Cloud Adiabaticity and Its Relationship to Marine Stratocumulus Characteristics Over the Northeast Pacific Ocean

Cloud adiabaticity (α) is defined as the ratio of the actual liquid water path (LWP_(measured)) in a cloud to its corresponding adiabatic value (LWP_(ad)). Processes such as drizzle and entrainment can lead to subadiabatic LWP_(measured). This study examines α and its relationship to microphysical properties for 86 cloud events over the Northeast Pacific Ocean based on data collected during four separate summertime airborne campaigns. For the study region, α was found to be 0.766 ± 0.134. For most cases, clouds with a low value of α were found to have lower droplet number concentration (N_d), higher droplet effective radius (r_e), higher relative dispersion (d), and higher rain rate (R). The subcloud aerosol concentration (N_a) was often less for the low‐α cases. The relationship between α and the vertical profiles and cloud‐top characteristics for both the cloud droplet‐only spectrum and full spectrum (cloud and rain droplets) is also examined. Inclusion of rain droplets produced a larger change in d for the low‐α clouds as compared to the high‐α clouds. On average, R increased at cloud top for high‐α clouds but decreased at cloud top for low‐α clouds. Accounting for α when estimating N_d from Moderate Resolution Imaging Spectroradiometer retrievals results in better agreement with in situ N_d values. Results of this work motivate the need for additional focus on the factors governing α, such as cloud type, and implications of its value, especially for remote‐sensing retrievals

Two-Dimensional Helioseismic Power, Phase, and Coherence Spectra of {\it Solar Dynamics Observatory} Photospheric and Chromospheric Observables

While the {\it Helioseismic and Magnetic Imager} (HMI) onboard the {\it Solar Dynamics Observatory} (SDO) provides Doppler velocity [$V$], continuum intensity [$I_C$], and line-depth [$Ld$] observations, each of which is sensitive to the five-minute acoustic spectrum, the {\it Atmospheric Imaging Array} (AIA) also observes at wavelengths -- specifically the 1600 and 1700 Angstrom bands -- that are partly formed in the upper photosphere and have good sensitivity to acoustic modes. In this article we consider the characteristics of the spatio--temporal Fourier spectra in AIA and HMI observables for a 15-degree region around NOAA Active Region 11072. We map the spatio--temporal-power distribution for the different observables and the HMI Line Core [$I_L$], or Continuum minus Line Depth, and the phase and coherence functions for selected observable pairs, as a function of position and frequency. Five-minute oscillation power in all observables is suppressed in the sunspot and also in plage areas. Above the acoustic cut-off frequency, the behaviour is more complicated: power in HMI $I_C$ is still suppressed in the presence of surface magnetic fields, while power in HMI $I_L$ and the AIA bands is suppressed in areas of surface field but enhanced in an extended area around the active region, and power in HMI $V$ is enhanced in a narrow zone around strong-field concentrations and suppressed in a wider surrounding area. The relative phase of the observables, and their cross-coherence functions, are also altered around the active region. These effects may help us to understand the interaction of waves and magnetic fields in the different layers of the photosphere, and will need to be taken into account in multi-wavelength local helioseismic analysis of active regions.Comment: 18 pages, 15 figures, to be published in Solar Physic

Stubborn Aerosol: Why Particulate Mass Concentrations Do Not Drop During the Wet Season in Metro Manila, Philippines

Wet scavenging is the most important sink for particulate matter (PM) and is expected to decrease PM concentrations in the wet season. However, Metro Manila, Philippines has highly similar PM mass across seasons despite large differences in seasonal rainfall. It is important to identify factors contributing to seasonally consistent PM mass as these may be present in similar developing megacities besides Metro Manila, leading to PM accumulation and posing significant health risks. We use size-resolved aerosol composition, aerosol optical depth, and meteorological data to reveal that the seasonally consistent PM mass in Metro Manila is due to (1) opposing seasonal cycles of black carbon and water-soluble PM, (2) inefficient scavenging by short rain events (\u3c1 h), and (3) the high frequency (50%) of these short rain events. Water-soluble PM was most sensitive to scavenging within the 0.18–1.0 μm and 1.8–5.6 μm size ranges but more clearly for rain events lasting over an hour, pointing to the importance of rain duration for efficient scavenging. We demonstrate that the presence of rain does not imply wet scavenging is taking place efficiently and rain characteristics are critical to properly estimating wet scavenging. In a changing climate, our understanding of factors such as rain duration and aerosol accumulation will become more important for guiding air quality-related policymaking and ensuring sustainable growth in developing megacities

