scholarly journals Global radiative effects of solid fuel cookstove aerosol emissions

2018 ◽  
Vol 18 (8) ◽  
pp. 5219-5233 ◽  
Author(s):  
Yaoxian Huang ◽  
Nadine Unger ◽  
Trude Storelvmo ◽  
Kandice Harper ◽  
Yiqi Zheng ◽  
...  
Keyword(s):  
Black Carbon ◽  
Solid Fuel ◽  
Surface Albedo ◽  
Mixed Phase ◽  
Radiative Effects ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Radiative Impacts ◽  
Standard Deviations ◽  
Aerosol Emissions

Abstract. We apply the NCAR CAM5-Chem global aerosol-climate model to quantify the net global radiative effects of black and organic carbon aerosols from global and Indian solid fuel cookstove emissions for the year 2010. Our assessment accounts for the direct radiative effects, changes to cloud albedo and lifetime (aerosol indirect effect, AIE), impacts on clouds via the vertical temperature profile (semi-direct effect, SDE) and changes in the surface albedo of snow and ice (surface albedo effect). In addition, we provide the first estimate of household solid fuel black carbon emission effects on ice clouds. Anthropogenic emissions are from the IIASA GAINS ECLIPSE V5a inventory. A global dataset of black carbon (BC) and organic aerosol (OA) measurements from surface sites and aerosol optical depth (AOD) from AERONET is used to evaluate the model skill. Compared with observations, the model successfully reproduces the spatial patterns of atmospheric BC and OA concentrations, and agrees with measurements to within a factor of 2. Globally, the simulated AOD agrees well with observations, with a normalized mean bias close to zero. However, the model tends to underestimate AOD over India and China by  ∼  19 ± 4 % but overestimate it over Africa by  ∼  25 ± 11 % (± represents modeled temporal standard deviations for n = 5 run years). Without BC serving as ice nuclei (IN), global and Indian solid fuel cookstove aerosol emissions have net global cooling radiative effects of −141 ± 4 mW m−2 and −12 ± 4 mW m−2, respectively (± represents modeled temporal standard deviations for n = 5 run years). The net radiative impacts are dominated by the AIE and SDE mechanisms, which originate from enhanced cloud condensation nuclei concentrations for the formation of liquid and mixed-phase clouds, and a suppression of convective transport of water vapor from the lower troposphere to the upper troposphere/lower stratosphere that in turn leads to reduced ice cloud formation. When BC is allowed to behave as a source of IN, the net global radiative impacts of the global and Indian solid fuel cookstove emissions range from −275 to +154 mW m−2 and −33 to +24 mW m−2, with globally averaged values of −59 ± 215 and 0.3 ± 29 mW m−2, respectively. Here, the uncertainty range is based on sensitivity simulations that alter the maximum freezing efficiency of BC across a plausible range: 0.01, 0.05 and 0.1. BC–ice cloud interactions lead to substantial increases in high cloud (<  500 hPa) fractions. Thus, the net sign of the impacts of carbonaceous aerosols from solid fuel cookstoves on global climate (warming or cooling) remains ambiguous until improved constraints on BC interactions with mixed-phase and ice clouds are available.

scholarly journals Global radiative effects of solid fuel cookstove aerosol emissions

2017 ◽  
Author(s):  
Yaoxian Huang ◽  
Nadine Unger ◽  
Trude Storelvmo ◽  
Kandice Harper ◽  
Yiqi Zheng ◽  
...  
Keyword(s):  
Black Carbon ◽  
Solid Fuel ◽  
Surface Albedo ◽  
Global Climate ◽  
Convective Transport ◽  
Climate Impacts ◽  
Radiative Effects ◽  
Vertical Temperature Profile ◽  
Ice Cloud ◽  
Aerosol Emissions

