Andrew DeLaFrance

Ice crystal surface roughness influences the global shortwave cloud radiative effect by an estimated 1-2 Wm-2 and affects backscattering properties required for lidar retrievals, yet the microscale structure of atmospheric ice particles remains poorly constrained. In-situ observations indicate that rough and irregular surfaces are common, but insufficient measurements linking particle imagery to angular scattering data limit the development of representative shape models.During a flight of the CIRRUS-HL campaign in summer 2021, an unusually large proportion of quasi-spherical ice particles resembling frozen droplets were observed by the Particle Habit Imaging and Polar Scattering probe (PHIPS). We use this dataset as a case study to constrain surface roughness in ice clouds. PHIPS provides particle imagery from two viewing angles alongside simultaneous scattering measurements from 18 to 170°. Several thousand single, chain, and aggregated frozen droplets were identified, with mean radius ~14 μm (size parameter X ≈ 200).We model these particles using the droxtal geometry, and compute scattering properties using a beam tracing physical optics method. Preliminary results indicate pristine droxtals are insufficient to reproduce observed scattering, suggesting that surface roughness cannot be ignored.The surface roughness implementation is characterised by a mesh edge length and vertex displacement amplitude. Ensembles of roughened droxtals with radii sampled from the measured size distribution are compared against PHIPS measurements using a novel Bayesian optimisation implementation to efficiently explore the 2D roughness parameter space. We present results and discuss implications for constraining ice crystal roughness from in-situ measurements.

Microscale properties of cloud particles govern processes that influence weather and climate from local to global scales, yet accurate detection and quantification of these properties remains a fundamental challenge. Addressing this, recently launched and planned satellite missions have prioritized instrument development based on multi-angle polarimetric imaging of particle light scattering. However, obtaining quantitative microscale properties from these measurements relies on retrieval algorithms that require robust validation against high-fidelity, in-situ data.To address this critical need, we introduce the Hyper-Angular Cloud Polarimeter - Prototype Version (HACP-PV), a novel in-situ instrument designed and manufactured by schnaiTEC. The instrument's design foundation is shared with the optical principles of satellite-platform multi-angle polarimetry. Independent modulation of the instrument’s emitted and received light polarization states enables direct measurements of the unique elements needed to fully constrain the scattering matrix of the sample volume. We resolve angular scattering functions from approximately 101.5° to 168.5° at a resolution finer than 0.1°, tightly constraining measurements of the Particle Size Distribution (PSD). Crucially, the HACP-PV features an open-path sampling design, eliminating inlet-based sampling artifacts that typically introduce measurement uncertainty. We leverage these complete, artifact-free, scattering signatures to quantify key cloud microphysical quantities, including liquid water content and effective droplet diameter. In addition, the polarimetric measurements offer high sensitivity for discriminating ice from liquid particles, which is crucial for understanding phase-partitioning in mixed-phase clouds.We report on the progress in bringing this prototype version of the HACP from concept to reality. Our presentation overviews its novel design and summarizes calibration metrics and performance benchmarks from laboratory characterization. We highlight results from an initial deployment in a controlled, cloud-simulating wind tunnel environment, demonstrating the first retrievals of high-fidelity, complete scattering matrix measurements for liquid droplet clouds. Subsequent evaluation of these measurements against scattering calculations based on Mie theory validates the instrument's measurement principle and demonstrates its readiness for synergistic cloud physics research across laboratory and field domains.This prototype establishes a pathway towards a new benchmark for satellite validation or even serving as a reference standard at operational monitoring networks. Its direct, high-resolution measurements enable rigorous validation of remote sensing algorithms and assumptions. Ultimately, this work contributes to more accurate polarimetric scattering measurements of clouds, facilitating improved constraints on quantitative microphysical estimates, and an advanced understanding of small-scale cloud physics.

