Aerosol Optical Depth measurements in the Azores Fernanda Carvalho 1 Diamantino Henriques 1 Paulo Fialho 2 Vera Bettencourt 1 1 Instituto de Meteorologia 2 Universidade dos Açores

The José Agostinho Observatory, is located in Angra do Heroísmo town, is part of the regional station GAW network since The very first global irradiance measurements in Portugal using conventional instruments and methods were done in this Observatory in GAW GAW Global Atmosphere Watch BSRN BSRN Baseline Station Radation Network WMO WMO World Meteorological Organisation

In the scope of CLIMAAT project (Climate and Meteorology of Atlantic Islands), it was possible to fund and install an automatic system for solar and terrestrial radiation measurement. The results will provide a detailed characterization of atmospheric radiative properties.

ParameterInstrumentAccuracy BSRN Direct solar irradianceNIP Eppley1% or 2 Wm -2 Diffuse radiationCM11 Kipp&Zonen4% or 5 Wm -2 Global radiadionCM11 Kipp&Zonen4% or 5 Wm -2 Longwave downwelling radiation flux CG4 Kipp&Zonen5% or 10 Wm -2 UV radiationBrewer Mark II10% Total ozoneBrewer Mark II1% Aerosol optical depth Middleton SP02 BSRN 412, 500, 645, 862 nm CG2 Kipp&Zonen Sci-Tec 2AP DTK 500

ParameterPrecisionAccuracy Air temperature0,1 ºC+/- 0,3 ºC Dew point temperature0,1 ºC+/- 0,5 ºC Soil surface temperature0,1 ºC+/- 0,3 ºC Relative humidity1%+/- 7% Wind speed0,5 ms -1 +/- 5% or 2 ms -1 Wind direction5º+/- 10% Total precipitation amount0,2 mmGreather than +/- 0,2 mm or +/- 2% of total Precipitation rate0,2 mm h -1 Greather than +/- 0,2 mm h -1 or +/- 2% Atmospheric pressure0,1 hPa+/- 0,5 hPa Visual direct observations (cloudiness, present weather past weaher) Ancillary meteorological information

Calibration, data processing and archive Sensor calibration - ISO 9846: 1993(E). Under development: Application of QC/QA procedures; BSRN Station-to-Archive File Format. BSRN Operations Manual, WMO/TD-No.879 Technical Plan for BSRN, WMO TD N.443

Aerosol Optical Depth (  a, ) computations  a, = -(1/m) ln( E / E 0, ) -  R, -  O, -  H2O m =1./(cos(za*pi/180.)+0.15*( za)**(-1.253)) mr=m*p/p0 vdo=10000./cdo( )  R, =mr*7.994*(vdo**4.)/( e e9*vdo**2.)  O, =ao3( )*o3*mo3 mo3=35.0/(1224.0*(cos(za*pi/180.)**2)+1.)**.5  H2O =0.3285*aH2O( )*(w+(1.42-w)*.5)*m/( *aH2O( )*m)**0.45

Aerosol Optical Depth (  a, ) computations (Cont.) Precipitable water (w): 2.0 cm Total ozone (o3): Brewer observed nearest value

Data acquisition and processing Acquisition system: DTK500 Integration: 5 s (avg;std) Filter: data with: signal < night background (zero); signal noise: std/ avg > night readings (za >90) should not be considered. 10 minute AOD averages computed only with n >= 30 readings

Results Results (August 2004-September 2005)

500 nm Angra do Heroismo Cimel SP02

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Acknowledments: To WMO Secretariat for kindly funding this participation. To CLIMAAT project for funding part of the equipment.