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.
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