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Abstract
Charge is observed in clouds of all forms, which may influence their development and properties. In-cloud charge measurements require a wide dynamic range, extending from charge in aerosols and dusts to that present in thunderstorms. Unexpectedly large charge densities (>200 pC m-3) have recently been detected in layer clouds using balloon-carried linear electrometers. These, however, lead to instrument saturation if sufficient sensitivity for aerosol and droplet charge is maintained. Logarithmic electrometers provide an alternative but suffer strong non-linear thermal effects. This is a limitation for balloon-carried instruments that encounter temperature changes up to ∼100 °C, as full thermal compensation requires complexity inappropriate for disposable devices. Here, a novel hybrid system is described, combining linear and logarithmic electrometers to provide extended dynamic range (±50 pA), employing the negligible (±4%) total temperature drift of the linear device to provide in situ calibration of the logarithmic device. This combination opens up new measurement opportunities for charge in clouds, dusts, and aerosols.
Highlights
Enhancing the standard use of in situ measurement platforms, such as meteorological balloons already used for cosmic rays,1 energetic particles,2 cloud backscatter,3 turbulence,4 and charge,5 provides a flexible method for data collection at heights extending from the surface to 30 km
A possible alternative is to use a logarithmic response; light-tight light-emitting diodes (LEDs) provide this characteristic, previously used in an electrometer operating over many orders of magnitude of current
Compensated logarithmic electrometers are useful for more slowly changing surface atmospheric temperatures,10 but even implementing this requires the inclusion of symmetrical circuit elements having a matched thermal response, as well as ensuring temperature tracking in other components accurately follows that in the logarithmic elements
Summary
Enhancing the standard use of in situ measurement platforms, such as meteorological balloons already used for cosmic rays,1 energetic particles,2 cloud backscatter,3 turbulence,4 and charge,5 provides a flexible method for data collection at heights extending from the surface to 30 km. A possible alternative is to use a logarithmic response; light-tight light-emitting diodes (LEDs) provide this characteristic, previously used in an electrometer operating over many orders of magnitude of current.9
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