Mesoscale bands develop within winter cyclones as concentrated regions of locally enhanced radar reflectivity, often corresponding to intensified precipitation rates lasting several hours. Surface precipitation characteristics are governed by the microphysical properties of the ice-phase particles aloft, yet their unique microphysical evolutionary pathways and ambient environmental dependencies in banded regions remain poorly understood, in part due to a paucity of observations within clouds. Addressing this need, the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms measured properties of winter cyclones from airborne in situ and remote sensing platforms. Observations collected within a banded region of a decaying-stage northeast United States cyclone revealed a microphysical pathway characterized by precipitation fallout from a weak generating cell layer through an ∼ 2 km deep subsaturated downdraft region. Sublimation was a dominant evolutionary process, resulting in a > 70 % reduction in the initial characteristic ice water content (IWC). This vertical evolution was reproduced by a one-dimensional (1D) particle-based model simulation constrained by observations, conveying accuracy in the process representation. Four sensitivity simulations assessed evolutionary dependencies based on observationally informed perturbations of the ambient relative humidity, RH, and vertical air motion, w. Perturbations of ∼ 2 % RH significantly varied the resultant characteristic IWC loss, by as much as 29 %, whereas comparable perturbations of w had negligible effects. Intrinsic particle evolution during sublimation demonstrated a notable imprint on vertical profiles of radar reflectivity, but the Doppler velocity was more strongly governed by the ambient w profile. These findings contextualize radar-based discrimination of sublimation from other ice-phase processes, including riming and aggregation.

Mesoscale bands develop within winter cyclones as concentrated regions of locally enhanced radar reflectivity, often producing intensified precipitation rates lasting several hours. Surface precipitation characteristics are governed by the microphysical properties of the ice-phase particles aloft, yet their unique microphysical evolutionary pathways and ambient environmental dependencies in banded regions remain poorly understood, in part due to a paucity of observations within natural clouds. Addressing this need, the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms recently measured properties of winter cyclones from airborne in situ and remote sensing platforms. Observations collected within a banded region of a decaying-stage northeast United States cyclone revealed a microphysical pathway characterized by precipitation fallout from a weak generating cell layer through an ~2 km deep subsaturated downdraft region. Sublimation was a dominant evolutionary process, resulting in > 70 % reduction of the initial ice water content (IWC). This vertical evolution was reproduced by a 1D particle-based model simulation constrained by observations, conveying accuracy in the process representation. Four sensitivity simulations assessed evolutionary dependencies based on observationally-informed perturbations of the ambient relative humidity, RH, and vertical air motion, w. Perturbations of ~2 % RH significantly varied the resultant IWC loss, as much as 29 %, whereas comparable perturbations of w had negligible effects. Intrinsic particle evolution during sublimation demonstrated a notable imprint on vertical profiles of radar reflectivity, but Doppler velocity was more strongly governed by the ambient w profile. These findings contextualize radar-based discrimination of sublimation from other ice-phase processes, including riming and aggregation.

Mesoscale bands develop within winter cyclones as concentrated regions of locally enhanced radar reflectivity, often producing intensified precipitation rates lasting several hours. Surface precipitation characteristics are governed by the microphysical properties of the ice-phase particles aloft, yet their unique microphysical evolutionary pathways and ambient environmental dependencies in banded regions remain poorly understood, in part due to a paucity of observations within natural clouds. Addressing this need, the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms recently measured properties of winter cyclones from airborne in situ and remote sensing platforms. Observations collected within a banded region of a decaying-stage northeast United States cyclone revealed a microphysical pathway characterized by precipitation fallout from a weak generating cell layer through an ~2 km deep subsaturated downdraft region. Sublimation was a dominant evolutionary process, resulting in > 70 % reduction of the initial ice water content (IWC). This vertical evolution was reproduced by a 1D particle-based model simulation constrained by observations, conveying accuracy in the process representation. Four sensitivity simulations assessed evolutionary dependencies based on observationally-informed perturbations of the ambient relative humidity, RH, and vertical air motion, w. Perturbations of ~2 % RH significantly varied the resultant IWC loss, as much as 29 %, whereas comparable perturbations of w had negligible effects. Intrinsic particle evolution during sublimation demonstrated a notable imprint on vertical profiles of radar reflectivity, but Doppler velocity was more strongly governed by the ambient w profile. These findings contextualize radar-based discrimination of sublimation from other ice-phase processes, including riming and aggregation.

