Joint second-order parameter estimation for spatio-temporal log-Gaussian Cox processes

2018 ◽  
Vol 32 (12) ◽  
pp. 3525-3539 ◽  
Author(s):  
Marianna Siino ◽  
Giada Adelfio ◽  
Jorge Mateu
Keyword(s):  
Parameter Estimation ◽  
Order Parameter ◽  
Second Order ◽  
Cox Processes ◽  
Spatio Temporal ◽  
Second Order Parameter

scholarly journals Can we determine what controls the spatio-temporal distribution of d-excess and <sup>17</sup>O-excess in precipitation using the LMDZ general circulation model?

2013 ◽  
Vol 9 (5) ◽  
pp. 2173-2193 ◽  
Author(s):  
C. Risi ◽  
A. Landais ◽  
R. Winkler ◽  
F. Vimeux
Keyword(s):  
General Circulation Model ◽  
Order Parameter ◽  
General Circulation ◽  
Temporal Distribution ◽  
Circulation Model ◽  
Second Order ◽  
Polar Ice ◽  
Spatio Temporal ◽  
Different Origins ◽  
Second Order Parameter

Abstract. Combined measurements of the H218O and HDO isotopic ratios in precipitation, leading to second-order parameter D-excess, have provided additional constraints on past climates compared to the H218O isotopic ratio alone. More recently, measurements of H217O have led to another second-order parameter: 17O-excess. Recent studies suggest that 17O-excess in polar ice may provide information on evaporative conditions at the moisture source. However, the processes controlling the spatio-temporal distribution of 17O-excess are still far from being fully understood. We use the isotopic general circulation model (GCM) LMDZ to better understand what controls d-excess and 17O-excess in precipitation at present-day (PD) and during the last glacial maximum (LGM). The simulation of D-excess and 17O-excess is evaluated against measurements in meteoric water, water vapor and polar ice cores. A set of sensitivity tests and diagnostics are used to quantify the relative effects of evaporative conditions (sea surface temperature and relative humidity), Rayleigh distillation, mixing between vapors from different origins, precipitation re-evaporation and supersaturation during condensation at low temperature. In LMDZ, simulations suggest that in the tropics convective processes and rain re-evaporation are important controls on precipitation D-excess and 17O-excess. In higher latitudes, the effect of distillation, mixing between vapors from different origins and supersaturation are the most important controls. For example, the lower d-excess and 17O-excess at LGM simulated at LGM are mainly due to the supersaturation effect. The effect of supersaturation is however very sensitive to a parameter whose tuning would require more measurements and laboratory experiments. Evaporative conditions had previously been suggested to be key controlling factors of d-excess and 17O-excess, but LMDZ underestimates their role. More generally, some shortcomings in the simulation of 17O-excess by LMDZ suggest that general circulation models are not yet the perfect tool to quantify with confidence all processes controlling 17O-excess.

scholarly journals Second-order parameter estimation

2005 ◽  
Vol 53 (7) ◽  
pp. 2408-2420 ◽  
Author(s):  
J. Villares ◽  
G. Vazquez
Keyword(s):  
Parameter Estimation ◽  
Order Parameter ◽  
Second Order ◽  
Second Order Parameter

scholarly journals What controls the spatio-temporal distribution of D-excess and <sup>17</sup>O-excess in precipitation? A general circulation model study

2012 ◽  
Vol 8 (6) ◽  
pp. 5493-5543 ◽  
Author(s):  
C. Risi ◽  
A. Landais ◽  
R. Winkler ◽  
F. Vimeux
Keyword(s):  
General Circulation Model ◽  
Order Parameter ◽  
General Circulation ◽  
Temporal Distribution ◽  
Circulation Model ◽  
Ice Cores ◽  
Second Order ◽  
Polar Ice ◽  
Spatio Temporal ◽  
Second Order Parameter

Abstract. Combined measurements of the H218O and HDO isotopic ratios in precipitation, leading to second-order parameter D-excess, have provided additional constraints on past climates compared to the H218O isotopic ratio alone. More recently, measurements of H217O have led to another second-order parameter: 17O-excess. Recent studies suggest that 17O-excess in polar ice may provide information on evaporative conditions at the moisture source. However, the processes controlling the spatio-temporal distribution of 17O-excess are still far from being fully understood. We use the isotopic general circulation model LMDZ to better understand what controls D-excess and 17O-excess in precipitation at present-day (PD) and during the last glacial maximum (LGM). The simulation of D-excess and 17O-excess is evaluated against measurements in meteoric water, water vapor and polar ice cores. A set of sensitivity tests and diagnostics are used to quantify the relative effects of evaporative conditions (sea surface temperature and relative humidity), Rayleigh distillation, precipitation re-evaporation and supersaturation during condensation at low temperature. Simulations suggest that in the tropics convective processes and rain re-evaporation are important controls on D-excess and 17O-excess. In higher latitudes, the effect of distillation, transport and mixing balance the effect of supersaturation. Since these terms are very large and near cancellation, results for both PD and LGM are very sensitive to the supersaturation function. The lower D-excess and 17O-excess at LGM simulated at LGM are dominated by the supersaturation effect. Evaporative conditions had previously been suggested to be key controling factors of D-excess and 17O-excess. In LMDZ, evaporative conditions are key in explaining the PD latitudinal and seasonal distributions, but play little role for 17O-excess and for LGM variations. However, the LMDZ may underestimate this role. More generally, some shortcomings in the simulation of 17O-excess by LMDZ suggest that GCMs are not yet the perfect tool to quantify with confidence all processes controlling 17O-excess.

An Analysis of the Robust Convergent Method for a Singularly Perturbed Linear System of Reaction–Diffusion Type Having Nonsmooth Data

2021 ◽  
pp. 2150056
Author(s):  
Sheetal Chawla ◽  
Jagbir Singh ◽  
Urmil
Keyword(s):  
Uniform Convergence ◽  
Order Parameter ◽  
Source Term ◽  
Reaction Diffusion ◽  
Shishkin Mesh ◽  
Second Order ◽  
Singularly Perturbed ◽  
Diffusion Type ◽  
Bakhvalov Mesh ◽  
Second Order Parameter

In this paper, a coupled system of [Formula: see text] second-order singularly perturbed differential equations of reaction–diffusion type with discontinuous source term subject to Dirichlet boundary conditions is studied, where the diffusive term of each equation is being multiplied by the small perturbation parameters having different magnitudes and coupled through their reactive term. A discontinuity in the source term causes the appearance of interior layers on either side of the point of discontinuity in the continuous solution in addition to the boundary layer at the end points of the domain. Unlike the case of a single equation, the considered system does not obey the maximum principle. To construct a numerical method, a classical finite difference scheme is defined in conjunction with a piecewise-uniform Shishkin mesh and a graded Bakhvalov mesh. Based on Green’s function theory, it has been proved that the proposed numerical scheme leads to an almost second-order parameter-uniform convergence for the Shishkin mesh and second-order parameter-uniform convergence for the Bakhvalov mesh. Numerical experiments are presented to illustrate the theoretical findings.

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