Effects of long-range aerosol transport on the microphysical properties of low-level liquid clouds in the Arctic

Abstract. The properties of low-level liquid clouds in the Arctic can be altered by long-range pollution transport to the region. Satellite, tracer transport model, and meteorological data sets are used here to determine a net aerosol–cloud interaction (ACInet) parameter that expresses the ratio of relative changes in cloud microphysical properties to relative variations in pollution concentrations while accounting for dry or wet scavenging of aerosols en route to the Arctic. For a period between 2008 and 2010, ACInet is calculated as a function of the cloud liquid water path, temperature, altitude, specific humidity, and lower tropospheric stability. For all data, ACInet averages 0.12 ± 0.02 for cloud-droplet effective radius and 0.16 ± 0.02 for cloud optical depth. It increases with specific humidity and lower tropospheric stability and is highest when pollution concentrations are low. Carefully controlling for meteorological conditions we find that the liquid water path of arctic clouds does not respond strongly to aerosols within pollution plumes. Or, not stratifying the data according to meteorological state can lead to artificially exaggerated calculations of the magnitude of the impacts of pollution on arctic clouds.

Download Full-text

Effects of long-range aerosol transport on the microphysical properties of low-level liquid clouds in the Arctic

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-31823-2015 ◽

2015 ◽

Vol 15 (21) ◽

pp. 31823-31866

Author(s):

Q. Coopman ◽

T. J. Garrett ◽

J. Riedi ◽

S. Eckhardt ◽

A. Stohl

Keyword(s):

Indirect Effect ◽

Transport Model ◽

Specific Humidity ◽

The Arctic ◽

Tracer Transport ◽

Aerosol Transport ◽

Liquid Water Path ◽

Arctic Clouds ◽

Microphysical Properties ◽

Pollution Concentrations

Abstract. The properties of clouds in the Arctic can be altered by long-range aerosol transport to the region. The goal of this study is to use satellite, tracer transport model, and meteorological data sets to determine the effects of pollution on cloud microphysics due only to pollution itself and not to the meteorological state. Here, A-Train, POLDER-3 and MODIS satellite instruments are used to retrieve low-level liquid cloud microphysical properties over the Arctic between 2008 and 2010. Cloud retrievals are co-located with simulated pollution represented by carbon-monoxide concentrations from the FLEXPART tracer transport model. The sensitivity of clouds to pollution plumes – including aerosols – is constrained for cloud liquid water path, temperature, altitude, specific humidity, and lower tropospheric stability (LTS). We define an Indirect Effect (IE) parameter from the ratio of relative changes in cloud microphysical properties to relative variations in pollution concentrations. Retrievals indicate that, depending on the meteorological regime, IE parameters range between 0 and 0.34 for the cloud droplet effective radius, and between −0.10 and 0.35 for the optical depth, with average values of 0.12 ± 0.02 and 0.15 ± 0.02 respectively. The IE parameter increases with increasing specific humidity and LTS. Further, the results suggest that for a given set of meteorological conditions, the liquid water path of arctic clouds does not respond strongly to pollution. Or, not constraining sufficiently for meteorology may lead to artifacts that exaggerate the magnitude of the aerosol indirect effect. The converse is that the response of arctic clouds to pollution does depend on the meteorologic state. Finally, we find that IE values are highest when pollution concentrations are low, and that they depend on the source of pollution.

Download Full-text

Implications of Limited Liquid Water Path on Static Mixing within Arctic Low-Level Clouds

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-14-0065.1 ◽

2014 ◽

Vol 53 (12) ◽

pp. 2775-2789 ◽

Cited By ~ 11

Author(s):

Joseph Sedlar

Keyword(s):

