1.1 Purpose and Scope. A radiosonde is a balloon-borne instrument used to simultaneously measure and transmit meteorological data while ascending through the atmosphere. The instrument consists of sensors for the measurement of pressure, temperature, and relative humidity. The sensors' information is transmitted in a predetermined sequence to the ground receiving station where that information is processed at some fixed time interval. When wind information is processed by tracking the balloon's movement the instrument package is termed a rawinsonde. Thus, rawinsonde observations of the atmosphere describe the vertical profile of temperature, humidity, and wind direction and speed as a function of pressure and height from the surface to the altitude where the sounding is terminated. Other derived parameters are also determined from a rawinsonde observation. The rawinsonde system consists of a balloon-borne radiosonde, receiving and tracking equipment, and computer systems for data processing. Pibal (pilot balloon) observations are soundings to delineate the vertical profile of wind direction and speed as a function of height. They are made by the tracking of a balloon by optical means or by radar equipment. In this Handbook only the optically-tracked balloon will be considered.
This Handbook prescribes federal standards for taking rawinsonde and pibal observations; for processing the observations; and for encoding, telecommunicating, and archiving the data. Also provided are procedures for quality control throughout the various phases of data acquisition, processing, and dissemination. All methodology contained in this Handbook is consistent with that stipulated by the World Meteorological Organization (WMO).
The standards defined in this Handbook apply to all U.S. government agencies or other U.S. facilities which take routine synoptic or unscheduled rawinsonde and pibal observations. The dissemination standards and requirements herein apply to all rawinsonde and pibal data transmitted over broadcast communication systems and/or use by the public or the government. Examples of such broadcast systems are satellites, the Automation of Field Operations and Services (AFOS) system, the Automated Weather Network (AWN) system, and the Global Telecommunications System (GTS). The standards and requirements also apply to all U.S. Agencies which provide rawinsonde and pibal data for archival at the World Data Center-A for Meteorology located at the National Climatic Data Center (NCDC), Asheville, North Carolina. Further, this Handbook is a reference and guide to the various users of upper-air data and to private enterprises engaged in the development of observational systems.
Throughout this manual, the following definitions apply:
"shall" indicates that a procedure or practice is mandatory.
"should" indicates that a procedure or practice is recommended.
"may" indicates that a procedure or practice is optional.
"will" indicates futurity, not a requirement to be applied to current practices.
1.2 Relation to Other Handbooks and Manuals. This version of FMH No. 3, Rawinsonde and Pibal Observations, supersedes and replaces the predecessor Federal Meteorological Handbooks:
1.3 Changes and Revisions. Changes and revisions to this Handbook will be made under the direction of the Office of the Federal Coordinator for Meteorological Services and Supporting Research (OFCM). Agencies shall submit recommendations for changes through their representatives to the OFCM.
1.4 Agency Specific Procedures. Agencies may issue supplemental instructions, but such instructions are not to be identified as part of this Handbook. If agencies intend to enter data collected under the supplemental instructions into the GTS, the data shall meet or exceed the basic provisions of this Handbook.
1.5 Rawinsonde Program - General. The United States and other WMO member countries maintain, on a cooperative basis, observing locations that cumulatively form part of The Global Observing System of the World Weather Watch (WWW) network. The synoptic rawinsonde observing programs of the United States and the other WMO member countries are designed to meet real-time operational needs for weather analysis and forecasting. These observations also provide a national and international data base of upper-air observations for research and climatological purposes. Synoptic observations are defined as those that are being taken simultaneously at fixed, scheduled times at a large number of locations. Unscheduled observations are those taken in support of specific missions without regard to long-term continuing, fixed scheduled times.
1.6 History of U.S. Upper-air Observing Programs. Upper-air observations began in the United States as early as 1749 with experiments using large kites to carry aloft primitive instruments. Later in the eighteenth century, experiments were conducted using tethered balloons so that observations could be made on calm as well as windy days. The advent of the airplane provided a means to carry aloft and safely return recording instruments that were impractical for use with balloons. In 1920, the U.S. Weather Bureau and the Army Air Corps established a program of daily airplane upper-air observations at about 20 locations nationwide. These provided the first national coverage of upper-air data.
In 1921, the U.S. Weather Bureau established a kite network which remained in operation until 1933. In the meantime, free-flight pilot balloons, tracked visually with a theodolite, were being used to determine winds aloft.
Around 1930, radio telemetry was successfully incorporated with balloon-borne atmospheric sensing instrumentation, the forerunner of today's rawinsonde/radiosonde program. A radiosonde network in the coterminous U.S. was begun by the (then) Weather Bureau in 1937-38. World War II provided special impetus in development of the rawinsonde/radiosonde technology and fostered the growth of upper-air observing networks.
Before computerized processing of upper-air observation data became the norm, the process involved a significant amount of manual labor. The observation process was generally considered a two-person effort, with a third person frequently involved for quality control, general oversight of procedures, and assistance. All aspects of the observation, from preparation for the sounding release through subjective recorder record-trace evaluation to preparation of adiabatic charts and the coded message, were manually performed and labor intensive. The process of preparation, evaluation, and coded message generation typically took an additional period of time equal to or greater than the period of time required for the actual observation. U.S. agencies began experimenting with computerized reduction of rawinsonde data during the late 1960s and early 1970s.
