Towards kilometer-scale climate modelingC2SM - ETH - MeteoSwiss collaboration

Wolfgang Langhans

Institute for Atmospheric and Climate Science, ETH Zurich

February 26, 2009

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 1 / 25

Outline

1 Introduction

2 First Cosmo runsCOPS DAQUAJuly 2006

3 Outlook I: Near future

4 Outlook II: General

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 2 / 25

Introduction

2003: Abitur in Traunstein/Germany2003-2008: Study of Meteorology and Geophysics inInnsbruck/AustriaInternship at IACETH under the guidance of CathyHohenegger:“Dynamical aspects of August 2005 Alpine flood”Internship at MPI in Hamburg:“Intercomparison of ECHAM5 and REMO simulations forclimate scenario A1B”Diploma thesis under the guidance of Alexander Gohm:“Cloud-resolving simulations of August 2005 Alpine flood -the sensitivity to microphysical parametrizations”January 2009: PhD at IAC, ETH Zürich

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 3 / 25

First Cosmo runs - COPS DAQUA

Period: 8. - 17. August 2007Characteristics:

strong synoptic forcing on August 8th (flooding event in westSwitzerland)and on August 16thintermediate strong convection inbetween

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 4 / 25

COPS DAQUA - Initialization

ECMWF operational analysis int2lm

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 5 / 25

COPS DAQUA - Model setup

Version: CLM 4.3Dynamics:

3rd order TVD-RK scheme

5th order advection, pos. definite qx advection

Physics:

prognostic TKE-based turbulence scheme

no cumulus scheme

graupel scheme

TERRA_ML

Implementation of topographic correction scheme for radiation ? (V4.7)

Large Alpine domain:

501× 451× 45 gridpoints

dϕ = dλ = 0.02◦, dt = 30 s

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 6 / 25

COPS DAQUA - Nesting experiments

Experiments:

ECMWF (25 km) → CLM 2 km (6 h LBC update)

ECMWF (25 km) → CLM 25 km → CLM 2 km (1 h LBC update)

ECMWF (25 km) → CLM 7 km → CLM 2 km (1 h LBC update)

ECMWF (25 km) → CLM 25 km → CLM 2 km (6 h LBC update)

ECMWF (25 km) → CLM 2 km (6 h LBC update, init_time = -6 h)

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 7 / 25

COPS DAQUA - ECMWF vs. 25 km CLM LBC

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 8 / 25

COPS DAQUA - ECMWF vs. 25 km CLM LBC

Accumulated precipitation (mm)ECMWF driven 25 km CLM driven

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 9 / 25

COPS DAQUA - ECMWF vs. 25 km CLM LBC

qv (g kg−1) at 700 hPa at 00 UTC 13 August 2007

ECMWF analysis ECMWF driven run 25 km CLM driven run

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 10 / 25

COPS DAQUA - ECMWF vs. 25 km CLM LBC

θe (K) at 850 hPa at 00 UTC 15 August 2007

ECMWF analysis ECMWF driven run 25 km CLM driven run

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 11 / 25

COPS DAQUA - ECMWF vs. 25 km CLM LBC

ECMWF driven

25 km CLM driven

Cold bias!?

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 12 / 25

COPS DAQUA - ECMWF vs. 25 km CLM LBC

ECMWF driven

25 km CLM driven

Cold bias!?Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 12 / 25

COPS DAQUA - 25 km CLM vs. 7 km CLM LBC

Also the magnitude of the deviations to the ECMWF analysismoisture and temperature fields is roughly the same.

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 13 / 25

COPS DAQUA - 1-h vs. 6-h LBC updatefrequency

Differences between area averaged rainrates (mm h−1)

1-h 25 km CLM - ECMWF driven 25 km CLM - 6-h 25 km CLM

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COPS DAQUA - Predictability issue

Shifted initialization time (6 h earlier)

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 15 / 25

COPS DAQUA - Conclusions

1 The differences to ECMWF analysis fields are larger, whennesting chains are used.

2 The sensitivity of simulated precipitation to LBC updatefrequency is smaller than the sensitivity to nestingtechnique, despite strong synoptic forcing

3 When the ECMWF analysis is regarded to be the “truth", anECMWF driven 2-km resolution is most appropriate for thisstudy.

4 The chaotic discrepancies between runs with shiftedinitialization are low after ∼ 2 days simulation time, whichsupports the feasibility of meaningful simulations of summertime convection at this scale.

Note: For final conclusions a comparison to observations would be necessary/helpful

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 16 / 25

COPS DAQUA - Conclusions

1 The differences to ECMWF analysis fields are larger, whennesting chains are used.

2 The sensitivity of simulated precipitation to LBC updatefrequency is smaller than the sensitivity to nestingtechnique, despite strong synoptic forcing

3 When the ECMWF analysis is regarded to be the “truth", anECMWF driven 2-km resolution is most appropriate for thisstudy.