Mixed Layer ◽

Liquid Water ◽

Heat Budget ◽

Single Layer ◽

Specific Humidity ◽

The Arctic ◽

Liquid Water Path ◽

Stable Layer ◽

Water Path ◽

Low Level

AbstractObservations of cloud properties and thermodynamics from two Arctic locations, Barrow, Alaska, and Surface Heat Budget of the Arctic (SHEBA), are examined. A comparison of in-cloud thermodynamic mixing characteristics for low-level, single-layer clouds from nearly a decade of data at Barrow and one full annual cycle over the sea ice at SHEBA is performed. These cloud types occur relatively frequently, evident in 27%–30% of all cloudy cases. To understand the role of liquid water path (LWP), or lack thereof, on static in-cloud mixing, cloud layers are separated into optically thin and optically thick LWP subclasses. Clouds with larger LWPs tend to have a deeper in-cloud mixed layer relative to optically thinner clouds. However, both cloud LWP subclasses are frequently characterized by an in-cloud stable layer above the mixed layer top. The depth of the stable layer generally correlates with an increased temperature gradient across the layer. This layer often contains a specific humidity inversion, but it is more frequently present when cloud LWP is optically thinner (LWP < 50 g m−2). It is suggested that horizontal thermodynamic advection plays a key role modifying the vertical extent of in-cloud mixing and likewise the depth of in-cloud stable layers. Furthermore, longwave atmospheric opacity above the cloud top is generally enhanced during cases with optically thinner clouds. Thermodynamic advection, cloud condensate distribution within the stable layer, and enhanced atmospheric radiation above the cloud are found to introduce a thermodynamic–radiative feedback that potentially modifies the extent of LWP and subsequent in-cloud mixing.

Download Full-text

Arctic low-level clouds and their importance for radiative transfer simulations

10.5194/dach2022-135 ◽

2021 ◽

Author(s):

Hannes Griesche ◽

Carola Barrientos Velasco ◽

Patric Seifert

Keyword(s):

Remote Sensing ◽

Radiative Transfer ◽

Liquid Water ◽

Remote Sensing Data ◽

The Arctic ◽

Liquid Water Path ◽

Low Level ◽

Cloud Radar ◽

Microphysical Properties ◽

Water Detection

The observation of low-level stratocumulus cloud decks in the Arctic poses challenges to ground-based remote sensing. These clouds frequently occur during summer below the lowest range gate of common zenith-pointing cloud radar instruments, like the KAZR and the Mira-35. In addition, the optical thickness of these low-level clouds often do cause a complete attenuation of the lidar beam. For remote-sensing instrument synergy retrievals, as Cloudnet (Illingworth, 2007) or ARSCL (Active Remote Sensing of Clouds, Shupe, 2007), liquid-water detection in clouds is usually based on lidar backscatter. Thus, a complete attenuation can cause misclassification of mixed-phase clouds as pure-ice clouds. Moreover, the missing cloud radar information makes it difficult to derive the cloud microphysical properties, as most common retrievals are based on cloud radar reflectivity. A new low-level stratus detection mask (Griesche, 2020) was used to detect these clouds. The liquid-water cloud microphysical properties were derived by a simple but effective analysis of the liquid-water path. This approach was applied to remote-sensing data from a shipborne expedition performed in the Arctic summer 2017. The values calculated by applying the adjusted method improve the results of radiative transfer simulations yielding the determination of radiative closure. &#160; &#160; Illingworth et al. (2007). &#8220;Cloudnet&#8221;. BAMS. Shupe (2007). &#8220;A ground-based multisensor cloud phase classifier&#8221;. GRL. Griesche et al. (2020). &#8220;Application of the shipborne remote sensing supersite OCEANET for profiling of Arctic aerosols and clouds during Polarstern cruise PS106&#8221;. AMT.

Download Full-text

Stability dependent increases in liquid water with droplet number in the Arctic

10.5194/acp-2021-861 ◽

2021 ◽

Author(s):

Rebecca Jonette Murray-Watson ◽

Edward Gryspeerdt

Keyword(s):

