Feng Tian

National Center for Atmospheric Research, Boulder, Colorado, United States

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Publications (9)26.63 Total impact

  • Feng Tian · J. F. Kasting · K. Zahnle

    No preview · Article · Jan 2011 · Earth and Planetary Science Letters
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    ABSTRACT: Today Titan's surface temperature is 95 K and its atmosphere contains 1.5 bars of N2. The standard model for Titan is that the current thick atmosphere has been present over the age of the Solar System. However, observations of Titan present some paradoxes for the standard model: the short life time of methane, the lack of good evidence for active cryovolcanism, and the inadequate surface deposit to account for the photochemical products that would have accumulated over 4.5 billion years. Thus alternative models are motivated. Today both surface albedo and greenhouse warming contribute to Titan's surface temperature and its atmosphere condition. The albedo could have been different if the surface of ancient Titan was covered by liquid nitrogen/methane or solid methane ice. The greenhouse effect depends on the existence of atmospheric methane and nitrogen. The variations of either factor could have made ancient Titan similar to present Triton with high surface albedo and little atmosphere. Alternatively early Titan could have had much larger fraction of its nitrogen and methane in liquid phase (ocean/lakes), which would have interesting geological implications. In this work we will explore the effect of changing surface albedo, surface reservoirs of nitrogen and methane, and greenhouse warming on ancient Titan's climate.
    No preview · Article · Oct 2010
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    ABSTRACT: The evolution of planetary atmospheres and their water inventories are strongly related to the evolution of the solar radiation and plasma environment, which was much more active when the young Sun arrived at the Zero-Age-Main-Sequence. After formation of the terrestrial planets and their early atmospheres, due to the active young Sun and large impacts, heavy species and their isotopes were most likely fractionated to their present values by impact related dynamical escape. Higher solar X-ray and EUV fluxes heated and expanded the thermospheres of the early planets. Under such solar conditions, depending on the thermospheric composition, the amount of IR-coolers and the mass and size of the planet, hydrostatic equilibrium was not always maintained and hydrodynamic flow and expansion of the upper atmosphere resulting in adiabatic cooling of the exobase temperature could develop. Depending on atmospheric protection by magnetospheres, the current atmospheric abundances and isotopic compositions were determined by the action of thermal (Jeans, impact related hydrodynamic escape) and non-thermal (ion pick up, polar outflow, cool plasma flow into the tail, plasma instabilities, sputtering, photochemical loss) escape processes of gases supplied by outgassing during the later evolutionary epochs. Furthermore, it is shown how atmosphere-surface interaction processes such as carbonate weathering, volcanic outgassing, and carbonate recycling, and feedback stabilization under green-house conditions, as well as the origin of life, play important roles in the evolution of planetary atmospheres. (Cited by 73 in Google Scholar)
    Full-text · Chapter · Jan 2009
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    Z Liu · Y Teng · X Xie · H Li · J Lv · L Gao · F Tian · Y Jiang · Z Chu · C Xie · H Liu
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    ABSTRACT: Spring viraemia of carp virus (SVCV) is the causative agent of SVC disease. The main aim of our study was to develop a one-step reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay for rapid, sensitive and effective detection of SVCV. A set of four specific primers, two outer and two inner primers were designed based on the SVCV M gene for RT-LAMP assay. The sensitivity and specificity of RT-LAMP were determined and clinical test was performed under optimized amplification conditions (64 degrees C, 60 min). The results showed that the assay has a high specificity and the detection limit was 80 copies using 10-fold series dilutions of SVCV RNA, 10 times more sensitive than nest reverse transcription-polymerase chain reaction. In the detection of 472 fish samples, this assay showed excellent agreement with the standard virus isolation method (kappa = 0.807). A sensitive and specific RT-LAMP assay was successfully developed to monitor and detect SVCV. This work provides a robust method for evaluating the risk of SVCV. Given the advantages of LAMP in the detection of SVCV, this method can be applied to diagnose other viruses, which pose serious threats to the aquaculture industry.
    Full-text · Article · Oct 2008 · Journal of Applied Microbiology
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    ABSTRACT: The origin and evolution of Venus’, Earth’s, Mars’ and Titan’s atmospheres are discussed from the time when the active young Sun arrived at the Zero-Age-Main-Sequence. We show that the high EUV flux of the young Sun, depending on the thermospheric composition, the amount of IR-coolers and the mass and size of the planet, could have been responsible that hydrostatic equilibrium was not always maintained and hydrodynamic flow and expansion of the upper atmosphere resulting in adiabatic cooling of the exobase temperature could develop. Furthermore, thermal and various nonthermal atmospheric escape processes influenced the evolution and isotope fractionation of the atmospheres and water inventories of the terrestrial planets and Saturn’s large satellite Titan efficiently.
    No preview · Article · Aug 2008 · Space Science Reviews
