DRA
Delta-t = 12 hr
(Click to Enlarge)
VBG
Delta-t = 12 hr
(Click to Enlarge)
DRA, VBG, EDW
Delta-t = 0 hr
(Click to Enlarge)
Three CIREX flights were potentially useful: 19981115, the Southern
Survey, and 19981119 and 19981120, the two local stack flights. Because
there was no Edwards AFB RAOB launch for the Southern Survey flight, we
chose to attempt a calibration using the two local stack flights. On both
of these days however, there were significant spatial and temporal temperature
gradients in the atmosphere, as indicated by RAOBs launched from Vandenburg
AFB (VBG) and Desert Rock (DRA). At several levels in the atmosphere VBG
and DRA differed by as much as 5 K, and ROABs 12 hours apart at these stations
also differed by this much at some levels. In addition, the RAOB launched
from Edwards AFB (EDW) differed from VBG and DRA
|
DRA Delta-t = 12 hr (Click to Enlarge) |
VBG Delta-t = 12 hr (Click to Enlarge) |
DRA, VBG, EDW Delta-t = 0 hr (Click to Enlarge) |
The first two figures above show the large temperature changes at Desert Rock (DRA) and Vandenburg AFB (VBG) over a 12 hour period bracketing the stack flight on Nov 20, 1998. The third figure shows the large spatial variations in temperature between DRA (mauve), VBG (green) and Edwards AFB (EDW) (cyan).
Because of the large temporal temperature gradients at DRA and VBG, and the large spatial temperature variations between DRA and VBG, and because the ER2 was nearest EDW, we ended up using the average of the ascent and decent aircraft outside air temperature (OAT) -- instead of the EDW RAOB -- so as to minimize errors! This of course provided no information above 19.4 km, the maximum ER-2 altitude, and that information could not be filled in by the EDW sonde launched during the flight because it burst at 22 km. Therefore, the temperature field above 19.4 km had to be derived from the average of the DRA and VBG sondes. The 19981119 flight was not used because there was evidence of gravity waves in the atmosphere, which would have increased the errors in the calibration.
San Diego RAOBs on 19981115 (Click to Enlarge) |
MTP ATP at 2300 UT on 19981115 (Click to Enlarge) |
OAT-derived Tropopause (Click to Enlarge) |
The figure above on the left shows two RAOBs launched from San Diego (NKX) on Nov 15, 1998, at 1200 UT (light blue) and Nov 16, 1999, at 0000 UT (green). The figure in the middle is the MTP altitude temperature profile (ATP) on Nov 15, 1998, at 2300 UT just before landing at Edwards AFB. Note that the ATP tropopause altitude (~15 km) is in reasonably good agreement with the ROAB value (~16 km) given that the ER-2 is nearly 5 km away. Also, the coldest temperatures (~204 K) are in agreement between the MTP ATP and the RAOB launched 1 hour later. This is encouraging, but probably fortuitous as we do not believe that our calibration is that good.
The final image above is OAT-derived tropopause determined during the
dip at the southern end of the flight. OAT was used to determine that the
tropopause was at 16.8 km (16.7 km on descent and 16.9 km on ascent), with
the temperature reaching 194.4 K. In the Color-Coded Temperature Curtain
(CTC) for this flight (shown below), the MTP-derived tropopause altitude
is shown in white and the aircraft altitude is shown in black. The
OAT-derived tropopause is the horizontal white line between 71 and
73 ks. Even though the MTP tropopause is in better agreement with the San
Diego, CA, RAOB at the end of the flight, we believe the OAT tropopause
at the dip. Given the nearly 5 km that the ER-2 was above the tropopause,
and the shape of the RAOB, it is not at all suprizing that the MTP-derived
tropopause is 1 km low.
MTP CTC for 19981115 (Click to Enlarge) |
Note that while the troposphere appears to remain relatively stable as the ER-2 flies south, the stratosphere warms at any given altitude, and this is reversed on the return flight north.
The MP file -- containing the normal Gaines/Hipskind format MTP data
-- can be found here.
MTP CTC for 19981120 (Click to Enlarge) |
The CTC above shows the results for the local stack flight on 19981120 -- the last CIREX mission flight. This in fact was the flight that we used to calibrate the MTP. It is evident that there is significant variation in the MTP tropopause solution! We of course expect the trop solution to have an error which is a function of the distance that the ER2 is either above or below the trop, and some of the scatter is due to that. However, examination of the RAOBs for Desert Rock 12 hours apart shows trop solutions of 13.1 km and 14.6 km, while Vandenburg had trops at 11.2 and 14.9 km. MTP profiles (see for example, data near 68 ks) show a region between 11 and 17 km where the slope is very close to -2 K/km, the criterium used to define the thermal tropopause. As a result noise differences from scan to scan can cause the trop solution to vary significantly, in this case 6 km, and in fact, even the RAOBs for this period of time show this magnitude of variation. Note also the data from 65.5 to 68.0 ks where the ER2 retraced it's flight track. This close to the tropopause, the MTP trop solution should be good, yet we see a very clear variation both in the height of the tropopause and in the stratospheric temperature field which repeated itself, lending credence to the measurement and to the fact that there were significant spatial variations in the temperature field..The MTP temperatures at flight level agreed very well with the RAOBs. Recall also that because we were aware of this variability, we chose to use an OAT-derived temperature profile from ER2 ascent and descent to calibrate the MTP.
The MP file -- containing the normal Gaines/Hipskind format MTP data -- can be found here.
There is no Nav data for the 19981113 flight because the Nav recorder
failed. Talk to Sky Yarbourgh at DFRC to get this data from the back up
record.