scholarly journals Intermittent saltation drives Mars-like sand transport on Titan

2021 ◽  
Author(s):  
Francesco Comola ◽  
Jasper Kok ◽  
Juan Lora ◽  
Kaylie Cohanim ◽  
Xinting Yu ◽  
...  
Keyword(s):  
Mass Flux ◽  
General Circulation ◽  
Circulation Model ◽  
Sand Transport ◽  
Strong Wind ◽  
Comprehensive Understanding ◽  
Wind Speeds ◽  
Open Questions ◽  
Flux Parameterization ◽  
Theory And Modeling

Abstract Titan, the largest moon of Saturn, is characterized by gigantic linear dunes and an active dust cycle. Much like on Earth, these and other aeolian processes are caused by the wind-driven mobilization of surface grains, known as saltation. To date, very little is known about the conditions that allow for the occurrence of saltation on Titan. In fact, Titan saltation may be fundamentally different from Earth saltation given the denser atmosphere, the lower gravity, and the cohesion of its surface grains. Here, we draw on experiments, theory, and modeling to progress towards a comprehensive understanding of saltation on Titan. We find that aerodynamic lifting of surface grains requires strong wind speeds due to the high cohesion of the grains. However, saltation may be sustained through granular splash at wind speeds much smaller than those required to initiate grain motion. This suggests that most saltation transport on Titan is intermittent rather than continuous. We account for these insights by proposing a saltation mass flux parameterization specific for Titan conditions that accounts for transport intermittency, and use it to quantify yearly sediment transport with a general circulation model. The results show that Titan's prevailing atmospheric circulation is capable of generating highly intermittent yet significant saltation, yielding yearly transport rates similar to those on the most active dunes of Mars. Furthermore, we find that accounting for surface topography might be critical to answering open questions related to Titan's landscape evolution, including the formation of linear dunes in opposite direction to the prevailing circulation.

scholarly journals First simulation results of Titan's atmosphere dynamics with a global 3-D non-hydrostatic circulation model

2006 ◽  
Vol 24 (8) ◽  
pp. 2115-2129 ◽  
Author(s):  
I. V. Mingalev ◽  
V. S. Mingalev ◽  
O. V. Mingalev ◽  
B. Kazeminejad ◽  
H. Lammer ◽  
...  
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Wind Speeds ◽  
Neutral Gas ◽  
Complex Simulation ◽  
First Results ◽  
Simulation Results ◽  
Model Region

Abstract. We present the first results of a 3-D General Circulation Model of Titan's atmosphere which differs from traditional models in that the hydrostatic equation is not used and all three components of the neutral gas velocity are obtained from the numerical solution of the Navier-Stokes equation. The current version of our GCM is, however, a simplified version, as it uses a predescribed temperature field in the model region thereby avoiding the complex simulation of radiative transfer based on the energy equation. We present the first simulation results and compare them to the results of existing GCMs and direct wind observations. The wind speeds obtained from our GCM correspond well with data obtained during the Huygens probe descent through Titan's atmosphere. We interpret the most unexpected feature of these data which consist of the presence of a non-monotonicity of the altitude profile of the zonal wind speed between 60 and 75 km.

scholarly journals Venus Atmospheric Dynamics at Two Altitudes: Akatsuki and Venus Express Cloud Tracking, Ground-Based Doppler Observations and Comparison with Modelling

Atmosphere ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 506
Author(s):  
Pedro Machado ◽  
Thomas Widemann ◽  
Javier Peralta ◽  
Gabriella Gilli ◽  
Daniela Espadinha ◽  
...  
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Time Window ◽  
Vertical Wind Shear ◽  
Circulation Model ◽  
Phase Correlation ◽  
Doppler Velocimetry ◽  
Present Evidence ◽  
Wind Speeds ◽  
Altitude Level

