scholarly journals Cloud-system resolving model simulations of aerosol indirect effects on tropical deep convection and its thermodynamic environment

2011 ◽  
Vol 11 (5) ◽  
pp. 15573-15629 ◽  
Author(s):  
H. Morrison ◽  
W. W. Grabowski
Keyword(s):  
Indirect Effects ◽  
Large Scale ◽  
Deep Convection ◽  
Radiative Heating ◽  
Cloud System ◽  
Direct Result ◽  
Radiative Fluxes ◽  
Aerosol Indirect Effects ◽  
Ensemble Approach ◽  
Tropical Deep Convection

Abstract. This paper presents results from 240-member ensemble simulations of aerosol indirect effects on tropical deep convection and its thermodynamic environment. Simulations using a two-dimensional cloud system-resolving model are run with pristine, polluted, or highly polluted aerosol conditions and large-scale forcing from a 6-day period of active monsoon conditions during the 2006 Tropical Warm Pool – International Cloud Experiment (TWP-ICE). Domain-mean surface precipitation is insensitive to aerosols primarily because the large-scale forcing is prescribed and dominates the water and static energy budgets. The spread of the top-of-atmosphere (TOA) shortwave and longwave radiative fluxes among different ensemble members for the same aerosol loading is surprisingly large, exceeding 25 W m−2 even when averaged over the 6-day period. This variability is caused by random fluctuations in the strength and timing of individual deep convective events. The ensemble approach demonstrates a small weakening of convection averaged over the 6-day period in the polluted simulations compared to pristine. Despite this weakening, the cloud top heights and anvil ice mixing ratios are higher in polluted conditions. This occurs because of the larger concentrations of cloud droplets that freeze, leading directly to higher ice particle concentrations, smaller ice particle sizes, and smaller fall velocities compared to simulations with pristine aerosols. Weaker convection in polluted conditions is a direct result of the changes in anvil ice characteristics and subsequent upper-tropospheric radiative heating and weaker tropospheric destabilization. Such a conclusion offers a different interpretation of recent satellite observations of tropical deep convection in pristine and polluted environments compared to the hypothesis of aerosol-induced convective invigoration. Sensitivity tests using the ensemble approach with modified microphysical parameters or domain configuration (horizontal gridlength, domain size) produce results that are similar to baseline, although there are quantitative differences in estimates of aerosol impacts on TOA radiative fluxes.

scholarly journals Cloud-system resolving model simulations of aerosol indirect effects on tropical deep convection and its thermodynamic environment

2011 ◽  
Vol 11 (20) ◽  
pp. 10503-10523 ◽  
Author(s):  
H. Morrison ◽  
W. W. Grabowski
Keyword(s):  
Indirect Effects ◽  
Large Scale ◽  
Deep Convection ◽  
Radiative Heating ◽  
Cloud System ◽  
Direct Result ◽  
Radiative Fluxes ◽  
Aerosol Indirect Effects ◽  
Ensemble Approach ◽  
Tropical Deep Convection

Abstract. This paper presents results from 240-member ensemble simulations of aerosol indirect effects on tropical deep convection and its thermodynamic environment. Simulations using a two-dimensional cloud-system resolving model are run with pristine, polluted, or highly polluted aerosol conditions and large-scale forcing from a 6-day period of active monsoon conditions during the 2006 Tropical Warm Pool – International Cloud Experiment (TWP-ICE). Domain-mean surface precipitation is insensitive to aerosols primarily because the large-scale forcing is prescribed and dominates the water and static energy budgets. The spread of the top-of-atmosphere (TOA) shortwave and longwave radiative fluxes among different ensemble members for the same aerosol loading is surprisingly large, exceeding 25 W m−2 even when averaged over the 6-day period. This variability is caused by random fluctuations in the strength and timing of individual deep convective events. The ensemble approach demonstrates a small weakening of convection averaged over the 6-day period in the polluted simulations compared to pristine. Despite this weakening, the cloud top heights and anvil ice mixing ratios are higher in polluted conditions. This occurs because of the larger concentrations of cloud droplets that freeze, leading directly to higher ice particle concentrations, smaller ice particle sizes, and smaller fall velocities compared to simulations with pristine aerosols. Weaker convection in polluted conditions is a direct result of the changes in anvil ice characteristics and subsequent upper-tropospheric radiative heating and weaker tropospheric destabilization. Such a conclusion offers a different interpretation of recent satellite observations of tropical deep convection in pristine and polluted environments compared to the hypothesis of aerosol-induced convective invigoration. Sensitivity tests using the ensemble approach with modified microphysical parameters or domain configuration (horizontal gridlength, domain size) produce results that are similar to baseline, although there are quantitative differences in estimates of aerosol impacts on TOA radiative fluxes.

