Secondary Cyclone Research Articles

Synoptic climatology of winter intense precipitation events along the Mediterranean coasts

Abstract. The link between winter (December-January-February) precipitation events at 15 Mediterranean coastal locations and synoptic features (cyclones and Northern Hemisphere teleconnection patterns) is analyzed. A list of precipitation events has been produced; q percentile thresholds (Thq) and corresponding frequency Nq (for q equal to 25, 50, 90 and 98) have been considered. A negative trend has been detected in total precipitation and N50 at many locations, while no significant trend in N25, N90 and N98 has been found. The negative phase of the North Atlantic Oscillation (NAO) and the East Atlantic/West Russia pattern (EAWR) compete for exerting the largest influence on the frequency of the 25th, 50th and 90th percentiles, with EAWR and NAO exerting their largest influence in the central and western Mediterranean areas, respectively. All percentiles show a similar behavior except for the 98th percentile, which shows no convincing link to any teleconnection pattern. The cyclone tracks that are associated with precipitation events have been selected using the ERA-40 reanalysis data, and a strong link between intense precipitation and cyclones is shown for all stations. In general, the probability of detecting a cyclone within a distance of 20° from each station increases with the intensity of the precipitation event and decreases with the duration of a dry period. The origin and track of cyclones producing intense precipitation differ among different areas. When precipitation occurs in the northwestern Mediterranean, cyclones are generally either of Atlantic origin or secondary cyclones associated with the passage of major cyclones north of the Mediterranean Basin, while they are mostly generated inside the region itself for events at the eastern Mediterranean coast. An important fraction of intense events in the southern areas is produced by cyclones that are generated over northern Africa. The analysis of sea level pressure and geopotential height at 500 hPa highlights the important role of cyclone depth, circulation strength, surrounding synoptic condition, and of slow speed of the cyclone center for producing intense precipitation events.

Heavy metal characterization of CFB-derived coal fly ash

The present study investigates the heavy metal content of coal fly ash (FA) samples coming from three different sampling points (secondary cyclone, cooler and filter) of a pilot plant combustion facility. The combustion experiments were carried out in a 0.1MW Circulated Fluidized Bed (CFB) boiler using South African coal, with the addition of limestone for sulfur capture. FA was tested for the presence of selected heavy metals using inductively coupled plasma optical emission spectrometry (ICP-OES); batch leaching tests were conducted as well. The samples were also characterized in terms of their microstructure, chemical and mineralogical composition, total surface area and particle size distribution. Most of the studied metals (Cd, Cr, Cu, Ni, Mn, Zn) showed enrichment in the fine, filter FA particles, while Pb was mostly concentrated in the cooler sample. Regarding leaching characteristics of the examined samples, Cr was found to occur in considerable amounts. Although the use of CFB technology for the combustion of solid fuels steadily gets bigger worldwide, only a very limited number of studies have environmentally assessed CFB-coal FAs to date. Thus, the current study aims to contribute toward building a more integrated knowledge on the environmental impact of this abundant power production by-product.

Simulations of Subtropical Cyclones in a Baroclinic Channel Model

Abstract The present study considers a variety of cyclone developments that occur in an idealized, baroclinic channel model featuring full condensation heating effects over an ocean with prescribed sea surface temperature variation. The geostrophic basic-state jet is specified by the tropopause shape, and horizontal shear is included by specifying the meridional variation of zonal wind on the lower boundary. The horizontal shear induces anticyclonic wave breaking of baroclinic waves. Normal mode perturbations are computed using a “fake-dry” version of the model but integrated forward using full physics. Low-latitude moist convection is particularly strong in simulations with strong surface easterlies that destabilize the troposphere through water vapor fluxes from the ocean surface. Deep convection produces a locally elevated dynamic tropopause and an associated anticyclone. This modified zonal flow supports moist baroclinic instability. The resulting cyclones, identified as subtropical cyclones, occur in deep westerly vertical wind shear but are nearly devoid of lower-tropospheric baroclinicity initially. These systems are distinguished from baroclinically dominated secondary cyclones that also form at relatively low latitudes in the simulations. For weak jets and strong subtropical surface easterlies, subtropical cyclone development dominates formation on the midlatitude jet. For strong westerly jets or weak horizontal shear, the situation is reversed and the midlatitude baroclinic wave can help or hinder the ultimate intensification of the subtropical cyclone. The similarity of this cross-latitude influence to the extratropical transition of tropical cyclones is noted.

