Arctic Mixed-phase Clouds from the Micro- to the Mesoscale - Insights from High-resolution Modeling PDF Download

Author: Gesa K. Eirund
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Languages : en
Pages :

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Author: Loewe, Katharina
Publisher: KIT Scientific Publishing
ISBN: 3731506866
Category : Physics
Languages : en
Pages : 174

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This work provides new insights into macro- and microphysical properties of Arctic mixed-phase clouds: first, by comparing semi-idealized large eddy simulations with observations; second, by dissecting the influences of different surface types and boundary layer structures on Arctic mixed- phase clouds; third, by elucidating the dissipation process; and finally by analyzing the main microphysical processes inside Arctic mixed-phase clouds.

Author: Katharina Loewe
Publisher:
ISBN: 9781013281211
Category : Science
Languages : en
Pages : 160

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This work provides new insights into macro- and microphysical properties of Arctic mixed-phase clouds: first, by comparing semi-idealized large eddy simulations with observations; second, by dissecting the influences of different surface types and boundary layer structures on Arctic mixed- phase clouds; third, by elucidating the dissipation process; and finally by analyzing the main microphysical processes inside Arctic mixed-phase clouds. This work was published by Saint Philip Street Press pursuant to a Creative Commons license permitting commercial use. All rights not granted by the work's license are retained by the author or authors.

Author:
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Languages : en
Pages : 5

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Mixed-phase arctic stratus clouds are the predominant cloud type in the Arctic (Curry et al. 2000) and through various feedback mechanisms exert a strong influence on the Arctic climate. Perhaps one of the most intriguing of their features is that they tend to have liquid tops that precipitate ice. Despite the fact that this situation is colloidally unstable, these cloud systems are quite long lived - from a few days to over a couple of weeks. It has been hypothesized that mixed-phase clouds are maintained through a balance between liquid water condensation resulting from the cloud-top radiative cooling and ice removal by precipitation (Pinto 1998; Harrington et al. 1999). In their modeling study Harrington et al. (1999) found that the maintenance of this balance depends strongly on the ambient concentration of ice forming nucleus (IFN). In a follow-up study, Jiang et al. (2002), using only 30% of IFN concentration predicted by Meyers et al. (1992) IFN parameterization were able to obtain results similar to the observations reported by Pinto (1998). The IFN concentration measurements collected during the Mixed-Phase Arctic Cloud Experiment (M-PACE), conducted in October 2004 over the North Slope of Alaska and the Beaufort Sea (Verlinde et al. 2005), also showed much lower values then those predicted (Prenne, pers. comm.) by currently accepted ice nucleation parameterizations (e.g. Meyers et al. 1992). The goal of this study is to use the extensive IFN data taken during M-PACE to examine what effects low IFN concentrations have on mesoscale cloud structure and coastal dynamics.

Author: Constantin Andronache
Publisher: Elsevier
ISBN: 012810550X
Category : Science
Languages : en
Pages : 302

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Mixed-Phase Clouds: Observations and Modeling presents advanced research topics on mixed-phase clouds. As the societal impacts of extreme weather and its forecasting grow, there is a continuous need to refine atmospheric observations, techniques and numerical models. Understanding the role of clouds in the atmosphere is increasingly vital for current applications, such as prediction and prevention of aircraft icing, weather modification, and the assessment of the effects of cloud phase partition in climate models. This book provides the essential information needed to address these problems with a focus on current observations, simulations and applications. Provides in-depth knowledge and simulation of mixed-phase clouds over many regions of Earth, explaining their role in weather and climate Features current research examples and case studies, including those on advanced research methods from authors with experience in both academia and the industry Discusses the latest advances in this subject area, providing the reader with access to best practices for remote sensing and numerical modeling

Author: Ming Zhao
Publisher:
ISBN: 9781303050398
Category : Arctic regions
Languages : en
Pages : 93

