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Shamekh, Sara, Caroline Muller, Jean-Philippe Duvel, and Fabio D’Andrea. "How Do Ocean Warm Anomalies Favor the Aggregation of Deep Convective Clouds?" Journal of the Atmospheric Sciences 77, no. 11 (2020): 3733–45. http://dx.doi.org/10.1175/jas-d-18-0369.1.
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AbstractWe investigate the role of a warm sea surface temperature (SST) anomaly (hot spot of typically 3 to 5 K) on the aggregation of convection using cloud-resolving simulations in a nonrotating framework. It is well known that SST gradients can spatially organize convection. Even with uniform SST, the spontaneous self-aggregation of convection is possible above a critical SST (here 295 K), arising mainly from radiative feedbacks. We investigate how a circular hot spot helps organize convection, and how self-aggregation feedbacks modulate this organization. The hot spot significantly accelerates aggregation, particularly for warmer/larger hot spots, and extends the range of SSTs for which aggregation occurs; however, at cold SST (290 K) the aggregated cluster disaggregates if we remove the hot spot. A large convective instability over the hot spot leads to stronger convection and generates a large-scale circulation which forces the subsidence drying outside the hot spot. Indeed, convection over the hot spot brings the atmosphere toward a warmer temperature. The warmer temperatures are imprinted over the whole domain by gravity waves and subsidence warming. The initial transient warming and concomitant subsidence drying suppress convection outside the hot spot, thus driving the aggregation. The hot-spot-induced large-scale circulation can enforce the aggregation even without radiative feedbacks for hot spots sufficiently large/warm. The strength of the large-scale circulation, which defines the speed of aggregation, is a function of the hot spot fractional area. At equilibrium, once the aggregation is well established, the moist convective region with upward midtropospheric motion, centered over the hot spot, has an area surprisingly independent of the hot spot size.
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Jung, Hyunju, Ann Kristin Naumann, and Bjorn Stevens. "Convective self–aggregation in a mean flow." Atmospheric Chemistry and Physics 21, no. 13 (2021): 10337–45. http://dx.doi.org/10.5194/acp-21-10337-2021.
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Abstract. Convective self-aggregation is an atmospheric phenomenon seen in numerical simulations in a radiative convective equilibrium framework thought to be informative of some aspects of the behavior of real-world convection in the deep tropics. We impose a background mean wind flow on convection-permitting simulations through the surface flux calculation in an effort to understand how the asymmetry imposed by a mean wind influences the propagation of aggregated structures in convection. The simulations show that, with imposing mean flow, the organized convective system propagates in the direction of the flow but slows down compared to what pure advection would suggest, and it eventually becomes stationary relative to the surface after 15 simulation days. The termination of the propagation arises from momentum flux, which acts as a drag on the near-surface horizontal wind. In contrast, the thermodynamic response through the wind-induced surface heat exchange feedback is a relatively small effect, which slightly retards the propagation of the convection relative to the mean wind.
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Bretherton, Christopher S., Peter N. Blossey, and Marat Khairoutdinov. "An Energy-Balance Analysis of Deep Convective Self-Aggregation above Uniform SST." Journal of the Atmospheric Sciences 62, no. 12 (2005): 4273–92. http://dx.doi.org/10.1175/jas3614.1.
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Abstract The spatial organization of deep moist convection in radiative–convective equilibrium over a constant sea surface temperature is studied. A 100-day simulation is performed with a three-dimensional cloud-resolving model over a (576 km)2 domain with no ambient rotation and no mean wind. The convection self-aggregates within 10 days into quasi-stationary mesoscale patches of dry, subsiding and moist, rainy air columns. The patches ultimately merge into a single intensely convecting moist patch surrounded by a broad region of very dry subsiding air. The self-aggregation is analyzed as an instability of a horizontally homogeneous convecting atmosphere driven by convection–water vapor–radiation feedbacks that systematically dry the drier air columns and moisten the moister air columns. Column-integrated heat, water, and moist static energy budgets over (72 km)2 horizontal blocks show that this instability is primarily initiated by the reduced radiative cooling of air columns in which there is extensive anvil cirrus, augmented by enhanced surface latent and sensible heat fluxes under convectively active regions due to storm-induced gustiness. Mesoscale circulations intensify the later stages of self-aggregation by fluxing moist static energy from the dry to the moist regions. A simple mathematical model of the initial phase of self-aggregation is proposed based on the simulations. In accordance with this model, the self-aggregation can be suppressed by horizontally homogenizing the radiative cooling or surface fluxes. Lower-tropospheric wind shear leads to slightly slower and less pronounced self-aggregation into bands aligned along the shear vector. Self-aggregation is sensitive to the ice microphysical parameterization, which affects the location and extent of cirrus clouds and their radiative forcing. Self-aggregation is also sensitive to ambient Coriolis parameter f, and can induce spontaneous tropical cyclogenesis for large f. Inclusion of an interactive mixed-layer ocean slows but does not prevent self-aggregation.
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Schulz, Hauke, and Bjorn Stevens. "Observing the Tropical Atmosphere in Moisture Space." Journal of the Atmospheric Sciences 75, no. 10 (2018): 3313–30. http://dx.doi.org/10.1175/jas-d-17-0375.1.
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Measurements from the Barbados Cloud Observatory are analyzed to identify the processes influencing the distribution of moist static energy and the large-scale organization of tropical convection. Five years of water vapor and cloud profiles from a Raman lidar and cloud radar are composed to construct the structure of the observed atmosphere in moisture space. The large-scale structure of the atmosphere is similar to that now familiar from idealized studies of convective self-aggregation, with shallow clouds prevailing over a moist marine layer in regions of low-rank humidity, and deep convection in a nearly saturated atmosphere in regions of high-rank humidity. With supplementary reanalysis datasets the overall circulation pattern is reconstructed in moisture space, and shows evidence of a substantial lower-tropospheric component to the circulation. This shallow component of the circulation helps support the differentiation between the moist and dry columns, similar to what is found in simulations of convective self-aggregation. Radiative calculations show that clear-sky radiative differences can explain a substantial part of this circulation, with further contributions expected from cloud radiative effects. The shallow component appears to be important for maintaining the low gross moist stability of the convecting column. A positive feedback between a shallow circulation driven by differential radiative cooling and the low-level moisture gradients that help support it is hypothesized to play an important role in conditioning the atmosphere for deep convection. The analysis suggests that the radiatively driven shallow circulations identified by modeling studies as contributing to the self-aggregation of convection in radiative–convective equilibrium similarly play a role in shaping the intertropical convergence zone and, hence, the large-scale structure of the tropical atmosphere.
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Tobin, Isabelle, Sandrine Bony, and Remy Roca. "Observational Evidence for Relationships between the Degree of Aggregation of Deep Convection, Water Vapor, Surface Fluxes, and Radiation." Journal of Climate 25, no. 20 (2012): 6885–904. http://dx.doi.org/10.1175/jcli-d-11-00258.1.
