Differences in the lower troposphere in two- and three-dimensional cloud-resolving model simulations of deep convection

2008 ◽  
pp. n/a-n/a ◽  
Author(s):  
J. C. Petch ◽  
P. N. Blossey ◽  
C .S. Bretherton
Keyword(s):  
Deep Convection ◽  
Three Dimensional ◽  
Lower Troposphere ◽  
Model Simulations ◽  
Cloud Resolving Model

scholarly journals tobac 1.2: towards a flexible framework for tracking and analysis of clouds in diverse datasets

2019 ◽  
Vol 12 (11) ◽  
pp. 4551-4570 ◽  
Author(s):  
Max Heikenfeld ◽  
Peter J. Marinescu ◽  
Matthew Christensen ◽  
Duncan Watson-Parris ◽  
Fabian Senf ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Longwave Radiation ◽  
Geostationary Satellite ◽  
Model Assessment ◽  
Model Simulations ◽  
Cloud Properties ◽  
Level Data ◽  
Different Types ◽  
Cloud Resolving Model ◽  
High Level

Abstract. We introduce tobac (Tracking and Object-Based Analysis of Clouds), a newly developed framework for tracking and analysing individual clouds in different types of datasets, such as cloud-resolving model simulations and geostationary satellite retrievals. The software has been designed to be used flexibly with any two- or three-dimensional time-varying input. The application of high-level data formats, such as Iris cubes or xarray arrays, for input and output allows for convenient use of metadata in the tracking analysis and visualisation. Comprehensive analysis routines are provided to derive properties like cloud lifetimes or statistics of cloud properties along with tools to visualise the results in a convenient way. The application of tobac is presented in two examples. We first track and analyse scattered deep convective cells based on maximum vertical velocity and the three-dimensional condensate mixing ratio field in cloud-resolving model simulations. We also investigate the performance of the tracking algorithm for different choices of time resolution of the model output. In the second application, we show how the framework can be used to effectively combine information from two different types of datasets by simultaneously tracking convective clouds in model simulations and in geostationary satellite images based on outgoing longwave radiation. The tobac framework provides a flexible new way to include the evolution of the characteristics of individual clouds in a range of important analyses like model intercomparison studies or model assessment based on observational data.

Two- and Three-Dimensional Cloud-Resolving Model Simulations of the Mesoscale Enhancement of Surface Heat Fluxes by Precipitating Deep Convection

2006 ◽  
Vol 19 (1) ◽  
pp. 139-149 ◽  
Author(s):  
Xiaoqing Wu ◽  
Stephen Guimond
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Deep Convection ◽  
Three Dimensional ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Total Flux ◽  
Surface Heat Fluxes ◽  
Cloud Resolving Model ◽  
2D And 3D

Abstract Two-dimensional (2D) and three-dimensional (3D) cloud-resolving model (CRM) simulations are conducted to quantify the enhancement of surface sensible and latent heat fluxes by tropical precipitating cloud systems for 20 days (10–30 December 1992) during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). The mesoscale enhancement appears to be analogous across both 2D and 3D CRMs, with the enhancement for the sensible heat flux accounting for 17% of the total flux for each model and the enhancement for the latent heat flux representing 18% and 16% of the total flux for 2D and 3D CRMs, respectively. The convection-induced gustiness is mainly responsible for the enhancement observed in each model simulation. The parameterization schemes of the mesoscale enhancement by the gustiness in terms of convective updraft, downdraft, and precipitation, respectively, are examined using each version of the CRM. The scheme utilizing the precipitation was found to yield the most desirable estimations of the mean fluxes with the smallest rms error. The results together with previous findings from other studies suggest that the mesoscale enhancement of surface heat fluxes by the precipitating deep convection is a subgrid process apparent across various CRMs and is imperative to incorporate into general circulation models (GCMs) for improved climate simulation.

scholarly journals Cloud-Resolving Model Simulations of KWAJEX: Model Sensitivities and Comparisons with Satellite and Radar Observations

