An analysis of an unusually heavy rain in Meizhou

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An analysis of an unusually heavy rain in Meizhou

• Jinghua Yan
• (Guangzhou Institute of Tropical Marine
  Meterology,Guangzhou 510080)
• Jun 1-3,2005 Wuhan

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Contents

• Introduction
• Weather pattern
• Numerical simulation
• Mesoscale analysis

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Rain storm and flood

• an unusually heavy rain occurred in Meizhou area
  on May 17, 2003.
• 4 hourly precipitation of 196mm,unusual in
  history,in Meixi town.
• huge amount, concentrated period, high intensity
  and intense momentum, the rain pushed up water
  levels rapidly in rivers and reservoirs, caused
  severe damages.
• 20 people were killed. Total economic loss of 398
  million yuan.

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24h precipitation 12Z May 12z May 17.
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Hourly precipitation at Meixian
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Damages
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Circulation00z May16,2003 500hPa
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Circulation00z May17,2003 500hPa
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Numerical simulation

• German HRM model
• 14km horizontal resolution,31 layers
• Full physical processes
• Success in simulating rain storm
  meso-perturbations
• Mechanism analysis using modeling data

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4 hour precipitation from simulation
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Hourlyevolution of precipitation
Obs
model
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• Diagnosis

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Wave train like perturbations and heavy rain
20z May16
21z May 16
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Wave train like precipitation in simulation
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Wave train like vertical motion in simulation
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Weather pattern
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Time-frequency distribution of wavelet amplitude
of vertical velocity
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Time-frequency section of power spectral density
of vertical velocity
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• 2-4hour periods are evident in slp and om,from
  6th to 13th prediction hour
• Coincide between strongest wave and rain storm
• Period and phase speed(33m/s, 120km/h)in
  consistent with gravity (inertia) wave.

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Stability and perturbations
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Features of gravity wave

• Stable stratification,larger vertical shear
• 10 minutes several hours of periods
• Phase speed 10-50m/s
• Vertical velocity (shift) 0.25m/s (800m)
• It may be seen as point origin of gravity
  wave,when convection occurs under stable upper
  layer condition
• Convection may be triggered when gravity wave
  spread over unstable stratification area.
• Match the features of gravity waves

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1000hPa geopotential height in simulation
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Vertical motion evolution in simulation
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Time evolution of stability
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Time evolution of divergence at (24ºN,116.5ºE)
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OM after 250km filtering typical
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Conclusions (discussions)

• The rain storm occurs in warm area ahead of the
  front
• Front precipitation shows wave train like
  distribution
• Precipitation area moves east ward with speed of
  33m/s
• 2-4 hour period atmospheric oscillation is
  evident during rain storm
• It is stable in upper layer, over wave area
• Wave propagates in upper air, but may spread
  downward
• Features of the wave train match that of gravity
  wave
• Convection triggered at front may be the wave
  fountain of wave train
• As the front moves slow in east part, Meizhou is
  situated at the unstable warm area ahead of front
  for long time. Convections are triggered out in
  Meizhou when eastward moving wave train passes
  over in upper air

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• Thanks!
• Comments Please