Ryan Patnaude

Closed-to-open cell mixed-phase cloud transitions within marine cold air outbreaks remain poorly understood despite their importance to high-latitude climate. The Cold-Air outbreak Experiment in the Sub-Arctic Region (CAESAR) research aircraft sampled a cold and polluted closed-to-open cell transition with cloud-top temperatures below −20 °C and upstream cloud condensation nuclei concentrations surpassing 600 cm ⁻³ . The aerosol likely originates from Siberian industrial emissions. As the boundary layer deepens prior to and across the transition, driven by strong turbulent surface fluxes and aided by a weakening cloud-top inversion, aerosol number concentrations decrease and supercooled droplet sizes increase, causing ice particles to shift from primarily vapor depositional growth towards riming. Precipitation shafts within open-cells contain abundant large graupel (>5 mm diameter) with liquid-equivalent precipitation intensities reaching 3 mm h ⁻¹ . Ice precipitation co-exists with lidar-observed surface cold pools, modulated by entrainment events, juxtaposed with surface-based plumes of warm moist air. Updrafts support liquid water production along convergence boundaries at the upwind cold pool edge. Nonetheless, strong buoyancy fluxes exceeding 200 W m ⁻² prevent sub-cloud decoupling. Ice particle number concentrations increase tenfold across the transition, surpassing 10 L ⁻¹ within open-cells, more than 1000× ice nucleating particle number concentrations. Given that cloud temperatures are too cold for Hallett-Mossop rime splintering, this indicates the importance of other secondary ice production mechanisms. This case expands the observations needed to better understand mixed-phase Arctic cloud processes.

Closed-to-open cell mixed-phase cloud transitions within marine cold air outbreaks subjected to strong turbulent surface fluxes remain poorly understood despite their importance to high-latitude climate. The Cold-Air outbreak Experiment in the Sub-Arctic Region (CAESAR) research aircraft sampled closed-cells with cloud condensation nuclei concentrations surpassing 680 cm^-3, decreasing to 90 cm^-3 across a transition to open-cells. The aerosol likely originated from Siberian industrial emissions. With fetch, liquid water paths (LWPs) increase from 120 g m^-2 to 270 g m^-2 and cloud-top effective diameters increase from 10 μm to 16 μm, coincident with more riming. Ice particle number concentrations (N_i) are generally 2 L^-1 or less, but exceed ice nucleating particle number concentrations by 100x. As the cloud-top inversion weakens and the boundary layer deepens further, ice precipitation co-exists with lidar-observed surface cold pools, modulated by entrainment events, juxtaposed with surface-based plumes of warm moist air. Open-cells contain isolated LWP peaks surpassing 500 g m^-2 collocated with strong updrafts, adjacent to glaciated cloud. N_i surpasses 10 L^-1 at cloud temperatures < -15 °C. Precipitation shafts contain abundant large graupel (> 5 mm diameter) with liquid-equivalent precipitation intensities reaching 3 mm hr^-1 developing cold pools with virtual potential temperature depressions reaching 1.3 K. Nonetheless, buoyancy fluxes of 200-250 W m^-2 prevent sub-cloud decoupling. The updrafts supporting liquid water production occur at the upwind edge of the cold pools. This case expands the observations needed to better understand mixed-phase Arctic cloud processes.

Closed-to-open cell mixed-phase cloud transitions within marine cold air outbreaks subjected to strong turbulent surface fluxes remain poorly understood despite their importance to high-latitude climate. The Cold-Air outbreak Experiment in the Sub-Arctic Region (CAESAR) research aircraft sampled closed-cells with cloud condensation nuclei concentrations surpassing 680 cm^-3, decreasing to 90 cm^-3 across a transition to open-cells. The aerosol likely originated from Siberian industrial emissions. With fetch, liquid water paths (LWPs) increase from 120 g m^-2 to 270 g m^-2 and cloud-top effective diameters increase from 10 μm to 16 μm, coincident with more riming. Ice particle number concentrations (N_i) are generally 2 L^-1 or less, but exceed ice nucleating particle number concentrations by 100x. As the cloud-top inversion weakens and the boundary layer deepens further, ice precipitation co-exists with lidar-observed surface cold pools, modulated by entrainment events, juxtaposed with surface-based plumes of warm moist air. Open-cells contain isolated LWP peaks surpassing 500 g m^-2 collocated with strong updrafts, adjacent to glaciated cloud. N_i surpasses 10 L^-1 at cloud temperatures < -15 °C. Precipitation shafts contain abundant large graupel (> 5 mm diameter) with liquid-equivalent precipitation intensities reaching 3 mm hr^-1 developing cold pools with virtual potential temperature depressions reaching 1.3 K. Nonetheless, buoyancy fluxes of 200-250 W m^-2 prevent sub-cloud decoupling. The updrafts supporting liquid water production occur at the upwind edge of the cold pools. This case expands the observations needed to better understand mixed-phase Arctic cloud processes.