2007 ◽  
Vol 64 (5) ◽  
pp. 1488-1508 ◽  
Author(s):  
Peter N. Blossey ◽  
Christopher S. Bretherton ◽  
Jasmine Cetrone ◽  
Marat Kharoutdinov
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Longwave Radiation ◽  
Radiative Fluxes ◽  
Model Simulations ◽  
Time Period ◽  
Ground Validation ◽  
Cloud Resolving Model ◽  
Sensitivity Studies ◽  
Upper Level

Abstract Three-dimensional cloud-resolving model simulations of a mesoscale region around Kwajalein Island during the Kwajalein Experiment (KWAJEX) are performed. Using observed winds along with surface and large-scale thermodynamic forcings, the model tracks the observed mean thermodynamic soundings without thermodynamic nudging during 52-day simulations spanning the whole experiment time period, 24 July–14 September 1999. Detailed comparisons of the results with cloud and precipitation observations, including radar reflectivities from the Kwajalein ground validation radar and International Satellite Cloud Climatology Project (ISCCP) cloud amounts and radiative fluxes, reveal the biases and sensitivities of the model’s simulated clouds. The amount and optical depth of high cloud are underpredicted by the model during less rainy periods, leading to excessive outgoing longwave radiation (OLR) and insufficient albedo. The simulated radar reflectivities tend to be excessive, especially in the upper troposphere, suggesting that simulated high clouds are precipitating large hydrometeors too efficiently. Occasionally, large-scale advective forcing errors also seem to contribute to upper-level cloud and relative humidity biases. An extensive suite of sensitivity studies to different microphysical and radiative parameterizations is performed, with surprisingly little impact on the results in most cases.

Transient Environmental Sensitivities of Explicitly Simulated Tropical Convection

2010 ◽  
Vol 67 (4) ◽  
pp. 923-940 ◽  
Author(s):  
Stefan N. Tulich ◽  
Brian E. Mapes
Keyword(s):  
Deep Convection ◽  
Three Dimensional ◽  
Convective Clouds ◽  
Model Response ◽  
Effective Inhibition ◽  
Cloud Resolving Model ◽  
Response Enhancement ◽  
Vertical Displacements ◽  
Nonlocal Part ◽  
Homogeneous Temperature

Abstract A three-dimensional cloud-resolving model, maintained in a statistically steady convecting state by tropics-like forcing, is subjected to sudden (10 min) stimuli consisting of horizontally homogeneous temperature and/or moisture sources with various profiles. Ensembles of simulations are used to increase the statistical robustness of the results and to assess the deterministic nature of the model response for domain sizes near contemporary global model resolution. The response to middle- and upper-tropospheric perturbations is predominantly local in the vertical: convection damps the imposed stimulus over a few hours. Low-level perturbations are similarly damped, but also produce a vertically nonlocal response: enhancement or suppression of new deep convective clouds extending above the perturbed level. Experiments show that the “effective inhibition layer” for deep convection is about 4 km deep, far deeper than traditional convective inhibition defined for undilute lifted parcels. Both the local and nonlocal responses are remarkably linear but can be highly stochastic, especially if deep convection is only intermittently present (small domains, weak forcing). Quantitatively, temperature-versus-moisture perturbations in a ratio corresponding to adiabatic vertical displacements produce responses of roughly equal magnitude. However, moisture perturbations seem to provoke the nonlocal (upward spreading) type of response more effectively. This nonlocal part of the response is also more effective when background forcing intensity is weak. Only at very high intensity does the response approach the limits of purely local damping and pure determinism that would be most convenient for theory and parameterization.

scholarly journals A model study on the influence of overshooting convection on TTL water vapour

2010 ◽  
Vol 10 (20) ◽  
pp. 9833-9849 ◽  
Author(s):  
M. E. E. Hassim ◽  
T. P. Lane
Keyword(s):  
Water Vapour ◽  
Deep Convection ◽  
Three Dimensional ◽  
Direct Role ◽  
Water Vapour Content ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Model Study ◽  
Cloud Resolving Model ◽  
Passive Tracers

