Low-level air flow circulation over the Arabian Sea during the summer monsoon as deduced from satellite-tracked superpressure balloons. Part I—Balloon trajectories

✍ Scribed by Daniel Cadet; Henri Ovarlez

• Publisher: John Wiley and Sons
• Year: 1976
• Tongue: English
• Weight: 712 KB
• Volume: 102
• Category: Article
• ISSN: 0035-9009
• DOI: 10.1002/qj.49710243410

✦ Synopsis

Abstract

During the northern summer of 1975, 45 superpressure constant‐level balloons were released from the Seychelles Islands (4.7°S 55.5°E) for flight at 955mb (500m), 910mb (1000m) and 860mb (1500m) within the tropical boundary layer. The balloons were located by the Random Access Measurement System (RAMS) of the Nimbus‐6 satellite. This spacecraft also operated as a data relay system and collected pressure measurements performed by transducers carried by the balloons. The mean lifetime of the balloons was about 4–5 days, some of them lasting more than 8 days. Low‐level Lagrangian air trajectories in the southwesterly flow over the Arabian Sea are presented. They show the drastic changes in the airflow direction over the southwestern Arabian Sea associated with high or low activity periods of the monsoon over the western coast of India. During the first period of the experiment, the airflow over the southwestern Arabian Sea joins the low‐level jet flowing to the east of the Somali coast. This change, due to intense convective activity near Somalia, can be associated with a break in the monsoon activity. During the second period the air joins the Bay of Bengal branch of the monsoon over the southwest coast of India. Before the end of July a complete reversal of the winds over the Seychelles Islands is observed and some balloons drift towards Madagascar. During the third period the air flow over the Arabian Sea resumes a southwesterly direction and at the beginning of August it seems to join again the Bay of Bengal branch of the monsoon.

Thus this experiment shows that low‐level ballooning can be used to map air currents over vast unsurveyed areas of the oceans.