Secondary Cyclone Research Articles

The Histories of Well-Documented Maritime Cyclones as Portrayed by an Automated Tracking Method

Abstract This study examines extratropical cyclone tracks, central pressure, and maximum intensification rates from a widely used automated cyclone tracking scheme and compares them with the manual tracking of five well-known North Atlantic cyclones whose histories are available in the refereed literature. The automated tracking scheme is applied to sea level pressure data from four different reanalyses of varying levels of sophistication to test the sensitivity of the results to input data resolution and quality. Further, we test the tracking scheme using lower-tropospheric vorticity obtained from the most recent reanalysis (ERA5) for four of these cyclone events. Substantial discrepancies in cyclone position, intensity, and maximum intensification rates exist between the manual tracking and the automated tracking and are not eliminated by using higher-resolution reanalyses or by “turning off” the spatial smoothing feature of the automated tracking scheme (needed to reduce spurious cyclone detections). The results point to a particular problem in detecting weaker and earlier stage cyclones and confirm findings from studies that have examined a broad range of cyclone tracking schemes for a range of reanalyses. Notably, this early cyclone stage often involves a smaller-scale secondary cyclogenesis or cyclone wave, which are detected by the automated scheme only after subsequent growth in the ensuing 6–12 h. It is known that these early stages are critical for a comprehensive understanding of rapid intensification events. A discussion of possible future solutions to this problem is presented. Significance Statement Because of the availability of large modern datasets portraying sea level pressure across the globe, meteorologists have turned to automated detection and tracking of midlatitude cyclones. Detection and tracking are of interest since these storm systems play an important role in weather and climate and potential changes in their location, frequency, and intensity are of considerable societal interest given climate change. This paper compares the results obtained from one commonly used automated tracking method with tracks obtained by human analysts. We find substantial discrepancies in cyclone position, intensity, and intensification rates and that these differences are not eliminated by using improved analyses. A discussion of possible future solutions is presented.

Increasing the efficiency of burning solid fuel in the layer

he main directions of increasing the efficiency of solid fuel heat generators are analyzed. It is noted that in industrial designs of heat generating installations depending on their class technological schemes of burning of solid fuel are applied at various levels on capital and operational expenses. The most expensive are the technologies of combustion of pre-prepared high-quality fuel in heat generators with complex mechanization at all stages of the combustion process, which provide high thermal and environmental performance. Cheaper combustion technologies are widespread, according to which the normative performance of heat generators is achieved due to the rational ratio of design and mode parameters of the combustion zone with the thermophysical characteristics of the burned fuel, including low-grade. Examples of realization of such technological schemes of combustion on the basis of results of theoretical and experimental researches in designs of solid propellant heat generators are resulted. The paper proposes a constructive scheme of a small-capacity heat generator with a combined technology of two-chamber solid fuel combustion, in which a layered (or shaft-layered) combustion process with combustion in volume is combined: in the primary combustion chamber above the burning fuel layer on the grate, and in the secondary cyclone chamber (or cameras). Due to the vortex motion in the lined secondary chamber of high-temperature gases containing solid particles carried by the flow from the combustion zone of the primary chamber, there is both afterburning of combustible substances and separation of ash particles with their discharge into the ash generator. This combustion technology also allows increasing the forcing of the combustion layer on the grate, increasing the stability of the process and reducing the dimensions of the structure. Improving the efficiency of a solid fuel heat generator with a two-chamber furnace is achieved by reducing heat loss with mechanical incomplete combustion of carbon particles in the exhaust gases, as well as reducing the concentration of ash particles in the gas stream at the inlet of convective heat exchange surfaces and increase their thermal efficiency. This is confirmed by the calculated dependences of the efficiency of the mechanized solid fuel heat generator under different technological schemes of solid fuel combustion

Composition and properties of fly ash collected from a multifuel fluidized bed boiler co-firing refuse derived fuel (RDF) and hard coal

In Poland, Refuse Derived Fuel (RDF) potential is significant, but high heterogeneity and contamination of the fuel limit its direct use in power industry. In this work samples were collected from a real-scale multifuel unit co-firing RDF with hard coal. Fuel samples and fly ashes collected from secondary cyclone and from bag filter were analysed in details. The thermal behaviour of fly ashes was investigated using X-ray diffraction (XRD), simultaneous thermal analysis (STA) and high-temperature microscope. High content of calcium compounds in both ash samples was noted. To determine the influence of flue gas treatment installation on the ash morphology and composition, Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS) was used. Fly ash after flue gas treatment (FGT) system was much finer and higher content of heavy metals was observed. The mass distribution of mercury and leachability of selected heavy metals from the fly ashes were performed for the analysed unit. The concentration of mercury was several times higher in case of first collected fly ash due to longer contact time of flue gases with ash. Fly ashes contained high amounts of copper, lead and vanadium, but leachability of analysed metals was lower in case of bag filter ash.