Abstract. We apply the NCAR CAM5-Chem global aerosol–climate model to quantify the net global radiative effects of black and organic carbon aerosols from global and Indian solid fuel cookstove emissions for the year 2010. Our updated assessment accounts for the direct radiative effects, changes to cloud albedo and lifetime (aerosol indirect effect, AIE), impacts on clouds via the vertical temperature profile (semi-direct effect, SDE), and changes in the surface albedo of snow and ice (surface albedo effect). In addition, we provide the first estimate of household solid fuel black carbon emission effects on ice clouds. Anthropogenic emissions are from the IIASA GAINS ECLIPSE V5a inventory. A global dataset of black carbon (BC) and organic aerosol (OA) measurements from surface sites and aerosol optical depth (AOD) from AERONET is used to evaluate the model skill. Compared with observations, the model successfully reproduces the spatial patterns of atmospheric BC and OA concentrations, and agrees with measurements to within a factor of 2. Globally, the simulated AOD agrees well with observations, with normalized mean bias close to zero. However, the model tends to underestimate AOD over India and China by ~ 19 % but overestimate it over Africa by ~ 25 %. Without BC serving as ice nuclei (IN), global and Indian solid fuel cookstove aerosol emissions have a net cooling impact on global climate of −141 ± 4 mW m−2 and −12 ± 4 mW m−2, respectively. The net radiative impacts are dominated by the AIE and SDE mechanisms, which originate from enhanced cloud condensation nuclei concentrations for the formation of liquid and mixed-phase clouds, and a suppression of convective transport of water vapor from the lower troposphere to the upper troposphere/lower stratosphere that in turn leads to reduced ice cloud formation. When BC is allowed to behave as a source of IN, the net global climate impacts of the global and Indian solid fuel cookstove emissions range from −260 to +135 mW m−2 and −33 to +24 mW m−2, with globally averaged values −51 ± 210 and 0.3 ± 29 mW m−2 respectively. The uncertainty range is calculated from sensitivity simulations that alter the maximum freezing efficiency of BC across a plausible range: 0.01, 0.05 and 0.1. BC–ice cloud interactions lead to substantial increases in high cloud (

scholarly journals Assessing the Radiative Effects of Global Ice Clouds Based on CloudSat and CALIPSO Measurements

2016 ◽  
Vol 29 (21) ◽  
pp. 7651-7674 ◽  
Author(s):  
Yulan Hong ◽  
Guosheng Liu ◽  
J.-L. F. Li
Keyword(s):  
Longwave Radiation ◽  
Cooling Effect ◽  
Radiation Budget ◽  
Radiative Effect ◽  
Radiative Effects ◽  
Ice Clouds ◽  
Cloud Optical Depth ◽  
Ice Cloud ◽  
Heating And Cooling ◽  
The Tropics

Abstract Although it is well established that cirrus warms Earth, the radiative effect of the entire spectrum of ice clouds is not well understood. In this study, the role of all ice clouds in Earth’s radiation budget is investigated by performing radiative transfer modeling using ice cloud properties retrieved from CloudSat and CALIPSO measurements as inputs. Results show that, for the 2008 period, the warming effect (~21.8 ± 5.4 W m−2) induced by ice clouds trapping longwave radiation exceeds their cooling effect (~−16.7 ± 1.7 W m−2) caused by shortwave reflection, resulting in a net warming effect (~5.1 ± 3.8 W m−2) globally on the earth–atmosphere system. The net warming is over 15 W m−2 in the tropical deep convective regions, whereas cooling occurs in the midlatitudes, which is less than 10 W m−2 in magnitude. Seasonal variations of ice cloud radiative effects are evident in the midlatitudes where the net effect changes from warming during winter to cooling during summer, whereas warming occurs all year-round in the tropics. Ice cloud optical depth τ is shown to be an important factor in determining the sign and magnitude of the net radiative effect. Ice clouds with τ &lt; 4.6 display a warming effect with the largest contributions from those with τ ≈ 1.0. In addition, ice clouds cause vertically differential heating and cooling of the atmosphere, particularly with strong heating in the upper troposphere over the tropics. At Earth’s surface, ice clouds produce a cooling effect no matter how small the τ value is.

scholarly journals Antarctic clouds, supercooled liquid water and mixed-phase investigated with DARDAR: geographical and seasonal variations

2018 ◽  
Author(s):  
Constantino Listowski ◽  
Julien Delanoë ◽  
Amélie Kirchgaessner ◽  
Tom Lachlan-Cope ◽  
John King
Keyword(s):  
Sea Ice ◽  
Liquid Water ◽  
Supercooled Liquid ◽  
Mixed Phase ◽  
Ice Clouds ◽  
Ice Cloud ◽  
The One ◽  
Autumn And Winter ◽  
Mixed Phase Clouds ◽  
Ice Fraction

