IMPLICIT COUPLING BETWEEN ATMOSPHERIC AND SURFACE PHYSICS. Patrick Le Moigne. 15th ALADIN Workshop: 6-10 June, Bratislava

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1 IMPLICIT COUPLING BETWEEN ATMOSPHERIC AND SURFACE PHYSICS Patrck Le Mogne 15th ALADIN Workshop: 6-10 June Bratslava

2 IMPLICIT COUPLING BETWEEN ATMOSPHERIC AND SURFACE PHYSICS Introducton Externalzaton of Isba surface scheme from Arpege-Clmat GCM ACSURFE: nterface to SURFE module Eurocs case study usng SURFE n off-lne mode wthn 1D Arpege-Clmat model Concluson / Perspectves

3 Introducton Best et al (after work of Polcher et al. 1998) propose a generalzed couplng between atmospherc models and surface schemes where: 1. The atmospherc varables from lowest model level and ther relaton to correspondng fluxes are passed to the surface scheme. 2. Surface scheme returns the fluxes (used as boundary condton by the atmosphere) In these condtons the atmosphere doesn t have to know detals about surface. Ths couplng has been appled n Arpege- Clmat model.

4 Externalzaton of Isba surface scheme from Arpege-Clmat GCM [Gbeln 2003 and Zuurendonk 2004] More and more sophstcated surface parameterzatons lead to externalze the LSS from Arpege-Clmat GCM Objectves: Easy to mantan surface parameterzaton surface code. Both coupled and forced model can be used (Intercomparson projects). Easy to use dfferent surface models n the atmospherc model. Essental step for partcpatng n PRISM (Project for ntegrated earth system modellng) project.

5 Couplng wth the atmosphere ( ) ( ) = ω ω 0 0 F = B A 1 = ( ) ( ) = = B f B A f A ω ω ω ω = N S N N B F A ( ) = N N S S H N p T T C V C H β β ρ ( ) = G LE H R T T t C n S S s Vertcal dffuson q v u θ Downward sweep Lower atmospherc level Surface Ts Fluxes on each tles Average fluxes Upward sweep N 1

6 cpg aplpar cptend cpwts acsol achmt acveg acdfus cpg aplpar apllss (1) ls_acsol ls_acsurf achmtls acdfv1 ls_acsolw acdrov Orgnal flowchart Prncple of externalzaton n clmate verson of Arpege Flowchart after externalsaton of surface parameterzaton and temporal evoluton of surface varables n Arpege-Clmat apllss (2) acdfv2 ls_acsol ls_acsurf ls_acveg ls_acbleng ls_acflxqdm ls_acdrov ls_cptends ls_cpwts ls_acsolw

7 ACSURFE nterface to SURFE [P. Marquet Aprl 05] acsurfex s the nterface between aplpar (Arpege) and couplng_surf_atmn (Surfex) where Arpege felds are transformed to feed the surface module: cpg aplpar apllss (1) achmtls acdfv1 apllss (2) acdfv2 acsurfex couplng_surf_atmn

8 1. Varables defned durng surface setup INPUT Name of the varable Tme step of the physcs (s) SURFE ZTSTEP_ISBA ARPEGE PDTPHY Year Day Month Seconds from start Horzontal space dmenson Forcng heght of T and q (m) Forcng heght of wnd (m) Orography (m) Surface pressure (Pa) IYEAR IDAY IMONTH ZTIME INI ZREF UREF ZS PS NINDAT/10000 MOD(NINDAT100) MOD((NINDAT-IDAY)/100100) RSTATI KLON=1 (PAPHIF(1KLEV)-PAPHI(1KLEV)) / RG (PAPHIF(1KLEV)-PAPHI(1KLEV)) / RG PAPHI(1KLEV) / RG PAPRS(1KLEV)

9 2. Atmospherc forcng at lowest model level INPUT Name of the varable Zonal wnd (m/s) Merdan wnd (m/s) Temperature (K) Pressure (Pa) Densty (Kg/m3) Specfc humdty (kg/m3) Lqud precptaton rate (Kg2/m/s) Sold precptaton rate (Kg/m2/s) Downward longwave radaton (W/m2) Downward dffuse solar radaton (W/m2) Downward drect solar radaton (W/m2) SURFE U V TA PA RHOA QA RAIN SNOW LW SCA_SW DIR_SW ARPEGE PU(1KLEV) PV(1KLEV) PT(1KLEV) PAPRSF(1KLEV) PA / TA / PR(1KLEV) PQ(1KLEV) * RHOA PFRTHDS(1) / PEMIS(1) PFRSO(1KLEV) / (1.-PALB(1)) * PFRSOPS(1) / (PFRSODS(1) PFRSOPS(1)) PFRSO(1KLEV) / (1.-PALB(1)) * PFRSODS(1) / (PFRSODS(1) PFRSOPS(1))