Liquid Water ◽

Cloud Droplet ◽

Surface Energy Budget ◽

Radiative Properties ◽

The Arctic ◽

Polar Regions ◽

Liquid Water Path ◽

Arctic Clouds ◽

Microphysical Properties ◽

The Relationship

Abstract. The effects of aerosols on cloud microphysical properties are a large source of uncertainty when assessing anthropogenic climate change. The aerosol-cloud relationship is particularly unclear in high-latitude polar regions due to a limited number of observations. Cloud liquid water path (LWP) is an important control on cloud radiative properties, particularly in the Arctic, where clouds play a central role in the surface energy budget. Therefore, understanding how aerosols may alter cloud LWP is important, especially as aerosol sources such as industry and shipping move further north in a warming Arctic. Using satellite data, this work investigates the effects of aerosols on liquid Arctic clouds over open ocean by considering the relationship between cloud droplet number concentration (Nd) and LWP, an important component of the aerosol-LWP relationship. The LWP response to Nd varies significantly across the region, with increases in LWP with Nd observed at very high latitudes in multiple satellite datasets, with this positive signal observed most strongly during the summer months. This result is in contrast to the negative response typically seen in global satellite studies and previous work on Arctic clouds showing little LWP response to aerosols. The lower tropospheric stability (LTS) was found to be the driving force behind the spatial variations in LWP response, strongly influencing the sign and magnitude of the Nd-LWP relationship, with increases in LWP in high stability environments. The influence of humidity varied depending on the stability, with little impact at low LTS but a strong influence at high. The background Nd state does not seem to dominate the LWP response, despite the non-linearities in the relationship. As the LTS is projected to decrease in a future, warmer Arctic, these results show that increases may produce lower cloud water paths, offsetting their shortwave cooling effect.

Download Full-text

Sensitivity of CAM5-Simulated Arctic Clouds and Radiation to Ice Nucleation Parameterization

Journal of Climate ◽

10.1175/jcli-d-12-00517.1 ◽

2013 ◽

Vol 26 (16) ◽

pp. 5981-5999 ◽

Cited By ~ 55

Author(s):

Shaocheng Xie ◽

Xiaohong Liu ◽

Chuanfeng Zhao ◽

Yuying Zhang

Keyword(s):

Radiative Forcing ◽

Large Scale ◽

Arctic Region ◽

Atmospheric Model ◽

Ice Nucleation ◽

The Arctic ◽

Liquid Water Path ◽

Arctic Clouds ◽

Water Path ◽

Low Level

Abstract Sensitivity of Arctic clouds and radiation in the Community Atmospheric Model, version 5, to the ice nucleation process is examined by testing a new physically based ice nucleation scheme that links the variation of ice nuclei (IN) number concentration to aerosol properties. The default scheme parameterizes the IN concentration simply as a function of ice supersaturation. The new scheme leads to a significant reduction in simulated IN concentration at all latitudes while changes in cloud amounts and properties are mainly seen at high- and midlatitude storm tracks. In the Arctic, there is a considerable increase in midlevel clouds and a decrease in low-level clouds, which result from the complex interaction among the cloud macrophysics, microphysics, and large-scale environment. The smaller IN concentrations result in an increase in liquid water path and a decrease in ice water path caused by the slowdown of the Bergeron–Findeisen process in mixed-phase clouds. Overall, there is an increase in the optical depth of Arctic clouds, which leads to a stronger cloud radiative forcing (net cooling) at the top of the atmosphere. The comparison with satellite data shows that the new scheme slightly improves low-level cloud simulations over most of the Arctic but produces too many midlevel clouds. Considerable improvements are seen in the simulated low-level clouds and their properties when compared with Arctic ground-based measurements. Issues with the observations and the model–observation comparison in the Arctic region are discussed.

Download Full-text

The Influence of Cloud and Surface Properties on the Arctic Ocean Shortwave Radiation Budget in Coupled Models*

Journal of Climate ◽

10.1175/2007jcli1614.1 ◽

2008 ◽

Vol 21 (5) ◽

pp. 866-882 ◽

Cited By ~ 44

Author(s):

Irina V. Gorodetskaya ◽

L-Bruno Tremblay ◽

Beate Liepert ◽

Mark A. Cane ◽

Richard I. Cullather

Keyword(s):

