4.1.5. Ozonesondes

Table 4.7 summarizes the 1996-1997 CMDL ozonesonde projects. This includes weekly ozone soundings at NOAA long-term monitoring stations in Boulder, Colorado; Hilo, Hawaii; and SPO, as well as a new long-term site in Trinidad Head, California, funded by the NOAA “Health of the Atmosphere” program. The new west coast site started launching weekly ozonesondes on August 20, 1997. This station will provide an upstream look at ozone concentrations reaching the continent from the prevailing west to east flow. Other campaigns that CMDL participated in included Pacific Exploratory Mission in the Tropics (PEM-Tropics), Atmosphere/Ocean Chemistry Experiment (AEROCE), Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS), and 1 month of daily ozonesondes at Sable Island, Canada, in September 1997 as part of the NOAA Climate and Global Change Program (CGCP) Atmospheric Chemistry Project.

TABLE 4.7. Summary of 1994-1995 Ozonesonde Projects

PEM-Tropics - Pacific Exploratory Mission in the Tropics (a global tropospheric experiment).

POLARIS - Photochemistry of Ozone Loss in the Arctic Region in Summer

AEROCE - Atmosphere/Ocean Chemistry Experiment

The SPO ozonesonde program has been essential for monitoring the development of the yearly ozone hole over Antarctica. In addition, the continuous data set from 1986 to 1997 was analyzed for potential ozone hole recovery indicators by Hofmann et al. [1997]. The profiles from the 1996-1997 season are shown in Figure 4.3. The minimum total ozone was observed in early October, similar to past years, with 118 DU recorded in 1996 and 112 DU in 1997. The totals are above the record low of 86 DU recorded on October 12, 1993, when the effect of the Mount Pinatubo aerosol was at a maximum [Hofmann et al., 1994; 1997]. However, depletion in the 14-20 km layer continues to show nearly zero ozone. In 1997 there is evidence that the altitude range of zero ozone has expanded upward.

Fig. 4.3. Vertical profiles of ozone partial pressure in millipascals (mPa) at SPO during the ozone hole of 1996 and 1997. The thin line represents the predepletion profile. The thicker line is the profile observed during the minimum in total ozone.

The ongoing PEM-Tropics campaign has been investigating tropospheric chemistry related to the oxidizing capacity of the global troposphere. The focus is on the very clean atmosphere in the tropical Pacific ocean basin. CMDL participation included weekly ozonesonde flights at SMO, Tahiti, and Fiji. The frequency of ozonesondes was increased to two per week at SMO from August 1 to October 29, 1996, to coordinate with an aircraft campaign. CMDL station personnel launched ozonesondes at SMO, while personnel at Meteo, France, in Papeete, Tahiti, and the University of Southern Pacific in Suva, Fiji, were trained for launching ozonesondes at each of those sites. To date, the ozone profiles have shown typical low ozone mixing ratios of 10-20 ppbv throughout the troposphere, but layers of 80-110 ppbv ozone were observed in the middle and upper troposphere.

The AEROCE campaign in 1996 was the last of a series of springtime intensive ozonesonde launches in North American and North Atlantic sites. Since the spring of 1993, the AEROCE and North Atlantic Regional Experiment (NARE) campaigns have investigated the origin of tropospheric ozone over the North Atlantic [Oltmans et al., 1996]. There were three sites located approximately 1200 km apart in West Lafayette, Indiana; Charlottesville, Virginia; and Bermuda. The University of Virginia at Charlottesville also monitored synoptic conditions and timed the daily launches in order to measure ozone behind the passing cold fronts [Cooper et al., 1998].

CMDL set up, supplied, and provided training to the Geophysical Institute personnel at the University of Alaska, Fairbanks, to launch ozonesondes during POLARIS. The campaign objective was to investigate the stratospheric ozone loss rate in the spring and summer at northern latitudes. A secondary benefit from the ozonesondes was that they provided a total ozone comparison for TOMS satellite measurements during a period of low sun angle.

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