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, 43-64.

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 t

owers b.outside of the eyewall the condensation occurs in weaker u

pdrafts, 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 descriptionCoarse-resolution:Started at 1200 UTC 22/08/1998 (36 hrs) 36 km: 91× 97

12 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)

Vr’ (contour)

W (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 velocity radial velocity

vertical velocity qv

qcl + qci qrain, qsnow, qgr

56ms-1

Budget Formulation

qv is mixing ratio of water vapor;qc is the mixing ratio of cloud liquid water and ice;qp is the mixing ratio of rain, snow and graupel;V’ is the storm-relative horizontal air motion;w is the vertical air motion;VT 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)Zx 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

condensation horizontal flux divergence,

evaporation vertical flux divergence,

Cond + Evap HF + VF divergence

divergence term boundary 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 (70-200 km)

b. Condensed water budget

cloud sink horizontal flux divergence

net source vertical flux divergence

boundary layer source added water mass to offset negative mixing ratios

condensation (total source of cloud)

cloud budget

rain

graupel

snow

sinkSourcecloud budget

net microphysical source horizontal flux divergence

precipitation fallout andvertical flux divergence

added water mass to offsetnegative mixing ratios

precipitation budget

cloud sink

Horizontal distributioncondensation evaporation

precipitation falloutqv

Horizontal distributiontotal 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 content Precipitation content

raincloud water

graupel

Conclusion A detailed water budget is performed using a high-resoluti

on 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 eyewa

ll 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.