Linking Sub‐Tropical Evaporation and Extreme Precipitation Over East Antarctica: An Atmospheric River Case Study

AbstractWe investigate an intense snowfall event between 15 and 18 February 2011 over the East Antarctic coastal region which contributed to roughly 24% of the annual snow accumulation. The event was previously associated with an atmospheric river, and here we use both Eulerian and Lagrangian analysis to gain an understanding of the processes contributing to the atmospheric river signature. The planetary‐scale configuration during the event consisted of a persistent blocking situation resulting in a sustained meridional flow from the sub‐tropics to the Antarctic ice sheet between 20 and 50°E. Within this configuration, synoptic‐scale cyclogenesis contributed to slantwise ascent of moisture loaded air parcels toward Antarctica. Landfall of this cyclone’s warm sector coincided with the onset of Antarctic precipitation. Subsequently, a secondary cyclone developed along a pre‐existing baroclinic zone. The rapid intensification and propagation speed of this mesoscale cyclone alongside the warm, moist air mass resulted in strong moisture flux convergence ahead of the cyclone, providing additional poleward moisture transport. The poleward progression of warm moist air and a corresponding decrease of sea‐surface temperatures implied downward surface sensible and latent heat fluxes throughout the region of intense poleward moisture, roughly between 40 and 60°S. Hence, moisture uptake via surface evaporation was suppressed between the sub‐tropics and the polar continent, favoring long‐range transport. Identification of the surface moisture uptake region by tracing changes in moisture in air parcels confirmed the limited uptake of moisture during the poleward transport in this case study, with the primary moisture source for Antarctic precipitation located in the sub‐tropics.

Functional group characteristics and pyrolysis/combustion performance of fly ashes from Karamay oily sludge based on FT-IR and TG-DTG analyses

Three fly ashes, sequentially from the primary cyclone separator (CS1), the secondary cyclone separator (CS2) and the bag-type dust collector (BDC) at the outlet of industrial oily sludge pyrolyzer, were characterized by proximate analysis, ultimate analysis, FT-IR and TG-DTG methods. Molecular structure, pyrolysis and combustion performance of each fly ash were discussed. Results showed that content of volatile matter in BDC was 16.92% (dry base), and the contents in CS1 and CS2 were similar of 11.18% and 12.51%, respectively. Pyrolysis performance of each fly ash was quite different, among which the weight loss of BDC was higher of 44.3%, while the losses of CS1 and CS2 were 8.77% and 9.66%, respectively. Combustion performance showed that the comprehensive combustion characteristic index (SN) and combustion stability index (DW) of BDC were higher of 25.03 %2·min−2·°C−3 and 10.45 %2·min−1·°C−3, respectively, presenting well combustion performance. Pyrolysis kinetics based on Coats-Redfern model presented that the reaction order of three fly ashes could be selected as n = 5. While the order of combustion kinetics for CS1, CS2 and BDC might be assigned to 1 (or 2), 2 (or 3) and 1, respectively.

Synoptic‐scale and mesoscale controls for tornadogenesis on cold fronts: A generalised measure of tornado risk and identification of synoptic types

