Enhanced Ozone Vertical Profiles in Hawaii and California During TRACE-P

Principal Investigator: Samuel J. Oltmans
Co-Investigators: Bryan J. Johnson and Joyce M. Harris
NOAA Climate Monitoring and Diagnostics Laboratory, Boulder, Colorado

During the TRACE-P aircraft missions in spring 2001 we will increase the frequency of ozone soundings at Hilo, Hawaii (20N) and Trinidad Head, California (40N) to three times per week in order to better capture the frequency of potential ozone enhancing events that may reach the mid-Pacific or west coast of the U.S. from Asia. This will coincide with the period when an enhanced number of ozone soundings will also be done in Hong Kong and Taiwan. In addition to the enhanced soundings we will provide the weekly ozonesonde data from Hilo and Trinidad Head from the beginning of 2000 through Spring 2002 to the TRACE-P data archive. Earlier data (from 1991 at Hilo and 1997 at Trinidad Head) will also be available through the investigators. We will do 20 soundings during a six-week period at each site.

The soundings will be carried out using electrochemical concentration cell ozonesondes (ECC), a standard technique for ozone vertical profile measurements. The balloon-borne instruments achieve an altitude of about 32 km and data will be provided at 100 m altitude resolution. Accuracy and precision of ±5% are achieved with this instrument in the troposphere. The accompanying Vaisala radiosonde also provides temperature and tropospheric humidity information along with the ozone data. The humidity data provide an important additional piece of information, since very low humidity may be indicative of a stratospheric source and/or significant subsidence of an air parcel. Data from the period of enhanced soundings will be provided to the archive within 6 weeks of the completion of the intensive sounding period. Data from the routine weekly soundings will be provided to the archive on a quarterly basis in the quarter following the completion of the measurements for each quarter.

Our analysis of the ozone profile data will include the use of isentropic back trajectory calculations to characterize the flow patterns that bring air parcels to these sites. Individual trajectories will be analyzed for the period of intensive measurements to try to identify the source of features such as enhanced ozone layers seen in the tropospheric ozone profiles. We will also develop climitological trajectory analyses for a longer period for comparison with the longer-term ozone profile data that has been obtained at these sites. This has been done (Harris et al., 1998) for the Mauna Loa Observatory altitude (3.4 km) but will be extended to other selected altitudes in the troposphere for Hilo and Trinidad Head.

The enhanced number of ozone vertical profiles to be carried out at two downwind sites during the TRACE-P aircraft mission period will provide an opportunity to investigate the extent to which Asian emissions may be affecting ozone in the troposphere over the Pacific and at the west coast of North America. Since it is likely that the stratosphere also makes an important contribution to the budget and variability of tropospheric ozone at the two measurement sites, the use of trajectory analysis to attempt to separate the sources will provide important information on the relative importance of these sources. In addition the regular weekly profile measurements at Hilo and Trinidad Head will provide a valuable context for the TRACE-P period relative to other seasons and years.