on the 2m temperature and dew point diagnostics in the cosmo … · 2016. 12. 20. · on the 2m...

Eidgenössisches Departement des Innern EDIBundesamt für Meteorologie und Klimatologie MeteoSchweiz

On the 2m temperature and dew point diagnostics in the

COSMO model

Matteo Buzzi and M.W. Rotach MeteoSwiss

2On the 2m temperature diagnostics in the COSMO model | [email protected]

Overview

• Introduction• Surface layer• Operational 2m temperature and dew point diagnostics

• Possible sources of error• The role of subgrid scale orography

• Alternatives: new interpolation formulas or profiles• Case studies

• Intercomparison: verification results• Conclusions


Surface layer

0

Inertial sublayer (ISL)

Roughness sublayer (RSL)

hcan

z*

0.1zi

Θ'w' sensible heat fluxQv'w' latent heat flux

Θ'w'surf or Qv'w'surf

constant turbulent fluxes

inconstant fluxes

NWP modelsfirst model layer

2m

z*= 2hcan


COSMO 2m temperature and dew point diagnostics: 3 cases

T(ke), Q(ke)

H1=z0

0Ts,Qs

H2=z0+h(ke)

z0+h(ke-1) T(ke-1), Q(ke-1)

hcan

skin

laye

r!

EXP LOG LOG INTERP

( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛ ++= H

lam

Htur

HlamH

turH

lamcan rrrrrRCh log


2m temperature: possible sources of error

• Surface temperature:• soil model (surface energy balance, LH, SH, GF, SWbal, LWbal)

• Atmosphere temperature:• dynamics (e.g. advection), convection, turbulence scheme

• Interpolation profile in the diagnostics:• choice of “wrong” profile function

• Surface description:• Roughness length:

• canopy height


COSMO-7 roughness length (7 km)[m]


COSMO-7 roughness length: local and orographic component (7 km)

z0 = z0, loc + z0,oro

z0, loc z0,oro[m] [m]

hcan


Unrealistic canopy height (7km)20.12.2006 6 UTC 20.12.2006 12 UTC [m]

exp profile is too often used!

hcan =z0, loc

0.1

( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛ ++= H

lam

Htur

HlamH

turH

lamcan rrrrrRCh log


Averaged diurnal cycle: 15.04.2007

z0,oro< 0.2 m 0.2 m < z0,oro< 0.5 m

COSMO-7 over the alpine region


Phase error

26.07.2007 COSMO-7- Swiss SYNOP stations


Comparison of different diagnosticsProblem:

2 m temperature is too close to the surface temperatureSolution:

introduction of a local roughness length and try others diagnostics0. Introduce a realistic hcan in operational diagnostics

• But inconsistent with resistances (option only possible if surface transfer scheme and turbulence scheme are called twice)

1. Use a simple logarithmic interpolation as used for wind (newlog)• But not consistent with RSL (z0,loc >0.2m)!

2. ECMWF IFS diagnostics (logarithmic interpolation based on Monin-Obuchov similarity) (ecmwf)• But not consistent with RSL (z0,loc >0.2m)!

3. New approach (new):• New logarithmic profile (as 1.) only for gridcells with z0,loc < 0.2m• z0,loc > 0.2m new RSL profiles independent from surface

temperature4. Diagnostics for a SYNOP garden (by Matthias R.) (dwdnew)

• But not consistent with RSL (z0,loc >0.2m)!5. As 4. but with z0,loc instead of typical SYNOP z0 (dwdnew z0loc)


H2 = H(ke) + z0, loc + d

New profiles: general aspects

0

Inertial sublayer ISL

Roughness sublayer RSL

hcan

z*

0.1zi

Temperature

T*, ISL fluxes

hcan =z0, loc

0.1z* = 2hcan

d =23

hcan

Approach for large z0,loc: derive temperature and specific humidity profile from turbulent flux profiles and atmospheric values

First model atmospheric levelH2

d

T,QV,H0,LH0, Mo0


New profiles: 3 cases

newlog


New profiles: formulationdθdz

=θ*(z)

α ⋅ (z − z0, loc )

θ*(z) =w'θ '(z)u*(z)

=w'θ '(z)

u'w'(z)2 + v'w'(z)2( )1 / 4

θ(z) = θ(z*) −θ*(z)

α ⋅ (z − z0, loc )dz

z0

z

∫

θ*(z*)α ⋅ (z* − z0, loc )