We present new results of our studies of zonal and meridional winds in both hemispheres of Venus, using ground- and space-based coordinated observations. The results obtained from telescope observations were retrieved with a Doppler velocimetry method. The wind velocities retrieved from space used an improved cloud-tracked technique based on the phase correlation between images. We present evidence that the altitude level sensed by our Doppler velocimetry method is approximately four kilometres higher (~4 km) than that using ground-tracked winds (using 380 or 365 nm). Since we often take advantage of coordinated space and ground observations simultaneously, this altitude difference will be very relevant in order to estimate the vertical wind shear at the related heights in future observation campaigns. We also explored a previous coordinated campaign using Akatsuki observations and its Ultraviolet Imager (UVI) at 283 and 365 nm filters, which showed that cloud-tracked winds showed a difference of about 10–15 ms−1, as in the case of the comparison between the Doppler velocimetry winds and the 365 nm cloudtracked winds. The results’ comparison also strongly suggested that the cloud-tracked winds based on the 283 nm filter’s images were sensing at about the same atmospheric altitude level as the Doppler winds. The observational results were compared with the ground-to-thermosphere 3D model developed at the Laboratoire de Meteorologie Dynamique (IPSL-Venus General Circulation Model (VGCM)) and AFES-Venus General Circulation Model (GCM), at several pressure levels (and related heights). The analysis and results showed the following: (1) additional confirmation of the coherence and complementarity in the results provided by these techniques on both the spatial and temporal time scales of the two methods; (2) we noticed in the following that the results from the two different Akatsuki/UVI filters (283 and 365 nm) showed an average difference of about 10–15 ± 5 ms−1, and we suggest this may be related to SO2 atmospheric fluctuations and the particular conditions in the coordinated observing time window; (3) we present evidence indicating that, in the context of our observations, visible Doppler methods (highly self-consistent) seem to sense wind speeds at a vertical level closer to or within the range sensed by the UVI 283 nm filter images (again, in the context of our observations); (4) modelling predicted wind profiles suggests that the layers of the atmosphere of Venus sensed by the methods referred to in Point 3 differ by approximately four km in altitude (~4 ± 2 km) regarding the cloud-tracked winds retrieved using 365 or 380 nm images.

scholarly journals Decline and poleward shift in Indian summer monsoon synoptic activity in a warming climate

2018 ◽  
Vol 115 (11) ◽  
pp. 2681-2686 ◽  
Author(s):  
S. Sandeep ◽  
R. S. Ajayamohan ◽  
William R. Boos ◽  
T. P. Sabin ◽  
V. Praveen
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Coupled Model ◽  
Circulation Model ◽  
Central India ◽  
Wind Speeds ◽  
Northern India ◽  
Extreme Precipitation Events ◽  
Poleward Shift ◽  
Atmospheric Vortices

Cyclonic atmospheric vortices of varying intensity, collectively known as low-pressure systems (LPS), travel northwest across central India and produce more than half of the precipitation received by that fertile region and its ∼600 million inhabitants. Yet, future changes in LPS activity are poorly understood, due in part to inadequate representation of these storms in current climate models. Using a high-resolution atmospheric general circulation model that realistically simulates the genesis distribution of LPS, here we show that Indian monsoon LPS activity declines about 45% by the late 21st century in simulations of a business-as-usual emission scenario. The distribution of LPS genesis shifts poleward as it weakens, with oceanic genesis decreasing by ∼60% and continental genesis increasing by ∼10%; over land the increase in storm counts is accompanied by a shift toward lower storm wind speeds. The weakening and poleward shift of the genesis distribution in a warmer climate are confirmed and attributed, via a statistical model, to the reduction and poleward shift of low-level absolute vorticity over the monsoon region, which in turn are robust features of most coupled model projections. The poleward shift in LPS activity results in an increased frequency of extreme precipitation events over northern India.

scholarly journals Structure of AGCM-Simulated Convectively Coupled Kelvin Waves and Sensitivity to Convective Parameterization

2011 ◽  
Vol 68 (1) ◽  
pp. 26-45 ◽  
Author(s):  
Dargan M. W. Frierson ◽  
Daehyun Kim ◽  
In-Sik Kang ◽  
Myong-In Lee ◽  
Jialin Lin
Keyword(s):  
Mass Flux ◽  
General Circulation ◽  
Phase Speed ◽  
Circulation Model ◽  
Radiative Heating ◽  
Moisture Convergence ◽  
Kelvin Wave ◽  
Convection Schemes ◽  
Gross Moist Stability ◽  
The Waves

Abstract A study of the convectively coupled Kelvin wave (CCKW) properties from a series of atmospheric general circulation model experiments over observed sea surface temperatures is presented. The simulations are performed with two different convection schemes (a mass flux scheme and a moisture convergence scheme) using a range of convective triggers, which inhibit convection in different ways. Increasing the strength of the convective trigger leads to significantly slower and more intense CCKW activity in both convection schemes. With the most stringent trigger in the mass flux scheme, the waves have realistic speed and variance and also exhibit clear shallow-to-deep-to-stratiform phase tilts in the vertical, as in observations. While adding a moisture trigger results in vertical phase tilts in the mass flux scheme, the moisture convergence scheme CCKWs show no such phase tilts even with a stringent convective trigger. The changes in phase speed in the simulations are interpreted using the concept of “gross moist stability” (GMS). Inhibition of convection results in a more unstable tropical atmosphere in the time mean, and convection is shallower on average as well. Both of these effects lead to a smaller GMS, which leads to slower propagation of the waves, as expected from theoretical studies. Effects such as changes in radiative heating, atmospheric humidity, and vertical velocity following the wave have a relatively small effect on the GMS as compared with the time mean state determined by the convection scheme.

What Sets the Surface Eddy Mass Flux in the Southern Ocean?