Gas flow behavior and residence time distribution in a FCC disengager vessel with different coupling configurations between two-stage separators

To deeply understand the effect of coupled configuration between two-stage separators on the gas flow behavior in fluid catalytic cracking disengager space, the gas flow field and residence time distribution in a bench-scale disengager is numerically studied on the platform of the commercial computational fluid dynamics software package, Fluent 6.1. Two conventionally used coupling configurations in refineries and a newly-designed configuration are investigated. The Reynolds stress model is applied to simulate the gas flow field and the results agree well with the experimental values measured by a smart five-hole probe. Coupled with the Reynolds stress model, a scalar transport equation is used to obtain the gas residence time distribution. It is shown that the coupling configuration between the primary and secondary cyclones has an apparent effect on the gas flow behavior. The newly-designed configuration is better to quickly discharge the gas into the secondary cyclone inlet with a maximum residence time of 0.38 s, compared to 7.72 s and 2.79 s for the two conventional configurations. The simulation results indicated that the appropriate modification of the coupling configuration can help to improve the gas flow. The knowledge of the gas flow field also help to understand the coke formation process in the disengager space.

Multiobjective optimization of an industrial grinding operation under uncertainty

Abstract Multiobjective optimization of an industrial grinding operation under various parameter uncertainties is carried out in this work. Two sources of uncertainties considered here are related to the (i) parameters that are used inside a model representing the process under consideration and subjected to experimental and regression errors and (ii) parameters that express operators’ choice for assigning bounds in the constraints and operators prefer them to be expressed around some value rather than certain crisp value. Uncertainty propagation of these parameters through nonlinear model equations is reflected in terms of system constraints and objectives that are treated here using chance constrained fuzzy simulation based approach. Such problems are treated in literature using the standard two stage stochastic programming methodology that has a drawback of leading to combinatorial explosion with an increase in the number of uncertain parameters. This problem is overcome here using a combination of fuzzy and chance constrained programming approach that tackles the problem by representing and treating the uncertain parameters in a different manner. Simultaneous maximization of grinding circuit throughput and percent passing mid size fraction are studied here with upper bound constraints for various performance metrics for the grinding circuit, e.g. percent passing of fine and coarse size classes, percent solids in the grinding circuit final outlet stream and circulation load of the grinding circuit. Uncertain parameters considered are grindability indices of rod mill and ball mill, sharpness indices of primary and secondary cyclones and the respective upper bounds for the constraints mentioned above. The deterministic multiobjective grinding optimization model of Mitra and Gopinath [2004. Multiobjective optimization of an industrial grinding operation using elitist nondominated sorting genetic algorithm. Chem. Eng. Sci. 59, 385–396.] forms the basis of this work on which various effects of uncertain parameters are shown and analyzed in a Pareto fashion. Nondominated sorting genetic algorithm, NSGA II, a popular elitist evolutionary multiobjective optimization approach, is used for this purpose.

