Modelling of cloud and desert dust properties over the

Iberian Peninsula and Atlantic Ocean

Fifth Meso-NH User's Meeting

Dina Santos, Maria João Costa, Ana Maria Silva e Rui Salgado

Objective

To study the properties of clouds and aerosols during strong Sahara desert dust episodes, May 2006 and September 2007, using MesoNH results, over the Iberian Peninsula and Atlantic Ocean.

Top of the Atmosphere - TOA

Scattering & absorption of radiation

Increase CDNC & suppress precipitation

Increase cloud height

Increase cloud lifetime

Heating causes cloud burn-off

Simulations initiated and forced by ECMWF analyses Run in a two way nested mode, 2 nested models:

- Father: 4000 x 5000 km2 horizontal resolution:50km - Son1: 1000 x 1000 km2 source res:10km - Son2: 2000 x 2225 km2 study area res:10km

Simulation periods: 26 – 29 May 2006 e 04 – 09 September 2007

49 stretched layers from the surface up to 24km altitude

MesoNH Simulations

Dust scheme activated (Dust Entrainment And Deposition - DEAD)

Physical parameterizations

CloudsMixed microphysical scheme including ice, snow, and graupel (6 classes of hydrometeors)

Boundary Layer TKE equation

Convection Kain and Fritsch typeSurface processes

ISBATEB

Data bases for surface parameters

GTOPO30 for orography; Ecoclimap for land cover

Radiation ECMWF radiative scheme

Comparison with Satellite ImagesCloud Fraction - CLDFR

28 May1105UTC

the total CLDFR simulated results are in agreement with the actual situation (represented by MODIS RGB images)

the simulated results obtained seem to overestimate the observed cloud fraction

(satellite)

29 May - 1145UTC

27 May 1200UTC

Cloud Fraction - CLDFR07 September -1315UTC

the total CLDFR simulated results seem to overestimate the observed cloud fraction (satellite)

08 September – 1040UTC

Comparison with Satellite Images

06 September - 1410UTC

Aerosol Optical Depth – DSTAOD2D

06 September

07 September

The DSTAOD2D pattern results are in a good agreement with the actual situation

Comparison with Satellite Images

AOD (870 nm)

Measured Simulated

28 May 2006 0.210 ± 0.040 0.096 ± 0.001

08 September 2007 0.27 ± 0.03 0.18 ± 0.01

08 September 1055UTC

The ODAER_NIR4 present lower values when compared with the corresponding values measured by MERIS sensor

Comparison with Satellite ImagesAerosol Optical Depth - ODAER_NIR428 May

1103UTC

28 May

Cloud Top Pressure - PRES

Cloud Top Pressure (hPa)Measured Simulated

28 May 2006 351 ± 34 332 ± 35 08 September 2007 821 ± 12 890 ± 7.0

The simulated Cloud Top Pressure values are in good agreement with the corresponding values measured by MERIS sensor

08 September

Comparison with Satellite Images

Comparison with Ceilometer VAISALA

27 May 2006 28 May 2006

Hora

UTC

Measured Cloud Base

Height (km)

Simulated Cloud Base

Height(km)

Measured Cloud Base

Height(km)

Simulated Cloud Base

Height(km)

18 3.5 ± 0.5 3.3 ± 0.3 3.4 ± 0.6 3.6 ± 0.4 19 3.5 ± 0.5 3.3 ± 0.5 3.4 ± 0.6 3.5 ± 0.7 20 3.8 ± 0.5 3.4 ± 0.2 3.6 ± 1.6 3.4 ± 0.8 21 4.0 ± 0.9 3.5 ± 0.2 - 3.5 ± 0.8 22 4.0 ± 0.2 3.6 ± 0.2 4.7 ± 0.2 3.5 ± 0.8

Base Height of Convective Cloud - CLBASCONV

The simulated CLDBASCONV values agree very well with the corresponding values measured by the ceilometer

