Part IStatus of BSRN: database and FTP file archive April 27, 2005 CEOS/ WGCV/Land Product Validation Workshop on Albedo Products, Vienna Andreas Roeschreas Institute for Atmospheric and Climate Research, ETH Zurich
Current status of the database • Synop/ Radiosounding • Albedo (reflected SW radiation) • UV/AOD (Aerosol optical depth) • FTP file archive
Status of BSRN database Status of BSRN database NOAA ARM SURFRAD
13 BSRN stations with SYNOP measurements (logical record 1000, tables STA_SYNOPBAS_YEAR and STA_SYNOPEXT_YEAR)
18 BSRN stations with radiosonde measurements 1992-2002: BAR, BER, BOU, GVN, KWA, NYA, SPO 1994-2004: BIL 1995-2003: BON, BOS 1996-2003: PAY 1996-2004: TAT 1997-2004: E13, MAN 1998-2003: DRA 1998-2004: NAU 2000-2004: DAA 2003: SBO
BSRN stations reporting 10m-observation to BSRN (logical record 3010, table „STA_RMH1000_YEAR“) All these stations provide reflected SW radiation and thus surface albedo
BSRN stations reporting reflected SW radiation (at standard height)
BSRN stations reporting UV to BSRN (logical record 500, table „STA_RMUV_YEAR“) Payerne provides both direct and diffuse UV-a and UV-b, all others only provide total UV-b
BSRN stations measuring UV, not reporting to BSRN From B. Forgan, based on information from station scientists (at the request of Ohmura/ Roesch)
BSRN stations planning to measure UV radiation From B. Forgan, based on information from station scientists
Aerosol optical depth (AOD) in BSRN Current status: No station provides spectral shortwave radiation (record 200 or 400) Only GVN and NYA includes record 1300 (but provides missing values for spectral AODs) Future plan: Database: Insertion of computed AOD values (for 3 wavelengths) into record 1300 only after transmission data have passed several consistency checks. -> No change in the database schema is required. -> Block 1300 is excluded from the instrument consistency checks. File archive: All measured and calculated data (at all wavelengths) are included in the ftp file archive, including QC/ QA
FTP file archive (ftp://ezksun3.ethz.ch) • Motivation • Most scientists are more familiar with file archives than with databases • The web interface does not allow the retrieval of all data • Access and download via file archive is simple and fast • Can be easily modified (value-added data) • Current status • The file archive is automatically updated (cron-job) every night -> The database • and the file archive generally contain identical data. • Differences between the database and the file archive • Improved quality check flags (recommended by Ells Dutton and Chuck Long) • Global radiation „global1“ added (sum diffuse plus direct SW radiation) • Format • Compressed ASCII-files (use „gunzip“ to uncompress data)
FTP file archive - some details to the format • Format is the same as described in the „Update of the Technical plan for data management (1998)“ but with the following extensions: • Logical record 100 • line 1: X, I1, X, I1, X, I1, X, I1 • Global radiation: Physically possible, extremely rare • Direct radiation: Physically possible, extremely rare • line 2: X, I1, X, I1, X, I1, X, I1, X, I1, X, I1, X, I1, X, I1 • Diffuse radiation: Physically possible, extremely rare • Longwave downward rad. : Physically possible, extremely rare • Global radiation: Comparison between „global 1“ and „global 2“ • Comparison between diffuse and direct radiation • Comparison of longwave downward and 2m- temperature
FTP file archive - some details to the format (ff) • Logical record 300 • Extension to each line: X, I1, X, I1, X, I1, X, I1, X, I1, X, I1, X, I1, X, I1 • LW upward radiation: Physically possible, extremely rare • Reflected SW radiation : Physically possible, extremely rare • Global radiation: Comparison between reflected SW and global radiation • Comparison of LW up to air temperature • LW up to LW down comparison • Meaning of the quality flags • 2 -> suspected to be erronous • 5 -> cannot be performed • 9 -> passed the procedure
Conclusions (Part I) • The BSRN database currently contains 37 operating stations with a total of approximately 2950 monthly data files. • Number of stations which report • SYNOP: 13 • Radiosounding: 18 • UV: 10 • Albedo: 15 • More and more scientists prefer to download data from the FTP file archive. • The FTP file archive is automatically updated from files that have been successfully inserted into the BSRN database. • The FTP file archive includes the quality flags according to E. Dutton and C. Long as well as „global 1“ (computed from direct and diffuse measurements). • Data in the FTP file archive can be easily modified/ extended.
Part II Some applications of MODIS/ BRDF data
Sub-grid scale variability and how representative are point measurements?
BS ZH PAY PAY
Data from Greenland summit have been kindly provided by Sebastian Hoch, ETH Zurich
MODIS white sky albedo minus black sky albedo VIS: blue NIR: red Solar angle at local solar noon
Conclusions (Part II) • MODIS/ BRDF provides high-quality data for validation of GCMs and improving their parameterizations • MODIS (at 0.05 resolution) agrees well with ground truth from BSRN sites during snow-free periods. Under snow conditions, deviations are significant due to differing vegetation cover (-> snow masking of forest). • MODIS Version 4 differs from Version 3 (in both the mean and the variability) • MODIS Version 3 is too low over pure snow such as Greenland (Version 4 provides improved data). • ECHAM4 surface albedo is too high over boreal forests and the Himalayas/ Tibetan Plateau. • ECHAM5 is closer to the observations over the Himalayas than ECHAM4, but positive albedo biases over snow-covered boreal forests are even more pronounced in ECHAM5.
Conclusions (ff) • MODIS & BSRN clearly show that neglecting the zenith angle dependence leads to significant errors in the net shortwave radiation. The approach of Briegleb et al. (1986) is suggested for land surface albedo models. • Intracell variability of surface albedo is largest in snow-covered areas and deserts. Normalized intracell variances are largest in mountainous regions. • Intracell variability in the VIS spectrum is much higher than in the NIR band over (partially) snow covered regions (difference asnow - a,no snow is also higher in the VIS) • Surface albedo at specific sites are generally representative for a limited area only.