Abstract. Antarctic tropospheric clouds are investigated using the radar-lidar DARDAR (raDAR/liDAR)-MASK products. The cloud fraction is divided into the supercooled liquid water (SLW)-containing clouds and the all-ice clouds. The low-level SLW fraction varies according to temperature and sea ice fraction. It is the largest over water. In East Antarctica, the SLW fraction decreases sharply polewards. It is twice to three times higher in West Antarctica. The all-ice cloud geographical distribution is shaped by the interaction of the main low-pressure systems surrounding the continent and the orography, with little links with sea ice fraction. We demonstrate the largest impact of sea ice on SLW (mostly mixed-phase clouds, MPC) in autumn and winter, while it is almost null in summer and intermediate in spring. Monthly variability of MPC shows a maximum fraction at the end of summer and minimum in winter. Conversely, the unglaciated (pure) SLW (USLW) fraction has a maximum at the beginning of summer. Monthly evolutions of MPC and USLW fractions do not differ on the continent. This demonstrates a seasonality in the glaciation process in marine liquid-bearing clouds. From the literature, we identify the pattern of the monthly evolution of the MPC fraction as being similar to the one of the aerosols, which is related to marine biological activity. Marine bioaerosols are known to be efficient Ice Nucleating Particles (INPs). The emission of these INPs into the atmosphere from open waters would come on top of the temperature and sea ice fraction seasonalities as factors explaining the mixed-phase clouds monthly evolution.

scholarly journals Physical properties of High Arctic tropospheric particles during winter

2009 ◽  
Vol 9 (18) ◽  
pp. 6881-6897 ◽  
Author(s):  
L. Bourdages ◽  
T. J. Duck ◽  
G. Lesins ◽  
J. R. Drummond ◽  
E. W. Eloranta
Keyword(s):  
Boundary Layer ◽  
Lower Troposphere ◽  
High Arctic ◽  
Mixed Phase ◽  
Blowing Snow ◽  
Particle Scattering ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Mixed Phase Clouds

Abstract. A climatology of particle scattering properties in the wintertime High Arctic troposphere, including vertical distributions and effective radii, is presented. The measurements were obtained using a lidar and cloud radar located at Eureka, Nunavut Territory (80° N, 86° W). Four different particle groupings are considered: boundary-layer ice crystals, ice clouds, mixed-phase clouds, and aerosols. Two-dimensional histograms of occurrence probabilities against depolarization, radar/lidar colour ratio and height are given. Colour ratios are related to particle minimum dimensions (i.e., widths rather than lengths) using a Mie scattering model. Ice cloud crystals have effective radii spanning 25–220 µm, with larger particles observed at lower altitudes. Topographic blowing snow residuals in the boundary layer have the smallest crystals at 15–70 µm. Mixed-phase clouds have water droplets and ice crystal precipitation in the 5–40 µm and 40–220 µm ranges, respectively. Ice cloud crystals have depolarization decreasing with height. The depolarization trend is associated with the large ice crystal sub-population. Small crystals depolarize more than large ones in ice clouds at a given altitude, and show constant modal depolarization with height. Ice clouds in the mid-troposphere are sometimes observed to precipitate to the ground. Water clouds are constrained to the lower troposphere (0.5–3.5 km altitude). Aerosols are most abundant near the ground and are frequently mixed with the other particle types. The data are used to construct a classification chart for particle scattering in wintertime Arctic conditions.

A Comparison of Aphelion Cloud Belt Phase Functions Before and After the Mars Year 34 Global Dust Storm

2021 ◽  
Author(s):  
Alex Innanen ◽  
Brittney Cooper ◽  
Charissa Campbell ◽  
Scott Guzewich ◽  
Jacob Kloos ◽  
...  
Keyword(s):  
Dust Storm ◽  
Phase Function ◽  
Dust Storms ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Water Ice ◽  
Ice Cloud ◽  
Sky Survey ◽  
Scattering Phase ◽  
Scattering Phase Function

