High resolution wind and temperature data automatically measured on commercial aircraft are becoming an increasingly critical component of both the numerical and subjective forecast process. In the U.S., these data are downlinked and redistributed to NOAA through the Aircraft Communications and Addressing and Reporting System (ACARS). More than 40,000 en route and sounding observations are reported each day by American Airlines, Delta, Federal Express, Northwest, United, and United Parcel Service. While evaluations have demonstrated the value of automated aircraft reports in numerical models, little experience exists in the direct use of ACARS sounding and enroute data in forecast offices and centers. As part of the North American Atmospheric Observing System test and evaluation activities, an assessment of the potential value of ACARS data to operational meteorologists is being conducted at 20 offices for 15 months.
The ACARS Operational Assessment will determine the utility, availability and quality of ACARS sounding and en route data to support operational warning and forecast services. The results will complement the findings of NWP evaluations concerning the data utility and influence the design of a future composite upper air observing system. The assessment will allow those who are developing systems requirements and designs to benefit from the experience of operational meteorologists using new observing systems. Seventeen National Weather Service Offices and Centers, two Environment Canada Offices and the United Airlines Forecast Center are participating. Among the characteristics being evaluated are the: 1) utility of the data in short term forecasting, 2) value as a supplemental source of upper air data, 3) availability of the data, 4) vertical resolution of the soundings, and 5) absence of moisture profiles. Assessment mechanisms being used are the preparation of documented cases, examination of prognostic forecast discussions, surveys and collection of data retrieval statistics. The assessment is being carried out in two phases and will conclude by April 1999.
Preliminary results are showing ACARS sounding data to be a valuable tool in determining convective initiation and severity, forecasting precipitation phase, radiation fog, high wind events and low level wind shear. Participating U.S. and Canadian Forecast Offices on the west coast are using the data to determine the height of the marine layer and forecast the low clouds, fog and precipitation often associated with it. It is also being used for model validation, confirmation of other observing systems and in NEXRAD hail algorithms. Many of the soundings presently lack sufficient resolution in the boundary layer and are unevenly distributed in time and space. This reduces the value of data sets at some offices, but working with cooperating air carriers to implement a comprehensive system design can overcome these limitations. The wide deployment of the, presently experimental, Water Vapor Sensing System to provide vertical moisture soundings will also be important to expanded use of automated aircraft reporting systems in numerical models and directly in forecast offices and centers