scholarly journals Effects of aerosol in simulations of realistic shallow cumulus cloud fields in a large domain

2019 ◽  
Vol 19 (21) ◽  
pp. 13507-13517 ◽  
Author(s):  
George Spill ◽  
Philip Stier ◽  
Paul R. Field ◽  
Guy Dagan
Keyword(s):  
Large Scale ◽  
Domain Size ◽  
Trade Wind ◽  
Shallow Convection ◽  
Liquid Water Path ◽  
Microphysics Scheme ◽  
Shallow Cumulus ◽  
Double Moment ◽  
Rain Rates

Abstract. Previous study of shallow convection has generally suffered from having to balance domain size with resolution, resulting in high-resolution studies which do not capture large-scale behaviour of the cloud fields. In this work we hope to go some way towards addressing this by carrying out cloud-resolving simulations on large domains. Simulations of trade wind cumulus are carried out using the Met Office Unified Model (UM), based on a case study from the Rain In Cumulus over the Ocean (RICO) field campaign. The UM is run with a nested domain of 500 km with 500 m resolution, in order to capture the large-scale behaviour of the cloud field, and with a double-moment interactive microphysics scheme. Simulations are run using baseline aerosol profiles based on observations from RICO, which are then perturbed. We find that the aerosol perturbations result in changes to the convective behaviour of the cloud field, with higher aerosol leading to an increase (decrease) in the number of deeper (shallower) clouds. However, despite this deepening, there is little increase in the frequency of higher rain rates. This is in contrast to the findings of previous work making use of idealised simulation setups. In further contrast, we find that increasing aerosol results in a persistent increase in domain mean liquid water path and decrease in precipitation, with little impact on cloud fraction.

scholarly journals Effects of aerosol in simulations of realistic shallow cumulus cloud fields in a large domain

2019 ◽  
Author(s):  
George Spill ◽  
Philip Stier ◽  
Paul R. Field ◽  
Guy Dagan
Keyword(s):  
Large Scale ◽  
Domain Size ◽  
Trade Wind ◽  
Shallow Convection ◽  
Liquid Water Path ◽  
Microphysics Scheme ◽  
Shallow Cumulus ◽  
Double Moment ◽  
Rain Rates

Abstract. Previous study of shallow convection has generally suffered from having to balance domain size with resolution, resulting in high resolution studies which do not capture large scale behaviour of the cloud fields. In this work we hope to go some way towards addressing this by carrying out cloud resolving simulations on large domains. Simulations of trade wind cumulus are carried out using the Met Office Unified Model (UM), based on a case study from the Rain In Cumulus over the Ocean (RICO) field campaign. The UM is run with a nested domain of 500 km with 500 m resolution, in order to capture the large scale behaviour of the cloud field, and with a double-moment interactive microphysics scheme. Simulations are run using baseline aerosol profiles based on observations from RICO, which are then perturbed. We find that the aerosol perturbations result in changes to the convective behaviour of the cloud field, with higher aerosol leading to an increase (decrease) in the number of deeper (shallower) clouds. However, despite this deepening, there is little increase in the frequency of higher rain rates. This is in contrast to the findings of previous work making use of idealised simulation setups. In further contrast, we find that increasing aerosol results in a persistent increase in domain mean liquid water path and decrease in precipitation, with little impact on cloud fraction.

