scholarly journals Updraft dynamics and microphysics: on the added value of the cumulus thermal reference frame in simulations of aerosol-deep convection interactions

2021 ◽  
Author(s):  
Daniel Hernandez-Deckers ◽  
Toshihisa Matsui ◽  
Ann M. Fridlind
Keyword(s):  
Reference Frames ◽  
Climate Models ◽  
Deep Convection ◽  
Building Blocks ◽  
Quantitative Information ◽  
Added Value ◽  
Cumulus Convection ◽  
Moist Convection ◽  
Microphysical Processes

Abstract. One fundamental question about atmospheric moist convection processes that remains debated is whether or under what conditions a relevant variability in background aerosol concentrations may have a significant dynamical impact on convective clouds and their associated precipitation. Furthermore, current climate models must parameterize both the microphysical and the cumulus convection processes, but this is usually implemented separately, whereas in nature there is a strong coupling between them. As a first step to improve our understanding of these two problems, we investigate how aerosol concentrations modify key properties of updrafts in eight large-eddy permitting regional simulations of a case study of scattered convection over Houston, Texas, in which convection is explicitly simulated and microphysical processes are parameterized. Dynamical and liquid-phase microphysical responses are investigated using two different reference frames: static cloudy-updraft grid cells versus tracked cumulus thermals. In both frameworks we observe the expected microphysical responses to higher aerosol concentrations, such as higher cloud number concentrations and lower rain number concentrations. In terms of the dynamical responses, both frameworks indicate weak impacts of varying aerosol concentrations relative to the noise between simulations over the observationally derived range of aerosol variability for this case study. On the other hand, results suggest that analysis of thermals can provide a better pathway to sample the most relevant convective processes. For instance, vertical velocity from thermals is significantly higher at upper levels than when sampled from cloudy-updraft grid points, and several microphysical variables have higher average values in the cumulus thermal framework than in the cloudy-updraft framework. In addition, the thermal analysis is seen to add rich quantitative information about the rates and covariability of microphysical processes spatially and throughout tracked thermal lifecycles, which can serve as a stronger foundation for improving subgrid-scale parameterizations. These results suggest that cumulus thermals are more realistic dynamical building blocks of cumulus convection, acting as natural cloud chambers for microphysical processes.

scholarly journals Tropical convection regimes in climate models: evaluation with satellite observations

2017 ◽  
Author(s):  
Andrea K. Steiner ◽  
Bettina C. Lackner ◽  
Mark A. Ringer
Keyword(s):  
Climate Models ◽  
Lower Stratosphere ◽  
Deep Convection ◽  
Atmospheric Temperature ◽  
Tropical Convection ◽  
Specific Humidity ◽  
Moist Convection ◽  
Tropopause Region ◽  
Tropical Troposphere ◽  
Unique Source

Abstract. High quality observations are powerful tools for the evaluation of climate models towards improvement and reduction of uncertainty. Particularly at low latitudes, the most uncertain aspect lies in the representation of moist convection and interaction with dynamics, where rising motion is tied to deep convection and sinking motion to dry regimes. Since humidity is closely coupled with temperature feedbacks in the tropical troposphere a proper representation of this region is essential. Here we demonstrate the evaluation of atmospheric climate models with satellite-based observations from Global Positioning System (GPS) radio occultation (RO), which feature high vertical resolution and accuracy in the troposphere to lower stratosphere. We focus on the representation of the vertical atmospheric structure in tropical convection regimes, defined by high updraft velocity over warm surfaces, and investigate atmospheric temperature and humidity profiles. Results reveal that some models do not fully capture convection regions, particularly over land, and only partly represent high updraft or downdraft velocities. Models show large biases in tropical mean temperature of more than 4 K in the tropopause region and the lower stratosphere. Reasonable agreement with observations is given in mean specific humidity in the lower to mid-troposphere. In moist convection regions, models tend to underestimate moisture by 10 % to 30 % over oceans whereas in dry downdraft regions they overestimate moisture by 100 %. Our findings provide evidence that RO observations are a unique source of information, with a range of further atmospheric variables to be exploited, for the evaluation and advancement of next generation climate models.

