scholarly journals Impact of aerosols on precipitation over the Maritime Continent simulated by a convection-permitting model

2016 ◽  
Author(s):  
Muhammad E. E. Hassim ◽  
W. W. Grabowski ◽  
T. P. Lane
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Cloud Droplet ◽  
New Guinea ◽  
Cloud Microphysics ◽  
Height Distribution ◽  
North East ◽  
Droplet Concentration ◽  
Cloud Tops ◽  
The Impact

Abstract. We examine the impact of assumed cloud droplet concentration on the simulated diurnal cycle of rainfall over New Guinea and surrounding seas using convection-permitting numerical simulations with the Weather Research and Forecasting (WRF) model. The simulations mimic effects of cloud condensation nuclei on cloud and precipitation processes. They follow simulations reported in Hassim et al (ACP 2016) that focused on dynamical aspects, namely the topographic forcing and the off-shore propagation of convective systems that contribute to the observed early-morning rainfall maximum north-east of New Guinea. Simulations reported in this current study apply the bulk cloud microphysics of Thompson et al. with contrasting cloud droplet concentrations of 100 and 1,000 per cc, referred to as pristine and polluted conditions, respectively. Overall, the assumed cloud droplet concentration has a small impact on the simulated convection. This emphasizes the predominant control from the diurnal cycle and the large-scale conditions. Pristine convection results in a 15–20 % larger surface accumulated rainfall over both land and ocean, and a noticeable shift of the cloud top height distribution, a reduction of the contribution of shallow cloudiness (cloud tops below 3 km) and an increase of the population of deep clouds (cloud tops above 9 km). The simulated impact on precipitation and cloud fields is in stark contrast to previous modelling studies that document small enhancement of surface precipitation and significant increase of the cloud top height in polluted conditions. Analysis of microphysical fields suggests that the simulated small enhancement of precipitation in pristine conditions comes from more efficient rain processes below the freezing level and enhanced graupel initiation and growth aloft. The increase of the cloud top height is arguably due to precipitation off-loading increasing cloud buoyancy aloft that has been shown to operate in shallow warm convection. However, the relatively low horizontal resolution and application of the bulk cloud microphysics warrants follow-up studies to assess validity of the impacts documented in the current study.

scholarly journals Aerosol Impacts on the Diurnal Cycle of Marine Stratocumulus

2008 ◽  
Vol 65 (8) ◽  
pp. 2705-2718 ◽  
Author(s):  
Irina Sandu ◽  
Jean-Louis Brenguier ◽  
Olivier Geoffroy ◽  
Odile Thouron ◽  
Valery Masson
Keyword(s):  
Boundary Layer ◽  
Diurnal Cycle ◽  
Liquid Water ◽  
Large Scale ◽  
Cloud Microphysics ◽  
Cloud Base ◽  
Liquid Water Path ◽  
Marine Stratocumulus ◽  
Water Path ◽  
The Impact

Abstract Recent large-eddy simulation (LES) studies of the impact of aerosol on the dynamics of nocturnal marine stratocumulus revealed that, depending on the large-scale forcings, an aerosol-induced increase of the droplet concentration can lead to either an increase or a decrease of the liquid water path, hence contrasting with the cloud thickening that is expected from a reduction of the precipitation efficiency. In this study, the aerosol impacts on cloud microphysics are examined in the context of the boundary-layer diurnal cycle using 36-h LES simulations of pristine and polluted clouds. These simulations corroborate previous findings that during nighttime aerosol-induced liquid water path changes are sensitive to the large-scale forcings via enhancement of cloud-top entrainment such that, ultimately, the liquid water path may be reduced when the free-tropospheric-entrained air is drier. During the day, however, enhanced entrainment, inhibition of drizzle evaporation below cloud base, and reduced sensible heat flux from the surface lead to a more pronounced decoupling of the boundary layer, which significantly amplifies the liquid water path reduction of the polluted clouds. At night the sign of the liquid water path difference between pristine and polluted clouds depends upon large-scale forcings, while during the day the liquid water path of polluted clouds is always smaller than the one of the pristine clouds. Suggestions are made on how observational studies could be designed for validation of these simulations.

scholarly journals Broadening of Cloud Droplet Spectra through Eddy Hopping: Turbulent Entraining Parcel Simulations

