1. Where PV2 >> PV1 (so PV1 / PV2 is nearly zero) Low-to-mid tropospheric PV generated by diabatic heating is dominant over PV generated due to near surface baroclinicity Deep and relatively strong vertical wind shear 10-15 m s -1 (900 – 300-hPa) Initial Development Subtropical Cyclone

2. Where PV2 >> PV1 (so PV1 / PV2 is nearly zero) Low-to-mid tropospheric PV generated by diabatic heating is dominant over PV generated due to near surface baroclinicity Deep and relatively strong vertical wind shear 10-15 m s -1 (900 – 300-hPa) Initial Development = 0 >> 0

3. Where PV2 >> PV1 (so PV1 / PV2 is nearly zero) Low-to-mid tropospheric PV generated by diabatic heating is dominant over PV generated due to near surface baroclinicity Deep and relatively strong vertical wind shear 10-15 m s -1 (900 – 300-hPa) Initial Development = 0 >> 0 V T = 10 – 15 m s -1 Subtropical Cyclone

4. Cyclone C 1 exhibits subtropical dynamics during its evolution Cyclone generated primarily by diabatic heating PV1 / PV2 < 0.25 Vertical wind shear (1000 km box) ~13 m s -1 at start (90 h) Average 16.6 m s -1 (90-192 h) Subtropical Cyclone 120 h PV1 PV2 S15_U30 Simulation

5. Cyclone C 1 exhibits subtropical dynamics during its evolution Cyclone generated primarily by diabatic heating PV1 / PV2 < 0.25 Vertical wind shear (1000 km box) ~13 m s -1 at start (90 h) Average 16.6 m s -1 (90-192 h) Subtropical Cyclone 156 h PV1 PV2 S15_U30 Simulation

6. Cyclone C 1 exhibits subtropical dynamics during its evolution Cyclone generated primarily by diabatic heating PV1 / PV2 < 0.25 Vertical wind shear (1000 km box) ~13 m s -1 at start (90 h) Average 16.6 m s -1 (90-192 h) Subtropical Cyclone 192 h PV1 PV2 S15_U30 Simulation

7. PV1 PV2 Cyclone C 1 exhibits subtropical dynamics during its evolution Cyclone generated primarily by diabatic heating PV1 / PV2 < 0.25 Vertical wind shear (1000 km box) ~13 m s -1 at start (90 h) Average 16.6 m s -1 (90-192 h) Subtropical Cyclone 240 h S15_U30 Simulation

8. Cyclone generated primarily by diabatic heating PV1 / PV2 < 0.25 Vertical wind shear (1000 km box) Average 10 m s -1 Subtropical Cyclone Cyclone C 2 exhibits subtropical dynamics during its evolution 240 h PV1/PV2 Is this even a closed cyclone at this time? S15_U30 Simulation

9. Compare primary cyclone to subtropical cyclones Subtropical Cyclone PV1/PV2 Cyclone generated primarily by baroclinic processes PV1 / PV2 < 2 Diabatic heating becomes important in latter lifecycle (relative to dry simulation) > 144 h 264 h S15_U40 Simulation Vorticity Rapidly Increasing

10. 264 h Subtropical Cyclone Compare primary cyclone to subtropical cyclones Cyclone generated primarily by baroclinic processes PV1 / PV2 < 2 Still PV2 generation in Dry Simulation PV2 generated at top of boundary layer due to turbulent mixing in boundary layer (Stoelinga 1996). S15_U40_D Simulation PV1/PV2 Vorticity Slowly Increasing

11. S15_U40 Simulation @ 120 h Subtropical Cyclone Observe C 3 (subtropical cyclone) perturbing environment Similar to C 1 and C 2 ; very limited surface baroclinicity and ample condensational heating PV1 / PV2 < 0.2 Vertical Wind Shear 14 m s -1 average during development (westerly)

12. S15_U40 Simulation @ 168 h Subtropical Cyclone Observe C 3 (subtropical cyclone) perturbing environment Primary cyclone perturbs the subtropical waveguide creates “waviness” in the low latitude Low-latitude convection favors downstream corridor of developing wave

13. S15_U40 Simulation @ 216 h Subtropical Cyclone Observe C 3 (subtropical cyclone) perturbing environment Robust upper-level wave in low latitudes Results in surface cyclogenesis with large corridor of convection Convection building downstream anticyclone

14. S15_U40 Simulation @ 264 h Subtropical Cyclone Observe C 3 (subtropical cyclone) perturbing environment Highly amplified wave on lower latitude waveguide Intense subtropical cyclone at peak intensity Strong diabatic ridge growth Easterly jet equatorward of anticyclone only perturbed in latter time periods