Role of Convection–circulation Coupling in the Propagation Mechanism of the Madden–Julian Oscillation over the Maritime Continent in Climate Models

2021 ◽  
Author(s):  
Yi-Chi Wang ◽  
Wan-Ling Tseng ◽  
Huang-Hsiung Hsu
Keyword(s):  
Climate Models ◽  
Environmental Changes ◽  
Deep Convection ◽  
Ocean Model ◽  
Cumulus Parameterization ◽  
Propagation Mechanism ◽  
Madden Julian Oscillation ◽  
Moist Convection ◽  
Maritime Continent

Abstract This study investigates the role of convection–circulation coupling on the simulated eastward propagation of the Madden–Julian Oscillation (MJO) over the Maritime Continent (MC). Experiments are conducted with the European Centre Hamburg Model Version 5 (ECHAM5) coupled with the one-column ocean model – Snow-Ice-Thermocline (SIT) and two different cumulus schemes, Nordeng (E5SIT-Nord) and Tiedtke (E5SIT-Tied). During the early phase of MJO composites, the E5SIT-Nord simulation reveals stronger intraseasonal anomalies in the apparent heat source (Q1) over the convective center, however, the E5SIT-Tied produces a stronger background Q1, suggesting that deep convection prevails over the MC but does not couple with the MJO circulation. Similarly, in the E5SIT-Tied simulation, in-column moisture is kept mostly by local deep convection over the MC, which is in contrast to the well-correlated relationship between moisture anomaly and MJO circulation in E5SIT-Nord. A case study based on an observational MJO reveals similar biases concerning of convection–circulation coupling emerges within a few days of simulations. The E5SIT-Tied simulation produces weaker heating at the convective center of the MJO than the E5SIT-Nord a few days after model initiation, resulting weaker subsidence to the east and less favorable for propagation. The present findings highlight the instantaneous responses of cumulus parameterization schemes to MJO-related environmental changes can further affect intraseasonal variability through altering convection–circulation coupling over the MC. Physical schemes of moist convection are essential to realistically represent this coupling and thereby improve the simulation of the eastward propagation of the MJO.

scholarly journals Tropical convection regimes in climate models: evaluation with satellite observations

2018 ◽  
Vol 18 (7) ◽  
pp. 4657-4672 ◽  
Author(s):  
Andrea K. Steiner ◽  
Bettina C. Lackner ◽  
Mark A. Ringer
Keyword(s):  
Climate Models ◽  
Lower Stratosphere ◽  
Deep Convection ◽  
Atmospheric Temperature ◽  
Tropical Convection ◽  
Specific Humidity ◽  
Moist Convection ◽  
Tropopause Region ◽  
Tropical Troposphere ◽  
Unique Source

Abstract. High-quality observations are powerful tools for the evaluation of climate models towards improvement and reduction of uncertainty. Particularly at low latitudes, the most uncertain aspect lies in the representation of moist convection and interaction with dynamics, where rising motion is tied to deep convection and sinking motion to dry regimes. Since humidity is closely coupled with temperature feedbacks in the tropical troposphere, a proper representation of this region is essential. Here we demonstrate the evaluation of atmospheric climate models with satellite-based observations from Global Positioning System (GPS) radio occultation (RO), which feature high vertical resolution and accuracy in the troposphere to lower stratosphere. We focus on the representation of the vertical atmospheric structure in tropical convection regimes, defined by high updraft velocity over warm surfaces, and investigate atmospheric temperature and humidity profiles. Results reveal that some models do not fully capture convection regions, particularly over land, and only partly represent strong vertical wind classes. Models show large biases in tropical mean temperature of more than 4 K in the tropopause region and the lower stratosphere. Reasonable agreement with observations is given in mean specific humidity in the lower to mid-troposphere. In moist convection regions, models tend to underestimate moisture by 10 to 40 % over oceans, whereas in dry downdraft regions they overestimate moisture by 100 %. Our findings provide evidence that RO observations are a unique source of information, with a range of further atmospheric variables to be exploited, for the evaluation and advancement of next-generation climate models.

scholarly journals Triggering Deep Convection with a Probabilistic Plume Model

2014 ◽  
Vol 71 (11) ◽  
pp. 3881-3901 ◽  
Author(s):  
Fabio D’Andrea ◽  
Pierre Gentine ◽  
Alan K. Betts ◽  
Benjamin R. Lintner
Keyword(s):  
Climate Models ◽  
Proper Time ◽  
Deep Convection ◽  
Potential Temperature ◽  
Specific Humidity ◽  
Cloud Base ◽  
Moist Convection ◽  
Density Currents ◽  
Shallow Convection ◽  
Plume Model

