Mountain Lee Waves on 981013 Transit Flight from
California to Maine
This isentrope altitude cross-scction (IAC) is the first case
of a MTP detecting and characterizing a mountain wave during flight below
the tropopause, and it is noteworthy that credible isentrope displacement
behavior is observed at altitudes well above the tropopause.This IAC is
for a longer longitude region but smaller altitude region than the one
shown below. Whereas fewer isentropes are shown, the altitudes of the DC-8
and the MTP-derived tropopause solutions have been added. The "pinching"
of isentropes during the approach to the highest and eastern-most mountain
peak (at -105.6° longitude) is more apparent here. This
opposite sloping of insentropes above versus below the tropopause
is probably caused by the synoptic setting, with "sub-tropical" air to
the west (note the 14 km tropopause at -116°) and "mid-latitude" air
to the east (where the tropopause is at 11 km before the DC-8 descends).
Rocky Mountain portion of DC-8 flight 971013, from CA to ME, showing isentropes
5 K apart (at -110° longitude, the 320 K isentrope is at 6.8 km). The
DC-8 was flying at 10 km during this flight portion, and the tropopause
descended from 12.8 km at -112° longitude) to 11.0 km at -104°
longitude. Below the tropopause the isentropes are sloping up
(flying toward the east) while above the tropopause they are sloping down
(toward the east). The isentrope at 11.1 km (335 K) has no slope, and is
featureless except for a downward dip at -106.1°, followed by an upward
rise at -105.3°. The dip feature can be traced downward, and extrapolating
would intercept the east face of the mountain at about -105.2°.
This phase line is therefore sloped to the west, upwind, as models predict
it should; it can be traced as far as 14 km, where it is at -106.5°.
At -107.8° the high altitudes show a horizontally confined upward displacement
with an amplitude that increases with altitude. At -108.5°, from
7 to 9 km, there's a 500 meter upward displacement that disappears at 11
km, then reappears at 13 km, and increases in amplitude with altitude as
far as 18 km. As the various horizontal spatial wavelengths propagate
upward, they are horizontally displaced and add with each other to provide
occasional cancellation, which is apparently what happened at 11 km in
the -110° to -107° region. The figure below has the vertical scale
increased by two times to enhance the visibility of the isentropes.
Comparison of LaRC/DIAL IR Wave and JPL/MTP Isentrope
Surfaces
The heavy red lines in the above figure shows the location of nadir and
zenith IR relative atmospheric scattering ratio measurements (shown below)
made by the LaRC/DIAL lidar.For the nadir DIAL data, the agreement is excellent!
For the zenith DIAL data the agreement is poorer. DIAL shows an upwind
phase slope, in agreement with MTP and theory. Both DIAL and MTP
show that the amplitude of the wave decreases with altitude (at 61300 ustec,
17:01 UT), going from 1000 meters at 8.3 km to 600 meters at 11.4 km.
The DIAL zenith wave, at 11.4 km (pressure altitude), is very close to
the MTP tropopause (11.5+/-0.1 km), so there's an association. The
MTP wave at 11.5 km shows less structure than DIAL, but this could be because
MTP can't follow isentropes very accurately near the tropopause due to
MTP's "smoothing out" of sharp T(z) features in the retrieval process.
DC971025 tropopause altitude, DC-8 altitude, and tracers ozone and CO.When
the tropopause is below the DC-8 tracers ozone and CO have "stratospheric"
values. Small changes in tropopause altitude are also correlated
with expected changes in the two tracers (i.e., at 34.8, 43.4 and 52.6
ks).
DC971025 ozone is related to DC-8 altitude referenced to the MTP-based
tropopause altitude, showing an abrupt increase in ozone above the tropopause.
(This data is for the first 1/3 of the flight, and avoids the confusing
region at 43.4 ks.)
DC971015 ozone versus DC-8 altitude referenced to the MTP-based tropopause
altitude, showing amixture of tropospheric and stratospheric air within
the 2 km layer immediately below the tropopause. This is the normal
situation, where the slightly enhanced ozone below the tropopause is probably
the result of a steady-state diabatic descent of stratospheric air downward
through the tropopause, accompanied by a steady mixing of the higher ozone
air with low ozone ambient air. The previous figure is anomalous,
and may be caused by storm-related rapid mixing of recently-descended stratospheric
air across the tropopause.
