Level Of Buoyancy Research Articles

Quantifying the deep convective temperature signal within the tropical tropopause layer (TTL)

Abstract. Dynamics on a vast range of spatial and temporal scales, from individual convective plumes to planetary-scale circulations, play a role in driving the temperature variability in the tropical tropopause layer (TTL). Here, we aim to better quantify the deep convective temperature signal within the TTL using multiple datasets. First, we investigate the link between ozone and temperature in the TTL using the Southern Hemisphere Additional Ozonesondes (SHADOZ) dataset. Low ozone concentrations in the TTL are indicative of deep convective transport from the boundary layer. We confirm the usefulness of ozone as an indicator of deep convection by identifying a typical temperature signal associated with reduced ozone events: an anomalously warm mid to upper troposphere and an anomalously cold upper TTL. We quantify these temperature signals using two diagnostics: (1) the "ozone minimum" diagnostic, which has been used in previous studies and identifies the upper tropospheric minimum ozone concentration as a proxy for the level of main convective outflow; and (2) the "ozone mixing height", which we introduce in order to identify the maximum altitude in a vertical ozone profile up to which reduced ozone concentrations, typical of transport from the boundary layer are observed. Results indicate that the ozone mixing height diagnostic better separates profiles with convective influence than the ozone minimum diagnostic. Next, we collocate deep convective clouds identified by CloudSat 2B-CLDCLASS with temperature profiles based on Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Global Position System (GPS) radio occultations. We find a robust large-scale deep convective TTL temperature signal, that is persistent in time. However, it is only the convective events that penetrate into the upper half of the TTL that have a significant impact on TTL temperature. A distinct seasonal difference in the spatial scale and the persistence of the temperature signal is identified. Deep-convective cloud top heights are on average found to be well described by the level of neutral buoyancy.

A simulation modeling approach to hydrothermal plumes and its comparison to analytical models

We study the dynamics of hydrothermal plumes with the 3D time-dependent, Eulerian, adaptive mesh refinement code Gerris, which solves the equations of viscous, incompressible hydrodynamics. We have implemented a new module into Gerris that treats buoyancy-driven turbulence by means of a subgrid mode. Our model is validated in numerical experiment and applied to the dynamics of a rising plume. First we simulate hydrothermal plumes in a static environment and compare our results to the widely used integral models (MTT or Briggs’ model). The entrainment coefficient that we deduce from simulations falls into the range of the experimentally determined values. We also investigate the ratio between the level of the neutral-buoyancy layer and the maximum plume height. This ratio is frequently used to estimate plume heat flux via the measured level of neutral buoyancy. Although the ratio is only moderately (less than 10%) higher than the one predicted by the integral model, heat flux estimations can be substantially different. Finally, we explore the importance of background currents. We find that the simulated trajectories agree with integral models in the rising stage but the subsequent oscillations around the neutral-buoyancy layer are damped much more quickly and the level of the neutral buoyancy is also higher, same as the calm environment cases. By simulating the oscillation of a plume with suppressed transported turbulence and find a stronger oscillation than the original simulation, we suggest that a significant fraction of the difference between our model and the integral model can be explained by the absence of the turbulent transport of the latter.

Emplacement mechanism of off‐axis large submarine lava field from the Oman Ophiolite

Large submarine lava flows with thicknesses >100 m and volumes exceeding a few km3are not uncommon volcanic constructs of mid‐ocean ridges and around Hawaii Islands, yet details of the physical processes of eruption of these large lava flows are poorly understood. The V3 unit of the Oman Ophiolite extruded onto pelagic sediment far off the paleospreading axis as thick lava flows with an areal extent of >11 km by 1.5 km and the maximum thickness >270 m, yielding an estimated volume >1.2 km3. The feeder dike for the V3 flow field has an unusual thickness up to 60 m, striking at a high angle to the paleospreading axis. The skewed variation in thickness suggests an intrusion at the apparent level of neutral buoyancy in off‐axis crust. The thick sheet flows consist of massive core and columnar jointed crust. Finer‐grained, finely jointed layers and lenses embedded in coarser‐grained, roughly jointed lava show a complex cooling and growth history of the lava crust. In the periphery of the flow field, sheet flows lack developed core textures and change laterally into compound flows of pillow and subaqueous pahoehoe lobes, which are occasionally intermingled with pelagic shale. On the other hand, core lacks fine columnar joints and shows a typical doleritic texture. We conclude that the V3 flow field formed by extrusion of lava at low to moderate rates onto a subhorizontal seafloor covered with thick pelagic sediment, burying topographic relief >100 m of abyssal hills and fault grabens.

