BSRN 2002 Regina May Aerosol Optical Depth with PFR instruments in GAW Trial Network Christoph Wehrli Physikalisch-Meteorologisches Observatorium Dorfstrasse 33, 7260 Davos Dorf, Switzerland Goals of trial network State of the network Calibration scheme Data processing approach Results from selected stations Comparison with other data

BSRN 2002 Regina May GAW/WORCC trial network Subsequent to the AOD fiasco in BAPMon, WORCC was proposed and established in 1996 at Davos, sponsored by Switzerland. Goals Implement AOD measurements at 12 global observatories with new instrumentation, sound calibration, data quality control and protocols. Test and verify new instruments and methods under operational network conditions. Train station operators in AOD measurements. WORCC is assisted by a international group of experts and works in cooperation with GAW QA/SAC SAG/Aerosols assumes these roles. WMO initiated contacts between potential stations and WORCC for placement of instruments donated by MeteoSwiss. Host stations are to provide tracking facility and limited manpower.

BSRN 2002 Regina May State of trial network 1.Hohenpeissenberg, Germany, Jun Mace Head, Ireland, Jul Boulder, USA, Aug. – Oct Mauna Loa, Ha, USA, Nov (Aeronet) 4.Bratt‘s Lake, Canada, Apr.2001 (BSRN, Aeronet) 5.Izaña, Spain, Jun Ryori, Japan, Jun Alice Springs, Australia, Jul (BSRN) 8.Ny Ålesund, Norway, Apr (BSRN) 9.Irkutsk, Russia 10.Bukit Koto Tobang, Indonesia 11.Brazil ? (Acre | Manaos) 12.Africa ? (Lamto) Jungfraujoch, Switzerland, Mar. since 1999 (CHARM) Davos, Switzerland, Nov – Nov. 2000

BSRN 2002 Regina May Precision Filter Radiometer PFR specifications Automated, solar spectral radiometer 4 WMO channels at 862, 500, 412, 368nm using IAD interference filters Field of View: ±2.5°, slope angle 0.7° Dimensions: Ø90 x L300mm, Mass 3 kg Sensor at 20±0.1°C in range –25 ÷ 35°C internal shutter; N 2 purged, airtight housing High cadence (2 or 1 min.) measurements Data logger with 30 day storage capacity, built- in pressure and pointing sensors PFR N21 at Ryori, Japan.

BSRN 2002 Regina May WORCC Calibration Hierarchy Standard instruments are calibrated at high altitude stations (Jungfraujoch, Mauna Loa) by atmospheric extrapolation methods. Working standards are calibrated by com- parison with WORCC standards at Davos or Jungfraujoch. Stability of standard instruments is moni- tored by spectral comparison with a metro- logically traceable absolute detector. Station instruments are linked to WORCC reference by travelling standards or ex- change of sensors. Performance is tested through intercom- parison of field instruments with other co- located networks.

BSRN 2002 Regina May Stratospheric Balloon Flight Verification of Langley method by in situ measurements from SIMBA balloon flight in Oct.98 PFR N01 measurements at 40 km height. Atmospheric transmission corrected by MODTRAN calculation PFR N02 mean of 19 refined Langley calibrations, obtained in Dec. 98 and Jan.99 at Jungfraujoch (3580m) Comparison between N01 and N02 found agreement to < 1% Langley calibration V 0 are con- sistently higher than balloon.

BSRN 2002 Regina May High Altitude Calibration Sphinx Research Station at Jungfraujoch Altitude 3580m Latitude46°32’55” N Longitude 7°59’11” E Fully automated dome Operation of 4 PFRs Wavelength : [nm] Langley V o : [V] Stdev V o : [V] Slope/year : [%] ±Slope : [%]

BSRN 2002 Regina May Radiometric Calibration Spectral irradiance scale based on cryogenic radiometer of PTB (Berlin) transferred via calibrated trap detector (uncertainty < ) Stdeviation <0.33% (0.5%) Annual drift <(0.6±3)10 -3 Bandpass integral deter- mined every 6 months. Instrument N01 is assumed to be radiometrically stable to <±0.5% Solar calibration V 0 could be determined if an accurate extraterrestrial spectrum was available.

BSRN 2002 Regina May Operations & data processing At GAW stations –Periodic download from logger to local PC –Periodic maintenance (cleaning, pointing, clock) –External provision of ancillary data (O3, meteo) –Production of Level2 data, quality control –Upload to WORCC by mail or ftp At WORCC –Monthly archive updates –Monthly overview summaries and tests –Production of AOD files At WDCA undefined yet

BSRN 2002 Regina May Data Products, Quality control and Archives Products Level1: bulk raw measurements, 1 m cadence. Level2: daily files in standardized format. Level3: daily files of derived AOD, 2 releases. Quality control Quality flags added to Level2 data on-site with warning/error messages during processing. Preliminary Level3.1 data generated assuming constant calibration. Final Level3.2 after assessment of calibration by travelling standard and evtl. re-processing. Archives and data volume Level1:GAW-GO, WORCC ~3.5MB/month Level2:GAW-GO, WORCC <128kB/day Level3:WORCC  WDCA <20kB/day GAW-GO  WDCA (final network)

BSRN 2002 Regina May Level2 Data format Self-contained daily ASCII files Header with keyword = parameter set Generated by standardized software %STATION =MaunaLoa %LATITUDE = %North %LONGITUDE = %West %ALTITUDE = %above sea level %ZONE = 0%UTC=logger time - Zone %STATIDENT = 11 %DATE = %date containing solar noon %AIRPRESS = 666.7%average Sun above horizon %AIRTEMP = 23.8%instrument body %OZONE = 277.3%climatological or actual DU %INSTRUMENT=PFR-N27 %INSTIDENT = 27 %NCHANNELS = 4 %NREADINGS =1439%actual number of records %WAVELENGTH= %nominal or measured %CALDATE = %recalibrated at MLO %CALIBRAT = %Extraterrestrial signal %SLOPE = %mV per day since CALDATE %O3ABS = %Gueymard, filter averaged %RAYLSCATT = %Bodhain at WAVELENGTH %SUNEARTH = % %DECLINAT = %EQOFTIME = %NOON = %LOGFILE =H:\WORCC\PFR\MaunaLoa\mlo_n27.LOG %VERSION = 2.80 %COMMENT =for column description, see PFRLEV2.HLP %END % UTC SunElv Barom Tsens Tbody PntgV PntgH Flg

BSRN 2002 Regina May Cloud Filtering Cloud flags for individual high cadence samples 1.Harrison & Michalsky algorithm, modified for air masses <2 2.Aeronet algorithm applied as moving filter on continuous samples 3.Optically thick (OD>3) clouds

BSRN 2002 Regina May Instrument health control

BSRN 2002 Regina May Bratt’s Lake

BSRN 2002 Regina May Hohenpeissenberg

BSRN 2002 Regina May Sahara Dust event

BSRN 2002 Regina May Mace Head

BSRN 2002 Regina May MLO Comparison 2000 Methodology AERONET/CIMEL and WORCC/PFR data compared at individual samples level Aeronet Level2 data † as published on web WORCC/PFR with interpolated calibration CIMEL channels are interpolated to WMO wavelengths of PFR by Ångström’s law PFR one minute samples are interpolated in time to CIMEL observation scheme Data gap in PFR from late May to early July † with kind permission of Dr. Brent Holben, Aeronet PI, NASA/GSFC

BSRN 2002 Regina May MLO Comparison 2000 Aerosol Optical Depths

BSRN 2002 Regina May MLO Comparison 2000 Ångström α