= φhθ*

k(z* − d)⇒ α =

k(z* − z0, loc )φh (z* − d)

φh ( zL

)

Profile matching at z*

RSL: local scaling

Integration

ISLRSL


Sensible heat flux and vertical temperature derivative


Temperature and specific humidity


Case studies and model settings

• 5 cases 24h forecast COSMO 7km (fairly good weather)• 20.12.2006, 15.04.2007, 18.06.2006, 26.07.2007,

15.10.2007• COMSO 3.20, Runge-Kutta, IFS Analysis as BC, COSMO

analysis as IC• Verification with SYNOP stations for the domain covering

the alpine region (COSMO-2) (for all 6 variants)


Variants compared with operational diagnostics

1. Simple logarithmic interpolation as used for wind (newlog)

2. ECMWF IFS diagnostics (ecmwf)

3. New approach (new): RSL profiles z0,loc > 0.2m

4. Diagnostics for a SYNOP garden (dwdnew)

5. As 4. but with z0,loc instead of typical SYNOP z0 (dwdnew z0loc)


Results: diurnal cycle 15.04.2007


Averaged diurnal cycle: 15.04.2007


Comparison of the vertical profiles


Verification: SYNOP alpine region 2m temperature 20.12.2006


Verification: SYNOP alpine region2m dew point (RMSE)


2m temperature: results summary

RMSE[°C]

ME[°C]

STDEV ME[°C]

Operational 3.15 -0.86 3.03

new RSL 2.86 -0.62 2.79

newlog 2.74 -0.52 2.69

dwdnew 2.73 -0.44 2.70

dwdnew z0,loc 2.75 -0.56 2.69

ecmwf 2.74 -0.56 2.68

COSMO-7 verified on COMSO-2 domain (only 5 days)!


Conclusions

• 2 m temperature and 2m dew point: multiple sources of error (soil, atmosphere, choice of the interpolation profile)

• Unrealistic canopy height (from subgridscale orography) is a significant source of error (choice between EXP and LOG profile)

• Operational diagnostics compared to 5 options based on local roughness length or on SYNOP garden


Conclusions• Better verification results for all the 5 options:

• Phase shift improved• Cold bias in winter significantly reduced

but still important!• Logarithmic interpolation: the best results, BUT inconsistent

with the RSL (for z0,loc>0.2)!• The new RSL profiles perform comparably well and are

consistent with the RSL• Local roughness length necessary for diagnostics: should be

introduced in COSMO• Downscaling on a SYNOP garden:

• inconsistent with the mean gridbox conditions in the model• but gives better verification results (better SMA @ DWD)

Eidgenössisches Departement des Innern EDIBundesamt für Meteorologie und Klimatologie MeteoSchweiz

Thank you for your attention!


Verification: SYNOP Switzerland 2m temperature 20.12.2006


New profiles: turbulent fluxes

u'w' = c ⋅ u'w'ISLz − z0zs − z0

⎛ ⎝ ⎜

⎞ ⎠ ⎟

2

exp a(1−z − z0zs − z0

⎛ ⎝ ⎜

⎞ ⎠ ⎟

⎛

⎝ ⎜

⎞

⎠ ⎟

v'w' = c ⋅ v'w'ISLz − z0zs − z0

⎛ ⎝ ⎜

⎞ ⎠ ⎟

2

exp a(1−z − z0zs − z0

⎛ ⎝ ⎜

⎞ ⎠ ⎟

⎛

⎝ ⎜

⎞

⎠ ⎟

u'w'(z*) = u'w'ISL v'w'(z*) = v 'w'ISL ⇒ c =z * −z0zs − z0

⎛ ⎝ ⎜

⎞ ⎠ ⎟

−2

exp a(1−z * −z0zs − z0

⎛ ⎝ ⎜

⎞ ⎠ ⎟

⎛

⎝ ⎜

⎞

⎠ ⎟

Momentum fluxes

Kaster-Klein and Rotach (2004)

Sensible heat flux

w'θ ' = w'θ 'ISLz − z0zs − z0

⎛

⎝ ⎜

⎞

⎠ ⎟

2

exp −ch zs − zzs

⎛

⎝ ⎜

⎞

⎠ ⎟

⎛

⎝ ⎜

⎞

⎠ ⎟ z < zs

w'θ ' = w'θ 'ISL z ≥ zs Modified from Christen (2005)

ch=1.2

a=2

on the 2m temperature and dew point diagnostics in the cosmo … · 2016. 12. 20. · on the 2m...

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