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STP12 Abstracts Berlin, 12 - 16 July 2010 SCOSTEP Symposium 2010 Observations of Polar Mesospheric Clouds from Space and Their Scientific Implications Russell III James M 1 , Bailey Scott M 2 1 2 Hampton University Center for Atmospheric Sciences, Virginia Tech Depart of Electrical and Computer Engineering Observations of Polar Mesospheric Clouds (PMCs), also called Noctilucent Clouds, were first reported in 1885 by the amateur astronomer Robert Leslie. Since that time there has been a growing public and scientific interest in these beautiful, iridescent clouds. This is most probably because they can be easily seen from the ground at latitudes above about 55 degrees and in addition numerous papers have reported quantitative cloud properties from space borne measurements. In recent years the focus on PMCs has intensified as a result of satellite measurements that show increasing cloud brightness and frequency of occurrence over the last ~ 27 years. Also, while not conclusively shown, it seems that there are more frequent cloud sightings at lower latitudes, e.g. 40 N, than have been reported in the past. Finally, there is the unproven but plausible theory that the observed changes in cloud properties are connected with global change due to the buildup of the greenhouse gases, CO2 and CH4, in the atmosphere. This paper will present an overview of space-based observations of PMCs and scientific implications of the data. The clouds have been extensively observed by a number of satellite experiments including SME, HALOE, SNOE, SCHIAMACHY, OSIRIS, SBUV, OMI and AIM. The latter mission, AIM, is the first mission dedicated to the study of PMCs with the overall goal being to understand why they form and vary. PMC temporal variability on time scales of a solar cycle and the 27-day solar rotation have been reported. We also now know that PMCs are highly variable from orbit-to-orbit and day-to-day with significant complex structure. Other analyses show that temperature change is a dominant factor in controlling season onset, variability during the season and season end. Rising water vapor levels at the beginning and falling values at the end also play a key role in season initiation and cessation. Structures seen in the clouds look very much like complex features seen in tropospheric clouds including large regions of near circular ice voids. Planetary waves modulate PMC occurrence and can effectively extend the PMC season by providing several days of localized regions of saturated air in the troughs of the waves. By contrast, gravity waves appear to locally diminish PMC frequency even though global scale gravity wave drag is acknowledged as the prime cause of the cold polar summer mesopause. Satellite results also provide evidence that interhemispheric coupling, from the winter hemisphere to the summer hemisphere affects PMC variability.
STP12 Abstracts Berlin, 12 - 16 July 2010 SCOSTEP Symposium 2010 Microphysics of electrified aerosols and cloud droplets: Laboratory experiments Rzesanke Daniel 1 , Leisner Thomas 2 1 Karlsruhe Institute of Technology (KIT), IMK-AAF, 2 KIT and IUP Heidelberg The global electric circuit is one of the candidates for a coupling of terrestrial climate with solar activity [1]. It has been suggested that the vertical electric currents in the atmosphere, which are carried by ions, ionic clusters and electrified aerosol particles can modify the cloud microphysics and thereby can link the atmospheric layers [2]. In the framework of the DFG priority program CAWSES we conduct laboratory experiments which quantify the interaction between electrified aerosol particles and cloud droplets in order to assess the atmospheric relevance of this link between the higher and lower atmosphere. More specific, we quantify the influence of charges, electrical fields and ionizing radiation on the heterogeneous and homogeneous freezing nucleation in cloud droplets, their evaporation behaviour and their scavenging efficiency for aerosol particles. The latter are relevant for contact freezing rates in clouds and therefore cloud development and lifetime. The experiments are carried out under realistic atmospheric conditions on individual particles in electrodynamic levitation within a miniaturized climate chamber [3, 4]. The main methods of investigations are microscopy, microspectroscopy and light scattering analysis [5]. In our contribution, we present an overview of the effects analyzed so far, demonstrate charge dependent evaporation and scattering efficiencies and estimate their atmospheric relevance. References: [1] - E. Friis-Christensen, "Solar variability and climate", Space Science Review 94, 2000 [2] - B. Tinsley, "Influence of solar wind on the global electric circuit, and inferred effects on cloud microphysics, temperature, and dynamics in the troposphere", Space Science Review 94, 2000 [3] - E. J. Davis, "A history of single aerosol particle levitation", Aerosol Science and Technology 26, 1997 [4] - D. Duft, et al., "Shape oscilliations and stability of charged microdroplets", Physical Review Letters 89 (8), 2002 [5] - D. Duft and T. Leisner, "The index of refraction of supercooled solutions determined by the analysis of optical rainbow scattering from levitated droplets", International Journal of Mass Spectrometry 233 (1-3), 2004
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scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

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