Abstract. Overshooting deep convection that penetrates into the Tropical Tropopause Layer (TTL) is thought to have an important role in regulating the water vapour content of this region. Yet, the net effect of such convection and the dominant mechanisms remain unclear. This study uses two idealised three-dimensional cloud-resolving model simulations to examine the influence of overshooting convection on water vapour when it penetrates into two different TTL environments, one supersaturated and the other subsaturated with respect to ice. These simulations show that the overshooting convection plays a direct role in driving the ambient environment towards ice saturation through either net moistening (subsaturated TTL) or net dehydration (supersaturated TTL). Moreover, in these cases the extent of dehydration in supersaturated conditions is greater than the moistening in subsaturated conditions. With the aid of modelled passive tracers, the relative roles of transport, mixing and ice microphysics are assessed; ultimately, ice sublimation and scavenging processes play the most important role in defining the different TTL relative humidity tendencies. In addition, significant moistening in both cases is modelled well into the subsaturated tropical lower stratosphere (up to 450 K), even though the overshooting turrets only reach approximately 420 K. It is shown that this moistening is the result of jumping cirrus, which is induced by the localised upward transport and mixing of TTL air following the collapse of the overshooting turret.

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 Determination of Best Tropopause Definition for Convective Transport Studies

2018 ◽  
Vol 75 (10) ◽  
pp. 3433-3446 ◽  
Author(s):  
Emily M. Maddox ◽  
Gretchen L. Mullendore
Keyword(s):  
Mass Transport ◽  
Potential Vorticity ◽  
Deep Convection ◽  
Three Dimensional ◽  
Static Stability ◽  
Convective Transport ◽  
Lapse Rate ◽  
Tracer Concentration ◽  
Temperature Lapse Rate ◽  
Cloud Resolving Model

An idealized three-dimensional cloud-resolving model is used to investigate the sensitivity of cross-tropopause convective mass transport to tropopause definition. A simulation is conducted to encompass the growth and decay cycle of a supercell thunderstorm, with a focus on irreversible transport above the tropopause. Five previously published tropopause definitions are evaluated: World Meteorological Organization (WMO) temperature lapse rate, potential vorticity, static stability, vertical curvature of the Brunt–Väisälä frequency, and stratospheric tracer concentration. By analyzing the behavior of different definitions both during and after active convection, we are able to define “best” choices for tropopause definitions as those that return to states most closely matching the preconvective environment. Potential vorticity and stratospheric tracer concentration are shown to perform poorly when analyzing deep convection. The WMO thermal tropopause and static stability definitions are found to perform the best, providing similar tropopause placement and quantities of irreversible mass transport. This investigation highlights the challenges of defining a tropopause in the vicinity of deep convection and demonstrates the need to clearly communicate calculation methods and threshold choices in the literature.

scholarly journals A model study on the influence of overshooting convection on TTL water vapour

2010 ◽  
Vol 10 (7) ◽  
pp. 16969-17007
Author(s):  
M. E. E. Hassim ◽  
T. P. Lane
Keyword(s):  
Water Vapour ◽  
Deep Convection ◽  
Three Dimensional ◽  
Direct Role ◽  
Water Vapour Content ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Model Study ◽  
Cloud Resolving Model ◽  
Passive Tracers

