High-Resolution Simulation of Hurricane Bonnie (1998). Part II: Water Budget Braun, S. A., 2006: High-Resolution Simulation of Hurricane Bonnie (1998). Part II: Water Budget. J. Atmos. Sci., 63, 演講人 : 陳登舜

Outline  Introduction  Simulation and analysis description a.Simulation description b.Simulated structure and validation  Budget formulation  Budget results a.Water vapor budget b.Condesed water budget c.Volume – integrated budget d.The artificial water source  Conclusions

Introduction  The water vapor budget a.the condensation in the eyewall occurs hot convective hot towers b.outside of the eyewall the condensation occurs in weaker updrafts, indicative of a larger role of stratiform precipitation processes.  Horizontal advection tended to transport drier air into the core in the boundary layer and moist air from the eye to the eyewall within the low-level outflow above the boundary layer (Zhang et al. 2002).  In this study, we compute budgets of both water vapor and total condensed water (cloud condensate, and precipitation) from a high-resolution simulation of Hurricane Bonnie (1998).

Simulation and analysis description  a. Simulation description Coarse-resolution: Started at 1200 UTC 22/08/1998 (36 hrs) 36 km: 91× km: 160×160 High-resolution: Started at 1800 UTC 22/08/1998 (30 hrs) 6 km: 225×225 2 km: 226×226 Vertical: 27 levels

1800 UTC 22 Aug. TRMM 1050 UTC 24 Aug. TRMM 1200 UTC 23 Aug MM5

Radar Reflectivity CFAD 1800 UTC 22 Aug. TRMM 1200 UTC 23 Aug. MM5 contoured frequency by altitude diagrams (CFADs)

40 m 2.7km 6.8km 12km Vr ’ (contour) W (contour) 1-h Time Average (24-25 h)

dBZ (shading) W (contour) Qc+Qi (shading) W (contour) dBZ (shading) Vr ’ (contour) 1-h Time Average (24-25 h)

dBZ + w (qcl+qci) + w dBZ + Vr 1-h Time Average (24-25 h)

tangential velocityradial velocity vertical velocityqv qcl + qciqrain, qsnow, qgr 56ms -1

Budget Formulation q v is mixing ratio of water vapor; q c is the mixing ratio of cloud liquid water and ice; q p is the mixing ratio of rain, snow and graupel; V ’ is the storm-relative horizontal air motion; w is the vertical air motion; V T is the hydrometeor motion; + is source; - is sink; C is the condensation and deposition; E is the evaporation and sublimation; B is the contribution from the planetary boundary layer; D is the turbulent diffusion term; Z is the artificial source term associated with setting negative mixing ratios to zero.

the temporal and azimuthal mean: the time-averaged and vertically integrated amount: the time-averaged, volumetrically integrated amount: (kg·m -3 ·h -1 ) (kg·m -2 ·h -1 ) (kg·h -1 ) Budget Formulation(con ’ t) the azimuthally averaged horizontal advective flux is simply that associated with radial transport

Budget Formulation(con ’ t) Z x is artificial source terms associated with setting negative mixing ratios (caused by errors associated with the finite differencing of the advective terms) to zero, that is, mass is added to eliminate negative mixing ratios.

Budget results condensationhorizontal flux divergence, evaporationvertical flux divergence, Cond + EvapHF + VF divergence divergence termboundary layer source term 1-h Average (24-25 h) a. Water vapor budget Melting layer

updraft condensation occurring in updraft much of the eyewall condensation is associated with hot towers. The smaller contribution of stronger updrafts is indicative of the larger role of stratiform precipitation processes outside of the eyewall. eyewall region (30-70 km)outer region ( km)

b. Condensed water budget cloud sinkhorizontal flux divergence net sourcevertical flux divergence boundary layer source added water mass to offset negative mixing ratios condensation (total source of cloud) cloud budget

rain graupel snow sinkSource cloud budget

net microphysical source horizontal flux divergence precipitation fallout and vertical flux divergence added water mass to offset negative mixing ratios precipitation budget cloud sink

Horizontal distribution condensation evaporation precipitation fallout qv

Horizontal distribution total rain source warm rain source cold rain source graupel source Rain source + graupel sink Graupel sink

c.Volume–integrated budget

d. The artificial water source cloud liquid water cloud ice rain snow graupel Cloud contentPrecipitation content

raincloud water graupel

Conclusion  A detailed water budget is performed using a high- resolution simulation of Hurricane Bonnie (1998). The simulation generally reproduces the track, intensity, and structure of the storm, but overpredicts the precipitation as inferred from comparison of model and TRMM radar reflectivities.  The water vapor budget confirms that the ocean source of vapor in the eyewall region is very small relative to the condensation and inward transport of vapor, with the ocean vapor source in the eyewall (0.7) being approximately 4% of the inward vapor transport into the eyewall (16.8) region.  In the eyewall, most of the condensation occurs within convective towers while in the outer regions condensation results from a mix of convective and stratiform precipitation processes, with the stratiform component tending to dominate.

Conclusion  Precipitation processes acting outside of the eyewall region are not very dependent on the condensate mass produced within and transported outward from the eyewall.  Although the artificial water mass source is very small at any given grid point, its cumulative impact over large areas and over time is more substantial, contributing an amount of water that is equivalent to 15% – 20% of the total surface precipitation.