293 research outputs found
Uncertainties in future climate predictions due to convection parameterisations
In the last decades several convection parameterisations have been developed
to consider the impact of small-scale unresolved processes in Earth System
Models associated with convective clouds. Global model simulations, which
have been performed under current climate conditions with different
convection schemes, significantly differ among each other in the simulated
transport of trace gases and precipitation patterns due to the
parameterisation assumptions and formulations, e.g. the computation of
convective rainfall rates, calculation of entrainment and detrainment rates
etc. Here we address sensitivity studies comparing four different convection
schemes under alternative climate conditions (with doubling of the CO<sub>2</sub>
concentrations) to identify uncertainties related to convective processes.
The increase in surface temperature reveals regional differences up to 4 K
dependent on the chosen convection parameterisation. These differences are
statistically significant almost everywhere in the troposphere of the
intertropical convergence zone. The increase in upper tropospheric
temperature affects the amount of water vapour transported to the lower
stratosphere, leading to enhanced water vapour contents between 40% and
60% at the cold point temperature in the Tropics. Furthermore, the change
in transporting short-lived pollutants within the atmosphere is highly
ambiguous for the lower and upper troposphere. These results reflect that
different approaches to compute mass fluxes, detrainment levels or trigger
functions determine the transport of short-lived trace gases from the
planetary boundary layer to lower, middle or upper tropospheric levels.
Finally, cloud radiative effects have been analysed, uncovering a shift in
different cloud types in the Tropics, especially for cirrus and deep
convective clouds. These cloud types induce a change in net cloud radiative
forcing varying from 0.5 W m<sup>−2</sup> to 2.0 W m<sup>−2</sup>
A caricature of a singular curvature flow in the plane
We study a singular parabolic equation of the total variation type in one
dimension. The problem is a simplification of the singular curvature flow. We
show existence and uniqueness of weak solutions. We also prove existence of
weak solutions to the semi-discretization of the problem as well as convergence
of the approximating sequences. The semi-discretization shows that facets must
form. For a class of initial data we are able to study in details the facet
formation and interactions and their asymptotic behavior. We notice that our
qualitative results may be interpreted with the help of a special composition
of multivalued operators
Astrometric Control of the Inertiality of the Hipparcos Catalog
Based on the most complete list of the results of an individual comparison of
the proper motions for stars of various programs common to the Hipparcos
catalog, each of which is an independent realization of the inertial reference
frame with regard to stellar proper motions, we redetermined the vector
of residual rotation of the ICRS system relative to the extragalactic
reference frame. The equatorial components of this vector were found to be the
following: mas yr,
mas yr, and mas yr.Comment: 8 pages, 1 figur
Proceedings of minisemester on evolution of interfaces, Sapporo 2010
conf: Special Project A, Proceedings of minisemester on evolution of interfaces, Sapporo (Department of Mathematics, Hokkaido University, July 12- August 13, 2010
- …