AbstractEnvironments of tornadic and non‐tornadic narrow cold‐frontal rain bands (NCFRs) are investigated using ERA‐Interim reanalyses for a sample of 114 events over the United Kingdom and Ireland (44 tornadic). The results offer a practical tool for prediction of the likelihood of tornadoes in these potentially high‐impact events. Of 22 analysed parameters, a bulk measure of shear vorticity, and the front‐normal wind component on the cold side of the front, yield the best discrimination between event classes, showing significantly larger values in tornadic events. A generalised measure of tornado probability, p[TN], is obtained using the distribution of points within the two‐dimensional parameter space defined by these parameters. Synoptic situations commonly associated with tornadic NCFRs are identified and conceptual models describing the large‐scale evolution are developed. Most events are associated with developing secondary cyclones (i.e., frontal waves) along trailing cold fronts (≥54.5%), generally within west to southwesterly large‐scale flow. Another significant class of event corresponds to situations where a strong mid‐ to upper‐level jet streak cuts across the front within an amplifying large‐scale flow pattern (upstream ridge building and downstream trough extension), generally within northwesterly flow (27.3%). In frontal waves, tornadoes occurred relatively early in the wave's development and just down‐front of the wave centre, where rapid increases in p[TN] occurred as the wave amplified. In northwesterly flow cases, tornadoes occurred along a well‐defined NCFR bulge close to where the mid‐ to upper‐level jet streak and an associated positive potential‐vorticity anomaly intersected the front. Analysis of a high‐tornadic subset of tornadic events (NCFRs producing ≥7 tornadoes) revealed an even stronger association with frontal waves (72.2% of cases), suggesting that the highest‐impact events are usually associated with secondary cyclogenesis. The possible relevance of identified environmental parameters to candidate vortex‐genesis and tornadogenesis mechanisms within NCFRs and quasi‐linear convective systems is discussed.

Diabatic Heating as a Pathway for Cyclone Clustering Encompassing the Extreme Storm Dagmar

AbstractContrary to the general notion that extratropical cyclones reduce baroclinicity, the baroclinicity is found to be enhanced in the wake of the extreme winter storm Dagmar. Thus, individual storms can increase baroclinicity, yielding a pathway to secondary cyclogenesis and cyclone clustering. We use a recently introduced diagnostic for baroclinicity—the tendency equation for the isentropic slope—and found that strong diabatic heating due to moisture supply from the subtropical Atlantic led to the enhanced baroclinicity in the rear of Dagmar. Storms ensuing Dagmar benefited from this increased baroclinicity. In contrast to previous studies on the mechanisms of cyclone clustering, we only find weak evidence for Rossby wave breaking and thus propose diabatic heating as an alternative pathway to cyclone clustering.

Diagnosis of a high-impact secondary cyclone during HyMeX-SOP1 IOP18

Multiple high-impact weather events occurred during HyMeX-SOP1, which was intensively monitored by a large number of ordinary and extraordinary observations. The availability of special observations offers an unprecedented opportunity to explore these events in depth and assess the capabilities of current numerical weather prediction tools. In this case, a small-scale secondary cyclone formed within a prominent cyclone that intensified in the north-western part of the western Mediterranean during IOP18 on October 31, 2012. The small secondary system formed near Catalonia, where heavy rain was observed, and then moved to the northern part of the island of Minorca, producing very strong winds. Finally, the secondary cyclone moved northeast while merging with the main cyclone and evolving as a cyclonic perturbation towards the Gulf of Genoa, bringing heavy precipitation to some Italian regions.This work aims at providing a detailed diagnosis of the genesis and evolution of the secondary cyclone, using high-resolution numerical tools. Furthermore, with the main objective of identifying the main physical mechanisms involved in the genesis and evolution of the small-scale secondary cyclone, sensitivity experiments were performed taking into account three main factors: latent heat release, upper-level dynamical forcing and topographical effects. Results show that in terms of individual cyclogenetic contributions, the upper level PV anomaly contribution dominated the initial phase and the diabatic heating from condensation contributed to the further deepening during the later stages of the secondary cyclone. The initial dynamical effect from the upper-levels forcing was amplified by the local topographic features, becoming a key synergistic factor for the formation of the damaging secondary cyclonic system.

The role of secondary cyclones and cyclone families for the North Atlantic storm track and clustering over western Europe

AbstractSecondary cyclones are those that form in association with a pre‐existing primary cyclone, typically along a trailing cold front. In previously studied cases they have been shown to cause extreme damage across Europe, particularly when multiple cyclones track over the same location in rapid succession (known as cyclone clustering). To determine the dynamical relationship between primary and secondary cyclones over the North Atlantic, a frontal identification algorithm is partnered with a cyclone identification method to objectively identify secondary cyclones in 35 extended winter periods using reanalysis data. Cyclones are grouped into “cyclone families” consisting of a single primary cyclone and one or more secondary cyclones. This paper aims to quantify the differences between secondary and primary cyclones over the North Atlantic, and how cyclone families contribute to episodes of cyclone clustering across western Europe. Secondary cyclones are shown to occur most frequently in the central and eastern North Atlantic, whereas primary cyclones are commonly found over the western North Atlantic. Cyclone families have their strongest presence over the North Atlantic Ocean and contribute more than 50% of cyclones over the main North Atlantic storm track. A final category, solo cyclones, which are not associated with cyclogenesis on any connected fronts, are most commonly identified over continental regions as well as the Mediterranean Sea. Primary cyclones are associated with the development of an environment that is favourable for secondary cyclone growth. Enhanced Rossby wave breaking following primary cyclone development leads to an increase in the upper‐level jet speed and a decrease in low‐level stability. Secondary cyclogenesis commonly occurs in this region of anomalously low stability, close to the European continent. During periods of cyclone clustering, secondary cyclones are responsible for approximately 50% of the total number of cyclones. The increase in jet speed and decrease in static stability initiated by the primary cyclones acts to concentrate the genesis region of secondary cyclones and direct the cyclones that form along a similar track. While there is an increase in the secondary cyclogenesis rate near western Europe during periods of European clustering, the basin‐wide secondary cyclogenesis rate decreases during these periods. Thus the large‐scale environment redistributes secondary cyclones during periods of clustering rather than increasing the total number of secondary cyclones.