Sea Ice ◽

Arctic Ocean ◽

Liquid Water ◽

Surface Albedo ◽

Liquid Water Content ◽

Radiation Budget ◽

The Arctic ◽

Coupled Models ◽

Arctic Clouds ◽

The Arctic Ocean

Abstract The impact of Arctic sea ice concentrations, surface albedo, cloud fraction, and cloud ice and liquid water paths on the surface shortwave (SW) radiation budget is analyzed in the twentieth-century simulations of three coupled models participating in the Intergovernmental Panel on Climate Change Fourth Assessment Report. The models are the Goddard Institute for Space Studies Model E-R (GISS-ER), the Met Office Third Hadley Centre Coupled Ocean–Atmosphere GCM (UKMO HadCM3), and the National Center for Atmosphere Research Community Climate System Model, version 3 (NCAR CCSM3). In agreement with observations, the models all have high Arctic mean cloud fractions in summer; however, large differences are found in the cloud ice and liquid water contents. The simulated Arctic clouds of CCSM3 have the highest liquid water content, greatly exceeding the values observed during the Surface Heat Budget of the Arctic Ocean (SHEBA) campaign. Both GISS-ER and HadCM3 lack liquid water and have excessive ice amounts in Arctic clouds compared to SHEBA observations. In CCSM3, the high surface albedo and strong cloud SW radiative forcing both significantly decrease the amount of SW radiation absorbed by the Arctic Ocean surface during the summer. In the GISS-ER and HadCM3 models, the surface and cloud effects compensate one another: GISS-ER has both a higher summer surface albedo and a larger surface incoming SW flux when compared to HadCM3. Because of the differences in the models’ cloud and surface properties, the Arctic Ocean surface gains about 20% and 40% more solar energy during the melt period in the GISS-ER and HadCM3 models, respectively, compared to CCSM3. In twenty-first-century climate runs, discrepancies in the surface net SW flux partly explain the range in the models’ sea ice area changes. Substantial decrease in sea ice area simulated during the twenty-first century in CCSM3 is associated with a large drop in surface albedo that is only partly compensated by increased cloud SW forcing. In this model, an initially high cloud liquid water content reduces the effect of the increase in cloud fraction and cloud liquid water on the cloud optical thickness, limiting the ability of clouds to compensate for the large surface albedo decrease. In HadCM3 and GISS-ER, the compensation of the surface albedo and cloud SW forcing results in negligible changes in the net SW flux and is one of the factors explaining moderate future sea ice area trends. Thus, model representations of cloud properties for today’s climate determine the ability of clouds to compensate for the effect of surface albedo decrease on the future shortwave radiative budget of the Arctic Ocean and, as a consequence, the sea ice mass balance.

Download Full-text

A New Double-Moment Microphysics Parameterization for Application in Cloud and Climate Models. Part II: Single-Column Modeling of Arctic Clouds

Journal of the Atmospheric Sciences ◽

10.1175/jas3447.1 ◽

2005 ◽

Vol 62 (6) ◽

pp. 1678-1693 ◽

Cited By ~ 72

Author(s):

H. Morrison ◽

J. A. Curry ◽

M. D. Shupe ◽

P. Zuidema

Keyword(s):

Climate Models ◽

Heat Budget ◽

Number Concentration ◽

The Arctic ◽

Liquid Water Path ◽

Microphysics Scheme ◽

Radiative Fluxes ◽

Arctic Clouds ◽

Single Column ◽

Double Moment

Abstract The new double-moment microphysics scheme described in Part I of this paper is implemented into a single-column model to simulate clouds and radiation observed during the period 1 April–15 May 1998 of the Surface Heat Budget of the Arctic (SHEBA) and First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment–Arctic Clouds Experiment (FIRE–ACE) field projects. Mean predicted cloud boundaries and total cloud fraction compare reasonably well with observations. Cloud phase partitioning, which is crucial in determining the surface radiative fluxes, is fairly similar to ground-based retrievals. However, the fraction of time that liquid is present in the column is somewhat underpredicted, leading to small biases in the downwelling shortwave and longwave radiative fluxes at the surface. Results using the new scheme are compared to parallel simulations using other microphysics parameterizations of varying complexity. The predicted liquid water path and cloud phase is significantly improved using the new scheme relative to a single-moment parameterization predicting only the mixing ratio of the water species. Results indicate that a realistic treatment of cloud ice number concentration (prognosing rather than diagnosing) is needed to simulate arctic clouds. Sensitivity tests are also performed by varying the aerosol size, solubility, and number concentration to explore potential cloud–aerosol–radiation interactions in arctic stratus.

