The prime objective of the North American Atmospheric Observing System (NAOS) Program is to provide recommendations on cost-effective changes to the upper-air system over North America. This paper discusses the NAOS process by which those recommendations are being formulated, and the implications of making decisions based on them. One specific question is used to illustrate the process: Can automated soundings from aircraft takeoff and landings be effectively substituted for nearby radiosonde launches?
Both the radiosonde and the Meteorological Data Collection and Reporting System (MDCRS) provide temperature and wind information in the vertical. There are significant differences in geographic location, frequency of reporting, altitudes reached, spatial configuration of the radiosonde soundings and the MDCRS profiles obtained, and cost. Both provide vertical profiles of temperature and wind at present. (A demonstration program is in progress to obtain moisture information from the aircraft in the near future.) These data sets are fully integrated into operational NWP assimilation and are used by forecasters and others. NAOS is asking: "Are some of the radiosonde data redundant with the MDCRS data?" and "Under which conditions and for what purposes?"
If unnecessary redundancies are found, and changes might be made, what are they? Should costs be reduced? Should better coverage be sought? Is it some combination of these or others? Addressing aspects of that set of questions is the purpose of the first series of hypothesis testing under NAOS, as well as of an "operational" assessment. Preliminary results of the testing and assessment are available. How is that information to be assimilated with other parts of the knowledge base to arrive at recommendations?
The knowledge base for arriving at recommendations includes: (1) user requirements , (2) strategic planning documents, (3) the results of NAOS tests and "operational" assessments, (4) operational experience and considerations, and (5) system costs for both implementation and long-term operation. The NAOS System Design Work Group (SDWG) has been assembling that knowledge base and assessing the information in the context of reaching logical recommendations.
It is possible to conclude from that knowledge base, for example, that an effective upper air network configuration could begin with a "skeleton" of sites based on climate considerations, be expanded by identifying specific airports where suitable MDCRS data are available, and finally, be completed by eliminating any residual holes by moving or excising radiosonde sites not included in the above. This paper explores how such a conclusion might be reached, and some implications of, and risks involved in, its acceptance and implementation.
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