scholarly journals Evaluating convective parameterization closures using cloud-resolving model simulation of tropical deep convection

2015 ◽  
Vol 120 (4) ◽  
pp. 1260-1277 ◽  
Author(s):  
E. Suhas ◽  
Guang J. Zhang
Keyword(s):  
Model Simulation ◽  
Deep Convection ◽  
Convective Parameterization ◽  
Tropical Deep Convection ◽  
Cloud Resolving Model

scholarly journals Entrainment versus Dilution in Tropical Deep Convection

2017 ◽  
Vol 74 (11) ◽  
pp. 3725-3747 ◽  
Author(s):  
Walter M. Hannah
Keyword(s):  
Thermal Model ◽  
Deep Convection ◽  
Negative Relationship ◽  
Tropical Environment ◽  
Moist Air ◽  
Convective Parameterization ◽  
The Core ◽  
Tropical Deep Convection ◽  
Source Sink

Abstract The distinction between entrainment and dilution is investigated with cloud-resolving simulations of deep convection in a tropical environment. A method for estimating the rate of dilution by entrainment and detrainment is presented and calculated for a series of bubble simulations with a range of initial radii. Entrainment generally corresponds to dilution of convection, but the two quantities are not well correlated. Core dilution by entrainment is significantly reduced by the presence of a shell of moist air around the core. Dilution by entrainment also increases with increasing updraft velocity but only for sufficiently strong updrafts. Entrainment contributes significantly to the total net dilution, but detrainment and the various source/sink terms play large roles depending on the variable in question. Detrainment has a concentrating effect on average that balances out the dilution by entrainment. The experiments are also used to examine whether entrainment or dilution scale with cloud radius. The results support a weak negative relationship for dilution but not for entrainment. The sensitivity to resolution is briefly discussed. A toy Lagrangian thermal model is used to demonstrate the importance of the cloud shell as a thermodynamic buffer to reduce the dilution of the core by entrainment. The results suggest that explicit cloud heterogeneity may be a useful consideration for future convective parameterization development.

scholarly journals Evaluation of Hydrometeor Phase and Ice Properties in Cloud-Resolving Model Simulations of Tropical Deep Convection Using Radiance and Polarization Measurements

2012 ◽  
Vol 69 (11) ◽  
pp. 3290-3314 ◽  
Author(s):  
Bastiaan van Diedenhoven ◽  
Ann M. Fridlind ◽  
Andrew S. Ackerman ◽  
Brian Cairns
Keyword(s):  
Asymmetry Parameter ◽  
Near Infrared ◽  
Deep Convection ◽  
Effective Radius ◽  
Ice Crystals ◽  
Model Simulations ◽  
Brightness Temperatures ◽  
Aspect Ratios ◽  
Tropical Deep Convection ◽  
Cloud Resolving Model

Abstract Satellite measurements are used to evaluate the glaciation, particle shape, and effective radius in cloud-resolving model simulations of tropical deep convection. Multidirectional polarized reflectances constrain the ice crystal geometry and the thermodynamic phase of the cloud tops, which in turn are used to calculate near-infrared reflectances so as to constrain the simulated ice effective radius, thereby avoiding inconsistencies between retrieval algorithms and model simulations. Liquid index values derived from Polarization and Directionality of the Earth’s Reflectances (POLDER) measurements indicate only ice-topped clouds at brightness temperatures (BTs) lower than −40°C, only liquid clouds at BT > −20°C, and both phases occurring at temperatures in between. Liquid index values calculated from model simulations generally reveal too many ice-topped clouds at BT > −20°C. The model assumption of platelike ice crystals with an aspect ratio of 0.7 is found consistent with POLDER measurements for BT < −40°C when very rough ice crystals are assumed, leading to an asymmetry parameter of 0.74, whereas measurements indicate more extreme aspect ratios of ~0.15 at higher temperatures, yielding an asymmetry parameter of 0.84. MODIS-retrieved ice effective radii are found to be 18–28 μm at BT < −40°C, but biased low by about 5 μm owing primarily to the assumption of pristine crystals in the retrieval. Simulated 2.13-μm reflectances at BT < −40°C are found to be about 0.05–0.1 too large compared to measurements, suggesting that model-simulated effective radii are 7–15 μm too small. Two simulations with contrasting ice nucleation schemes showed little difference in simulated effective radii at BT < −40°C, indicating that homogeneous nucleation is dominating in the simulations. Changes around −40°C in satellite observations suggest a change in cloud-top ice shape and/or size in natural deep convection possibly related to a change in the freezing mechanism.

