ALBERT

Description: The Ny-Ålesund Ozone Monitoring Intercomparison (NAOMI) took place at Ny-Ålesund,Spitsbergen (78.92 degrees N, 11.95 degrees E), from January 20 to February 10, 1998.This paper focuses on comparing stratospheric ozone profiles measured by the Alfred WegenerInstitute differential absorption lidar (AWI DIAL), in routine Network for Detection ofStratospheric Change (NDSC) operation at Ny-Ålesund, the mobile Goddard Space Flight CenterDIAL (GSFC DIAL), the University of Bremen microwave radiometer (mu Wave), andelectrochemical concentration cell (ECC) ozonesondes, flown routinely by AWI. Below 30 km thetwo DIALs and the ECC sondes give virtually the same results, with instrumental precision(repeatability) better than +/-5% and no detectable bias. When their coarser altitude resolution isnot accounted for, the mu Wave data show 15% low bias at 16 km and 15% high bias at 23 km,Considerably better agreement, better than +/-5% around 20 km and above 30 km, is found whenthe altitude resolution of the other data is degraded to match that of the mu Wave. During NAOMIthe mu Wave data show high bias of up to 10% in a mixing ratio plateau around 25 km. Such biashas not been seen in routine intercomparisons between mu Wave and ECC sonde data atNy-Ålesund. It is likely caused by an a priori profile 40% higher than the true profile duringNAOMI, Above 30 km the mu Wave data show the best precision (repeatability), about +/-3 to+/-5%. Precision of the GSFC DIAL data decreases from better than +/-5% at 30 km to about+/-10% at 40 km, and the precision for the AWI DIAL data decreases from better than +/-5% at30 km to +/-30% at 40 km. From 34 to 38 km the AWI profile is 12% lower than the GSFCprofile. AWI DIAL measurements that are low at 35 km often end below 40 km of show highvalues at 40 or 45 km, This behavior seems related to the way in which the AWI processingalgorithm changes altitude resolution for data with poor signal-to-noise ratio.