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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.09.021 Byline: Takeshi Imamura (a), Hiroko Kobayashi (b) Keywords: Atmospheres; dynamics; Mars; atmosphere Abstract: Wavenumber spectra of the martian atmosphere covering zonal wavenumbers s=1-6 were obtained as a function of latitude and season for the first time from the temperatures measured by the Thermal Emission Spectrometer onboard the Mars Global Surveyor. The stationary component tends to peak at s=2, where the martian topography has large amplitude, and drops rapidly at higher wavenumbers. The transient component in the middle and high latitudes tends to peak at s=1, which is lower than the most unstable wavenumber based on linear theories, and exhibits spectral slopes much flatter than the stationary component. In the equatorial region, the spectra of the transient component are almost flat, indicating that the organization of large-scale structures is less efficient in this region. The spectral shapes are similar between the 0.5 and 2.2 hPa surfaces, except that the slopes are slightly steeper at 0.5 than at 2.2 hPa, probably due to selective vertical transmission at low wavenumbers. The seasonal variation is relatively large in the middle and high latitudes, where the maximum power occurs in winter and the minimum occurs in summer, with an exception that the transient component is maximum in spring in the southern hemisphere. Intensification of s=1 transient waves is observed around the period of the initiation of global dust storms. Author Affiliation: (a) Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara 229-8510, Japan (b) NEC Aerospace Systems, Ltd., 1-10 Nisshin-cho, Fuchu 183-8501, Japan Article History: Received 7 July 2008; Revised 14 September 2008; Accepted 20 September 2008

Lava eruptions can be observed remotely on Venus' nightside using a near-infrared window at a 1.0-micrometer wavelength, i.e., radiation at this wavelength emitted from the planetary surface traverses through the thick Venus atmosphere and clouds. Due to the strong dependence of the intensity of thermal emission on temperature, a hot surface produced by a lava eruption emits intense radiation, with the intensity of the excess radiation depending on the surface area and temperature of the lava flow. The excess emission from the hot surface is blurred by clouds, yet a 1-[km.sup.2] 1500-K basaltic lava lake and a 50-[km.sup.2] 1000-K lava flow are readily detected using this technique. Rapid cooling of exposed lava results in excess surface radiation that is detectable for just one Earth day after the end of an eruption; hence short-term eruptions are only detectable on the side of the planet where night is occurring. Eruptions lasting more than half a Venus day (i.e., more than about 60 Earth days), however, are detectable across the globe as nighttime occurs sometime during this period for every such event. Due to limited observational geometries, a complete global survey of active volcanos cannot be achieved from Earth, and in fact, only about 10% of short-lived major volcanic eruptions are observable. Alternatively, a satellite orbiting high above Venus (~6 Venus radii) could detect virtually all short-lived nighttime volcanic events, or about half the events expected to occur across the globe. Key Words: Venus; volcanism; Venus, surface; geological processes; radiative transfer.