections and similar topics. This is often a topic not very well discussed on other weather places, and places like Twitter. We have a number of experts, enthusiasts, and meteorologists, who are knowledgeable in this area. So this is a thread for technical discussion about the teleconnections, etc, as well as a place for questions about these topics. We need to start talking about these climate drivers more, as they are the key to unlocking medium-long term forecasts. We are making a place for technical discussion about these factors away from the main thread/s. So this thread is born. Teleconnections that could be up for discussion are: MJO, AAM/GWO, NAO, RRWT, NP jet, Mountain & Frictional Torques, AO/AAO, ENSO, IOD, AMO, SSTs in general, SOI, QBO, the Stratosphere, etc. Feel free to talk about related topics, but stick to this general topic. I encourage all posters to discuss and pose questions relating to the topic, and keep it a relaxed atmosphere. Any questions, just PM me or comment here. Hope we can make this work Links Section ERSL Link, Up to 24 hours behind. GWO 90 day Victor Gensini Site. http://atlas.niu.edu/gwo/ Features Total AAM, Bias Corrected Rel AAM GEFS, CFS GWO Forecast. He stated he is soon to add torque products. Nick Schraldi GWO Site http://www.atmos.albany.edu/student/nschiral/gwo.html Non-Bias Corrected GEFS GWO forecast. Michael Ventrice http://mikeventrice.weebly.com/hovmollers.html Hovmoller from MV, to help spot AAM trends and patterns. GEFS. Carl Schreck https://ncics.org/portfolio/monitor/mjo/ More Hovmollers and other tropical charts to spot trends in the AAM. CFS forecast. NPJ Phase Diagrams/Albany http://www.atmos.albany.edu/facstaff/awinters/realtime/Deterministic_NPJPD.php Shows a GEFS forecast and observation of NP jetstream, which is largely controlled by the AAM. From @Bring Back 1962-63: Since the service provided through WDT was withdrawn there was a gap in this vitally important data. I've been in touch with Ed Berry, who along with Dr Klaus Weickmann (who retired 2 years ago) developed the GSDM (I posted on that on both the 33 and NetWx forums with Ed's excellent presentation earlier this year) and he told me that a friend of his still processes this data. He has kindly provided a link to that site plus the access user name and password: http://gsdmsolutions.com/~gsdm/clim/aam.rean.shtml un = gsdm01 pw = gu3st#1 That will take you to this page where you'll find a lot more than just the ex WDT data: Monitoring of Global Atmospheric Angular Momentum (AAM) Budget NCEP-NCAR Reanalysis DAILY DATA Vertically-integrated 5-day running mean: 1968-1997 Climatology Plots show some of the features: MJO, SUB-MONTHLY, & RAPID TRANSITIONS. ( Plots contain data through (MM/DD/YYYY) = 09/26/2018 ) PLOTS LATEST 90 DAYS LATEST 90 DAYS w/ Seasonal Cycle CURRENT YEAR CURRENT YEAR w/ Seasonal Cycle Data Files AAM data file (Updated: Friday, 28-Sep-2018 08:35:48 CDT) AAM 1-21 data file (Updated: Friday, 28-Sep-2018 08:35:50 CDT) TAUC data file (Updated: Friday, 28-Sep-2018 08:35:57 CDT) TAUF data file (Updated: Friday, 28-Sep-2018 08:35:57 CDT) TAUG data file (Updated: Friday, 28-Sep-2018 08:35:57 CDT) TAUM data file (Updated: Friday, 28-Sep-2018 08:35:57 CDT) TEND data file (Updated: Friday, 28-Sep-2018 08:36:00 CDT) TEND (1-21) data file (Updated: Friday, 28-Sep-2018 08:36:02 CDT) TRANSP data file (Updated: Friday, 28-Sep-2018 08:36:00 CDT) MONTHLY DATA Vertically-integrated: 1968-1997 Climatology Plots show some of the features: ENSO, QBO, & TRENDS. ( Plots contain data through 08/31/2018 ) PLOTS 1958-PRESENT: Total Fields 1958-PRESENT: Anomaly Fields MJO Composites: http://www.atmos.albany.edu/facstaff/roundy/waves/rmmcyc/index200reg.html
  15. 1 point
  16. 1 point
    Stop teasing me like this damn it lol.. hopefully this is a sign of things to come
  17. 1 point
    We have been getting unlikely solutions in this decade.
