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In 1908, when the giant Tunguska meteor disintegrated in the earth's atmosphere over Siberia, it may have generated as much as 30 million metric tons of nitric oxide (NO) in the stratosphere and mesosphere. The photochemical aftereffects of the event have been simulated using a comprehensive model of atmospheric trace composition. Calculations indicate that up to 45 percent of the ozone in the Northern Hemisphere may have been depleted by Tunguska's nitric oxide cloud early in 1909 and large ozone reductions may have persisted until 1912. Measurements of atmospheric transparentiy by the Smithsonian Astrophysical Observatory for the years 1909 to 1911 show evidence of a steady ozone recovery from unusually low levels in early 1909, implying a total ozone deficit of 30 +/- 15 percent. The coincidence in time between the observed ozone recovery and the Tunguska meteor fall indicates that the event may provide a test of current ozone depletion theories.

A throat plug is a device to prevent fragments produced by the bursting of the primary diaphragm of a shock tunnel from entering the nozzle and damaging the model. An experimental study has been carried out to investigate the flow in the KAIST shock tunnel with two stationary throat plugs at primary shock velocities of 1.19 and 1.28 km/s. These shocks generate tailored conditions when helium and air are used as the driver and driven gases, respectively, at room temperature. Nozzle reservoir pressures and Pitot pressures at the nozzle exit are measured to examine the influence of the stationary throat plug on these properties. The throat plug that has an areal blockage of 6.2 % is found to have negligible effects on shock tunnel flow. However, the throat plug of 19.4 % blockage shows an appreciable influence by generating a pressure bump. Although it retards the establishment time of the nozzle flow, after the transient period, it does not cause deviation of the pressure from that for the clean nozzle configuration. It is found that the reduction of the cross-sectional area, which results from the presence of the throat plug, causes the pressure bump. By increasing the diameter of the driven tube in the region where the throat plug is located appropriately, the magnitude of the pressure bump is reduced significantly.

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