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The Arctic is a region that is very sensitive to global climate change while also experiencing significant changes in its surface air temperature, sea-ice cover, atmospheric circulation, precipitation, snowfall, biogeochemical cycling, and land surface. Although previous studies have shown that the arctic clouds play an important role in the arctic climate changes, the arctic clouds are poorly understood and simulated in climate model due to limited observations. Furthermore, most of the studies were based on short-term experiments and typically only cover the warm seasons, which do not provide a full understanding of the seasonal cycle of arctic clouds. To address the above concerns and to improve our understanding of arctic clouds, six years of observational and retrieval data from 1999 to 2004 at the Atmospheric Radiation Management (ARM) Climate Research Facility (ACRF) North Slope of Alaska (NSA) Barrow site are used to understand the arctic clouds and related radiative processes. In particular, we focus on the liquid-ice mass partition in the mixed-phase cloud layer. Statistical results show that aerosol type and concentration are important factors that impact the mixed-phase stratus (MPS) cloud microphysical properties: liquid water path (LWP) and liquid water fraction (LWF) decrease with the increase of cloud condensation nuclei (CCN) number concentration; the high dust loading and dust occurrence in the spring are possible reasons for the much lower LWF than the other seasons. The importance of liquid-ice mass partition on surface radiation budgets was analyzed by comparing cloud longwave radiative forcings under the same LWP but different ice water path (IWP) ranges. Results show the ice phase enhance the surface cloud longwave (LW) forcing by 8~9 W m−2 in the moderately thin MPS. This result provides an observational evidence on the aerosol glaciation effect in the moderately thin MPS, which is largely unknown so far. The above new insights are important to guide the model parameterizations of liquid-ice mass partition in arctic mixed-phase clouds, and are served as a test bed to cloud models and cloud microphysical schemes. The observational data between 1999 and 2007 are used to assess the performance of the European Center for Medium-Range Weather Forecasts (ECMWF) model in the Arctic region. The ECMWF model-simulated near-surface humidity had seasonal dependent biases as large as 20%, while also experiencing difficulty representing boundary layer (BL) temperature inversion height and strength during the transition seasons. Although the ECMWF model captured the seasonal variation of surface heat fluxes, it had sensible heat flux biases over 20 W m−2 in most of the cold months. Furthermore, even though the model captured the general seasonal variations of low-level cloud fraction (LCF) and LWP, it still overestimated the LCF by 20% or more and underestimated the LWP over 50% in the cold season. On average, the ECMWF model underestimated LWP by ~30 g m−2 but more accurately predicted ice water path for BL clouds. For BL mixed-phase clouds, the model predicted water-ice mass partition was significantly lower than the observations, largely due to the temperature dependence of water-ice mass partition used in the model. The new cloud and BL schemes of the ECMWF model that were implemented after 2003 only resulted in minor improvements in BL cloud simulations in summer. These results indicate that significant improvements in cold season BL and mixed-phase cloud processes in the model are needed. In this study, single-layer MPS clouds were simulated by the Weather Research and Forecasting (WRF) model under different microphysical schemes and different ice nuclei (IN) number concentrations. Results show that by using proper IN concentration, the WRF model incorporated with Morrison microphysical scheme can reasonably capture the observed seasonal differences in temperature dependent liquid-ice mass partition. However, WRF simulations underestimate both LWP and IWP indicating its deficiency in capturing the radiative impacts of arctic MPS clouds.

Author: Hui Lai
Publisher:
ISBN:
Category :
Languages : en
Pages :

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To better understand the dynamic and thermodynamic processes that form and maintain Arctic multilayered mixed-phase clouds, Moderate Resolution Imaging Spectroradiometer (MODIS) radiances, High Spectral Resolution Lidar (HSRL) backscatter, and Ka-band ARM zenith radar (KAZR) returns along with balloon-borne sounding thermodynamic profiles, were analyzed from 1-3 May 2013. The observations, together with ERA-Interim Reanalysis data, indicate that three cloud regimes were present during this period. Frontal clouds occurred in a north to south band with Barrow located on their eastern edge at 00:00 UTC 2 May. By mid-day the frontal clouds had moved into the Barrow region. A broad low-altitude stratus deck existed to the west and north of Barrow, advecting into the Barrow region by the end of 2 May as the frontal clouds cleared the region. The stratus deck remained over Barrow throughout 3 May and several days beyond it. Boundary layer cellular convection was the predominant cloud type in the vicinity of the low pressure to the east and north of Barrow on 1-2 May.On 2 May 2013 shallow single- and multi-layered, mixed-phase clouds observed by the HSRL and KAZR were present above Barrow, Alaska, leading at various times to pristine crystals, rimed crystals and aggregates of crystals at the surface. During this case study period, a weak surface trough was located to the north and east of Barrow with a high pressure ridge to its west. The associated surface front was located over Barrow and extended to the north over the Arctic Ocean. High spatial (250-m) pixel resolution MODIS radiances show low level cloud streets in the vicinity of Barrow and just to its east oriented perpendicular to the mean wind around 00:00 UTC 2 May. Low altitude cloud streets also existed to the west of Barrow at this time, though oriented parallel to the mean wind. Finally, additional cloud streets to the southwest of Barrow and perpendicular to the mean wind also were present but in the higher altitude frontal clouds. The low altitude cloud streets just to the east and west of Barrow, and under the frontal cloud layer, were the source of the multilayered clouds on this day; this study focused on the ones to the west. These cloud streets formed in an environment of strong vertical wind shear with an underlying shallow buoyant layer near the surface.The Weather and Research Forecasting (WRF) model was used to conduct mesoscale simulations for this day and the two surrounding ones. For the three-day period from 1-3 May 2013 the 27-km spatial grid spacing WRF model reproduced mesoscale geopotential height, wind, relative humidity and sea-level pressure fields similar to those contained in the (0.75 lat/lon) ERA-Interim Reanalysis. Moreover, the model was able to reproduce the three cloud systems evident in the observations: the low cloud-liquid stratus to the west of Barrow, the deep frontal cloud layer in the vicinity of Barrow, and the more convective cloud cells with heights in-between to the east of Barrow.In the WRF modeling approach six nested domains were used with horizontal grid spacings starting from 27 km and scaling down in ratios of 3 to 1, with the finest domain run in large eddy simulation mode at 111-m horizontal grid spacing in an attempt to capture the short (~ 1.5-km) wavelength of the cloud streets apparent in the satellite data. Model results show that warm air advection and surface radiative heating created enhanced near surface instability, providing the buoyancy necessary to drive the initial convection. These buoyant parcels entered the region of strong vertical shear, leading to Richardson numbers around 0.2 and the conditions favorable for the formation of roll clouds. The wavelengths of the roll clouds produced by the inner four nested domains varied from 33 km for the outermost 3-km domain to 1 km for the finest 0.111-km grid spacing domain. The finest grid spacing domain roll-cloud wavelengths were comparable to those observed by MODIS, illustrating the necessity of using a grid spacing sufficiently small to place at least 7 to 10 grid points across a roll in order to resolve it.

