A WRF Simulation of the Genesis of Tropical Storm Eugene (2005) Associated With the ITCZ Breakdowns The UMD/NASA-GSFC Users' and Developers' Workshop, September 2007

Chanh Q Kieu and Da-Lin ZhangDepartment of Atmospheric and Oceanic ScienceUniversity of Maryland

Content

Introduction Overview Model description Results Conclusions

Climatological conditions for TC genesis:

An underlying warm SST of at least 260C; A finite-amplitude low-level cyclonic disturbance; Weak vertical wind shear; A tropical upper tropospheric trough (TUTT); A moist lower to middle troposphere; and A location poleward of 50 latitude.

TC genesis may occur from Synoptic-scale control, e.g., MJO, AEWs, monsoon

troughs, cold surges Mesoscale convective systems or MCVs Mixed gravity-Rossby waves topography ITCZ breakdown

Breakdown due to barotropic instability, so-called Vortex Rollup (Charney 1962; Nieto Ferreira and Schubert 1997)

Breakdown due to the interaction of ITCZ and easterly MCVs (obs, Wang and Magnusdottir 2005,2006)

Statistical study by WM06 shows that VR-breakdown is less likely to generate a storm of tropical storm strength compared with MCV-ITCZ interactions

Scientific questions: What are the roles of the ITCZ breakdown and

MCVs in tropical cyclogenesis? What are the effects of vertical shear on tropical

cyclogenesis?

They will be addressed through a case study of the processes leading to the genesis of Tropical Storm Eugene (2005) using the NCEP reanalysis and satellite data, and 4-day cloud-resolving (WRF) simulations with the finest grid size of 1.33 km.

Overview: NCEP’s reanalysis

V2

V1

E

Hovmöller diagram of the 850-hPa vertical relative vorticity (unit: 10-5 s-1)

GOES-10/12 VIS 0000 UTC 17 Jul 2005

V2 V1

Overview of Eugene: TCSP-CIMSS satellite observations

GOES-10/12 VIS 0300 UTC 17 Jul 2005

V2 V1

Overview of Eugene: TCSP-CIMSS satellite observations

GOES-10/12 VIS 0600 UTC 17 Jul 2005

V2 V1

Overview of Eugene: TCSP-CIMSS satellite observations

GOES-10/12 VIS 0900 UTC 17 Jul 2005

V2 V1

Overview of Eugene: TCSP-CIMSS satellite observations

GOES-10/12 VIS 1200 UTC 17 Jul 2005

V2 V1

Overview of Eugene: TCSP-CIMSS satellite observations

GOES-10/12 VIS 1500 UTC 17 Jul 2005

V2 V1

Overview of Eugene: TCSP-CIMSS satellite observations

GOES-10/12 VIS 1800 UTC 17 Jul 2005

V2 V1

Overview of Eugene: TCSP-CIMSS satellite observations

GOES-10/12 VIS 2100 UTC 17 Jul 2005

V2 V1

Overview of Eugene: TCSP-CIMSS satellite observations

GOES-10/12 VIS 0000 UTC 18 Jul 2005

V2 V1

Overview of Eugene: TCSP-CIMSS satellite observations

GOES-10/12 VIS 0300 UTC 18 Jul 2005

V2 V1

Overview of Eugene: TCSP-CIMSS satellite observations

GOES-10/12 VIS 0600 UTC 18 Jul 2005

E

Overview of Eugene: TCSP-CIMSS satellite observations

GOES-10/12 VIS 0900 UTC 18 Jul 2005

E

Overview of Eugene: TCSP-CIMSS satellite observations

GOES-10/12 VIS 1200 UTC 18 Jul 2005

E

Overview of Eugene: TCSP-CIMSS satellite observations

Model setup NCEP Initialization at 0000Z 17 July 2005 when

MCVs V1 and V2 are about 1000 km apart Nested resolutions: 36, 12, 4 and 1.33 km. The 1.33 km domain is activated at 0000Z 18

July and moved manually, following the storm center

Lateral boundaries updated every 6-h Integrate 4 days to capture the life cycle of the

storm

Model configuration

A B

C

DN

D1

Tracks and Intensities

(a)

(b)

989 hPa

987 hPa

31 m s-138 m s-1

V2 V1

E

Hovmöller diagram of the 850-hPa vertical relative vorticity (unit: 10-5 s-1) for the period of 0000 UTC 17 - 0000 UTC 21 July 2005 and the longitude interval of 1150 – 950W.

