Friday, July 27, 2007

Dog Days Update

This will be short. There is not much overall change to my thoughts posted 24 July, including the global hazards mentioned. As was discussed, we are likely to observe variations in both the movement and intensity of our MJO. As indicated by tools such as Hovmoller plots of time-filtered coherent modes of tropical convection, there is a Kelvin wave moving into the west central Pacific Ocean. I would expect this feature to propagate into the Western Hemisphere next week possibly reversing the current strong negative Andes Mountain torque of ~minus 20 Hadleys per R1 data through 23 July.

Meanwhile, I think the dynamical MJO signal is still back in the Indian Ocean ~80E, and it appears to be stalling. The global circulation has been responding to the tropical forcing (in addition to the MJO) with upper tropospheric Indian Ocean anomalous twin anticyclones and down stream twin cyclones over the west central Pacific. In fact, associated with the twin troughs equatorial upper tropospheric westerly wind flow anomalies have been developing. Magnitudes are ~25m/s just west of the date line with weaker anomalies extending almost to the coast of South America. The is also a trade wind surge developing along the equator and is as far east as the date line per TAO data (which may have implications for La-Nina). Rossby wave energy dispersions interacting with these and other circulation anomalies have led to some weakening and progression of the wicked ridge of the western USA.

Most numerical and statistical tools from international weather agencies suggest the MJO to continue weakening. My own feelings are that we have serious predictability issues present no matter what objective technique anyone wants to use. Full disk satellite imagery already shows come evidence of consolidation in the region of 80-120E along the equator. The tropical northwest Pacific Ocean (TNWP) is very warm and I think it is probable to see strong convective forcing from much of China into the TWNP during weeks 2-3. Hence there will be an increasing tropical cyclone threat for locations such as the Philippines and Japan.

The Global Wind Oscillation (GWO) updated through 21 July (5-day average based on R1 data) presents a strong signal for GSDM Stage 1. This is the most robust shift to the left side of this quasi-phase space plot in at least a couple of months. I think it is probable to see a circuit toward GSDM Stage 2 during the next few weeks, especially if the TNWP becomes active, before orbiting back toward Stage 1. Again, uncertainty remains extremely high, including any weeks 2-4 prediction for the PNA sector. However, I do think the dog days of the Devil western USA ridge are waning, and seasonal cycle considerations alone suggest the westerlies to come south into the USA. Excessive heat may spread into the upper midwest and eastern USA weeks 2-3 while the western states cool down with increasing thunderstorm activity. In fact, if the TNWP becomes quite active with a few strong typhoons during the next few weeks, by mid August an anomalously deep trough across the Rockies with a Deep Southeast states ridge will become increasingly probable. Stay tuned.


An experimental quasi-phase space plot of the GSDM utilizing a time series of normalized relative AAM tendency anomaly (Y-axis) and normalized relative AAM anomaly time series (X-axis) can be found at

We call the behavior of this plot the Global Wind Oscillation (GWO), and one of its purposes is to extend thinking beyond the MJO.These are probabilistic statements, and work is ongoing to quantify in future posts. We hope that an opportunity will arise for us to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will try to issue a discussion next Tuesday, 31 July. In general, due to covering shifts and travel, my postings will be irregular through at least August.

Ed Berry

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