  18. 1 point
    A Climatology of Central American Gyres Authors: Philippe P. Papin, Lance F. Bosar, and Ryan D. Torn Published: 2nd May, 2017 Abstract: Central American gyres (CAGs) are large, closed, cyclonic circulations that occur during the rainy season (May–November), which can yield exceptional rainfall leading to catastrophic flooding and large societal impacts. A reanalysis-based climatology of CAGs is developed from an algorithm that distinguishes CAG cases from other systems. This algorithm identified CAG cases based on circulation intensity, a broad radius of maximum winds, and the existence of closed, Earth-relative, cyclonic flow. Based on these criteria, 47 CAG cases were identified from 1980 to 2010, featuring a bimodal distribution of cases with maxima in May–June and September–November. CAG cases are composited into two categories based on their upper-tropospheric PV structure: nonbaroclinic CAGs are more common (N = 42) and characterized by an upper-tropospheric anticyclone, while baroclinic CAGs are less common (N = 5) and characterized by an upper-tropospheric trough. Whereas a nonbaroclinic CAG has anomalous moisture and precipitation surrounding the center, a baroclinic CAG has anomalous moisture and precipitation concentrated east of the center, with these structural differences attributed to their upper-tropospheric PV structure. Both nonbaroclinic and baroclinic CAGs are preceded by anomalous westerly lower-tropospheric flow in the eastern Pacific before their development, which is linked to a climatological reduction in easterly trade winds and is coincident with MJO phases 1, 2, and 8. Extreme precipitation is observed over multiple days in all available CAG cases, most commonly along the Central American coastline and on average over a large fractional area (25%) within 10° of their center. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/MWR-D-16-0411.1
  19. 1 point
    The interaction between the Western Indian Ocean and ENSO in CESM Authors: Claudia E. Wieners, Henk A. Dijkstra and Will P. M. de Ruijter Published: 18th September, 2018 Abstract: Several previous studies have suggested that a cool western Indian Ocean may induce convection over Indonesia, leading to surface convergence and easterlies over the western equatorial Pacific Ocean. These easterlies then increase the Pacific Warm Water Volume favouring El Niño in the next year. We investigate this mechanism of Indian-Pacific interaction using output from two simulations (at 0.1∘0.1∘ and 1∘1∘ ocean model resolution) with the Community Earth System Model (CESM). No conclusive evidence for the suggested interaction mechanism is found in CESM. Like many other coupled models, CESM has an overly strong sea surface temperature variability in the eastern Indian Ocean due to an exaggerated sensitivity of the sea surface temperature to thermocline variations. Due to this bias the effect of the western Indian Ocean signals on the Pacific, as found from observational analysis, is hidden. Our analysis shows that this bias can be traced to errors in the time-mean vertical temperature profile in the Indian Ocean. This bias needs to be reduced to allow a better investigation of the subtle interactions between the Indian and Pacific Oceans. Link to full paper: https://link.springer.com/content/pdf/10.1007%2Fs00382-018-4438-2.pdf
  20. 1 point
    The dynamics of NAO teleconnection pattern growth and decay Authors: Steven B. Feldstein Published: 29th December, 2006 Abstract: This investigation performs both diagnostic analyses with NCEP/NCAR re‐analysis data and forced, barotropic model calculations to examine the dynamical mechanisms associated with the growth and decay of the North Atlantic Oscillation (NAO) teleconnection pattern. The diagnostic calculations include projection and composite analyses of each term in the stream‐function‐tendency equation. The results of the analyses reveal a complete life cycle of growth and decay within approximately two weeks. The positive NAO phase is found to develop after anomalous wavetrain propagation across the North Pacific to the east coast of North America. This contrasts with the negative NAO phase which appeared to develop in situ. Both high‐frequency (period <10 days) and low‐frequency (period >10 days) transient eddy fluxes drive the NAO growth. After the NAO anomaly attains its maximum amplitude, the high‐frequency transient eddy fluxes continue to drive the NAO anomaly in a manner that is consistent with a positive feedback process. The decay of the NAO occurs through both the divergence term and the low‐frequency transient eddy fluxes. The temporal and spatial properties of the divergence term are found to be consistent with Ekman pumping. These results illustrate many important differences between the NAO and Pacific/North American (PNA) teleconnection patterns, perhaps most striking being that the NAO life cycle is dominated by nonlinear processes, whereas the PNA evolution is primarily linear, In addition, the relation between the NAO and the zonal index is discussed. Copyright © 2003 Royal Meteorological Society Citing Literature Link to full paper: https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1256/qj.02.76
