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Servei Meteorològic de Catalunya
Generalitat de CatalunyaDepartament de Medi Ambient
FORECASTING WEATHER RADAR PROPAGATION CONDITIONS USING
NWP MESOSCALE MODEL DATA
25th EWGLAM and 10th SRNWP Meetings. Joint SRNWP/COST 717 Session. Lisbon 8th October 2003
Joan Bech1, Bernat Codina2 and Jeroni Lorente2
1Servei Meteorològic de Catalunya2Universitat de Barcelona
Servei Meteorològic de Catalunya
Generalitat de CatalunyaDepartament de Medi Ambient
Index
1. Introduction.
4. Final remarks.
3. NWP Forecasts vs. Observations. Modified Forecasts.
2. Methodology: Vertical Refractivity Gradients & Ducting Index
Servei Meteorològic de Catalunya
Generalitat de CatalunyaDepartament de Medi Ambient
ANOMALOUS PROPAGATION (ANAPROP)
“ANOMALOUS PROPAGATION (ANAPROP) OF THE WEATHER RADAR BEAM OCCURS WHEN MOISTURE AND TEMPERATURE PROFILES VARY SIGNIFICANTLY FROM NORMAL”
SOME OBSERVED EXTREME ANAPROP CASES:
MEDITERRANEAN SEA (Battan,1973)INDIC OCEAN (UKMO, 1994)US WEST COAST (Babin,1995)BALTIC SEA (Anderson et al, 1997)
.
.
Sub refraction
Standard refraction
Super refraction
Servei Meteorològic de Catalunya
Generalitat de CatalunyaDepartament de Medi Ambient
REFRACTIVITY & VRG
REFRACTIVITY N & MODIFIED REFRACTIVITY M (Bean and Dutton, 1968) :
SUB REFRACTIVE
NORMAL
SUPER REFRACTIVE
(“DUCT”)
T
ep
TnN
48106.7710)1(
6
1
1
1
157
40
0
kmzN
kmzN
kmzN
VERTICAL REFRACTIVITY GRADIENT (VRG)
ahNM /
Servei Meteorològic de Catalunya
Generalitat de CatalunyaDepartament de Medi Ambient
(Turton et al., 1988)
Servei Meteorològic de Catalunya
Generalitat de CatalunyaDepartament de Medi Ambient
PROPAGATION CONDITIONS AND RADAR BEAM HEIGHT (1)
• Anaprop leads to differences in expected radar beam heights.
• Example for PBE radar beam height (0º elevation) with observed subrefractive and superrefractive VRG.
Servei Meteorològic de Catalunya
Generalitat de CatalunyaDepartament de Medi Ambient
PROPAGATION CONDITIONS AND RADAR BEAM HEIGHT (2)
PBE radar PPI (0.7º elevation) with observed superrefractive VRG (-106 N units/km).
Servei Meteorològic de Catalunya
Generalitat de CatalunyaDepartament de Medi Ambient
VRG & DUCTING INDEX
VRG = N / z ITU (1997)
ID = 78 z - M Johson et al. (1999)
November 2002 to February 2003 (183 cases)
MASS model refractivity profiles00 & 12 Z
RAOB
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Generalitat de CatalunyaDepartament de Medi Ambient
REFRACTIVITY VERTICAL PROFILE (OBS & FOR)
Vertical profile of modified refractivity on 13th Novembre 2002 at 12 Z over Barcelona: observation (OBS, thick
solid line) and model forecast (FOR, crosses, dotted line).
Servei Meteorològic de Catalunya
Generalitat de CatalunyaDepartament de Medi Ambient
VRG & DUCTING INDEX (OBS & FOR)
Servei Meteorològic de Catalunya
Generalitat de CatalunyaDepartament de Medi Ambient
DUCTING INDEX (OBS & FOR AVERAGES)
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Generalitat de CatalunyaDepartament de Medi Ambient
OBSERVED VRG AUTOC., MAE, ME & RMSE
Servei Meteorològic de Catalunya
Generalitat de CatalunyaDepartament de Medi Ambient
DUCTING INDEX MODIFIED FORECASTS
P´i = P´i0 + P´i
NAME P´i0P´i Cases ME MAE
A Pi-1 Pi - Pi-1 180 9,92 10,00
B Oi-1 Pi - Pi-1 164 0,03 4,98
C (Oi-1 + Oi-2 ) / 2 Pi – (Pi-1 + Pi-2) / 2 151 0,01 4,44
D Oi-2 Pi - Pi-2 162 0,07 5,14
E (Oi-1 + Oi-2 ) / 2 Pi - Pi-1 155 -0,02 4,83
F Oi-1 Pi – (Pi-1 + Pi-2) / 2 159 0,04 4,63
G (Oi-1 + Oi-2 + Oi-3) / 3 Pi – (Pi-1 + Pi-2 + Pi-3 ) / 3 139 -0,20 4,13
H (Oi-1 + Oi-2 + Oi-3 + Oi-4) / 4 Pi – (Pi-1 + Pi-2 + Pi-3 + Pi-4) / 4 128 -0,21 3,87
I (Oi-1 + Oi-2 + Oi-3 + Oi-4 + Oi-5) / 5 Pi – (Pi-1 + Pi-2 + Pi-3 + Pi-4+ Pi-5) / 5 127 -0,29 3,96
Servei Meteorològic de Catalunya
Generalitat de CatalunyaDepartament de Medi Ambient
Final Remarks
1. Four months of NWP derived VRG and ID forecasts have been compared with RAOB diagnosed VRG and ID.
4. Model forecasts were useful to anticipate anaprop conditions but in some aspects RAOB persistency was better.
3. Considering model tendency and previous OBS, new forecasts produced better verification scores.
2. Original model forecasts were biased towards subrefraction (specially ducting index).