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Abstract Tropical deep convection exhibits complex organization over a wide range of scales. This study investigates the relationships between the spatial organization of deep convection and the large-scale atmospheric state. By using several satellite datasets and reanalyses, and by defining a simple diagnostic of convective aggregation, relationships between the degree of convective aggregation and the amount of water vapor, turbulent surface fluxes, and radiation are highlighted above tropical oceans. When deep convection is more aggregated, the middle and upper troposphere are drier in the convection-free environment, turbulent surface fluxes are enhanced, and the low-level and midlevel cloudiness is reduced in the environment. Humidity and cloudiness changes lead to a large increase in outgoing longwave radiation. Cloud changes also result in reduced reflected shortwave radiation. Owing to these opposing effects, the sensitivity of the radiative budget at the top of the atmosphere to convective aggregation turns out to be weak, but the distribution of radiative heating throughout the troposphere is affected. These results suggest that feedbacks between convective aggregation and the large-scale atmospheric state might influence large-scale dynamics and the transports of water and energy and, thus, play a role in the climate variability and change. These observational findings are qualitatively consistent with previous cloud-resolving model results, except for the effects on cloudiness and reflected shortwave radiation. The proposed methodology may be useful for assessing the representation of convective aggregation and its interaction with the large-scale atmospheric state in various numerical models.
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Warren, P. B., R. C. Ball, and A. Boelle. "Convection-Limited Aggregation." Europhysics Letters (EPL) 29, no. 4 (1995): 339–44. http://dx.doi.org/10.1209/0295-5075/29/4/012.
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Li, Bo-Wei, Min-Cheng Zhong, and Feng Ji. "Laser Induced Aggregation of Light Absorbing Particles by Marangoni Convection." Applied Sciences 10, no. 21 (2020): 7795. http://dx.doi.org/10.3390/app10217795.
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Laser induced Marangoni convection can be used to accumulate micro-particles. In this paper, a method is developed to control and accumulate the light absorbing particles dispersed in a thin solution layer. The particles are irradiated by a focused laser beam. Due to the photothermal effect of the particles, the laser heating generates a thermal gradient and induces a convective flow around the laser’s heating center. The convective flow drives the particles to accumulate and form a particle aggregate close to the laser’s heating center. The motion of particles is dominated by the Marangoni convection. When the laser power is high, the vapor bubbles generated by laser heating on particles strengthen the convection, which accelerates the particles’ aggregation.
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Muller, Caroline J., and Isaac M. Held. "Detailed Investigation of the Self-Aggregation of Convection in Cloud-Resolving Simulations." Journal of the Atmospheric Sciences 69, no. 8 (2012): 2551–65. http://dx.doi.org/10.1175/jas-d-11-0257.1.
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Abstract In models of radiative–convective equilibrium it is known that convection can spontaneously aggregate into one single localized moist region if the domain is large enough. The large changes in the mean climate state and radiative fluxes accompanying this self-aggregation raise questions as to what simulations at lower resolutions with parameterized convection, in similar homogeneous geometries, should be expected to produce to be considered successful in mimicking a cloud-resolving model. The authors investigate this self-aggregation in a nonrotating, three-dimensional cloud-resolving model on a square domain without large-scale forcing. It is found that self-aggregation is sensitive not only to the domain size, but also to the horizontal resolution. With horizontally homogeneous initial conditions, convective aggregation only occurs on domains larger than about 200km and with resolutions coarser than about 2km in the model examined. The system exhibits hysteresis, so that with aggregated initial conditions, convection remains aggregated even at our finest resolution, 500m, as long as the domain is greater than 200–300km. The sensitivity of self-aggregation to resolution and domain size in this model is due to the sensitivity of the distribution of low clouds to these two parameters. Indeed, the mechanism responsible for the aggregation of convection is the dynamical response to the longwave radiative cooling from low clouds. Strong longwave cooling near cloud top in dry regions forces downward motion, which by continuity generates inflow near cloud top and near-surface outflow from dry regions. This circulation results in the net export of moist static energy from regions with low moist static energy, yielding a positive feedback.
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Windmiller, Julia M., and George C. Craig. "Universality in the Spatial Evolution of Self-Aggregation of Tropical Convection." Journal of the Atmospheric Sciences 76, no. 6 (2019): 1677–96. http://dx.doi.org/10.1175/jas-d-18-0129.1.
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Abstract Self-aggregation in numerical simulations of tropical convection is described by an upscale growth and intensification of dry and moist regions. Previous work has focused on determining the relevant mechanism that induces moist regions to get moister and dry regions to get drier. Though different mechanisms have been identified, the spatial evolution of self-aggregation is remarkably universal. The first part of this study shows that different mechanisms can lead to a similar evolution of self-aggregation, if self-aggregation is described by a phase separation of moist and dry regions, through a process called coarsening. Though it was previously introduced based on a convection–humidity feedback, coarsening, importantly, is not tied to a specific feedback process but only requires an intensification of local humidity perturbations. Based on different feedback loops, three simple models of the evolution of the humidity field are introduced, all of which lead to coarsening. In each model, diffusive transport of humidity is assumed, which approximates a humidity increase due to convection, within a finite region around convective cores. In the second part, predictions made by coarsening are compared with atmospheric model simulations. Analyzing a set of radiative–convective equilibrium simulations shows that coarsening correctly predicts the upscale growth of the moist and dry regions in the early stages of self-aggregation. In addition, coarsening can explain why self-aggregation is not observed for small domains and why the shape of the final moist region changes with the shape of the domain.
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Boos, William R., Alexey Fedorov, and Les Muir. "Convective Self-Aggregation and Tropical Cyclogenesis under the Hypohydrostatic Rescaling." Journal of the Atmospheric Sciences 73, no. 2 (2016): 525–44. http://dx.doi.org/10.1175/jas-d-15-0049.1.
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Abstract The behavior of rotating and nonrotating aggregated convection is examined at various horizontal resolutions using the hypohydrostatic, or reduced acceleration in the vertical (RAVE), rescaling. This modification of the equations of motion reduces the scale separation between convective- and larger-scale motions, enabling the simultaneous and explicit representation of both types of flow in a single model without convective parameterization. Without the RAVE rescaling, a dry bias develops when simulations of nonrotating radiative–convective equilibrium are integrated at coarse resolution in domains large enough to permit convective self-aggregation. The rescaling reduces this dry bias, and here it is suggested that the rescaling moistens the troposphere by weakening the amplitude and slowing the group velocity of gravity waves, thus reducing the subsidence drying around aggregated convection. Separate simulations of rotating radiative–convective equilibrium exhibit tropical cyclogenesis; as horizontal resolution is coarsened without the rescaling, the resulting storms intensify more slowly and achieve lower peak intensities. At a given horizontal resolution, using RAVE increases peak storm intensity and reduces the time needed for tropical cyclogenesis—effects here suggested to be caused at least in part by the environmental moistening produced by RAVE. Consequently, the RAVE rescaling has the potential to improve simulations of tropical cyclones and other aggregated convection in models with horizontal resolutions of order 10–100 km.