An event of stratospheric air intrusion and its associated secondary surface cyclogenesis over the South Atlantic Ocean

This work presents an analysis of a lowermost stratospheric air intrusion event over the coast of Brazil, which may have been responsible for a secondary surface cyclogenesis over the southwestern Atlantic Ocean. The surface cyclone initiated at 0600 UTC 17 April 1999 in a cold air mass in the rear of a cold front after a primary cyclone developed over the same region. The analysis of the secondary cyclone revealed the presence of lowermost stratospheric air intrusion characterized by anomalous potential vorticity (PV), dry air, and high concentration of ozone in atmospheric column. The system developed on the eastern side of an upper level core of PV anomaly, which induced a cyclonic wind circulation at lower levels and favored the onset of the secondary cyclone. In midlevels (500 hPa), the cutoff low development contributed to reduce the propagation speed of the wave pattern. This feature seemed to (1) allow the low‐level cold/dry air to heat/moisten associated with sensible and latent fluxes transferred from the ocean to the atmosphere, which intensified a baroclinic zone parallel to the coast, and (2) contribute to the long duration of the system. The present analysis indicates that this secondary cyclone development could be the result of the coupling between the PV anomaly in the upper levels and low‐level air‐sea interaction.

The Spatial Distribution and Evolution Characteristics of North Atlantic Cyclones

Abstract A climatology of extratropical cyclones is produced using an objective method of identifying cyclones based on gradients of 1-km height wet-bulb potential temperature. Cyclone track and genesis density statistics are analyzed and this method is found to compare well with other cyclone identification methods. The North Atlantic storm track is reproduced along with the major regions of genesis. Cyclones are grouped according to their genesis location and the corresponding lysis regions are identified. Most of the cyclones that cross western Europe originate in the east Atlantic where the baroclinicity and the sea surface temperature gradients are weak compared to the west Atlantic. East Atlantic cyclones also have higher 1-km height relative vorticity and lower mean sea level pressure at their genesis point than west Atlantic cyclones. This is consistent with the hypothesis that they are secondary cyclones developing on the trailing fronts of preexisting “parent” cyclones. The evolution characteristics of composite west and east Atlantic cyclones have been compared. The ratio of their upper- to lower-level forcing indicates that type B cyclones are predominant in both the west and east Atlantic, with strong upper- and lower-level features. Among the remaining cyclones, there is a higher proportion of type C cyclones in the east Atlantic, whereas types A and C are equally frequent in the west Atlantic.

Leaching of ashes from co-combustion of sewage sludge and wood—Part II: The mobility of metals during phosphorus extraction

Sewage sludge and its ashes after combustion are contaminated with metals in various concentrations. In the work described in this paper, the mobility of metals during recovery of phosphorus by acid leaching of fly ashes from co-combustion of sewage sludge with wood was investigated. The metal concentrations in two sewage sludges, fly ashes and leachates from acid phosphorus extraction, were compared with phosphorus rock and different fertilisers used in agriculture. The secondary cyclone ashes were found to be less contaminated with trace elements than the bag-filter ashes. The largest problem is cadmium, which in all ashes studied has a too high level to meet the legislative limits for the maximum dosage in Sweden and the proposed limits in the European Union. The legislation includes limits for cadmium (Cd), mercury (Hg), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) calculated for an amendment of X kg of fertiliser per year and hectare of land. The solubility of the trace metals in the cyclone ash, with Cd as an exception, is in general much lower than the solubility of phosphorus. A decrease in pH results in an increased release of Cd but has just a slight influence on the other metals analysed in this study. The Cd yield increases by 30% when pH is lowered from 2.5 to 1.0, whereas the Hg release is not affected at all. The trace element concentrations in the leachates are far below the European and Swedish limitations of metal concentrations in fertilisers. The leachates thus fit as fertilisers and also as raw material to the industry, if Cd is removed. In Part I of the project [Pettersson A, Åmand L-E, Steenari B-M. Leaching of ashes from co-combustion of sewage sludge and wood. Part I: recovery of phosphorus. Biomass and Bioenergy, 2007, accepted for publication [1]] focus was on the phosphorus recovery only.