Long-range aerosol transport and impacts on size-resolved aerosol composition in Metro Manila, Philippines

This study analyzes long-range transport of aerosol and aerosol chemical characteristics based on instances of high- and low-aerosol-loading events determined via ground-based size-resolved aerosol measurements collected at the Manila Observatory in Metro Manila, Philippines, from July to October 2018. Multiple data sources, including models, remote sensing, and in situ measurements, are used to analyze the impacts of long-range aerosol transport on Metro Manila and the conditions at the local and synoptic scales facilitating this transport. Through the use of case studies, evidence of long-range transport of biomass burning aerosol and continental emissions is identified in Metro Manila. Long-range transport of biomass burning aerosol from the Maritime Continent, bolstered by southwesterly flow and permitted by low rainfall, was identified through model results and the presence of biomass burning tracers (e.g., K, Rb) in the ground-based measurements. The impacts of emissions transported from continental East Asia on the aerosol characteristics in Metro Manila are also identified; for one of the events analyzed, this transport was facilitated by the nearby passage of a typhoon. Changes in the aerosol size distributions, water-soluble chemical composition, and contributions of various organic aerosol species to the total water-soluble organic aerosol were examined for the different cases. The events impacted by biomass burning transport had the overall highest concentration of water-soluble organic acids, while the events impacted by long-range transport from continental East Asia showed high percent contributions from shorter-chain dicarboxylic acids (i.e., oxalate) that are often representative of photochemical and aqueous processing in the atmosphere. The low-aerosol-loading event was subject to a larger precipitation accumulation than the high-aerosol events, indicative of wet scavenging as an aerosol sink in the study region. This low-aerosol event was characterized by a larger relative contribution from supermicrometer aerosols and had a higher percent contribution from longer-chain dicarboxylic acids (i.e., maleate) to the water-soluble organic aerosol fraction, indicating the importance of both primary aerosol emissions and local emissions

Sources and characteristics of size-resolved particulate organic acids and methanesulfonate in a coastal megacity: Manila, Philippines

A 16-month (July 2018–October 2019) dataset of size-resolved aerosol composition is used to examine the sources and characteristics of five organic acids (oxalate, succinate, adipate, maleate, phthalate) and methanesulfonate (MSA) in Metro Manila, Philippines. As one of the most polluted megacities globally, Metro Manila offers a view of how diverse sources and meteorology impact the relative amounts and size distributions of these species. A total of 66 sample sets were collected with a Micro-Orifice Uniform Deposit Impactor (MOUDI), of which 54 sets were analyzed for composition. Organic acids and MSA surprisingly were less abundant than in other global regions that are also densely populated. The combined species accounted for an average of 0.80 ± 0.66 % of total gravimetric mass between 0.056 and 18 µm, still leaving 33.74 % of mass unaccounted for after considering black carbon and water-soluble ions and elements. The unresolved mass is suggested to consist of non-water-soluble metals as well as both water-soluble and non-water-soluble organics. Oxalate was approximately an order of magnitude more abundant than the other five species (149 ± 94 ng m−3 versus others being \u3c 10 ng m−3) across the 0.056–18 µm size range. Both positive matrix factorization (PMF) and correlation analysis are conducted with tracer species to investigate the possible sources of organic acids and MSA. Enhanced biomass burning influence in the 2018 southwest monsoon resulted in especially high levels of submicrometer succinate, MSA, oxalate, and phthalate. Peculiarly, MSA had negligible contributions from marine sources but instead was linked to biomass burning and combustion. Enhanced precipitation during the two monsoon seasons (8 June–4 October 2018 and 14 June–7 October 2019) coincided with a stronger influence from local emissions rather than long-range transport, leading to notable concentration enhancements in both the sub- and supermicrometer ranges for some species (e.g., maleate and phthalate). While secondary formation via gas-to-particle conversion is consistent with submicrometer peaks for the organic acids and MSA, several species (i.e., phthalate, adipate, succinate, oxalate) exhibited a prominent peak in the coarse mode, largely owing to their association with crustal emissions (i.e., more alkaline aerosol type) rather than sea salt. Oxalate\u27s strong association with sulfate in the submicrometer mode supports an aqueous-phase formation pathway for the study region. However, high concentrations during periods of low rain and high solar radiation suggest photo-oxidation is an important formation pathway