2018 ◽  
Vol 75 (10) ◽  
pp. 3365-3379 ◽  
Author(s):  
Gustavo C. Abade ◽  
Wojciech W. Grabowski ◽  
Hanna Pawlowska
Keyword(s):  
Droplet Size ◽  
Turbulent Mixing ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Cloud Microphysics ◽  
Droplet Growth ◽  
Size Spectrum ◽  
Entrainment Rate ◽  
The Mean ◽  
The Impact

This paper discusses the effects of cloud turbulence, turbulent entrainment, and entrained cloud condensation nuclei (CCN) activation on the evolution of the cloud droplet size spectrum. We simulate an ensemble of idealized turbulent cloud parcels that are subject to entrainment events modeled as a random process. Entrainment events, subsequent turbulent mixing inside the parcel, supersaturation fluctuations, and the resulting stochastic droplet activation and growth by condensation are simulated using a Monte Carlo scheme. Quantities characterizing the turbulence intensity, entrainment rate, CCN concentration, and the mean fraction of environmental air entrained in an event are all specified as independent external parameters. Cloud microphysics is described by applying Lagrangian particles, the so-called superdroplets. These are either unactivated CCN or cloud droplets that grow from activated CCN. The model accounts for the addition of environmental CCN into the cloud by entraining eddies at the cloud edge. Turbulent mixing of the entrained dry air with cloudy air is described using the classical linear relaxation to the mean model. We show that turbulence plays an important role in aiding entrained CCN to activate, and thus broadening the droplet size distribution. These findings are consistent with previous large-eddy simulations (LESs) that consider the impact of variable droplet growth histories on the droplet size spectra in small cumuli. The scheme developed in this work is ready to be used as a stochastic subgrid-scale scheme in LESs of natural clouds.

scholarly journals Monte Carlo-based subgrid parameterization of vertical velocity and stratiform cloud microphysics in ECHAM5.5-HAM2

2013 ◽  
Vol 13 (2) ◽  
pp. 5477-5507
Author(s):  
J. Tonttila ◽  
P. Räisänen ◽  
H. Järvinen
Keyword(s):  
Monte Carlo ◽  
Vertical Velocity ◽  
Cloud Droplet ◽  
Cloud Microphysics ◽  
Radiative Effects ◽  
Cloud Droplets ◽  
Microphysical Properties ◽  
Cloud Radiative Effects ◽  
Cloud Activation ◽  
The Impact

Abstract. A new method for parameterizing the subgrid variations of vertical velocity and cloud droplet number concentration (CDNC) is presented for GCMs. These parameterizations build on top of existing parameterizations that create stochastic subgrid cloud columns inside the GCM grid-cells, which can be employed by the Monte Carlo independent column approximation approach for radiative transfer. The new model version adds a description for vertical velocity in individual subgrid columns, which can be used to compute cloud activation and the subgrid distribution of the number of cloud droplets explicitly. This provides a consistent way for simulating the cloud radiative effects with two-moment cloud microphysical properties defined in subgrid-scale. The primary impact of the new parameterizations is to decrease the CDNC over polluted continents, while over the oceans the impact is smaller. This promotes changes in the global distribution of the cloud radiative effects and might thus have implications on model estimation of the indirect radiative effect of aerosols.

Warm Cloud Evolution, Precipitation, and Their Weak Linkage in HadGEM3: New Process-Level Diagnostics using A-Train Observations

2021 ◽  
Author(s):  
Hanii Takahashi ◽  
Alejandro Bodas-Salcedo ◽  
Graeme Stephens
Keyword(s):  
Large Scale ◽  
Cloud Droplet ◽  
Formation Processes ◽  
Evaluation Tool ◽  
Liquid Water Path ◽  
Microphysics Scheme ◽  
Warm Rain ◽  
Weak Linkage ◽  
The Impact ◽  
Rain Formation

