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International audienceBy analogy with Earth, methane in the Martian atmosphere is a potential signature of ongoing or past biological activity. During the past decade, Earth-based telescopic observations reported "plumes" of methane of tens of parts per billion by volume (ppbv), and those from Mars orbit showed localized patches, prompting speculation of sources from subsurface bacteria or nonbiological sources. From in situ measurements made with the Tunable Laser Spectrometer (TLS) on Curiosity using a distinctive spectral pattern specific to methane, we report no detection of atmospheric methane with a measured value of 0.18 +/- 0.67 ppbv corresponding to an upper limit of only 1.3 ppbv (95% confidence level), which reduces the probability of current methanogenic microbial activity on Mars and limits the recent contribution from extraplanetary and geologic sources

[1] We present direct observational evidence for solar cycle influence on the infrared energy budget and radiative cooling of the thermosphere. By analyzing nearly five years of data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, we show that the annual mean infrared power radiated by the nitric oxide (NO) molecule at 5.3 mm has decreased by a factor of 2.9. This decrease is correlated (r = 0.96) with the decrease in the annual mean F10.7 solar index. Despite the sharp decrease in radiated power (which is equivalent to a decrease in the vertical integrated radiative cooling rate), the variability of the power as given in the standard deviation of the annual means remains approximately constant. A simple relationship is shown to exist between the infrared power radiated by NO and the F10.7 index, thus providing a fundamental relationship between solar activity and the thermospheric cooling rate for use in thermospheric models. The change in NO radiated power is also consistent with changes in absorbed ultraviolet radiation over the same time period. Computations of radiated power using an empirical model show much less variability than observed by SABER.

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A model was developed for predicting sediment graphs from agricultural watersheds. Storm sediment graphs are predicted by convolving source runoff with an instantaneous unit sediment graph (IUSG). The IUSG is the distribution of sediment from an instantaneous burst of rainfall producing one unit of runoff. The IUSG is the product of an instantaneous unit hydrograph and the sediment concentration distribution. Initial sediment concentration of the IUSG is assumed to vary linearly with source runoff volume. A sediment‐routing function, based on travel time and sediment particle size, is used to predict the sediment concentration distribution. Tests with 50 storms from five watersheds showed that the model is applicable to agricultural watersheds in the Texas blacklands. It should be useful in designing reservoirs or in waterquality‐modeling problems.