“The views expressed are those of the author and do not necessarily represent those of the National Weather Service.”
Time constraints (and scientific/efficiency considerations) continue dictate for these discussions to be scaled back. The 6 June posting has relevant links, and there is no need to be redundant.
Short and simple, starting in March and “maturing” during April and May, the global ocean-land-atmosphere dynamical system has shifted toward a weak El-Nino base state. The phase space plots depicting the WH (2004) measure of the MJO and WB (2009) measure of the GWO clearly show this. That is, a general displacement toward octants 7-8. The GWO projection has been “weaker” because of complicated issues involving the dynamics of the earth-atmosphere AAM budget including zonal mean contributions. Remember that the WB (2009) GWO is a global dynamical measure of the circulation as opposed to the empirical and equatorially confined WH (2004) MJO.
SST anomalies across the entire equatorial Pacific Ocean basin including the Nino regions are positive, including ~plus 1C and greater east of 160W. Further, the 29C isotherm is well to the east of the Dateline (see TAO and other plots). However, the subsurface anomalies across the west Pacific are not that robust, only ~plus 1-2C down to around 200m. In any case, this basin-wide warming of the Nino SSTs is a response to the global circulation (more said below), and our weak El-Nino is already (and has been) impacting global weather including the USA. Additionally, as discussed previously, the evolution to get to where we are at (in phase space) has been impacting global weather since December 2008 (recall the GWO driven “cheap” MJOs).
My “punch line” for today is that, in general, the global circulation, as part of a complex forcing-response-feedback “loop”, has been leading the SSTs since about boreal autumn 2006 (see previous posts). The latter includes projections on the “beloved” ONI and other measures such as the PDO. I am concerned this is still going on, perhaps working with the seasonal and annual cycles (there are reasons).
Since about mid-May, anomalous zonal mean westerly wind flows have been shifting off the equator into the subtropical and midlatitude atmospheres, with the largest magnitudes across the winter Southern Hemisphere (greater than 10m/s at 200mb). Frictional dissipation due to interactions with tropical forcing (including a recent weak MJO; e.g., WWBs) and midlatitude eddies led to a strong negative global frictional torque by mid-June. Updated through 24 June the there is a clustered negative global mountain torque of roughly minus 20 Hadleys. The point is this is an example of a negative global friction-mountain torque index cycle linked to atmospheric processes including tropical forcing (GWO 8-1). Global relative AAM has decreased to near the R1 data climatology, and tropical convection has become re-established ~10N/90E, good news for the Indian monsoon system. Will this tropical forcing coherently propagate into the west Pacific Ocean during the next few weeks? Stay tuned.
Like the recent behavior of the financial markets, we have seen an “AAM correction”. However, is this simply a subseasonal variation destructively interfering with El-Nino, or is a process beginning that not only could weaken EL-Nino this upcoming boreal autumn, but perhaps bring a La-Nina situation boreal winter 2009-10? The answer is unclear, and careful daily rigorous monitoring is critical. Hopefully at some point the atmosphere and the financial markets will become decoupled!
Animations of upper tropospheric daily mean vector wind fields do show that anomalous subtropical and midlatitude ridges have returned (bearish). Loosely, phases 1-2 of the both the MJO and GWO 250mb psi composite anomaly plots represent the global atmosphere. Responding to the weakening of the North Pacific Ocean jet, the warm ridge in place across the south central and southeastern states last week is retrograding. That behavior is consistent with a brief excursion toward phases 3-5. However, with low confidence, I think another loop in GWO/MJO phase spaces displaced toward octants 7-8-1 is probable during the next 1-3 weeks. As seen from the snr composites, temperature anomalies across the lower 48 states are very sensitive in this region of phase space (as is numerical model predictability skill). My own thought is the intense heat may be focused across the south central states the rest of this summer, with increasing probabilities of northeastward expansions during August. I will try to write a short posting 3 July.