&lt;p&gt;1. INTRODUCTION&lt;/p&gt;&lt;p&gt;The Mars Science Laboratory (MSL) is located in Gale Crater (4.5&amp;#176;S, 137.4&amp;#176;E), and has been performing cloud observations for the entirety of its mission, since its landing in 2012 [eg. 1,2,3]. One such observation is the Phase Function Sky Survey (PFSS), developed by Cooper et al [3] and instituted in Mars Year (MY) 34 to determine the scattering phase function of Martian water-ice clouds. The clouds of interest form during the Aphelion Cloud Belt (ACB) season (L&lt;sub&gt;s&lt;/sub&gt;=50&amp;#176;-150&amp;#176;), a period of time during which there is an increase in the formation of water-ice clouds around the Martian equator [4]. The PFSS observation was also performed during the MY 35 ACB season and the current MY 36 ACB season.&lt;/p&gt;&lt;p&gt;Following the MY 34 ACB season, Mars experienced a global dust storm which lasted from L&lt;sub&gt;s&lt;/sub&gt;~188&amp;#176; to L&lt;sub&gt;s&lt;/sub&gt;~250&amp;#176; of that Mars year [5]. Global dust storms are planet-encircling storms which occur every few Mars years and can significantly impact the atmosphere leading to increased dust aerosol sizes [6], an increase in middle atmosphere water vapour [7], and the formation of unseasonal water-ice clouds [8]. While the decrease in visibility during the global dust storm itself made cloud observation difficult, comparing the scattering phase function prior to and following the global dust storm can help to understand the long-term impacts of global dust storms on water-ice clouds.&lt;/p&gt;&lt;p&gt;2. METHODS&lt;/p&gt;&lt;p&gt;The PFSS consists of 9 cloud movies of three frames each, taken using MSL&amp;#8217;s navigation cameras, at a variety of pointings in order to observe a large range of scattering angles. The goal of the PFSS is to characterise the scattering properties of water-ice clouds and to determine ice crystal geometry.&amp;#160; In each movie, clouds are identified using mean frame subtraction, and the phase function is computed using the formula derived by Cooper et al [3]. An average phase function can then be computed for the entirety of the ACB season.&lt;/p&gt;&lt;p&gt;&lt;img src=&quot;https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.eda718c85da062913791261/sdaolpUECMynit/1202CSPE&amp;app=m&amp;a=0&amp;c=67584351a5c2fde95856e0760f04bbf3&amp;ct=x&amp;pn=gnp.elif&amp;d=1&quot; alt=&quot;Figure 1 &amp;#8211; Temporal Distribution of Phase Function Sky Survey Observations for Mars Years 34 and 35&quot; width=&quot;800&quot; height=&quot;681&quot;&gt;&lt;/p&gt;&lt;p&gt;Figure 1 shows the temporal distributions of PFSS observations taken during MYs 34 and 35. We aim to capture both morning and afternoon observations in order to study any diurnal variability in water-ice clouds.&lt;/p&gt;&lt;p&gt;3. RESULTS AND DISCUSSION&lt;/p&gt;&lt;p&gt;There were a total of 26 PFSS observations taken in MY 35 between L&lt;sub&gt;s&lt;/sub&gt;~50&amp;#176;-160&amp;#176;, evenly distributed between AM and PM observations. Typically, times further from local noon (i.e. earlier in the morning or later in the afternoon) show stronger cloud features, and run less risk of being obscured by the presence of the sun. In all movies in which clouds are detected, a phase function can be calculated, and an average phase function determined for the whole ACB season. &amp;#160;&lt;/p&gt;&lt;p&gt;Future work will look at the water-ice cloud scattering properties for the MY 36 ACB season, allowing us to get more information about the interannual variability of the ACB and to further constrain the ice crystal habit. The PFSS observations will not only assist in our understanding of the long-term atmospheric impacts of global dust storms but also add to a more complete image of time-varying water-ice cloud properties.&lt;/p&gt;

scholarly journals Scale dependence of cirrus heterogeneity effects. Part II: MODIS NIR and SWIR channels

2018 ◽  
Vol 18 (16) ◽  
pp. 12105-12121 ◽  
Author(s):  
Thomas Fauchez ◽  
Steven Platnick ◽  
Tamás Várnai ◽  
Kerry Meyer ◽  
Céline Cornet ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Spatial Resolution ◽  
Thermal Infrared ◽  
Radiative Effects ◽  
Ice Clouds ◽  
Plane Parallel ◽  
Wide Range ◽  
The Impact ◽  
Side Illumination

