How comets work: nucleus erosion versus dehydration

2020 ◽  
Vol 493 (3) ◽  
pp. 4039-4044 ◽  
Author(s):  
Marco Fulle ◽  
J Blum ◽  
A Rotundi ◽  
B Gundlach ◽  
C Güttler ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Water Vapour ◽  
Erosion Rate ◽  
Cometary Nucleus ◽  
Gas Diffusion ◽  
Quasi Equilibrium ◽  
Water Vapour Flux ◽  
Water Ice ◽  
Nucleus Surface ◽  
Vapour Flux

ABSTRACT We develop an activity model based on ice sublimation and gas diffusion inside cm-sized pebbles making-up a cometary nucleus. Our model explains cometary activity assuming no free parameters and fixing the nucleus surface temperature Ts, its gradient below the nucleus surface at thermal equilibrium, the pressure inside the porous pebbles, and the gas flux from them. We find that (i) the nucleus erosion rate and water vapour flux are independent of the nucleus refractory-to-ice ratio, which affects the dehydration rate only; (ii) water-driven dust ejection occurs in thermal quasi-equilibrium at Ts > 205 K; (iii) the smallest and largest ejected dust sizes depend on the nucleus surface temperature and its gradient at depths of few cm; and (iv) the water-driven nucleus erosion rate is independent of the water vapour flux. Regarding comet 67P/Churyumov–Gerasimenko, we find that (i) during the northern and southern polar summers, the nucleus active areas are ≈5 km2; (ii) >95 per cent of the southern pristine nucleus has a refractory-to-water-ice mass ratio >5; and (iii) the different temperature dependences of the dehydration and erosion rates explain the seasonal cycle: at perihelion, dm-sized chunks ejected by the sublimation of CO2 ices are rapidly enveloped by an insulating crust, preserving most water ice up to their fallout on the northern dust deposits; the inbound water-driven activity at low temperatures triggers a complete erosion of the fallout if its water-ice mass fraction is >0.1 per cent.

Spatiotemporal variability of Hokkaido's seasonal precipitation in recent decades and connection to water vapour flux

2016 ◽  
Vol 37 (9) ◽  
pp. 3660-3673 ◽  
Author(s):  
Weili Duan ◽  
Bin He ◽  
Netrananda Sahu ◽  
Pingping Luo ◽  
Daniel Nover ◽  
...  
Keyword(s):  
Water Vapour ◽  
Spatiotemporal Variability ◽  
Seasonal Precipitation ◽  
Water Vapour Flux ◽  
Vapour Flux

scholarly journals Ice Particle Emission from Cometary Analogues

1991 ◽  
Vol 126 ◽  
pp. 257-260
Author(s):  
H. Kohl ◽  
E. Grün
Keyword(s):  
Cometary Nucleus ◽  
Interplanetary Dust ◽  
Particle Emission ◽  
Dust Particles ◽  
Vacuum System ◽  
Simulation Experiments ◽  
Water Ice ◽  
Mineral Particles ◽  
Nucleus Surface ◽  
Particle Ejection

AbstractDust particles originating from comets are an important constituent of the interplanetary dust regime. In order to study the ejection mechanisms from the cometary nucleus surface simulation experiments in the laboratory have been performed. Samples consisting of water ice, carbon dioxide ice and dust grains have been studied when they are irradiated by artificial sunlight within a cooled vacuum system. It has been shown that particle emission is extremely dependent on the initial composition of the samples. For samples with a distinct amount of non-volatile, mineral particles the formation of a dust mantle and, as a consequence, rapid decrease of particle ejection has been observed.