Mesoscale bands develop within winter cyclones as concentrated regions of locally enhanced radar reflectivity, often producing intensified precipitation rates lasting several hours. Surface precipitation characteristics are governed by the microphysical properties of the ice-phase particles aloft, yet their unique microphysical evolutionary pathways and ambient environmental dependencies in banded regions remain poorly understood, in part due to a paucity of observations within natural clouds. Addressing this need, the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms recently measured properties of winter cyclones from airborne in situ and remote sensing platforms. Observations collected within a banded region of a decaying-stage northeast United States cyclone revealed a microphysical pathway characterized by precipitation fallout from a weak generating cell layer through an ~2 km deep subsaturated downdraft region. Sublimation was a dominant evolutionary process, resulting in > 70 % reduction of the initial ice water content (IWC). This vertical evolution was reproduced by a 1D particle-based model simulation constrained by observations, conveying accuracy in the process representation. Four sensitivity simulations assessed evolutionary dependencies based on observationally-informed perturbations of the ambient relative humidity, RH, and vertical air motion, w. Perturbations of ~2 % RH significantly varied the resultant IWC loss, as much as 29 %, whereas comparable perturbations of w had negligible effects. Intrinsic particle evolution during sublimation demonstrated a notable imprint on vertical profiles of radar reflectivity, but Doppler velocity was more strongly governed by the ambient w profile. These findings contextualize radar-based discrimination of sublimation from other ice-phase processes, including riming and aggregation.

Mesoscale bands develop within winter cyclones as concentrated regions of locally enhanced radar reflectivity, often producing intensified precipitation rates lasting several hours. Surface precipitation characteristics are governed by the microphysical properties of the ice-phase particles aloft, yet their unique microphysical evolutionary pathways and ambient environmental dependencies in banded regions remain poorly understood, in part due to a paucity of observations within natural clouds. Addressing this need, the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms recently measured properties of winter cyclones from airborne in situ and remote sensing platforms. Observations collected within a banded region of a decaying-stage northeast United States cyclone revealed a microphysical pathway characterized by precipitation fallout from a weak generating cell layer through an ~2 km deep subsaturated downdraft region. Sublimation was a dominant evolutionary process, resulting in > 70 % reduction of the initial ice water content (IWC). This vertical evolution was reproduced by a 1D particle-based model simulation constrained by observations, conveying accuracy in the process representation. Four sensitivity simulations assessed evolutionary dependencies based on observationally-informed perturbations of the ambient relative humidity, RH, and vertical air motion, w. Perturbations of ~2 % RH significantly varied the resultant IWC loss, as much as 29 %, whereas comparable perturbations of w had negligible effects. Intrinsic particle evolution during sublimation demonstrated a notable imprint on vertical profiles of radar reflectivity, but Doppler velocity was more strongly governed by the ambient w profile. These findings contextualize radar-based discrimination of sublimation from other ice-phase processes, including riming and aggregation.

