Regularity of higher codimension area minimizing integral currents

This lecture notes are an expanded version of the course given at the ERC-School on Geometric Measure Theory and Real Analysis, held in Pisa, September 30th - October 30th 2013. The lectures aim to explain the main steps of a new proof of the partial regularity of area minimizing integer rectifiable currents in higher codimension, due originally to F. Almgren, which is contained in a series of papers in collaboration with C. De Lellis (University of Zurich).Comment: This text will appear in "Geometric Measure Theory and Real Analysis", pp. 131--192, Proceedings of the ERC school in Pisa (2013), L. Ambrosio Ed., Edizioni SNS (CRM Series

Numerical simulation of the impact of COVID-19 lockdown on tropospheric composition and aerosol radiative forcing in Europe

Aerosols influence the Earth\u27s energy balance directly by modifying the radiation transfer and indirectly by altering the cloud microphysics. Anthropogenic aerosol emissions dropped considerably when the global COVID-19 pandemic resulted in severe restraints on mobility, production, and public life in spring 2020. We assess the effects of these reduced emissions on direct and indirect aerosol radiative forcing over Europe, excluding contributions from contrails. We simulate the atmospheric composition with the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model in a baseline (business-as-usual) and a reduced emission scenario. The model results are compared to aircraft observations from the BLUESKY aircraft campaign performed in May–June 2020 over Europe. The model agrees well with most of the observations, except for sulfur dioxide, particulate sulfate, and nitrate in the upper troposphere, likely due to a biased representation of stratospheric aerosol chemistry and missing information about volcanic eruptions. The comparison with a baseline scenario shows that the largest relative differences for tracers and aerosols are found in the upper troposphere, around the aircraft cruise altitude, due to the reduced aircraft emissions, while the largest absolute changes are present at the surface. We also find an increase in all-sky shortwave radiation of 0.21 ± 0.05 W m⁻² at the surface in Europe for May 2020, solely attributable to the direct aerosol effect, which is dominated by decreased aerosol scattering of sunlight, followed by reduced aerosol absorption caused by lower concentrations of inorganic and black carbon aerosols in the troposphere. A further increase in shortwave radiation from aerosol indirect effects was found to be much smaller than its variability. Impacts on ice crystal concentrations, cloud droplet number concentrations, and effective crystal radii are found to be negligible

A direct approach to Plateau's problem in any codimension

This paper proposes a direct approach to solve the Plateau's problem in codimension higher than one. The problem is formulated as the minimization of the Hausdorff measure among a family of d-rectifiable closed subsets of Rn: following the previous work [13], the existence result is obtained by a compactness principle valid under fairly general assumptions on the class of competitors. Such class is then specified to give meaning to boundary conditions. We also show that the obtained minimizers are regular up to a set of dimension less than (d-1). \ua9 2015 Elsevier Inc. All rights reserved

Simulation of organics in the atmosphere : evaluation of EMACv2.54 with the Mainz Organic Mechanism (MOM) coupled to the ORACLE (v1.0) submodel

An updated and expanded representation of organics in the chemistry general circulation model EMAC (ECHAM5/MESSy for Atmospheric Chemistry) has been evaluated. First, the comprehensive Mainz Organic Mechanism (MOM) in the submodel MECCA (Module Efficiently Calculating the Chemistry of the Atmosphere) was activated with explicit degradation of organic species up to five carbon atoms and a simplified mechanism for larger molecules. Second, the ORACLE submodel (version 1.0) now considers condensation on aerosols for all organics in the mechanism. Parameterizations for aerosol yields are used only for the lumped species that are not included in the explicit mechanism. The simultaneous usage of MOM and ORACLE allows an efficient estimation of not only the chemical degradation of the simulated volatile organic compounds but also the contribution of organics to the growth and fate of (organic) aerosol, with the complexity of the mechanism largely increased compared to EMAC simulations with more simplified chemistry. The model evaluation presented here reveals that the OH concentration is reproduced well globally, whereas significant biases for observed oxygenated organics are present. We also investigate the general properties of the aerosols and their composition, showing that the more sophisticated and process-oriented secondary aerosol formation does not degrade the good agreement of previous model configurations with observations at the surface, allowing further research in the field of gas–aerosol interactions