Effect of Surface Fluxes versus Radiative Heating on Tropical Deep Convection

2015 ◽  
Vol 72 (9) ◽  
pp. 3378-3388 ◽  
Author(s):  
Usama Anber ◽  
Shuguang Wang ◽  
Adam Sobel
Keyword(s):  
Large Scale ◽  
Multiple Equilibria ◽  
Initial Conditions ◽  
Deep Convection ◽  
Surface Fluxes ◽  
Radiative Heating ◽  
Net Energy ◽  
Wide Range ◽  
Tropical Deep Convection ◽  
Gross Moist Stability

Abstract The effects of turbulent surface fluxes and radiative heating on tropical deep convection are compared in a series of idealized cloud-system-resolving simulations with parameterized large-scale dynamics. Two methods of parameterizing the large-scale dynamics are used: the weak temperature gradient (WTG) approximation and the damped gravity wave (DGW) method. Both surface fluxes and radiative heating are specified, with radiative heating taken as constant in the vertical in the troposphere. All simulations are run to statistical equilibrium. In the precipitating equilibria, which result from sufficiently moist initial conditions, an increment in surface fluxes produces more precipitation than an equal increment of column-integrated radiative heating. This is straightforwardly understood in terms of the column-integrated moist static energy budget with constant normalized gross moist stability. Under both large-scale parameterizations, the gross moist stability does in fact remain close to constant over a wide range of forcings, and the small variations that occur are similar for equal increments of surface flux and radiative heating. With completely dry initial conditions, the WTG simulations exhibit hysteresis, maintaining a dry state with no precipitation for a wide range of net energy inputs to the atmospheric column. The same boundary conditions and forcings admit a rainy state also (for moist initial conditions), and thus multiple equilibria exist under WTG. When the net forcing (surface fluxes minus radiative heating) is increased enough that simulations that begin dry eventually develop precipitation, the dry state persists longer after initialization when the surface fluxes are increased than when radiative heating is increased. The DGW method, however, shows no multiple equilibria in any of the simulations.

Aerosol Indirect Effects on Tropical Convection Characteristics under Conditions of Radiative–Convective Equilibrium

2011 ◽  
Vol 68 (4) ◽  
pp. 699-718 ◽  
Author(s):  
Susan C. van den Heever ◽  
Graeme L. Stephens ◽  
Norman B. Wood
Keyword(s):  
Indirect Effects ◽  
Large Scale ◽  
Cloud Condensation Nuclei ◽  
Deep Convection ◽  
Tropical Convection ◽  
Aerosol Indirect Effects ◽  
Cloud Resolving Model ◽  
Shallow Clouds ◽  
Grid Points ◽  
Indirect Forcing

