scholarly journals Measuring Atmospheric Icing Rate in Mixed-Phase Clouds Using Filtered Particle Data

2021 ◽  
Vol 70 ◽  
pp. 1-8
Author(s):  
Eero O. Molkoselka ◽  
Ville A. Kaikkonen ◽  
Anssi J. Makynen
Keyword(s):  
Mixed Phase ◽  
Atmospheric Icing ◽  
Mixed Phase Clouds

scholarly journals A Modeling Case Study of Mixed-Phase Clouds over the Southern Ocean and Tasmania

2010 ◽  
Vol 138 (3) ◽  
pp. 839-862 ◽  
Author(s):  
Anthony E. Morrison ◽  
Steven T. Siems ◽  
Michael J. Manton ◽  
Alex Nazarov
Keyword(s):  
Southern Ocean ◽  
Supercooled Liquid ◽  
Mixed Phase ◽  
Weather Research And Forecasting ◽  
Marine Stratocumulus ◽  
Cloud Structure ◽  
In Situ Observations ◽  
Cloud Tops ◽  
Mixed Phase Clouds

Abstract The cloud structure associated with two frontal passages over the Southern Ocean and Tasmania is investigated. The first event, during August 2006, is characterized by large quantities of supercooled liquid water and little ice. The second case, during October 2007, is more mixed phase. The Weather Research and Forecasting model (WRFV2.2.1) is evaluated using remote sensed and in situ observations within the post frontal air mass. The Thompson microphysics module is used to describe in-cloud processes, where ice is initiated using the Cooper parameterization at temperatures lower than −8°C or at ice supersaturations greater than 8%. The evaluated cases are then used to numerically investigate the prevalence of supercooled and mixed-phase clouds over Tasmania and the ocean to the west. The simulations produce marine stratocumulus-like clouds with maximum heights of between 3 and 5 km. These are capped by weak temperature and strong moisture inversions. When the inversion is at temperatures warmer than −10°C, WRF produces widespread supercooled cloud fields with little glaciation. This is consistent with the limited in situ observations. When the inversion is at higher altitudes, allowing cooler cloud tops, glaciated (and to a lesser extent mixed phase) clouds are more common. The simulations are further explored to evaluate any orographic signature within the cloud structure over Tasmania. No consistent signature is found between the two cases.

scholarly journals Processes that generate and deplete liquid water and snow in thin midlevel mixed-phase clouds

2009 ◽  
Vol 114 (D12) ◽  
Author(s):  
Adam J. Smith ◽  
Vincent E. Larson ◽  
Jianguo Niu ◽  
J. Adam Kankiewicz ◽  
Lawrence D. Carey
Keyword(s):  
Liquid Water ◽  
Mixed Phase ◽  
Mixed Phase Clouds

Constraining Neoproterozoic subtropical low-level clouds to assess the plausibility of near-Snowball Earth states

2021 ◽  
Author(s):  
Christoph Braun ◽  
Aiko Voigt ◽  
Johannes Hörner ◽  
Joaquim G. Pinto
Keyword(s):  
Sea Ice ◽  
Climate Models ◽  
Global Climate ◽  
Global Climate Models ◽  
Mixed Phase ◽  
Snowball Earth ◽  
Stable Range ◽  
Climate Regime ◽  
Low Level ◽  
Mixed Phase Clouds

<p>Stable waterbelt climate states with close to global ice cover challenge the classical Snowball Earth hypothesis because they provide a robust explanation for the survival of advanced marine species during the Neoproterozoic glaciations (1000 – 541 Million years ago). Whether Earth’s climate stabilizes in a waterbelt state or rushes towards a Snowball state is determined by the magnitude of the ice-albedo feedback in the subtropics, where dark, bare sea ice instead of snow-covered sea ice prevails. For a given bare sea-ice albedo, the subtropical ice-albedo feedback and thus the stable range of the waterbelt climate regime is sensitive to the albedo over ice-free ocean, which is largely determined by shortwave cloud-radiative effects (CRE). In the present-day climate, CRE are known to dominate the spread of climate sensitivity across global climate models. We here study the impact of uncertainty associated with CRE on the existence of geologically relevant waterbelt climate regimes using two global climate models and an idealized energy balance model. We find that the stable range of the waterbelt climate regime is very sensitive to the abundance of subtropical low-level mixed-phase clouds. If subtropical cloud cover is low, climate sensitivity becomes so high as to inhibit stable waterbelt states.</p><p>The treatment of mixed-phase clouds is highly uncertain in global climate models. Therefore we aim to constrain the uncertainty associated with their CRE by means of a hierarchy of global and regional simulations that span horizontal grid resolutions from 160 km to 300m, and in particular include large eddy simulations of subtropical mixed-phase clouds located over a low-latitude ice edge. In the cold waterbelt climate subtropical CRE arise from convective events caused by strong meridional temperature gradients and stratocumulus decks located in areas of large-scale descending motion. We identify the latter to dominate subtropical CRE and therefore focus our large eddy simulations on subtropical stratocumulus clouds. By conducting simulations with two extreme scenarios for the abundance of atmospheric mineral dust, which serves as ice-nucleating particles and therefore can control mixed-phase cloud physics, we aim to estimate the possible spread of CRE associated with subtropical mixed-phase clouds. From this estimate we may assess whether Neoproterozoic low-level cloud abundance may have been high enough to sustain a stable waterbelt climate regime.</p>