scholarly journals Detailed cloud resolving model simulations of the impacts of Saharan air layer dust on tropical deep convection – Part 1: Dust acts as ice nuclei

2010 ◽  
Vol 10 (5) ◽  
pp. 12907-12952 ◽  
Author(s):  
W. Gong ◽  
Q. Min ◽  
R. Li ◽  
A. Teller ◽  
E. Joseph ◽  
...  
Keyword(s):  
Water Vapor ◽  
Heterogeneous Nucleation ◽  
Mineral Dust ◽  
Deep Convection ◽  
Number Concentration ◽  
Middle Troposphere ◽  
Saharan Air Layer ◽  
Ice Nuclei ◽  
Tropical Deep Convection ◽  
Cloud Resolving Model

Abstract. Observational studies suggest that the Saharan Air Layer (SAL), an elevated layer (850–500 hPa) of Saharan air and mineral dust, has strong impacts on the microphysical as well as dynamical properties of tropical deep convective cloud systems along its track. In this case study, numerical simulations using a two-dimensional Detailed Cloud Resolving Model (DCRM) were carried out to investigate the dust-cloud interactions in the tropical deep convection, focusing on the dust role as Ice Nuclei (IN). The simulations showed that mineral dust considerably enhanced heterogeneous nucleation and freezing at temperatures warmer than −40 °C, resulting in more ice hydrometeors number concentration and reduced precipitating size of ice particles. Because of the lower in the saturation over ice as well as more droplet freezing, total latent heating increased, and consequently the updraft velocity was stronger. On the other hand, the increased ice deposition consumed more water vapor at middle troposphere, which induces a competition for water vapor between heterogeneous and homogeneous freezing and nucleation. As a result, dust suppressed the homogeneous droplet freezing and nucleation due to the heterogeneous droplet freezing and the weakened transport of water vapor at lower stratosphere, respectively. These effects led to decreased number concentration of ice cloud particles in the upper troposphere, and consequently lowered the cloud top height during the stratus precipitating stage. Acting as IN, mineral dust also influenced precipitation in deep convection. It initiated earlier the collection because dust-related heterogeneous nucleation and freezing at middle troposphere occur earlier than homogeneous nucleation at higher altitudes. Nevertheless, the convective precipitation was suppressed by reduced collection of large graupel particles and insufficient fallout related to decreased sizes of precipitating ice hydrometeors. On the contrary, dust increased the precipitation in stratiform precipitation through deposition growth. Overall, the comprehensive effects of mineral dust suppressed the precipitation by up to 22%.

scholarly journals A PDF-Based Parameterization of Subgrid-Scale Hydrometeor Transport in Deep Convection

2017 ◽  
Vol 74 (4) ◽  
pp. 1293-1309 ◽  
Author(s):  
May Wong ◽  
Mikhail Ovchinnikov
Keyword(s):  
Vertical Velocity ◽  
Deep Convection ◽  
Cloud Droplet ◽  
Subgrid Scale ◽  
Microphysics Scheme ◽  
Marginal Distributions ◽  
Mixing Ratios ◽  
Tropical Deep Convection ◽  
Cloud Resolving Model ◽  
Benchmark Solutions