Rapid Cyclogenesis from a Mesoscale Frontal Wave on an Atmospheric River: Impacts on Forecast Skill and Predictability during Atmospheric River Landfall

Abstract Mesoscale frontal waves have the potential to modify the hydrometeorological impacts of atmospheric rivers (ARs). The small scale and rapid growth of these waves pose significant forecast challenges. We examined a frontal wave that developed a secondary cyclone during the landfall of an extreme AR in Northern California. We document rapid changes in significant storm features including integrated vapor transport and precipitation and connect these to high forecast uncertainty at 1–4-days’ lead time. We also analyze the skill of the Global Ensemble Forecast System in predicting secondary cyclogenesis and relate secondary cyclogenesis prediction skill to forecasts of AR intensity, AR duration, and upslope water vapor flux in the orographic controlling layer. Leveraging a measure of reference accuracy designed for cyclogenesis, we found forecasts were only able to skillfully predict secondary cyclogenesis for lead times less than 36 h. Forecast skill in predicting the large-scale pressure pattern and integrated vapor transport was lost by 96-h lead time. For lead times longer than 36 h, the failure to predict secondary cyclogenesis led to significant uncertainty in forecast AR intensity and to long bias in AR forecast duration. Failure to forecast a warm front associated with the secondary cyclone at lead times less than 36 h caused large overprediction of upslope water vapor flux, an important indicator of orographic precipitation forcing. This study highlights the need to identify offshore mesoscale frontal waves in real time and to characterize the forecast uncertainty inherent in these events when creating hydrometeorological forecasts.

The Classification Performance of a Three-Product Cyclone

Conventional (two products) cyclone have been widely used for classification in most mineral plants. But it is hard to satisfy the requirements of some productions by changing the parameter, such as cylindrical length and cone angle. In this paper, a three-product cyclone was developed and tested for recovery of the solid particles, which was composed of a primary cylinder and a secondary cyclone. Most of the fine particles were separated in the primary cylinder of the three-product cyclone by over flow, in order to reduce the particle size distribution before the separation of second stage. The remaining particles would be further classified by the secondary cyclone of the three-product cyclone. The design and operation of the three-product cyclone was systematically studied, and the size distribution have been analyzed of the three produces. The influence of the major parameters of cyclone, such as the spigot diameter, vortex finder diameter, and vortex finder length, on the solid recovery were investigated. Meanwhile, the regression models of the solid percent of the cylinder overflow, the cyclone overflow, and the cyclone underflow were developed through computer fitting analysis, which fitted well with the experimental values of solids recovered in the three products. The application of the regression models on the three products was proposed.

Flow dynamics study of catalyst powder in catalytic cracking unit for troubleshooting