Dependence of ensemble spread on model uncertainties for extratropical cyclone simulations

AbstractIn order to examine the dependence of the ensemble forecast spread on model uncertainty, we use the model grid‐point spacing and the index of shallow‐convection top as surrogates for model uncertainty, to construct two groups of ensemble forecasts (‘experiments’). In each ensemble, we use several members that differ only in the size of their model uncertainties. An initial baroclinic‐jet basic state is constructed, with a balanced three‐dimensional perturbation, to trigger development of a baroclinic wave.In terms of the minimum central surface pressure, the spread associated with each ensemble increases with increasing model uncertainty. Similar sensitivity is observed for the maximum ensemble spread and the domain‐averaged spread in terms of surface pressure. In both experiments, the domain‐averaged spread is linearly proportional to the size of the model uncertainty, and varies in time with a power‐law dependence.The ensemble spread is mainly collocated with the primary cyclone during the cyclone development stage, when amplitude error dominates, and is elongated along the regions with strong gradients during the mature stage, when the phase error dominates.Forecast errors also grow in association with the secondary cyclones that develop in the simulation. The maximum ensemble spread associated with secondary cyclones increases with increasing model uncertainty, as for the primary cyclones. It is found that model uncertainties have a larger effect at the surface on the spread associated with the upstream cyclone, compared to the downstream cyclone (at the same integration time), because of the different stages of development of the upstream and downstream cyclones. Copyright © 2007 Royal Meteorological Society

Multiple Series Cyclones for High Particulate Matter Concentrations

Cyclones are commonly used in agricultural processing as primary particulate emission abatement devices. A study was conducted to evaluate the effectiveness of one, two, three, or four 1D3D cyclones, in series, on airstreams heavily loaded (236 g/m3) with particulate (mass median diameter <10 m). A single cyclone was consistently less efficient (91%) and had a higher static pressure loss [1356 Pa (5.4 in. w.g.)] than the No. 1 cyclone in the series configurations [94% efficiency and 881 Pa (3.5 in. w.g.) static pressure loss]. Particle size distributions showed that there was a significant shift toward smaller sized particles in particulate captured by the cyclones (8.78 to 1.86 m) and the particulate emitted by the cyclones (3.23 to 1.52 m) as the number of series cyclones increased from one to four. A secondary cyclone increased overall efficiency significantly with a 27% rise in static pressure loss, while additional cyclones raised efficiency only about 1% more and increased pressure losses by 150%.

The fate of trace elements in fluidised bed combustion of sewage sludge and wood

Combustion tests have been carried out in a fluidised bed boiler to investigate the fate of trace elements during co-combustion of wood and municipal sewage sludge. The approach was to collect fuel and ash samples and to perform thermodynamic equilibrium calculations for gasification (reducing) and combustion (oxidising) conditions. Trace elements are found in the ash. Even most of the highly volatile Hg is captured in the bag filter ash. The bag filter ash offers higher surface area than the secondary cyclone ash and enhances the capture of Hg. There is no obvious correlation between capture and parameters investigated (sludge precipitation agent and lime addition). As, Cd, Hg, Pb, Se, Sb and Tl are predicted by equilibrium calculations to be volatile in the combustion chamber under oxidising conditions and Hg even at the filter temperature (150 °C). Reducing conditions promote, in some case more than others, the volatility of As, Cd, Pb, Sb, Se, Tl and Zn. The opposite effect was observed for Cu and Ni. Data points to the necessity of including bag filter in the gas cleaning system in order to achieve good removal of toxic trace elements.

An analysis of medium losses in coal washing plants

A major operating cost in dense-medium separation is in replacement of lost medium solids. The loss of medium solids, being costly, plays a crucial role in determining the economics of any preparation operation. Coal washeries that employ dense-medium cyclones often attempt optimization of the processes by varying the vortex or the spigot diameter and the feed relative density. While these changes help in closer control of the separation process, they also result in medium losses due to changes in the medium split ratio (ratio of the medium flow rate in overflow to underflow). Since medium solids are lost by adhesion to products and as magnetic separator effluent, the effect of the change in medium split ratio on the drain-and-rinse screens and, hence, the magnetic separator circuit needs to be studied. In Tata Steel's coal washeries, at Jharkhand India, which employs primary and secondary dense-medium cyclones in series to produce clean coal, middlings and rejects, reducing the relative density of feed medium, had an insignificant effect on the medium split ratio. On the other hand, changing the cone ratio (ratio of the overflow diameter to the underflow diameter) changed the relative density and the flow rates through the cyclone outlets, thus affecting the performance of the magnetite recovery circuit. A systematic study through laboratory tests and a detailed plant sampling campaign helped in identifying the causes of magnetite loss. Upon implementation of the recommendations, the magnetite losses decreased, resulting in a saving of approximately US$27,500 per annum. The study also helped in evolving some checkpoints for plant operators for identifying magnetite losses.