Where is the level of neutral buoyancy for deep convection?

This study revisits an old concept in meteorology ‐ level of neutral buoyancy (LNB). The classic definition of LNB is derived from the parcel theory and can be estimated from the ambient sounding (LNB_sounding) without having to observe any actual convective cloud development. In reality, however, convection interacts with the environment in complicated ways; it will eventually manage to find its own effective LNB and manifests it through detraining masses and developing anvils (LNB_observation). This study conducts a near‐global survey of LNB_observation for tropical deep convection using CloudSat data and makes comparison with the corresponding LNB_sounding. The principal findings are as follows: First, although LNB_sounding provides a reasonable upper bound for convective development, correlation between LNB_sounding and LNB_observation is low suggesting that ambient sounding contains limited information for accurately predicting the actual LNB. Second, maximum mass outflow is located more than 3 km lower than LNB_sounding. Hence, from convective transport perspective, LNB_sounding is a significant overestimate of the “destination” height level of the detrained mass. Third, LNB_observation is consistently higher over land than over ocean, although LNB_sounding is similar between land and ocean. This difference is likely related to the contrasts in convective strength and environment between land and ocean. Finally, we estimate the bulk entrainment rates associated with the observed deep convection, which can serve as an observational basis for adjusting GCM cumulus parameterization.

Mixtures of stratospheric and overshooting air measured using A-Train sensors

[1] Synergetic spaceborne observations of overshooting air, defined as cloud intrusion through the level of neutral buoyancy above deep convection, are analyzed using various thresholds introduced in previous studies to detect overshooting. The brightness temperature of the overshooting air measured by the Moderate Resolution Imaging Spectroradiometer (MODIS) is generally 2 K higher than that retrieved by the radiative transfer model, in which the size distribution of ice cloud particles is estimated from Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and CloudSat data and the vertical temperature profile of cloud is assumed to follow that of the European Centre for Medium Range Weather Forecast (ECMWF). The lapse rate of overshooting whose cloud top is higher than the level of the cold-point temperature (CPT) is lower than that of an adiabatic expansion. These observations can be rationalized as being due to the overshooting air being locally warmed by a mixture of warmer stratospheric air. Analysis of CALIOP and CloudSat data by using a radar-lidar algorithm shows that the mode of averaged ice water content of the overshoot above the CPT height is 6.3–10 mg/m3. Therefore, if 5% or more of ice particles in the overshoot are sublimated and mixed into the lower stratosphere, the lower stratospheric air will be hydrated. The difference between the brightness temperatures of 6.7 and 11 μm channels observed with MODIS demonstrates that the overshoot enhances stratospheric water vapor. These results indicate that the warm stratospheric air moves downward at and around the overshoot and mixes with the overshooting air and that the overshooting hydrates the lower stratosphere.

Seismic imaging of the water-column deep layer associated with the Deepwater Horizon oil spill

The submerged hydrocarbon layer at a depth of approximately 1100–1200 m in the water column near the Deepwater Horizon well site was associated with a temperature anomaly that was imaged by seismic reflection data collected two days before and one day after the well shut-in. Conventional multichannel seismic reflection profiling data were processed to enhance water-column reflections by filtering out low-frequency energy and applying higher gain than typically used for imaging subsurface geology. The deep layer reflectivity, within a few km of the well site, has an impedance less than seawater by about a factor of approximately [Formula: see text], or equivalently, a negative sound-velocity step of about [Formula: see text]. Water-column profile data collected at the same time as the seismic data show a comparable sound velocity and temperature decrease associated with the deep layer. Mixing of less dense hydrocarbons entrains cold seawater, resulting in a temperature anomaly within the deep layer at the level of neutral buoyancy. This temperature contrast explains the negative sound-velocity anomaly associated with the deep reflector. Because of the small hydrocarbon concentration in the deep layer, their contribution to the seismic velocity anomaly is too small to be significant. The high horizontal resolution (3 m) of the seismic image reveals a layer with patchiness of several hundred meters lateral extent.

