METEOROLOGICAL CONDITIONS DURING PILOT-BALLOON FLIGHTS 

 PROCEEDURE 



Efforts were made to obtain a pilot-balloon flight on 

 every day it seemed probable that the observer could 

 follow the balloon for at least ten minutes. It required 

 about thirty minutes for unstowing the theodolite, setting 

 up the inflation balance, inflating the balloon, and making 

 minor preparations for a flight. On a number of occa- 

 sions during the period of preparation, weather and sky 

 conditions changed materially, so that the balloons were 

 lost at low altitudes in quickly formed low clouds. 



The Carnegie could not be maneuvered so as to re- 

 main at one point during the period of a flight. The gen- 



eral procedure was to set the ship's heading so as to 

 keep a steady course. If, while on this course, the bal- 

 loon went behind the ship's sails or rigging, a new 

 course was chosen, which it was considered would bring 

 the balloon in sight for a considerable time. In calm 

 weather, or when the winds were so light that the helms- 

 man could not keep the ship on a course, it was the prac- 

 tice to start the small auxiliary engine, which gave the 

 Carnegie a speed of five or six knots and allowed a good 

 course to be sailed. 



METEOROLOGICAL CONDITIONS DURING PILOT-BALLOON FLIGHTS 



The meteorological log of the Carnegie with entries 

 of weather conditions, constituted an invaluable record 

 for interpreting the upper -wind data. Unfortunately, the 

 meteorological log was destroyed with the Carnegie in 

 Apia harbor. Captain Ault had made an abstract of the 

 ship's log for each leg of the cruise, however, which he 

 forwarded immediately after the Carnegie reached a 

 port of call. Meteorological observations were made 

 regularly at Greenwich mean noon, and observers noted 

 certain weather conditions during atmospheric -electric 

 determinations. From all these sources a fairly com- 

 prehensive account of the prevailing weather has been 

 compiled for periods when pilot-balloon flights were 

 made. 



Flights 1 to 4, October 27 to 31, 1928 



The first four flights were made in the Gulf of Pan- 

 ama from October 27 to 31, 1928. Owing to low cumu- 

 lus or nimbus clouds on three occasions, and once 

 largely to the observer's inexperience none of the bal- 

 loons were followed higher than 1 km. The surface 

 winds of Beaufort force 3 or 4 varied from west to 

 southwest. On three out of four flights the west-south- 

 west surface winds turned to a more northerly direc- 

 tion, the mean velocity apparently increasing from 5.4 

 m per second at the surface of the ocean to 7.4 m per 

 second at levels of 0.25 and 0.50 km. The observed 

 west-southwest surface winds agree with those shown on 

 the United States Pilot Chart of the South Pacific Ocean 

 for the September -November quarter, and represent an 

 inflow of colder air from above the waters at abnormally 



low temperature off the South American coast [1], This 

 area, forming the eastern extremity of the doldrums of 

 the Pacific, lies protected behind the mountains of Pana- 

 ma and Colombia, which interrupt the regular east-west 

 circulation of the atmosphere. At lower levels there 

 are doubtless strong upward vertical currents which 

 cause the cumulus clouds observed. The weather during 

 the week these flights were made was characterized by 

 frequent rain squalls and variable winds with thunder 

 and lightning reported on October 27 and 28. All these 

 are indications of the strong convection going on in this 

 area. 



Flights 5 to 8, November 9 to 17, 1928 



Owing to continuous overcast and cloudy weather 

 from November 1 to 9, no flights were made. The Car - 

 negie in these eight days sailed only 626 miles. The 

 equator was crossed on November 6 with southwest 

 breezes generally occurring. Flights 5 to 8 were made 

 as the Carnegie sailed westward, just south of the equa- 

 tor, from 85.°2 to 105.°4 west. The surface winds blew 

 from south or southeast, the typical trade-wind condi- 

 tion existing at all seasons in this area. According to 

 the United States South Pacific Pilot Chart the winds 

 blow 85 per cent of the time from south or southeast on 



Table 2. Wind directions in flights 5 to 8, showing com- 

 plexity of winds immediately above southeast trades 



Flight 



Wind direction 



Sur- 

 face 



1 km 2 km 



3 km 



4 km 



an eight-point wind rose. Despite its great constancy at 

 sea level, the southerly current was very shallow, being 

 displaced by northerly winds in every flight below 2.5 

 km. Table 2 shows the complexity of the winds from 1 

 to 4 km above the ocean. 



