nwp models. strengths and weaknesses

NWP models. Strengths and weaknesses.

Morten Køltzow, met.noNOMEK 22.04.2010

Norwegian Meteorological Institute met.no

Outline

• Models employed at met.no

• Models ability to forecast:– Precipitation.– 2m air temperature.– Extreme weather (wind).

Norwegian Meteorological Institute met.no

Models employed at met.no

• Hirlam, 12km, 8km, 4km– (NOR)LAMEPS 12km

• UM, 4km -> 1km

• ECMWF (approximately 16km)

• Simra, turbulence model, 100m -> 50m• AirQUIS, urban air quality model• Wave and ocean models• SNAP, (nuclear accident) transport model• EMEP, chemical transport model

Norwegian Meteorological Institute met.no

• Hirlam - hydrostatic model.– Assumes that the vertical acceleration

is much smaller than g. The vertical velocity is found by diagnostics. Good approximation for coarse models.

• UM – non hydrostatic model.

Non-hydrostatic models are important when features with large vertical velocities is resolved (i.e. convection or flow around steep orography).

Norwegian Meteorological Institute met.no

H12, H08, H4, UM4:

H12

H08

4km

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Norwegian Meteorological Institute met.no

Precipitation

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Seasonal mean, 24h precipitation:

JJA SON

UM4km

HIRLAM 8km

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Precipitation from a fine scale model (left), a global model (mid) and observations (right). From Ebert (2009).

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Verification of precipitation DJF:(models ability to forecast correctly 24h precipitation above a certain threshold)

HIT RATE

FALSE ALARM RATIO

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• Binary approach:– Each coloured grid cell precipitation > 0.0mm

• Compare fraction of occurences from forecast and radar for different areas. On which spatial scales are the fractions similar?

Forecast Radar

At what spatial scales show the models

useful information?

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Spin-up, cloud cover.

HIRLAM 4HIRLAM 8HIRLAM 12UM4

9months june - February

JJA

DJF

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Spin-up of precipitation (mm/h)

HIRLAM 4HIRLAM 8HIRLAM 12UM4

JJA

DJF

9mnd June - Februay

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Near surface temperature (T2m).

• Coastlines.• Heightcorrection of T2m.

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T2m bias, coastal stations.

WINTER

SUMMER

Warm bias in winter and cold bias in summer due to toohigh influence by the sea surface temperature on T2m.

BIAS BIAS

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Coast “coarse model” ECMWF.

B

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Interpolation:bi-linear

Nearest grid pointNearest land grid point

(B is a ocean grid point in the model)

B

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Bi-linear interpolation:

22°

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Observed 28.7°

Nearest land point “interpolation”

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Difference in topography 8km and 500m horizontal resolution

Blue – real topoless than

model topo

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Height corrections of T2m is necessary!

BIA

S

Model topography – real topography

HIRLAM8 T2m

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ALNABLINDERN

TRYVANN

BJØRNHOLT

HAKADAL

KJELLER

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Variasjon i tid og rom:

Nov. Dec. Jan. Feb.

Sort – meanStiplet – stdevVarsel;T+0->T+48

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Modelling wind in Norway

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Low pressure system 1000 hPa, Newfoundland 31.12.91 kl. 00 Utc.

From Karsten Eitrheim,

VpV, met.no

Norwegian Meteorological Institute met.no

Analysis 18 Utc 31.12.91.

FromKarsten Eitrheim,

VpV, met.no

Norwegian Meteorological Institute met.no

Analysis 00 UTC 01.01.92

From Karsten Eitrheim,

VpV, met.no

Norwegian Meteorological Institute met.no

Analysis Kl. 06 UTC 01.01.92

From Karsten Eitrheim,

VpV, met.no

Norwegian Meteorological Institute met.no

FromTrygve Aspenes

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Maksvind~33.5m/s

From Karsten Eitrheim,

VpV, met.no

Norwegian Meteorological Institute met.no

The new year storm, observed wind strength:

Færder to Bodø:

More than strong gale (>20.8m/s).

Hardangerfjorden to Sklinna Fyr:

More than violent storm (>28.5m/s).

Stad to Vikna:

More than hurricane force (>32.6m/s).

Maximum wind strength (10min average) at Svinøy and Skalmen Fyr.

Most probably the most severe storm in Norway the last 110 years.

Skalmen Svinøy

Norwegian Meteorological Institute met.no

Norwegian Meteorological Institute met.no

A rerun with a state of the art NWP model (HIRLAM, 8km) valid: 09UTC 1.1.1992

+45h +21h

Green > 20m/s, Yellow > 24m/s, Red > 30m/s

Maximum 35m/s

Initial and lateral boundaries from ERA-interim.

Norwegian Meteorological Institute met.no

Probability based on the Norwegian EnsemblePrediction System (NORLAMEPS)

+60h valid 06UTC 1.1.1992Probabilities for more than 25m/s (green)

Probabilities for more than 30m/s (red)

NORLAMEPS

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Ulrik, 2008

Black: Analysis HIRLAM 00UTC 26.October. Red : HIRLAM forecast +48h

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Ulrik, 2008

Black: Analysis HIRLAM8 00UTC 26.October Red: HIRLAM forecast +24h

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Vera, Polar low, November 2008:

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Vera – “offshore”:

Observations - black curve

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Vera – “outer coast line”:

ECMWF

Observations - black curve

Norwegian Meteorological Institute met.no

Vera – “inner coast line”:

Observations - black curve

Norwegian Meteorological Institute met.no

Mo

del

Verification of wind (+0 to +60) at 6 Norwegian offshore stationsDecember 2009 - February 2010

ObservationObservations are originally taken approximately 100masl and reduced to 10masl assuming neutral conditions.

Norwegian Meteorological Institute met.no

Observation

Mod

el

Verification of wind (+0 to +60) at 28 Norwegian coast stations (lighthouses). December 2009 - February 2010.

Norwegian Meteorological Institute met.no

Mod

el

Observation

Verification of wind (+0 to +60) at 9 Norwegian mountain stations (>930masl)

December 2009 - February 2010

Norwegian Meteorological Institute met.no

Thank you for your attention!