J055014 密度成層中を運動する層流熱ブルームの温度場・組成場・速度場の同時可視化

Fluid dynamics of thermo-chemical plumes in viscous fluids was investigated. Flow pattern, temperature and compositional fields were quantitatively visualized by microcapsules of thermo chromic liquid crystals, fluorescent dye, and a laser light sheet. The behavior of thermo-chemical plumes depends on the initial buoyancy ratio B_0, which is the ratio of the stabilizing chemical buoyancy to the destabilizing thermal buoyancy at the onset of convection, and also on time. For intermediate B_0, the interplay between the thermal and compositional effects generates complicated behaviors. Because all hot plumes cool by thermal diffusion as they rise, a chemically composite thermal plume eventually attain a level of neutral buoyancy, and a secondary plume is generated from the tip of the chemical dome, then at which it begins to collapse. The thermo-chemical blob is refueled after the falling process because heat flux of the heater is constant in our experiment. Here we describe the oscillation behavior of the thermo-chemical plumes for the intermediate B_o based on the results of the heat flux by the thermo-chemical plumes.

Diagnosis and forecasting of the probability spectra of precipitation rate ranges

Diagnostic computations of two main characteristics of grid-scale forcing of ascending motions in the atmosphere, that is, of frontal parameter F and level of neutral buoyancy (convection level) LNB are presented as based on the objective analysis and numerical forecasting data. The computed diagnostics are compared with the observed precipitation amounts at the stations. It is found that convective instability in the deep layers (of large vertical thickness) mostly results in heavy precipitation, while shallow instability (of small vertical thickness), mostly in light precipitation. It manifests itself in monotonous growth of frequency of moderate, heavy, and very heavy precipitation with growing F and LNB; on the contrary, the light precipitation frequency is maximum under LNB = 2−3 km. At the intense fronts, convective instability is found to be forced in about a half of the case numbers; in winter and summer, instability is forced mainly in the shallow and deep layers, respectively. Frequency distributions of the precipitation rate ranges as dependent on F and LNB are presented as computed from the 10-year data series in the European territory of the former USSR: they are interpreted as the area- and time-averaged spectra of precipitation rate probabilities. As more practical and descriptive, the precipitation probability spectra are introduced as dependent on the predicted precipitation amount in the gridsquare. By the example of semi-Lagrangian model of Hydrometeorological Center of Russia and the NCEP global model (the United States), it is shown that generally the predicted precipitation range is not the most probable: as a rule, the most probable is a lower range of precipitation rate. The presented results can be considered as a demonstration of a possible way to develop a substantiated and reliable method to forecast the probability distribution of the precipitation rate ranges based on the numerical categorical forecast.

Localized algal blooms induced by river inflows in a canyon type reservoir

The local response of the phytoplankton community to river inflow processes was investigated with modeling and field analyses in a long and narrow, stratified reservoir in mid-summer. The river water had high concentrations of phosphorus and nitrogen (ammonium and nitrate) and temperature had large variations at diurnal scales. As a consequence of the large variation in river temperature, the level of neutral buoyancy (the depth where the river water spreads laterally in the reservoir) oscillated between the surface (overflows) during the day, and the depth of the metalimnion (interflows) during the night. The reservoir remained strongly stratified, which favoured the presence of cyanobacteria. It is shown that under these conditions, nutrient-rich river water injected during overflows into the surface layers promoted the occurrence of localized algal blooms in the zones where the overflow mixed with the quiescent water of the reservoir. A series of hydrodynamic simulations of the reservoir were conducted both with synthetic and realistic forcing to assess the importance of river temperatures and wind-driven hydrodynamics for algal blooms. The simulations confirmed that the river inflow was the main forcing mechanism generating the localized bloom.

