The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform
Robert M. Haberle - One of the best experts on this subject based on the ideXlab platform.
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origin and role of water ice clouds in the martian water cycle as inferred from a general circulation model
Journal of Geophysical Research, 2004Co-Authors: Franck Montmessin, Francois Forget, Pascal Rannou, Michel Cabane, Robert M. HaberleAbstract:[1] In this paper, we present the results obtained by the general circulation model developed at the Laboratoire de Meteorologie Dynamique which has been used to simulate the Martian hydrological cycle. Our model, which employs a simplified cloud scheme, reproduces the observed Martian water cycle with unprecedented agreement. The modeled seasonal evolution of cloudiness, which also compares well with data, is described in terms of the meteorological phenomena that control the Martian cloud distribution. Whereas cloud formation in the tropical region results from seasonal changes in the overturning circulation, Polar Hood clouds are mostly driven by variations of Atmospheric Wave activity. A sensitivity study allows us to quantify the effects of the transport of water ice clouds on the seasonal evolution of the water cycle. The residence time of cloud particles is long enough to allow cloud advection over great distances (typically thousands of kilometers). Despite the relatively low proportion of clouds (∼10%) in the total Atmospheric inventory of water, their ability to be transported over large distances generally acts at the expense of the north polar cap and generates a water cycle globally wetter by a factor of 2 than a cycle produced by a model neglecting cloud transport. Around aphelion season, clouds modulate the north to south migration of water in a significant fashion and participate just as much as vapor in the cross-equatorial transport of total water. Most of the year, Atmospheric Waves generate an equatorward motion of water ice clouds near the polar vortex boundaries, partially balancing the opposite poleward flux of water vapor. The combination of both effects delays the return of water to the north polar cap and allows water to build up in the Martian tropics.
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Origin and role of water ice clouds in the Martian water cycle as inferred from a general circulation model
Journal of Geophysical Research. Planets, 2004Co-Authors: Franck Montmessin, Francois Forget, Pascal Rannou, Michel Cabane, Robert M. HaberleAbstract:In this paper, we present the results obtained by the general circulation model developed at the Laboratoire de Météorologie Dynamique which has been used to simulate the Martian hydrological cycle. Our model, which employs a simplified cloud scheme, reproduces the observed Martian water cycle with unprecedented agreement. The modeled seasonal evolution of cloudiness, which also compares well with data, is described in terms of the meteorological phenomena that control the Martian cloud distribution. Whereas cloud formation in the tropical region results from seasonal changes in the overturning circulation, Polar Hood clouds are mostly driven by variations of Atmospheric Wave activity. A sensitivity study allows us to quantify the effects of the transport of water ice clouds on the seasonal evolution of the water cycle. The residence time of cloud particles is long enough to allow cloud advection over great distances (typically thousands of kilometers). Despite the relatively low proportion of clouds ($10%) in the total Atmospheric inventory of water, their ability to be transported over large distances generally acts at the expense of the north polar cap and generates a water cycle globally wetter by a factor of 2 than a cycle produced by a model neglecting cloud transport. Around aphelion season, clouds modulate the north to south migration of water in a significant fashion and participate just as much as vapor in the cross-equatorial transport of total water. Most of the year, Atmospheric Waves generate an equatorward motion of water ice clouds near the polar vortex boundaries, partially balancing the opposite poleward flux of water vapor. The combination of both effects delays the return of water to the north polar cap and allows water to build up in the Martian tropics.
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Eddy transport of water vapor in the Martian atmosphere
1993Co-Authors: James R. Murphy, Robert M. HaberleAbstract:Viking orbiter measurements of the Martian atmosphere suggest that the residual north polar water-ice cap is the primary source of Atmospheric water vapor, which appears at successively lower northern latitudes as the summer season progresses. Zonally symmetric studies of water vapor transport indicate that the zonal mean meridional circulation is incapable of transporting from north polar regions to low latitudes the quantity of water vapor observed. This result has been interpreted as implying the presence of nonpolar sources of water. Another possibility is the ability of Atmospheric Wave motions, which are not accounted for in a zonally symmetric framework, to efficiently accomplish the transport from a north polar source to the entirety of the Northern Hemisphere. The ability or inability of the full range of Atmospheric motions to accomplish this transport has important implications regarding the questions of water sources and sinks on Mars: if the full spectrum of Atmospheric motions proves to be incapable of accomplishing the transport, it strengthens arguments in favor of additional water sources. Preliminary results from a three dimensional Atmospheric dynamical/water vapor transport numerical model are presented. The model accounts for the physics of a subliming water-ice cap, but does not yet incorporate recondensation of this sublimed water. Transport of vapor away from this water-ice cap in this three dimensional framework is compared with previously obtained zonally symmetric (two dimensional) results to quantify effects of water vapor transport by Atmospheric eddies.