Biomass Burning Plumes in the Vicinity of the California Coast: Airborne Characterization of Physicochemical Properties, Heating Rates, and Spatiotemporal Features

This study characterizes in situ airborne properties associated with biomass burning (BB) plumes in the vicinity of the California coast. Out of 231 total aircraft soundings in July–August 2013 and 2016, 81 were impacted by BB layers. A number of vertical characteristics of BB layers are summarized in this work (altitude, location relative to cloud top height, thickness, number of vertically adjacent layers, interlayer distances) in addition to differences in vertical aerosol concentration profiles due to either surface type (e.g., land or ocean) or time of day. Significant BB layer stratification occurred, especially over ocean versus land, with the majority of layers in the free troposphere and within 100 m of the boundary layer top. Heating rate profiles demonstrated the combined effect of cloud and BB layers and their mutual interactions, with enhanced heating in BB layers with clouds present underneath. Aerosol size distribution data are summarized below and above the boundary layer, with a notable finding being enhanced concentrations of supermicrometer particles in BB conditions. A plume aging case study revealed the dominance of organics in the free troposphere, with secondary production of inorganic and organic species and coagulation as a function of distance from fire source up to 450 km. Rather than higher horizontal and vertical resolution, a new smoke injection height method was the source of improved agreement for the vertical distribution of BB aerosol in the Navy Aerosol Analysis and Prediction System model when compared to airborne data

An annual time series of weekly size-resolved aerosol properties in the megacity of Metro Manila, Philippines

Size-resolved aerosol samples were collected in Metro Manila between July 2018 and October 2019. Two Micro-Orifice Uniform Deposit Impactors (MOUDI) were deployed at Manila Observatory in Quezon City, Metro Manila with samples collected on a weekly basis for water-soluble speciation and mass quantification. Additional sets were collected for gravimetric and black carbon analysis, including during special events such as holidays. The unique aspect of the presented data is a year-long record with weekly frequency of size-resolved aerosol composition in a highly populated megacity where there is a lack of measurements. The data are suitable for research to understand the sources, evolution, and fate of atmospheric aerosols, as well as studies focusing on phenomena such as aerosol-cloud-precipitation-meteorology interactions, regional climate, boundary layer processes, and health effects. The dataset can be used to initialize, validate, and/or improve models and remote sensing algorithms

Particulate Oxalate-To-Sulfate Ratio as an Aqueous Processing Marker: Similarity Across Field Campaigns and Limitations

Leveraging aerosol data from multiple airborne and surface-based field campaigns encompassing diverse environmental conditions, we calculate statistics of the oxalate-sulfate mass ratio (median: 0.0217; 95% confidence interval: 0.0154–0.0296; R = 0.76; N = 2,948). Ground-based measurements of the oxalate-sulfate ratio fall within our 95% confidence interval, suggesting the range is robust within the mixed layer for the submicrometer particle size range. We demonstrate that dust and biomass burning emissions can separately bias this ratio toward higher values by at least one order of magnitude. In the absence of these confounding factors, the 95% confidence interval of the ratio may be used to estimate the relative extent of aqueous processing by comparing inferred oxalate concentrations between air masses, with the assumption that sulfate primarily originates from aqueous processing