Mesoscale bands develop within winter cyclones as concentrated regions of locally enhanced radar reflectivity, often producing intensified precipitation rates lasting several hours. Surface precipitation characteristics are governed by the microphysical properties of the ice-phase particles aloft, yet their unique microphysical evolutionary pathways and ambient environmental dependencies in banded regions remain poorly understood, in part due to a paucity of observations within natural clouds. Addressing this need, the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms recently measured properties of winter cyclones from airborne in situ and remote sensing platforms. Observations collected within a banded region of a decaying-stage northeast United States cyclone revealed a microphysical pathway characterized by precipitation fallout from a weak generating cell layer through an ~2 km deep subsaturated downdraft region. Sublimation was a dominant evolutionary process, resulting in > 70 % reduction of the initial ice water content (IWC). This vertical evolution was reproduced by a 1D particle-based model simulation constrained by observations, conveying accuracy in the process representation. Four sensitivity simulations assessed evolutionary dependencies based on observationally-informed perturbations of the ambient relative humidity, RH, and vertical air motion, w. Perturbations of ~2 % RH significantly varied the resultant IWC loss, as much as 29 %, whereas comparable perturbations of w had negligible effects. Intrinsic particle evolution during sublimation demonstrated a notable imprint on vertical profiles of radar reflectivity, but Doppler velocity was more strongly governed by the ambient w profile. These findings contextualize radar-based discrimination of sublimation from other ice-phase processes, including riming and aggregation.

Mesoscale bands develop within winter cyclones as concentrated regions of locally enhanced radar reflectivity, often producing intensified precipitation rates lasting several hours. Surface precipitation characteristics are governed by the microphysical properties of the ice-phase particles aloft, yet their unique microphysical evolutionary pathways and ambient environmental dependencies in banded regions remain poorly understood, in part due to a paucity of observations within natural clouds. Addressing this need, the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms recently measured properties of winter cyclones from airborne in situ and remote sensing platforms. Observations collected within a banded region of a decaying-stage northeast United States cyclone revealed a microphysical pathway characterized by precipitation fallout from a weak generating cell layer through an ~2 km deep subsaturated downdraft region. Sublimation was a dominant evolutionary process, resulting in > 70 % reduction of the initial ice water content (IWC). This vertical evolution was reproduced by a 1D particle-based model simulation constrained by observations, conveying accuracy in the process representation. Four sensitivity simulations assessed evolutionary dependencies based on observationally-informed perturbations of the ambient relative humidity, RH, and vertical air motion, w. Perturbations of ~2 % RH significantly varied the resultant IWC loss, as much as 29 %, whereas comparable perturbations of w had negligible effects. Intrinsic particle evolution during sublimation demonstrated a notable imprint on vertical profiles of radar reflectivity, but Doppler velocity was more strongly governed by the ambient w profile. These findings contextualize radar-based discrimination of sublimation from other ice-phase processes, including riming and aggregation.

Mesoscale bands develop within winter cyclones as concentrated regions of locally enhanced radar reflectivity, often producing intensified precipitation rates lasting several hours. Surface precipitation characteristics are governed by the microphysical properties of the ice-phase particles aloft, yet their unique microphysical evolutionary pathways and ambient environmental dependencies in banded regions remain poorly understood, in part due to a paucity of observations within natural clouds. Addressing this need, the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms recently measured properties of winter cyclones from airborne in situ and remote sensing platforms. Observations collected within a banded region of a decaying-stage northeast United States cyclone revealed a microphysical pathway characterized by precipitation fallout from a weak generating cell layer through an ~2 km deep subsaturated downdraft region. Sublimation was a dominant evolutionary process, resulting in > 70 % reduction of the initial ice water content (IWC). This vertical evolution was reproduced by a 1D particle-based model simulation constrained by observations, conveying accuracy in the process representation. Four sensitivity simulations assessed evolutionary dependencies based on observationally-informed perturbations of the ambient relative humidity, RH, and vertical air motion, w. Perturbations of ~2 % RH significantly varied the resultant IWC loss, as much as 29 %, whereas comparable perturbations of w had negligible effects. Intrinsic particle evolution during sublimation demonstrated a notable imprint on vertical profiles of radar reflectivity, but Doppler velocity was more strongly governed by the ambient w profile. These findings contextualize radar-based discrimination of sublimation from other ice-phase processes, including riming and aggregation.