Author:
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Languages : en
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The goal of this project is the development and evaluation of improved parameterization of arctic cloud and radiation processes and implementation of the parameterizations into a climate model. Our research focuses specifically on the following issues: (1) continued development and evaluation of cloud microphysical parameterizations, focusing on issues of particular relevance for mixed phase clouds; and (2) evaluation of the mesoscale simulation of arctic cloud system life cycles.

Author:
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ISBN:
Category :
Languages : en
Pages : 45

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[1] Simulations of mixed-phase clouds in forecasts with the NCAR Atmosphere Model version 3 (CAM3) and the GFDL Atmospheric Model version 2 (AM2) for the Mixed-Phase Arctic Cloud Experiment (M-PACE) are performed using analysis data from numerical weather prediction centers. CAM3 significantly underestimates the observed boundary layer mixed-phase cloud fraction and cannot realistically simulate the variations of liquid water fraction with temperature and cloud height due to its oversimplified cloud microphysical scheme. In contrast, AM2 reasonably reproduces the observed boundary layer cloud fraction while its clouds contain much less cloud condensate than CAM3 and the observations. The simulation of the boundary layer mixed-phase clouds and their microphysical properties is considerably improved in CAM3 when a new physically based cloud microphysical scheme is used (CAM3LIU). The new scheme also leads to an improved simulation of the surface and top of the atmosphere longwave radiative fluxes. Sensitivity tests show that these results are not sensitive to the analysis data used for model initialization. Increasing model horizontal resolution helps capture the subgrid-scale features in Arctic frontal clouds but does not help improve the simulation of the single-layer boundary layer clouds. AM2 simulated cloud fraction and LWP are sensitive to the change in cloud ice number concentrations used in the Wegener-Bergeron-Findeisen process while CAM3LIU only shows moderate sensitivity in its cloud fields to this change. Furthermore, this paper shows that the Wegener-Bergeron-Findeisen process is important for these models to correctly simulate the observed features of mixed-phase clouds.

Author: Yaosheng Chen
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Arctic mixed-phase clouds are often multi-layered. Different cloud layers interact through radiation as well as ice precipitation falling from upper layer clouds into the lower layer clouds. The evolution of an Arctic mixed-phase stratiform cloud under prescribed perturbations from an overlaying cloud in the form of downwelling longwave radiation and ice precipitation was simulated and documented. The perturbations created regions with heterogeneous properties in the horizontal direction within the lower level cloud, the consequence of which was the development of a mesoscale circulation that propagated the perturbations well beyond the location of the initial perturbed region.In a separate study, we forward modeled radar Doppler spectra based on a large-eddy simulation (LES) model simulation of a single layer Arctic mixed-phase cloud and compared the modeled quantities with those retrieved from the observations. We show that there was a significant contribution from the microphysical broadening to the cloud radar Doppler spectral width in Arctic mixed-phase clouds. LES simulations configured with different ice particle characteristics captured different aspects of the observations in the simulated case, where a mixture of ice particles of different properties were likely present. The dynamics of the LES simulations, characterized with the total turbulent kinetic energy dissipation rate, agreed fairly well with the values retrieved from the observations. Due to significant numerical dissipation in the model for the case evaluated here, the TKE dissipation rate from the subgrid-scale model did not represent the dissipation rate in the model.