Abstract The impacts of enhanced aerosol concentrations such as those associated with dust intrusions on the trimodal distribution of tropical convection have been investigated through the use of large-domain (10 000 grid points), fine-resolution (1 km), long-duration (100 days), two-dimensional idealized cloud-resolving model simulations conducted under conditions of radiative–convective equilibrium (RCE). The focus of this research is on those aerosols that serve primarily as cloud condensation nuclei (CCN). The results demonstrate that the large-scale organization of convection, the domain-averaged precipitation, and the total cloud fraction show only show a weak response to enhanced aerosol concentrations. However, while the domainwide responses to enhanced aerosol concentrations are weak, aerosol indirect effects on the three tropical cloud modes are found to be quite significant and often opposite in sign, a fact that appears to contribute to the weaker domain response. The results suggest that aerosol indirect effects associated with shallow clouds may offset or compensate for the aerosol indirect effects associated with congestus and deep convection systems and vice versa, thus producing a more moderate domainwide response to aerosol indirect forcing. Finally, when assessing the impacts of aerosol indirect forcing associated with CCN on the characteristics of tropical convection, several aspects need to be considered, including which cloud mode or type is being investigated, the field of interest, and whether localized or systemwide responses are being examined.

scholarly journals An Observational Overview of Dusty Deep Convection in Martian Dust Storms

2019 ◽  
Vol 76 (11) ◽  
pp. 3299-3326 ◽  
Author(s):  
Nicholas G. Heavens ◽  
David M. Kass ◽  
James H. Shirley ◽  
Sylvain Piqueux ◽  
Bruce A. Cantor
Keyword(s):  
Dust Storm ◽  
Large Scale ◽  
Middle Atmosphere ◽  
Deep Convection ◽  
High Surface ◽  
Dust Storms ◽  
Radiative Heating ◽  
Storm Activity ◽  
Mesoscale Circulations ◽  
Convective Structures

Abstract Deep convection, as used in meteorology, refers to the rapid ascent of air parcels in Earth’s troposphere driven by the buoyancy generated by phase change in water. Deep convection undergirds some of Earth’s most important and violent weather phenomena and is responsible for many aspects of the observed distribution of energy, momentum, and constituents (particularly water) in Earth’s atmosphere. Deep convection driven by buoyancy generated by the radiative heating of atmospheric dust may be similarly important in the atmosphere of Mars but lacks a systematic description. Here we propose a comprehensive framework for this phenomenon of dusty deep convection (DDC) that is supported by energetic calculations and observations of the vertical dust distribution and exemplary dusty deep convective structures within local, regional, and global dust storm activity. In this framework, DDC is distinct from a spectrum of weaker dusty convective activity because DDC originates from preexisting or concurrently forming mesoscale circulations that generate high surface dust fluxes, oppose large-scale horizontal advective–diffusive processes, and are thus able to maintain higher dust concentrations than typically simulated. DDC takes two distinctive forms. Mesoscale circulations that form near Mars’s highest volcanoes in dust storms of all scales can transport dust to the base of the upper atmosphere in as little as 2 h. In the second distinctive form, mesoscale circulations at low elevations within regional and global dust storm activity generate freely convecting streamers of dust that are sheared into the middle atmosphere over the diurnal cycle.

scholarly journals Cloud system resolving model study of the roles of deep convection for photo-chemistry in the TOGA COARE/CEPEX region

2008 ◽  
Vol 8 (10) ◽  
pp. 2741-2757 ◽  
Author(s):  
M. Salzmann ◽  
M. G. Lawrence ◽  
V. T. J. Phillips ◽  
L. J. Donner
Keyword(s):  
Large Scale ◽  
Marine Boundary Layer ◽  
Deep Convection ◽  
Trace Gases ◽  
Convective Transport ◽  
Cloud System ◽  
Limited Area ◽  
Toga Coare ◽  
Upward Transport ◽  
Photo Chemistry