  21. 1 point
    Why do Earth's equatorial waves head east? Authors: Joseph A. Biello and Tudor Dimofte Published: 24th November, 2017 Abstract: Equatorial Kelvin waves occur constantly in Earth's atmosphere and ocean. They constitute an isolated and powerful component of the observed atmospheric wave spectrum (1), whereas oceanic Kelvin waves drive up- and downwelling in the Pacific Ocean thermocline, which affects the El Niño–Southern Oscillation. In the atmosphere, Kelvin waves are initiated by and coupled to convective activity (storm systems), mostly over the Indian and the western Pacific Oceans, whereas in periods of large-scale convective organization, such as the Madden-Julian Oscillation, equatorial Kelvin wave activity is suppressed. On page 1075 of this issue, Delplace et al. (2) attempt to answer the questions of why there are three equatorially confined waves, and why they all have eastward group velocity. They propose a fascinating perspective on the existence of unidirectional, equatorially confined atmospheric waves by developing an analogy with similar phenomena that occur in electronic materials—in particular, in quantum Hall states and topological insulators. Link to full paper: Unfortunately this great looking recent paper is still behind a "Science" Webinar paywall but it should be available on a free to view basis next year and I will provide the pdf link as soon as I can after that. For those who have a subscription, here's the link to the abstract on the "Science" website: http://science.sciencemag.org/content/358/6366/990 I found an image of the cover page:
  22. 1 point
    A real-time Global Warming Index Authors: Dr. K. Haustein, M. R. Allen, P. M. Forster, F. E. L. Otto, D. M. Mitchell, H. D. Matthews and D. J. Frame Published: 13th November, 2017 Abstract: We propose a simple real-time index of global human-induced warming and assess its robustness to uncertainties in climate forcing and short-term climate fluctuations. This index provides improved scientific context for temperature stabilisation targets and has the potential to decrease the volatility of climate policy. We quantify uncertainties arising from temperature observations, climate radiative forcings, internal variability and the model response. Our index and the associated rate of human-induced warming is compatible with a range of other more sophisticated methods to estimate the human contribution to observed global temperature change. Link to full paper: https://www.nature.com/articles/s41598-017-14828-5
  23. 1 point
    A 'hello' from me as one of the new member little group that @Snowy Hibbowas kind enough to introduce Thanks to him for starting this excellent and highly valuable thread which should provide an abundance of new information for everyone - and will I am sure cater for all the different individual learning curves of various members. A few years back I was struck by how the Global Synoptic Dynamical Model (GSDM) could be used as a heads-up assist to gauging future weather patterns and decided to do some quiet self study combining outside reading with some existing practice work from expert meteorologists already hooked by the concept ideas of this model. There have already been some great posts on this thread and I hope that my own offering here avoids too much duplication and can be of some help to the discussion The Global Wind Oscillation is a plot depicted measurement of net total global wind-flows aggregated through tropical momentum transport energies - constantly fluxed and exchanged between the tropics and extra tropics by changes in atmospheric angular momentum (AAM). These dynamic processes effectively provide good markers as to how the global jet stream might behave - AAM itself is a measure in simple terms of the turning force of the Jetstream (through frictional and mountain torques). The GWO is depicted by a phase plot spider graph (below) which reflects whether the global atmosphere is pre-disposed towards easterly wind additions (La Nina-like) or westerly wind additions (El Nino-like). There are eight phases in total. Three La Nina attractor phases 1,2 and 3. Three El Nino attractor phases 5,6 and 7. And two 'transitional' phases 4 and 8. The former transitional phase 4 depicts rising AAM in a La Nina state (or westerlies being added to an easterly trade wind dominated state) and the latter phase 8 depicts falling AAM within an El Nino atmospheric state or (easterly trades being added to an atmospheric state that has greater overall westerly wind inertia within it). See below a basic template of this next to a live plot depiction of the atmospheric state in action. The tropical (MJO) and extra tropical (GWO) elements of the atmospheric circulation are reflected within the contents of this template and an introduction of how momentum transport within the tropics is processed in the extra tropics through a programme of frictional and mountain torque mechanisms. For purposes of this post I am not going to discuss the latest position wrt GWO - keeping it informative rather than any forecasting element The hard part, is gauging in the future how