ALBERT

Description: Ice nucleating particles (INPs) are required for initial ice crystal formation in clouds at temperatures warmer than about -36 °C and thus play a crucial role in cloud and precipitation formation. Biomass burning has been found to be a source of INPs in previous studies, and is also a major contributor to atmospheric black carbon (BC) concentrations. This study focuses on isolating the BC contribution to the INP population associated with biomass combustion. Emissions of condensation mode INPs from a number of globally relevant biomass fuels were measured at -30 °C and above water saturation as fires progressed from ignition to extinguishment in a laboratory setting. Number emissions of INPs were found to be highest during intense flaming combustion (modified combustion efficiency 〉 0.95). Overall, combustion emissions from 13 of 22 different biomass fuel types produced measurable INP concentrations for at least one replicate experiment. On average, all burns that produced measureable INPs had higher combustion efficiency, which is associated with higher BC emissions, than those that did not produce measureable INPs. Across all burns that produced measureable INPs, concentrations ranged from 0.1 – 10 cm -3 and the median emission factor was about 2 × 10 7 INPs per kilogram of fuel burned. For a subset of the burns, the contribution of refractory black carbon (rBC) to INP concentrations was determined by removing rBC via laser induced incandescence (LII). Reductions in INPs of 0 – 70% were observed, indicating an important contribution of rBC particles to INP concentrations for some burns, especially marsh grasses.

Description: Mode Selective Enhanced Surveillance (Mode-S EHS) reports are aircraft-based observations that have value in numerical weather prediction (NWP). These reports contain the aircraft's state vector in terms of its speed, direction, altitude and Mach number. Using the state vector, meteorological observations of temperature and horizontal wind can be derived. However, Mode-S EHS processing reduces the precision of the state vector from 16-bit to 10-bit binary representation. We use full precision data from research grade instruments, on-board the United Kingdom's Facility for Atmospheric Airborne Measurements, to emulate Mode-S EHS reports and to compare with derived observations. We aim to understand the observation errors due to the reduced precision of Mode-S EHS reports. We derive error models to estimate these observation errors. The temperature error increases from 1.25 K to 2.5 K between an altitude of 10 km and the surface due to its dependency on Mach number and also Mode-S EHS precision. For the cases studied, the zonal wind error is around 0.50 ms − 1 and the meridional wind error is 0.25 ms − 1 . The wind is also subject to systematic errors that are directionally dependent. We conclude that Mode-S EHS derived horizontal winds are suitable for data assimilation in high-resolution NWP. Temperature reports may be usable when aggregated from multiple aircraft. While these reduced precision, high frequency data provide useful, albeit noisy, observations; direct reports of the higher precision data would be preferable.

Description: Continuous measurements of atmospheric methane (CH 4 ) mole fractions measured by NOAA's Global Greenhouse Gas Reference Network in Barrow, AK (BRW), show strong enhancements above background values when winds come from the land sector from July through December from 1986-2014, indicating that emissions from arctic tundra continue through autumn and into early winter. Twenty-nine years of measurements show little change in seasonal mean land-sector CH 4 enhancements, despite an increase in annual mean temperatures of 1.2 ± 0.8 °C/decade (2σ). The record does reveal small increases in CH 4 enhancements in November and December after 2010 due to increased late-season emissions. The lack of significant long-term trends suggests more complex biogeochemical processes are counteracting the observed short-term (monthly) temperature sensitivity of 5.0 ± 3.6 ppb CH 4 /°C. Our results suggest that even the observed short-term temperature sensitivity from the Arctic will have little impact on the global atmospheric CH 4 budget in the long-term if future trajectories evolve with the same temperature sensitivity.

Description: The surface radiation budget (SRB) is modulated by smoke aerosols that attenuate solar and emit thermal infrared radiation. Direct radiative impacts of smoke depend on several factors that lead to large uncertainties in assessing how wildfires influence climate. To quantify the impact of smoke on the SRB, evaluations of the longwave (LW) as well as the shortwave (SW) radiative forcing efficiencies (RFElw and RFEsw) are needed. Radiative forcing efficiency (RFE) is defined as the change in net irradiance per unit increase in aerosol optical depth at 500 nm (AOD500). An opportunity to evaluate RFElw and RFEsw of smoke presented itself on 6–7 September 2010, when a wildfire burned west of Boulder, Colorado. Smoke passed over sites where SRB, atmospheric state, and AOD measurements were being made. Values of RFE were derived empirically from coincident SRB and AOD measurements made over a range of Sun angles. RFEsw ranged between −65 and −194 Wm−2AOD500−1 as solar zenith angles decreased from 73° to 34° (at solar noon). RFElw averaged ∼10 (±7) Wm−2AOD500−1 throughout the daylight hours. During the event, the diurnally integrated value of net RFE was −51.5 Wm−2AOD500−1, revealing the dominance of SW cooling over LW warming attributed to the smoke. In response, the surface under the smoke plume cooled by 2°–5°C during the day, depending on the smoke's opacity. No evaluation of nighttime effects were possible, although very slight warming may have occurred owing to thermal emissions from the plume.