10 3. Tr-dagonal matrx substtuton coeffcents INPUT Name of the varable A_u A_theta A_q B_u B_theta B_q SURFE PEW_A_COEF PET_A_COEF PEQ_A_COEF PEW_B_COEF PET_B_COEF PEQ_B_COEF ARPEGE PCFAU(1KLEV) PCFATH(1KLEV) PCFAQ(1KLEV) SQRT(PCFBU(1KLEV)**2PCFBV(1KLEV)**2) PCFBTH(1KLEV) PCFBQ(1KLEV) * RHOA Only one coeffcent for wnd snce surface treats wnd speed and not u and v components. Not a problem f atmospherc and surface grds are the same

11 call to SURFE module OUTPUT Name of the varable Latent heat flux (W/m2) Sensble heat flux (Kg/m2/s) Zonal momentum flux (m/s) Merdan momentum flux (m/s) Radatve temperature (K) Drect albedo for each band Dffuse albedo for each band Emssvty SURFE SFTQ SFTH SFU SFV TSRAD DIR_ALB SCA_ALB EMIS ARPEGE PFEV = - SFTQ PFCS = - SFTH PFMDU = SFU PFMDV = SFV PTSN = TSRAD PALB = (DIR_ALB SCA_ALB) / 2. PEMIS = EMIS

12 Eurocs case study usng SURFE n off-lne mode wthn 1D Arpege-Clmat model [P. Le Mogne and E. Martn May 2005] Frst run n off-lne mode usng mplct formulatons wth the followng optons: ISBA FR 2L for both LSS Surface parameters are derved from ECOCLIMAP (ntegrated n SURFE) and mposed n Arpege ntal fle: percentage of sand and clay sol depth fracton of vegetaton LAI mnmal stomatal resstance roughness length albedo emssvty thermal conductvtes for sol and vegetaton (C G and C V ) and orography are mposed

13 Eurocs case study usng SURFE n off-lne mode wthn 1D Arpege-Clmat model [P. Le Mogne and E. Martn May 2005] ΔH MA ~ 120 W/m2 ΔLE MA ~ 15 W/m2 H LE

14 Several possbltes to explan these dfferences: Ch Cd Cdn: exchange coeffcents are not the same between atmosphere and surface L: latent heat s kept constant n SURFE whle t should depend on T as n Arpege Cp: specfc heat doesn t depend on q n SURFE 1. Ch Cd and Cdn are mposed n achmtls and n drag 2. L becomes constant 3. Dependancy on q s elmnated for Cp (accoefk acdfv2 achmtls and ls_acbleng)

15 Eurocs case study usng SURFE n off-lne mode wthn 1D Arpege-Clmat model [P. Le Mogne and E. Martn May 2005] Second try: ΔH < 1 W/m2 ΔLE < 2 W/m2 ΔTs < 0.4 K H LE

16 Influence of dfference of Cp between Arpege and SURFE: Exchange coeffcents and L are kept constant H 20 W/m2 LE 5 W/m2 One way to cure ths problem could be to have an explct dependance on q for C P

17 CONCLUSION / PERSPECTIVES 1D Arpege model s good tool to start studyng the couplng between atmosphere and surface Surfex s able to reproduce correctly the turbulent fluxes temperature and sol water content under certan condtons n forced mode There are potental problems lnked to Cp L Ch (f they are not mposed fluxes are dfferent (not for L n ths test))

18 CONCLUSION / PERSPECTIVES Consstency between SURFE and exstng Arpege LSS Possblty to ntroduce the dependancy on q for Cp n surfex Possblty to take nto account the dependancy on T for latent heat n surfex Study more carefully the Ch formulaton Flow of nformaton between SURFE and Arpege albedo (drect and dffuse) and emssvty are computed n surfex and Arpege radaton scheme should take them nto account Intalzaton of surface felds I/O Start the work of on-lne mplct couplng between Arpege and surfex (nteracton atmosphere /surface)