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Clouds have an important role in Earth's radiative budget. Since the late1970s, considerable instrumental developments have been made in order toquantify cloud microphysical and optical properties, for both airborne andground-based applications. Intercomparison studies have been carried out inthe past to assess the reliability of cloud microphysical propertiesinferred from various measurement techniques. However, observationaluncertainties still exist, especially for droplet size distributionmeasurements and need to be reduced.  In this work, we discuss results from an intercomparison campaign, performedat the Puy de Dôme in May 2013. During this campaign, a unique set ofcloud instruments was operating simultaneously in ambient air conditions andin a wind tunnel. A Particle Volume Monitor (PVM-100), a Forward ScatteringSpectrometer Probe (FSSP), a Fog Monitor (FM-100), and a Present WeatherDetector (PWD) were sampling on the roof of the station. Within a wind tunnellocated underneath the roof, two Cloud Droplet Probes (CDPs) and a modifiedFSSP (SPP-100) were operating. The main objectives of this paper are (1) tostudy the effects of wind direction and speed on ground-based cloudobservations, (2) to quantify the cloud parameters discrepancies observed bythe different instruments, and (3) to develop methods to improve thequantification of the measurements.  The results revealed that all instruments showed a good agreement in theirsizing abilities, both in terms of amplitude and variability. However, someof them, especially the FM-100, the FSSP and the SPP, displayed largediscrepancies in their capability to assess the magnitude of the totalnumber concentration of the cloud droplets. As a result, the total liquidwater content can differ by up to a factor of 5 between the probes. The useof a standardization procedure, based on data of integrating probes (PVM-100or visibilimeter) and extinction coefficient comparison substantiallyenhanced the instrumental agreement. During this experiment, the totalconcentration agreed in variations with the visibilimeter, except for theFSSP, so a corrective factor can be applied and it ranges from 0.44 to 2.2.This intercomparison study highlights the necessity to have an instrumentwhich provides a bulk measurement of cloud microphysical or opticalproperties during cloud ground-based campaigns. Moreover, the FM and FSSPorientation was modified with an angle ranging from 30  to90° angle with wind speeds from 3 to 7 m s<sup>−1</sup>. The resultsshow that the induced number concentration loss is between 29 and 98 %for the FSSP and between 15 and 68 % for the FM-100. In particular, FSSPexperiments showed strong discrepancies when the wind speed was lower than 3 m s<sup>−1</sup> and/or when the angle between the wind direction and theorientation of the instruments is greater than 30°. An inadequateorientation of the FSSP towards the wind direction leads to anunderestimation of the measured effective diameter

Quantitative evaluation of seven optical sensors for cloud microphysical measurements at the Puy-de-Dôme Observatory, France