Abstract Gamma scanning and radiotracer applications are very effective and inexpensive tools to understand and optimize the process as well as troubleshoot the various types of problems in many chemical, petrochemical industries and refineries. These techniques are non-invasive; hence, the problems can be pinpointed online, which leads to reduce the downtime, schedule the shutdown and maintenance of the plant equipment, rendering huge economic benefits. In a leading refinery of India, the catalytic cracking unit (CCU) was malfunctioning. It was suspected by the refinery engineers that the catalyst powder was being carried over to the fractionator, which could have led to erosion of the fractionator column internals resulting in their rupture, and consequentially, to the fire hazard. To understand the flow behaviour of the catalyst powder and to ensure the mechanical integrity, catalyst accumulation and choking, both radiotracer study and gamma scanning of the CCU reactor was carried out. The reactor consists of a riser, three primary cyclones and three secondary cyclones. Gamma scanning of the reactor was carried out with the help of an automatic gamma scanner using 1.8 GBq of Co-60 sealed source. Results showed that the catalyst powder was accumulated in one of the secondary cyclones and uneven density distribution was observed in another secondary cyclone. The radiotracer study was carried out using the irradiated catalyst powder as a radiotracer, which contains 0.9 GBq of Na-24. The radiotracer was injected in the reactor through the specially fabricated injection system. Radiation measurement was done using the thermally insulated and collimated NaI(Tl) scintillation detectors located at various strategic locations coupled to a multi-detector data acquisition system. The data were mathematically analysed. It was confirmed that the catalyst powder was accumulated in one of the secondary cyclones with no flow downwards. This resulted in excess powder available to travel along with hydrocarbon towards fractionator. Since the quantity of powder released through the hydrocarbon outlet of CCU was higher than the designed value, the catalyst powder was observed in various zones of the fractionator. Mathematical modelling of the radiotracer data obtained at various locations corroborated the scanning results; also, the flow pattern was obtained. Partially blocked secondary cyclone showed plug flow with recirculation; normal working cyclone had plug flow behaviour and the vortex breaker showed parallel flow.

Uneven distribution of particle flow in RFCC reactor riser

The uneven distribution of particle flow, i.e., a different particle mass flow rate in each outlet of the riser in residue fluidized catalytic cracking (RFCC) processes, is one major problem associated with commercial RFCC processes. This problem affects the formation of carbonaceous deposits in the secondary reactor cyclone, which incurs serious catalyst carryover in the fractionators. This study analyzes particle-fluid flow patterns in the riser, and diagnoses the uneven distribution of particle flow using a computational particle fluid dynamics (CPFD) method to solve this real industrial problem. Through this analysis, the effect of the number of feed injectors is investigated. The CPFD method, which has been developed to complement the Eulerian-Eulerian and Eulerian-Lagrangian methods, applies the Navier-Stokes equation for fluid phase and multi-phase-particle-in-cell (MP-PIC) models for particle phase. The particle flow distribution was found to vary by 15.5–18.7% at different outlets in the 1 injector case, which implies that the solid loading ratio in each cyclone is different, thereby affecting the separation efficiency of the cyclone and the formation of carbonaceous deposits. The uneven distribution of particle flow phenomena was identified, and the standard deviations of particle mass flow rates were evaluated for the cases of 1, 2, 4, 6, 8 and 12 injectors, and were found to be 7.52, 4.07, 2.66, 1.78, 2.85 and 3.82, respectively. From these results, the 6 injectors case was found to have a largely even particle flow distribution.

A Polar Mesoscale Cyclone Formed over the East China Sea and Developed into a Secondary Cyclone over the Northwestern Pacific — An Observational Case Study on 19-22 February 1975 —

Polar mesoscale cyclones (PMCs) frequently develop over the Japan Sea. Genesis of PMCs over the East China Sea is rare, but can occur under certain synoptic-scale conditions. In this observational case study, the feature of a PMC generated over the eastern East China Sea on 20 February 1975 is studied using observation data including those obtained during Air-mass Transformation Experiment, satellite cloud images, and objective-reanalysis data.

Experimental and CFD study of particle deposition on the outer surface of vortex finder of a cyclone separator

Based on the industrial background of carbonaceous deposition in secondary cyclone separators of FCC units, this paper focuses on particle deposition pattern and investigation of factors on deposition on the outer surface of vortex finder of secondary cyclone. Particle deposition experiments were carried out with a 500mm-diameter cyclone in a cold-model pilot test platform. Deposition patterns were obtained under different inlet gas velocities, particle concentrations and experimental materials etc. Furthermore, discrete phase model (DPM) was applied to obtain particles distribution in the annular space and the effect of particle properties and operational conditions on mass of deposited particles was also investigated. In addition, Gas shielding method was preliminarily explored to avoid particle deposition. The results will provide experimental evidence for analyzing the deposition process and help to further understand the deposition mechanism.

Carbonaceous deposition onto the outer surface of vortex finder of commercial RFCC cyclones and role of gas flow to the buildup of the deposits

Unwanted build-up of carbonaceous deposits on RFCC equipment surface is a key process limitation to achieving the economic benefits of longer run length. This paper focuses on the carbonaceous deposition on the outer surface of vortex finder of secondary cyclone. