The M-Meter: A Simple Airborne Hydrometeor Measurement Instrument

Abstract

The M-meter is designed to measure total mass concentration of hydrometeors from aircraft aloft. Its essence is a free-rotating, vaned disk with face normal to the freestream; rotation is driven by airflow through the vanes. Hydrometeors collected on the disk surface are expelled by being flung tangentially from its periphery. This expulsion causes a reduction of equilibrium rotation rate that is proportional to freestream hydrometeor mass concentration. A prototype was carried under the wing of a research airplane as it probed precipitating clouds at levels from just above to just below the melting layer. M-meter measurements of hydrometeor mass concentrations are demonstrated to be in qualitative agreement with independent measurements. This unique, simple, rugged instrument with high sampling volume probably can be refined to provide accurate in situ measurement of cloud plus precipitation water mass?a capability sorely needed. It warrants additional research and development, which is not planned by those involved at present. This note is for the purpose of stimulating further interest in this promising concept.