Abstract A model unifying the representation of the planetary boundary layer and dry, shallow, and deep convection, the probabilistic plume model (PPM), is presented. Its capacity to reproduce the triggering of deep convection over land is analyzed in detail. The model accurately reproduces the timing of shallow convection and of deep convection onset over land, which is a major issue in many current general climate models. PPM is based on a distribution of plumes with varying thermodynamic states (potential temperature and specific humidity) induced by surface-layer turbulence. Precipitation is computed by a simple ice microphysics, and with the onset of precipitation, downdrafts are initiated and lateral entrainment of environmental air into updrafts is reduced. The most buoyant updrafts are responsible for the triggering of moist convection, causing the rapid growth of clouds and precipitation. Organization of turbulence in the subcloud layer is induced by unsaturated downdrafts, and the effect of density currents is modeled through a reduction of the lateral entrainment. The reduction of entrainment induces further development from the precipitating congestus phase to full deep cumulonimbus. Model validation is performed by comparing cloud base, cloud-top heights, timing of precipitation, and environmental profiles against cloud-resolving models and large-eddy simulations for two test cases. These comparisons demonstrate that PPM triggers deep convection at the proper time in the diurnal cycle and produces reasonable precipitation. On the other hand, PPM underestimates cloud-top height.

When the trigger of deep convection gets tricky in idealized climate simulations

2021 ◽  
Author(s):  
Dominic Matte ◽  
Jens H. Christensen ◽  
Henrik Fedderson ◽  
Rasmus A. Pederson ◽  
Henrik Vedel ◽  
...  
Keyword(s):  
Climate Models ◽  
Initial Conditions ◽  
Flash Flood ◽  
Deep Convection ◽  
Regional Climate ◽  
Lapse Rate ◽  
Moist Convection ◽  
Extreme Precipitation Events ◽  
Synoptic Conditions ◽  
Deep Moist Convection

<p><span>On the evening on July 2, 2011 a severe cloud burst occurred in the Copenhagen area. During the late afternoon deep moist convection developed over nearby Skåne (the southernmost part of Sweden) in an airstream from east-northeast. In the early evening the DMC passed over Øresund to Copenhagen, where it created a severe flash flood. Between 90 and 135 mm of precipitation in less than 2 hours was recorded ooding cellars, streets, and key roads. The deluge caused 6 billion Danish kroner in damage. Although that such extreme events are rare, the impacts on society is important and should be understood under a warmer climate. Although regional climate models have recently reached the convection permitting resolution, reproducing such events is still challenging.</span></p><p><span>Several studies suggest that extreme precipitations should increase under a future warmer climate using transient simulation or a pseudo-warming approach. It is still unclear how such event would behave under warmer or colder synoptic conditions. Using a forecast-ensemble method, but keeping a climate perspective, this study assesses the risk rising from such an event under otherwise almost identical, but warmer or colder conditions. With this set-up, we find that the development of the system that resulted in observed downpour exhibit quite a sensitivity to the initial conditions and contrary to a linear thinking, the risk of flooding is decreasing as the climate warms due to the inhibition of the CAPE by the additional lapse-rate anomalies used in this study. We therefore propose that the PGW method should be used with caution and that extreme precipitation events also in transient simulations of future climates need to be studied in detailed to address the limitations to models ability to produce those most extreme and by nature inherently rare events.</span></p>

scholarly journals Towards European-Scale Convection-Resolving Climate Simulations

2016 ◽  
Author(s):  
David Leutwyler ◽  
Oliver Fuhrer ◽  
Xavier Lapillonne ◽  
Daniel Lüthi ◽  
Christoph Schär
Keyword(s):  
Graphics Processing Units ◽  
Climate Models ◽  
Climate Model ◽  
Deep Convection ◽  
Moist Convection ◽  
Cold Pools ◽  
Cosmo Model ◽  
Climate Simulations ◽  
Graphics Processing ◽  
Horizontal Grid

