| Date | Change |
|---|---|
| 1943 | Lithium chloride humidity element replaced hair hygrometer. |
| 1943 | Dark ceramic resistance sensor replaced glass-tube electrolytic temperature element. |
| 1948 | Relative humidity computed using saturation relative to water instead of ice |
| 1948 | Change observing times from 2300, 1100 UTC to 0300, 1500 UTC. |
| 1949 | Smaller temperature sensor to reduce response time. |
| 1950 | Correction for solar radiation introduced (until 1960). |
| 1957 | Change observing times from 0300, 1500 UTC to 0000, 1200 UTC. |
| 1960 | Introduced white-coated temperature elements. |
| 1965 | Carbon humidity element, began reporting low humidities. |
| 1972 | Redesigned humidity ducts to reduce solar effects. |
| 1973 | Stopped reporting relative humidity below 20%. |
| 1980 | New carbon hygristors, new relative humidity transfer equation. |
| 1988 | Precalibrated hygristor replaced type requiring preflight calibration. |
| 1988 | New VIZ sonde with new humidity duct. |
| late- 1980's | New Space Data Division (SDD) manufactured radiosonde at some stations. Differences between VIZ and SDD noted. |
| 1993 | Relative humidity to be reported over broader range, values <20% and up to 98% (instead of 95%) in cloud. |
| 1993 | Gravitational constant used to define geopotential height from geopotential changed from 9.8 to 9.80665 m s . |
| * From Trenberth, K.E., 1994: Atmospheric Circulation Climate Changes, 21, 427-453. | |