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Yang, Bolei, and Zhe-Min Tan. "The Initiation of Dry Patches in Cloud-Resolving Convective Self-Aggregation Simulations: Boundary Layer Dry-Subsidence Feedback." Journal of the Atmospheric Sciences 77, no. 12 (2020): 4129–41. http://dx.doi.org/10.1175/jas-d-20-0133.1.
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AbstractSelf-aggregation of convection can be considered as the simultaneous occurrence of dry patch initiation/amplification and wet patch contraction/intensification from initially uniform moisture and temperature fields. As the twin of wet patches, dry patches play an important role in moisture and energy balance during convective self-aggregation. In this study, the WRF Model is used to study the initiation of dry patches in convective self-aggregation, especially the continuous drying in their boundary layer (BL). In the dry patch BL, increased air density leads to an enhanced high pressure anomaly, which drives an amplifying BL divergent flow and induces an amplifying BL subsidence. The virtual effect of drying by subsidence counteracts warming by subsidence and the BL process, further increasing BL air density. Our analysis indicates the existence of a dry-subsidence feedback, which leads to the initiation of dry patches in convective self-aggregation. This feedback is shown to be important even in very large-scale (3000 km × 9000 km) cloud-resolving convective self-aggregation simulations.
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Wing, Allison A., Kevin A. Reed, Masaki Satoh, Bjorn Stevens, Sandrine Bony, and Tomoki Ohno. "Radiative–convective equilibrium model intercomparison project." Geoscientific Model Development 11, no. 2 (2018): 793–813. http://dx.doi.org/10.5194/gmd-11-793-2018.
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Abstract. RCEMIP, an intercomparison of multiple types of models configured in radiative–convective equilibrium (RCE), is proposed. RCE is an idealization of the climate system in which there is a balance between radiative cooling of the atmosphere and heating by convection. The scientific objectives of RCEMIP are three-fold. First, clouds and climate sensitivity will be investigated in the RCE setting. This includes determining how cloud fraction changes with warming and the role of self-aggregation of convection in climate sensitivity. Second, RCEMIP will quantify the dependence of the degree of convective aggregation and tropical circulation regimes on temperature. Finally, by providing a common baseline, RCEMIP will allow the robustness of the RCE state across the spectrum of models to be assessed, which is essential for interpreting the results found regarding clouds, climate sensitivity, and aggregation, and more generally, determining which features of tropical climate a RCE framework is useful for. A novel aspect and major advantage of RCEMIP is the accessibility of the RCE framework to a variety of models, including cloud-resolving models, general circulation models, global cloud-resolving models, single-column models, and large-eddy simulation models.
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Zhu, Shichao, Xueliang Guo, Guangxian Lu, and Lijun Guo. "Ice Crystal Habits and Growth Processes in Stratiform Clouds with Embedded Convection Examined through Aircraft Observation in Northern China." Journal of the Atmospheric Sciences 72, no. 5 (2015): 2011–32. http://dx.doi.org/10.1175/jas-d-14-0194.1.
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Abstract Ice crystal habits and growth processes in two cases of stratiform clouds with embedded convection are investigated using data observed simultaneously from three aircraft on 18 April 2009 and 1 May 2009 as part of the Beijing Cloud Experiment (BCE). The results show that the majority of ice crystal habits found in the two cases at temperatures between 0° and −16°C included platelike, needle column, capped column, dendrite, and irregular. A mixture of several ice crystal habits was identified in all of the clouds studied. However, the ice crystals recorded in the embedded convection regions contained more dendrites and possessed heavier riming degrees, and the ice crystals identified in the stratiform clouds contained more hexagonal plate crystals. Both riming and aggregation processes played central roles in the broadening of particle size distributions (PSDs), and these processes were more active in embedded convection regions than in stratiform regions. However, riming was more prevalent in the 18 April case than aggregation, though aggregates were evident. In contrast, the 1 May case had a more dominant aggregation processes, but also riming. With the decrease in height, PSDs broadened in both embedded convection regions and stratiform regions, but the broadening rates between 4.8 km (T ≈ −11.6°C) and 4.2 km (T ≈ −8°C) were larger than those between 4.2 km (T ≈ −8°C) and 3.6 km (T ≈ −5°C). In addition, the broadening rates of PSDs in the embedded convection regions were larger than those in the stratiform clouds, as the aggregation and riming processes of ice particles in embedded convection regions were active. High supercooled water content is critical to enhancing riming and aggregation processes in embedded convection regions.
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Muller, Caroline J., and David M. Romps. "Acceleration of tropical cyclogenesis by self-aggregation feedbacks." Proceedings of the National Academy of Sciences 115, no. 12 (2018): 2930–35. http://dx.doi.org/10.1073/pnas.1719967115.
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Idealized simulations of tropical moist convection have revealed that clouds can spontaneously clump together in a process called self-aggregation. This results in a state where a moist cloudy region with intense deep convection is surrounded by extremely dry subsiding air devoid of deep convection. Because of the idealized settings of the simulations where it was discovered, the relevance of self-aggregation to the real world is still debated. Here, we show that self-aggregation feedbacks play a leading-order role in the spontaneous genesis of tropical cyclones in cloud-resolving simulations. Those feedbacks accelerate the cyclogenesis process by a factor of 2, and the feedbacks contributing to the cyclone formation show qualitative and quantitative agreement with the self-aggregation process. Once the cyclone is formed, wind-induced surface heat exchange (WISHE) effects dominate, although we find that self-aggregation feedbacks have a small but nonnegligible contribution to the maintenance of the mature cyclone. Our results suggest that self-aggregation, and the framework developed for its study, can help shed more light into the physical processes leading to cyclogenesis and cyclone intensification. In particular, our results point out the importance of the longwave radiative cooling outside the cyclone.
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Stein, T. H. M., C. E. Holloway, I. Tobin, and S. Bony. "Observed Relationships between Cloud Vertical Structure and Convective Aggregation over Tropical Ocean." Journal of Climate 30, no. 6 (2017): 2187–207. http://dx.doi.org/10.1175/jcli-d-16-0125.1.
