21 research outputs found
Modeled and Observed Volcanic Aerosol Control on Stratospheric NOy and Cly
Decreases in stratospheric NOx associated with enhanced aerosol have been observed after large volcanic eruptions, for example, after the eruption of Mount Pinatubo in 1991. While the 1991 Mount Pinatubo eruption was the last large explosive eruption, recent studies have shed light on the impacts of moderate-sized eruptions since the year 2000 on the global stratospheric aerosol budget. We use an ensemble of simulations from a coupled climate-chemistry model to quantify and analyze changes in NO and NO2 (NOx), N2O5, HNO3, ClO, and ClONO2 during periods of increased stratospheric volcanic aerosol concentrations since 2000. By using an ensemble approach, we are able to distinguish forced responses from internal variability. We also compare the model ensemble results to satellite measurements of these changes in atmospheric composition, including measurements from the Optical Spectrograph and Infrared Imaging Spectrometer on the Odin satellite and the Aura Microwave Limb Sounder. We find decreases in stratospheric NOx concentrations up to 20 hPa, consistent with increases in stratospheric HNO3 concentrations. The HNO3 perturbations also extend higher, up to 5 hPa, associated with periods of increased volcanic aerosol concentrations in both model simulations and observations, though correlations with volcanic aerosol are considerably higher in the model simulations. The model simulates increases in ClO at altitudes and magnitudes similar to the NOx reductions, but this response is below the detectable limit in the available observations (100 pptv). We also demonstrate the value of accounting for transport-related anomalies of atmospheric trace gases by regression onto N2O anomalies
The G4Foam Experiment: global climate impacts of regional ocean albedo modification
Reducing insolation has been proposed as a geoengineering
response to global warming. Here we present the results of climate model
simulations of a unique Geoengineering Model Intercomparison Project Testbed
experiment to investigate the benefits and risks of a scheme that would
brighten certain oceanic regions. The National Center for Atmospheric
Research CESM CAM4-Chem global climate model was modified to simulate a
scheme in which the albedo of the ocean surface is increased over the
subtropical ocean gyres in the Southern Hemisphere. In theory, this could be
accomplished using a stable, nondispersive foam, comprised of tiny, highly
reflective microbubbles. Such a foam has been developed under idealized
conditions, although deployment at a large scale is presently infeasible. We
conducted three ensemble members of a simulation (G4Foam) from 2020 through
to 2069 in which the albedo of the ocean surface is set to 0.15 (an increase of
150 %) over the three subtropical ocean gyres in the Southern Hemisphere,
against a background of the RCP6.0 (representative concentration pathway
resulting in +6 W m<sup>−2</sup> radiative forcing by 2100) scenario. After
2069, geoengineering is ceased, and the simulation is run for an additional
20 years. Global mean surface temperature in G4Foam is 0.6 K lower than
RCP6.0, with statistically significant cooling relative to RCP6.0 south of
30° N. There is an increase in rainfall over land, most
pronouncedly in the tropics during the June–July–August season, relative to
both G4SSA (specified stratospheric aerosols) and RCP6.0. Heavily populated
and highly cultivated regions throughout the tropics, including the Sahel,
southern Asia, the Maritime Continent, Central America, and much of the
Amazon experience a statistically significant increase in precipitation
minus evaporation. The temperature response to the relatively modest global
average forcing of −1.5 W m<sup>−2</sup> is amplified through a series of
positive cloud feedbacks, in which more shortwave radiation is reflected.
The precipitation response is primarily the result of the intensification of
the southern Hadley cell, as its mean position migrates northward and away
from the Equator in response to the asymmetric cooling
Modeling the 1783–1784 Laki Eruption in Iceland: 1. Aerosol Evolution and Global Stratospheric Circulation Impacts
E-learning to Improve Healthcare Professionals' Attitudes and Practices on Breastfeeding
Breastfeeding training has a crucial role in increasing healthcare professionals' attitudes and in improving professional support for breastfeeding. The collaboration between the Italian National Institute of Health, UNICEF, and the Local Health Authority of Milan has led to the development of an online course on lactation and infant feeding practices
Ionic conductivity studies of chitosan-based polymer electrolytes doped with adipic acid
Fabrication of a wearable antenna with defected ground structure on a flexible TPU-polyester substrate
Abstract
This work presents a patch antenna with defected ground structure (DGS) on flexible materials for wearable applications. It is fed a 50 Ω inset feed and designed for operation at 2.45 GHz on a thermoplastic polyurethane-polyester fabric substrate. The DGS are integrated to ensure a compact design and improved bandwidth, efficiency, and gain. Simulations indicated that the antenna bandwidth is enhanced from 28.4 MHz without DGS to 79.3 MHz. Besides that, its gain is also improved from 2.01 dBi without DGS to 3.62 dBi and efficiency from 30% to 74%. Both antenna designs are fabricated and measured and provide good results and performance with efficiency greater than 50%