• Energy Research

Abstract Ice concentrations in orographic wave clouds at temperatures between −24° and −29°C were shown to be related to aerosol characteristics in nearby clear air during five research flights over the Rocky Mountains. When clouds with influence from colder temperatures were excluded from the dataset, mean ice nuclei and cloud ice number concentrations were very low, on the order of 1–5 L−1. In this environment, ice number concentrations were found to be significantly correlated with the number concentration of larger particles, those larger than both 0.1- and 0.5-μm diameter. A variety of complementary techniques was used to measure aerosol size distributions and chemical composition. Strong correlations were also observed between ice concentrations and the number concentrations of soot and biomass-burning aerosols. Ice nuclei concentrations directly measured in biomass-burning plumes were the highest detected during the project. Taken together, this evidence indicates a potential role for biomass-burning aerosols in ice formation, particularly in regions with relatively low concentrations of other ice nucleating aerosols.

AbstractSeasonal characteristics of aerosol optical properties in Sky Radiometer Network (SKYNET) Hefei site are studied using a sky radiometer from March 2007 to May 2013. The aerosol optical depth (AOD), Angstrom exponent (AE), volume size distributions, single‐scattering albedo (SSA), refractive index, and asymmetry factor (ASY) of aerosols are simultaneously retrieved using the SKYRAD.pack version 4.2 software. During the study period, the AOD varied seasonally, with the maximum value of 1.02 ± 0.42 at 500 nm occurring in the summer, and the highest AOD (1.13 ± 0.42) occurred in June due to stagnant climate conditions and accumulation of polluted aerosols before the East Asian summer monsoon. The variation in AE showed a different pattern, with the minimum (0.97 ± 0.28) and maximum values (1.30 ± 0.22) occurring during the spring and fall seasons, respectively. The relatively low value of AE in spring is related to the emission of Asian dust events. The aerosol volume size distributions can be expressed by the trimodal patterns for each season, consisting of a fine mode with R < 0.6 µm, a coarse mode with R > 2.5 µm, and a middle mode located between them. The real part of the refractive index increased with wavelength (380–870 nm) while the imaginary part of the refractive index decreased for all seasons except for the summer. The seasonal mean values of SSA were 0.97 ± 0.02 (summer), 0.95 ± 0.03 (spring), 0.93 ± 0.04 (autumn), and 0.91 ± 0.04 (winter) at 380 nm indicating more absorbing aerosol in the autumn and winter months. Furthermore, aerosol properties were greatly modified by condensation growth as evidenced by the positive dependencies of AOD, SSA, and ASY on relative humidity.

AbstractThe Chequamegon Heterogeneous Ecosystem Energy-Balance Study Enabled by a High-Density Extensive Array of Detectors 2019 (CHEESEHEAD19) is an ongoing National Science Foundation project based on an intensive field campaign that occurred from June to October 2019. The purpose of the study is to examine how the atmospheric boundary layer (ABL) responds to spatial heterogeneity in surface energy fluxes. One of the main objectives is to test whether lack of energy balance closure measured by eddy covariance (EC) towers is related to mesoscale atmospheric processes. Finally, the project evaluates data-driven methods for scaling surface energy fluxes, with the aim to improve model–data comparison and integration. To address these questions, an extensive suite of ground, tower, profiling, and airborne instrumentation was deployed over a 10 km × 10 km domain of a heterogeneous forest ecosystem in the Chequamegon–Nicolet National Forest in northern Wisconsin, United States, centered on an existing 447-m tower that anchors an AmeriFlux/NOAA supersite (US-PFa/WLEF). The project deployed one of the world’s highest-density networks of above-canopy EC measurements of surface energy fluxes. This tower EC network was coupled with spatial measurements of EC fluxes from aircraft; maps of leaf and canopy properties derived from airborne spectroscopy, ground-based measurements of plant productivity, phenology, and physiology; and atmospheric profiles of wind, water vapor, and temperature using radar, sodar, lidar, microwave radiometers, infrared interferometers, and radiosondes. These observations are being used with large-eddy simulation and scaling experiments to better understand submesoscale processes and improve formulations of subgrid-scale processes in numerical weather and climate models.

Abstract During the Ice in Clouds Experiment–Layer Clouds (ICE-L), aged biomass-burning particles were identified within two orographic wave cloud regions over Wyoming using single-particle mass spectrometry and electron microscopy. Using a suite of instrumentation, particle chemistry was characterized in tandem with cloud microphysics. The aged biomass-burning particles comprised ∼30%–40% by number of the 0.1–1.0-μm clear-air particles and were composed of potassium, organic carbon, elemental carbon, and sulfate. Aerosol mass spectrometry measurements suggested these cloud-processed particles were predominantly sulfate by mass. The first cloud region sampled was characterized by primarily homogeneously nucleated ice particles formed at temperatures near −40°C. The second cloud period was characterized by high cloud droplet concentrations (∼150–300 cm−3) and lower heterogeneously nucleated ice concentrations (7–18 L−1) at cloud temperatures of −24° to −25°C. As expected for the observed particle chemistry and dynamics of the observed wave clouds, few significant differences were observed between the clear-air particles and cloud residues. However, suggestive of a possible heterogeneous nucleation mechanism within the first cloud region, ice residues showed enrichments in the number fractions of soot and mass fractions of black carbon, measured by a single-particle mass spectrometer and a single-particle soot photometer, respectively. In addition, enrichment of biomass-burning particles internally mixed with oxalic acid in both the homogeneously nucleated ice and cloud droplets compared to clear air suggests either preferential activation as cloud condensation nuclei or aqueous phase cloud processing.