Abstract A parameterization scheme is proposed for the subgrid-scale transport of hydrometeors in an assumed probability density function (PDF) scheme. Joint distributions of vertical velocity and hydrometeor mixing ratios are typically unknown, but marginal (1D) PDFs of these variables are available. The parameterization is developed using high-resolution simulations of continental and tropical deep convection. A 3D cloud-resolving model (CRM) providing benchmark solutions has a horizontal grid spacing of 250 m and employs the Morrison microphysics scheme, which treats prognostically mass and number mixing ratios for four types of precipitating hydrometeors (rain, graupel, snow, and ice) as well as cloud droplet number mixing ratio. The subgrid-scale hydrometeor transport scheme assumes input given in the form of marginal PDFs of vertical velocity and hydrometeor mixing ratios; in this study, these marginal distributions are provided by the cloud-resolving model. Conditional sampling and scaling are then applied to the marginal distributions to account for subplume correlations. The parameterized fluxes tested for four episodes of deep convection show good agreement with benchmark fluxes computed directly from the CRM output. The results demonstrate the potential use of the subgrid-scale hydrometeor transport scheme in an assumed PDF scheme to parameterize the covariances of vertical velocity and hydrometeor mixing ratios.

scholarly journals Tropical Deep Convection Impact on Southern Winter Stationary Waves and Its Modulation by the Quasi-Biennial Oscillation

2019 ◽  
Vol 32 (21) ◽  
pp. 7453-7467 ◽  
Author(s):  
Cristina Peña-Ortiz ◽  
Elisa Manzini ◽  
Marco A. Giorgetta
Keyword(s):  
Model Simulation ◽  
Dominant Role ◽  
Deep Convection ◽  
Polar Vortex ◽  
Stationary Waves ◽  
Quasi Biennial Oscillation ◽  
Tropical Deep Convection ◽  
The Impact ◽  
Biennial Oscillation ◽  
Winter Hemisphere

Abstract The impact of tropical deep convection on southern winter stationary waves and its modulation by the quasi-biennial oscillation (QBO) have been investigated in a long (210 year) climate model simulation and in ERA-Interim reanalysis data for the period 1979–2018. Model results reveal that tropical deep convection over the region of its climatological maximum modulates high-latitude stationary planetary waves in the southern winter hemisphere, corroborating the dominant role of tropical thermal forcing in the generation of these waves. In the tropics, deep convection enhancement leads to wavenumber-1 eddy anomalies that reinforce the climatological Rossby–Kelvin wave couplet. The Rossby wave propagates toward the extratropical southern winter hemisphere and upward through the winter stratosphere reinforcing wavenumber-1 climatological eddies. As a consequence, stronger tropical deep convection is related to greater upward wave propagation and, consequently, to a stronger Brewer–Dobson circulation and a warmer polar winter stratosphere. This linkage between tropical deep convection and the Southern Hemisphere (SH) winter polar vortex is also found in the ERA-Interim reanalysis. Furthermore, model results indicate that the enhancement of deep convection observed during the easterly phase of the QBO (E-QBO) gives rise to a similar modulation of the southern winter extratropical stratosphere, which suggests that the QBO modulation of convection plays a fundamental role in the transmission of the QBO signature to the southern stratosphere during the austral winter, revealing a new pathway for the QBO–SH polar vortex connection. ERA-Interim corroborates a QBO modulation of deep convection; however, the shorter data record does not allow us to assess its possible impact on the SH polar vortex.

scholarly journals Latent Heating and Mixing due to Entrainment in Tropical Deep Convection

2014 ◽  
Vol 71 (2) ◽  
pp. 816-832 ◽  
Author(s):  
Clayton J. McGee ◽  
Susan C. van den Heever
Keyword(s):  
High Resolution ◽  
Deep Convection ◽  
Potential Temperature ◽  
Latent Heating ◽  
Freezing Level ◽  
Tropical Deep Convection ◽  
Cloud Resolving Model ◽  
Nested Grid ◽  
Environmental Air ◽  
Convective Cells

