27 research outputs found
Gliese 581g as a scaled-up version of Earth: atmospheric circulation simulations
We use three-dimensional simulations to study the atmospheric circulation on
the first Earth-sized exoplanet discovered in the habitable zone of an M star.
We treat Gliese 581g as a scaled-up version of Earth by considering increased
values for the exoplanetary radius and surface gravity, while retaining
terrestrial values for parameters which are unconstrained by current
observations. We examine the long-term, global temperature and wind maps near
the surface of the exoplanet --- the climate. The specific locations for
habitability on Gliese 581g depend on whether the exoplanet is tidally-locked
and how fast radiative cooling occurs on a global scale. Independent of whether
the existence of Gliese 581g is confirmed, our study highlights the use of
general circulation models to quantify the atmospheric circulation on
potentially habitable, Earth-sized exoplanets, which will be the prime targets
of exoplanet discovery and characterization campaigns in the next decade.Comment: Accepted by MNRAS. 15 pages, 13 figures. Sample movies of simulations
are available at http://www.phys.ethz.ch/~kheng/fms
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Parameterised diabatic processes in numerical simulations of an extratropical cyclone
The parameterisation of diabatic processes in numerical models is critical for the accuracy of weather forecasts and for climate projections. A novel approach to the evaluation of these processes in models is introduced in this contribution. The approach combines a suite of on-line tracer diagnostics with off-line trajectory calculations. Each tracer tracks accumulative changes in potential temperature associated with a particular parameterised diabatic process in the model. A comparison of tracers therefore allows the identification of the most active diabatic processes and their downstream impacts. The tracers are combined with trajectories computed using model-resolved winds, allowing the various diabatic contributions to be tracked back to their time and location of occurrence.
We have used this approach to investigate diabatic processes within a simulated extratropical cyclone. We focus on the warm conveyor belt, in which the dominant diabatic contributions come from large-scale latent heating and parameterised convection. By contrasting two simulations, one with standard convection parameterisation settings and another with reduced parameterised convection, the effects of parameterised convection on the structure of the cyclone have been determined. Under reduced parameterised convection conditions, the large-scale latent heating is forced to release convective instability that would otherwise have been released by the convection parameterisation. Although the spatial distribution of precipitation depends on the details of the split between parameterised convection and large-scale latent heating, the total precipitation amount associated with the cyclone remains largely unchanged. For reduced parameterised convection, a more rapid and stronger latent heating episode takes place as air ascends within the warm conveyor belt
Volume, heat, and freshwater transports of the global ocean circulation 1993-2000, estimated from a general circulation model constrained by World Ocean Circulation Experiment (WOCE) data.
An analysis of ocean volume, heat and freshwater transports from a fully con-strained general circulation model is described. Output from a data synthesis, or state estimation, method is used by which the model was forced to a large-scale, time varying global ocean data set over six years. Time-mean fluxes estimated from this fully time-dependent circulation have converged with independent time-independent estimates from box inversions over most parts of the world ocean but especially in the southern hemisphere. However, heat transport estimates differ substantially in
the North Atlantic where our estimates result in only 1/2 previous heat transports. The estimated mean circulation around Australia involves a net volume flux of 14
Sv through the Indonesian Through flow and the Mozambique Channel. In addition we show that this flow regime exist on all time scales above one month rendering the variability in the South Pacific strongly coupled to the Indian Ocean. Moreover, the dynamically consistent variations in the model show temporal variability of oceanic heat fluxes, heat storage and atmospheric exchanges that are complex and with a strong dependence upon location, depth, and time-scale. Results presented demonstrate the great potential of an ocean /state estimation system to provide a dynamical description of the time-dependent observed heat transport and heat
content changes and their relation to air-sea interactions
A Lorenz/Boer energy budget for the atmosphere of Mars from a “reanalysis” of spacecraft observations
We calculate a Lorenz energy budget for the Martian atmosphere from reanalysis derived from Mars Global Surveyor data for Mars years 24–27. We present global, annual mean energy and conversion rates per unit area and per unit mass and compare these to Earth data. The directions of the energy conversion terms for Mars are similar to Earth, with the exception of the barotropic conversion between zonal and eddy kinetic energy reservoirs. Further, seasonal and hemispheric decomposition reveals a strong conversion between zonal energy reservoirs over the year, but these balance each other out in global and annual mean. On separating the diurnal timescale, the contribution to the conversion terms and eddy kinetic energy for diurnal and shorter timescales in many cases (especially during planet-encircling dust storms) exceeds the contribution of longer timescales. This suggests that thermal tides have a significant effect on the generation of eddy kinetic energy
Atmospheric circulation of tidally locked exoplanets: II. Dual-band radiative transfer and convective adjustment
Improving upon our purely dynamical work, we present three-dimensional
simulations of the atmospheric circulation on Earth-like (exo)planets and hot
Jupiters using the GFDL-Princeton Flexible Modeling System (FMS). As the first
steps away from the dynamical benchmarks of Heng, Menou & Phillipps (2011), we
add dual-band radiative transfer and dry convective adjustment schemes to our
computational setup. Our treatment of radiative transfer assumes stellar
irradiation to peak at a wavelength shorter than and distinct from that at
which the exoplanet re-emits radiation ("shortwave" versus "longwave"), and
also uses a two-stream approximation. Convection is mimicked by adjusting
unstable lapse rates to the dry adiabat. The bottom of the atmosphere is
bounded by a uniform slab with a finite thermal inertia. For our models of hot
Jupiters, we include an analytical formalism for calculating
temperature-pressure profiles, in radiative equilibrium, which accounts for the
effect of collision-induced absorption via a single parameter. We discuss our
results within the context of: the predicted temperature-pressure profiles and
the absence/presence of a temperature inversion; the possible maintenance, via
atmospheric circulation, of the putative high-altitude, shortwave absorber
expected to produce these inversions; the angular/temporal offset of the hot
spot from the substellar point, its robustness to our ignorance of
hyperviscosity and hence its utility in distinguishing between different hot
Jovian atmospheres; and various zonal-mean flow quantities. Our work bridges
the gap between three-dimensional simulations which are purely dynamical and
those which incorporate multi-band radiative transfer, thus contributing to the
construction of a required hierarchy of three-dimensional theoretical models.Comment: Accepted by MNRAS. 28 pages, 19 figures. No changes to last version
except for title (to adhere to MNRAS guidelines
Arctic climate sensitivity to local black carbon
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97472/1/jgrd50176.pd
Istraživač svetih mjesta Bellarmino Bagatti, ofm
The Intertropical Convergence Zone (ITCZ) narrows in response to global warming in both observations and climate models. However, a physical understanding of this narrowing is lacking. Here we show that the narrowing of the ITCZ in simulations of future climate is related to changes in the moist static energy (MSE) budget. MSE advection by the mean circulation and MSE divergence by transient eddies tend to narrow the ITCZ, while changes in net energy input to the atmosphere and the gross moist stability tend to widen the ITCZ. The narrowing tendency arises because the meridional MSE gradient strengthens with warming, whereas the largest widening tendency is due to increasing shortwave heating of the atmosphere. The magnitude of the ITCZ narrowing depends strongly on the gross moist stability and clouds, emphasizing the need to better understand these fundamental processes in the tropical atmosphere