Intercomparison of Deep Convection over the Tibetan Plateau–Asian Monsoon Region and Subtropical North America in Boreal Summer Using CloudSat/CALIPSO Data

AbstractDeep convection in the Tibetan Plateau–southern Asian monsoon region (TP–SAMR) is analyzed using CloudSat and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) data for the boreal summer season (June–August) from 2006 to 2009. Three subregions are defined—the TP, the southern slope of the plateau (PSS), and the SAMR—and deep convection properties (such as occurrence frequency, internal vertical structure, system size, and local environment) are compared among these subregions. To cast them in a broader context, four additional regions that bear some similarity to the TP–SAMR are also discussed: East Asia (EA), tropical northwestern Pacific (NWP), and western and eastern North America (WNA and ENA, respectively).The principal findings are as follows: 1) Compared to the other two subregions of the TP–SAMR, deep convection over the TP is shallower, less frequent, and embedded in smaller-size convection systems, but the cloud tops are more densely packed. These characteristics of deep convection over the TP are closely related to the unique local environment, namely, a significantly lower level of neutral buoyancy (LNB) and much drier atmosphere. 2) In a broader context in which all seven regions are brought together, deep convection in the two tropical regions (NWP and SAMR; mostly over ocean) is similar in many regards. A similar conclusion can be drawn among the four subtropical continental regions (TP, EA, WNA, and ENA). However, tropical oceanic and subtropical land regions present some significant contrasts: deep convection in the latter region occurs less frequently, has lower cloud tops but comparable or slightly higher tops of large radar echo (e.g., 0 and 10 dBZ), and is embedded in smaller systems. The cloud tops of the subtropical land regions are generally more densely packed. Hence, the difference between the TP and SAMR is more of a general contrast between subtropical land regions and tropical oceanic regions during the boreal summer. 3) Deep convection over the PSS possesses some uniqueness of its own because of the distinctive terrain (slopes) and moist low-level monsoon flow. 4) Results from a comparison between the daytime (1:30 p.m.) and nighttime (1:30 a.m.) overpasses are largely consistent with researchers’ general understanding of the diurnal variation of tropical and subtropical deep convection.

Transient dike propagation and arrest near the level of neutral buoyancy

Abstract We present a finite difference/perturbation method to investigate transient dike propagation from a magma chamber 1–2 km below the level of neutral buoyancy in oceanic crust and explore the role of density gradation in dike propagation arrest. The dike is modeled as a magma-filled blade crack and the host rock is assumed to be a linear elastic medium with graded mass density. An integral equation approach is used to obtain the dike propagation velocity and stress intensity factor at the propagating dike tip. The finite difference/perturbation method is applicable generally to mafic dikes with ηV less than 50 Pa-m, where η is the magma viscosity and V the dike propagation velocity. Numerical results show that dike propagation velocity initially increases with dike length, reaches a peak value when the dike tip reaches a position well above the level of neutral buoyancy and then rapidly decreases to zero after the dike propagates further into the region above the level of neutral buoyancy, which indicates that density gradation is an effective mechanism for dike arrest. The effects of host-rock fracture toughness and magma chamber depth relative to the level of neutral buoyancy are also discussed.

Nowcasting thunderstorms with graph spectral distance and entropy estimation

AbstractThe aim of the present study is to forecast thunderstorms over Kolkata (22°32′N, 88°20′E), India, during the pre‐monsoon season (April–May) with graph spectral distance and entropy analysis. Graph vertices represent points connected by lines or edges, and lifting condensation level, convective condensation level, level of free convection, freezing level, level of neutral buoyancy and the surface level are taken as the input of the graph vertices. The variation in the most probable distance between the vertices is investigated. The result reveals a particular orientation of the vertex distances for thunderstorm days which is significantly different from the non‐thunderstorm days. The reference graphs for thunderstorm and non‐thunderstorm days are formed using the most probable vertex distances. The spectral distance between the reference graph and the graphs corresponding to thunderstorms are computed with the data collected during the period 1997–2009. The entropies, or the measure of disorderliness or uncertainty, are estimated for the graph distance matrices. The result shows that the thunderstorm days possess lower distance entropy than the non‐thunderstorm days. This indicates that the reference graph that has been constructed for thunderstorms is more consistent. The result further depicts that the forecast accuracy through the present method is 98% with 1 h lead time, whereas the accuracy is 93% with 6 h lead time. The forecast is validated with the India Meteorological Department observations for the years 2007, 2008 and 2009. Copyright © 2011 Royal Meteorological Society

