PIBAL Wind Only Sounding Data from PACS-SONET Data Set

1.0 General Description

This is one of the upper air data sets developed for the North American Monsoon Experiment (NAME). This data set includes the high resolution vertical (30 second to 480 seconds after release and 60 second from 480 seconds after release to the end of the sounding) pilot ballon (PIBAL) data from the Pan American Climate Studies-Sounding Network (PACS-SONET). For information on PACS-SONET visit the PACS-SONET home page. For NAME this network included data from 21 locations throughout Mexico and the Southwestern United States. This data set includes only wind and height information.

This dataset was provided and quality controlled by the National Oceanic and Atmospheric Administration National Severe Storms Laboratory (NOAA/NSSL). NCAR/EOL has not done any additional quality checking of these data.

2.0 Detailed Data Description

2.1 Detailed Format Description

All upper air soundings were converted to National Center for Atmospheric Research/Earth Observing Laboratory (NCAR/EOL) Sounding Composite Format (ESCF). ESCF is a version of the NCAR CLASS format and is an ASCII format consisting of 15 header records for each sounding followed by the data records with associated QC information.

Header Records

The header records (15 total records) contain data type, project ID, site ID, site location, release time, sonde type, meteorological and wind data processors, and the operator's name and comments. The first five header lines contain information identifying the sounding, and have a rigidly defined form. The following 7 header lines are used for auxiliary information and comments about the sounding, and may vary from dataset to dataset. The last 3 header records contain header information for the data columns. Line 13 holds the field names, line 14 the field units, and line 15 contains dashes ('-' characters) delineating the extent of the field.

The five standard header lines are as follows:

The release location is given as: lon (deg min), lat (deg min), lon (dec. deg), lat (dec. deg), alt (m)

Longitude in deg min is in the format: ddd mm.mm'W where ddd is the number of degrees from True North (with leading zeros if necessary), mm.mm is the decimal number of minutes, and W represents W or E for west or east longitude, respectively. Latitude has the same format as longitude, except there are only two digits for degrees and N or S for north/south latitude. The decimal equivalent of longitude and latitude and station elevation follow.

The seven non-standard header lines may contain any label and contents. The labels are padded to 35 characters to match the standard header lines. Records for this dataset include the following three non-standard header lines.

Data Records

The data records each contain time from release, pressure, temperature, dew point, relative humidity, U and V wind components, wind speed and direction, ascent rate, balloon position data, altitude, and quality control flags (see the QC code description). Each data line contains 21 fields, separated by spaces, with a total width of 130 characters. The data are right-justified within the fields. All fields have one decimal place of precision, with the exception of latitude and longitude, which have three decimal places of precision. The contents and sizes of the 21 fields that appear in each data record are as follows:

Fields 16 through 21 contain the Quality Control information derived at the NCAR Earth Observing Laboratory (NCAR/EOL). Any QC information from the original sounding is replaced by the following EOL Sounding Composite Format codes:

Sample Data

The following is a sample record of NAME PIBAL data in the EOL Sounding Composite format. The data portion is much longer than 80 characters and, therefore, wraps around to a second line. See section 2.1 for an exact format specification

