METEOROLOGICAL CONDITIONS DURING PILOT-BALLOON FLIGHTS 



Flights 50 to 59, February 17 to 25, 1929 



These flights were made toward the close of the 

 southern summer, about 14° south of the equator, mid- 

 way between the Tuamotu Archipelago and the Peruvian 

 coast. The weather continued fine and without rain, ex- 

 cept for a brief drizzle at 5 a.m. on February 17. The 

 cloudiness ranged from 1 to 8, with a daily mean of 4, 

 recorded in every entry as chiefly on the horizon. 



Whereas the surface winds along this parallel from 

 80° to 100° west longitude had been southerly, the sur- 

 face winds from 100° to 110° west shifted to southeast, 

 and from 110° to 120° west, farther to east or even 

 slightly north of east. The southeast winds reached a 

 maximum height of 4 km on February 17, but the change 

 in constancy from 0.95 at 1.5 km for a resultant direc- 

 tion of 116° (east -southeast) to a constancy of 0.55 at a 

 height of 2.5 km, and 0.25 at 3 km, indicates that the av- 

 erage height of the southeast winds in the central tropi- 

 cal South Pacific between 10° to 15° south lies between 

 2 and 3 km. Although the computed resultant is north- 

 east at 3 km, the winds in almost every case turned 

 through south to southwest and northwest. 



The highest observation at 7 km showed west-north- 

 west winds at this level. The four balloons reaching 6.5 

 km had directions 285°, 210°, 268°, and 286°. All these 

 flights exhibit great uniformity over an east-west dis- 

 tance of 2000 km, especially as the value of 210 is rath- 

 er questionable because the choppy sea made observa- 

 tions difficult. 



Flights 60 to 68, 

 February 26 to March 7, 1929 



These flights were made for the greater part about 

 latitude 17° south in the eastern outskirts of the Tuamo- 

 tu Archipelago. This very thinly scattered group of 

 coral islands of the Pacific rarely has an elevation of 50 

 m above the surface, yet it may exert considerable 

 effect on the air currents in this region of the Pacific. 

 Tatakoto Island was sighted at 5:30 a.m. on March 7, 

 and Amanu Island on March 8 at 5:00 a.m. Gentle east- 

 erly to southeast breezes and airs blew steadily for ten 

 days except for March 5 and 6 when the winds moved 

 around to east-northeast and northeast, bringing on a 

 rain squall at 1:30 a.m., March 6, followed by a 36-hour 

 period of calm. Drizzling rain and a rain squall oc- 

 curred between 1:00 and 3:00 a.m. on February 27, but 

 otherwise the weather continued extremely pleasant with 

 the usual clear blue tropical sky, and the horizon fringed 

 about with cumulus clouds for heights between one and 

 four tenths of the whole sky. 



The winds show great uniformity of motion, especial- 

 ly up to a height of 1.5 km, the direction turning slowly 

 from east-southeast almost to northeast at a height of 

 1.5 km, and then turning back to east at a height of 2.5 

 and 3 km. From 3.5 to 4.5 km there is great variabil- 

 ity of direction, but above this the winds turn very defi- 

 nitely to northwest. 



On March 5 a very high flight reaching 10 km was 

 made, which showed solid but light southwest winds from 

 3.5 to 8 km. The northeast stratum, which for the pre- 

 vious week lay from 0.25 to 0.75 km above the east- 

 southeast stratum, actually broke down through the trades 

 and came to the surface on March 6. This interruption 

 of the trades was responsible for the rain squalls on 



March 6. The southwest winds persisted at levels from 

 4 km from March 4 to 12. The change from northeast 

 to southwest winds, as shown diagrammatically in fig- 

 ure 34 (which shows resulting data for flights 61 to 70), 

 is very abrupt, but in the majority of cases the winds in 

 the transition layer are southeast rather than southwest. 



Flights 69 to 83, 

 March 10 to April 23, 1929 



These flights were made while the Carnegie was 

 passing through the Society and Samoan island groups 

 between 18° and 10° south, slightly west of the central 

 line of the South Pacific Ocean. Of this time, March 13 

 to 20 was spent at anchor at Papeete, and April 1 to 10 

 at Pago Pago and Apia. Rain squalls occurred from 

 March 10 to 22, 24 to 28, 30, and 31, that is, on all ex- 

 cept two of fourteen days at sea prior to reaching Pago 

 Pago harbor. Lightning was observed on March 10 and 

 25. 



Surface winds between Tahiti and Samoa were vari- 

 able, but in flights 82 and 83, made after leaving Apia, 

 southeast trades were blowing up to 1 and 4 km, re- 

 spectively. 



Flights 84 to 91, April 24 to 30, 1929 



These eight flights were made between 8° south and 

 0.°5 north latitude as the Carnegie sailed almost due 

 north from Samoa in longitude 171° to 174° west. Al- 

 though a few rain squalls occurred on April 24 and 25, 

 the weather was good, with relatively few clouds and 

 light variable airs. 



The upper winds were also light, but very uniform 

 in direction from almost due east up to 2.5 km. Above 

 this there was a turning to southeast with extremely 

 light velocities above 4 km, the mean for the three 

 flights available from 4.5 to 5.5 km being only 1.6 m per 

 second. 



This is the equatorial area, where the most promi- 

 nent feature is the easterly drift of air. 



Flights 92 to 95, May 4 to 9, 1929 



Short wind squalls with rain occurred every day 

 during this period, with skies generally half overcast. 

 The northeast trades blew fresh to strong during the 

 whole time, setting up choppy or moderate seas. Both 

 factors combined to make observing difficulties so great 

 that the highest flight reached was only 4.5 km, and the 

 other three could not be followed above 1.5 km. These 

 few flights showed generally a slight turning from north- 

 east to east from the surface up to 4 km. 



Flights 96 to 103, May 13 to 27, 1929 



This group of eight flights was made in the general 

 vicinity of the Marianas, the Carnegie having been 

 moored in Port Apra, Guam, from May 20 to 25. From 

 May 13 to 20 the Carnegie sailed west-southwest, mak- 

 ing long day's runs in the favorable moderate to fresh 

 southeast breezes prevailing. Lightning was observed 

 in the early morning of July 15 at about 18° north, 205.°3 



