HadAT: Upper-air temperatures from weather balloons

HadAT consists of temperature anomaly timeseries from radiosondes (weather balloons) on 9 standard reporting pressure levels (850 hPa (about 1.5 km altitude) to 30 hPa (nearly 25 km).

The data are also available as equivalent measures to the broad Microwave Sounding Unit satellite weighting functions. The gridded product is derived from 676 individual radiosonde stations with long-term records. Because of the criteria of data longevity the resulting data set is limited to land areas and primarily Northern Hemisphere locations. Radiosondes are single launch instruments and there have been many changes in instruments and observing practices with time. HadAT has used a neighbour-based approach to attempt to compensate for these effects and produce a homogeneous product suitable for climate applications.

Significant uncertainty remains in estimates of long-term changes from both satellite and radiosonde observations. Although the month to month and year to year variations are in reasonable agreement (left hand panels), there is significant disagreement over the long-term trends. It is uncertain whether the lower troposphere (roughly 1-5 km altitude) in the tropics is warming or cooling relative to the surface (lower right hand panel). This has important implications as climate models robustly yield greater warming in the lower troposphere than at the surface in this region. Our work on assessing uncertainty in radiosonde records implies that it is unlikely that we will be able to reduce this uncertainty.

The zonally averaged trends show that the maximum warming within the troposphere has occurred in the Northern Hemisphere over recent years. Above the troposphere the stratosphere has been cooling. This general pattern matches the expected results of greenhouse gases and ozone-depleting substances, and this has been used to attribute recent climate change to human influences in work carried out at the Met Office Hadley Centre.

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