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    ABSTRACT: 1] An electron transport/energy deposition model is expanded to include atomic nitrogen and is coupled with a 1-D hydrodynamic thermosphere model. The coupled model is used to investigate the response of the Earth's thermosphere under extreme solar EUV conditions and is compared with previous studies. It is found that (1) the parameterization of Swartz and Nisbet (1972) underestimates the ambient electron heating by photoelectrons significantly in the upper thermosphere of the Earth under conditions with greater than 3 times the present solar EUV irradiance; (2) the transition of the Earth's thermosphere from a hydrostatic equilibrium regime to a hydrodynamic regime occurs at a smaller solar EUV flux condition when enhanced, more realistic, and self-consistent, ambient electron heating by photoelectrons is accounted for; (3) atomic nitrogen becomes the dominant neutral species in the upper thermosphere (competing against atomic oxygen) under extreme solar EUV conditions, and the electron impact processes of atomic nitrogen are important for both the chemistry and energetics in the corresponding thermosphere/ionosphere; (4) N + remains a minor ion compared to O + , even when atomic nitrogen dominates the exobase; and (5) adiabatic cooling does not play an important role in electron gas energy budget. These findings highlight the importance of an electron transport/energy deposition model when investigating the thermosphere and ionosphere of terrestrial planets in their early evolutionary stages. (2008), Hydrodynamic planetary thermosphere model: 2. Coupling of an electron transport/energy deposition model, J. Geophys. Res., 113, E07005, doi:10.1029/2007JE003043.
    Full-text · Article · Jul 2008 · Journal of Geophysical Research Atmospheres
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    ABSTRACT: (1) It has been suggested that the exobase temperature of early terrestrial planetary atmosphere could have reached over 10,000 K. Although such high exobase temperatures should have caused the major gases at the exobase to experience fast Jeans escape, and the entire thermosphere should have experienced hydrodynamic flow, hydrostatic equilibrium was assumed to be valid in this earlier model. In this paper we develop a multicomponent hydrodynamic thermosphere model to self-consistently study the Earth's thermosphere under extreme solar EUV conditions. The model is validated against observations and other models for the present Earth's thermosphere. Simulations show that if forced in hydrostatic equilibrium and maintaining the current composition, the Earth's thermosphere could experience a fast transition to an atmospheric blowoff state when exposed to solar EUV radiation stronger than certain critical flux. When hydrodynamic flow and its associated adiabatic cooling are included, atmospheric blowoff is prevented and Earth's exobase temperature decreases with increasing solar EUV beyond the critical solar EUV flux. Simulations show that the transition of the thermosphere from the hydrostatic equilibrium regime to the hydrodynamic regime occurs when the exobase temperature reaches 7000 to 8000 K if atomic O and N dominate the upper thermosphere. The fast variations of the bulk motion velocities under different exobase temperatures suggest that the adiabatic cooling effect could have kept the exobase temperature lower than � 1000 K if light gases such as atomic hydrogen were the dominant species in the Earth's thermosphere. We propose that hydrodynamic flow and associated adiabatic cooling should exist in the thermospheres of a broad range of early and/or close-in terrestrial type planets and that the adiabatic cooling effect must be included in the energy balance in order to correctly estimate their thermospheric structures and their evolutionary paths.
    Preview · Article · May 2008 · Journal of Geophysical Research Atmospheres
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    ABSTRACT: It has been suggested that the exobase temperature of early terrestrial planetary atmosphere could have reached over 10,000 K (Kulikov et al. 2006) due to the extreme (up to 100 times that of today) solar EUV energy flux from the young Sun during the early stage of planetary evolution. Such high exobase temperature should have caused the dominant species at the exobase to escape at significant rate. Extremely fast escape of major gases in planetary atmospheres will lead to deviation from hydrostatic equilibrium. A newly developed 1-D, multi-component, hydrodynamic model has been used to investigate the response of Earth's thermosphere/ionosphere to extreme solar EUV conditions (Tian et al. 2007). We found that Earth's thermosphere/ionosphere could experience the transition from a hydrostatic equilibrium regime into a hydrodynamic regime when exposed to solar EUV fluxes exceeding certain critical level. In this regime, adiabatic cooling related to the hydrodynamic flow must be taken into the energy consideration. Due to extreme solar EUV fluxes, atomic nitrogen may have been the dominant species in upper thermosphere instead of atomic oxygen. In this work, we couple the hydrodynamic thermosphere model with an expanded GLOW model (including the electron impact ionization and excitation of nitrogen atoms) to investigate the contributions of photoelectrons and secondary electrons to thermospheric energetics under extreme conditions. The combined model provides self- consistent heating efficiency estimates for the Earth's atmosphere under extreme conditions. Implications of the simulation results to other early planetary atmospheres and their evolutions will be discussed.
    No preview · Article · Dec 2007
  • F. Tian · H. Li · S. Murugesu
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    ABSTRACT: This paper analyzes the temporal variability of the hydrological response in Blue River basin (Oklahoma, USA) and detects the possible controlling processes with downward approach aided by a physical distributed model (THREW, previously known as THModel). A switching pattern of runoff generation is identified by event analysis. The event storm-flow coefficients in wet season (February through April) are systematically higher than those in dry season (May through August). Such switching pattern seems to be driven by seasonal variability of potential evaporation as suggested by data analysis. It's well understood that the nonlinear relation between initial loss and soil moisture will result in the lower storm- flow coefficients under the dry conditions. However, the simulation results of THREW model show that the soil drying up only cannot fully explain the dramatic drop of storm-flow coefficients which imply some additional abstractions. Three possible abstraction processes including ground surface depression, canopy interception and soil crack are hypothesized and tested with downward approach, of which soil crack is suggested to be the most possible underlying process of the additional water loss.
    No preview · Article ·

Publication Stats

222 Citations
26.63 Total Impact Points

Institutions

  • 2008
    • National Center for Atmospheric Research
      • High Altitude Observatory
      Boulder, Colorado, United States
    • Huazhong Agricultural University
      • College of Fisheries
      Wu-han-shih, Hubei, China