422
J A M 1 3 I(. AN(illl.1
the Air Resources I.;iborii~ories. llie Eulcriiin spectra so obtained emconip;iss periods of oscillation ranging from I7 min t o 2 scc.
Tctroon positions were obtaincd (and stored on magnetic tape) at 1-sec
intervals by means of il M-33 tracking radar from the Air Resources Field
Rcsearcli Officc. National Reactor Testing Station, Idaho Falls. Tetroon
IiIunch mobility was providcd by a large truck fitted out as an inflation van.
As usual, transponders were attached to the tetroons to avoid the problem of
ground clutter and hcncc to permit accurate tetroon positioning at very low
elevation angles. The tctroons wcrc inllated to float at 300 m in order that
realistic comparisons could be made with the tower data, but because of the
updrafts induced by the city, the mean tetroon height for the flights ur;cd
herein was 360 m. O n the average, each tetroon was positioned for 125 min,
corresponding to an average tracking distance of about KO km.
The tctroon positions at I-scc intervals were averaged over 30 sec. yielding vertical velocities al 30-sec intervals in the Lagrangian (actually quitsiLagriingi;%n) system. The radar positioning was not thought sufficiently
accurate to provide meaningful vertical velocities for shorter time intervals.
L,agrnngian verticsl-velocity spectra, based on data for the entire length of
cach lctroon flight, were determined by means of a conventional spectrum
analysis with a maximum lag of 60 min. The Lagrangian spectra so obtained
Siiicc ;ill the tower data havc not yet been reduced, and since each tetroon
llight H;LS 1r;ickcd for about twice the tower sampling time (67 min), the
sin11~lti~t1cous data sample for the following analysis consist of 21 tetroon
Spccirii and 36 tower spectra. Accordingly. for purposes o l comparison, a
tctroon spectrum is often matched with two successive tower spectra. All
spectra il1.c bawd on vcrtiail-velocity data obtained essentially in daytime.
’ encoiiqxiss periods of oscillation ranging from 60 to 3 min.
2. ~‘OMIWSITE E l II.EKIAN A N D LAORANGIAN SI”TKA
Figure 3 presents composite Eulerian and Lagrangian n S ( n ) vcrticalvelocity spcctrii based on the 10 hourly intervals when the tower was upwind
of the city and the associated seven tetroon flights did not pass over the city.
At a height of 355 m the tower (Eulerian) spectral peak is found at a period
of 5.9 min (the exact period is determined by comparison of the varianccs
each sidc of the peak variance), while the tetroon (quasi-Lagrangian) spcctral peak is found at a period of 14.0min. yielding a mean value for the
L.agrangian-.Eulerian time scale ratio fl of 2.4. Since the mean tetroon height
was 310 m. and the dominant Laprangian period of oscillation increases
somewhat with increasing height (Fig. 4). the value of 2.4 is a slight
undcrcstinliitc.
J A M 1 3 I(. AN(illl.1
the Air Resources I.;iborii~ories. llie Eulcriiin spectra so obtained emconip;iss periods of oscillation ranging from I7 min t o 2 scc.
Tctroon positions were obtaincd (and stored on magnetic tape) at 1-sec
intervals by means of il M-33 tracking radar from the Air Resources Field
Rcsearcli Officc. National Reactor Testing Station, Idaho Falls. Tetroon
IiIunch mobility was providcd by a large truck fitted out as an inflation van.
As usual, transponders were attached to the tetroons to avoid the problem of
ground clutter and hcncc to permit accurate tetroon positioning at very low
elevation angles. The tctroons wcrc inllated to float at 300 m in order that
realistic comparisons could be made with the tower data, but because of the
updrafts induced by the city, the mean tetroon height for the flights ur;cd
herein was 360 m. O n the average, each tetroon was positioned for 125 min,
corresponding to an average tracking distance of about KO km.
The tctroon positions at I-scc intervals were averaged over 30 sec. yielding vertical velocities al 30-sec intervals in the Lagrangian (actually quitsiLagriingi;%n) system. The radar positioning was not thought sufficiently
accurate to provide meaningful vertical velocities for shorter time intervals.
L,agrnngian verticsl-velocity spectra, based on data for the entire length of
cach lctroon flight, were determined by means of a conventional spectrum
analysis with a maximum lag of 60 min. The Lagrangian spectra so obtained
Siiicc ;ill the tower data havc not yet been reduced, and since each tetroon
llight H;LS 1r;ickcd for about twice the tower sampling time (67 min), the
sin11~lti~t1cous data sample for the following analysis consist of 21 tetroon
Spccirii and 36 tower spectra. Accordingly. for purposes o l comparison, a
tctroon spectrum is often matched with two successive tower spectra. All
spectra il1.c bawd on vcrtiail-velocity data obtained essentially in daytime.
’ encoiiqxiss periods of oscillation ranging from 60 to 3 min.
2. ~‘OMIWSITE E l II.EKIAN A N D LAORANGIAN SI”TKA
Figure 3 presents composite Eulerian and Lagrangian n S ( n ) vcrticalvelocity spcctrii based on the 10 hourly intervals when the tower was upwind
of the city and the associated seven tetroon flights did not pass over the city.
At a height of 355 m the tower (Eulerian) spectral peak is found at a period
of 5.9 min (the exact period is determined by comparison of the varianccs
each sidc of the peak variance), while the tetroon (quasi-Lagrangian) spcctral peak is found at a period of 14.0min. yielding a mean value for the
L.agrangian-.Eulerian time scale ratio fl of 2.4. Since the mean tetroon height
was 310 m. and the dominant Laprangian period of oscillation increases
somewhat with increasing height (Fig. 4). the value of 2.4 is a slight
undcrcstinliitc.