Aerosol effects on shallow cumulus cloud fields in idealised and realistic simulations

2020 ◽  
Author(s):  
George Spill ◽  
Philip Stier ◽  
Paul Field ◽  
Guy Dagan
Keyword(s):  
Large Scale ◽  
Trade Wind ◽  
Quasi Equilibrium ◽  
Cumulus Cloud ◽  
Shallow Convection ◽  
Shallow Cumulus ◽  
Synoptic Conditions ◽  
Large Eddy ◽  
Transient Forcing ◽  
Periodic Domains

<p>Shallow cumulus clouds interact with their environment in myriad significant ways, and yet their behavour is still poorly understood, and is responsible for much uncertainty in climate models. Improving our understanding of these clouds is therefore an important part of improving our understanding of the climate system as a whole.</p><p>Modelling studies of shallow convection have traditionally made use of highly idealised simulations using large-eddy models, which allow for high resolution, detailed simulations. However, this idealised nature, with periodic boundaries and constant forcing, and the quasi-equilibrium cloud fields produced, means that they do not capture the effect of transient forcing and conditions found in the real atmosphere, which contains shallow cumulus cloud fields unlikely to be in equilibrium.<span> </span></p><p>Simulations with more realistic nested domains and forcings have previously been shown to have significant persistent responses differently to aerosol perturbations, in contrast to many large eddy simulations in which perturbed runs tend to reach a similar quasi-equilibrium.<span> </span></p><p>Here, we further this investigation by using a single model to present a comparison of familiar idealised simulations of trade wind cumuli in periodic domains, and simulations with a nested domain, whose boundary conditions are provided by a global driving model, able to simulate transient synoptic conditions.<span> </span></p><p>The simulations are carried out using the Met Office Unified Model (UM), and are based on a case study from the Rain In Cumulus over the Ocean (RICO) field campaign. Large domains of 500km are chosen in order to capture large scale cloud field behaviour. A double-moment interactive microphysics scheme is used, along with prescribed aerosol profiles based on RICO observations, which are then perturbed.</p><p>We find that the choice between realistic nested domains with transient forcing and idealised periodic domains with constant forcing does indeed affect the nature of the response to aerosol perturbations, with the realistic simulations displaying much larger persistent changes in domain mean fields such as liquid water path and precipitation rate.<span> </span></p>

scholarly journals The effects of turbulent collision–coalescence on precipitation formation and precipitation-dynamical feedbacks in simulations of stratocumulus and shallow cumulus convection

2014 ◽  
Vol 14 (13) ◽  
pp. 6557-6570 ◽  
Author(s):  
C. N. Franklin
Keyword(s):  
Cloud Droplet ◽  
Shallow Convection ◽  
Microphysics Scheme ◽  
Droplet Collision ◽  
Shallow Cumulus ◽  
Turbulence Effects ◽  
Double Moment ◽  
Sensitivity Studies ◽  
Microphysical Processes ◽  
The Impact

Abstract. A double moment warm rain scheme that includes the effects of turbulence on droplet collision rates has been implemented in a large-eddy model to investigate the impact of turbulence effects on clouds and precipitation. Simulations of shallow cumulus and stratocumulus show that different precipitation-dynamical feedbacks occur in these regimes when the effects of turbulence are included in the microphysical processes. In both cases inclusion of turbulent microphysics increases precipitation due to a more rapid conversion of cloud water to rain. In the shallow convection case, the greater water loading in the upper cloud levels reduces the buoyancy production of turbulent kinetic energy and the entrainment. The stratocumulus case on the other hand shows a weak positive precipitation feedback, with enhanced rainwater producing greater evaporation, stronger circulations and more turbulence. Sensitivity studies in which the cloud droplet number was varied show that greater number concentrations suppress the stratocumulus precipitation leading to larger liquid water paths. This positive second indirect aerosol effect shows no sensitivity to whether or not the effects of turbulence on droplet collision rates are included. While the sign of the second indirect effect is negative in the shallow convection case whether the effects of turbulence are considered or not, the magnitude of the effect is doubled when the turbulent microphysics are used. It is found that for these two different cloud regimes turbulence has a larger effect than cloud droplet number and the use of a different bulk microphysics scheme on producing rainfall in shallow cumuli. However, for the stratocumulus case examined here, the effects of turbulence on rainfall are not statistically significant and instead it is the cloud droplet number concentration or the choice of bulk microphysics scheme that has the largest control on the rain water.