Abstract. Overshooting deep convection that penetrates into the Tropical Tropopause Layer (TTL) is thought to have an important role in regulating the water vapour content of this region. Yet, the net effect of such convection and the dominant mechanisms remain unclear. This study uses two idealised three-dimensional cloud-resolving model simulations to examine the influence of overshooting convection on water vapour when it penetrates into two different TTL environments, one supersaturated and the other subsaturated with respect to ice. These simulations show that the overshooting convection plays a direct role in driving the ambient environment towards ice saturation through either net moistening (subsaturated TTL) or net dehydration (supersaturated TTL). Moreover, in these cases the extent of dehydration in supersaturated conditions is greater than the moistening in subsaturated conditions. With the aid of modelled passive tracers, the relative roles of transport, mixing and ice microphysics are assessed; ultimately, ice sublimation and scavenging processes play the most important role in defining the different TTL relative humidity tendencies. In addition, significant moistening in both cases is modelled well into the subsaturated tropical lower stratosphere (up to 450 K), even though the overshooting turrets only reach approximately 420 K. It is shown that this moistening is the result of jumping cirrus, which is induced by the localised upward transport and mixing of TTL air following the collapse of the overshooting turret.

The Role of Convective Moistening in the Madden–Julian Oscillation

2009 ◽  
Vol 66 (11) ◽  
pp. 3297-3312 ◽  
Author(s):  
Katherine Thayer-Calder ◽  
David A. Randall
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Lower Troposphere ◽  
High Humidity ◽  
Madden Julian Oscillation ◽  
Near Surface ◽  
Community Atmosphere Model ◽  
Cloud Resolving Model ◽  
Environmental Relative Humidity ◽  
High Humidity Environment

Abstract This study compares two models that differ primarily in their cloud parameterizations and produce extremely different simulations of the Madden–Julian oscillation (MJO). The Community Atmosphere Model (CAM) version 3.0 from NCAR uses the Zhang–McFarlane scheme for deep convection and does not produce an MJO. The “superparameterized” version of the CAM (SP-CAM) replaces the cloud parameterizations with a two-dimensional cloud-resolving model (CRM) in each grid column and produces an extremely vigorous MJO. This analysis shows that the CAM is unable to produce high-humidity regions in the mid- to lower troposphere because of a lack of coupling between parameterized convection and environmental relative humidity. The SP-CAM produces an overly moist column due in part to excessive near-surface winds and evaporation during strong convective events. In the real tropics and the SP-CAM, convection within a high-humidity environment produces intense latent heating, which excites the large-scale circulation that is the signature of the MJO. The authors suggest that a model must realistically represent convective processes that moisten the entire tropical troposphere in order to produce a simulation of the MJO.

scholarly journals tobac v1.0: towards a flexible framework for tracking and analysis of clouds in diverse datasets

2019 ◽  
Author(s):  
Max Heikenfeld ◽  
Peter J. Marinescu ◽  
Matthew Christensen ◽  
Duncan Watson-Parris ◽  
Fabian Senf ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Longwave Radiation ◽  
Geostationary Satellite ◽  
Model Assessment ◽  
Model Simulations ◽  
Cloud Properties ◽  
Level Data ◽  
Different Types ◽  
Cloud Resolving Model ◽  
High Level

Abstract. We introduce tobac (Tracking and Object-Based Analysis of Clouds), a newly developed framework for tracking and analysing individual clouds in different types of datasets, such as cloud-resolving model simulations and geostationary satellite retrievals. The software has been designed to be used flexibly with any two- or three-dimensional time-varying input. The application of high-level data formats, such as iris cubes or xarray arrays, for input and output allows for convenient use of metadata in the tracking analysis and visualisation. Comprehensive analysis routines are provided to derive properties like cloud lifetimes or statistics of cloud properties along with tools to visualise the results in a convenient way. The application of tobac is presented in two examples. We first track and analyse scattered deep convective cells based on maximum vertical velocity and the three-dimensional condensate mixing ratio field in cloud-resolving model simulations. We also investigate the performance of the tracking algorithm for different choices of time resolution of the model output. In the second application, we show how the framework can be used to effectively combine information from two different types of datasets by simultaneously tracking convective clouds in model simulations and in geostationary satellite images based on outgoing longwave radiation. tobac provides a flexible new way to include the evolution of the characteristics of individual clouds in a range of important analyses like model intercomparison studies or model assessment based on observational data.

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