Wave Packet Diagnostics for Winter TPARC

Generated by Edmund Chang, Stony Brook University

 

Forecast Validation

To assess how useful the wave packet diagnostics based on a single deterministic forecast are, the forecast hovmoller diagram is validated against the analysis. Here, the forecasts from January 13th through January 31st, a total of 38 forecasts, are validated. We will update the validation statistics as we build up more archives.

The correlation between the forecast and analyzed hovmoller plot (based on averaging 300 hPa v between 30-60N) as a function of longitude and time, is plotted on the LHS. The RHS plot gives the RMS difference between the forecast and analyzed hovmoller plot (normalized by the analyzed standard deviation at each longitude and time).

If we take a correlation of 0.6 as being useful, then the LHS plot suggests that the deterministic forecast should be useful out to nearly 10 days over east Asia and western Pacific, and out to 6-8 days elsewhere. The RHS plot also shows that the normalized RMS difference is also smallest over east Asia and western Pacific. This may be related to the findings of Chang and Yu (1999) that wave packets propagate most coherently across Asia.

Forecasts of wave packet envelopes have also been validated. The correlation between forecast and analyzed hovmoller diagrams for both v (shown in black) and envelope (red), averaged over 0-360E and 120-180E, are shown in the figure below. We can see that out to day 10, the envelope is forecast a bit better than v itself. Both v and the envelope are forecast better over the western Pacific.