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The dust probe DUSTY, first launched during the summer of 1994\ud(flights ECT–02 and ECT–07) from Andøya Rocket Range, northern Norway,\udwas the first probe to unambiguously detect heavy charged mesospheric\udaerosols, from hereon referred to as dust. In ECT–02\udthe probe detected negatively charged dust particles in the height\udinterval of 83 to 88.5 km.\udIn this flight, the lower grid in the detector (Grid 2) measures both\udpositive and negative currents in various regions, and we find that the\udrelationship between the current measurements of Grid 2 and the bottom\udplate can only be explained by influence from secondary charge\udproduction on Grid 2.\udIn ECT–07, which had a large coning,\udpositive currents reaching the top grid of the probe were interpreted as due\udto the impact of positively charged dust particles. We have now reanalyzed\udthe data from ECT–07 and arrived at the conclusion that the measured\udpositive currents to this grid must have been mainly due to secondary\udcharging effects from the impacting dust particles. The grid consists of\uda set of parallel wires crossed with an identical set of wires on top of\udit, and we find that if the observed currents were created from the direct\udimpact of charged dust particles, then they should be very weakly modulated at\udfour times the rocket spin rate ωR. Observations show, however, that the\udobserved currents are strongly modulated at 2ωR. We cannot\udreproduce the\udobserved large modulations of the impact currents in the dust layer if the\udcurrents are due only to the transfer of the charges on the impacted dust\udparticles.\udBased on the results of recent ice cluster impact secondary charging\udexperiments by\udTomsic (2003),\udwhich found that a small fraction of\udthe ice clusters, when impacting with nearly grazing incidence,\ud carried away one negative charge −1e, we have\udarrived at the conclusion that similar, but significantly more\udeffective, charging effects must be\udpredominantly responsible for the positive currents measured by the top\udgrid in ECT–07 and their large rotational modulation at 2ωR.\ud\ud \ud\udSince the secondary effect is dependent on\udthe size of the impacting dust, this opens up for the possibility of\udmapping the relative dust sizes throughout a dust layer by comparing\udthe observed direct and secondary currents

On the secondary charging effects and structure of mesospheric dust particles impacting on rocket probes