Abstract. A cloud system resolving model including photo-chemistry (CSRMC) has been developed based on a prototype version of the Weather Research and Forecasting (WRF) model and is used to study influences of deep convection on chemistry in the TOGA COARE/CEPEX region. Lateral boundary conditions for trace gases are prescribed from global chemistry-transport simulations, and the vertical advection of trace gases by large scale dynamics, which is not reproduced in a limited area cloud system resolving model, is taken into account. The influences of deep convective transport and of lightning on NOx, O3, and HOx(=HO2+OH), in the vicinity of the deep convective systems are investigated in a 7-day 3-D 248×248 km2 horizontal domain simulation and several 2-D sensitivity runs with a 500 km horizontal domain. Mid-tropospheric entrainment is more important on average for the upward transport of O3 in the 3-D run than in the 2-D runs, but at the same time undiluted O3-poor air from the marine boundary layer reaches the upper troposphere more frequently in the 3-D run than in the 2-D runs, indicating the presence of undiluted convective cores. In all runs, in situ lightning is found to have only minor impacts on the local O3 budget. Near zero O3 volume mixing ratios due to the reaction with lightning-produced NO are only simulated in a 2-D sensitivity run with an extremely high number of NO molecules per flash, which is outside the range of current estimates. The fraction of NOx chemically lost within the domain varies between 20 and 24% in the 2-D runs, but is negligible in the 3-D run, in agreement with a lower average NOx concentration in the 3-D run despite a greater number of flashes. Stratosphere to troposphere transport of O3 is simulated to occur episodically in thin filaments in the 2-D runs, but on average net upward transport of O3 from below ~16 km is simulated in association with mean large scale ascent in the region. Ozone profiles in the TOGA COARE/CEPEX region are suggested to be strongly influenced by the intra-seasonal (Madden-Julian) oscillation.

scholarly journals Potential aerosol indirect effects on atmospheric circulation and radiative forcing through deep convection

2012 ◽  
Vol 39 (9) ◽  
pp. n/a-n/a ◽  
Author(s):  
Jiwen Fan ◽  
Daniel Rosenfeld ◽  
Yanni Ding ◽  
L. Ruby Leung ◽  
Zhanqing Li
Keyword(s):  
Atmospheric Circulation ◽  
Indirect Effects ◽  
Radiative Forcing ◽  
Deep Convection ◽  
Aerosol Indirect Effects

scholarly journals Shallow and Deep Latent Heating Modes over Tropical Oceans Observed with TRMM PR Spectral Latent Heating Data

2010 ◽  
Vol 23 (8) ◽  
pp. 2030-2046 ◽  
Author(s):  
Yukari N. Takayabu ◽  
Shoichi Shige ◽  
Wei-Kuo Tao ◽  
Nagio Hirota
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Three Dimensional ◽  
Tropical Rainfall Measuring Mission ◽  
Radiative Heating ◽  
Latent Heating ◽  
Tropical Oceans ◽  
Trmm Precipitation ◽  
Subtropical Oceans ◽  
Cumulus Congestus

Abstract Three-dimensional distributions of the apparent heat source (Q1) − radiative heating (QR) estimated from Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) utilizing the spectral latent heating (SLH) algorithm are analyzed. Mass-weighted and vertically integrated Q1 − QR averaged over the tropical oceans is estimated as ∼72.6 J s−1 (∼2.51 mm day−1) and that over tropical land is ∼73.7 J s−1 (∼2.55 mm day−1) for 30°N–30°S. It is shown that nondrizzle precipitation over tropical and subtropical oceans consists of two dominant modes of rainfall systems: deep systems and congestus. A rough estimate of the shallow-heating contribution against the total heating is about 46.7% for the average tropical oceans, which is substantially larger than the 23.7% over tropical land. Although cumulus congestus heating linearly correlates with SST, deep-mode heating is dynamically bounded by large-scale subsidence. It is notable that a substantial amount of rain, as large as 2.38 mm day−1 on average, is brought from congestus clouds under the large-scale subsiding circulation. It is also notable that, even in the region with SSTs warmer than 28°C, large-scale subsidence effectively suppresses the deep convection, with the remaining heating by congestus clouds. The results support that the entrainment of mid–lower-tropospheric dry air, which accompanies the large-scale subsidence, is the major factor suppressing the deep convection. Therefore, a representation of the realistic entrainment is very important for proper reproduction of precipitation distribution and the resultant large-scale circulation.

scholarly journals Reconciling Ground-Based and Space-Based Estimates of the Frequency of Occurrence and Radiative Effect of Clouds around Darwin, Australia