28 May27 May

Aerosol Effects

Clean days DEAD scheme Off

Aerosol Scavening

Absorption/ diffusionof sunlight

surface cooling u*

Émission

Saltation

SURFEX

MesoNH

Water infiltration

atmospheric heating

Radiative scheme

Aerosol Scavening

Absorption/ diffusionof sunlight

surface cooling u*

Émission

Saltation

SURFEX

MesoNH

Water infiltration

atmospheric heating

Radiative scheme

DEAD scheme

4 5 6 7 8 9 10 110

1

2

3

4

5

6

Hei

ght (

km)

Cloud Liquid Water Effective Radius (m)

Dust Free Dust

28 May

4 5 6 7 8 9 100

1

2

3

4

5

Dust Free Dust

Hei

ght (

km)

Cloud Liquid Water Effective Radius (m)

27 May

4 5 6 7 8 9 100

1

2

3

4

5

629 May

Dust Free Dust

Cloud Liquid Water Effective Radius (m)

Hei

ght (

km)

Cloud Liquid Water Effective Radius - EFRADL

The biggest EFRADL values are found at higher altitudes for a dusty atmosphere than the correspondent EFRADL values for a Dust Free atmosphere.

For clouds below 1.5km high level dusty atmosphere EFRADL values are slightly lower than the correspondent EFRADL values for a Dust Free atmosphere.

Aerosol Radiative ForcingAerosol Optical Depth - DSTAOD2D

27 May 28 May

Since the objective is to estimate the direct radiative forcing due to DD aerosols, the cloudy regions are not considered and the assessment of desert dust radiative forcing is therefore only made for clear sky conditions.

AOD and DD Aerosol SWRF and LWRF

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.080

5

10

15

20

25

27 May 28 May

Aerosol Optical Depth

Hei

ght (

km)

-105 -90 -75 -60 -45 -30 -15 0 150

5

10

15

20

25

Hei

ght (

km)

Radiative Forcing (Wm-2)

27 May SWF 28 May SWF 27 May LWF 28 May LWF

netCLEAN

netAER FF=F FF=F net

On the 27 May the DD event was more effecttive. Lower SWF values are found, at TOA and surface levels, on the 27 May

compared with the corresponding values for 28 May (probably related to the fact that higher AOD values are found for 27May than the corresponding ones for the 28 May).

A cooling LW effect at surface level, is found for the 28 May, but for 27 May a warming LW effect is found (maybe related, once again, with higher AOD values found on 27May).

Nevertheless, the LWF values in altitude, for both days, have a tendency to approximate and, at the TOA, the values are very close.

Over Land Region

SWF_NET

LWF_NET

SWF_NET_CS

LWF_NET_CS

0.00 0.02 0.04 0.06 0.08 0.100

5

10

15

20

25

27 May 28 May

Hei

ght (

km)

Aerosol Optical Depth

-120 -100 -80 -60 -40 -20 0 200

5

10

15

20

25

Hei

ght (

km)

27 May SWF 28 May SWF 27 May LWF 28 May LWF

Radiative Forcing (Wm-2)

AOD and DD Aerosol SWRF and LWRF

Over Sea Region

On the 27 May the DD event was more effective. For the 27 May, lower SWF values are found again compared with the

corresponding values for 28 May. This difference can, once again, be related to the fact that the AOD values, on 27 May, are higher than the AOD values for 28 May.

On 27 May, for the most part, a LW warming effect is found. On 28 May a LW cooling effect is found being more pronounced below 5km

altitude.

DayDust Dust Free

SWCRF LWCRF CRF SWCRF LWCRF CRF

27 May -130 10 -120 -127 24 -103

28 May -158 9 -149 -149 7 -142

29 May -204 6 -198 -198 7 -191

ClearLWSWCloud

LWSW NNNNCRF

Cloud Radiative Forcing (TOA) - CRF

the TOA SWCRF for a dusty atmosphere and for a dust free atmosphere present always a negative sign, indicating a SW cooling effect at the TOA. the TOA LWCRF for a dusty atmosphere and for a dust free atmosphere presents positive signs for all the cases, indicating then a LW warming effect at the TOA. the TOA CRF for a dusty atmosphere presents more negative values than the TOA CRF for a dust free atmosphere, connected to the fact that the dusty clouds reflect more sunlight.

