6. Plans for the WVSS-I and access to the data

There has been about a one-year delay in installing further WVSS-I units on UPS aircraft as they have switched DFDAU avionics vendors from AlliedSignal to Teledyne. The current plan as of this writing is for UPS to renew implementation of the WVSS-I on Teledyne equipped aircraft in the second quarter of the year 2000. In parallel, American Airlines is also going to the new Teledyne DFDAU. American Airlines' B-757 aircraft should begin implementation in August-September 2000, after an STC is granted for the passenger B-757 aircraft. The plan is to have 30 UPS and 24 American Airlines deployed with the WVSS-I. These 54 B-757 aircraft will be kept flying continually for about two years with 9 spare units on the ground. Each WVSS-I unit will have its RH sensor recalibrated after six months, and the RH sensor will be replaced and calibrated every year.

It should be noted that because of the delay in the avionics switch described above, five of the six UPS aircraft have had their WVSS units running for over a year without any recalibration. Table 1 below summarizes the installation dates and data availability of the six UPS aircraft. The actual tail numbers have been replaced with pseudo ID's per the agreement with the air carriers in sharing their data on the Internet.

Table 1. Period of Operations of the UPS B-757 Cargo Aircraft Equipped with the WVSS

Pseudo ID Installation Date Status (1 April 2000)
00378 02/04/99 Unit switched to Teledyne, Jan 2000.
00376 02/06/99 Working
00441 02/12/99 Working
00714 04/01/99 Working
00097 04/15/99 Working
00375 09/02/99 Working

All meteorological data (winds, temperatures, and water vapor information) from commercial aircraft are available in real time via the Aircraft Communication Addressing and Reporting System (ACARS). Details of this system can be found in Appendix B. This information is available now on the Internet and soon will be available at the National Center for Environmental Prediction (NCEP). Dewpoint information on the Internet has been corrected (see Appendix A), however, mixing ratio information on the Internet provided by NOAA's Forecast System Laboratory (FLS) has not been corrected and is, on average, about 5% too wet.

This WVSS-I data is also distributed on the UNIDATA NETCDF local data manager (LDM). However, we caution the user about the quality of this data. Not only is mixing ratio information inconsistent with the dewpoint information (see above), there appears to be occurrences of missing data, data with no dewpoints, and inappropriate Mach number fields.

Researchers are encouraged to use the quality-controlled WVSS-I data through UCAR's Joint Office for Science Support (JOSS). This data is available through CODIAC at http://www.joss.ucar.edu/codiac/. This data has consistent water vapor information (dewpoint, RH, and mixing ratio are consistent), and has the benefit of time continuity to check for changes in WVSS-I calibration. Recall from above that these units have been flying for twice as long as expected without the ability to remove the units and recalibrate the sensors. This will be rectified as the new Teledyne avionics are installed. The fleet of WVSS-I aircraft will fly as a "system test" for about 1.5 - 2 years after the last aircraft is installed. After that time, the WVSS-I units will be replaced with the second generation WVSS (WVSS-II).