Examinando por Autor "Flesch, Gregory J."

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Background levels of methane in Mars’ atmosphere show strong seasonal variations
(Science, 2018-06-08) Webster, Christopher R.; Mahaffy, Paul R.; Atreya, Sushil K.; Moores, John E.; Flesch, Gregory J.; Malespin, Charles A.; McKay, Christopher P.; Martínez, Germán M.; Smith, Christina L.; Martín Torres, Javier; Gómez Elvira, J.; Zorzano, María-Paz; Wong, Michael H.; Trainer, Melissa G.; Steele, Andrew; Archer, Doug; Sutter, Brad; Coll, Patrice J.; Freissinet, Caroline; Meslin, Pierre-Yves; Gough, Raina V.; House, Christopher H.; Pavlov, Alexander; Eigenbrode, Jennifer L.; Glavin, Daniel P.; Pearson, John C.; Keymeulen, Didier; Christensen, Lance E.; Schwenzer, Susanne P.; Navarro González, R.; Pla García, J.; Rafkin, Scot C. R.; Vicente Retortillo, Álvaro; Kahanpää, H.; Viúdez Moreiras, Daniel; Smith, Michael D.; Harri, Ari-Matti; Genzer, María; Hassler, Donald M.; Lemmon, M. T.; Crisp, Joy; Sander, Stanley P.; Zurek, Richard W.; Vasavada, Ashwin R.; National Aeronautics and Space Administration (NASA)
Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location. We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover. The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv). This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle. The large seasonal variation in the background and occurrences of higher temporary spikes (~7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs.
Acceso Abierto
Chemical depletion of Arctic ozone in winter 1999/2000
(American Geophysical Union, 2002-09-20) Rex, Markus; Salawitch, R. J.; Harris, Neil R. P.; Gathen, Peter von der; Braathen, Geir O.; Schulz, Astrid; Deckelmann, H.; Chipperfield, M.; Sinnhuber, B. M.; Reimer, E.; Alfier, R.; Bevilacqua, R.; Hoppel, K.; Fromm, M.; Lumpe, J.; Küllmann, H.; Kleinböhl, A.; Bremer, H.; Von König, M.; Künzi, K.; Toohey, D.; Vömel, H.; Richard, E.; Aikin, K.; Jost, H.; Greenblatt, J. B.; Loewenstein, M.; Podolske, J. R.; Webster, Christopher R.; Flesch, Gregory J.; Scott, D. C.; Herman, R. L.; Elkins, J. W.; Ray, E. A.; Moore, F. L.; Hurst, D. F.; Romashkin, P.; Toon, G. C.; Sen, B.; Margitan, J. J.; Wennberg, P.; Neuber, R.; Allart, M.; Bojkov, B. R.; Claude, H.; Davies, Jonathan; Davies, W.; De Backer, H.; Dier, Horst; Dorokhov, Valery; Fast, H.; Kondo, Yutaka; Kyrö, E.; Litynska, Z.; Mikkelsen, I. S.; Molyneux, M. J.; Moran, E.; Nagai, T.; H. Nakane; Parrondo, María Concepción; Ravegnani, Fabrizio; Skrivánková, Pavla; Viatte, P.; Yushkov, Vladimir; European Commission (EC); National Aeronautics and Space Administration (NASA)
[1] During Arctic winters with a cold, stable stratospheric circulation, reactions on the surface of polar stratospheric clouds (PSCs) lead to elevated abundances of chlorine monoxide (ClO) that, in the presence of sunlight, destroy ozone. Here we show that PSCs were more widespread during the 1999/2000 Arctic winter than for any other Arctic winter in the past two decades. We have used three fundamentally different approaches to derive the degree of chemical ozone loss from ozonesonde, balloon, aircraft, and satellite instruments. We show that the ozone losses derived from these different instruments and approaches agree very well, resulting in a high level of confidence in the results. Chemical processes led to a 70% reduction of ozone for a region ∼1 km thick of the lower stratosphere, the largest degree of local loss ever reported for the Arctic. The Match analysis of ozonesonde data shows that the accumulated chemical loss of ozone inside the Arctic vortex totaled 117 ± 14 Dobson units (DU) by the end of winter. This loss, combined with dynamical redistribution of air parcels, resulted in a 88 ± 13 DU reduction in total column ozone compared to the amount that would have been present in the absence of any chemical loss. The chemical loss of ozone throughout the winter was nearly balanced by dynamical resupply of ozone to the vortex, resulting in a relatively constant value of total ozone of 340 ± 50 DU between early January and late March. This observation of nearly constant total ozone in the Arctic vortex is in contrast to the increase of total column ozone between January and March that is observed during most years.
Acceso Abierto
Day-night differences in Mars methane suggest nighttime containment at Gale crater
(EDP Sciences, 2021-06-29) Webster, Christopher R.; Mahaffy, Paul R.; Pla García, J.; Rafkin, Scot C. R.; Moores, J. E.; Atreya, S. K.; Flesch, Gregory J.; Malespin, C. A.; Teinturier, S. M.; Kalucha, H.; Smith, C. L.; Viúdez Moreiras, Daniel; Vasavada, Ashwin R.; Agencia Estatal de Investigación (AEI)
We report new measurements of atmospheric methane by the Curiosity rover’s Tunable Laser Spectrometer that is part of the Sample Analysis at Mars suite (TLS-SAM), finding nondetections during two daytime measurements of average value 0.05 ± 0.22 ppbv (95% confidence interval CI). These are in marked contrast with nighttime background levels of 0.52 ± 0.10 (95% CI) from four measurements taken during the same season of northern summer. This large day-night difference suggests that methane accumulates while contained near the surface at night, but drops below TLS-SAM detection limits during the day, consistent with the daytime nondetection by instruments on board the ExoMars Trace Gas Orbiter. With no evidence for methane production by the rover itself, we propose that the source is one of planetary micro-seepage. Dynamical modeling indicates that such methane release is contained within the collapsed planetary boundary layer (PBL) at night due to a combination of nocturnal inversion and convergent downslope flow winds that confine the methane inside the crater close to the point where it is released. The methane abundance is then diluted during the day through increased vertical mixing associated with a higher altitude PBL and divergent upslope flow that advects methane out of the crater region. We also report detection of a large spike of methane in June 2019 with a mean in situ value over a two-hour ingest of 20.5 ± 4 ppbv (95% CI). If near-surface production is occurring widely across Mars, it must be accompanied by a fast methane destruction or sequestration mechanism, or both.