anticipated tropical convection patterns will evolve those wind-flows in the extra tropics, as rossby wave trains (which are triggered by the windflows created ahead of tropical thunderstorm activity) propagate eastward and northwards into the extra tropics. The initial consequence of an event in the tropics is a frictional torque at the ocean surface, and depending on the strength of the resultant rossby wave, this can propagate polewards and set up the mountain torque in the extra tropics. These mountain torque processes in turn have implications for the tropospheric/stratospheric relationship - and the relative strength/weakness and organisation/disorganisation of the seasonal polar vortex. So getting right to that hard part. Tropical convection with its associated wind-flow additions and torque mechanisms is an expression of change to atmospheric angular momentum. As indicated above, AAM is quite literally referring to the turning force exhibited on the jet stream. That makes sense when you think of convergence and outflow wind mechanisms that are associated with convection events even on a minor micro-scale level with local thunderstorm development. Extrapolate that much larger with MJO convection and you get a large scale forcing across the tropics with the linear bands of convection that occur with the cyclical timelines of this phenomena. So, that means westerly wind burst additions (WWB) are added across the tropics associated with the MJO as it heads eastwards from the western hemisphere. Westerly winds create a +ve frictional torque (convergent) which can under suitable conditions propagate with sufficient strength into a +ve mountain torque 'event'. The turning force in this case is of westerly winds hitting a tall mountain range (such as the Himalayas or Rockies), deflecting wave activity upwards into the stratosphere All good so far. However, Mother Nature abhors a vacuum - and where westerly winds are added, there has to be a compensation elsewhere in the atmosphere with easterly winds to fill the inertia vacuum This compensation process of wind-flow exchange to maintain atmospheric parity is referred to in the GSDM as the 'AAM budget'. This post cannot cover the whole science in fell swoop, but lets take a look at some of the main elements of the GWO budget. The descriptors below are not all of the categories that comprise the whole AAM budget - but are main contributors that make up the global jet stream (as NWP drivers) and having some understanding of these is a solid introduction to the GSDM Calculated AAM tendency: This plot depicts the net total global wind-flows calculated from frictional and mountain torques in the tropics and extra tropics. In other words a useful guide to the net budget of tropical momentum process (as discussed above). If calculated tendency is -ve, then this tells you that net global wind-flows as calculated by torque forcing have greater easterly (La Nina-like) inertia to AAM budgets. The converse iS true if calculated tendency is +ve - suggesting that westerly winds are being added to global wind-flows through +ve torque mechanisms via tropics>extra tropics Relative AAM tendency: . This is an indicator of the direction of travel of angular momentum relative to GLAAM . If tendency is sharply down as indicated on the latest plot for example, this suggests that at the given time large amounts of easterlies are being added to the atmosphere through -ve torque processes - and relative to total AAM, will likely pull GLAAM further downwards. Again the converse is true for +ve torque processes. So this means that atmospheric angular momentum tendency is a refection of the size of the frictional torque created by MJO activity in the tropics (see above for frictional torque definition and plot) Total Atmospheric Angular Momentum: . . Essentially already explained. - This plot depicts the measure of the total global wind-flows (westerly and easterly) that the atmospheric circulation has the capacity to hold at a given time. Its the bell-weather indicator for the ENSO ocean>atmosphere relationship and calculates the net total wind-flows globally (easterly or westerly as the case maybe) after both calculated tendency and relative tendency have been included. However, as indicated above, total AAM is set against the trend direction of atmospheric feedback which is measured by relative AAM tendency. Clearly, the ENSO state is a large scale governor of total AAM as defined by La Nina or El Nino and the extent of the total forcing that SST feedbacks have on the behaviour of MJO and other forms of tropical convection such as cyclones or typhoons (depending on which part of the world they occur) On that basis, modelling of the MJO is notoriously tricky, and prone to error beyond, say, especially 5 days out. That is before attempting to gauge the extra-tropical (GWO) response in terms of net total windlfows that will be a consequence of any MJO event. With La Nina present for some time (and only now waning) its always been logically intuitive to expect there to be a surfeit of easterly wind inertia in the mix - a natural product of the stronger trade winds which occur under a Nina Plot