Intrusion and deformation at Campi Flegrei, southern Italy: Sills, dikes, and regional extension

The Campi Flegrei volcanic district, in southern Italy, has been uplifted since 1968 by a net maximum of 3 m during the intervals 1968–1972 and 1982–1984. The uplift represents a permanent deformation against a background rate of subsidence of about 17 mm a−1. Previous models have reproduced the observed vertical deformation but not the full pattern of horizontal movements. The 1982–1983 deformation is here reanalyzed in terms of a penny‐shaped sill on its own, with a tabular surface protrusion, or in an extensional stress field. It can be explained best by the intrusion of a sill (of 0.03–0.04 km3 at a depth of 2.75 km) in a crust that is being stretched ESE‐WNW at a strain rate of about 5.6 × 10−5 a−1. The sill's volume is similar to the common volumes of Campi Flegrei's eruptions since the Neapolitan Yellow Tuff (NYT) caldera was formed 15.6 ka ago. This similarity and the permanent nature of the uplift favor magmatic intrusion as the primary source of unrest. Sill formation may thus reflect the spreading of magma at a level of neutral buoyancy or along lateral discontinuities in the crust. The southern part of the caldera has been shielded from post‐NYT eruptions, despite some 33 m of permanent uplift since Roman times. Precursors to eruptions may thus be related not to caldera‐wide uplift but to the preceding conditions that determine whether magma ascends beneath the southern part of the caldera (favoring sill intrusion) or elsewhere (favoring an eruption).

Sheets within diapirs – Results of a centrifuge experiment

We carried out a centrifuge experiment to model the diapiric rise of a stratified PDMS layer from three perturbations through a non-Newtonian, ductile overburden. The experiment carried out at 700 g resulted in three composite diapirs fed by different PDMS layers. The three resulting diapirs represent two different stages of diapirism. One of the diapirs (diapir 1), which reached its level of neutral buoyancy and extruded at the surface of the model, was tabular in profile and copied by an internal intrusive body. The other two diapirs (diapirs 2 and 3) were still in the ascending stage when centrifuging was stopped and thus did not extrude at the surface. They displayed a typical balloon-on-string geometry, which develops at a high viscosity contrast between a highly viscous overburden and a less viscous buoyant material. The internal geometry of these last two diapirs, fed by the lower impure PDMS, however, did not copy the shape of their precursors. Instead, they had a finger-like shape. The finger geometry of the internal part of the diapirs might be the result of the higher viscosity of the impure lower PDMS intruding a less viscous clean PDMS. Compared to nature, diapir 1 represents a fully developed concentrically expanded pluton or nested diapir, while diapirs 2 and 3 resemble composite plutons which host magma batches of dyke-like geometry. Based on the results of our experiment we suggest that truly concentrically expanded plutons develop from the latter.

Effects of Calcium Levels on Colonial Aggregation and Buoyancy of Microcystis aeruginosa

Colonial aggregation of Microcystis plays a key role in bloom formation. Limited studies have been reported about effects of environmental factors on the aggregation of Microcystis. Calcium is an important chemical element in water system. In this study, we investigated the effects of a low- (0.015 g l⁻¹) and a high-concentration of calcium (0.100 g l⁻¹) on the aggregation and buoyancy of a colonial strain M. aeruginosa XW01. Results show that compared to the low concentration of calcium, the high-calcium condition results in bigger colonial size, higher level of buoyancy and increased production of extracellular polysaccharides (EPS) of M. aeruginosa XW01. Increased production of EPS induced by the high-calcium concentration should contribute to the colonial aggregation and buoyancy of M. aeruginosa XW01. These results suggest that an increase in calcium concentration may be beneficial for Microcystis blooms occurring in a soft water lake.