H. Treut - One of the best experts on this subject based on the ideXlab platform.
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Impact of projected SST changes on summer rainfall in southeastern South America
Climate Dynamics, 2013Co-Authors: C. Junquas, C. S. Vera, H. TreutAbstract:Recent studies have shown that global warming and associated sea-surface temperature (SST) changes may trigger an important rainfall increase in southeastern South America (SESA) during the austral summer (December–January–February, DJF). The goal of this paper is to provide some insight into processes which may link global and SESA changes. For this purpose, a “two-way nesting” system coupling interactively the regional and global versions of the LMDZ4 Atmospheric model is used to study the response to prescribed SST changes. The regional model is a variable-grid version of the global model, with a zoom focused over South America. An ensemble of simulations forced by distinct patterns of DJF SST changes has been carried out using a decomposition of full SST changes into their longitudinal and latitudinal components. The full SST changes are based on projections for the end of the twenty-first century from a multi-model ensemble of WCRP/CMIP3. Results confirm the presence of a major rainfall dipole structure, characterized by an increase in SESA and a decrease in the South Atlantic Convergence Zone region. Rainfall changes found in the WCRP/CMIP3 models are largely explained as a response of this dipole structure to the zonally-asymmetric (or longitudinal) component of SST changes. The rainfall response to the zonal-mean (or latitudinal) SST changes (including the global warming signal itself) shows an opposite contribution. The processes explaining the role of zonally-asymmetric SST changes involve remote effects of SST warming over the equatorial Indian and Pacific oceans inducing an Atmospheric Wave-train extended across the South Pacific into South America.
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Impact of projected SST changes on summer rainfall in southeastern South America
Climate Dynamics, 2013Co-Authors: C. Junquas, C. S. Vera, H. TreutAbstract:Recent studies have shown that global warming and associated sea-surface temperature (SST) changes may trigger an important rainfall increase in southeastern South America (SESA) during the austral summer (December-January-February, DJF). The goal of this paper is to provide some insight into processes which may link global and SESA changes. For this purpose, a "two-way nesting" system coupling interactively the regional and global versions of the LMDZ4 Atmospheric model is used to study the response to prescribed SST changes. The regional model is a variable-grid version of the global model, with a zoom focused over South America. An ensemble of simulations forced by distinct patterns of DJF SST changes has been carried out using a decomposition of full SST changes into their longitudinal and latitudinal components. The full SST changes are based on projections for the end of the twenty-first century from a multi-model ensemble of WCRP/CMIP3. Results confirm the presence of a major rainfall dipole structure, characterized by an increase in SESA and a decrease in the South Atlantic Convergence Zone region. Rainfall changes found in the WCRP/CMIP3 models are largely explained as a response of this dipole structure to the zonally-asymmetric (or longitudinal) component of SST changes. The rainfall response to the zonal-mean (or latitudinal) SST changes (including the global warming signal itself) shows an opposite contribution. The processes explaining the role of zonally-asymmetric SST changes involve remote effects of SST warming over the equatorial Indian and Pacific oceans inducing an Atmospheric Wave-train extended across the South Pacific into South America. © 2013 Springer-Verlag Berlin Heidelberg.
Franck Montmessin - One of the best experts on this subject based on the ideXlab platform.
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origin and role of water ice clouds in the martian water cycle as inferred from a general circulation model
Journal of Geophysical Research, 2004Co-Authors: Franck Montmessin, Francois Forget, Pascal Rannou, Michel Cabane, Robert M. HaberleAbstract:[1] In this paper, we present the results obtained by the general circulation model developed at the Laboratoire de Meteorologie Dynamique which has been used to simulate the Martian hydrological cycle. Our model, which employs a simplified cloud scheme, reproduces the observed Martian water cycle with unprecedented agreement. The modeled seasonal evolution of cloudiness, which also compares well with data, is described in terms of the meteorological phenomena that control the Martian cloud distribution. Whereas cloud formation in the tropical region results from seasonal changes in the overturning circulation, Polar Hood clouds are mostly driven by variations of Atmospheric Wave activity. A sensitivity study allows us to quantify the effects of the transport of water ice clouds on the seasonal evolution of the water cycle. The residence time of cloud particles is long enough to allow cloud advection over great distances (typically thousands of kilometers). Despite the relatively low proportion of clouds (∼10%) in the total Atmospheric inventory of water, their ability to be transported over large distances generally acts at the expense of the north polar cap and generates a water cycle globally wetter by a factor of 2 than a cycle produced by a model neglecting cloud transport. Around aphelion season, clouds modulate the north to south migration of water in a significant fashion and participate just as much as vapor in the cross-equatorial transport of total water. Most of the year, Atmospheric Waves generate an equatorward motion of water ice clouds near the polar vortex boundaries, partially balancing the opposite poleward flux of water vapor. The combination of both effects delays the return of water to the north polar cap and allows water to build up in the Martian tropics.