Recent advances in FCC technology

Although the fluid catalytic cracking (FCC) process has been commercially established for over 60 years, the technology continues to evolve to meet new challenges. This paper presents examples of recent FCC technology advances through integrated R&D programs that bridge understanding in process science and engineering practice in which Shell Global Solutions 1 1 Shell Global Solutions is a network of independent technology companies in the Royal Dutch/Shell Group. In this material the expression ‘Shell Global Solutions’ is sometimes used for convenience where reference is made to these companies in general, or where no useful purpose is served by identifying a particular company. has contributed significantly. On the reactor side, advances in feed injection, riser internals and riser termination have been proven to work synergistically to improve reactor performance. Earlier generation of modern feed injection technology was introduced in the 1980's, using direct impact mechanisms for atomization. This paper discusses the newest generation of the technology utilizing two-phase choking for atomization, which has been demonstrated to be much more energy efficient, as validated by consistently achieving more uniform temperature profiles across the riser. The FCC riser is known for its shortcomings of density and velocity variations. The newest riser internal technology minimizes these shortcomings and promotes ideal plug flow. The FCC is a sequential reaction process in which many desirable products are the intermediates. Thus, cracking reactions must be terminated after a desirable reaction time; otherwise, desirable products will continue to crack, leading to excess productions of light gases and coke. Improved riser termination technology sharpens the termination of reactions by the combination of the unique design of primary stripper cyclones and close coupled secondary cyclones. On the regenerator side, conventional flue gas cleaning requires two stages of cyclone separation followed by electro-static precipitators (ESP) or scrubbers. New developments in the Third Stage Separator (TSS) technology provide enhanced capability for achieving low particulate emissions in flue gas to comply with the requirements more stringent, particulate control environmental regulations. The majority of FCC units in the US have gone through various stages of de-bottlenecking, and many are limited by catalyst circulation. Catalyst circulation enhancing technology (CCET) has been demonstrated to improve standpipe stability, resulting in significant improvements in catalyst circulation rates.

Cesium as a Tracer for Alkali Processes in a Circulating Fluidized Bed Reactor

Addition of cesium salt has been used to study the removal rate, transport, and fate of alkali components during combustion of a mixture of wood chips and pellets in a 12-MW circulating fluidized bed (CFB) reactor. The alkali concentration in the flue gas was monitored with a recently developed aerosol mass spectrometer to provide on-line measurements of alkali-containing submicron particles. Cs2CO3 was fed with the fuel during a 5.5-h period, and the Cs concentration in the flue gas and in ash samples was followed for 70 h. Cesium addition resulted in a 1000-fold increase in Cs concentrations, followed by a slow decay of the concentrations during the following days. Cs was concluded to bind strongly to the fluidized bed material and to be removed with the bed ash or by slow release to the gas phase. The apparent rate coefficient for Cs removal from the bed was approximately 0.03 h-1. After 70 h, 33 ± 10% of the added cesium had been removed with the bottom ash, 7 ± 5% with secondary cyclone ash, and 45 ± 10% with the bag-house filter ash. About 15% of the Cs remained in the facility at this time, either bound to the fluidized bed material or as deposits on surfaces. Cesium compounds released from the bed participate in the formation of new particles that are efficiently collected by the bag-house filters. A minor Cs fraction also condenses on fly ash particles that are removed by the secondary cyclone. The study shows that the results of cesium addition can be followed in detail under typical operation conditions, and the potential of the tracer method for studies of transformations and fate of alkali compounds in commercial scale boilers is discussed.