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Abstract Using the satellite-infrared-based Simple Convective Aggregation Index (SCAI) to determine the degree of aggregation, 5 years of CloudSat–CALIPSO cloud profiles are composited at a spatial scale of 10 degrees to study the relationship between cloud vertical structure and aggregation. For a given large-scale vertical motion and domain-averaged precipitation rate, there is a large decrease in anvil cloud (and in cloudiness as a whole) and an increase in clear sky and low cloud as aggregation increases. The changes in thick anvil cloud are proportional to the changes in total areal cover of brightness temperatures below 240 K [cold cloud area (CCA)], which is negatively correlated with SCAI. Optically thin anvil cover decreases significantly when aggregation increases, even for a fixed CCA, supporting previous findings of a higher precipitation efficiency for aggregated convection. Cirrus, congestus, and midlevel clouds do not display a consistent relationship with the degree of aggregation. Lidar-observed low-level cloud cover (where the lidar is not attenuated) is presented herein as the best estimate of the true low-level cloud cover, and it is shown that it increases as aggregation increases. Qualitatively, the relationships between cloud distribution and SCAI do not change with sea surface temperature, while cirrus clouds are more abundant and low-level clouds less at higher sea surface temperatures. For the observed regimes, the vertical cloud profile varies more evidently with SCAI than with mean precipitation rate. These results confirm that convective scenes with similar vertical motion and rainfall can be associated with vastly different cloudiness (both high and low cloud) and humidity depending on the degree of convective aggregation.
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Ruppert, James H., and Cathy Hohenegger. "Diurnal Circulation Adjustment and Organized Deep Convection." Journal of Climate 31, no. 12 (2018): 4899–916. http://dx.doi.org/10.1175/jcli-d-17-0693.1.
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This study investigates the diurnal cycle of tropical organized deep convection and the feedback in large-scale circulation. By considering gravity wave phase speeds, we find that the circulation adjustment into weak temperature gradient (WTG) balance occurs rapidly (<6 h) relative to diurnal diabatic forcing on the spatial scales typical of organized convection (≤500 km). Convection-permitting numerical simulations of self-aggregation in diurnal radiative–convective equilibrium (RCE) are conducted to explore this further. These simulations depict a pronounced diurnal cycle of circulation linked to organized convection, which indeed maintains WTG balance to first order. A set of sensitivity experiments is conducted to assess what governs the diurnal cycle of organized convection. We find that the “direct radiation–convection interaction” (or lapse-rate) mechanism is of primary importance for diurnal precipitation range, while the “dynamic cloudy–clear differential radiation” mechanism amplifies the range by approximately 30%, and delays the nocturnal precipitation peak by around 5 h. The differential radiation mechanism therefore explains the tendency for tropical heavy rainfall to peak in the early morning, while the lapse-rate mechanism primarily governs diurnal amplitude. The diurnal evolution of circulation can be understood as follows. While nocturnal deep convection invigorated by cloud-top cooling (i.e., the lapse-rate mechanism) leads to strong bottom-heavy circulation at nighttime, the localized (i.e., differential) top-heavy shortwave warming in the convective region invigorates circulation at upper levels in daytime. A diurnal evolution of the circulation therefore arises, from bottom heavy at nighttime to top heavy in daytime, in a qualitatively consistent manner with the observed diurnal pulsing of the Hadley cell driven by the ITCZ.
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Notay, Yvan. "Aggregation-Based Algebraic Multigrid for Convection-Diffusion Equations." SIAM Journal on Scientific Computing 34, no. 4 (2012): A2288—A2316. http://dx.doi.org/10.1137/110835347.
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Wing, Allison A., and Timothy W. Cronin. "Self-aggregation of convection in long channel geometry." Quarterly Journal of the Royal Meteorological Society 142, no. 694 (2015): 1–15. http://dx.doi.org/10.1002/qj.2628.
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Wing, Allison A., Suzana J. Camargo, and Adam H. Sobel. "Role of Radiative–Convective Feedbacks in Spontaneous Tropical Cyclogenesis in Idealized Numerical Simulations." Journal of the Atmospheric Sciences 73, no. 7 (2016): 2633–42. http://dx.doi.org/10.1175/jas-d-15-0380.1.
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Abstract The authors perform 3D cloud-resolving simulations of radiative–convective equilibrium (RCE) in a rotating framework, with interactive radiation and surface fluxes and fixed sea surface temperature. A tropical cyclone is allowed to develop spontaneously from a homogeneous environment, rather than initializing the circulation with a weak vortex or moist bubble (as is often done in numerical simulations of tropical cyclones). The resulting tropical cyclogenesis is compared to the self-aggregation of convection that occurs in nonrotating RCE simulations. The feedbacks leading to cyclogenesis are quantified using a variance budget equation for the column-integrated frozen moist static energy. In the initial development of a broad circulation, feedbacks involving longwave radiation and surface enthalpy fluxes dominate, which is similar to the initial phase of nonrotating self-aggregation. Mechanism denial experiments are also performed to determine the extent to which the radiative feedbacks that are essential to nonrotating self-aggregation are important for tropical cyclogenesis. Results show that radiative feedbacks aid cyclogenesis but are not strictly necessary.
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Emanuel, Kerry. "Inferences from Simple Models of Slow, Convectively Coupled Processes." Journal of the Atmospheric Sciences 76, no. 1 (2019): 195–208. http://dx.doi.org/10.1175/jas-d-18-0090.1.
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Abstract A framework for conceptual understanding of slow, convectively coupled disturbances is developed and applied to several canonical tropical problems, including the water vapor content of an atmosphere in radiative–convective equilibrium, the relationship between convective precipitation and column water vapor, Walker-like circulations, self-aggregation of convection, and the Madden–Julian oscillation. The framework is a synthesis of previous work that developed four key approximations: boundary layer energy quasi equilibrium, conservation of free-tropospheric moist and dry static energies, and the weak temperature gradient approximation. It is demonstrated that essential features of slow, convectively coupled processes can be understood without reference to complex turbulent and microphysical processes, even though accounting for such complexity is essential to quantitatively accurate modeling. In particular, we demonstrate that the robust relationship between column water vapor and precipitation observed over tropical oceans does not necessarily imply direct sensitivity of convection to free-tropospheric moisture. We also show that to destabilize the radiative–convective equilibrium state, feedbacks between radiation and clouds and water vapor must be sufficiently strong relative to the gross moist stability.
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Fang, Juan, and Fuqing Zhang. "Contribution of Tropical Waves to the Formation of Supertyphoon Megi (2010)." Journal of the Atmospheric Sciences 73, no. 11 (2016): 4387–405. http://dx.doi.org/10.1175/jas-d-15-0179.1.