6-h accumulated rainfall

Comparison of the simulated 6-h accumulated rainfall shaded, mm) over a subdomain of C to the corresponding 6-h TRMM satellite-estimated (contoured).

3-D flows during the merging period

V1

V2

V1

V2

T = 0600UTC18JUL T = 1200UTC18JUL

B

B

AA

E E

T = 0600UTC19JULT = 1800UTC18JUL

BB

A

A

Vertical cross sections of tangential flow and PV (shadings) during the merging period

V1 V2

V2 V1

E

V1 V2

Vertical cross sections of the normal component of horizontal winds (at 2 m s-1 intervals), PV (shaded at intervals of 0.5 PVU), superimposed by the system-relative in-plane flow vectors along the centers of V1 and V2

Radar reflectivity and vertical shear

900

500

700200

900500

700

200

900

500 700

200

900

500700

200

900500

700

200

900

500

700

200

19/18-66

20/06-78

Horizontal distribution of the radar reflectivity (shaded at 5-dBz intervals). Hodographs with VWS (solid) between 900 and 200 hPa (800 km 800 km) is also sketched. Upper right panels are e 352 K-isosurface

Vertical shear and moist downdrafts

A

B(a)

(b)

(c)

a) Horizontal distribution of e (2 K), and w (shaded at intervals 0.1 m s-1 for descending and 0.3 m s-1 for ascending) at 700 hPa at 19/12-60; (b) as in (a) but for vertical cross section through the storm center of e (at intervals of 2 K) and deviation potential temperature (’, shaded); and (c) as in (b) but for 19/18-66.

Conclusions The ITCZ breakdown is important, but merging MCVs are

critical in the genesis of Eugene Intensity and track are in mutual influence, especially in

shear environment. Too strong storm will impact the movement of simulated storm

Confirms previous findings: Interactions of VWS, ambient dry air intrusion result in a strong asymmetry of rainfall patterns

The interaction between VWS and ambient environment are not limited just to dry intrusion but to an elevated dust layer. This also has some implications to the high frequency cyclogenesis events in East Pacific.

Appendix 1 Parameterizations: (a) Kain-Fritsch (1990) cumulus parameterization

scheme for the 36- and 12-km resolution domains; (b) the Yonsei University planetary boundary layer (PBL) parameterization; (c) the Monin-Obukhov surface layer scheme. Note that no cumulus parameterization is used in the 4- and 1.33-km resolution domains.

Radiation: the Rapid Radiative Transfer Model (RRTM) scheme for both longwave and shortwave radiations (Mlawer et al. 1997)

Microphysics schemes: Lin et al. (1983) cloud microphysics scheme containing six classes of hydrometeors

The four nested-grid domains have the (x, y) dimensions of 251 201 (A), 252 ´ 252 (B), 388 ´ 382 (C), and 451 ´ 451 (D) with the grid size of 36, 12, 4, and 1.33 km, respectively

38 s levels: 1.000, 0.993, 0.980, 0.966, 0.950, 0.933, 0.913, 0.892, 0.869, 0.844, 0.816, 0.786, 0.753, 0.718, 0.680, 0.643, 0.607, 0.572, 0.538, 0.505, 0.473, 0.441, 0.409, 0.378, 0.348, 0.318, 0.289, 0.260, 0.232, 0.204, 0.176, 0.149, 0.122, 0.095, 0.068, 0.042, 0.018, and 0.000.

The model top is defined at 30 hPa.