Bruce L. Gary
This web page is devoted to a "calibration" of the PTW and MMS instruments that were flown during the Crystal-Face mission in July, 2002. I describe the calibration of 3 in situ temperature instruments on this web page: the PTW instrument which was aboard the WB-57, and MMS instruments that were aboard the ER-2 and WB-57. I have calibrated them using RAOBs as a standard.
These in situ Outside Air Temperature, OAT, calibrations are useful for various analyses of data produced by the Microwave Temperature Profiler, MTP. Since the derivation of MTP "window corrections" requires RAOBs it is convenient to also perform the OAT calibrations. The OAT calibrations are presented on this web page with the thought that other Crystal Face experimenters might need calibrated OATs.
The procedure for obtaining the OAT calibration begins with an inspection of a flight track to determine which RAOB sites are located closer than ~150 km. A list of times and RAOB site designations is produced, and the RAOBs are downloaded from the following web site: http://weather.uwyo.edu/upperair/sounding.html These RAOB profiles are displayed in a spreadsheet and plots of temperature versus pressure are printed. Times when the aircraft flew close to the RAOB site are noted, and the pressure altitude for these times is converted to ambient pressure. For each OAT/RAOB comparison event a RAOB interpolation fraction is calculated for temporal interpolation between the closest previous and following RAOBs. The graph of the several RAOB T(P) is then consulted for calculating a temperature at the appropriate pressure level and interpolated in time for each OAT/RAOB event. An average OAT is calculated by averaging ~2.5 minutes worth of OAT measurements.
PTW on WB-57
So far, 6 flights have yielded a total of 27 RAOB/PTW temperature comparisons. The results of those comparisons is shown in the figure below.
Figure 1. PTW's OAT versus RAOB temperature at WB-57 altitude. The dotted line is a fit to the PTW data, and is offset +0.34 K from RAOB temperatures.
Under the assumption that PTW temperatures are merely offset from RAOB temepratures, PTW temperatures are related to RAOB temperatures in the following way: Tptw = Traob +0.34 +/- 0.22 K
In other words, the correction term for PTW/WB57 temperatures is:
OATptwCORwb57CF = -0.34 +/- 0.22 K.
MMS on ER-2
There was a MMS system aboard both the WB-57 and ER-2. This section compares the MMS/ER2 system's OAT with RAOBs.
The MMS data used here was archived in July and August, 2002.
Figure 2. MMS/ER2 OAT versus RAOB temperature at ER-2 altitude. The dotted line is a fit to the MMS data, and is offset -0.30 K from RAOB temperatures.
So far, four Crystal-Face ER-2 flights have been processed, ER020701, 020703, 020711, 020713 & 020716. They provide 25 RAOB/MMS comparisons which yield the following result: Tmms = Traob -0.30 +/- 0.21 K
In other words,
OATmmsCORer2CF = +0.30 +/- 0.21 K.
MMS on WB57
The MMS aboard the WB-57 was compared with the same RAOB passes described above for the PTW system aboard the WB-57.
Figure 2. MMS/ER2 OAT versus RAOB temperature at ER-2 altitude. The dotted line is a fit to the MMS data, and is offset +0.51 K from RAOB temperatures.
So far, six Crystal-Face WB57 flights have been processed, WB020629, 020703, 020707, 020711, 020713 & 020731. The originally-submitted MMS exchange files were used in all analyses reported here (having submission dates of 2002 July and August). Flight WB020629 was a cross-country flight that flew directly over 5 RAOB stations. Flgiht WB020703 was in the Miami area, and RAOB data was derived from the NCAR Vaisala archive files (Larry Miloshevich, PI) with filenames starting with MI (Miami) and PA (PARSL). Since time after launch was included in the NCAR archvied data it was possible to perform an accurate temporal interpolation between RAOBs for times the WB-57 flew over the MI and PA sites. Other flight dates used NOAA RAOB data.
These 6 flights provide 27 RAOB/MMS comparisons which yield the following result: Tmms = Traob +0.51 +/- 0.22 K
In other words, the correction is:
OATmmsCORwb57CF = -0.51 +/- 0.22 K.
This correction is compatible with a decade of MMS/ER2 temperature data that I have determined to be always warm with respect to RAOBs by about 0.8 K, with the exception of resubmissions of MMS data for SOLVE which had an offset of ~ 0.4 K (too warm).
This site opened: February 11, 2003. Last Update: February 19, 2003