Data Type:                         Pibal
Project ID:                        NAME
Release Site Type/Site ID:         CA Catavina BC
Release Location (lon,lat,alt):    114 47.40'W, 29 50.40'N, -114.790, 29.840, 554.0
UTC Release Time (y,m,d,h,m,s):    2004, 07, 16, 14:32:00
Assumed Ascension Rate:            3.61 m/s
Balloon Data:                      Size: 30 grams
/
/
/
/
Nominal Release Time (y,m,d,h,m,s): 2004, 07, 16, 14:32:00
 Time  Press  Temp  Dewpt  RH    Ucmp   Vcmp   spd   dir   Wcmp     Lon     Lat    Ele   Azi   Alt    Qp   Qt   Qrh  Qu   Qv   QdZ
  sec    mb     C     C     %     m/s    m/s   m/s   deg   m/s      deg     deg    deg   deg    m    code code code code code code
------ ------ ----- ----- ----- ------ ------ ----- ----- ----- -------- ------- ----- ----- ------- ---- ---- ---- ---- ---- ----
  30.0 9999.0 999.0 999.0 999.0    1.5    0.9   1.8 240.0 999.0 9999.000 999.000 999.0 999.0   662.3  9.0  9.0  9.0 99.0 99.0  9.0
  60.0 9999.0 999.0 999.0 999.0    1.6    1.3   2.1 230.7   3.6 9999.000 999.000 999.0 999.0   770.6  9.0  9.0  9.0 99.0 99.0 99.0
  90.0 9999.0 999.0 999.0 999.0    2.5    1.1   2.8 246.1   3.6 9999.000 999.000 999.0 999.0   878.9  9.0  9.0  9.0 99.0 99.0 99.0
 120.0 9999.0 999.0 999.0 999.0    4.7   -0.9   4.7 280.7   3.6 9999.000 999.000 999.0 999.0   987.2  9.0  9.0  9.0 99.0 99.0 99.0
 150.0 9999.0 999.0 999.0 999.0    6.2   -3.3   7.0 298.0   3.6 9999.000 999.000 999.0 999.0  1095.5  9.0  9.0  9.0 99.0 99.0 99.0

2.2 Station List

The following is a portion of the document "The Design and Evolution
of the PACS-SONET Observing System in Latin America" by Douglas et al.

        2.2.1 Pilot balloon observations

        The use of pilot balloons for determining winds above the surface has 
        been carried out for more than 100 years, and is still widespread in 
        some regions  today.  In principle it is straightforward, though many 
        details must be considered to make the highest quality observations. 
        The main advantage of pilot balloon observations is that they are 
        inexpensive. Typically, a 30 gm pilot balloon launch, excluding labor 
        costs, is only 5-10% the cost of a radiosonde launch.  In addition, 
        they require a relatively simple instrument 
        (a meteorological theodolite), require no electric power, and the 
        observer does not need to be computer-literate.

	The main uncertainty in the winds calculated from pilot balloon 
        observations does not result from errors in measuring the angles - 
        such errors can usually be detected and corrected by data editing 
        procedures.  Rather it is a consequence of turbulence in the 
        atmosphere which causes the balloon's ascent rate to deviate from the 
        assumed value.  On a hot, windy afternoon the vertical motions 
        associated with turbulence one km above the surface can be 1-2m/s or 
        even more, introducing departures of 25-50% from the assumed ascent 
        rate.  This source of error was recognized, and the PACS-SONET 
        observations were scheduled for early morning or late afternoon, 
        when boundary layer turbulence is generally weak.  For monthly mean 
        values, this source of error should be fairly small, since the 
        turbulence fluctuations are random, and the average ascent rate should
        be close to the assumed rate for an average composed of approximately 
        30 observations.
        
	2.2.2 The original network configuration

	The original PACS-SONET configuration, consisted of 12 pilot balloon 
        sites. The stations were established during April and May of 1997 in 
        Mexico, Nicaragua, Costa Rica, Panama, Colombia, Ecuador and Peru, 
        together with one radiosonde station on Cocos Island in the eastern 
        Pacific Ocean.  The intended duration of the observations was 6 months,
        ideally extending through October, and close to the end of the rainy 
        season in much of Central America.  The pilot balloon soundings were 
        made twice-daily at all sites. This permits an assessment of the 
        uncertainties inherent in climatological upper-air wind analyses that 
        are generally based upon only once-daily soundings.