Abstract. The representation of moist convection in climate models represents a major challenge, due to the small scales involved. Using horizontal grid spacings of O(1km), convection-resolving weather and climate models allow to explicitly resolve deep convection. However, due to their extremely demanding computational requirements, they have so far been limited to short simulations and/or small computational domains. Innovations in supercomputing have led to new hybrid node designs, mixing conventional multicore CPUs and accelerators such as graphics processing units (GPUs). One of the first atmospheric models that has been fully ported to these architectures is the COSMO model. Here we demonstrate the convection-resolving COSMO model on continental scales using a version of the model capable of using GPU accelerators. The verification of a week-long simulation containing winter storm Kyrill shows that, for this case, convection-parameterizing simulations and convection-resolving simulations agree well. Furthermore we demonstrate the applicability of the approach to longer simulations by conducting a three-month long simulation of the summer season 2006. Its results corroborate the findings found on smaller domains such as more credible representation of the diurnal cycle of precipitation in convection-resolving models and a tendency to produce more intensive hourly precipitation events. Both simulations also show how the approach allows for the representation of interactions between synoptic-scale and meso-scale atmospheric circulations at scales ranging from 1000 to 10 km. This includes the formation of sharp cold frontal structures, convection embedded in fronts and small eddies, or the formation and organization of propagating cold pools. Finally we assess the performance gain from using heterogeneous hardware equipped with GPUs with respect to multi-core hardware. With the COSMO model, we now use a climate model that has all the necessary modules required for real-case convection-resolving climate simulations on GPUs.

scholarly journals Towards European-scale convection-resolving climate simulations with GPUs: a study with COSMO 4.19

2016 ◽  
Vol 9 (9) ◽  
pp. 3393-3412 ◽  
Author(s):  
David Leutwyler ◽  
Oliver Fuhrer ◽  
Xavier Lapillonne ◽  
Daniel Lüthi ◽  
Christoph Schär
Keyword(s):  
Graphics Processing Units ◽  
Climate Models ◽  
Climate Model ◽  
Deep Convection ◽  
Regional Climate ◽  
Small Scale ◽  
Moist Convection ◽  
Cosmo Model ◽  
Climate Simulations ◽  
Weather And Climate

Abstract. The representation of moist convection in climate models represents a major challenge, due to the small scales involved. Using horizontal grid spacings of O(1km), convection-resolving weather and climate models allows one to explicitly resolve deep convection. However, due to their extremely demanding computational requirements, they have so far been limited to short simulations and/or small computational domains. Innovations in supercomputing have led to new hybrid node designs, mixing conventional multi-core hardware and accelerators such as graphics processing units (GPUs). One of the first atmospheric models that has been fully ported to these architectures is the COSMO (Consortium for Small-scale Modeling) model.Here we present the convection-resolving COSMO model on continental scales using a version of the model capable of using GPU accelerators. The verification of a week-long simulation containing winter storm Kyrill shows that, for this case, convection-parameterizing simulations and convection-resolving simulations agree well. Furthermore, we demonstrate the applicability of the approach to longer simulations by conducting a 3-month-long simulation of the summer season 2006. Its results corroborate the findings found on smaller domains such as more credible representation of the diurnal cycle of precipitation in convection-resolving models and a tendency to produce more intensive hourly precipitation events. Both simulations also show how the approach allows for the representation of interactions between synoptic-scale and meso-scale atmospheric circulations at scales ranging from 1000 to 10 km. This includes the formation of sharp cold frontal structures, convection embedded in fronts and small eddies, or the formation and organization of propagating cold pools. Finally, we assess the performance gain from using heterogeneous hardware equipped with GPUs relative to multi-core hardware. With the COSMO model, we now use a weather and climate model that has all the necessary modules required for real-case convection-resolving regional climate simulations on GPUs.