4 The chaotic discrepancies between runs with shiftedinitialization are low after ∼ 2 days simulation time, whichsupports the feasibility of meaningful simulations of summertime convection at this scale.

Note: For final conclusions a comparison to observations would be necessary/helpful

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 16 / 25

COPS DAQUA - Conclusions

1 The differences to ECMWF analysis fields are larger, whennesting chains are used.

2 The sensitivity of simulated precipitation to LBC updatefrequency is smaller than the sensitivity to nestingtechnique, despite strong synoptic forcing

3 When the ECMWF analysis is regarded to be the “truth", anECMWF driven 2-km resolution is most appropriate for thisstudy.

4 The chaotic discrepancies between runs with shiftedinitialization are low after ∼ 2 days simulation time, whichsupports the feasibility of meaningful simulations of summertime convection at this scale.

Note: For final conclusions a comparison to observations would be necessary/helpful

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 16 / 25

COPS DAQUA - Conclusions

1 The differences to ECMWF analysis fields are larger, whennesting chains are used.

2 The sensitivity of simulated precipitation to LBC updatefrequency is smaller than the sensitivity to nestingtechnique, despite strong synoptic forcing

3 When the ECMWF analysis is regarded to be the “truth", anECMWF driven 2-km resolution is most appropriate for thisstudy.

4 The chaotic discrepancies between runs with shiftedinitialization are low after ∼ 2 days simulation time, whichsupports the feasibility of meaningful simulations of summertime convection at this scale.

Note: For final conclusions a comparison to observations would be necessary/helpful

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 16 / 25

First Cosmo runs - July 2006

Period: 11. - 20. July 2006Characteristics:

Highly convective period in the Alps, Jura, Black ForestWeak synoptic forcingWe also assume stronger thermally driven circulations

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 17 / 25

July 2006 - Model setup

Same as for COPS DAQUA period, but:

Problem: Stripy patterns mostly visible in qv field at lowlevels.Solution: Modify horizontal diffusion

Note: Domain shifted slightly to the south, because of 50 kmrelaxation zone.

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 18 / 25

July 2006 - Sensitivity to horizontal diffusion

qv at 1200 UTC 13 July 2006, level 30/45

hdcoeff_t=0.75hdcoeff_u= 0.75

hdcoeff_q=0.

hdcoeff_t=0.5hdcoeff_u=0.5

hdcoeff_q=0.5lhdiff_mask=True

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 19 / 25

July 2006 - Sensitivity to horizontal diffusion

Area averaged rainrates

hdcoeff_t=0.75hdcoeff_u= 0.75

hdcoeff_q=0.

hdcoeff_t=0.5hdcoeff_u=0.5

hdcoeff_q=0.5lhdiff_mask=True

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 20 / 25

July 2006 - Period mean sounding Payerne

12 UTC

OBSCLM

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 21 / 25

July 2006 - Period mean sounding Payerne

00 UTC

OBSCLM

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 22 / 25

Outlook I: Near future

Comparison of July 2006 simulation with observational dataConvergence project: The influence of resolution on

moist convectionheat and moisture exchanges between PBL and freeatmosphere→ budget analysis

∂T∂t

= ADV +1

ρcpd

dpdt

+Lv

cpdSl +

Lv

cpdSf + Qr + MT + MHD

∂qx

∂t= ADV − (Sl + Sf )−

1

ρ√

G

∂

∂ζ(ρvT

x qx ) + MTqx + MHDqx

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 23 / 25

Outlook I: Near future

Thermally driven flows (“Alpine pumping”)representation in the modelimpact on triggering of moist convectionsensitivity to climate change using, e.g., surrogate scenarios

Lugauer , MZ 2005

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Outlook II: General (CHIRP proposal)

Improve our understanding of moist convection overcomplex terrainSensitivity of numerical components upon the simulation ofmoist convection:

vertical resolutionhorizontal diffusionturbulence parametrization

Development of a cloud-resolving climate modeling suite

Enhance our knowledge about climate feedback processesand their influence on convection (e.g., soil moisture,cloudiness , temperature feedbacks)Long-term simulations (at least 20 years)Answer/reconsiderate typical climate-communityquestions/problems:

Higher frequency of heavy precipitation events, despite adecrease in mean precipitation?Interannual variability of temperature and precipitation?

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 25 / 25

Outlook II: General (CHIRP proposal)

Improve our understanding of moist convection overcomplex terrainSensitivity of numerical components upon the simulation ofmoist convection:

vertical resolutionhorizontal diffusionturbulence parametrization

Development of a cloud-resolving climate modeling suiteEnhance our knowledge about climate feedback processesand their influence on convection (e.g., soil moisture,cloudiness , temperature feedbacks)Long-term simulations (at least 20 years)Answer/reconsiderate typical climate-communityquestions/problems:

Higher frequency of heavy precipitation events, despite adecrease in mean precipitation?Interannual variability of temperature and precipitation?

Wolfgang Langhans C2SM - ETH - MeteoSwiss collaboration February 26, 2009 25 / 25