NASA’s Southern Hemisphere ADditional OZonesondes network reached 10,000 archived ozone and pressure-temperature-humidity profile pairs by October 2023, surpassing a modest three-year proposal drafted in 1998 to become one of the longest-running coordinated records of tropical ozone profiles.
The Tropical Blind Spot That Sparked a Global Effort
By the late 20th century, atmospheric science faced a glaring geographic imbalance. Ozone observations were dense across mid and high latitudes, while the tropics remained largely undersampled. Natal, Brazil, supplied the main regular tropical soundings during the 1970s and 1980s, supplemented only by intermittent measurements from American Samoa and Hawaii.
That absence of data posed a persistent challenge for space-based observation. Satellite instruments cannot simply read a perfectly resolved vertical profile straight from orbit. Retrieval algorithms must infer the vertical distribution from measured radiation, requiring direct profiles from the atmosphere itself to develop and check those estimates.
Major field campaigns laid the logistical groundwork for a permanent fix. NASA’s TRACE-A campaign in 1992 used aircraft and ozonesondes across the tropical Atlantic, and PEM-Tropics-A in 1996 extended intensive atmospheric measurements across the Pacific.
How a Three-Year Experiment Extended to 25 Years
When Anne Thompson and colleagues at NASA Goddard organized the network in 1998, the ambition was intentionally modest. The plan called for coordinating launches, standardizing data, building a common archive, and improving tropical profiles for satellite validation over a three-year span.
Instead of wrapping up, the network endured because a coordinated tropical record gained scientific utility as it grew longer. NASA Goddard and Wallops Flight Facility supplied coordination, archiving, and equipment. NOAA contributed measurements at several locations, while international meteorological agencies, universities, and research institutes operated stations globally.
By its 2023 milestone, the partnership involved organizations from 14 nations across five continents. The network coordinated 14 long-term stations, producing roughly 20 percent of the data from long-term ozonesonde stations worldwide, according to NASA’s accounting.
Inside the Instrumentation of a Balloon Sounding
The mechanics of each data collection flight remain remarkably consistent. On any given launch day, a rubber weather balloon carries an ozonesonde and a standard meteorological radiosonde into the atmosphere.
According to NOAA’s Global Monitoring Laboratory, the ozonesonde features an electrochemical sensor that pumps ambient air through a potassium iodide solution. Ozone triggers an electrical signal proportional to its concentration. The attached radiosonde then transmits ozone readings alongside pressure, temperature, and humidity back to a ground station.
A typical balloon climbs to roughly 35 kilometers in about two hours before bursting, producing a detailed vertical profile from the surface through much of the stratospheric ozone layer. Because recovery is uncertain, instruments are treated as expendable.
Despite that designation, complete loss is not guaranteed. Programs such as NOAA’s Hilo ozonesonde operation recover and reuse a minority of their instruments after descent.
A Stop-Start Operational History Across the Network
The 25-year archive is extensive, but it is not uniformly continuous. NASA’s 2023 inventory identified 14 stations with at least 10 years of operation, while several individual records contain operational pauses. Tahiti, Malindi, and Cotonou contributed shorter historical records that remain preserved within the archive.
Interruptions are treated as part of the network’s reality rather than exceptions. Watukosek in Java resumed balloon launches after a multiyear interruption, reflecting the persistence required to maintain tropical sounding sites.
Broadening Stratospheric Horizons Beyond Ozone
The logistical framework built for tropical ozone profiling now underpins broader atmospheric research. The stratospheric aerosol layer directly influences surface temperatures and the global hydrological cycle.
While optical properties have been monitored via satellite for more than four decades, satellite measurements require multiple assumptions to derive aerosol concentrations and suffer from limited vertical, horizontal, and temporal resolution. To address those analytical gaps, the Balloon Network for Stratospheric Aerosol Observations brings together research laboratories from the United States, Brazil, France, and India.
This aerosol initiative draws directly on balloon deployments funded by the Upper Atmospheric Composition Observation program at NASA Langley Research Center. By profiling aerosol concentrations from the ground to the stratosphere, these coordinated field campaigns continue to clarify how stratospheric variability impacts Earth’s climate system.
