More than 2,500 rawinsondes were released during BOMEX from the five 

 ships, with surface temperature, humidity, and wind being measured both 

 manually by observers aboard ship and electronically by sensors mounted on a 

 boom extending from the bow of each ship. This memorandum presents a pre- 

 liminary comparison of the first 200 m of the rawinsonde temperature data 

 with the manually observed and electronically recorded surface temperature 

 data to determine (1) whether the ships' effects might have contaminated 

 the lower levels of the rawinsonde data and (2) if contamination is evident, 

 whether use of the electronically measured surface temperature data would 

 tend to reduce or eliminate the contamination. As analyses in the Barbados 

 Oceanographic and Meteorological Analysis Project (BOMAP) progress, it is 

 anticipated that updated comparisons will be made and published. This first 

 comparison, then, serves only to highlight some of the problems and to fur- 

 nish some guidance to users of BOMEX data. 



2. INSTRUMENTATION 



As noted in the Introduction, each ship was equipped with a boom surface 

 instrumentation system and a rawinsonde tracking system. The boom extended 

 outward about 10 m above the ocean surface and about 30° off the port bow 

 (fig. 3). Sensors mounted on the boom measured dry- and wet-bulb tempera- 

 tures, humidity, wind speed and direction, and other parameters. Each meas- 

 urement, including that of barometric pressure and the ship's gyrocompass 

 (true heading) , were recorded every 30 sec on one channel of an analog tape 

 by a signal conditioning and recording device (SCARD) . 



The data analyzed here represent samples from BOMEX Period III (June 19 

 through July 2) . During this period, rawinsondes were released approximately 

 every 90 min (except at 0130 GMT) from the four U.S. Coast and Geodetic Sur- 

 vey ships and every 3 hours from the U.S. Coast Guard cutter Hoakaway , posi- 

 tioned in the center of the BOMEX square. Each rawinsonde flight train con- 

 sisted of two specially modified instruments carried aloft by the same balloon. 

 The instruments were of standard Weather Bureau'- type, but modified so that 

 one measured temperature only while the other measured humidity only. The 

 temperature and humidity signals arriving at two separate receivers aboard 

 each ship were recorded on analog tape by SCARD. At the time of each release, 

 an observer visually obtained and manually recorded standard meteorological 

 data from shipboard instruments. These data included dry- and wet-bulb 

 temperatures, and wind speed and direction. 



3. SELECTION OF DATA 



Ten-minute averages of the boom temperatures were chosen for compari- 

 son with the temperatures recorded manually with a sling psychrometer on 

 board each ship. The 10-min boom values with a listed time of 06:05:15 

 represent the averages of all 30-sec values recorded between 05:55:16 and 

 06:05:15. This average was selected for comparison with shipboard obser- 

 vations between 0555 and 0605 GMT. The number of 30-sec samples in the 10- 

 min averages used in this study varied from 10 to 21. 



2 

 Now the National Weather Service. 



