1. Real-time processed data
   The first is the data that was processed in real-time on-board the deploying aircraft either by a sonde scientist or through automated procedures and then subsquently transmitted to the National Centers for Environmental Prediction (NCEP) and other units of the National Weather Service. The actual transmitted data consist of TEMP DROP code messages in a standardized World Meteorological Organization (WMO) format. All messages from a particular flight are stored within an ASCII file, which has the nomenclature of "flight_ID".xmt. Alternately, the transmitted data can be accessed from a companion file containing ASCII records in a decoded HRD Spline Analysis (HSA) format with the nomenclature of "flight_ID".hsa. The resolution of the archived transmitted observations is somewhat limited, comprising bascially of mandatory levels (surface, 1000 mb, 925 mb, 850 mb, 700 mb, 500 mb, 400 mb, 300 mb, 250 mb, 200 mb, 150 mb, and 100 mb) and significant levels (where there are local extrema of thermodynamic and/or wind data). Normally, some airborne QC measures were performed on the sondes before they were transmitted. Another file containing plan-view horizontal plots of these observations at mandatory levels in PDF format is sometimes also available; it has the nomenclature of "flight_ID".pdf. High-resolution (2 Hz) versions of these data are available from NOAA aircraft only since 2002. These files are labeled "flight_ID".frd .

   Caution:
   Since thorough QC procedures and software algorithm corrections have not been applied, the real-time transmitted sonde data may occasionally be erroneous.

2. Raw dropsonde data
   The second type of operational data that HRD provides is the actual raw dropsonde observations from the Airborne Vertical Atmospheric Profiling System (AVAPS). Measurements of pressure, temperature, relative humidity, and wind are obtained at 0.5 s [2 Hz] resolution (for certain dropsonde models the wind measurements are only available at 1.0 s [1 Hz] resolution). The observations are stored in long ASCII records inside individual AVAPS files for each sonde. All the AVAPS files for a single mission have been aggregated together into one Unix tar file; and the tar file has been subsequently compressed using GNU-zip. The nomenclature is "flight_ID".avp.tar.gz. No processing or QC has been performed on the raw data. Consequently, it is recommended that you first process these sondes using the National Center for Atmospheric Research's (NCAR) Atmospheric Sounding Processing Environment (ASPEN) program . Please note that there are issues concerning data quality from ASPEN-processed sondes, especially in the tropical cyclone eyewall, that are being addressed. Click here for more information. The ASPEN software is freeware and can run on any Windows compatible computer platform. To download a copy of the latest version and obtain documentation, please visit the following web site from the NCAR Atmospheric Technology Division (ATD):
   http://www.atd.ucar.edu/rtf/facilities/software/aspen/aspen.html
   For many of the flights, there is an accompanying text file version of the mission drosponde log sheet, which contains a 132-character ASCII table; the nomenclature is "flight_ID".txt. The table is useful in identifying the nine-digit serial number, launch time, geographical location, and other attributes of each dropsonde deployed during the flight. It is also helpful in identifying the individual AVAPS files, which will have the naming convention of g"Serial_number".avp when unpacked.

3. Post-processed GPS-Dropsonde Data

   HRD personnel post-process some of the raw AVAPS high-resolution dropsonde observations on an as-needed basis using special in-house software. Generally, the post-processed sonde data are used in studies and analyses conducted by HRD scientists and outside collaborators. Product files from specific flights are only accessible on-line through an internal AOML server and are not readily available to the general public. All inquiries about obtaining and utilizing these files should be submitted to the HRD sonde data manager. Please include your name, affiliation, any collaborators, justification, and research plans. Each request will be considered on a case by case basis. Individuals will be required to grant co-authorship or give an acknowledgement to all HRD staff members involved in the post-processing effort for the requested flights in any manuscript produced using these data files.

GPS-dropsonde data are provided courtesy of the NOAA/AOML/Hurricane Research Division in Miami, FL (USA).

Also, it would be greatly appreciated if you could send a message to the HRD sonde data manager explaining how you plan to utilize the data. This will keep HRD abreast of your research efforts, allow suggestions for possible collaborations, and help avoid potential conflicts or duplication with other scientists, particularly those within HRD.