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Abstract Through observational analysis and numerical simulations, this study examines the roles of the Madden–Julian oscillation (MJO) and tropical waves in the three-stage formation of Supertyphoon Megi (2010) including 1) convective bursts followed by vorticity aggregation, 2) vortex rearrangement during decaying convection, and 3) convective reinvigoration and vortex intensification. The MJO was responsible for preconditioning the large-scale circulation and low-level moisture favorable for convection during all stages, while the counterpropagating Kelvin and equatorial Rossby (ER) waves brought low-level convergence and cyclonic vorticity anomalies to enhance massive convection in the western tropical Pacific in stage 1. Convection strengthened the vorticity anomalies nearby, which subsequently developed into Megi’s embryo by the end of stage 1 through merging with the positive vorticity anomaly carried by a westward-propagating mixed Rossby–gravity and tropical depression (MRG–TD)-type wave. The ER- and MRG–TD-type waves might also contribute to Megi’s formation through increasing low-level southwesterlies to the southwest of the precursor during stages 2 and 3. These tropical waves also indirectly affect Megi’s genesis through modulating surroundings near the precursor. Without the MJO, the low-level vorticity anomaly to the near west of the precursor would intensify more effectively and develop into a tropical cyclone instead of the observed Megi. Removing the Kelvin or ER wave would enhance convection to the far west of Megi’s precursor, which was less favorable for low-level convergence in the region of the precursor, and thus the formation of Megi.
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UEDA, Tadao, Kakuji OGAWARA, and Souichi SAEKI. "Numerical Study on Particle Aggregation Caused by Natural Convection." Transactions of the Japan Society of Mechanical Engineers Series B 68, no. 674 (2002): 2735–40. http://dx.doi.org/10.1299/kikaib.68.2735.
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Pauluis, O., and J. Schumacher. "Self-aggregation of clouds in conditionally unstable moist convection." Proceedings of the National Academy of Sciences 108, no. 31 (2011): 12623–28. http://dx.doi.org/10.1073/pnas.1102339108.
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Teschke, O., M. U. Kleinke, and M. A. Tenan. "Surface tension-induced convection as a particle aggregation mechanism." Journal of Colloid and Interface Science 151, no. 2 (1992): 477–89. http://dx.doi.org/10.1016/0021-9797(92)90495-8.
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Pickles, D. M., D. Ogston, and A. G. MacDonald. "Effects of gas bubbling and other forms of convection on platelets in vitro." Journal of Applied Physiology 67, no. 3 (1989): 1250–55. http://dx.doi.org/10.1152/jappl.1989.67.3.1250.
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Citrated platelet-rich human plasma was subjected to one of three experimental treatments at 37 degrees C for 15 min: stirring, bubbling (with stirring), and gentle agitation achieved by a rocking motion. The last two were “equiconvective” as judged by equilibration rates with CO2 and O2 but presumably differed in the shear stress they imposed on the cells. Stirring platelets in normal air or 5% CO2-air caused no significant aggregation. Bubbling air through platelet-rich plasma increased its pH and marked aggregation occurred. Bubbling CO2-air caused the platelet-rich plasma pH to attain its physiological level of 7.4 with less aggregation. In both cases, subsequent ADP-induced aggregation was diminished. Rocking (without stirring) in the presence of CO2-air caused negligible aggregation in platelets and an enhanced response to ADP. Because of the marked difference between the two equiconvective treatments, bubbling and rocking, the main factor in activating the human platelets is suggested to be shear stress (potentiated by high pH), with perhaps a lesser contribution from the air-plasma interface.
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Загидуллин, Р. Р. "Construction of a three-dimensional modelof the convection of aggregating particles." Numerical Methods and Programming (Vychislitel'nye Metody i Programmirovanie) 24, no. 4 (2023): 430–39. http://dx.doi.org/10.26089/nummet.v24r429.
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Рассматриваются технические аспекты, связанные с моделированием процессов агрегации в неоднородной среде в условиях неустоявшихся скоростей. Для учета агрегации в модель добавлены операторы Смолуховского. Пространственная неоднородность моделируется операторами переноса и диффузии. Поле скоростей получено с помощью фреймворка для моделирования гидродинамических систем OpenFOAM. This paper discusses technical aspects related to modeling aggregation processes in a heterogeneous medium with unsteady velocities. Smoluchowski operators are added to the model to account for aggregation. Spatial heterogeneity is modeled by advection and diffusion operators. The velocity field was obtained using OpenFOAM — the framework for modeling hydrodynamic systems.
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Misyura, S. Y., A. V. Bilsky, O. A. Gobyzov, M. N. Ryabov, and V. S. Morozov. "Convection in an evaporating drop of aqueous solution at a high concentration of microscopic particles." Journal of Physics: Conference Series 2057, no. 1 (2021): 012100. http://dx.doi.org/10.1088/1742-6596/2057/1/012100.
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Abstract This article presents the performed experimental studies on the effect of the concentration of microparticles on free convection in a water drop located on a heated smooth and textured wall surface. It is shown that at a high concentration of particles, their aggregation and deposition take place on the wall and on the free surface of droplet. As a result, the average convection velocity in the droplet decreases significantly. Suppression of convection is important to consider when simulating heat transfer and droplet evaporation. The results obtained are important for technologies that use colloidal solutions (drops, films).
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Dias, Juliana, Stefan N. Tulich, and George N. Kiladis. "An Object-Based Approach to Assessing the Organization of Tropical Convection." Journal of the Atmospheric Sciences 69, no. 8 (2012): 2488–504. http://dx.doi.org/10.1175/jas-d-11-0293.1.
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Abstract The organization of tropical convection is assessed through an object-based analysis of satellite brightness temperature data Tb, a proxy for convective activity. The analysis involves the detection of contiguous cloud regions (CCRs) in the three-dimensional space of latitude, longitude, and time where Tb falls below a given threshold. A range of thresholds is considered and only CCRs that satisfy a minimum size constraint are retained in the analysis. Various statistical properties of CCRs are documented including their zonal speed of propagation, which is estimated using a Radon transformation technique. Consistent with previous studies, a majority of CCRs are found to propagate westward, typically at speeds of around 15 m s−1, regardless of underlying Tb threshold. Most of these zonally propagating CCRs have lifetimes less than 2 days and zonal widths less than 800 km, implying aggregation of just a few individual mesoscale convective systems. This object-based perspective is somewhat different than that obtained in previous Fourier-based analyses, which primarily emphasize the organization of convection on synoptic and planetary scales via wave–convection coupling. To reconcile these contrasting views, an object-based data reconstruction is developed that objectively demonstrates how the spectral peaks of synoptic- to planetary-scale waves can be attributed to the organization of CCRs into larger-scale wave envelopes. A novel method based on the randomization of CCRs in physical space leads to an empirical background spectrum for organized tropical convection that does not rely on any smoothing in spectral space. Normalization by this background reveals spectral peaks associated with synoptic- and planetary-scale waves that are consistent with previous studies.
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Wing, Allison A. "Self-Aggregation of Deep Convection and its Implications for Climate." Current Climate Change Reports 5, no. 1 (2019): 1–11. http://dx.doi.org/10.1007/s40641-019-00120-3.
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Laurenzi, Ian J., and Scott L. Diamond. "Bidisperse Aggregation and Gel Formation via Simultaneous Convection and Diffusion." Industrial & Engineering Chemistry Research 41, no. 3 (2002): 413–20. http://dx.doi.org/10.1021/ie010197j.