depiction of La Nina-like easterly trades (blue) set against propagated westerlies c/o tropical convection (orange/red) . Synoptically, a surfeit of easterly winds in the atmospheric circulation system will be represented by divergent (stable) patterns across the ENSO zones. This leads to a build of the circum-global ferrel cell sub tropical anticyclones - stemming initially from the tropics > into the Pacific and then extending around the globe as part of a typical long-wave pattern. These anticyclones dictate patterns at Northern Hemisphere mid latitudes, whilst at higher latitudes the pattern is controlled by the strength of the seasonal polar vortex in winter-time. So its easy to see how increased polar jet flow occurs above these sub tropical highs, whilst underpinning beneath them the -AAM tropical easterly trade winds . The amount of easterlies added in the tropics will naturally determine the extent that westerly wind additions can be made through tropical convection. If you think of easterly wind shear buffering up against tropical convection, then its not hard to visualise how the WWB's are 'sheared off' and neutralised. This, effectively kills off the forcing of the MJO activity and hence under La Nina conditions its easy to see why easterly wind inertia commonly inhibits activity the further east one heads from the western hemisphere. The departed winter season so far however has been a-typical in terms of the SST distribution of the La Nina across the Pacific. There have been reasonably warm anomalies in the western most Pacific plus the areas of ocean of the Gold Coast, and towards Indonesia than often is the case in a traditional La Nina event. This means a Nina atmosphere/ocean disconnect has been attempted through the winter, culminating in the massive tropical momentum event propagating from tropics>extra tropics>SSW. To conclude this long post, I am including a technical link that describes the processes of the GSDM (Global Synoptic Dynamical Model) http://journals.ametsoc.org/doi/full/10.1175/MWR3293.1 The post is already way too long (!) so no to attempt to go into detail of its contents, but maybe some are brave enough to try to read through it. Its bound to create some difficulties, but it is a large part of what I have tried to wade through in the last couple of years to try and get some further insight into this fascinating but not widely known concept model of atmospheric dynamics. It was put together by Klaus Weickmann and Ed Berry, two officers from noaa who have subsequently retired and taken the official links at NOAA away with them. I think these guys have left an incredible legacy that folk of all different meteorological levels should support in their learning and in turn put forward as an integral part of their forecasting aims. The GSDM surely provides an essential insight into the complexities of trying to forecast and anticipate the evolution of medium and longer range NWP. Anyway, more than enough from me I think
  24. 1 point
    There are 2 key teleconnections I look to in the Pacific which drive the foundation for everything I look at. The first is the WPO as I look to it when I am looking for a cold air to seed Canada out of Siberia Then I focus on the EPO as it serves several functions for me I look for that negative to bend the jet off the Asian continent which help pump the ridge on the WC poleward and send that cold Canadian air back down the backside of the ridge into the midsection Its why I focus so much on looking for HP to slip thru Montana and enter the CONUS -EPO s are famous for producing Arctic waves , the length of the wave pattern typically allows the Arctic front to sit right along the coastal front which is a natural barroclinic zone for LP Now the ridge axis has a lot to say about that , but we have seen over and over again , Just like Jan 4 th , these will focus on the coast The models miss 2 things in -EPO patterns , HP and the placement on the Arctic front closer to the coast and not the polar boundary further east. So in -EPO patterns the errors that are easy to pick out are feedback , HP will slip east of the Rockies not west and the fallacy of an EC ridge , it gets resolved . The missing of HP pressing thru Montana , ( that's where it likes to funnel ) and lastly the slip east on the EC are 2 things missed in the midrange . EC LP find the coastal front , it has been something that I have been able to beat in the guidance for the last few years. Those NEGs diving off the WC will teleconnect on the EC and usually close to the same latitude. It's a great excercise where teleconnections beat a model simulation.
  25. 1 point
    https://journals.ametsoc.org/doi/full/10.1175/1520-0493(2003)131<2608%3AMTGFTA>2.0.CO%3B2 This is the formal paper from Klaus Weickmann, who was one of the leaders in early GWO research. Basically Frictional Torque is the tropical component, and the mountain torque is the extratropical component, togther they form the AAM. The MJO can also be used to indicate the AAM, with Phases 5-8 more associated with positive AAM and Phases 1-4 with negative AAM. But this isn't always the case, so you have to look at the torques as well.
×