Description: The first Nitryl Chloride (ClNO 2 ) measurements in the United Kingdom were made during the summer 2012 ClearfLo campaign with a chemical ionisation mass spectrometer, utilising an I − ionisation scheme. Concentrations of ClNO 2 exceeded detectable limits (11 ppt) every night with a maximum concentration of 724 ppt. A diurnal profile of ClNO 2 peaking between 4 and 5 am, decreasing directly after sunrise was observed. Concentrations of ClNO 2 above the detection limit are generally observed between 8 pm and 11 am. Different ratios of the production of ClNO 2 : N 2 O 5 were observed throughout with both positive and negative correlations between the two species being reported. The photolysis of ClNO 2 and a box model utilising the Master Chemical Mechanism modified to include chlorine chemistry was used to calculate Cl atom concentrations. Simultaneous measurements of hydroxyl radicals (OH) using low pressure laser-induced fluorescence and ozone enabled the relative importance of the oxidation of three groups of measured VOCs (alkanes, alkenes and alkynes) by OH radicals, Cl atoms and O 3 to be compared. For the day with the maximum calculated Cl atom concentration, Cl atoms in the early morning were the dominant oxidant for alkanes, and over the entire day contributed 15%, 3% and 26% towards the oxidation of alkanes, alkenes and alkynes, respectively.

Description: A massive ice body buried under several decimeters of dry regolith in Beacon Valley, Antarctica is believed to be more than 1 Ma old and perhaps over 8.1 Ma; however, vapor-diffusion models suggest that subsurface ice in this region is not stable under current climate conditions. To better understand the controls on sublimation rates and stability of this massive ice, we have modeled vapor-diffusion process utilizing 12 years of climate and soil temperature data from 1999 to 2011, including field measurements of episodic snow cover and snowmelt events that have not been represented in previous models of the ground-ice sublimation. The model is then extended to reconstruct the sublimation history over the last 200 ka using paleo-temperatures estimated from ice-core data from nearby Taylor Dome and a defined relationship between atmospheric temperature and humidity derived from our meteorological records. The model quantifies the impact of episodic snow events; they account for a nearly 30% reduction in the massive ice loss. The sublimation rate averages 0.11 mm ice a −1 between 1999 and 2011 in Beacon Valley. Parameterized with past environmental conditions and assuming the same regolith thickness, the modeled sublimation rate in Beacon Valley averages 0.09 mm ice a −1 for the last 200 ka, comparable to the long-term average rate estimated independently from various studies based on cosmogenic isotopes. This study provides a realistic estimate of the long-term sublimation history and supports the inference that the buried ice in Beacon Valley is older than 1 Ma.

Description: Measurements of OH and HO2 concentrations were made at the surface of the eastern coast of the Hudson Bay during the COBRA campaign from February 18th to March 8th 2008. Diurnally averaged OH and HO2 concentrations peaked at 1.16 (±1.02) × 106 molecule cm−3 and 1.42 (±0.64) × 108 molecule cm−3 respectively. A box-model, constrained to supporting observations, is used to access the radical budget in this cold, northerly environment. Formaldehyde (HCHO) photolysis is found to be the dominant daytime radical source, providing 74% of the observed HOx. A considerable (〉80% of the total source) surface HCHO source is required to reconcile the model and observed HCHO concentrations. Model simulations also suggest significant roles for the heterogeneous loss of HO2 and for halogen chemistry in the cycling of HO2 to OH. The formation of HO2NO2 is identified as an important radical reservoir, reducing HOx concentrations during the day and enhancing them at night. This impacts both local oxidizing capacity and reduces local ozone production by approximately 30%. The sensitivity of the local chemistry to uncertainties in these processes is explored. The majority of these processes are not currently represented in global chemistry models.