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Bony, Sandrine, Bjorn Stevens, David Coppin, et al. "Thermodynamic control of anvil cloud amount." Proceedings of the National Academy of Sciences 113, no. 32 (2016): 8927–32. http://dx.doi.org/10.1073/pnas.1601472113.
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General circulation models show that as the surface temperature increases, the convective anvil clouds shrink. By analyzing radiative–convective equilibrium simulations, we show that this behavior is rooted in basic energetic and thermodynamic properties of the atmosphere: As the climate warms, the clouds rise and remain at nearly the same temperature, but find themselves in a more stable atmosphere; this enhanced stability reduces the convective outflow in the upper troposphere and decreases the anvil cloud fraction. By warming the troposphere and increasing the upper-tropospheric stability, the clustering of deep convection also reduces the convective outflow and the anvil cloud fraction. When clouds are radiatively active, this robust coupling between temperature, high clouds, and circulation exerts a positive feedback on convective aggregation and favors the maintenance of strongly aggregated atmospheric states at high temperatures. This stability iris mechanism likely contributes to the narrowing of rainy areas as the climate warms. Whether or not it influences climate sensitivity requires further investigation.
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Jing, Xiaoqin, and Bart Geerts. "Dual-Polarization Radar Data Analysis of the Impact of Ground-Based Glaciogenic Seeding on Winter Orographic Clouds. Part II: Convective Clouds." Journal of Applied Meteorology and Climatology 54, no. 10 (2015): 2099–117. http://dx.doi.org/10.1175/jamc-d-15-0056.1.
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AbstractThis second paper of a two-part series aims to explore the ground-based glaciogenic seeding impact on wintertime orographic clouds using an X-band dual-polarization radar. It focuses on three cases with shallow to moderately deep orographic convection that were observed in January–February of 2012 as part of the AgI Seeding Cloud Impact Investigation (ASCII) project over the Sierra Madre in Wyoming. In each of the storms the bulk upstream Froude number exceeded 1, suggesting unblocked flow. Low-level potential instability was present, explaining orographic convection. The clouds contained little supercooled liquid water on account of the low cloud-base temperature. Ice-crystal photography shows that snow mainly grew by diffusion and aggregation. To examine the seeding effect of silver iodide (AgI), five study areas are defined: two target areas and three control areas. Comparisons are made between the control and target areas as well as between a treated, or seeded, period and an untreated period. Low-level reflectivity tends to increase in the target areas relative to the control. This increase is larger in the lee target area than in the upwind target area, suggesting that precipitation enhancement is delayed in the presence of convection. The echo tops of the convective cells are not higher during seeding, relative to simultaneous changes in the control regions. This result suggests that the dynamic-seeding mechanism does not apply for the cold-base convective clouds that are studied here. An analysis of differential reflectivity and snow photography suggests that static seeding is the more likely snow-enhancement mechanism in these clouds.
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Davis, Christopher A. "The Formation of Moist Vortices and Tropical Cyclones in Idealized Simulations." Journal of the Atmospheric Sciences 72, no. 9 (2015): 3499–516. http://dx.doi.org/10.1175/jas-d-15-0027.1.
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Abstract The upscale aggregation of convection is used to understand the emergence of rotating, coherent midtropospheric structures and the subsequent process of tropical cyclone formation. The Cloud Model, version 1 (CM1), is integrated on an f plane with uniform sea surface temperature (SST) and prescribed uniform background flow. Deep convection is maintained by surface fluxes from an ocean with uniform surface temperature. Convection begins to organize simultaneously into moist and dry midtropospheric patches after 10 days. After 20 days, the patches begin to rotate on relatively small scales. Moist cyclonic vortices merge, eventually forming a single dominant vortex that subsequently forms a tropical cyclone on a realistic time scale of about 5 days. Radiation that interacts with clouds and water vapor aids in forming coherent rotating structures. Using the path to genesis provided by the aggregated solution, the relationship between thermodynamic changes within the vortex and changes in the character of convection prior to genesis is explored. Consistent with previous studies, the approach to saturation within the midtropospheric vortex accelerates the genesis process. A novel result is that, prior to genesis, downdrafts become widespread and somewhat stronger. The increased downdraft mass flux leads to stronger and larger surface cold pools. Shear–cold pool dynamics promote the organization of lower-tropospheric updrafts that spin up the surface vortex. It is inferred that the observed inconsistency between convective intensity and thermodynamic stabilization prior to genesis results from sampling limitations of the observations wherein the important cold pool gradients are unresolved.
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Gurnis, Michael. "Large-scale mantle convection and the aggregation and dispersal of supercontinents." Nature 332, no. 6166 (1988): 695–99. http://dx.doi.org/10.1038/332695a0.
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Nagatani, Takashi. "Convection effect on the diffusion-limited-aggregation fractal: Renormalization-group approach." Physical Review A 37, no. 11 (1988): 4461–68. http://dx.doi.org/10.1103/physreva.37.4461.
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Bretherton, C. S., and P. N. Blossey. "Understanding Mesoscale Aggregation of Shallow Cumulus Convection Using Large‐Eddy Simulation." Journal of Advances in Modeling Earth Systems 9, no. 8 (2017): 2798–821. http://dx.doi.org/10.1002/2017ms000981.
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Khairoutdinov, Marat F., and Kerry Emanuel. "Intraseasonal Variability in a Cloud-Permitting Near-Global Equatorial Aquaplanet Model." Journal of the Atmospheric Sciences 75, no. 12 (2018): 4337–55. http://dx.doi.org/10.1175/jas-d-18-0152.1.
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Abstract Recent studies have suggested that the Madden–Julian oscillation is a result of an instability driven mainly by cloud–radiation feedbacks, similar in character to self-aggregation of convection in nonrotating, cloud-permitting simulations of radiative–convective equilibrium (RCE). Here we bolster that inference by simulating radiative–convective equilibrium states on a rotating sphere with constant sea surface temperature, using the cloud-permitting System for Atmospheric Modeling (SAM) with 20-km grid spacing and extending to walls at 46° latitude in each hemisphere. Mechanism-denial experiments reveal that cloud–radiation interaction is the quintessential driving mechanism of the simulated MJO-like disturbances, but wind-induced surface heat exchange (WISHE) feedbacks are the primary driver of its eastward propagation. WISHE may also explain the faster Kelvin-like modes in the simulations. These conclusions are supported by a linear stability analysis of RCE states on an equatorial beta plane.
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Pritchard, Michael S., and Da Yang. "Response of the Superparameterized Madden–Julian Oscillation to Extreme Climate and Basic-State Variation Challenges a Moisture Mode View." Journal of Climate 29, no. 13 (2016): 4995–5008. http://dx.doi.org/10.1175/jcli-d-15-0790.1.
