4.1.2. Umkehr Observations
Umkehr observations made with the automated Dobson network instruments continued in 1996 and 1997 at Boulder, Colorado; Haute Provence, France; Lauder, New Zealand; Mauna Loa Observatory, Hawaii (MLO); Perth, Western Australia; and at the Geophysical Institute, University of Alaska. A major effort to bring the processing of Umkehr data up to date was initiated at the beginning of 1996. No data had been processed since the eruption of Mt. Pinatubo in 1991. The processing has been completed through 1997 and ozone profile data for the entire record at each site are available from the WOUDC. The data were used as part of the Stratospheric Processes and their Role in Climate/International/Ozone Commission/World Meteorological Organization (SPARC/IOC/WMO) sponsored assessment report (Trends in the Ozone Vertical Profile, to be published in 1998).
As part of the Mauna Loa Ozone Vertical Profile Intercomparison (MLO3) held in August and September 1995, Umkehr observations were made with MLO automated Dobson No. 76 and with World Standard Dobson No. 83. Fifteen matched profiles were obtained. Agreement between the profiles obtained by the two different instruments is remarkably good (Figure 4.1). The percentage of difference between the instruments (the numbers on the right side of the figure) for each layer do not exceed 4% and are generally less than 3%.
Fig. 4.1. Comparison of average ozone profiles derived from Umkehr measurements at MLO during the MLO3 campaign from two Dobson spectrophotometers (No 83 and No. 76). The profiles were obtained in August 1995. The numbers along the right side are the average percent difference in each layer.