FORECASTING WEATHER RADAR PROPAGATION CONDITIONS USING NWP MESOSCALE MODEL DATA

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



Index

1. Introduction.

4. Final remarks.

3. NWP Forecasts vs. Observations. Modified Forecasts.

2. Methodology: Vertical Refractivity Gradients & Ducting Index



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



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 /



(Turton et al., 1988)



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.



PROPAGATION CONDITIONS AND RADAR BEAM HEIGHT (2)

PBE radar PPI (0.7º elevation) with observed superrefractive VRG (-106 N units/km).



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



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).



VRG & DUCTING INDEX (OBS & FOR)



DUCTING INDEX (OBS & FOR AVERAGES)



OBSERVED VRG AUTOC., MAE, ME & RMSE



DUCTING INDEX MODIFIED FORECASTS

Pí = Pí0 + Pí

NAME Pí0Pí 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



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).

FORECASTING WEATHER RADAR PROPAGATION CONDITIONS USING NWP MESOSCALE MODEL DATA

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