Control Parameters for the Influence of a Mesoscale Mountain Range on Cyclone Track Continuity and Deflection

Abstract In this study prospective control parameters are identified for diagnosing the continuity and deflection of cyclone tracks across a mesoscale mountain range. Based on idealized simulations of a westward-moving cyclone, it was found that the cyclone track becomes a discontinuous (continuous) track and the cyclone experiences more (less) deflection with a combination of small (large) values of Vmax/Nh, U/Nh, R/Ly, U/fLx, and Vmax/fR, and large (small) value of h/Lx. The symbols are defined as follows: Vmax the maximum tangential wind, N the Brunt–Väisälä frequency, h the mountain height, U the basic wind speed, R the radius of Vmax, f the Coriolis parameter, and Lx and Ly the horizontal scales of the mountain in x and y directions, respectively. A conceptual model is proposed to explain track deflection and continuity for a westward-moving cyclone encountering idealized topography representative of the Central Mountain Range of Taiwan. With weak orographic blocking, a cyclone crosses over the mountain range with some northward deflection. With moderate orographic blocking, northward deflection of a cyclone is greater upstream of the mountain range and a secondary, leeside vortex forms to the southwest of the mountain range, indicative of discontinuity in the cyclone track. With strong orographic blocking, a westward-moving cyclone is deflected southward and a secondary cyclone forms to the northwest of the mountain range. The northward or southward deflection of a cyclone track is explained by the orographic blocking on the outer circulation of the cyclone.

Cyclone gasifier and cyclone combustor for the use of biomass derived gas in the operation of a small gas turbine in cogeneration plants

An inverted cyclone gasifier and secondary cyclone combustor have been developed for use in a biomass fired small-scale cogeneration plant. The gasifier was designed with a vortex collector pocket (VCP) and a central collector pocket (CCP) to maximise particle and ash separation from the flow, and remove alkali and other heavy metal traces that agglomerate with the ash particles. The gasifier design was robust and suitable for firing with varying input conditions. The gasifier exhaust gas is suitable for directly firing into the secondary cyclone combustor without any complex hot gas clean up systems. The cyclone combustor produces a strong swirling flow with good mixing and burnout patterns, creating stable combustion conditions. The use of an additional VCP situated before the combustor exit removes the need for additional cyclone separators. An exhaust mounted tangential off-take on the combustor reduces pressure drop across the system and gives near uniform exhaust velocity profiles. The gasifier achieved 98–99% burnout with good separation/retention rates and 50% alkali, Na and K removal. A good quality low calorific value (LCV) gas was produced that could be effectively utilised in the cyclone combustor. The cyclone combustor produces a stable flow, with good mixing and burnout rates, and uniform exit conditions and could be operated in a lean mode to minimize NO x . The additional use of a VCP removed particles above 5 μm, as specified by turbine inlet conditions. The gas was suitable for directly firing into the gas turbine. Low pressure drop was found across the system.

FRONTS AND FRONTAL WAVES OVER THE SOUTHERN CONE

Numerous cold fronts associated with mature extratropical storms sweep the coast of Chile every year. The large expanses of the Southern Pacific Ocean offer an ideal setting for up to 4000-km long cold fronts to develop as their parent cyclones travel from Australia to South America. These fronts sometimes break and spawn secondary cyclones that deepen significantly in one or two days. Examples of such frontal waves will be shown and discussed. An attribution technique applied to scatterometer wind measurements is used to diagnose the development of those frontal waves. Necessary conditions for their development are revealed

Upper- and lower-troposphere coupling processes involved in the FASTEX IOP16 frontal cyclone