Raw data files from autonomous instruments installed on Floe South in the marginal ice zone northwest of Svalbard in July 2022 as part of RV POLARSTERN expedition PS131 (ATWAICE)

During Polarstern expedition PS131 (ATWAICE: ATlantic WAter pathways to the ICE), a large number of autonomous instruments were installed on three representative ice floes across the marginal ice zone northwest of Svalbard in July 2022. The aim was to investigate sea ice summer melt processes, with a focus on the contribution of the Atlantic water inflow into the region. The attached .zip file includes raw data files obtained from all instruments deployed on the southernmost floe, also referred to as Floe South. Depending on the instrument, the data were transmitted via satellite, collected on internal memory, or both. The instruments were installed on Floe South on 14 July 2022, revisited for maintenance on 21 July 2022, and partially recovered on 31 July 2022. The sensors included 1 ADCP to measure ocean currents, a CTD buoy (SIT) with 5 SBE37IMP, a SIMBA- and a SIMB-type ice mass balance buoy to determine ice surface and bottom melt, an OpenMetBuoy (OMB) and iridium IMU logger for wave detection, two GPS drifters, and 2 timelapse cameras to document surface changes. All instruments performed as expected. All instruments except one OpenMetBuoy were recovered before leaving the study area on 31 July. The processed data will be provided and linked to when available

Raw data files from autonomous instruments installed on Floe Middle in the marginal ice zone northwest of Svalbard in July 2022 as part of RV POLARSTERN expedition PS131 (ATWAICE)

During Polarstern expedition PS131 (ATWAICE: ATlantic WAter pathways to the ICE), a large number of autonomous instruments were installed on three representative ice floes across the marginal ice zone northwest of Svalbard in July 2022. The aim was to investigate sea ice summer melt processes, with a focus on the contribution of the Atlantic water inflow into the region. The attached .zip file includes raw data files obtained from all instruments deployed on Floe Middle, located between Floe North and Floe South. Depending on the instrument, the data were transmitted via satellite, collected on internal memory, or both. The instruments were installed on Floe Middle on 15 July 2022, revisited for maintenance on 22 July 2022, and partially recovered on 31 July 2022. The sensors included 1 ADCP to measure ocean currents, a CTD buoy (SIT) with 5 SBE37IMP and 3 SBE56, a SIMBA-type ice mass balance buoy to determine ice surface and bottom melt, an OpenMetBuoy (OMB) and IMU logger for wave detection, one GPS drifter to mark the ADCP, and 3 timelapse cameras to document surface changes. All instruments performed as expected. All instruments except one OpenMetBuoy were recovered before leaving the study area on 31 July. The processed data will be provided and linked to when available

Numerical simulation of the impact of COVID-19 lockdown on tropospheric composition and aerosol radiative forcing in Europe

Aerosols influence the Earth's energy balance directly by modifying the radiation transfer and indirectly by altering the cloud microphysics. Anthropogenic aerosol emissions dropped considerably when the global COVID-19 pandemic resulted in severe restraints on mobility, production, and public life in spring 2020. We assess the effects of these reduced emissions on direct and indirect aerosol radiative forcing over Europe, excluding contributions from contrails. We simulate the atmospheric composition with the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model in a baseline (business-as-usual) and a reduced emission scenario. The model results are compared to aircraft observations from the BLUESKY aircraft campaign performed in May–June 2020 over Europe. The model agrees well with most of the observations, except for sulfur dioxide, particulate sulfate, and nitrate in the upper troposphere, likely due to a biased representation of stratospheric aerosol chemistry and missing information about volcanic eruptions. The comparison with a baseline scenario shows that the largest relative differences for tracers and aerosols are found in the upper troposphere, around the aircraft cruise altitude, due to the reduced aircraft emissions, while the largest absolute changes are present at the surface. We also find an increase in all-sky shortwave radiation of 0.21 ± 0.05 W m−2 at the surface in Europe for May 2020, solely attributable to the direct aerosol effect, which is dominated by decreased aerosol scattering of sunlight, followed by reduced aerosol absorption caused by lower concentrations of inorganic and black carbon aerosols in the troposphere. A further increase in shortwave radiation from aerosol indirect effects was found to be much smaller than its variability. Impacts on ice crystal concentrations, cloud droplet number concentrations, and effective crystal radii are found to be negligible