Final Considerations

The main objective of this work is to study the properties of clouds and aerosols during strong DD events, in the regions of the Iberian Peninsula and Atlantic Ocean. The method uses the results obtain by the MesoNH model.

When a comparison is made by the simulated results with the measured results, it is observed that the model overestimates the total CLDFR parameter, nevertheless the pattern is, generally, in conformity with the actual situation represented by MODIS. The CLBASCONV simulated values present also a good conformity with the corresponding values measured by the ceilometer. The simulated cloud top pressure values present a very good concordance with the respective values measured by MERIS.

The simulated AOD, when compared qualitatively with the satellite image, presents a very good agreement, yet, when quantitatively compared, presents lower values than the corresponding values measured by the satellite.

When DD aerosols are present in the atmosphere, a SW warming effect is observed, both at TOA and surface levels, being more negative at the surface. A LW warming effect is detected when AOD higher values are found.

For clouds developing in a atmosphere where DD are present, a more negative CRF is found, comparing with the corresponding CRF values for clouds developing in a DD free atmosphere.

Papers in Conferences Santos, D., M. J. Costa, A. M. Silva and R. Salgado,2008: "Cloud microphysical characterization in the

presence of a desert dust event over Portugal: a study based on atmospheric modelling and satellite remote sensing", in Remote Sensing of Clouds and the Atmosphere XIII, edited by Richard H. Picard, Adolfo Comeron, Klaus Schäfer, Aldo Amodeo, Michiel van Weele, Proc. of SPIE, Vol. 7107, 710714.

D. Santos, M. J. Costa, A.M. Silva e R. Salgado, 2009: " Modelação dos Efeitos Microfísicos e Radiativos de Poeiras do Deserto na Região da Península Ibérica ", 6º Simpósio de Meteorologia e Geofísica/10º Encuentro Luso-Español de Meteorologia,In Press.

M. J. Costa, D. Santos, R. Salgado, V. Levizzani, F. Pinelli, D. Bortoli, e A.M. Silva, 2009: ‘Modelling of orographic precipitation over Portugal and effects on the surrounding regions’, European Geosciences Union, General Assembly.

D. Santos, M. J. Costa, A. M. Silva, R. Salgado, A. Domingues e D. Bortoli, 2009: "Saharan Desert Dust Radiative Effects: A study based on atmospheric modeling ", Global Conference on Global Warming 2009. (Best Paper Award)

D. Santos, M. J. Costa, A.M. Silva e R. Salgado, 2009 : " Atmospheric modeling of Desert Dust Aerosols Effects on Clouds over the Atlantic Ocean “, 18th International Conference on Nucleation & Atmospheric Aerosols«.

Santos, D., M. J. Costa, A. M. Silva, R. Salgado and D. Bortoli, 2009: "Comparison of cloud height and depth from atmospheric modelling and ceilometer measurements", in Remote Sensing of Clouds and the Atmosphere XIV, edited by Richard H. Picard, Klaus Schäfer,Adolfo Comeron, Evgueni I. Kassianov, Christopher J. Mertens, Proc. of SPIE, Vol. 7475, 747512.

D. Santos, M. Potes, M. J. Costa, R. Salgado e A.M. Silva, 2009: "Comparison of atmospheric properties retrieved from MERIS and obtained from modelling studies ", Atmospheric Science Conference.

D. Santos, M. J. Costa, A.M. Silva e R. Salgado, 2009: ‘Modelação das propriedades das nuvens e de poeiras do deserto sobre a região da Península Ibérica e Oceano Atlântico ", IV Encontro de Pós-Graduação em Ciências Físicas e da Terra da Universidade de Évora, Évora.

Future work…

ACKNOWLEDGEMENTSThe work was funded by the Portuguese FCT through grant SFRH/BD/27870/2006 and through project PTDC/CTE-ATM/65307/2006.The authors are also grateful for the suggestions and kind availability of PierreTulet and Odile Thouron!

These results encourage the analysis of others situations and more days are planned to be investigated and compared.

Thank you!