A Quantitative Comparison of Ground-Based FSSP and PVM Measurements

Abstract

Cloud microphysical measurements of two ground-based field campaigns are analyzed in order to compare Particle Volume Monitor (PVM) measurements and Forward Scattering Spectrometer Probe (FSSP)-derived integrated quantities (mainly liquid water content LWC) for different types of drop size distributions. It is shown that in case of size distributions containing mostly small drops with diameters D < 25 ?m the PVM and FSSP measurements agree if respective data corrections (activity and changing VAR, Mie curve adjustment, and wind ramming) are applied to the FSSP raw data. Therefore, it is concluded that both PVM and FSSP are excellent microphysical sensors in continental, stratiform, or cumuliform clouds with mostly small drops. However, if low concentrations of large drops (D > 25 ?m) are present in the drop size distribution, which considerably increases LWC, discrepancies between PVM and FSSP measurements are established. The most likely explanation for the differences is that the sensitivity of the PVM decreases for low drop concentrations.