Guess who's back? I've been thinking about this forum/thread a lot lately. It may sound funny, but I've missed this forum/thread. Especially, ASLR, Deep Octo, and LMV. I sort of just disappeared without explanation and I've kind of felt bad about that. I started tracking this El Nino in another forum and I've picked up few new tools that we haven't used or discussed here. At least that I can remember. So I wanted to share them. If they have been discussed then I guess this will be an update. ;-)
The 1st attachment shows the ESPI, which precipitation based measure of ENSO. The ESPI is calculated with precipitation anomalies from two areas in the Equatorial Pacific (red boxes) and quantifies the strength of ENSO, in terms of regional rainfall changes. The ESPI 30 day avg is currently at +2.42. The graph is bimonthly and typically runs a few months behind. The black line is one wants to focus on. It's good for determining how well the atmosphere is responding to changes is SSTs. As we know, during El Nino the Walker circulation breaks down or reverses. Enhanced rainfall shifts from the Maritime continent into Central and Eastern equatorial Pacific, and becomes especially abundant near and just east of the Dateline. Rainfall becomes suppressed over the Maritime Continent. This results in negative rainfall anomalies over the Maritime continent and positive rainfall anomalies over the Central and Eastern equatorial Pacific. The stronger this anomalous pattern becomes, the more positive the ESPI becomes. The more positive the ESPI becomes, the stronger the El Nino event.
ESPI:
http://trmm.gsfc.nasa.gov/trmm_rain/Events/thirty_day.htmlThe 2nd attachment shows the show the ESPI overlaid with the Nino 3.4 index. Note that the ESPI can "sometimes" lead the Nino 3.4 index by up to a few months during stronger El Nino events once the ocean and atmosphere have become well coupled.
ESPI with Nino 3.4 index overlaid:
http://eagle1.umd.edu/GPCP_ICDR/espi.htmThe 3rd attachment shows Carl Schreck's new CFS driven MJO and equatorial wave Hovmoller. It shows a 120 day history and 30 day forecast of 850 hPa zonal wind, the MJO, Equatorial Rossby waves, Kelvin waves, and the low-frequency background/ENSO signal. It also identifies TC genesis during the last 120 days, which is an especially neat feature as it allows one to really visualize the role that the MJO and other modes of tropical variability play in TC activity. Solid contour lines identify enhanced convection/active phases, while dashed lines identify suppressed convection/inactive phases. Blue shading identifies easterly wind, while red shading identifies westerly wind. We currently have a convectively suppressed ER wave propagating through the Dateline region, which is destructively interfering with the low frequency background/ENSO signal. However, the El Nino base state is strong enough that it's only having a slight impact on enhanced convection and westerly wind/anomalies. A weak convectively active ER wave is projected to move in right behind, which should result in constructive interference and an amplification of westerly winds/anomalies over the Dateline. Note the suppressed convection and easterly wind over the Maritime continent (gray dashed contours and blue shading), and persistent enhanced convection and westerly wind over the Dateline region (solid gray contours and red shading). This is consistent with a strong El Nino and a reversed walker circulation.
Carl Shreck's CFS MJO and equatorial wave Hovmoller:
http://monitor.cicsnc.org/mjo/v2/ The 4th attachment is a compassion of OLR during the 1982-83 and 1997-98 El Nino events, with the MJO and the low frequency background overlaid. I shared this analysis in another forum but I wanted to share it here as well. The blue colors show negative OLR/active convection, while the orange and yellows show positive OLR/suppressed convection. The solid red contours identify the active phases of the MJO, while the dotted red contours identify the inactive phases of the MJO. The solid black contours identify active convection associated with the low frequency background/ENSO, while the dotted black contours identify suppressed convection associated with the low frequency background/ENSO. I've also marked the and labeled the equatorial Pacific for easier viewing purposes. Images courtesy Kyle MacRitchie.
With that said... I wanted to point out how the MJO signal essentially disappeared once the ocean-atmosphere coupling became well established (or once the Bjerkins Feedback was well established). That can be seen as solid black contours over the Central-Eastern Pacific, while dotted black contours are over the Maritime Continent (NOTE: The solid black contours over the western Indian Ocean are associated with the Positive IOD, which only enhanced the El Nino state by further suppressing convection over the Maritime Continent). Notice the lack of a coherent MJO signal from Fall of the first year into mid-Spring of the second year for both events. This is common for very strong El Nino events (but not always true for weak to moderate El Nino events). Also, notice how MJO activity was much more enhanced/stronger prior to the 1997-98 event than the 1982-83 event (though at least moderate+ MJO activity was observed prior to the 1982-83 event). The 2015-16 event is more like the 1997-98 event in that aspect. However, the 2015-16 event seems to be evolving at slower pace like the 1982-83 event (at least per SST data which is not shown). Anyway, I suspect that we won't see the MJO again until next year (or at least any moderate-strong MJO activity). The Walker circulation is essentially reversed, thus persistent westerly wind/anomalies will likely continue for the next several months. Atmospheric equatorial waves and TCs close enough to the equatorial will like constructively interfere with the El Nino base state from time to time, resulting in future WWB activity (but I suppose it's certainly possible that weak MJO activity could also contribute).
IF we are indeed moving toward a significant El Nino event, we should start to notice WWBs or at least westerly wind anomalies following/pushing the W PAC warm pool eastward across the equatorial Pacific. If all goes according to plan, the W PAC warm pool should enter the E PAC sometime in late Fall/early Winter (as it did in 1997 and presumably other very strong events). NOTE: Using historical W&H MJO index data, I was able to verify that the MJO was indeed weak or absent over the equatorial Pacific during the time-frames mentioned above.
