A Numerical Study of the Evolving Convective Boundary Layer and Orographic Circulation around the Santa Catalina Mountains in Arizona. Part II: Interaction with Deep Convection

2010 ◽  
Vol 138 (9) ◽  
pp. 3603-3622 ◽  
Author(s):  
J. Cory Demko ◽  
Bart Geerts
Keyword(s):  
Boundary Layer ◽  
Numerical Study ◽  
Deep Convection ◽  
Horizontal Resolution ◽  
Surface Flow ◽  
Convective Boundary ◽  
Convergence Line ◽  
Orographic Convection ◽  
Present Part ◽  
Santa Catalina Mountains

Abstract This is the second part of a study that examines the daytime evolution of the thermally forced boundary layer (BL) circulation over a relatively isolated mountain, about 30 km in diameter and 2 km high, and its interaction with locally initiated deep convection by means of numerical simulations validated with data collected in the 2006 Cumulus Photogrammetric, In Situ, and Doppler Observations (CuPIDO) field campaign in southeastern Arizona. Part I examined the BL circulation in cases with, at most, rather shallow orographic cumulus (Cu) convection; the present part addresses deep convection. The results are based on output from version 3 of the Weather Research and Forecasting model run at a horizontal resolution of 1 km. The model output verifies well against CuPIDO observations. In the absence of Cu convection, the thermally forced (solenoidal) circulation is largely contained within the BL over the mountain. Thunderstorm development deepens this BL circulation with inflow over the depth of the BL and outflow in the free troposphere aloft. Primary deep convection results from destabilization over elevated terrain and tends to be triggered along a convergence line, which arises from the solenoidal circulation but may drift downwind of the terrain crest. While the solenoidal anabatic flow converges moisture over the mountain, it also cools the air. Thus, a period of suppressed anabatic flow following a convective episode, at a time when surface heating is still intense, can trigger new and possibly deeper convection. The growth of deep convection may require enhanced convergent flow in the BL, but this is less apparent in the mountain-scale surface flow signal than the decay of orographic convection. A budget study over the mountain suggests that the precipitation efficiency of the afternoon convection is quite low, ~10% in this case.

A Numerical Study of the Evolving Convective Boundary Layer and Orographic Circulation around the Santa Catalina Mountains in Arizona. Part I: Circulation without Deep Convection

2010 ◽  
Vol 138 (5) ◽  
pp. 1902-1922 ◽  
Author(s):  
J. Cory Demko ◽  
Bart Geerts
Keyword(s):  
Boundary Layer ◽  
Numerical Study ◽  
Deep Convection ◽  
Weather Research And Forecasting ◽  
Return Flow ◽  
Convective Boundary ◽  
Warm Anomaly ◽  
Orographic Convection ◽  
Upper Level ◽  
Santa Catalina Mountains

Abstract The daytime evolution of the thermally forced boundary layer (BL) circulation over an isolated mountain, about 30 km in diameter and 2 km high, is examined by means of numerical simulations validated with data collected in the Cumulus Photogrammetric, In Situ, and Doppler Observations (CuPIDO) field campaign. Two cases are presented, one remains cloud free in the simulations, and the second produces orographic convection just deep enough to yield a trace of precipitation. The Weather Research and Forecasting version 3 simulations, at a resolution of 1 km, compare well with CuPIDO observations. The simulations reveal a solenoidal circulation mostly contained within the convective BL, but this circulation and especially its upper-level return flow branch are not immediately apparent since they are overwhelmed by BL thermals. A warm anomaly forms over the high terrain during the day, but it is rather shallow and does not extend over the depth of the convective BL, which bulges over the mountain. Low-level mountain-scale convergence (MSC), driven by an anabatic pressure gradient, deepens during the day. Even relatively shallow and relatively small cumulus convection can temporarily overwhelm surface MSC by cloud shading and convective downdraft dynamics. In the evening drainage flow develops near the surface before the anabatic forcing ceases, and anabatic flow is still present in the residual mixed layer, decoupled from the surface. The interaction of the boundary layer circulation with deep orographic convection is examined in Part II of this study.

The Cumulus, Photogrammetric, In Situ, and Doppler Observations Experiment of 2006

2008 ◽  
Vol 89 (1) ◽  
pp. 57-74 ◽  
Author(s):  
R. Damiani ◽  
J. Zehnder ◽  
B. Geerts ◽  
J. Demko ◽  
S. Haimov ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Radar Data ◽  
Boundary Layer Processes ◽  
Orographic Convection ◽  
Layer Flow ◽  
Santa Catalina Mountains ◽  
Experimental Strategies ◽  
Natural Laboratory

The finescale structure and dynamics of cumulus, evolving from shallow to deep convection, and the accompanying changes in the environment and boundary layer over mountainous terrain were the subjects of a field campaign in July–August 2006. Few measurements exist of the transport of boundary layer air into the deep troposphere by the orographic toroidal circulation and orographic convection. The campaign was conducted over the Santa Catalina Mountains in southern Arizona, a natural laboratory to study convection, given the spatially and temporally regular development of cumulus driven by elevated heating and convergent boundary layer flow. Cumuli and their environment were sampled via coordinated observations from the surface, radiosonde balloons, and aircraft, along with airborne radar data and stereophotogrammetry from two angles. The collected dataset is expected to yield new insights in the boundary layer processes leading to orographic convection, in the cumulus-induced transport of boundary layer air into the troposphere, and in fundamental cumulus dynamics. This article summarizes the motivations, objectives, experimental strategies, preliminary findings, and the potential research paths stirred by the project.