Description: The internal structure, loading processes, and effective boundary conditions of a volcano control the deformation observed at the Earth's surface. Using finite element models (FEMs), we simulate the response due to a pressurized magma chamber embedded in a domain having a distribution of elastic material properties. We present the Pinned Mesh Perturbation method (PMP) to automate the mesh generation process in response to perturbations of the position of a simulated magma chamber within an FEM domain. Using InSAR-observed deformation for the 1997 eruption of Okmok volcano, Alaska, as an example, we combine PMP with nested Monte Carlo methods to estimate a set of linear and nonlinear parameters that characterize the depressurization and location of the magma chamber beneath Okmok's caldera. The three-dimensional FEMs used in the PMP method simulate the distribution of material properties of tomography models and account for the irregular geometry of the topography and bathymetry. The estimated depth of an assumed spherical magma chamber is 3527−54+55 m below sea level and is sensitive to the distribution of material properties. This depth is consistent with lithostatic pressure constraints and very long period tremor observations. The fit of this FEM to the InSAR data is a significant improvement, at the 95% confidence level, compared to the fit of a corresponding FEM having homogeneous material properties. The methods presented here allow us to construct deformation models that integrate tomography models with geodetic observations, in an effort to achieve a deeper understanding of active volcanoes.

Description: Abstract Borates and borosilicates are potential candidates for the design and development of glass formulations with important industrial and technological applications. A major challenge that retards the pace of development of borate/borosilicate based glasses using predictive modeling is the lack of reliable computational models to predict the structure‐property relationships in these glasses over a wide compositional space. A major hindrance in this pursuit has been the complexity of boron‐oxygen bonding due to which it has been difficult to develop adequate B–O interatomic potentials. In this article, we have evaluated the performance of three B–O interatomic potential models recently developed by Bauchy et al [J. Non‐Cryst. Solids, 2018, 498, 294–304], Du et al [J. Am. Ceram. Soc. https://doi.org/10.1111/jace.16082] and Edèn et al [Phys. Chem. Chem. Phys., 2018, 20, 8192–8209] aiming to reproduce the short‐to‐medium range structures of sodium borosilicate glasses in the system 25 Na2O x B2O3 (75 − x) SiO2 (x = 0‐75 mol%). To evaluate the different force fields, we have computed at the density functional theory level the NMR parameters of 11B, 23Na, and 29Si of the models generated with the three potentials and the simulated MAS NMR spectra compared with the experimental counterparts. It was observed that the rigid ionic models proposed by Bauchy and Du can both reliably reproduce the partitioning between BO3 and BO4 species of the investigated glasses, along with the local environment around sodium in the glass structure. However, they do not accurately reproduce the second coordination sphere of silicon ions and the Si–O–T (T = Si, B) and B‐O‐T distribution angles in the investigated compositional space which strongly affect the NMR parameters and final spectral shape. On the other hand, the core‐shell parameterization model proposed by Edén underestimates the fraction of BO4 species of the glass with composition 25Na2O 18.4B2O3 56.6SiO2 but can accurately reproduce the shape of the 11B and 29Si MAS‐NMR spectra of the glasses investigations due to the narrower B–O–T and Si‐O‐T bond angle distributions. Finally, the effect of the number of boron atoms (also distinguishing the BO3 and BO4 units) in the second coordination sphere of the network former cations on the NMR parameters have been evaluated.

Description: Abstract Correlations between springtime stratospheric ozone extremes and subsequent surface temperatures have been previously reported for both models and observations at particular locations in the Northern Hemisphere. Here we quantify for the first time the potential use of ozone information for Northern Hemisphere seasonal forecasts, using observations and a nine‐member chemistry climate model ensemble. The ensemble composite correlations between March total column ozone (TCO) and April surface temperatures display a similar structure to observations, but with slightly lower correlation magnitudes. This is likely due to the larger number of cases smoothing out sampling error in the pattern, which is visible in the difference between correlations calculated from individual ensemble members. Using a linear regression model with March TCO as the predictor, predictions of the following April surface temperatures in regions that show large correlations are possible up to 4 years following the regression model end date in individual ensemble members, and up to 6 years in observations. We create an empirical forecast model to predict the sign of the observed as well as the modeled surface temperature anomalies using March TCO. Through a leave‐three‐years‐out cross‐validation method, we show that March TCO can forecast the sign of the April surface temperature anomalies well in parts of Eurasia that show the lowest model internal variability.