In the 1980's, technological advances in telemetry and small computers made near-fully automated rawinsonde observations feasible. At U.S. locations, manual involvement in taking rawinsonde observations was significantly reduced. By the middle 1980s both the National Oceanic and Atmospheric Administration (NOAA) and the Department of Defense (DoD) had made significant progress in automation. The use of station minicomputers and interfaces to automatically acquire flight data meant that the data computations, coded message generation, data transfer, and data storage functions could all be performed with minimal human intervention. The rawinsonde observation had thus become an operation with improved data quality, even though the time required for preparing radiosonde data for transmission had been reduced to, typically, less than one staff hour.
Currently, the upper-air observing program of the U.S. comprises a network of rawinsonde stations together with a number of additional observing systems, including pibals, a network of ground-based remote-sensing wind profilers, en route commercial aircraft, and satellite-based temperature profile and cloud-motion wind capability. Together these systems provide upper-air measurements that are basic to meeting the needs of operational weather forecasting, climatological data bases, and meteorological research programs.
1.7 Present Rawinsonde Program. The U.S. participates in the WMO's World Weather Watch program by maintaining and operating the Washington D.C. World Meteorological Center (WMC); the WMO Region IV Regional Telecommunication Hub (RTH), which is responsible for North and Central America and adjacent ocean areas; and radiosonde facilities at a network of civilian and military sites on its major land masses and remote island locations. The Washington D.C. WMC comprises the NOAA National Weather Service Telecommunication Gateway (NWSTG) and the National Centers for Environmental Prediction (NCEP). Together they fulfill global and regional telecommunications, data processing, and data monitoring responsibilities for the WMO.
The U.S. program for rawinsonde and pibal observations assists in meeting the data requirements of the international, regional, national, state, and local forecast centers and offices. The basic requirements include station spacing and density, frequency of observations, precision and accuracy of data, and resolution of measurements. The requirements may be supplemented to meet special mission needs but shall not be diminished, except in emergencies, to less than the standards for routine scheduled operations. A list of the upper-air sites operated by the U.S. is given in Appendix C.
Pibal observations are taken mainly by Department of Defense operations in the field, and are used primarily for artillery support.
1.7.1 Network of U.S. Stations. The U.S. network of stations comprises more than ten percent of the global rawinsonde network. The primary responsibility for maintaining this network rests with NOAA's National Weather Service (NWS). The network is augmented by observations made at military, National Aeronautics and Space Administration (NASA), Department of Energy (DoE), and other installations. Regardless of the purpose for the observations, agencies that do acquire rawinsonde and pibal observations and communicate them for general use shall comply with the provisions of this Handbook.
1.7.2 Network Design and Configuration. The proper frequency and spacing of rawinsonde and pibal observations, together with other types of upper-air measurements (i. e. satellite, aircraft and ground-based remote-sensing systems), enable identification and prediction of meteorological phenomena to protect human life and promote economic interests.
Many factors influence the size of the U.S. network and the locations of stations. Operational requirements play a central role in determining the network of stations and types of observing systems needed to describe the state of the atmosphere. Budgetary realities, in terms of existing and planned appropriations, determine agencies' ability to establish and sustain operations over an extended period of time. Logistics determine the ability to supply and maintain each station on a continuing basis. Geography determines an optimum location for each station, taking into account terrain, climatology, urban development, and other physical considerations. Other important factors include national security requirements, special research studies (particularly of severe storms and in support of international programs), and needs for observations in support of special events.
The WMO recommends a minimum upper-air station spacing of about 250 km over large land areas and 1000 km over sparsely populated and oceanic regions and further recommends that observations be taken one-to-four times daily (Ref 12: II.2, II.3). The average continental U.S. rawinsonde station separation is presently about 315 km, and two observations daily (at 0000 and 1200 UTC) are scheduled.
1.7.3 Transmission of Observations. The coded report containing data from the observation, when presented to the telecommunication system for dissemination to the general public and government agencies, shall adhere to the standards set forth in Chapter 7 and Appendix E. Telecommunication systems are described in Chapter 7 and detailed description of the coding procedure is contained in Appendix E.
1.7.4 Recording and Preserving Observations. An archive record of all regular synoptic rawinsonde and pibal observations shall be made for presentation to NCDC. An archive record shall also be made of unscheduled observations that are transmitted over telecommunications for use by the public or the government. The requirements for recording and transmitting these records to the NCDC are described in Appendix F.
1.7.5 Data Applications. Rawinsonde observation data are applied to a broad spectrum of operational, climatological, and research efforts. Applications include: initialization for numerical weather prediction models; input for pollution/dispersion models; severe storm, general, aviation, and marine forecasts; climatology records and atlases; ground truth for satellite retrieval algorithm development and verification; support for DoD programs; climate studies; and general research.
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