The Sensitivity of Simulated Shallow Cumulus Convection and Cold Pools to Microphysics

2015 ◽  
Vol 72 (9) ◽  
pp. 3340-3355 ◽  
Author(s):  
Zhujun Li ◽  
Paquita Zuidema ◽  
Ping Zhu ◽  
Hugh Morrison
Keyword(s):  
Radiative Forcing ◽  
Cloud Cover ◽  
Trade Wind ◽  
Shallow Convection ◽  
Shallow Marine ◽  
Cold Pools ◽  
Double Moment ◽  
Microphysical Parameterization ◽  
Rain Rates ◽  
The Impact

Abstract The sensitivity of nested WRF simulations of precipitating shallow marine cumuli and cold pools to microphysical parameterization is examined. The simulations differ only in their use of two widely used double-moment rain microphysical schemes: the Thompson and Morrison schemes. Both simulations produce similar mesoscale variability, with the Thompson scheme producing more weak cold pools and the Morrison scheme producing more strong cold pools, which are associated with more intense shallow convection. The most robust difference is that the cloud cover and LWP are significantly larger in the Morrison simulation than in the Thompson simulation. One-dimensional kinematic simulations confirm that dynamical feedbacks do not mask the impact of microphysics. These also help elucidate that a slower autoconversion process along with a stronger accretion process explains the Morrison scheme’s higher cloud fraction for a similar rain mixing ratio. Differences in the raindrop terminal fall speed parameters explain the higher evaporation rate of the Thompson scheme at moderate surface rain rates. Given the implications of the cloud-cover differences for the radiative forcing of the expansive trade wind regime, the microphysical scheme should be considered carefully when simulating precipitating shallow marine cumulus.

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

2005 ◽  
Vol 62 (6) ◽  
pp. 1678-1693 ◽  
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.

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.

A New Double-Moment Microphysics Parameterization for Application in Cloud and Climate Models. Part I: Description

2005 ◽  
Vol 62 (6) ◽  
pp. 1665-1677 ◽  
Author(s):  
H. Morrison ◽  
J. A. Curry ◽  
V. I. Khvorostyanov
Keyword(s):  
High Resolution ◽  
Vertical Velocity ◽  
Large Scale ◽  
Climate Models ◽  
The Other ◽  
Microphysics Scheme ◽  
Cloud Models ◽  
Droplet Nucleation ◽  
Double Moment ◽  
Droplet Activation

Abstract A new double-moment bulk microphysics scheme predicting the number concentrations and mixing ratios of four hydrometeor species (droplets, cloud ice, rain, snow) is described. New physically based parameterizations are developed for simulating homogeneous and heterogeneous ice nucleation, droplet activation, and the spectral index (width) of the droplet size spectra. Two versions of the scheme are described: one for application in high-resolution cloud models and the other for simulating grid-scale cloudiness in larger-scale models. The versions differ in their treatment of the supersaturation field and droplet nucleation. For the high-resolution approach, droplet nucleation is calculated from Kohler theory applied to a distribution of aerosol that activates at a given supersaturation. The resolved supersaturation field and condensation/deposition rates are predicted using a semianalytic approximation to the three-phase (vapor, ice, liquid) supersaturation equation. For the large-scale version of the scheme, it is assumed that the supersaturation field is not resolved and thus droplet activation is parameterized as a function of the vertical velocity and diabatic cooling rate. The vertical velocity includes a subgrid component that is parameterized in terms of the eddy diffusivity and mixing length. Droplet condensation is calculated using a quasi-steady, saturation adjustment approach. Evaporation/deposition onto the other water species is given by nonsteady vapor diffusion allowing excess vapor density relative to ice saturation.

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.