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Abstract The climate sensitivity of the Madden–Julian oscillation (MJO) is measured across a broad range of temperatures (1°–35°C) using a convection-permitting global climate model with homogenous sea surface temperatures. An MJO-like signal is found to be resilient in all simulations. These results are used to investigate two ideas related to the modern “moisture mode” view of MJO dynamics. The first hypothesis is that the MJO has dynamics analogous to a form of radiative convective self-aggregation in which longwave energy maintenance mechanisms shut down for SST ≪ 25°C. Inconsistent with this hypothesis, the explicitly simulated MJO survives cooling and retains leading moist static energy (MSE) budget terms associated with longwave destabilization even at SST &lt; 10°C. Thus, if the MJO is a form of longwave-assisted self-aggregation, it is not one that is temperature critical, as is observed in some cases of radiative–convective equilibrium (RCE) self-aggregation. The second hypothesis is that the MJO is propagated by horizontal advection of column MSE. Inconsistent with this view, the simulated MJO survives reversal of meridional moisture gradients in the basic state and a striking role for horizontal MSE advection in its propagation energy budget cannot be detected. Rather, its eastward motion is balanced by vertical MSE advection reminiscent of gravity or Kelvin wave dynamics. These findings could suggest a tight relation between the MJO and classic equatorial waves, which would tend to challenge moisture mode views of MJO dynamics that assume horizontal moisture advection as the MJO’s propagator. The simulation suite provides new opportunities for testing predictions from MJO theory across a broad climate regime.
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Rutherford, B., G. Dangelmayr, and M. T. Montgomery. "Lagrangian coherent structures in tropical cyclone intensification." Atmospheric Chemistry and Physics Discussions 11, no. 10 (2011): 28125–68. http://dx.doi.org/10.5194/acpd-11-28125-2011.
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Abstract. Recent work has suggested that tropical cyclones intensify via a pathway of rotating deep moist convection in the presence of enhanced fluxes of moisture from the ocean. The rotating deep convective structures possessing enhanced cyclonic vorticity within their cores have been dubbed Vortical Hot Towers (VHTs). In general, the interaction between VHTs and the system-scale vortex, as well as the corresponding evolution of equivalent potential temperature θe that modulates the VHT activity, is a complex problem in moist helical turbulence. To better understand the structural aspects of the three-dimensional intensification process, a Lagrangian perspective is explored that focuses on the localized stirring around VHTs and their vortical remnants, as well as the evolution and stirring of θe. Recently developed finite-time Lagrangian methods are limited in the three-dimensional turbulence and shear associated with the VHTs. In this paper, new Lagrangian techniques developed for three-dimensional velocity fields are summarized and we apply these techniques to study VHT and θe phenomenology. Our primary findings are that VHTs are coherent Lagrangian vortices that create a turbulent mixing environment. Associated with the VHTs are hyperbolic structures that modulate the aggregation of VHTs and their vortical remnants. Although the azimuthally-averaged inflow is responsible for the inward advection of boundary layer θe, the Lagrangian coherent structures are found to modulate the convection emanating from the boundary layer by stirring θe along organized attracting boundaries. Extensions of boundary layer coherent structures grow above the boundary layer during episodes of convection are responsible for organizing the remnants of the convective vortices. These hyperbolic structures form initially as boundaries between VHTs, but persist above the boundary layer and outlive the VHTs to eventually form the primary eyewall as the vortex attains maturity.
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Lowman, Julian P., and Carl W. Gable. "Thermal evolution of the mantle following continental aggregation in 3D convection models." Geophysical Research Letters 26, no. 17 (1999): 2649–52. http://dx.doi.org/10.1029/1999gl008332.
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Wing, Allison A. "Author Correction: Self-Aggregation of Deep Convection and its Implications for Climate." Current Climate Change Reports 5, no. 3 (2019): 258. http://dx.doi.org/10.1007/s40641-019-00139-6.
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Wing, Allison A., and Kerry A. Emanuel. "Physical mechanisms controlling self-aggregation of convection in idealized numerical modeling simulations." Journal of Advances in Modeling Earth Systems 6, no. 1 (2014): 59–74. http://dx.doi.org/10.1002/2013ms000269.
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Singh, Shweta, and Norbert Kalthoff. "Process Studies of the Impact of Land-Surface Resolution on Convective Precipitation Based on High-Resolution ICON Simulations." Meteorology 1, no. 3 (2022): 254–73. http://dx.doi.org/10.3390/meteorology1030017.
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This study investigated the relevant processes responsible for differences of convective precipitation caused by land-surface resolution. The simulations were performed with the ICOsahedral Nonhydrostatic model (ICON) with grid spacing of 156 m and Large Eddy Simulation physics. Regions of different orographic complexity, days with weak synoptic forcing and favourable convective conditions were selected. The resolution of land-surface properties (soil type, vegetation) and/or the orography was reduced from 156 to 5000 m. Analyses are based on backward trajectories (Lagrangian Analysis Tool (LAGRANTO)), heat budget and convective organisation potential (COP) calculations. On average, the relative difference of areal mean daily precipitation at 1250 and 5000 m land-surface resolutions compared to 156 m were 6% and 15%, respectively. No consistent dependency of precipitation on orography or land-surface properties was found. Both factors impact convective initiation over areas with embedded mesoscale-sized land-surface heterogeneities. The position of convective precipitation was often influenced by the resolution of orography. Coarsening from 156 to 5000 m considerably changed the location of wind convergence and associated convection initiation. It also affects the onset times of clouds (<20 min) and precipitation (≈1 h). Cloud aggregation and microphysical processes proved to be important for further development towards convective precipitation.
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VALENZUELA, J. F., and C. MONTEROLA. "CONVECTIVE FLOW-INDUCED SHORT TIMESCALE SEGREGATION IN A DILUTE BIDISPERSE PARTICLE SUSPENSION." International Journal of Modern Physics C 19, no. 12 (2008): 1829–45. http://dx.doi.org/10.1142/s0129183108013278.
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We examine the segregation and mixing dynamics of a dilute bidisperse suspension of particles in a fluid subjected to a temperature gradient. Configurations corresponding to varying uniform bottom wall temperatures, as well as various bottom wall temperature profiles, are examined. Measures of spatial segregation and aggregation are discussed and used to analyze the suspension's dynamics. The results show that the difference in mass lead to transient segregation at short time scales, together with long-term intermixing and aggregation. Comparison of the segregation and aggregation among different configurations reveal that the strength of the temperature gradient is the primary influence on both segregation and aggregation. The particles are driven the fastest into the long – term steady state in the uniform and Gaussian bottom temperature profiles. In addition, the qualitative features of transient segregation do not change if the difference in mass is varied. The results suggest that a fluid undergoing thermal convection can be used to segregate particles, but only at short times, as fluid reaches its steady state. Keeping a fluid indefinitely in a transient state may improve the duration of segregation.
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Lu, Xinyan, Kevin K. W. Cheung, and Yihong Duan. "Numerical Study on the Formation of Typhoon Ketsana (2003). Part I: Roles of the Mesoscale Convective Systems." Monthly Weather Review 140, no. 1 (2012): 100–120. http://dx.doi.org/10.1175/2011mwr3649.1.