Abstract. In a context of global climate change, the understanding of the radiative role of clouds is crucial. On average, ice clouds such as cirrus have a significant positive radiative effect, but under some conditions the effect may be negative. However, many uncertainties remain regarding the role of ice clouds on Earth's radiative budget and in a changing climate. Global satellite observations are particularly well suited to monitoring clouds, retrieving their characteristics and inferring their radiative impact. To retrieve ice cloud properties (optical thickness and ice crystal effective size), current operational algorithms assume that each pixel of the observed scene is plane-parallel and homogeneous, and that there is no radiative connection between neighboring pixels. Yet these retrieval assumptions are far from accurate, as real radiative transfer is 3-D. This leads to the plane-parallel and homogeneous bias (PPHB) plus the independent pixel approximation bias (IPAB), which impacts both the estimation of top-of-the-atmosphere (TOA) radiation and the retrievals. An important factor that determines the impact of these assumptions is the sensor spatial resolution. High-spatial-resolution pixels can better represent cloud variability (low PPHB), but the radiative path through the cloud can involve many pixels (high IPAB). In contrast, low-spatial-resolution pixels poorly represent the cloud variability (high PPHB), but the radiation is better contained within the pixel field of view (low IPAB). In addition, the solar and viewing geometry (as well as cloud optical properties) can modulate the magnitude of the PPHB and IPAB. In this, Part II of our study, we simulate TOA 0.86 and 2.13 µm solar reflectances over a cirrus uncinus scene produced by the 3DCLOUD model. Then, 3-D radiative transfer simulations are performed with the 3DMCPOL code at spatial resolutions ranging from 50 m to 10 km, for 12 viewing geometries and nine solar geometries. It is found that, for simulated nadir observations taken at resolution higher than 2.5 km, horizontal radiation transport (HRT) dominates biases between 3-D and 1-D reflectance calculations, but these biases are mitigated by the side illumination and shadowing effects for off-zenith solar geometries. At resolutions coarser than 2.5 km, PPHB dominates. For off-nadir observations at resolutions higher than 2.5 km, the effect that we call THEAB (tilted and homogeneous extinction approximation bias) due to the oblique line of sight passing through many cloud columns contributes to a large increase of the reflectances, but 3-D radiative effects such as shadowing and side illumination for oblique Sun are also important. At resolutions coarser than 2.5 km, the PPHB is again the dominant effect. The magnitude and resolution dependence of PPHB and IPAB is very different for visible, near-infrared and shortwave infrared channels compared with the thermal infrared channels discussed in Part I of this study. The contrast of 3-D radiative effects between solar and thermal infrared channels may be a significant issue for retrieval techniques that simultaneously use radiative measurements across a wide range of solar reflectance and infrared wavelengths.

scholarly journals Highly-controlled, reproducible measurements of aerosol emissions from African biomass combustion

2017 ◽  
Author(s):  
Sophie L. Haslett ◽  
J. Chris Thomas ◽  
William T. Morgan ◽  
Rory Hadden ◽  
Dantong Liu ◽  
...  
Keyword(s):  
Black Carbon ◽  
Thermal Environment ◽  
Organic Aerosol ◽  
Biomass Combustion ◽  
Particulate Emissions ◽  
Radiative Balance ◽  
Mass Spectral ◽  
Aerosol Emission ◽  
Flaming Combustion ◽  
Aerosol Emissions

Abstract. Particulate emissions from biomass burning can both alter the atmosphere's radiative balance and cause significant harm to human health. However, due to the large effect on emissions caused by even small alterations to the way in which a fuel burns, it is difficult to study particulate production of biomass combustion mechanistically and in a repeatable manner. In order to address this gap, in this study, small wood samples sourced from Côte D'Ivoire in West Africa were burned in a highly-controlled laboratory environment. The shape and mass of samples, available airflow and surrounding thermal environment were carefully regulated. Organic aerosol and refractory black carbon emissions were measured in real time using an Aerosol Mass Spectrometer and a Single Particle Soot Photometer, respectively. This methodology produced remarkably repeatable results, allowing aerosol emissions to be mapped directly onto different phases of combustion. Emissions from pyrolysis were visible as a distinct phase before flaming was established. After flaming combustion was initiated, a black-carbon-dominant flame was observed during which very little organic aerosol was produced, followed by a period that was dominated by organic-carbon-producing smouldering combustion, despite the presence of residual flaming. During pyrolysis and smouldering, the two phases producing organic aerosol, distinct mass spectral signatures that correspond to previously-reported variations in biofuel emissions measured in the atmosphere are found. Organic aerosol emission factors averaged over an entire combustion event were found to be representative of the time spent in the pyrolysis and smouldering phases, rather than reflecting a coupling between emissions and the mass loss of the sample. Further exploration of aerosol yields from similarly carefully controlled fires and a careful comparison with data from macroscopic fires and real-world emissions will help to deliver greater constraints on variability of particulate emissions in atmospheric systems.

