scholarly journals Stochastic Backscatter for Cloud-Resolving Models. Part I: Implementation and Testing in a Dry Convective Boundary Layer

2008 ◽  
Vol 65 (1) ◽  
pp. 123-139 ◽  
Author(s):  
Sonja Weinbrecht ◽  
Paul J. Mason
Keyword(s):  
Boundary Layer ◽  
Free Convection ◽  
Convective Boundary Layer ◽  
Deep Convection ◽  
Time Development ◽  
Convective Boundary ◽  
Near Surface ◽  
Complex Issue ◽  
Marked Influence ◽  
Mesh Refinements

Abstract In simulations of deep convection with cloud-resolving models the turbulence is often rather poorly resolved, and the influence of the subfilter-scale parameterization used in such circumstances is probably greater than in better-resolved simulations. Therefore a study to investigate the influence of stochastic backscatter was performed and presented in two papers. This first paper focuses on a description of the stochastic backscatter model and its effect on a neutral and a dry convective boundary layer. The second paper then deals with two cases of deep convection. The dry convective boundary layer is typical of the subcloud layer in deep convection and this study allows for influences on this layer to be investigated separately. As a simple case of convection it also allows for general effects to be identified. The implementation of stochastic backscatter was improved to ensure an appropriate scale of backscatter that is independent of any mesh refinements and always spatially isotropic. It can also be applied in a deep atmosphere with use of the anelastic approximation. Generally the backscatter is found to affect the velocity and scalar variances as well as the spatial structure and time development of the simulations. An additional issue is the marked influence of both varying resolution and backscatter on the near-surface temperature differences. This is an element of the complex issue of surface transfers under free convection conditions. Overall, the investigations show that the backscatter gives some beneficial changes to the simulations, which tend to keep results in less well- resolved cases closer to those in better-resolved simulations.

A Thermal Plume Model for the Convective Boundary Layer: Representation of Cumulus Clouds

2008 ◽  
Vol 65 (2) ◽  
pp. 407-425 ◽  
Author(s):  
Catherine Rio ◽  
Frédéric Hourdin
Keyword(s):  
Boundary Layer ◽  
Mass Flux ◽  
Convective Boundary Layer ◽  
Turbulent Transport ◽  
Thermal Plume ◽  
Cumulus Clouds ◽  
Convective Boundary ◽  
Near Surface ◽  
Plume Model ◽  
Surface Drying

Abstract The “thermal plume model,” a mass-flux scheme combined with a classical diffusive approach, originally developed to represent turbulent transport in the dry convective boundary layer, is extended here to the representation of cloud processes. The modified parameterization is validated in a 1D configuration against results of large eddy simulations (LES), as well as in a 3D configuration against in situ measurements, for a series of cases of dry and cloudy convective boundary layers. Accounting for coherent structures of the mixed layer with the mass-flux scheme improves the representation of the diurnal cycle of the boundary layer, particularly its progressive deepening during the day and the associated near-surface drying. Results also underline the role of the prescription of the mixing of air between the plume and its environment, and of submean-plume fluctuations.

scholarly journals Diurnal Preconditioning of Subtropical Coastal Convective Storm Environments

2017 ◽  
Vol 145 (9) ◽  
pp. 3839-3859 ◽  
Author(s):  
Joshua S. Soderholm ◽  
Hamish A. McGowan ◽  
Harald Richter ◽  
Kevin Walsh ◽  
Tony Wedd ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Doppler Radar ◽  
Deep Convection ◽  
Sea Breeze ◽  
Return Flow ◽  
Convective Storm ◽  
Convective Boundary ◽  
Near Surface ◽  
Mesoscale Convective ◽  
Supercell Storms

Boundary layer evolution in response to diurnal forcing is manifested at the mesobeta and smaller scales of the atmosphere. Because this variability resides on subsynoptic scales, the potential influence upon convective storm environments is often not captured in coarse observational and modeling datasets, particularly for complex physical settings such as coastal regions. A detailed observational analysis of diurnally forced preconditioning for convective storm environments of South East Queensland, Australia (SEQ), during the Coastal Convective Interactions Experiment (2013–15) is presented. The observations used include surface-based measurements, aerological soundings, and dual-polarization Doppler radar. The sea-breeze circulation was found to be the dominant influence; however, profile modification by the coastward advection of the continental boundary layer was found to be an essential mechanism for favorable preconditioning of deep convection. This includes 1) enhanced moisture in the city of Brisbane, potentiality due to an urban heat island–enhanced land–sea thermal contrast, 2) significant afternoon warming and moistening above the sea breeze resulting from the advection of the inland convective boundary layer coastward under prevailing westerly flow coupled with the sea-breeze return flow, and 3) substantial variations in near-surface moisture likely associated with topography and land use. For the 27 November 2014 Brisbane hailstorm, which caused damages exceeding $1.5 billion Australian dollars (AUD), the three introduced diurnal preconditioning processes are shown to favor a mesoscale convective environment supportive of large hailstone growth. The hybrid high-precipitation supercell storm mode noted for this event and previous similar events in SEQ is hypothesized to be more sensitive to variations in near-surface and boundary layer instability in contrast to contemporary supercell storms.

scholarly journals Convective Boundary Layer Clouds as Observed with Ground-Based Lidar at a Mid-Latitude Plain Site

2021 ◽  
Vol 13 (7) ◽  
pp. 1281
Author(s):  
Yifan Zhan ◽  
Fan Yi ◽  
Fuchao Liu ◽  
Yunpeng Zhang ◽  
Changming Yu ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Surface Air Temperature ◽  
Cloud Base ◽  
Convective Boundary ◽  
Height Range ◽  
Near Surface ◽  
Short Period ◽  
Ground Based Lidar ◽  
Water Vapor Mixing Ratio

A total of 3047 individual shallow cumuli were identified from 9 years of polarization lidar measurements (2011–2019) at Wuhan, China (30.5°N, 114.4°E). These fair-weather shallow cumuli occurred at the top edge of the convective boundary layer between April and October with the maximum occurrence in July over the 30°N plain site. They persisted mostly (>92%) for a short period of ~1–10 min and had a geometrical thickness of ~50–600 m (a mean of 209 ± 138 m). The majority (>94%) of the cloud bases of these cumuli were found to appear ~50–560 m (a mean of 308 ± 254 m) above the lifting condensation level (LCL). In this height range from the LCL to the cloud base, the lidar volume depolarization ratio (δδV) slightly decreased with increasing height, showing gradually increasing condensation in this sub-cloud region due to penetrative thermals. Most of the observed shallow cumuli (79%) formed under the conditions of high near-surface air temperature (>30 °C) and water vapor mixing ratio (>15 g kg−1).

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