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Origin and role of water ice clouds in the Martian water cycle as inferred from a general circulation model
Journal of Geophysical Research. Planets, 2004Co-Authors: Franck Montmessin, Francois Forget, Pascal Rannou, Michel Cabane, Robert M. HaberleAbstract:In this paper, we present the results obtained by the general circulation model developed at the Laboratoire de Météorologie Dynamique which has been used to simulate the Martian hydrological cycle. Our model, which employs a simplified cloud scheme, reproduces the observed Martian water cycle with unprecedented agreement. The modeled seasonal evolution of cloudiness, which also compares well with data, is described in terms of the meteorological phenomena that control the Martian cloud distribution. Whereas cloud formation in the tropical region results from seasonal changes in the overturning circulation, Polar Hood clouds are mostly driven by variations of Atmospheric Wave activity. A sensitivity study allows us to quantify the effects of the transport of water ice clouds on the seasonal evolution of the water cycle. The residence time of cloud particles is long enough to allow cloud advection over great distances (typically thousands of kilometers). Despite the relatively low proportion of clouds ($10%) in the total Atmospheric inventory of water, their ability to be transported over large distances generally acts at the expense of the north polar cap and generates a water cycle globally wetter by a factor of 2 than a cycle produced by a model neglecting cloud transport. Around aphelion season, clouds modulate the north to south migration of water in a significant fashion and participate just as much as vapor in the cross-equatorial transport of total water. Most of the year, Atmospheric Waves generate an equatorward motion of water ice clouds near the polar vortex boundaries, partially balancing the opposite poleward flux of water vapor. The combination of both effects delays the return of water to the north polar cap and allows water to build up in the Martian tropics.
C. Junquas - One of the best experts on this subject based on the ideXlab platform.
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Impact of projected SST changes on summer rainfall in southeastern South America
Climate Dynamics, 2013Co-Authors: C. Junquas, C. S. Vera, H. TreutAbstract:Recent studies have shown that global warming and associated sea-surface temperature (SST) changes may trigger an important rainfall increase in southeastern South America (SESA) during the austral summer (December–January–February, DJF). The goal of this paper is to provide some insight into processes which may link global and SESA changes. For this purpose, a “two-way nesting” system coupling interactively the regional and global versions of the LMDZ4 Atmospheric model is used to study the response to prescribed SST changes. The regional model is a variable-grid version of the global model, with a zoom focused over South America. An ensemble of simulations forced by distinct patterns of DJF SST changes has been carried out using a decomposition of full SST changes into their longitudinal and latitudinal components. The full SST changes are based on projections for the end of the twenty-first century from a multi-model ensemble of WCRP/CMIP3. Results confirm the presence of a major rainfall dipole structure, characterized by an increase in SESA and a decrease in the South Atlantic Convergence Zone region. Rainfall changes found in the WCRP/CMIP3 models are largely explained as a response of this dipole structure to the zonally-asymmetric (or longitudinal) component of SST changes. The rainfall response to the zonal-mean (or latitudinal) SST changes (including the global warming signal itself) shows an opposite contribution. The processes explaining the role of zonally-asymmetric SST changes involve remote effects of SST warming over the equatorial Indian and Pacific oceans inducing an Atmospheric Wave-train extended across the South Pacific into South America.