scholarly journals On the origin of subvisible cirrus clouds in the tropical upper troposphere

2012 ◽  
Vol 12 (6) ◽  
pp. 14875-14926 ◽  
Author(s):  
M. Reverdy ◽  
V. Noel ◽  
H. Chepfer ◽  
B. Legras
Keyword(s):  
Cloud Formation ◽  
Formation Processes ◽  
Ice Clouds ◽  
Back Trajectories ◽  
Air Masses ◽  
Ice Cloud ◽  
And Behavior ◽  
Atmospheric Phenomena ◽  
Mean Variance ◽  
Lidar Observations

Abstract. Spaceborne lidar observations have recently revealed a previously undetected significant population of SubVisible Cirrus (SVC). We show them to be colder than −74 °C, with an optical depth below 0.0015 on average. The formation and persistence over time of this new cloud population could be related to several atmospheric phenomena. In this paper, we investigate the importance of external processes in the creation of this cloud population, vs. the traditional ice cloud formation theory through convection. The importance of three scenarios in the formation of the global SVC population is investigated through different approaches that include comparisons with data imaging from several spaceborne instruments and back-trajectories that document the history and behavior of air masses leading to a point in time and space where subvisible cirrus were detected. In order simplify the study of cloud formation processes, we singled out SVC with coherent temperature histories (mean variance lower than 4 K) according to back-trajectories along 5, 10 or 15 days (respectively 58, 25 and 11% of SVC). Our results suggest that external processes, including local increases in liquid and hygroscopic aerosol concentration (either through biomass burning or volcanic injection forming sulfate-based aerosols in the troposphere or the stratosphere) have no noticeable short-term or mid-term impact on the SVC population. On the other hand, we find that ~60% of air masses interacted with convective activity in the days before they led to cloud formation and detection, which correspond to 37 to 65% of SVC. These results put forward the important influence of classical cloud formation processes compared to external influences in forming SVC. They support the view that the SVC population observed by CALIOP is an extension of the general upper tropospheric ice clouds population with its extreme thinness as its only differentiating factor.

Intercomparison of Bulk Cloud Microphysics Schemes in Mesoscale Simulations of Springtime Arctic Mixed-Phase Stratiform Clouds

2006 ◽  
Vol 134 (7) ◽  
pp. 1880-1900 ◽  
Author(s):  
H. Morrison ◽  
J. O. Pinto
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Heat Budget ◽  
Cloud Microphysics ◽  
Ice Nucleation ◽  
Mixed Phase ◽  
Precipitation Rate ◽  
The Arctic ◽  
Ice Clouds ◽  
Complex Scheme

Abstract A persistent, weakly forced, horizontally extensive mixed-phase boundary layer cloud observed on 4–5 May 1998 during the Surface Heat Budget of the Arctic Ocean (SHEBA)/First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment–Arctic Clouds Experiment (FIRE–ACE) is modeled using three different bulk microphysics parameterizations of varying complexity implemented into the polar version of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5). The two simpler schemes predict mostly ice clouds and very little liquid water, while the complex scheme is able to reproduce the observed persistence and horizontal extent of the mixed-phase stratus deck. This mixed-phase cloud results in radiative warming of the surface, the development of a cloud-topped, surface-based mixed layer, and an enhanced precipitation rate. In contrast, the optically thin ice clouds predicted by the simpler schemes lead to radiative cooling of the surface, a strong diurnal cycle in the boundary layer structure, and very weak precipitation. The larger surface precipitation rate using the complex scheme is partly balanced by an increase in the turbulent flux of water vapor from the surface to the atmosphere. This enhanced vapor flux is attributed to changes in the surface and boundary layer characteristics induced by the cloud itself, although cloud–surface interactions appear to be exaggerated in the model compared with reality. The prediction of extensive mixed-phase stratus by the complex scheme is also associated with increased surface pressure and subsidence relative to the other simulations. Sensitivity tests show that the detailed treatment of ice nucleation and prediction of snow particle number concentration in the complex scheme suppresses ice particle concentration relative to the simpler schemes, reducing the vapor deposition rate (for given values of bulk ice mass and ice supersaturation) and leading to much greater amounts of liquid water and mixed-phase cloudiness. These results suggest that the treatments of ice nucleation and the snow intercept parameter in the simpler schemes, which are based upon midlatitude observations, are inadequate for simulating the weakly forced mixed-phase clouds endemic to the Arctic.

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