Download Full-text

Ground-based remote sensing of thin clouds in the Arctic

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-5-8653-2012 ◽

2012 ◽

Vol 5 (6) ◽

pp. 8653-8699 ◽

Cited By ~ 3

Author(s):

T. J. Garrett ◽

C. Zhao

Keyword(s):

Water Vapor ◽

Thermal Emission ◽

Stratospheric Ozone ◽

Microwave Radiometer ◽

Single Layer ◽

Primary Source ◽

The Arctic ◽

Liquid Water Path ◽

Water Path ◽

Microphysical Properties

Abstract. This paper describes a method for using interferometer measurements of downwelling thermal radiation to retrieve the properties of single-layer clouds. Cloud phase is determined from ratios of thermal emission in three "micro-windows" where absorption by water vapor is particularly small. Cloud microphysical and optical properties are retrieved from thermal emission in two micro-windows, constrained by the transmission through clouds of stratospheric ozone emission. Assuming a cloud does not approximate a blackbody, the estimated 95% confidence retrieval errors in effective radius, visible optical depth, number concentration, and water path are, respectively, 10%, 20%, 38% (55% for ice crystals), and 16%. Applied to data from the Atmospheric Radiation Measurement program (ARM) North Slope of Alaska – Adjacent Arctic Ocean (NSA-AAO) site near Barrow, Alaska, retrievals show general agreement with ground-based microwave radiometer measurements of liquid water path. Compared to other retrieval methods, advantages of this technique include its ability to characterize thin clouds year round, that water vapor is not a primary source of retrieval error, and that the retrievals of microphysical properties are only weakly sensitive to retrieved cloud phase. The primary limitation is the inapplicability to thicker clouds that radiate as blackbodies.

Download Full-text

The Role of Eddy Diffusivity Profiles on Stratocumulus Liquid Water Path Biases

Monthly Weather Review ◽

10.1175/mwr3426.1 ◽

2007 ◽

Vol 135 (7) ◽

pp. 2786-2793 ◽

Cited By ~ 5

Author(s):

Stephan R. de Roode

Keyword(s):

Boundary Layer ◽

Liquid Water ◽

Sensible Heat Flux ◽

Eddy Diffusivity ◽

Specific Humidity ◽

Entrainment Rate ◽

Liquid Water Path ◽

Water Path ◽

Wide Range ◽

Heat And Moisture

Abstract Results from simulations of the stratocumulus-topped boundary layer with one-dimensional versions of general simulation models typically exhibit a wide range of spread in the modeled liquid water path (LWP). These discrepancies are often attributed to differences in the modeled entrainment rate. Results from a large eddy simulation of the First International Satellite Cloud Climatology Project Regional Experiment I stratocumulus case are analyzed. The diagnosed eddy diffusivities for heat and moisture are found to differ by about a factor of 3. Moreover, both have a much larger magnitude than the ones typically applied in boundary layer parameterization schemes. Motivated by these results mean state solutions are analyzed for the specific case in which the vertical fluxes of heat and moisture are prescribed, whereas eddy diffusivity profiles are systematically varied by multiplication with a constant factor. The solutions demonstrate that any value, ranging from zero to a maximum adiabatic value, can be obtained for the LWP. In the subtropical parts over the ocean where horizontally extended stratocumulus fields persist, the surface sensible heat flux is typically small, whereas surface evaporation and entrainment of relatively dry air from above the surface can result in significant moisture fluxes. If the eddy diffusivity values are small, then the mean specific humidity will tend to decrease quite rapidly with height in order to support the humidity flux. This results in erroneous low humidity values in the upper part of the boundary layers causing low LWP values.

Download Full-text