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Impact of projected SST changes on summer rainfall in southeastern South America
Climate Dynamics, 2013Co-Authors: C. Junquas, C. S. Vera, H. TreutAbstract:Recent studies have shown that global warming and associated sea-surface temperature (SST) changes may trigger an important rainfall increase in southeastern South America (SESA) during the austral summer (December-January-February, DJF). The goal of this paper is to provide some insight into processes which may link global and SESA changes. For this purpose, a "two-way nesting" system coupling interactively the regional and global versions of the LMDZ4 Atmospheric model is used to study the response to prescribed SST changes. The regional model is a variable-grid version of the global model, with a zoom focused over South America. An ensemble of simulations forced by distinct patterns of DJF SST changes has been carried out using a decomposition of full SST changes into their longitudinal and latitudinal components. The full SST changes are based on projections for the end of the twenty-first century from a multi-model ensemble of WCRP/CMIP3. Results confirm the presence of a major rainfall dipole structure, characterized by an increase in SESA and a decrease in the South Atlantic Convergence Zone region. Rainfall changes found in the WCRP/CMIP3 models are largely explained as a response of this dipole structure to the zonally-asymmetric (or longitudinal) component of SST changes. The rainfall response to the zonal-mean (or latitudinal) SST changes (including the global warming signal itself) shows an opposite contribution. The processes explaining the role of zonally-asymmetric SST changes involve remote effects of SST warming over the equatorial Indian and Pacific oceans inducing an Atmospheric Wave-train extended across the South Pacific into South America. © 2013 Springer-Verlag Berlin Heidelberg.
Philippe Lognonne - One of the best experts on this subject based on the ideXlab platform.
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acoustic Waves generated from seismic surface Waves propagation properties determined from doppler sounding observations and normal mode modelling
Geophysical Journal International, 2004Co-Authors: Juliette Artru, Thomas Farges, Philippe LognonneAbstract:SUMMARY Since 1960, experiments have shown that perturbations of the ionosphere can occur after earthquakes, by way of dynamic coupling between seismic surface Waves and the atmosphere. The Atmospheric Wave is amplified exponentially while propagating upwards due to the decrease of density, and interaction with the ionospheric plasma leads to clearly identified signals on both ground-based or satellite ionospheric measurements. In 1999 and 2000, after an upgrade of the HF Doppler sounder, the Commisariat ` ’´ Energie Atomique systematically recorded these effects in the ionosphere with the Francourville (France) network, by measuring vertical oscillations of ionospheric layers with the Doppler technique. Normal-mode theory extended to a solid Earth with an atmosphere allows successful modelling of such signals, even if this 1-D approach is probably too crude, especially in the solid Earth, where 20 s surface Waves see large lateral variations in the crust. The combination of observations and simulations provides a new tool to determine acoustic gravity Wave propagation characteristics from the ground to ionospheric height. Observed velocity and amplification of the Atmospheric Waves show good agreement from the ground up to moderate sounding altitudes (140‐150 km); however, at higher altitudes the propagation speed is found to be much smaller than predicted and attenuation is underestimated. This shows that the standard formalism of acoustic gravity Waves in the atmosphere cannot efficiently describe propagation in the ionized atmosphere. Further work is needed to characterize the propagation of acoustic Waves in this altitude range: we believe that seismic Waves can provide a well-constrained source for such study.
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acoustic Waves generated from seismic surface Waves propagation properties determined from doppler sounding observations and normal mode modelling
Geophysical Journal International, 2004Co-Authors: Juliette Artru, Thomas Farges, Philippe LognonneAbstract:SUMMARY Since 1960, experiments have shown that perturbations of the ionosphere can occur after earthquakes, by way of dynamic coupling between seismic surface Waves and the atmosphere. The Atmospheric Wave is amplified exponentially while propagating upwards due to the decrease of density, and interaction with the ionospheric plasma leads to clearly identified signals on both ground-based or satellite ionospheric measurements. In 1999 and 2000, after an upgrade of the HF Doppler sounder, the Commisariat ` ’´ Energie Atomique systematically recorded these effects in the ionosphere with the Francourville (France) network, by measuring vertical oscillations of ionospheric layers with the Doppler technique. Normal-mode theory extended to a solid Earth with an atmosphere allows successful modelling of such signals, even if this 1-D approach is probably too crude, especially in the solid Earth, where 20 s surface Waves see large lateral variations in the crust. The combination of observations and simulations provides a new tool to determine acoustic gravity Wave propagation characteristics from the ground to ionospheric height. Observed velocity and amplification of the Atmospheric Waves show good agreement from the ground up to moderate sounding altitudes (140‐150 km); however, at higher altitudes the propagation speed is found to be much smaller than predicted and attenuation is underestimated. This shows that the standard formalism of acoustic gravity Waves in the atmosphere cannot efficiently describe propagation in the ionized atmosphere. Further work is needed to characterize the propagation of acoustic Waves in this altitude range: we believe that seismic Waves can provide a well-constrained source for such study.