This paper investigates processes involved in the development of the secondary low sampled on 17 February 1997 during the field phase of the Fronts and Atlantic Storm-Track EXperiment (FASTEX). This low is a fast- moving frontal wave that emerged from the trailing cold front of a parent low situated over Greenland. The dynamics of this cyclone and its environment are described using the European Centre for Medium- Range Weather Forecasts analysis corresponding to Intensive Observing Period 16 of FASTEX. The ageostrophic circulation is retrieved and analysed in the upper and in the lower levels. In the upper levels it is found that the curvature of the upper-level jet plays a crucial role in suppressing or amplifying the vertical motions. In the lower levels, in the region where the cloud head emerges, the vertical motion is scrutinized in the light of forcings which are acting. It is found that the vertical motions are the response to a geostrophic forcing reinforced by diabatic processes. The conjunction of vertical motions in the lower levels associated with vertical motions in the upper levels leads, in the developing period, to a coupling process that seems to be (following theoretical calculations) at the origin of the subsequent development of the cyclone. The instability processes involved in the development of the studied secondary cyclone are also investigated. The atmosphere appears neutral for upright convection while the region of the coupling corresponds to a region which is potentially unstable with respect to slantwise convection. The tendency of the atmosphere is to relax this instability. The vertical motions of the coupling processes are then reinforced by the relaxation of slantwise instability. Copyright © 2002 Royal Meteorological Society

Extratropical Transition of Tropical Cyclones over the Western North Pacific. Part I: Evolution of Structural Characteristics during the Transition Process

Abstract The development of extratropical cyclone structural characteristics that resulted from the extratropical transition of Typhoon (TY) David (1997) and TY Opal (1997) over the western North Pacific is examined. David moved poleward ahead of a midlatitude trough that was moving eastward as the dominant midlatitude circulation feature over the western North Pacific. During the transition, David coupled with the midlatitude trough, which led to the evolution of an intense cyclone that became the primary circulation over the North Pacific. Although Opal also moved poleward ahead of a midlatitude trough, the principal midlatitude feature over the western North Pacific was a preexisting stationary cyclone over the Kamchatka peninsula. During transition, Opal weakened and became a secondary cyclone to the preexisting primary North Pacific cyclone. The structural characteristics of the evolving extratropical cyclone with respect to each case are examined in the context of the interaction between a vortex an...

Mesoscale dynamics of a deepening secondary cyclone in FASTEX IOP16: Three-dimensional structure retrieved from dropsonde data

The mesoscale dynamics of a secondary cyclone sampled during the field phase of the Fronts and Atlantic Storm-Track EXperiment (FASTEX) Intensive Observation Period (IOP) 16 are documented using airborne dropsonde data. the method proposed to recover the mesoscale analytical three-dimensional (3-D) dynamic fields from the dropsonde measurements is evaluated using simulated fields, airborne in situ measurements, and airborne Doppler radar measurements. These simulations and comparisons indicate that the method is able to resolve the mesoscale structures within the studied secondary cyclone both in the regions of clear air and precipitation. It appears, however, that the most accurate description of the 3-D dynamic fields in both these regions would be obtained by combining Doppler and dropsonde measurements. The studied secondary cyclone is a fast moving frontal wave that developed on the trailing cold front of a parent low situated over Greenland. Using the dropsonde-derived 3-D fields, the mesoscale flows involved in the organization of the secondary cyclone are described. the potential-vorticity and equivalent-potential-vorticity fields (deduced from the basic analytical fields) indicate that the atmosphere is roughly neutral to moist slantwise instability. This configuration is known to significantly promote frontogenesis. the vertical configuration of the jets and circulations within this secondary cyclone are compared with the coupling-uncoupling scheme of Shapiro. A slight coupling is found between the thermally indirect circulation and the ageostrophic circulation. the obtained coupling is, however, not as developed as in the ideal case described by Shapiro, which may explain the small upward velocities in our case. Airborne Doppler radar and dropsonde measurements are combined so as to infer the multi-scale processes involved in the mesoscale and convective-scale organization of the Atlantic secondary cyclones and to evaluate the new emerging theoretical interpretations of secondary cyclogenesis.