Diurnal Cycle of Shallow and Deep Convection for a Tropical Land and an Ocean Environment and Its Relationship to Synoptic Wind Regimes

2006 ◽  
Vol 134 (10) ◽  
pp. 2688-2701 ◽  
Author(s):  
L. Gustavo Pereira ◽  
Steven A. Rutledge
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Field Experiments ◽  
Deep Convection ◽  
Shallow Convection ◽  
Wind Regime ◽  
Diurnal Variability ◽  
Synoptic Wind ◽  
Wind Regimes ◽  
Rain Rates

Abstract The characteristics of shallow and deep convection during the Tropical Rainfall Measuring Mission/Large-Scale Biosphere–Atmosphere Experiment in Amazonia (TRMM/LBA) and the Eastern Pacific Investigation of Climate Processes in the Coupled Ocean–Atmosphere System (EPIC) are evaluated in this study. Using high-quality radar data collected during these two tropical field experiments, the reflectivity profiles, rain rates, fraction of convective area, and fraction of rainfall volume in each region are examined. This study focuses on the diurnal cycle of shallow and deep convection for the identified wind regimes in both regions. The easterly phase in TRMM/LBA and the northerly wind regime in EPIC were associated with the strongest convection, indicated by larger rain rates, higher reflectivities, and deeper convective cores compared to the westerly phase in TRMM/LBA and the southerly regime in EPIC. The diurnal cycle results indicated that convection initiates in the morning and peaks in the afternoon during TRMM/LBA, whereas in the east Pacific the diurnal cycle of convection is very dependent on the wind regime. Deep convection in the northerly regime peaks around midnight, nearly 6 h before its southerly regime counterpart. Moreover, the northerly regime of EPIC was dominated by convective rainfall, whereas the southerly regime was dominated by stratiform rainfall. The diurnal variability was more pronounced during TRMM/LBA than in EPIC. Shallow convection was associated with 10% and 3% of precipitation during TRMM/LBA and EPIC, respectively.

scholarly journals Statistics of Drop Size Distribution Parameters and Rain Rates for Stratiform and Convective Precipitation during the North Australian Wet Season

2013 ◽  
Vol 141 (9) ◽  
pp. 3222-3237 ◽  
Author(s):  
Guillaume Penide ◽  
Vickal V. Kumar ◽  
Alain Protat ◽  
Peter T. May
Keyword(s):  
Size Distribution ◽  
Large Scale ◽  
Drop Size ◽  
Drop Size Distribution ◽  
The Other ◽  
Convective Precipitation ◽  
Trade Wind ◽  
High Concentration ◽  
Wet Season ◽  
Rain Rates

Abstract C-band polarimetric radar measurements spanning two wet seasons are used to study the effects of the large-scale environment on the statistical properties of stratiform and convective rainfall around Darwin, Australia. The rainfall physical properties presented herein are the reflectivity fields, daily rainfall accumulations and raining area, rain rates, and drop size distribution (DSD) parameters (median volume diameter and “normalized” intercept parameter). Each of these properties is then analyzed according to five different atmospheric regimes and further separated into stratiform or convective rain categories following a DSD-based approach. The regimes, objectively identified by radiosonde thermodynamic and wind measurements, represent typical wet-season atmospheric conditions: the active monsoon regime, the “break” periods, the “buildup” regime, the trade wind regime, and a mixture of inactive/break periods. The large-scale context is found to strongly modulate rainfall and cloud microphysical properties. For example, during the active monsoon regime, the daily rain accumulation is higher than in the other regimes, while this regime is associated with the lowest rain rates. Precipitation in this active monsoon regime is found to be widespread and mainly composed of small particles in high concentration compared to the other regimes. Vertical profiles of reflectivity and DSD parameters suggest that warm rain processes are dominant during this regime. In contrast, rainfall properties in the drier regimes (trade wind/buildup regimes) are mostly of continental origin, with rain rates higher than in the moister regimes. In these drier regimes, precipitation is mainly formed of large raindrops in relatively low concentration due to a larger contribution of the ice microphysical processes on the rainfall formation.

Sign in / Sign up

Export Citation Format

Share Document