AbstractThe latest configuration of the Hadley Centre Global Environmental Model version 3 (HadGEM3) contains significant changes in the formulation of warm rain processes and aerosols. We evaluate the impacts of these changes in the simulation of warm rain formation processes using A-Train observations. We introduce a new model evaluation tool, quartile-based Contoured Frequency by Optical Depth Diagrams (CFODDs), in order to fill in some blind spots that conventional CFODDs have. Results indicate that HadGEM3 has weak linkage between the size of particle radius and warm rain formation processes, and switching to the new warm rain microphysics scheme causes more difference in warm rain formation processes than switching to the new aerosol scheme through reducing overly produced drizzle mode in HadGEM3. Finally, we run an experiment in which we perturb the second aerosol indirect effect (AIE) to study the rainfall-aerosol interaction in HadGEM3. Since the large changes in the cloud droplet number concentration (CDNC) appear in the AIE experiment, a large impact in warm rain diagnostics is expected. However, regions with large fractional changes in CDNC show a muted change in precipitation, arguably because large-scale constraints act to reduce the impact of such a big change in CDNC. The adjustment in cloud liquid water path to the AIE perturbation produces a large negative shortwave forcing in the midlatitudes.

scholarly journals 'Desecration' in a Place of Refuge

2013 ◽  
Vol 11 (1) ◽  
pp. 98-109 ◽  
Author(s):  
Diana Glazebrook
Keyword(s):  
Papua New Guinea ◽  
Large Scale ◽  
Forced Migration ◽  
New Guinea ◽  
Refugee Population ◽  
Irian Jaya ◽  
International Border ◽  
The Impact

In this paper I explore two related questions: how does a particular site come to be perceived as sacred, and what is the impact of the destruction of something sacred when it occurs in a place of ‘refuge’? This study is situated on the island of New Guinea, in the experiences of West Papuan people from the Indonesian Province of Papua (formerly Irian Jaya), living as refugees across the international border in Papua New Guinea. The inquiry is grounded in two instances involving a refugee population in a place of refuge. The first instance involves the burning of a church built by a refugee congregation, and the second involves the large-scale occupation by a refugee population of another people’s land. A doubling effect is intended here. Forced migration can simultaneously render refugees vulnerable to the violence of others, and in the process of resettlement, refugees may have no real choice but to engage in actions that violate the land of others.

The Strong Impact of Weak Horizontal Convergence on Continental Shallow Convection

2020 ◽  
Vol 77 (9) ◽  
pp. 3119-3137
Author(s):  
Marcin J. Kurowski ◽  
Wojciech W. Grabowski ◽  
Kay Suselj ◽  
João Teixeira
Keyword(s):  
Large Scale ◽  
Cloud Microphysics ◽  
Cloud Base ◽  
Small Scale ◽  
Strong Impact ◽  
Shallow Convection ◽  
Liquid Water Path ◽  
Strong Response ◽  
The Impact ◽  
Benchmark Solutions

Abstract Idealized large-eddy simulation (LES) is a basic tool for studying three-dimensional turbulence in the planetary boundary layer. LES is capable of providing benchmark solutions for parameterization development efforts. However, real small-scale atmospheric flows develop in heterogeneous and transient environments with locally varying vertical motions inherent to open multiscale interactive dynamical systems. These variations are often too subtle to detect them by state-of-the-art remote and in situ measurements, and are typically excluded from idealized simulations. The present study addresses the impact of weak [i.e., O(10−6) s−1] short-lived low-level large-scale convergence/divergence perturbations on continental shallow convection. The results show a strong response of shallow nonprecipitating convection to the applied weak large-scale dynamical forcing. Evolutions of CAPE, mean liquid water path, and cloud-top heights are significantly affected by the imposed convergence/divergence. In contrast, evolving cloud-base properties, such as the area coverage and mass flux, are only weakly affected. To contrast those impacts with microphysical sensitivity, the baseline simulations are perturbed assuming different observationally based cloud droplet number concentrations and thus different rainfall. For the tested range of microphysical perturbations, the imposed convergence/divergence provides significantly larger impact than changes in the cloud microphysics. Simulation results presented here provide a stringent test for convection parameterizations, especially important for large-scale models progressing toward resolving some nonhydrostatic effects.

