skip to main content


The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 11:00 PM ET on Thursday, June 13 until 2:00 AM ET on Friday, June 14 due to maintenance. We apologize for the inconvenience.

Title: Impacts of Representing Heterogeneous Distribution of Cloud Liquid and Ice on Phase Partitioning of Arctic Mixed‐Phase Clouds with NCAR CAM5

In this study, we conduct sensitivity experiments with the Community Atmosphere Model version 5 to understand the impact of representing heterogeneous distribution between cloud liquid and ice on the phase partitioning in mixed‐phase clouds through different perturbations on the Wegener‐Bergeron‐Findeisen (WBF) process. In two experiments, perturbation factors that are based on assumptions of pocket structure and the partial homogeneous cloud volume derived from the High‐performance Instrumented Airborne Platform for Environmental Research (HIAPER) Pole‐to‐Pole Observation (HIPPO) campaign are utilized. Alternately, a mass‐weighted assumption is used in the calculation of WBF process to mimic the appearance of unsaturated area in mixed‐phase clouds as the result of heterogeneous distribution. Model experiments are tested in both single column and weather forecast modes and evaluated against data from the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program's Mixed‐Phase Arctic Cloud Experiment (M‐PACE) field campaign and long‐term ground‐based multisensor measurements. Model results indicate that perturbations on the WBF process can significantly modify simulated microphysical properties of Arctic mixed‐phase clouds. The improvement of simulated cloud water phase partitioning tends to be linearly proportional to the perturbation magnitude that is applied in the three different sensitivity experiments. Cloud macrophysical properties such as cloud fraction and frequency of occurrence of low‐level mixed‐phase clouds are less sensitive to the perturbation magnitude than cloud microphysical properties. Moreover, this study indicates that heterogeneous distribution between cloud hydrometeors should be treated consistently for all cloud microphysical processes. The model vertical resolution is also important for liquid water maintenance in mixed‐phase clouds.

more » « less
Award ID(s):
1744965 1642291 2001903
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  ;  ;  ;  
Publisher / Repository:
DOI PREFIX: 10.1029
Date Published:
Journal Name:
Journal of Geophysical Research: Atmospheres
Page Range / eLocation ID:
p. 13071-13090
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Ground‐based remote sensing measurements from the Atmospheric Radiation Measurement Program (ARM) West Antarctic Radiation Experiment (AWARE) campaign at the McMurdo station and the ARM North Slope of Alaska (NSA) Utqiaġvik site are used to retrieve and analyze single‐layer stratiform mixed‐phase cloud macrophysical and microphysical properties for these different polar environments. Single‐layer stratiform mixed‐phase clouds have annual frequencies of occurrence of ~14.7% at Utqiaġvik and ~7.3% at McMurdo, with the highest occurrences in early autumn. Compared to Utqiaġvik, stratiform mixed‐phase clouds at McMurdo have overall higher and colder cloud‐tops, thicker ice layer depth, thinner liquid‐dominated layer depth, and smaller liquid water path. These properties show clear seasonal variations. Supercooled liquid fraction at McMurdo is greater than at Utqiaġvik because, at a given temperature, McMurdo clouds have comparable liquid water paths but smaller ice water paths. Analyses of retrieved cloud microphysical properties show that compared to Utqiaġvik, stratiform mixed‐phase clouds at McMurdo have greater liquid droplet number concentration, smaller layer‐mean effective radius, and smaller ice water content and ice number concentration at a given cloud‐top temperature. These relationships may be related to different aerosol loading and chemical composition, and environment dynamics. Results presented in this study can be used as observational constraints for model representations of stratiform mixed‐phase clouds.