Understanding the Extratropical Liquid Water Path Feedback in Mixed-Phase Clouds with an Idealized Global Climate Model

2022 ◽  
pp. 1-48
Author(s):  
Yi Ming
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Climate Model ◽  
Global Climate Model ◽  
Cloud Water ◽  
Mixed Phase ◽  
Liquid Water Path ◽  
Water Path ◽  
Cloud Water Content ◽  
Mixed Phase Clouds

Abstract A negative shortwave cloud feedback associated with higher extratropical liquid water content in mixed-phase clouds is a common feature of global warming simulations, and multiple mechanisms have been hypothesized. A set of process-level experiments performed with an idealized global climate model (a dynamical core with passive water and cloud tracers and full Rotstayn-Klein single-moment microphysics) show that the common picture of the liquid water path (LWP) feedback in mixed-phase clouds being controlled by the amount of ice susceptible to phase change is not robust. Dynamic condensate processes—rather than static phase partitioning—directly change with warming, with varied impacts on liquid and ice amounts. Here, three principal mechanisms are responsible for the LWP response, namely higher adiabatic cloud water content, weaker liquid-to-ice conversion through the Bergeron-Findeisen process, and faster melting of ice and snow to rain. Only melting is accompanied by a substantial loss of ice, while the adiabatic cloud water content increase gives rise to a net increase in ice water path (IWP) such that total cloud water also increases without an accompanying decrease in precipitation efficiency. Perturbed parameter experiments with a wide range of climatological LWP and IWP demonstrate a strong dependence of the LWP feedback on the climatological LWP and independence from the climatological IWP and supercooled liquid fraction. This idealized setup allows for a clean isolation of mechanisms and paints a more nuanced picture of the extratropical mixed-phase cloud water feedback than simple phase change.

The ice nucleating ability of macromolecules in immersion freezing decreases in the presence of salts: Implications for freezing point depression calculations

2021 ◽  
Author(s):  
Jon F. Went ◽  
Jeanette D. Wheeler ◽  
François J. Peaudecerf ◽  
Nadine Borduas-Dedekind
Keyword(s):  
Sea Water ◽  
Freezing Point ◽  
Pure Water ◽  
Salt Content ◽  
Mixed Phase ◽  
Cloud Formation ◽  
Sea Spray ◽  
Freezing Point Depression ◽  
Immersion Freezing ◽  
Mixed Phase Clouds

<p>Cloud formation represents a large uncertainty in current climate predictions. In particular, ice in mixed-phase clouds requires the presence of ice nucleating particles (INPs) or ice nucleating macromolecules (INMs). An influential population of INPs has been proposed to be organic sea spray aerosols in otherwise pristine ocean air. However, the interactions between INMs present in sea water and their freezing behavior under atmospheric immersion freezing conditions warrants further research to constrain the role of sea spray aerosols on cloud formation. Indeed, salt is known to lower the freezing temperature of water, through a process called freezing point depression (FPD). Yet, current FPD corrections are solely based on the salt content and assume that the INMs’ ice nucleation abilities are identical with and without salt. Thus, we measured the effect of salt content on the ice nucleating ability of INMs, known to be associated with marine phytoplankton, in immersion freezing experiments in the Freezing Ice Nuclei Counter (FINC) (Miller et al., AMTD, 2020). We measured eight INMs, namely taurine, isethionate, xylose, mannitol, dextran, laminarin, and xanthan as INMs in pure water at temperatures relevant for mixed-phase clouds (e.g. 50% activated fraction at temperatures above –23 °C at 10 mM concentration). Subsequently, INMs were analyzed in artificial sea water containing 36 g salt L<sup>-1</sup>. Most INMs, except laminarin and xanthan, showed a loss of ice activity in artificial sea water compared to pure water, even after FPD correction. Based on our results, we hypothesize sea salt has an inhibitory effect on the ice activity of INMs. This effect influences our understanding of how INMs nucleate ice as well as challenges our use of FPD correction and subsequent extrapolation to ice activity under mixed-phase cloud conditions.</p>

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