2014 ◽  
Vol 53 (2) ◽  
pp. 456-478 ◽  
Author(s):  
A. Protat ◽  
S. A. Young ◽  
S. A. McFarlane ◽  
T. L’Ecuyer ◽  
G. G. Mace ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Radiative Transfer ◽  
Radiative Forcing ◽  
Large Scale ◽  
Radiative Heating ◽  
Orthogonal Polarization ◽  
Frequency Of Occurrence ◽  
Radiative Fluxes ◽  
Radiative Impact ◽  
Satellite Radar

AbstractThe objective of this paper is to investigate whether estimates of the cloud frequency of occurrence and associated cloud radiative forcing as derived from ground-based and satellite active remote sensing and radiative transfer calculations can be reconciled over a well-instrumented active remote sensing site located in Darwin, Australia, despite the very different viewing geometry and instrument characteristics. It is found that the ground-based radar–lidar combination at Darwin does not detect most of the cirrus clouds above 10 km (because of limited lidar detection capability and signal obscuration by low-level clouds) and that the CloudSat radar–Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) combination underreports the hydrometeor frequency of occurrence below 2-km height because of instrument limitations at these heights. The radiative impact associated with these differences in cloud frequency of occurrence is large on the surface downwelling shortwave fluxes (ground and satellite) and the top-of-atmosphere upwelling shortwave and longwave fluxes (ground). Good agreement is found for other radiative fluxes. Large differences in radiative heating rate as derived from ground and satellite radar–lidar instruments and radiative transfer calculations are also found above 10 km (up to 0.35 K day−1 for the shortwave and 0.8 K day−1 for the longwave). Given that the ground-based and satellite estimates of cloud frequency of occurrence and radiative impact cannot be fully reconciled over Darwin, caution should be exercised when evaluating the representation of clouds and cloud–radiation interactions in large-scale models, and limitations of each set of instrumentation should be considered when interpreting model–observation differences.

scholarly journals Response of Tropical Deep Convection to Localized Heating Perturbations: Implications for Aerosol-Induced Convective Invigoration

2013 ◽  
Vol 70 (11) ◽  
pp. 3533-3555 ◽  
Author(s):  
Hugh Morrison ◽  
Wojciech W. Grabowski
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Warm Pool ◽  
Tropospheric Temperature ◽  
Surface Precipitation ◽  
Tropical Warm Pool ◽  
Adjustment Time ◽  
Localized Heating ◽  
Tropical Deep Convection ◽  
Convective Adjustment

Abstract A cloud-system-resolving model is used to investigate the effects of localized heating/cooling perturbations on tropical deep convection, in the context of the aerosol “invigoration effect.” This effect supposes that a reduction of droplet collision–coalescence in polluted conditions leads to lofting of cloud water in convective updrafts and enhanced freezing, latent heating, and buoyancy. To specifically isolate and test this mechanism, heating perturbations were applied to updrafts with corresponding cooling applied in downdrafts. Ensemble simulations were run with either perturbed or unperturbed conditions and large-scale forcing from a 7.5-day period of active monsoon conditions during the 2006 Tropical Warm Pool–International Cloud Experiment. In the perturbed simulations there was an initial invigoration of convective updrafts and surface precipitation, but convection returned to its unperturbed state after about 24 h because of feedback with the larger-scale environment. This feedback led to an increase in the horizontally averaged mid-/upper-tropospheric temperature of about 1 K relative to unperturbed simulations. When perturbed conditions were applied to only part of the domain, gravity waves rapidly dispersed buoyancy anomalies in the perturbed region to the rest of the domain, allowing convective invigoration from the heating perturbations to be sustained over the entire simulation period. This was associated with a mean mesoscale circulation consisting of ascent (descent) at mid-/upper levels in the perturbed (unperturbed) region. In contrast to recent studies, it is concluded that the invigoration effect is intimately coupled with larger-scale dynamics through a two-way feedback, and in the absence of alterations in the larger-scale circulation there is limited invigoration beyond the convective adjustment time scale.

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