The MAGIC Meteoric Smoke Particle Sampler - Description and Results

Between a few to several hundred tons of meteoric material enters the Earth's atmosphere each day, and much of this material ablates in the 70 -130 km region of the atmosphere. Already in the early 1960's it was suggested that meteoroid ablation products could recondense and form solid nanometer-scale smoke particles in the altitude range of the mesosphere and lower thermosphere (MLT). These so-called meteoric smoke particles (MSPs) are then subject to further coagulation, sedimentation, and transport by the mesospheric meridional circulation which in turn determines the latitudinal and seasonal variation of the MSP distribution. MSPs have been suggested to be important for a variety of atmospheric phenomena: 1. they are the most likely candidate for the nuclei of mesospheric ice particles (NLC and PMSE); 2. they provide surface area on which heterogeneous chemical reactions take place and may influence, for example, the water vapor distribution and Ox/HOx chemistry in the mesosphere; 3. they act as ultimate sink in mesospheric metal chemistry by scavenging various gas-phase products of meteoric ablation; 4. they can significantly influence the ionospheric D-region charge balance by scavenging free electrons and positive ions; and 5. they may be involved in the formation of NAT particles in polar stratospheric clouds and the destruction of ozone. Given the above points, it is obvious that there is a large scientific interest in the properties and global distribution of MSPs. Basic information about MSP properties is today available from optical occultation measurements (AIM/SOFIE) and, more indirectly, from in-situ measurements of the charged particle population. In order to understand the role of meteoric smoke particles in the mesosphere and their impact on that environment their presence must be certified and their physical characterization (number density, size distribution, shape, composition etc.) determined. A way to obtain maximum information about particle properties is by direct collection followed by detailed laboratory analysis. However, the sounding rocket approach, which is the only practical method to carry out a sampling experiment at the desired mesospheric altitudes, is subject to critical limitations imposed by aerodynamics. As nanometer size particles tend to follow the airflow around the rocket payload structure, their sampling is a substantial experimental challenge. The objective of the MAGIC project (Mesospheric Aerosol - Genesis, Interaction and Composition) was to design and build an instrument to directly sample meteoric smoke particles in the mesosphere and return them to ground for detailed laboratory investigations. Here we describe the MAGIC meteoric smoke particle sampler and present attempts to directly sample MSPs and the challenges and uncertainties in the sampling procedure.