        2.2.3 CHANGES TO PACS-SONET IN RESPONSE TO THE 1997-8 EL NI��O

        Shortly after the first stations were established in April 1997, 
        it became apparent that a significant warm event in the eastern and 
        central Pacific was developing.  By mid-summer, the extreme magnitude 
        of the event had become apparent.  This led to two conclusions: 
        1) the observations being made during the summer of 1997 would be very
        anomalous over Central America, thus putting into question the 
        extrapolation of potential scientific findings to other years, and 2) 
        there existed the possibility of obtaining an unprecedented data set 
        to describe the evolution of the windfield associated with the 
        developing El Ni��o.  Therefore, the observational plan was modified 
        to:  1) extend the observational period at many stations through the 
        end of October 1998, 2) establish additional pilot balloon stations in
        Ecuador and Peru to better sample conditions in the region of 
        anticipated heavy rainfall, and 3) include the installation of several
        hundred inexpensive raingauges in coastal Ecuador and Peru. The last 
        activity was necessary to assure  adequate measurement of daily 
        rainfall for comparison with pilot balloon and satellite observations.
        The financial, logistical, and technical difficulties involved in 
        establishing and expanding the network (ultimately to 17 pilot balloon
        sites) is described in this section.  


	2.2.4 Extension of the observing period

        Because the warm season rainfall over Central America was observed to 
        be well below normal, and it was apparent that El Ni��o was modifying 
        the normal conditions, it was considered desirable to make 
        observations during a more normal warm season.  This would not only 
        more closely satisfy the original objectives of the project, but also 
        provide an excellent comparison with the 1997 El Ni��o summer.  Thus, 
        plans were made to extend the observation program until the end of 
        October 1998, which is close to the end of the rainy season over 
        Central America.  Thus, two complete rainy seasons will have been 
        observed by PACS-SONET. The principal difficulty in extending the 
        observations for another year was related to the cost of the 
        additional observations.  To manage this, we had to reduce the
        observations from twice- to once-daily. However, even this created 
        considerable budgetary difficulties, due to the short notice that was 
        given to the funding agency.
        
	After about 45 mostly successful launches, we experienced difficulties
        with the operation of the radiosonde system on Cocos Island.  Based on
        these difficulties, it was decided to eliminate the radiosonde 
        observations there; a step that saved some $20-25,000.  The 
        elimination was deemed justifiable, since the loss of winds from the 
        majority of the radiosonde sites in the Caribbean, Central America and
        northern South America (due to the shutdown of the Omega system on 
        Sept 30, 1997) had already left huge gaps in the radiosonde network.  
        Thus, the Cocos observations would not have been especially useful to
	estimate typical NCEP analysis uncertainty over this data void, since 
        any difference between the analyses and the Cocos observations could 
        be ascribed to the lack of neighboring stations to help initialize 
        the analyses.  Also, given the anomalous year, the Cocos soundings 
        would not describe a "normal" boundary layer downwind of the zone of 
        cold ocean temperatures along the Equator (the oceanic "cold tongue"),
        which was an additional PACS-SONET objective.


       2.2.5 Increasing the number of pilot balloon stations

       By October 1997 it was apparent that the El Ni��o event was comparable 
       to one during 1982-3, and that heavy rains might again affect the 
       northern region of Peru.  During the 1982-3 event there were no regular
       radiosonde or other wind sounding systems anywhere in the coastal 
       region of Peru (north of Lima), or in any part of Ecuador.  This lack of
       atmospheric soundings has limited the meteorological interpretation and
       explanation of the distribution of heavy rainfall associated with the 
       1982-3 event.  Since such strong El Ni��o events are quite rare, we 
       deemed it wise not to pass up this opportunity for sampling a rare 
       phenomenon, especially since a basic sounding network was already in 
       place in Ecuador and Peru.
       
       During the 1982-3 El Ni��o there was a large north-south gradient in the
       rainfall along the Peruvian coast, with Piura, Peru receiving more than
       2000 mm over the 6 month period of rains, while Trujillo, only 300 km 
       to the south, received no rainfall.  To measure the north-south 
       variations in the windfield we decided to establish additional pilot 
       balloon stations at Tumbes, Trujillo, Chiclayo and Ancon2.  
       (Ancon2 was to partially replace the lost winds from the Lima 
       Omega-based radiosonde station.)  A site was also established at 
       Iquitos, in the Amazon Basin, which when coupled with the wind 
       observations along the coast, and at San Cristobal in the Galapagos 
       Islands, would better describe east-west windfield variations.  In 
       Ecuador, additional sites were established on the coast at Ancon 
       (near Salinas), and at Portoviejo. 
       

3.0 References