Closed-to-open cell mixed-phase cloud transitions within marine cold air outbreaks subjected to strong turbulent surface fluxes remain poorly understood despite their importance to high-latitude climate. The Cold-Air outbreak Experiment in the Sub-Arctic Region (CAESAR) research aircraft sampled closed-cells with cloud condensation nuclei concentrations surpassing 680 cm^-3, decreasing to 90 cm^-3 across a transition to open-cells. The aerosol likely originated from Siberian industrial emissions. With fetch, liquid water paths (LWPs) increase from 120 g m^-2 to 270 g m^-2 and cloud-top effective diameters increase from 10 μm to 16 μm, coincident with more riming. Ice particle number concentrations (N_i) are generally 2 L^-1 or less, but exceed ice nucleating particle number concentrations by 100x. As the cloud-top inversion weakens and the boundary layer deepens further, ice precipitation co-exists with lidar-observed surface cold pools, modulated by entrainment events, juxtaposed with surface-based plumes of warm moist air. Open-cells contain isolated LWP peaks surpassing 500 g m^-2 collocated with strong updrafts, adjacent to glaciated cloud. N_i surpasses 10 L^-1 at cloud temperatures < -15 °C. Precipitation shafts contain abundant large graupel (> 5 mm diameter) with liquid-equivalent precipitation intensities reaching 3 mm hr^-1 developing cold pools with virtual potential temperature depressions reaching 1.3 K. Nonetheless, buoyancy fluxes of 200-250 W m^-2 prevent sub-cloud decoupling. The updrafts supporting liquid water production occur at the upwind edge of the cold pools. This case expands the observations needed to better understand mixed-phase Arctic cloud processes.

Closed-to-open cell mixed-phase cloud transitions within marine cold air outbreaks subjected to strong turbulent surface fluxes remain poorly understood despite their importance to high-latitude climate. The Cold-Air outbreak Experiment in the Sub-Arctic Region (CAESAR) research aircraft sampled closed-cells with cloud condensation nuclei concentrations surpassing 680 cm-3, decreasing to 90 cm-3 across a transition to open-cells. The aerosol likely originated from Siberian industrial emissions. With fetch, liquid water paths (LWPs) increase from 120 g m-2 to 270 g m-2 and cloud-top effective diameters increase from 10 μm to 16 μm, coincident with more riming. Ice particle number concentrations (Ni) are generally 2 L-1 or less, but exceed ice nucleating particle number concentrations by 100x. As the cloud-top inversion weakens and the boundary layer deepens further, ice precipitation co-exists with lidar-observed surface cold pools, modulated by entrainment events, juxtaposed with surface-based plumes of warm moist air. Open-cells contain isolated LWP peaks surpassing 500 g m-2 collocated with strong updrafts, adjacent to glaciated cloud. Ni surpasses 10 L-1 at cloud temperatures < -15 °C. Precipitation shafts contain abundant large graupel (> 5 mm diameter) with liquid-equivalent precipitation intensities reaching 3 mm hr-1 developing cold pools with virtual potential temperature depressions reaching 1.3 K. Nonetheless, buoyancy fluxes of 200-250 W m-2 prevent sub-cloud decoupling. The updrafts supporting liquid water production occur at the upwind edge of the cold pools. This case expands the observations needed to better understand mixed-phase Arctic cloud processes.

Large-scale models struggle to accurately represent maritime low-level boundary layer clouds, leading to uncertainties in projecting a future climate. This study uses a regime-based approach to assess global climate model representation of warm-phase microphysical processes over the Southern Ocean (SO) and northeast Pacific, regions frequently characterized by the stratocumulus-to-cumulus transition (SCT) regime. In situ aircraft observations collected during the Southern Ocean Clouds, Radiation and Aerosol Transport Experimental Study (SOCRATES) and the Cloud Systems Evolution in the Trades (CSET) campaigns were used to evaluate simulated low-level cloud microphysical properties. Using environmental variables and airborne remote sensing, we investigate methods for compositing aircraft observations into stratocumulus, open-cell, and undetermined cloud sampling regimes. This approach aims to mitigate issues with scaling aircraft observations to model grid resolutions and discrepancies with collocating aircraft observations with simulated clouds. We assessed simulated warm-phase cloud processes in the Community Earth System Model (CESM) using new model diagnostics tools to improve our representation of the SCT regime, and results from both CESM2 and CESM3 will be presented.