Carbon dioxide and water vapour flux densities over a grassland area in the Netherlands

2003 ◽  
Vol 23 (13) ◽  
pp. 1663-1675 ◽  
Author(s):  
Adrie F. G. Jacobs ◽  
Bert G. Heusinkveld ◽  
Albert A. M. Holtslag
Keyword(s):  
Carbon Dioxide ◽  
The Netherlands ◽  
Water Vapour ◽  
Water Vapour Flux ◽  
Vapour Flux

scholarly journals Technical note: Water vapour concentration and flux measurements with PTR-MS

2006 ◽  
Vol 6 (3) ◽  
pp. 5329-5355 ◽  
Author(s):  
C. Ammann ◽  
A. Brunner ◽  
C. Spirig ◽  
A. Neftel
Keyword(s):  
Water Vapour ◽  
Eddy Covariance ◽  
High Frequency ◽  
Reference System ◽  
Transfer Functions ◽  
Terrestrial Ecosystems ◽  
Water Vapour Flux ◽  
Water Vapour Concentration ◽  
Vapour Concentration ◽  
Vapour Flux

Abstract. The most direct approach for measuring the exchange of biogenic volatile organic compounds between terrestrial ecosystems and the atmosphere is the eddy covariance technique. It has been applied several times in the last few years using fast response proton-transfer-reaction mass spectrometry (PTR-MS). We present an independent validation of this technique by applying it to measure the water vapour flux in comparison to a common reference system comprising an infra-red gas analyser (IRGA). Water vapour was detected in the PTR-MS at mass 37 (atomic mass units) corresponding to the cluster ion H3O+·H2O. During a five-week field campaign at a grassland site, we obtained a non-linear but stable calibration function between the mass 37 signal and the reference water vapour concentration. With a correction of the high-frequency damping loss based on empirical ogive analysis, the eddy covariance water vapour flux obtained with the PTR-MS showed a very good agreement with the flux of the reference system. The application of the empirical ogive method for high-frequency correction led to significantly better results than using a correction based on theoretical spectral transfer functions. This finding is attributed to adsorption effects on the tube walls that are presently not included in the theoretical correction approach.

scholarly journals Methanol exchange between grassland and the atmosphere

2007 ◽  
Vol 4 (3) ◽  
pp. 395-410 ◽  
Author(s):  
A. Brunner ◽  
C. Ammann ◽  
A. Neftel ◽  
C. Spirig
Keyword(s):  
Species Composition ◽  
Water Vapour ◽  
Net Primary Productivity ◽  
Global Radiation ◽  
Eddy Covariance Method ◽  
Area Index ◽  
Complex Species ◽  
Water Vapour Flux ◽  
Extensive Field ◽  
Vapour Flux

Abstract. Concentrations and fluxes of methanol were measured above two differently managed grassland fields (intensive and extensive) in central Switzerland during summer 2004. The measurements were performed with a proton-transfer-reaction mass-spectrometer and fluxes were determined by the eddy covariance method. The observed methanol emission showed a distinct diurnal cycle and was strongly correlated with global radiation and water vapour flux. Mean and maximum daily emissions were found to depend on grassland species composition and, for the intensive field, also on the growing state. The extensive field with a more complex species composition had higher emissions than the graminoid-dominated intensive field, both on an area and on a biomass basis. A simple parameterisation depending on the water vapour flux and the leaf area index allowed a satisfying simulation of the temporal variation of methanol emissions over the growing phase. Accumulated carbon losses due to methanol emissions accounted for 0.024 and 0.048% of net primary productivity for the intensive and extensive field, respectively. The integral methanol emissions over the growing periods were more than one order of magnitude higher than the emissions related to cut and drying events.

scholarly journals Strong low-pass filtering effects on water vapour flux measurements with closed-path eddy correlation systems

2007 ◽  
Vol 147 (3-4) ◽  
pp. 140-156 ◽  
Author(s):  
Andreas Ibrom ◽  
Ebba Dellwik ◽  
Henrik Flyvbjerg ◽  
Niels Otto Jensen ◽  
Kim Pilegaard
Keyword(s):  
Water Vapour ◽  
Eddy Correlation ◽  
Closed Path ◽  
Water Vapour Flux ◽  
Low Pass ◽  
Flux Measurements ◽  
Vapour Flux
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