Drizzle in Stratiform Boundary Layer Clouds. Part II: Microphysical Aspects

2005 ◽  
Vol 62 (9) ◽  
pp. 3034-3050 ◽  
Author(s):  
R. Wood
Keyword(s):  
Boundary Layer ◽  
Size Distribution ◽  
Large Scale ◽  
Cloud Droplet ◽  
Horizontal Structure ◽  
Boundary Layer Clouds ◽  
Droplet Concentration ◽  
Warm Rain ◽  
Lognormal Size Distribution ◽  
Accretion Rates

Abstract This is the second of two observational papers examining drizzle in stratiform boundary layer clouds. Part I details the vertical and horizontal structure of cloud and drizzle parameters, including some bulk microphysical variables. In this paper, the focus is on the in situ size-resolved microphysical measurements, particularly of drizzle drops (r > 20 μm). Layer-averaged size distributions of drizzle drops within cloud are shown to be well represented using either a truncated exponential or a truncated lognormal size distribution. The size-resolved microphysical measurements are used to estimate autoconversion and accretion rates by integration of the stochastic collection equation (SCE). These rates are compared with a number of commonly used bulk parameterizations of warm rain formation. While parameterized accretion rates agree well with those derived from the SCE initialized with observed spectra, the autoconversion rates seriously disagree in some cases. These disagreements need to be addressed in order to bolster confidence in large-scale numerical model predictions of the aerosol second indirect effect. Cloud droplet coalescence removal rates and mass and number fall rate relationships used in the bulk microphysical schemes are also compared, revealing some potentially important discrepancies. The relative roles of autoconversion and accretion are estimated by examination of composite profiles from the 12 flights. Autoconversion, although necessary for the production of drizzle drops, is much less important than accretion throughout the lower 80% of the cloud layer in terms of the production of drizzle liquid water. The SCE calculations indicate that the autoconversion rate depends strongly upon the cloud droplet concentration Nd such that a doubling of Nd would lead to a reduction in autoconversion rate of between 2 and 4. Radar reflectivity–precipitation rate (Z–R) relationships suitable for radar use are derived and are shown to be significantly biased in some cases by the undersampling of large (r > 200 μm) drops with the 2D-C probe. A correction based upon the extrapolation to larger sizes using the exponential size distribution changes the Z–R relationship, leading to the conclusion that consideration should be given to sampling issues when examining higher moments of the drop size distribution in drizzling stratiform boundary layer clouds.

scholarly journals Assessing impacts of land abandonment on Mediterranean biodiversity using indicators based on bird and butterfly monitoring data

2015 ◽  
Vol 43 (1) ◽  
pp. 69-78 ◽  
Author(s):  
SERGI HERRANDO ◽  
LLUÍS BROTONS ◽  
MARC ANTON ◽  
FERRAN PÁRAMO ◽  
DANI VILLERO ◽  
...  
Keyword(s):  
Large Scale ◽  
Forest Cover ◽  
Habitat Preferences ◽  
Land Abandonment ◽  
Monitoring Data ◽  
Open Habitat ◽  
North East ◽  
The North ◽  
Butterfly Monitoring ◽  
The Impact

SUMMARYIn Europe, and particularly in the Mediterranean Basin, the abandonment of traditional land-use practices has been reported as one of the main causes of decline for open-habitat species. Data from large-scale bird and butterfly monitoring schemes in the north-east Iberian Peninsula were used to evaluate the impact that land abandonment has had on local biodiversity. Species’ habitat preferences, along a gradient from open to forest habitats, were significantly related to population trends: for both birds and butterflies, open-habitat species showed the most marked declines while forest species increased moderately. Multi-species indicators for tracking the impact of land abandonment on bird and butterfly populations were developed using habitat preference estimates and population trend indices. The patterns shown by these indicators were in line with the changes occurring in forest cover in the monitoring sites. This study reveals that multi-species indicators based on monitoring data from different taxonomic groups (here, birds and butterflies) may usefully be employed to track impacts of environmental change on biodiversity.

scholarly journals A mixed-methods evaluation of transformational change in NHS North East

2014 ◽  
Vol 2 (47) ◽  
pp. 1-186 ◽  
Author(s):  
David J Hunter ◽  
Jonathan Erskine ◽  
Chris Hicks ◽  
Tom McGovern ◽  
Adrian Small ◽  
...  
Keyword(s):  
Mixed Methods ◽  
Focus Groups ◽  
Leadership Style ◽  
Large Scale ◽  
Research Programme ◽  
Transformational Change ◽  
North East ◽  
The North ◽  
Semistructured Interviews ◽  
The Impact

