Predicting the '97 El Niño event with a global climate model

A simple data assimilation technique has been applied for initializing coupled ocean‐atmosphere general circulation models, which is able to generate the three‐dimensional thermal state of the low‐latitude oceans by forcing the model with observed anomalies of sea surface temperature. The scheme has been tested in a multi‐year experiment in which the vertical temperature profiles in the equatorial Pacific measured by the TOGA‐TAO array have been successfully reproduced for the period '96 to '97. In a further series of eight hindcast experiments initialized between January '96 and September '97, the predictive skill of the model was tested. All experiments starting in '97 correctly simulated the evolution of the '97 El Niño, although the amplitude was slightly underestimated. While the ocean was pre‐conditioned to create an El Niño already in '96, the model correctly stayed in the cold (La Niña) phase initially. All experiments initialized in '97 forecast a La Niña event for the middle of'98

Global transpiration data from sap flow measurements : the SAPFLUXNET database

Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land-atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/, last access: 8 June 2021). We harmonized and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes, and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks, and remote sensing products to help increase our understanding of plant water use, plant responses to drought, and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository (https://doi.org/10.5281/zenodo.3971689; Poyatos et al., 2020a). The "sapfluxnetr" R package - designed to access, visualize, and process SAPFLUXNET data - is available from CRAN.Peer reviewe

The Effect of Phase Changes of Water on the Development of Volcanic Plumes

A complex thermodynamic--microphysical package has been formulated that is able to deal with the microphysical processes of condensed water vapour in a volcanic plume. The microphysics follows a prognostic bulk approach for cloud water, cloud ice, rain and graupel and the interaction between them. In a standard experiment, this module, applied within a Z. new nonhydrostatic volcano plume model, Active Tracer High Resolution Atmospheric Model ATHAM , produces reasonable concentrations of different types of hydrometeors. Under tropical conditions, the plume gains three times as much water from the environment through entrainment as from the volcanic source. The formed hydrometeors are dominated by the ice phase. Thermodynamic effects of phase changes contribute about 13% to the plume's total thermal energy and therefore have a considerable effect on the vertical development of the plume. q 1998 Elsevier Science B.V. All rights reserved. Keywords: phase change; water; volcanic plume 1

Volcanic Plume Simulation on Large Scales

Z. The plume model ATHAM Active Tracer High Resolution Atmospheric Model is designed to simulate explosive volcanic eruptions for a given mass flux of pyroclastic material under realistic atmospheric background conditions. Based on the assumption that all particles are small the model's equations are simplified such that, besides equations for gaseous, liquid and solid constituents of arbitrary concentrations, only the volume means of momentum and heat are predicted. The exchange of momentum and heat between the fluid's constituents are treated diagnostically. A prognostic turbulence closure scheme describing the entrainment of ambient air into the plume takes into account the anisotropy of the horizontal and vertical components of turbulence. Its length scale is assumed to be isotropic. Microphysical processes such as the exchange of heat and momentum between dry air, water vapor, cloud water, precipitable water, ice crystals and graupel are parameterized. Ash and lapilli represent the spectrum of silicate particles. A diagnostic sedimentation velocity allows for the separation of gas and particles. The model is formulated with an implicit time stepping scheme. The equations of motion and the transport equations for tracers are formulated in flux form in order to guarantee the conservation of momentum and all tracer masses. The heat transport equation is in advective form. The wave equation and the equations for the transport of momentum, heat and tracers are solved using a combined line-relaxation successive overrelaxation scheme. Two-dimensional experiments for symmetric cases with cylindrical coordinates yield qualitatively similar results to other dynamic--thermodynamic models. However, entrainment processes are now computed quantitatively through the turbulence cl..

Sensitivity Study of a Dynamic Thermodynamic Sea Ice Model

A numerical simulation of the seasonal sea ice cover in the Arctic Ocean and the Greenland, Iceland, and Norwegian seas is presented. The sea ice model is extracted from Oberhuber's (1990) coupled sea ice-mixed layer-isopycnal general circulation model and is written in spherical coordinates. The advantage of such a model over previous sea ice models is that it can be easily coupled to either global atmospheric or ocean general circulation models written in spherical coordinates. In this model, thethermodynamics are a modification of that of Parkinson and Washington (1979), while the dynamics use the full Hibler (1979) viscous-plastic rheology