    more » « less
  2. Abstract. Cirrus clouds that form in the tropical tropopause layer(TTL) can play a key role in vertical transport through the uppertroposphere and lower stratosphere, which can significantly impact theradiative energy budget and stratospheric chemistry. However, the lack ofrealistic representation of natural ice cloud habits in microphysicalparameterizations can lead to uncertainties in cloud-related processes andcloud–climate feedbacks. The main goal of this study is to investigate therole of different cloud regimes and the associated ice habits in regulatingthe properties of the TTL. We compare aircraft measurements from theStratoClim field campaign to a set of numerical experiments at the scale of large-eddy simulations (LESs) for the same case study that employ differentmicrophysics schemes. Aircraft measurements over the southern slopes of theHimalayas captured high ice water content (HIWC) up to 2400 ppmv and iceparticle aggregates exceeding 700 µm in size with unusually longresidence times. The observed ice particles were mainly of liquid origin,with a small amount formed in situ. The corresponding profile of ice water content (IWC) fromthe ERA5 reanalysis corroborates the presence of HIWC detrained from deep-convective plumes in the TTL but underestimates HIWC by an order ofmagnitude. In the TTL, only the scheme that predicts ice habits canreproduce the observed HIWC, ice number concentration, and bimodal iceparticle size distribution. The lower range of particle sizes is mostlyrepresented by planar and columnar habits, while the upper range isdominated by aggregates. Large aggregates with sizes between 600 and 800 µm have fall speeds of less than 20 cm s−1, which explains thelong residence time of the aggregates in the TTL. Planar ice particles ofliquid origin contribute substantially to HIWC. The columnar and aggregatehabits are in the in situ range with lower IWC and number concentrations. Forall habits, the ice number concentration increases with decreasingtemperature. For the planar ice habit, relative humidity is inverselycorrelated with fall speed. This correlation is less evident for the othertwo ice habits. In the lower range of supersaturation with respect to ice,the columnar habit has the highest fall speed. The difference in ice numberconcentration across habits can be up to 4 orders of magnitude, withaggregates occurring in much smaller numbers. We demonstrate and quantifythe linear relationship between the differential sedimentation of pristineice crystals and the size of the aggregates that form when pristine crystalscollide. The slope of this relationship depends on which pristine ice habitsediments faster. Each simulated ice habit is associated with distinctradiative and latent heating rates. This study suggests that a modelconfiguration nested down to LES scales with a microphysicalparameterization that predicts ice shape evolution is crucial to provide anaccurate representation of the microphysical properties of TTL cirrus andthus the associated (de)hydration process. 
    more » « less
  3. Abstract. Regions with high ice water content (HIWC), composed of mainly small ice crystals, frequently occur over convective clouds in the tropics. Such regions can have median mass diameters (MMDs) <300 µm and equivalent radar reflectivities <20 dBZ. To explore formation mechanisms for these HIWCs, high-resolution simulations of tropical convective clouds observed on 26 May 2015 during the High Altitude Ice Crystals – High Ice Water Content (HAIC-HIWC) international field campaign based out of Cayenne, French Guiana, are conducted using the Weather Research and Forecasting (WRF) model with four different bulk microphysics schemes: the WRF single‐moment 6‐class microphysics scheme (WSM6), the Morrison scheme, and the Predicted Particle Properties (P3) scheme with one- and two-ice options. The simulations are evaluated against data from airborne radar and multiple cloud microphysics probes installed on the French Falcon 20 and Canadian National Research Council (NRC) Convair 580 sampling clouds at different heights. WRF simulations with different microphysics schemes generally reproduce the vertical profiles of temperature, dew-point temperature, and winds during this event compared with radiosonde data, and the coverage and evolution of this tropical convective system compared to satellite retrievals. All of the simulations overestimate the intensity and spatial extent of radar reflectivity by over 30 % above the melting layer compared to the airborne X-band radar reflectivity data. They also miss the peak of the observed ice number distribution function for 0.1 more » « less
  4. Abstract

    This study presents the first numerical simulations of seeded clouds over the Snowy Mountains of Australia. WRF-WxMod, a novel glaciogenic cloud-seeding model, was utilized to simulate the cloud response to winter orographic seeding under various meteorological conditions. Three cases during the 2018 seeding periods were selected for model evaluation, coinciding with an intensive ground-based measurement campaign. The campaign data were used for model validation and evaluation. Comparisons between simulations and observations demonstrate that the model realistically represents cloud structures, liquid water path, and precipitation. Sensitivity tests were performed to pinpoint key uncertainties in simulating natural and seeded clouds and precipitation processes. They also shed light on the complex interplay between various physical parameters/processes and their interaction with large-scale meteorology. Our study found that in unseeded scenarios, the warm and cold biases in different initialization datasets can heavily influence the intensity and phase of natural precipitation. Secondary ice production via Hallett–Mossop processes exerts a secondary influence. On the other hand, the seeding impacts are primarily sensitive to aerosol conditions and the natural ice nucleation process. Both factors alter the supercooled liquid water availability and the precipitation phase, consequently impacting the silver iodide (AgI) nucleation rate. Furthermore, model sensitivities were inconsistent across cases, indicating that no single model configuration optimally represents all three cases. This highlights the necessity of employing an ensemble approach for a more comprehensive and accurate assessment of the seeding impact.

    Significance Statement

    Winter orographic cloud seeding has been conducted for decades over the Snowy Mountains of Australia for securing water resources. However, this study is the first to perform cloud-seeding simulation for a robust, event-based seeding impact evaluation. A state-of-the-art cloud-seeding model (WRF-WxMod) was used to simulate the cloud seeding and quantified its impact on the region. The Southern Hemisphere, due to low aerosol emissions and highly pristine cloud conditions, has distinctly different cloud microphysical characteristics than the Northern Hemisphere, where WRF-WxMod has been successfully applied in a few regions over the United States. The results showed that WRF-WxMod could accurately capture the clouds and precipitation in both the natural and seeded conditions.

    more » « less
  5. Abstract

    Large‐eddy simulations (LESs) that explicitly resolve boundary layer (BL) turbulence and clouds are used to explore the sensitivity of idealized Arctic BL clouds to climate perturbations. The LESs focus on conditions resembling springtime, when surface heat fluxes over sea ice are weak, and the cloud radiative effect is dominated by the long‐wave effect. In the LES, the condensed water path increases with BL temperature and free‐tropospheric relative humidity, but it decreases with inversion strength. The dependencies of cloud properties on environmental variables exhibited by the LES can largely be reproduced by a mixed‐layer model. Mixed‐layer model analysis shows that the liquid water path increases with warming because the liquid water gradient increase under warming overcompensates for geometric cloud thinning. This response contrasts with the response of subtropical stratocumulus to warming, whose liquid water path decreases as the clouds thin geometrically under warming. The results suggest that methods used to explain the response of lower‐latitude BL clouds to climate change can also elucidate changes in idealized Arctic BL clouds, although subtropical and Arctic clouds occupy different thermodynamic regimes.

    more » « less