1. How Do Outer Spiral Rainband Affect Tropical Cyclone Structure and Intensity?
The working hypothesis is based on the fact that the outer rainbands are driven mainly by diabatic heating due to phase changes in the rainband
Reference :
Wang, Y., 2009: How Do Outer Spiral Rainbands Affect Tropical Cyclone Structure and Intensity?. J. Atmos. Sci., 66, 1250–1273.

2. CONTENTS INTRODUCTION Add your title Numerical model description
TCM4
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Numerical model description
EXPERIMENTAL DESIGN
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Focus on the effect of the outer spiral rainbands on both the intensity and structure
RESULTS
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CONCLUSIONS
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3. Introduction
A long-standing issue on how outer spiral rainbands affect the structure and intensity of tropical cyclones
Wang(2008b) found that interaction between the eyewall and outer spiral rainbands can be lead to a size increase of storm’s eye and eyewall and formation of annular hurricane.
The particular focus is on the hydrostatic adjustment mechanism associated with diabatic heating in outer spiral rainbands and anvil clouds outside the inner core
Inner spiral rainband
在outer rainband 區域 會使得地面氣壓降低，使得與眼牆的氣壓梯度下降，進而減少眼牆的切線風速而增加颱風的最大風速半徑。
Heating outside the eyewall may cause pressure to fall in the lower boundary and reduce to pressure gradient across the eyewall, which will weaken the tangential wind near the RMW but increase the size of the TC inner core.

4. Tropical Cyclone Model (TCM-4)
Capable of simulating the inner-core structure and intensity change of TC at nearly cloud resolving resolution(Wang 2007,2008)
domain1
domain2
domain3
domain4
horizontal resolution
67.5 km
22.5 km
7.5 km
2.5 km
mesh size
201 X 181
109 X 109
127 X 127
163 X163
Vertical level
26 vertical levels

5. Tropical Cyclone Model (TCM-4)
(Durran and Klemp,1983)
38 km
solve sound and gravity waves problem
Initially, with an axisymmetric cyclonic vortex
Maximum wind speed of 20m/s at a radius of 80 km at the surface
f plane at 18oN in a quietscent environment
Constant SST of 29oC
Fully compressible
nonhydrostatic
primitive equation model
Explicit treatment of mixing-phase cloud microphysics(Wang 2001)
No cumulus parameterization is considered in any domain
MM5v3.3 distribution of IN and intercept of graupel is followed REISINER2
Mass coordinate in the vertical
An unperturbed surface pressure of 1010 hPa.

6. Experimental design
After a spinup period of 48 h ,the modle TC develops a structure similar to real TCs.
outer spiral rainbands are mainly driven by diabatic heating due to phase changes in the rainbands.
The heating due to condensa-tion, depostion, and freezing while the cooling due to sublimation of ice particle ,evaporation of rain and cloud droplets ,melting of snow and guapel.
The effect on TC intensity and structure can be evaluated by artifcially modifying the heating and cooling rate due to phase change .
Potential vorticity indicated the temperature and moisture
Angular momentum indicated tangential wind and radius

7. Experimental design

8. Experimental design C120 H110 HC80,C80,H80 CTRL Inner Spiral Rainbands
Outer Spiral Rainbands
RMW

9. Results 9h Weak tangential wind (K/h)
Cooling in the outer rainbands that leads the more rapid intensification and the strong storm
H110 much weaker than others
Cooling in the outer spiral rainbands lead to increasing the intensity ,whereas heating tend to decreasing the intensity and increase the radius of maximum wind .
Weak tangential wind
(K/h)

10. Results
>120 h
Reducing the heating rate (H80) or increasing the cooling rate (C120) considerably decreased the size of eye and eyewall relative to CTRL.
In contrast, reducing the cooling rate (C80) or increasing the heating rate (H110) considerably increased the size of eye and eyewall relative to CTRL.
The heating is critical to the maintenance of outer spiral rain-bands, whereas cooling is destructive.
Different size of the eye and eyewall in the simulated storm
Different in the rain structure outside the inner core in the simulated storms.
The stronger storms in HC80,H80, and C120 than in CTRL imply that outer spiral rainbands weaken a storm.

11. 小結
The stronger storms in HC80,H80, and C120 than in CTRL imply that outer spiral rainbands weaken a storm.

12. Results
120 h
Rain rate
The rain rate’s distribution of azimuthally average can evident the large eye and eyewall
And heating in the outer spiral rainbands will lead to the eyewall tilted .H110 and C80

13. Results Transition period
The RMW increased rapidly in C80 is the result of the development of annular hurricane in 60 – 78 h
The transition from the regular hurricane to the annular hurricane in C80 occurred between 30 and 72 h
Transition period

14. Results
The extension of the warm core in the upper layer provides a more stable vertical structure .
dry
dry
相當位溫
溫度距平
warm
moist
moist

15. Results
The correlation between surface Rain Rate and surface Pressure Drop
Compare with the surface pressure drop and surface rain rate, it is reasonable consistent with the hydrostatic adjustment.

16. Results
h time average
Eyewall size

17. Results 9 h This is eyewall Heating 120 h L z
Reduce pressure gradient force
120 h r z

18. Conclusion I
The previous views on the effect of outer spiral rainbands on TC intensity :
1. Blocking of the boundary layer inflow
2. Subsidence forced by diabatic heating
3. cooling and drying of the boundary layer inflow due to convective downdraft
Internal atmospheric heating (cooling ) would tend to decrease(increase) surface pressure underneath the column.
As a result above, it would reduce the horizontal pressure gradient across RMW and increase the inner-core size of the .storm

19. Conclusion II
Heating/cooling outside the inner core depends strongly on the relative humidity in the near-core environment.
Deep moist layer in the near-core environment may favor the development of large tropical cyclone ,annular hurricane, and concentric eyewall.
A relatively dry environment may favor small, compact tropical cyclones and is unfavorable to the formation of annular hurricane or concentric eyewall.
May and Holland(1999),PV generation in the outer spiral rainbands could contribute to the formation of a concentric eyewall.

20. Thank You!

21. C80

22. H110

23. H110

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34. content CONTENTS INTRODUCTION TCM4 EXPERIMENTAL DESIGH RESULTS
DISCUSSION
CONCLUSIONS