Author: Ming Zhao Publisher: ISBN: 9781303050398 Category : Arctic regions Languages : en Pages : 93
Book Description
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: Elin McIlhattan Publisher: ISBN: Category : Languages : en Pages : 141
Book Description
Clouds are the primary modulator of radiation and moisture received by the Arctic surface. Long term, large scale, and detailed observations of Arctic clouds are required to connect particular cloud macro- and microphysical characteristics to their influence on the varied surfaces of the Arctic. Constraining that influence is key to accurate projections of future climate, particularly sea level rise. Prior to the launch of CloudSat and CALIPSO in 2006, Arctic cloud observations were limited in either time (field campaigns), space (individual research stations), or sensitivity (passive satellites). CloudSat's Cloud Profiling Radar (CPR) and CALIPSO's Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) have provided detailed information on the location, phase, and vertical structure of Arctic clouds. This study leverages data from these two instruments to explore the connections between Arctic cloud phase, precipitation, and surface radiation. First, the connection between cloud phase and precipitation is documented over the Greenland Ice Sheet (GIS). Partitioning snowfall observed over the GIS into two regimes --- snowfall produced by ice-phase clouds and snowfall produced by Arctic mixed-phase clouds --- reveals that the two regimes are distinct beyond the cloud phase that defines them, including differing seasonal and regional frequency, snowfall rates, geometric cloud depth, and air mass origins. Next, Arctic cloud representation is compared between two versions of the Community Earth System Model (CESM), with CloudSat and CALIPSO observations used to provide physically reasonable benchmarks. The updated version of CESM has a markedly different mean state than the previous version, having addressed a known bias in Arctic mixed-phase clouds. Finally, the connection to surface radiation is examined using the Cloud Impact on Surface Radiation Ratio (CISRR). CISRR shows that over the icy surfaces of the Arctic, on average the warming effect of a cloud is at minimum twice as strong as its cooling effect.
Author: Constantin Andronache Publisher: Elsevier ISBN: 012810550X Category : Science Languages : en Pages : 302
Book Description
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: J. A. Curry Publisher: BiblioGov ISBN: 9781289272463 Category : Languages : en Pages : 58
Book Description
An overview is given of the First ISCCP Regional Experiment (FIRE) Arctic Clouds Experiment that was conducted in the Arctic during April through July, 1998. The principal goal of the field experiment was to gather the data needed to examine the impact of arctic clouds on the radiation exchange between the surface, atmosphere, and space, and to study how the surface influences the evolution of boundary layer clouds. The observations will be used to evaluate and improve climate model parameterizations of cloud and radiation processes, satellite remote sensing of cloud and surface characteristics, and understanding of cloud-radiation feedbacks in the Arctic. The experiment utilized four research aircraft that flew over surface-based observational sites in the Arctic Ocean and Barrow, Alaska. In this paper we describe the programmatic and science objectives of the project, the experimental design (including research platforms and instrumentation), conditions that were encountered during the field experiment, and some highlights of preliminary observations, modelling, and satellite remote sensing studies.
Author: Sylvia Sullivan Publisher: John Wiley & Sons ISBN: 1119700310 Category : Science Languages : en Pages : 371
Book Description
Clouds and Their Climatic Impacts Clouds are an influential and complex element of Earth’s climate system. They evolve rapidly in time and exist over small spatial scales, but also affect global radiative balance and large-scale circulations. With more powerful models and extensive observations now at our disposal, the climate impact of clouds is receiving ever more research attention. Clouds and Their Climatic Impacts: Radiation, Circulation, and Precipitation presents an overview of our current understanding on various types of clouds and cloud systems and their multifaceted role in the radiative budget, circulation patterns, and rainfall. Volume highlights include: Interactions of aerosol with both liquid and ice clouds Surface and atmospheric cloud radiative feedbacks and effects Arctic, extratropical, and tropical clouds Cloud-circulation coupling at global, meso, and micro scales Precipitation efficiency, phase, and measurements The role of machine learning in understanding clouds and climate The American Geophysical Union promotes discovery in Earth and space science for the benefit of humanity. Its publications disseminate scientific knowledge and provide resources for researchers, students, and professionals.
Author: Hui Lai Publisher: ISBN: Category : Languages : en Pages :
Book Description
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: Cécile Hannay Publisher: ISBN: Category : Atmospheric radiation Languages : en Pages : 120
Book Description
"We evaluate the ability of a typical cloud parameterization from a global model (CCM3 from NCAR) to simulate the Arctic cloudiness and longwave radiative fluxes during wintertime. Simulations are conducted with a Single-Column model (SCM) forced with observations and reanalysis data from the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment. Typically, the SCM overestimates the Arctic cloud fraction and the downwelling longwave flux. Moreover, the SCM does not capture accurately the temperature and moisture profiles, and the surface flux fields. Relaxing temperature and moisture profiles to observed values dramatically improves the simulations. This suggests that the cloud parameterization of CCM3 is suitable for Arctic clouds, as long as the temperature and moisture fields are captured correctly. Sensitivities studies show that the cloud fraction is not very sensitive to cloud type, ice effective radius, ice liquid ratio amount and uncertainty of the advective forcing"--Leaf 3.
Author: Loewe, Katharina Publisher: KIT Scientific Publishing ISBN: 3731506866 Category : Physics Languages : en Pages : 174
Book Description
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: Ming Zhao
Author: Elin McIlhattan
Author: Constantin Andronache
Author: J. A. Curry
Author: Sylvia Sullivan
Author: Hui Lai
Author: 
Author: Cécile Hannay
Author: Loewe, Katharina
Author: