1. Predictability Issues Associated with Explosive Cyclogenesis in the North-West Pacific Edmund K.M. Chang School of Marine and Atmospheric Sciences Stony Brook University Third THORPEX International Science Symposium Collaborators: Kevin Raeder, Nancy Collins and Jeff Andersen (DAReS, NCAR)

2.  Why do we care? –Local weather –Downstream impacts

3. Taken from THORPEX International Science Plan (Shapiro and Thorpe, 2004) Time

4. Taken from U.S. PARC science plan. Adopted from Hakim (2005) Initial analysis error structure 12-hr forecast uncertainty 24-hr forecast uncertainty

5. An example from winter TPARC Target: T+60 Verify: T+144 Time Verification Target

6. Hoskins and Hodges (2002) Dashed: 250 hPa Trough TracksSolid: 850 hPa Tracks  Cyclogenesis over W. Pacific often triggered by waves propagating out from Asia (Chang and Yu, 1999; Hoskins and Hodges, 2002)

7.   Question: – –Is cyclogenesis triggered by upstream waves more predictable?

8. Current Study  Case Selection (based on Chang 2005): –Explosive cyclogenesis over W. Pacific (Day 0) –Upstream wave packet over Asia at Day -3  Methodology –Ensemble forecasts and sensitivity analyses  CAM3 at T85, 80-member ensemble  Ensemble assimilation using DART at NCAR –OBS: Radiosondes, aircrafts, and SAT winds –Kevin Reader, Nancy Collins and Jeff Anderson at NCAR –Feature based sensitivity analyses  Preliminary studies using dry model (Chang 2006)

9.  Up to now, several cases have been examined –Here, results from 1 quite predictable case, and 1 not so predictable case will be presented

10. An example of explosive cyclogenesis 3 days after N packet ERA40 MSLP (contour interval 5 hPa) “Predictable” Case

11. ERA40 Z500 (contour interval 60 m)

12. ERA40 80-member Ensemble mean from Day -3 Ensemble mean from Day -5Ensemble mean from Day -6

13.  Between Day -1 and Day 0: –ERA40: cyclone deepened by 28.3 hPa –Ensemble forecast from Day -5:  Average deepening of 23.3 hPa  60 of 80 members give deepening > 1 Bergeron  RMS cyclone position error of 533 km at day 0  Average cyclone MSLP bias of +2.9 hPa at day 0

14. Feature Based Sensitivity Analysis using dry model Control Remove upstream waves (10-90E) Retain only upstream waves (10-90E) (Remove waves in 90E-10E) Remove all waves (15-day mean) Forecast from Day -5

15. 2nd example of explosive cyclogenesis 3 days after N packet “Not so Predictable” Case ERA40 MSLP (contour interval 5 hPa)

16. ERA40 Z500 (contour interval 60 m)

17. ERA40Ensemble mean from Day -3 Ensemble mean from Day -4Ensemble mean from Day -5

18.  Case 1 apparently much more predictable than case 2. Why? –Some speculations:  Upstream wave packet appears stronger in case 1: stronger dynamical forcing  Structure of cyclone much simpler in case 1, but much more complex in case 2  Cyclone development in case 2 apparently quite dependent on diabatic effects –Case 1 qualitatively similar results when CAM is run in “adiabatic” mode, or when water (vapor, liquid, and ice) quantities are all reset to 0 every 12 hours

19. ERA40 Control forecast from day -2 Moisture reset to 0 every 12 hoursCAM run in adiabatic mode from day -2 CASE 2

20.  Speculations: –Strongly dynamically forced cases are more predictable –Cases in which diabatic processes are important are less predictable –How general are these results?  Are strongly forced cases sensitive to existence of near surface diabatically generated vortices?  Further work: How do these developments affect downstream cyclone events and weather? Third THORPEX International Science Symposium

22. ERA40Control forecast from day -2 Moisture reset to 0 every 12 hoursCAM run in adiabatic mode from day -2 CASE 1

23. Shaded: 95% significant From Chang (2005)