Michael W. Douglas, National Severe Storms Laboratory - Javier Murillo, CIMMS / University of Oklahoma SCOPE The scope of PACS-SONET differs from many previous field programs in that: 1)it has been expanded to a broader geographical region from northern Mexico to Paraguay. 2)it has a relatively long duration for a field program. Initially planned for 6 months, it has since been extended for a total of almost 80 months. 3)communication of data is in near real-time via Internet. PILOT BALLOON OBSERVATIONS Pilot balloon soundings, rather than radiosonde observations, have been made throughout the PACS-SONET life span. The main advantage of pilot balloon observations is that they are inexpensive. Typically, a 30-gram balloon launch, excluding labor costs, is only 5-10% that of a radionsonde launch. To date the project has generated more than 30,000 soundings. The graphic below shows the number of observations per month generated by the network from April 1997 to August Future Trends in the Pan American Climate Studies Sounding Network (PACS-SONET) 1.4. Extension of the PACS-SONET program In late 1999 support was obtained for extension of the PACS-SONET program for an additional 3-year period. In addition to an extension in time, the network was expanded to a broader geographical region. Pilot balloon sites have been operating in Paraguay (2) and Bolivia (6). The primary objective of these additional observations was to describe the variability of the low-level flow east of the Andes and the circulation over the Bolivian altiplano. In Mexico, 7 sites are being operated by the Mexican navy, including two in northwestern Mexico to improve the description of the low-level flow along the Gulf of California. In March 2001, one station was established in Venezuela at San Fernando de Apure, a location in the very flat llanos north of the Orinoco River. The figure at right shows the current PACS- SONET configuration and other stations that have been operational with financial or logistic support from the project. The Pan American Climate Studies Sounding Network (PACS-SONET) is a research activity funded by the NOAA’s Office of Global Programs. It has evolved from a regional network of 6-month duration to a hemispheric activity that has been extended for a second 3-year period in THE FUTURE OF PACS-SONET PACS-SONET has been extended for a second 3-year period, subject to a re- evaluation of the activity and more consensus-seeking on the part of the project. As a first step towards renewing the direction of the activity, a meeting has very recently been held in Paraguay in late August The meeting was intended to develop a consensus among each of the participating institutions as how to proceed to increase the effectiveness of the PACS-SONET. All participant countries and institutions were represented at the meeting. Preliminary conclusions from the workshop indicate that future activities should include: Radiosonde observations (PTU only) at key sites such as the Galapagos Islands, Ecuador. An optical theodolite would be used to track the radiosonde in order to save funds by launching inexpensive non-GPS sondes. Radiosonde observations are feasible at locations were gas is generated. Continue to support educational activities to stimulate research with the data collected. Different options to better utilize the available funds were discussed during the workshop. Work with the participating institutions in designing ways to better quality control the data. Establishment of additional sites in Peru and Brazil with help from the national meteorological services. The main benefit of the reunion of the country coordinators has been to create an awareness among the participants about the necessity of optimizing the available resources of the project to stimulate research and applied forecasting activities throughout the region. It was emphasized that PACS-SONET is not a major source of resources for the countries involved, rather it can serve as a framework for the development of meteorological and climate activities in the region. 1. HISTORY AND EVOLUTION 1.1. Original network. The original PACS-SONET configuration consisted of 12 pilot balloon stations. The stations were established during March and April of 1997 in Mexico, Nicaragua, Costa Rica, Panama, Colombia, Ecuador and Peru. The objectives of this network included: )describing the amplitude of the diurnal variation of the windfield at a number of sites. 2)Determining the circulation anomalies associated with wet and dry spells over Central America. 3)Determining whether large differences existed between the NCEP reanalysis and observations in data sparse regions of the eastern tropical Pacific. Fig. 1. Map showing the original station configuration during mid Changes due to El Niño Due to the strong El Niño event of , the observational plan was modified to extend the observational period at many stations through the end of October 1998 and establish additional stations in Ecuador and Peru to better sample conditions in the region of anticipated heavy rainfall. Due to financial reasons, some of the stations actually stopped in August Nonetheless, an unprecedented data set was obtained to describe the wind field associated with the developing El Niño Fig. 2. Expanded network due to El Niño Special Mesoscale Campaign in Bolivia Pilot balloon observations were also made at Santa Cruz, Bolivia, as part of the special El Niño campaign. Although these were only made for 3 months they showed a strong and variable low-level jet at Santa Cruz, which had not been described from observations previously. These observations stimulated further observations from a more extensive network in Bolivia during The map at right shows the pilot balloon network in Bolivia during January- April Fig. 3. Pilot balloon network in Bolivia during Jan-Apr SCIENTIFIC OBJECTIVES The fundamental overall objective of the project is to establish a long-term atmospheric sounding network for providing baseline measurements for real-time climate monitoring and for comparison with model development activities over the PACS domain. The fundamental scientific objective of PACS-SONET is to determine both the annual cycle and interannual variability of the lower tropospheric windfield associated with the monsoon circulations over and around the Americas, with the aim of explaining the observed variability of precipitation over the land regions Relevance to PACS PACS-SONET observations provide the background field to the specialized field experiments: North American Monsoon Experiment (NAME) The observations at Puerto Peñasco and Topolobampo in northwestern Mexico are intended to help describe the low-level flow along the Gulf of California and will be of relevance for NAME. South American Low-level Jet Experiment (SALLJEX) The observations at two sites in Paraguay and 6 sites in Bolivia served as the ramp-up network for the upper-air component of SALLJEX. EPIC The stations deployed from southern Mexico to northern Peru provided a context for field activities related to EPIC The impact of the additional observations can be appreciated from the figure and the quality of the data quickly assessed by comparing neighbor stations. 3. PACS-SONET DELIVERABLES 3.1 Real-time data collection. In addition to more observing sites, efforts have been made to make the network a real-time data collection and distribution activity. This required communications to be upgraded at many sites, and the development of procedures to ensure the flow of data to research institutions and to all interested forecasting institutions. The latter is accomplished mainly through the development of the project’s web page, in which the observations are made available in real time, in the form of both raw data and synoptic maps plotted at selected levels. The figure at right shows wind barbs from pilot balloon soundings (blue) at 3 sites in Bolivia and one in Asuncion, Paraguay, along with winds obtained from the regular radiosonde network (green). 3.2 Climate monitoring Several stations have been operating since 1997 and just now the time series is large enough to make crude estimations of the interannual varibility. The figures show monthly means of the meridional wind at San Cristobal, Galapagos for the months of May (a), July (b) and December (c). Southerly cross-equatorial flow at Galapagos is moderately strong in May and has a maximum in July-August-September. December shows the greatest interannual variability. (a) May(c) December (b) July