Analysis of MONARC and ACTIVATE Airborne Aerosol Data for Aerosol-Cloud Interaction Investigations: Efficacy of Stairstepping Flight Legs for Airborne In Situ Sampling

Abstract

A challenging aspect of conducting airborne in situ observations of the atmosphere is how to optimize flight plans for specific objectives and constraints associated with weather and flight restrictions. For aerosol-cloud interaction research, two recent campaigns utilized a “stairstepping” approach whereby an aircraft conducts level legs at various altitudes while moving forward with each subsequent leg: the 2019 MONterey Aerosol Research Campaign (MONARC) over the northeast Pacific and the 2020–2022 Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) over the northwest Atlantic. We examine the homogeneity of several atmospheric variables both vertically and horizontally in the marine boundary layer with a focus on the sub-cloud environment. In well-mixed boundary layers, there was generally good horizontal and vertical homogeneity in potential temperature, winds, water vapor mixing ratio, various trace gases, and many aerosol variables. Selected aerosol variables exhibited the most variability owing to sensitivity to humidity and near-cloud conditions (supermicrometer aerosol concentrations), coastal pollution gradients (e.g., organic aerosol mass), and small spatial scale phenomena such as new particle formation (aerosol number concentration for particles with diameter >3 nm). Illustrative cases are described when stairstepping can pose issues requiring extra caution for data analysis: (i) poor vertical mixing and layers decoupled from those below; (ii) multiple cloud layers; (iii) fluctuating cloud base/top and boundary layer top heights; and (iv) horizontal variability across specific features leading to sharp gradients such as right near coastlines and over the Gulf Stream with strong sea surface temperature changes. Results from this study provide a guide both for future studies aiming to examine these mission datasets and for designing new airborne campaigns.

Airborne HSRL-2 measurements of elevated aerosol depolarization associated with non-spherical sea salt

“…The majority (~90%) of these flights were statistical survey flights. Brunke et al (2022) and Dadashazar et al (2022) provide descriptions of these flight patterns and maps showing flight locations.…”

Spatially-coordinated airborne data and complementary products for aerosol, gas, cloud, and meteorological studies: The NASA ACTIVATE dataset

“…Occasionally deviations occurred to these leg orders for both ensemble types based on atmospheric conditions and air traffic control challenges requiring changes in altitude. The time span (distance) of each leg and cloud ensemble was ~3.3 min (~24 km) and ~35 min (~250 km), respectively, while clear ensembles were typically ~15 min and ~100 km (Dadashazar et al, 2022b). Across 162 final joint flights, all but 12 were classified as statistical surveys (93%), with classifications of each flight shown in Table 2.…”

“…This resulted in an approach of flying "statistical surveys" comprised of repeated "ensembles" that we describe below (sect. 2.2) and that have been discussed in detail elsewhere for ACTIVATE flights (Dadashazar et al, 2022b).…”

Dimethylamine in cloud water: a case study over the northwest Atlantic Ocean

“…The Falcon ight path typically constituted a series of legs below, in, and above clouds. 58 The most relevant legs to this study are the "below cloud base (BCB)" legs from which we used meteorological data, and the "above cloud base (ACB)" and "below cloud top (BCT)" legs where cloud water samples were gathered. Cloud water samples might have also been collected during slant ascents and descents between the legs whenever the aircra was in cloud.…”

“…The Falcon flight path typically constituted a series of legs below, in, and above clouds. 58 The most relevant legs to this study are the “below cloud base (BCB)” legs from which we used meteorological data, and the “above cloud base (ACB)” and “below cloud top (BCT)” legs where cloud water samples were gathered. Cloud water samples might have also been collected during slant ascents and descents between the legs whenever the aircraft was in cloud.…”