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Abstract The effects of multiple mesoscale convective systems (MCSs) on the formation of Typhoon Ketsana (2003) are analyzed in this study. Numerical simulations using the Weather Research and Forecasting (WRF) model with assimilation of Quick Scatterometer (QuikSCAT) and Special Sensor Microwave Imager (SSM/I) oceanic winds and total precipitable water are performed. The WRF model simulates well the large-scale features, the convective episodes associated with the MCSs and their periods of development, and the formation time and location of Ketsana. With the successive occurrence of MCSs, midlevel average relative vorticity is strengthened through generation of mesoscale convective vortices (MCVs) mainly via the vertical stretching mechanism. Scale separation shows that the activity of the vortical hot tower (VHT)-type meso-γ-scale vortices correlated well with the development of the MCSs. These VHTs have large values of positive relative vorticity induced by intense low-level convergence, and thus play an important role in the low-level vortex enhancement with aggregation of VHTs as one of the possible mechanisms. Four sensitivity experiments are performed to analyze the possible different roles of the MCSs during the formation of Ketsana by modifying the vertical relative humidity profile in each MCS and consequently the strength of convection within. The results show that the development of an MCS depends substantially on that of the prior ones through remoistening of the midtroposphere, and thus leading to different scenarios of system intensification during the tropical cyclone (TC) formation. The earlier MCSs are responsible for the first stage vortex enhancement, and depending on the location can affect quite largely the simulated formation location. The extreme convection within the last MCS before formation largely determines the formation time.
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Rehman, Rabia, Hafiz Abdul Wahab, Nawa Alshammari, Umar Khan, and Ilyas Khan. "Aggregation Effects on Entropy Generation Analysis for Nanofluid Flow over a Wedge with Thermal Radiation: A Numerical Investigation." Journal of Nanomaterials 2022 (September 24, 2022): 1–10. http://dx.doi.org/10.1155/2022/3992590.
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The current study investigated the formation of entropy in a nanofluid flow in a wedge with thermal radiation and convective boundary conditions. Nanoparticle aggregation is also taken into consideration. The rate of heat transmission of a water-based aggregated fluid over a wedge has been investigated due to the effects of thermal radiation. A set of nonlinear differential equations governs the flow process, and these are numerically solved using a helpful approach called the Runge-Kutta-Fehlberg scheme. This method starts by breaking down the equations into a collection of first-order equations. The RK method then solves those equations. The effects on flow and heat transmission are studied using graphical analysis. Entropy generation and Bejan number changes are also graphically displayed, and the results are discussed in detail. These equations’ answers were also incorporated into a dimensionless entropy generating equation. According to the findings, raising the radiation parameter and decreasing boundary convection minimize entropy generation, while nanoparticles boost entropy production.
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Fang, Juan, and Fuqing Zhang. "Initial Development and Genesis of Hurricane Dolly (2008)." Journal of the Atmospheric Sciences 67, no. 3 (2010): 655–72. http://dx.doi.org/10.1175/2009jas3115.1.
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Abstract Based on a successful cloud-resolving simulation with the Weather Research and Forecasting Model, this study examines key processes that led to the early development of Hurricane Dolly (2008). The initial development of Dolly consisted of three stages: (i) an initial burst of convection; (ii) stratiform development, dry intrusion, and thermodynamic recovery; and (iii) reinvigoration of moist convection and rapid intensification. Advanced diagnosis of the simulation—including the use of vorticity budget analysis, contour frequency analysis diagrams, and two-dimensional spectral decomposition and filtering—suggests that the genesis of Dolly is essentially a “bottom-up” process. The enhancement of the low-level vorticity is mainly ascribed to the stretching effect, which converges the ambient vorticity through stretching enhanced by moist convection. In the rapid intensification stage, smaller-scale positive vorticity anomalies resulting from moist convection are wrapped into the storm center area under the influence of background convergent flow. The convergence and accompanying aggregation of vorticity anomalies project the vorticity into larger scales and finally lead to the spinup of the system-scale vortex. On the other hand, although there is apparent stratiform development in the inner-core areas of incipient storm after the initial burst of convection, little evidence is found to support the genesis of Dolly through downward extension of the midlevel vorticity, a key process in the “top-down” thinking.
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Stechman, Daniel M., Greg M. McFarquhar, Robert M. Rauber, Brian F. Jewett, and Robert A. Black. "Composite In Situ Microphysical Analysis of All Spiral Vertical Profiles Executed within BAMEX and PECAN Mesoscale Convective Systems." Journal of the Atmospheric Sciences 77, no. 7 (2020): 2541–65. http://dx.doi.org/10.1175/jas-d-19-0317.1.
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AbstractVertical profiles of temperature, relative humidity, cloud particle concentration, median mass dimension, and mass content were derived using instruments on the NOAA P-3 aircraft for 37 spiral ascents/descents flown within five mesoscale convective systems (MCSs) during the 2015 Plains Elevated Convection at Night (PECAN) project, and 16 spiral descents of the NOAA P-3 within 10 MCSs during the 2003 Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX). The statistical distribution of thermodynamic and microphysical properties within these spirals is presented in context of three primary MCS regions—the transition zone (TZ), enhanced stratiform rain region (ESR), and the anvil region (AR)—allowing deductions concerning the relative importance and nature of microphysical processes in each region. Aggregation was ubiquitous across all MCS zones at subfreezing temperatures, where the degree of ambient subsaturation, if present, moderated the effectiveness of this process via sublimation. The predominately ice-supersaturated ESR experienced the least impact of sublimation on microphysical characteristics relative to the TZ and AR. Aggregation was most limited by sublimation in the ice-subsaturated AR, where total particle number and mass concentrations decreased most rapidly with increasing temperature. Sublimation cooling at the surface of ice particles in the TZ, the driest of the three regions, allowed ice to survive to temperatures as high as +6.8°C. Two spirals executed behind a frontal squall line exhibited a high incidence of pristine ice crystals, and notably different characteristics from most other spirals. Gradual meso- to synoptic-scale ascent in this region likely contributed to the observed differences.
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Su, Hui, Christopher S. Bretherton, and Shuyi S. Chen. "Self-Aggregation and Large-Scale Control of Tropical Deep Convection: A Modeling Study." Journal of the Atmospheric Sciences 57, no. 11 (2000): 1797–816. http://dx.doi.org/10.1175/1520-0469(2000)057<1797:saalsc>2.0.co;2.
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Ellahi, R., M. Hassan, and A. Zeeshan. "Aggregation effects on water base Al2O3-nanofluid over permeable wedge in mixed convection." Asia-Pacific Journal of Chemical Engineering 11, no. 2 (2015): 179–86. http://dx.doi.org/10.1002/apj.1954.
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