The SDSMT
armored T-28 conducted 8 research flights during our 4-week deployment to
Missions
were conducted on the following days (all times UT):
16 May
19 May
23:40-25:00 (approx)
22 May
23 May
1
June
2
June 24:10-24:56 (clear air instrument
tests)
4
June
10 June
Our
primary scientific objectives were to monitor electric fields, nitric oxide
(NO), and hydrometeors in electrified storms. We also carried an X-ray detector
developed at New Mexico Institute of Mining and Technology by
The TEI
42C-TL NO/NOx analyzer, which is not designed for aircraft work, worked well in
the T-28 once we developed a scheme to feed pure oxygen into the ozone
generator in the instrument. In the instrument ozone reacts with NO in the air
to produce excited
NO2 molecules. Decay of these excited molecules results in emission
of light which is detected by a photomultiplier. The number of photons detected
is proportional to the NO concentration in the air. If insufficient ozone is
generated, the instrument works improperly. With only the oxygen
naturally present in ambient air available to the ozone generator, the
instrument works only up to 16,000 ft. MSL. With pure oxygen feeding the ozone
generator, the instrument worked well to 21,000 ft MSL, the highest altitude at
which we tested it.
Tests
showed that the TEI instrument combined with our sample inlet system has a
quasi-first-order time response, with a time constant of 3 to 4 seconds.
Relationships have been developed to estimate true NO concentration when the
sample is ingested into the instrument for only one or a few seconds as is the
case when the aircraft passes through a narrow region of NO recently generated
by a lightning discharge. A number of instances of narrow peaks in NO
concentration were observed that we attribute to cylindrical plumes of NO
created by recent lightning discharges that passed through the sampled region.
Peak values were typically from a few to several ppbv. In one instance
lightning attached to the propeller. NO concentration rose to ~180 ppbv in one
second, then decayed.
Depending on the actual time during which NO generated during this
discharge entered the inlet (probably less than one second), and subject to a
more refined calibration of the raw instrument reading, we estimate the peak concentration
exceeded 800 ppbv as the aircraft penetrated through the lightning channel
region..
A variety
of hydrometeor types were observed, including hail on several occasions. All
research flights were conducted while KOUN, the WSR-88D radar modified for
polarimetric capabilities, was scanning the region in which the aircraft was
sampling although these observations were only available post-flight. Real-time
access to KTLX WSR-88D operational radar observations facilitated flight
operations and data from both radars will facilitate analysis of storms
observed during these operations.
Although the aircraft was struck by lightning during one flight, and several flights were through thunderstorms with active lightning occurring, there were no detectable X-ray events during any of these missions.
We are grateful to our hosts and collaborators at the NSSL and OU/CIMMS for making our operations possible. These include Dave Rust, Don MacGorman, Terry Schuur, Dave Priegnitz, and the NSSL facilities, phone and IT crews. Further thanks go to Prof. Patrick McCann of the Dept. of Electrical Engineering at OU, and his associates, for help in verifying the concentration in our calibration mixture of NO, and for assisting in other aspects of calibration activities with the TEI 42C-TL.