Thermodynamic Variability within the Convective Boundary Layer Due to Horizontal Convective Rolls

Weckwerth, Tammy M.; Wilson, James W.; Wakimoto, Roger M.

doi:10.1175/1520-0493(1996)124<0769:tvwtcb>2.0.co;2

Cited by 160 publications

(134 citation statements)

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“…First comparisons with the DOW data indicated that these may be due to the presence of horizontal rolls advected over the supersite. In this case, the CBL WV variability of about 1 g m −3 was partly due to turbulence and partly due to mesoscale coherence caused by convective rolls, which is consistent with previous observations (Weckwerth et al, 1996).…”

Section: Thermally Induced Flow Systemssupporting

confidence: 92%

The Convective and Orographically‐induced Precipitation Study (COPS): the scientific strategy, the field phase, and research highlights

Wulfmeyer

Behrendt

Kottmeier

et al. 2011

Quart J Royal Meteoro Soc

196

136

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Within the framework of the international field campaign COPS (Convective and Orographically-induced Precipitation Study), a large suite of state-of-the-art meteorological instrumentation was operated, partially combined for the first time. This includes networks of in situ and remote-sensing systems such as the Global Positioning System as well as a synergy of multi-wavelength passive and active remote-sensing instruments such as advanced radar and lidar systems. The COPS field phase was performed from 01 June to 31 August 2007 in a low-mountain area in southwestern Germany/eastern France covering the Vosges mountains, the Rhine valley and the Black Forest mountains. The collected data set covers the entire evolution of convective precipitation events in complex terrain from their initiation, to their development and mature phase until their decay. Eighteen Intensive Observation Periods with 37 operation days and eight additional Special Observation Periods were performed, providing a comprehensive data set covering different forcing conditions. In this article, an overview of the COPS scientific strategy, the field phase, and its first accomplishments is given. Highlights of the campaign are illustrated with several measurement examples. It is demonstrated that COPS research provides new insight into key processes leading to convection initiation and to the modification of precipitation by orography, in the improvement of quantitative precipitation forecasting by the assimilation of new observations, and in the performance of ensembles of convection-permitting models in complex terrain.

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Section: Thermally Induced Flow Systemssupporting

confidence: 92%

The Convective and Orographically‐induced Precipitation Study (COPS): the scientific strategy, the field phase, and research highlights

Wulfmeyer

Behrendt

Kottmeier

et al. 2011

Quart J Royal Meteoro Soc

196

136

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“…Second, boundary-layer θ e is horizontally and temporally inhomogeneous on very small scales, especially in regions in which deep convection is underway (e.g. Weckwerth et al 1996).…”

Section: Discussionmentioning

confidence: 99%

Equilibrium Vs. Activation Control of Large-Scale Variations of Tropical Deep Convection

Mapes

1997

The Physics and Parameterization of Moist Atmospheric Convection

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What processes control large-scale variations of deep convection (LSVDC) in the tropics? Here 'large-scale' is taken to mean any coherent variations, in either space or time, comprised of statistical populations of separate convective cloud systems. This essay highlights the distinction between processes which supply moisture or available energy over the depth of the convecting layer (equilibrium control), versus inhibition and initiation processes at low levels (activation control), as hypotheses for explaining LSVDC.Conceptual separations of the LSVDC problem are reviewed. Scale separation, though rigorous, is artificial, since net heating makes deep convective clouds multiscale, or spectrally red. Moist-dry, or diabatic-adiabatic, separation is more useful. An ill-posed hybrid separation -'the interaction of moist convection with large scales' -has spawned confusion. Correlations between deep convection and its own large-scale components (suggestively labeled 'forcing') have been misinterpreted as evidence for equilibrium control. This externalization of large-scale vertical velocity also encourages overinterpretation of a fictitious 'compensating subsidence' term.Published evidence for equilibrium control theories is critically re-examined. The deep-cloud quasi-equilibrium observations of Arakawa and Schubert would hold for arbitrarily determined variations of convection, because stratified fluid dynamics efficiently redistributes localized heating, not because convection is controlled by slow deep large-scale 'forcing.' A more sensitive test indicates that most tropical LSVDC are not forced by preexisting deep upward motions.Activation-control processes can operate on the large space scales and long time scales that define LSVDC. Modulation of convection by easterly waves and upper-tropospheric troughs, and the climatological distribution of convective cloudiness, are examined as examples. Lower boundary flux enhancements and deep lifting exert both equilibrium and activation influences on convection. The hypothesis that activation control may prevail on all scales short of globally-averaged climate is difficult to refute.Systematic study of convective cloud-ensemble sensitivities is badly needed. Unfortunately, current cloud ensemble modeling strategies, based on unnatural equilibriumcontrol assumptions, render the results merely diagnostic.To represent activation controls, large-scale models need multiple levels, and some prognostic representation of the subgridscale inhomogeneity of low-level fields.

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“…The latter provide a snapshot of the CBL profile and thus do not capture the mean profiles needed for comparisons with models (Weckwerth et al 1996) nor can they provide information on turbulent fluctuations. The characteristics of humidity fluctuations in the CBL have been studied using in situ measurements (Mahrt 1976(Mahrt , 1991Lenschow et al 1994) and active remote sensing techniques, particularly water vapour differential absorption lidar (DIAL) (Kiemle et al 1997;Wulfmeyer 1999a, b;Giez et al 1999;Behrendt et al 2011) and water vapour Raman lidar Turner et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Turbulent Humidity Fluctuations in the Convective Boundary Layer: Case Studies Using Water Vapour Differential Absorption Lidar Measurements

Muppa

Behrendt

Späth

et al. 2015

Boundary-Layer Meteorol

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Turbulent humidity fluctuations in the convective boundary layer (CBL) under clear-sky conditions were investigated by deriving moments up to fourth-order. Highresolution humidity measurements were collected with a water vapour differential absorption lidar system during the HD(CP) 2 Observational Prototype Experiment (HOPE). Two cases, both representing a well-developed CBL around local noon, are discussed. While the first case (from the intensive observation period (IOP) 5 on 20 April 2013) compares well with what is considered typical CBL behaviour, the second case (from IOP 6 on 24 April 2013) shows a number of non-typical characteristics. Both cases show similar capping inversions and wind shear across the CBL top. However, a major difference between both cases is the advection of a humid layer above the CBL top during IOP 6. While the variance profile of IOP 5 shows a maximum at the interfacial layer, two variance peaks are observed near the CBL top for IOP 6. A marked difference can also be seen in the third-order moment and skewness profiles: while both are negative (positive) below (above) the CBL top for IOP 5, the structure is more complex for IOP 6. Kurtosis is about three for IOP 5, whereas for IOP 6, the distribution is slightly platykurtic. We believe that the entrainment of an elevated moist layer into the CBL is responsible for the unusual findings for IOP 6, which suggests that it is important to consider the structure of residual humidity layers entrained into the CBL.

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Thermodynamic Variability within the Convective Boundary Layer Due to Horizontal Convective Rolls

Cited by 160 publications

References 0 publications

The Convective and Orographically‐induced Precipitation Study (COPS): the scientific strategy, the field phase, and research highlights

The Convective and Orographically‐induced Precipitation Study (COPS): the scientific strategy, the field phase, and research highlights

Equilibrium Vs. Activation Control of Large-Scale Variations of Tropical Deep Convection

Turbulent Humidity Fluctuations in the Convective Boundary Layer: Case Studies Using Water Vapour Differential Absorption Lidar Measurements

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