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A physical initialization algorithm for non-hydrostatic NWP models using radar derived rain rates. Günther Haase Meteorological Institute, University of Bonn German Weather Service. radar LM. area: Northern Germany ~ 400x400 km 2 x = 7 km time period: May, 2000 (t = 1 h). - PowerPoint PPT Presentation
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A physical initialization algorithm for non-hydrostatic NWP models
using radar derived rain rates
Günther Haase
Meteorological Institute, University of BonnGerman Weather Service
Günther Haase Helsinki, 3 October 2002 2
area:
Northern Germany ~ 400x400 km2
x = 7 km
time period:
May, 2000 (t = 1 h)
radar LM
Günther Haase Helsinki, 3 October 2002 4
PIB Algorithmpreprocessing of reflectivity measurements
determine pre-forecast period, conversion efficiency and mean cloud top height
compute present LM-CCL (cloud base)
precipitation analysis saturation adjustment
modify LM variablesw, qv, and qc
Günther Haase Helsinki, 3 October 2002 5
DWD radar network
• 16 C-band radars: = 5.3 cm
• cartesian grid: x = 4 km
• temporal resolution: t = 15 minutes
• 6 reflectivity classes
• fixed Z/R relation
Günther Haase Helsinki, 3 October 2002 6
Cloud top height
Derivation of cloud top heights from averaged LMcloud water profiles
Alternative: application of a cloud initialization method using Meteosat measurements (F. Ament)
Günther Haase Helsinki, 3 October 2002 7
Cloud base height
CCL
LCL
• open symbols: LM without convection parameterization• closed symbols: LM with convection parameterization
Günther Haase Helsinki, 3 October 2002 8
Modifications
RRRAD > 0.1 mm/h RRRAD 0.1 mm/h
0qc85%) (rh, MINrh
0w
cbz z
cbct zz z
ctz z
0qc)(zqvqv
zzzz )(z ww
cb
srfcb
srfcbPI
changes no :qcqvqv
)(ww*
PI
z
0qc85%) (rh, MINrh
changes no :w
0qc85%) (rh, MINrh
changes no :w
0qc85%) (rh, MINrh
changes no :w
Günther Haase Helsinki, 3 October 2002 9
Vertical wind (PIB)
assumptions:• only two hyd. components:
water vapor and rain• only two cloud processes:
condensation and evapo-ration
• closure: conversion efficiency of saturated air into rain
Computation of vertical wind profiles using a 1-dim cloud model
0,1 wρ
RRc cbzzPI
*v
C = 0.1
Günther Haase Helsinki, 3 October 2002 10
Case study: 13 July 1999
Exp. pre-forecast period forecastCTL – 12 hPIB 12 – 13 UTC 12 hLHN 12 – 13 UTC 12 h
Günther Haase Helsinki, 3 October 2002 11
PIB sensitivity study
Günther Haase Helsinki, 3 October 2002 13
CTL LHNPIB radar
13 UTC
14 UTC
15 UTC
Günther Haase Helsinki, 3 October 2002 14
CTL with convection parameterization
Günther Haase Helsinki, 3 October 2002 15
Hydrology
a) Area averaged hourly accumulated precipita-tion
b) LWP and IWV: PIB generates more clouds than the control run (CTL)
Günther Haase Helsinki, 3 October 2002 16
a) Hit Rate
b) False Alarm Rate
c) Kuipers Score (measures the skill of a forecast relative to a random forecast)
Objective skill scores
Günther Haase Helsinki, 3 October 2002 17
Scale-dependency of the RMSE
• PIB provides better forecasts than the control run (CTL) on all scales• LHN is better on large scales
Günther Haase Helsinki, 3 October 2002 18
a) vertical wind (500 hPa)
b) surface pressure
c) absolute surface pres-sure tendency
Noise
Günther Haase Helsinki, 3 October 2002 19
Summary (1)
PIB is suitable for nowcasting of convective precipitation events on the meso--scale
reduction of spinup and position errors in the precipitation forecast over a couple of hours
closure of the information gap between LM forecasts and nowcasting based on observations
PIB uses only operational radar products as input
Günther Haase Helsinki, 3 October 2002 20
low computational costs
compatible with future model developments
column approach prevents the method from initializing large-scale precipitation events
PIB reacts very sensitive on variations of the input data (quality control!)
Summary (2)
Günther Haase Helsinki, 3 October 2002 21
combination with a cloud initialization method using Meteosat measurements
using 3-dim reflectivity fields (on model levels)
forcing a dynamic balance between mass and wind fields
application of a modified LM precipitation scheme
Future research