Depth and Evolution of a Silicic Magma Chamber: Melting Experiments on a Low-K Rhyolite from Usu Volcano, Japan

We estimated the depth of the magma chamber system beneath Usu volcano, one of the most active volcanoes inJapan, by melting experiments on the eruptive product of the AD 1663 plinian eruption (Us-b pumice).This pumice is a low-K rhyolite with a K2O content of only 1wt %. The experiments were conducted using internally heated pressure vessels at 98^392MPa and 700^9008C under nickel^nickel oxide (NNO)-buffered and water-saturated conditions. The pre-eruptive conditions of the 1663 eruption were estimated to be 780 208C and around 200^250MPa. The phase equilibria, mineral compositions (plagioclase, orthopyroxene, and Fe^Ti oxides), melt composition, and melt fraction are all in agreement with this conclusion. This pressure corresponds to a depth of 8^10 km, assuming a lithostatic condition with an appropriate crustal density structure.The magma was at near water-saturated conditions. Deviation between the estimated pressure and the true total pressure was estimated to be less than 50MPa. The Us-b magma was under very uniform conditions with a temperature variation of less than c. 208C, deduced from the narrow range of the phase equilibrium conditions (crystallizing orthopyroxene without quartz) and the homogeneous composition of plagioclase (c. An 41^45).We also estimated the pre-eruptive conditions of post-1663 eruptions, where it has been proposed that two magmas (high-P and low-P members) mixed prior to each eruption. The pressure of the deep magma was also around 200^250MPa, whereas that of the shallow magma was estimated to be 100^150MPa (4^6 km depth), according to the pressure dependence of the plagioclase composition obtained in our experiments.Thus, there appear to be two magma chambers beneath Usu volcano. Our estimate is consistent with geophysical observations made during the 2000 eruption, including identification of an inflation and deflation source at a depth of 10 km, a low-frequency (12 s) tremor source at a depth of 5^6 km, and an earthquake swarm at a depth of less than 4 km. The depth of the rhyolitic magma chamber (8^10 km) is deeper than the level of neutral buoyancy for the magma, and is comparable with that of mafic magma that existed beneath the rhyolitic magma.This suggests that the depth of the 8^10 km deep magma chamber was controlled by the emplacement of the mafic magma and that the rhyolitic magma was produced at that depth. When compared with other silicic magma systems, the Usu magma system has similar characteristics, including a similar pre-eruptive pressure of around 200MPa and a pressure decrease with time, suggesting upward magma movement towards a neutral buoyancy level. The low potassium content of the Usu magma prohibited crystallization of biotite, K-feldspar or hornblende, which are common phases in magmas with intermediate to high potassium contents. The absence of hydrous minerals at near-liquidus conditions may cause a rapid increase in water content

Large-eddy simulation of a buoyant plume in uniform and stably stratified environments

We consider large-eddy simulation (LES) of buoyant plumes in uniform and stably stratified environments. We show that in the former case the results agree well with the simple plume model of Morton, Taylor & Turner (Proc. R. Soc. Lond. A, vol. 234, 1956, p. 1). In particular, we calculate an entrainment constant which is consistent with laboratory and field measurements and find no significant difference between the radial spreading rates of vertical velocity and buoyancy. In a stably stratified environment, the LES plume shows better agreement with Morton et al. (1956) below the level at which the buoyancy first vanishes than above this level. Above the level of neutral buoyancy, the LES plume is characterized by an ascending core of negative buoyancy surrounded by a descending annulus of positive buoyancy. We compare the LES data with the model of Bloomfield & Kerr (J. Fluid Mech., vol. 424, 2000, p. 197), which explicitly accounts for these coherent motions. The model exhibits many qualitative aspects of the LES plume and quantitative agreement can be improved by adjusting the downward volume flux relative to the upward volume flux in a manner consistent with the LES plume. This simple adjustment, along with revised values of the entrainment constants, represents the combined effects of an overturning region at the top of the plume (where a fluid element reverses direction), ‘plume-top’ entrainment (whereby the plume entrains ambient fluid above the plume) as well as lateral entrainment and detrainment processes (both external and internal) occurring above the top of the model plume.

Do Undiluted Convective Plumes Exist in the Upper Tropical Troposphere?