Cryo-TEM of amphiphilic polymer and amphiphile/polymer solutions

1993 ◽  
Vol 51 ◽  
pp. 876-877
Author(s):  
Yeshayahu Talmon
Keyword(s):  
Microstructural Characterization ◽  
Building Blocks ◽  
Quantitative Information ◽  
Physical Models ◽  
Specimen Preparation ◽  
Time Resolved ◽  
Temperature Changes ◽  
Temperature And Humidity ◽  
Microstructured Fluids ◽  
Air Streams

To achieve complete microstructural characterization of self-aggregating systems, one needs direct images in addition to quantitative information from non-imaging, e.g., scattering or Theological measurements, techniques. Cryo-TEM enables us to image fluid microstructures at better than one nanometer resolution, with minimal specimen preparation artifacts. Direct images are used to determine the “building blocks” of the fluid microstructure; these are used to build reliable physical models with which quantitative information from techniques such as small-angle x-ray or neutron scattering can be analyzed.To prepare vitrified specimens of microstructured fluids, we have developed the Controlled Environment Vitrification System (CEVS), that enables us to prepare samples under controlled temperature and humidity conditions, thus minimizing microstructural rearrangement due to volatile evaporation or temperature changes. The CEVS may be used to trigger on-the-grid processes to induce formation of new phases, or to study intermediate, transient structures during change of phase (“time-resolved cryo-TEM”). Recently we have developed a new CEVS, where temperature and humidity are controlled by continuous flow of a mixture of humidified and dry air streams.

scholarly journals Attrition as a bottom-up pathway to subnational democratization

2021 ◽  
pp. 019251212110192
Author(s):  
Trix van Mierlo
Keyword(s):  
Civil Society ◽  
Field Research ◽  
Building Blocks ◽  
The Philippines ◽  
Causal Process ◽  
Bottom Up ◽  
System A ◽  
Extensive Field ◽  
Democratic System

Oftentimes, democracy is not spread out evenly over the territory of a country. Instead, pockets of authoritarianism can persist within a democratic system. A growing body of literature questions how such subnational authoritarian enclaves can be democratized. Despite fascinating insights, all existing pathways rely on the actions of elites and are therefore top-down. This article seeks to kick-start the discussion on a bottom-up pathway to subnational democratization, by proposing the attrition mechanism. This mechanism consists of four parts and is the product of abductive inference through theory-building causal process tracing. The building blocks consist of subnational democratization literature, social movement theory, and original empirical data gathered during extensive field research. This case study focuses on the ‘Dynasty Slayer’ in the province of Isabela, the Philippines, where civil society actors used the attrition mechanism to facilitate subnational democratization. This study implies that civil society actors in subnational authoritarian enclaves have agency.

scholarly journals Architectural and Urban Attractiveness of Small Towns: A Case Study of Polish Coastal Cittaslow Towns on the Pomeranian Way of St. James

Land ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 724
Author(s):  
Alicja K. Zawadzka
Keyword(s):  
Small Towns ◽  
Urban Life ◽  
Added Value ◽  
Development Policies ◽  
Quality Of Urban Life ◽  
Size Criterion ◽  
The Town ◽  
Modern Technologies

The paper presents the results of a study on the attractiveness to tourists and natives of the cultural qualities of coastal towns on The Pomeranian Way of St. James that are members of the Cittaslow network. Attention to the quality of urban life is inscribed in the development policies of towns applying to join the Cittaslow movement. In order to join the network (apart from the size criterion), towns need to meet a minimum of 50% plus one of the 72 criteria grouped into seven categories. One of the category is Quality of Urban Life Policy, so the towns applying to join Cittaslow commit themselves to actions aimed at improving the quality of urban life. The study on the attractiveness of cultural qualities of towns to tourists and natives was conducted using the author’s BRB method, whose added value is its universality and the possibility to study small towns regardless of their membership in the Cittaslow network. BRB is an acronym that stands for BUILDINGS, RELATIONSHIPS, BALANCE, and comprises three scopes of activities: BUILDINGS (iconic building and important sites where the inhabitants and the tourists are present); RELATIONSHIPS (the visual effects of the relations between the inhabitants and the town) and BALANCE (solutions that implement modern technologies). This method enables identification of places that are important to the inhabitants, where urban life takes place and which are often created with the involvement of the inhabitants. These are often the same spaces as those that attract tourists and perhaps stimulate them the desire to visit the town again (BRB—be right back). The aim of the BRB method is shown the attractiveness of small towns. The study has shown that the characteristic feature of Polish Cittaslow towns is their diversity: the architectural attractiveness of three towns is high both to tourists and natives. On the other hand, the urban attractiveness of the examined towns is an insufficient.

Sign in / Sign up

Export Citation Format

Share Document