Clouds over the Southern Ocean are critical to accurately representing Earth’s radiative properties, yet continue to challenge Earth System Models due to complex micro-scale processes that influence regional-scale radiation. Subgrid-scale processes, including turbulence, cloud droplet activation, droplet collision-coalescence, ice nucleation, secondary ice production, and ice growth, are represented in coarse resolution models with parameterizations. It is well-documented that coupled Earth System model simulation results are highly sensitive to changes in these subgrid processes and that both structural and parameter uncertainties remain large. In this talk, we will discuss a process system approach for interrogating the representation of model microphysical processes in the Community Atmosphere Model version 6 (CAM6). Instrument simulators that translate model output into “observable” quantities were developed based on the sampling and measurement capabilities of the field instruments and “deployed” during several SO field campaigns using a specified dynamics configuration of the CAM6. Assessments revealed a low bias in cloud droplet number concentrations (CDNC), consistent with a low bias in cloud condensation nuclei (CCN) from missing sulfate aerosol. Model predictions of SO ice nucleating particles (INPs) are skillful in the boundary layer, but are much more variable aloft. In a series of simulations aimed at determining the needed INP predictive skill for accurately representing SO clouds, we find little to no sensitivity in CAM6 clouds to changes in ice nucleation. Analysis of these simulations reveal that ice formation in CAM6 SO clouds is unrealistically dominated by heterogeneous freezing of supercooled rain and is linked to the CDNC-CCN bias chain. Efforts to address these biases will also be discussed.

Cirrus cloud formation and evolution are subject to the influences of thermodynamic and dynamic conditions and aerosols. This study developed near global-scale in situ aircraft observational datasets based on 12 field campaigns that spanned from the polar regions to the tropics from 2008 to 2016. Cirrus cloud microphysical properties were investigated at temperatures ≤ −40 °C, including ice water content (IWC), ice crystal number concentration (Ni​​​​​​​), and number-weighted mean diameter (Di). Positive correlations were found between the fluctuations of these ice microphysical properties and the fluctuations of aerosol number concentrations for larger (> 500 nm) and smaller (> 100 nm) aerosols (i.e. Na₅₀₀ and Na₁₀₀, respectively). Steeper linear regression slopes were seen for large aerosols compared with smaller aerosols. Machine learning (ML) models showed that using relative humidity with respect to ice (RHi) as a predictor significantly increased the accuracy of predicting cirrus occurrences compared with temperature, vertical velocity (w), and aerosol number concentrations. The ML predictions of IWC fluctuations showed higher accuracies when larger aerosols were used as a predictor compared with smaller aerosols, even though their effects were similar when predicting cirrus occurrences. To predict IWC magnitudes accurately, aerosol concentrations were particularly important at 50 to 250 s scales (i.e. 10–50 km) and showed increasing effects at low temperatures, small ice supersaturation, and strong updraughts/downdraughts. These results improve the understanding of aerosol–cloud interactions and can be used to evaluate model parameterizations of cirrus cloud properties and processes.

Transported mineral dust in a Saharan air layer (SAL) contains active ice‐nucleating particles (INPs) that may be transported across the Atlantic Ocean and subsequently seed clouds in the Caribbean and the Americas. During an aircraft campaign around Houston and the western U.S. Gulf Coast, a widespread SAL advected into the sampling region allowing for measurement of the ice‐nucleating ability of SD following long‐range transport. Results showed that the mean INP concentrations were 3–4.5 times higher than non‐Saharan dust (nSD), but only at temperatures <−21°C. Active surface site densities were also enhanced in the SD, exceeding the mean for nSD by over an order of magnitude at temperatures <−21°C. These INP measurements confirmed that SD remains an active INP even after >8,000 km westward transport across the Atlantic Ocean.

Formation of ice in mixed-phase clouds may proceed via primary nucleation and secondary ice production (SIP). Primary nucleation involves the presence of ice nucleating particles (INPs), while SIP follows primary nucleation, resulting in ice crystal number concentrations N_ice exceeding the number of INPs. The ice formation pathways in young congestus clouds are not well understood nor are the environmental conditions favorable for the onset of SIP. Coincident airborne measurements of INPs and N_ice collected during the Secondary Production of Ice in Cumulus Experiment (SPICULE) campaign over the U.S. central Great Plains are reported for young congestus clouds. Number concentrations of INPs and N_ice at temperatures between −10° and −20°C were used to categorize whether SIP was active in each analyzed cloud pass. Observational data suggested that fragmentation of freezing droplets (FFDs) was occurring and the most likely SIP mechanism for ice enhancement during the early stages of the sampled clouds, where higher cloud-base temperatures and stronger updrafts produced conditions favorable for the onset of FFD. Simple model simulations of a congestus cloud were used to compare predictions of N_ice from newly implemented SIP mechanisms (including FFD) alongside those from the existing Hallett–Mossop (HM) mechanism. Although predicted N_ice, when all SIP mechanisms were active, was in good agreement with observations, the dominant SIP mechanism in the model was predicted to be HM. The rate of heterogeneous freezing in raindrops was likely inhibiting realistic FFD rates in the simulated cloud. These discrepancies between the observations and simulations underscore the need for extended laboratory studies to formulate improved model representations of SIP in convective clouds.