AbstractUsing a passive tracer, entrainment is studied in cloud-resolving simulations of deep convection in radiative–convective equilibrium. It is found that the convective flux of undiluted parcels decays with height exponentially, indicating a constant probability per vertical distance of mixing with environmental air. This probability per distance is sufficiently large that undiluted updrafts are negligible above a height of 4–5 km and virtually absent above 10 km. These results are shown to be independent of the horizontal grid size within the range of 3.2 km to 100 m. Plumes that do reach the tropopause are found to be highly diluted.An equivalent potential temperature is defined that is exactly conserved for all reversible adiabatic transformations, including those with ice. Using this conserved variable, it is shown that the latent heat of fusion (from both freezing and deposition) causes only a small increase in the level of neutral buoyancy near the tropopause. In fact, when taken to sufficiently low pressures, a parcel with an ice phase ends up colder than it would without an ice phase. Nevertheless, the contribution from fusion to a parcel’s kinetic energy is quite large.Using an ensemble of tracers, information is encoded in parcels at the cloud base and decoded where the parcel is observed in the free troposphere. Using this technique, clouds at the tropopause are diagnosed for their cloud-base temperature, specific humidity, and vertical velocity. Using these as the initial values for a Lagrangian parcel model, it is shown that fusion provides the kinetic energy required for diluted parcels to reach the tropopause.

Turbulent plumes with heterogeneous chemical reaction on the surface of small buoyant droplets

A model is developed for a turbulent plume with heterogeneous chemical reaction rising in an unbounded environment. The chemical reaction, which may generate or deplete buoyancy in the plume, occurs at the interface between two phases, a continuous phase and a dispersed one. We study the case in which a buoyant reactant is released at the source and forms the dispersed phase, consisting of very small bubbles, droplets or particles. Once in contact with the ambient fluid, a first-order irreversible reaction takes place at the surface of the, for example, droplets. The behaviour of this plume in a uniform and stratified environment is examined. We show that the dynamics of a pure plume with such heterogeneous reaction is completely determined by the ratio of the environmental buoyancy frequency N and a frequency parameter associated with the chemical reaction, G. The group G is a measure of the ability of the reaction to generate buoyancy in the plume. In a uniform environment, the sign of parameter G fully determines the plume motion. When the reaction generates buoyancy (positive G) the motion is unbounded, whilst when reaction depletes buoyancy (negative G) the plume reaches a level of neutral buoyancy. A relation for this neutral buoyancy level as a function of the initial buoyancy flux of the plume and G is calculated. Our theoretical predictions compared well with experimental results using a plume of calcium carbonate particles descending in an acidic aqueous solution. In a stratified environment, the motion of the plume is always bounded, irrespective of the magnitude of G, and we determine the level of maximum buoyancy flux, as well as those of zero buoyancy and zero momentum as a function of N/G. Finally, our model is applied to study the dynamics of a localized release of carbon dioxide in the ocean.

Radar reflectivity as a proxy for convective mass transport

More observations of vertical mass transport in deep convection are needed to improve dynamical understanding of detrainment processes and for verification of transport models. A methodology for using radar reflectivity as a direct observation of vertical transport of mass from the boundary layer to the upper troposphere and lower stratosphere is investigated, and the “level of maximum detrainment” (LMD) is proposed. The case investigated is the 26 January 1999 squall line from the Tropical Rainfall Measuring Mission Large‐Scale Biosphere‐Atmosphere field campaign. Echo top heights and dual‐Doppler derived divergence profiles are used to define the mass detrainment range. Over 10% of anvil echo tops occurred above the sounding‐derived level of neutral buoyancy of 15.4 km during the mature stage of the storm, and convective tops reached above 18 km. Anvil ice water content, with a simple correction for ice fall speed, is found to be a good proxy for both the LMD, which for the storm analyzed is 11.25 km, and for the detrainment range of 6 to 17 km. More cases need to be analyzed to confirm the strength of this methodology, but the case study presented shows a strong correlation between anvil properties determined from radar reflectivity and the mass detrainment profile. Thus, radar reflectivity can be used as an indicator of the LMD to test model convective and transport parameterizations.