Boundary Layer Energy Transport and Cumulus Development over a Heated Mountain: An Observational Study

2009 ◽  
Vol 137 (1) ◽  
pp. 447-468 ◽  
Author(s):  
J. Cory Demko ◽  
Bart Geerts ◽  
Qun Miao ◽  
Joseph A. Zehnder
Keyword(s):  
Boundary Layer ◽  
Energy Transport ◽  
Deep Convection ◽  
Surface Wind ◽  
North American Monsoon ◽  
The North ◽  
Solar Noon ◽  
Cumulus Congestus ◽  
Weak Winds ◽  
Santa Catalina Mountains

Abstract Aircraft and surface measurements of the boundary layer transport of mass and moisture toward an isolated, heated mountain are presented. The data were collected around the Santa Catalina Mountains in Arizona, 20–30 km in diameter, during the North American monsoon, on days with weak winds and cumulus congestus to cumulonimbus development over the mountain. Flights in the boundary layer around the mountain and surface station data indicate that mountain-scale anabatic surface wind generally develops shortly after sunrise, peaking at ∼1 m s−1 in strength close to solar noon. There is some evidence for a toroidal heat island circulation, with divergence in the upper boundary layer. The aircraft data and mainly the diurnal surface temperature and pressure patterns confirm that this circulation is driven by surface heating over the mountain. Three case studies suggest that growth spurts of orographic cumulus and cumulonimbus are not preceded by enhanced mountain-scale mass convergence near the surface, and that the decay of orographic deep convection is associated with divergence around the mountain.

scholarly journals Turbulent dispersion in cloud-topped boundary layers

2008 ◽  
Vol 8 (6) ◽  
pp. 19637-19677
Author(s):  
R. A. Verzijlbergh ◽  
H. J. J. Jonker ◽  
T. Heus ◽  
J. Vilà-Guerau de Arellano
Keyword(s):  
Boundary Layer ◽  
Velocity Distribution ◽  
Boundary Layers ◽  
Convective Boundary Layer ◽  
Numerical Study ◽  
Turbulent Dispersion ◽  
Dispersion Characteristics ◽  
Atmospheric Boundary Layers ◽  
Convective Boundary ◽  
Shallow Cumulus

Abstract. Compared to dry boundary layers, dispersion in cloud-topped boundary layers has received less attention. In this LES based numerical study we investigate the dispersion of a passive tracer in the form of Lagrangian particles for four kinds of atmospheric boundary layers: 1) a dry convective boundary layer (for reference), 2) a "smoke" cloud boundary layer in which the turbulence is driven by radiative cooling, 3) a stratocumulus topped boundary layer and 4) a shallow cumulus topped boundary layer. We show that the dispersion characteristics of the smoke cloud boundary layer as well as the stratocumulus situation can be well understood by borrowing concepts from previous studies of dispersion in the dry convective boundary layer. A general result is that the presence of clouds enhances mixing and dispersion – a notion that is not always reflected well in traditional parameterization models, in which clouds usually suppress dispersion by diminishing solar irradiance. The dispersion characteristics of a cumulus cloud layer turn out to be markedly different from the other three cases and the results can not be explained by only considering the well-known top-hat velocity distribution. To understand the surprising characteristics in the shallow cumulus layer, this case has been examined in more detail by 1) determining the velocity distribution conditioned on the distance to the nearest cloud and 2) accounting for the wavelike behaviour associated with the stratified dry environment.

scholarly journals Conceptual study on nucleation burst evolution in the convective boundary layer – Part II: Meteorological characterization

2005 ◽  
Vol 5 (6) ◽  
pp. 11489-11515
Author(s):  
O. Hellmuth
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Convective Boundary ◽  
Large Eddy ◽  
Previous Hypothesis ◽  
Lidar Measurements ◽  
Present Part ◽  
Model Setup ◽  
Conceptual Study

Abstract. While in part I of the present paper a revised columnar high-order modelling approach to investigate gas-aerosol interactions in the convective boundary layer (CBL) was deduced, in the present part the model capability to predict the evolution of meteorological CBL parameters is demonstrated. Based on a model setup to simulate typical CBL conditions, predicted first-, second- and third-order moments were shown to agree very well with those obtained from in situ and remote sensing turbulence measurements such as aircraft, SODAR and LIDAR measurements as well as with those derived from ensemble-averaged large-eddy simulations and wind tunnel experiments. The results show that the model is able to predict the meteorological CBL parameters, required to verify or falsify, respectively, previous hypothesis on the interaction between CBL turbulence and new particle formation.

scholarly journals Oblique stagnation point flow of a non-Newtonian nanofluid over stretching surface with radiation: A numerical study

2017 ◽  
Vol 21 (5) ◽  
pp. 2139-2153 ◽  
Author(s):  
Abuzar Ghaffari ◽  
Tariq Javed ◽  
Fotini Labropulu
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Differential Equations ◽  
Layer Thickness ◽  
Stagnation Point ◽  
Boundary Layer Thickness ◽  
Numerical Study ◽  
Convective Boundary Condition ◽  
Stretching Surface ◽  
Convective Boundary

In this study, we discussed the enhancement of thermal conductivity of elasticoviscous fluid filled with nanoparticles, due to the implementation of radiation and convective boundary condition. The flow is considered impinging obliquely in the region of oblique stagnation point on the stretching surface. The obtained governing partial differential equations are transformed into a system of ordinary differential equations by employing a suitable transformation. The solution of the resulting equations is computed numerically using Chebyshev spectral newton iterative scheme. An excellent agreement with the results available in literature is obtained and shown through tables. The effects of involving parameters on the fluid flow and heat transfer are observed and shown through graphs. It is importantly noted that the larger values of Biot number imply the enhancement in heat transfer, thermal boundary layer thickness, and concentration boundary layer thickness.

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