Abstract Recent studies have noted the role of latent heating above the freezing level in reconciling Riehl and Malkus' hot tower hypothesis (HTH) with evidence of diluted tropical deep convective cores. This study evaluates recent modifications to the HTH through Lagrangian trajectory analysis of deep convective cores in an idealized, high-resolution cloud-resolving model (CRM) simulation that uses a sophisticated two-moment microphysical scheme. A line of tropical convective cells develops within a finer nested grid whose boundary conditions are obtained from a large-domain CRM simulation approaching radiative convective equilibrium (RCE). Microphysical impacts on latent heating and equivalent potential temperature (θe) are analyzed along trajectories ascending within convective regions of the high-resolution nested grid. Changes in θe along backward trajectories are partitioned into contributions from latent heating due to ice processes and a residual term that is shown to be an approximate representation of mixing. The simulations demonstrate that mixing with dry environmental air decreases θe along ascending trajectories below the freezing level, while latent heating due to freezing and vapor deposition increase θe above the freezing level. Latent heating contributions along trajectories from cloud nucleation, condensation, evaporation, freezing, deposition, and sublimation are also quantified. Finally, the source regions of trajectories reaching the upper troposphere are identified. Much of the air ascending within convective updrafts originates from above the lowest 2 km AGL, but the strongest updrafts are composed of air from closer to the surface. The importance of both boundary layer and midlevel inflow in moist environments is underscored in this study.

Impacts of mineral dust on ice clouds in tropical deep convection systems

2014 ◽  
Vol 143 ◽  
pp. 64-72 ◽  
Author(s):  
Q.-L. Min ◽  
R. Li ◽  
B. Lin ◽  
E. Joseph ◽  
V. Morris ◽  
...  
Keyword(s):  
Mineral Dust ◽  
Deep Convection ◽  
Ice Clouds ◽  
Tropical Deep Convection

Intensification of Tilted Tropical Cyclones Over Relatively Cool and Warm Oceans in Idealized Numerical Simulations

2021 ◽  
Author(s):  
David A. Schecter
Keyword(s):  
Relative Humidity ◽  
Tropical Cyclones ◽  
Inner Core ◽  
Structural Parameters ◽  
Deep Convection ◽  
Surface Wind ◽  
Vertical Wind Shear ◽  
Surface Wind Speed ◽  
Cloud Resolving Model ◽  
Complete Alignment

Abstract A cloud resolving model is used to examine the intensification of tilted tropical cyclones from depression to hurricane strength over relatively cool and warm oceans under idealized conditions where environmental vertical wind shear has become minimal. Variation of the SST does not substantially change the time-averaged relationship between tilt and the radial length scale of the inner core, or between tilt and the azimuthal distribution of precipitation during the hurricane formation period (HFP). By contrast, for systems having similar structural parameters, the HFP lengthens superlinearly in association with a decline of the precipitation rate as the SST decreases from 30 to 26 °C. In many simulations, hurricane formation progresses from a phase of slow or neutral intensification to fast spinup. The transition to fast spinup occurs after the magnitudes of tilt and convective asymmetry drop below certain SST-dependent levels following an alignment process explained in an earlier paper. For reasons examined herein, the alignment coincides with enhancements of lower–middle tropospheric relative humidity and lower tropospheric CAPE inward of the radius of maximum surface wind speed rm. Such moist-thermodynamic modifications appear to facilitate initiation of the faster mode of intensification, which involves contraction of rm and the characteristic radius of deep convection. The mean transitional values of the tilt magnitude and lower–middle tropospheric relative humidity for SSTs of 28-30 °C are respectively higher and lower than their counterparts at 26 °C. Greater magnitudes of the surface enthalpy flux and core deep-layer CAPE found at the higher SSTs plausibly compensate for less complete alignment and core humidification at the transition time.

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