2005 ◽  
Vol 35 (11) ◽  
pp. 2152-2166 ◽  
Author(s):  
S. S. Drijfhout
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Mass Flux ◽  
General Circulation ◽  
Circulation Model ◽  
Ekman Transport ◽  
Thermocline Depth ◽  
Mean Flow ◽  
Rotational Components ◽  
Eddy Fluxes

Abstract The Ocean Circulation and Climate Advanced Modelling (OCCAM) global, eddy-permitting ocean general circulation model has been used to investigate the surface eddy mass flux in the Southern Ocean. The isopycnal eddy mass flux in the surface layer is almost uniformly poleward and scales well with the local Ekman transport. This seems at odds with other models and observations suggesting topographic localization of the eddy fluxes with locally, large rotational components. Integrated over the thermocline depth the eddy fluxes do show such topographic localization. The surface eddy mass flux is mainly a consequence of the intermittent deepening of the mixed layer with the seasonal cycle, which redistributes the Ekman transport over the stack of layers that eventually become ventilated. Baroclinic instability gives rise to much smaller eddy-induced transports. Independent of the framework in which the residual mean flow is analyzed (isopycnal or geometric), the eddy-induced transport that opposes the wind-driven Ekman flow only partially compensates the Deacon cell. The associated overturning cell is about 5 Sv (where 1 Sv ≡ 106 m3 s−1), responsible for a cancellation of the Deacon cell of 30%. In geometric coordinates, a strong signature (14 Sv) of the Deacon cell remains for the residual mean flow. Only after transformation to density coordinates is a further reduction with 10 Sv obtained. Zonal tilting of isopycnals makes along-isopycnal recirculations appear as vertical overturning cells in geometric coordinates. These cells disappear in the isopycnal framework without any eddy-induced transport being involved.

Pemanfaatan CFSRv2 untuk Statistical Downscaling menggunakan Principal Component Regression dan Partial Least Square

2019 ◽  
Vol 8 (1) ◽  
Author(s):  
Khairunnisa Khairunnisa ◽  
Rizka Pitri ◽  
Victor P Butar-Butar ◽  
Agus M Soleh
Keyword(s):  
Statistical Downscaling ◽  
General Circulation ◽  
Principal Component Regression ◽  
Circulation Model ◽  
Principal Component ◽  
Meteorological Station ◽  
Grid Size ◽  
Partial Least Square ◽  
Least Square ◽  
Output Data

This research used CFSRv2 data as output data general circulation model. CFSRv2 involves some variables data with high correlation, so in this research is using principal component regression (PCR) and partial least square (PLS) to solve the multicollinearity occurring in CFSRv2 data. This research aims to determine the best model between PCR and PLS to estimate rainfall at Bandung geophysical station, Bogor climatology station, Citeko meteorological station, and Jatiwangi meteorological station by comparing RMSEP value and correlation value. Size used was 3×3, 4×4, 5×5, 6×6, 7×7, 8×8, 9×9, and 11×11 that was located between (-40) N - (-90) S and 1050 E -1100 E with a grid size of 0.5×0.5 The PLS model was the best model used in stastistical downscaling in this research than PCR model because of the PLS model obtained the lower RMSEP value and the higher correlation value. The best domain and RMSEP value for Bandung geophysical station, Bogor climatology station, Citeko meteorological station, and Jatiwangi meteorological station is 9 × 9 with 100.06, 6 × 6 with 194.3, 8 × 8 with 117.6, and 6 × 6 with 108.2, respectively.

On the impact of sea ice in a global ocean circulation model

1997 ◽  
Vol 25 ◽  
pp. 111-115 ◽  
Author(s):  
Achim Stössel
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Deep Ocean ◽  
Global Ocean ◽  
Convective Activity ◽  
The Impact

This paper investigates the long-term impact of sea ice on global climate using a global sea-ice–ocean general circulation model (OGCM). The sea-ice component involves state-of-the-art dynamics; the ocean component consists of a 3.5° × 3.5° × 11 layer primitive-equation model. Depending on the physical description of sea ice, significant changes are detected in the convective activity, in the hydrographic properties and in the thermohaline circulation of the ocean model. Most of these changes originate in the Southern Ocean, emphasizing the crucial role of sea ice in this marginally stably stratified region of the world's oceans. Specifically, if the effect of brine release is neglected, the deep layers of the Southern Ocean warm up considerably; this is associated with a weakening of the Southern Hemisphere overturning cell. The removal of the commonly used “salinity enhancement” leads to a similar effect. The deep-ocean salinity is almost unaffected in both experiments. Introducing explicit new-ice thickness growth in partially ice-covered gridcells leads to a substantial increase in convective activity, especially in the Southern Ocean, with a concomitant significant cooling and salinification of the deep ocean. Possible mechanisms for the resulting interactions between sea-ice processes and deep-ocean characteristics are suggested.

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