BackgroundThe North East Transformation System (NETS) was conceived as an experiment in adopting large-scale transformational change across a NHS region in England. Although the NHS in the North East performs well, the health of the population ranks among the poorest in the country. The NETS was viewed as a means of addressing this conundrum. It comprised three components: Vision, Compact and Method.ObjectivesThe evaluation study comprised six elements: a literature review; an evaluation of the evolution and impact of the NETS; an identification of the factors facilitating, and/or acting as barriers to, successful change; an assessment of the role of the NETS project team; establishing how far the changes introduced through the NETS became embedded and sustained; and an evaluation of the impact of the NETS on end users.DesignThe research comprised a longitudinal mixed-methods study conducted over 3.5 years. Research methods included 68 semistructured interviews, observation, two focus groups, documentary analysis and interrupted time series (ITS) analysis. The ITS component comprised analysis of five rapid process improvement workshops in two of the sites.SettingThe research setting was the NHS North East region until its abolition in April 2013 following the UK government’s NHS changes. Fourteen sites were selected for the study, comprising primary care trusts as commissioners, and provider trusts including mental health, community, acute care and ambulance services.ParticipantsThe study respondents were members of staff in the 14 sites drawn from different levels of their organisations.InterventionsThe NETS comprised a complex set of interventions aimed at improving the efficiency and effectiveness of care pathways for staff and patients.Main outcome measuresThe ‘receptive contexts for change’ framework was used to evaluate the transformational change process and its outcomes.Data sourcesQualitative parts of the study drew on semistructured interviews, focus groups, observation and documents. Quantitative parts of the study used routinely collected NHS data.ResultsTransformational change in a complex system takes time and demands consistency, constancy of purpose and organisational stability. The NETS was seriously disrupted by the NHS changes announced in July 2010. Progress was sustained at four of the study sites, but slowed or ceased at the other sites. Leadership style was found to be critical to the success of transformational change.ConclusionsThe NETS was a bold and ambitious initiative which succeeded in bringing about real and lasting change in some parts of the North East. However, it was unable to fully realise its vision and purpose partly because of the widespread reorganisation of the NHS by the new coalition government.Future workThere is a need to develop new methods to understand how change occurs, or fails, in complex settings like the NHS. There is a need for more in-depth studies in those sites that were able to implement and sustain change. This would inform future policy and practice. The results of the quantitative analyses were less conclusive than those obtained by qualitative methods. Further development of mixed-methods approaches would provide additional support for evidence-based decision-making.FundingThe National Institute for Health Research Health Services and Delivery Research programme.

Quasi-Biweekly Extensions of the Monsoon Winds and the Philippines Diurnal Cycle

2021 ◽  
Author(s):  
Michael B. Natoli ◽  
Eric D. Maloney
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Transition Period ◽  
Intraseasonal Oscillation ◽  
Maximum Amplitude ◽  
Longwave Radiation ◽  
The Philippines ◽  
Boreal Summer ◽  
Monsoon Winds ◽  
The Impact

AbstractThe impact of quasi-biweekly variability in the monsoon southwesterly winds on the precipitation diurnal cycle in the Philippines is examined using CMORPH precipitation, ERA5 reanalysis, and outgoing longwave radiation (OLR) fields. Both a case study during the 2018 Propagation of Intraseasonal Tropical Oscillations (PISTON) field campaign and a 23-year composite analysis are used to understand the effect of the QBWO on the diurnal cycle. QBWO events in the west Pacific, identified with an extended EOF index, bring increases in moisture, cloudiness, and westerly winds to the Philippines. Such events are associated with significant variability in daily mean precipitation and the diurnal cycle. It is shown that the modulation of the diurnal cycle by the QBWO is remarkably similar to that by the boreal summer intraseasonal oscillation (BSISO). The diurnal cycle reaches a maximum amplitude on the western side of the Philippines on days with average to above average moisture, sufficient insolation, and weakly offshore prevailing wind. This occurs during the transition period from suppressed to active large-scale convection for both the QBWO and BSISO.Westerly monsoon surges associated with QBWO variability generally exhibit active precipitation over the South China Sea (SCS), but a depressed diurnal cycle. These results highlight that modes of large-scale convective variability in the tropics can have a similar impact on the diurnal cycle if they influence the local scale environmental background state similarly.

Sign in / Sign up

Export Citation Format

Share Document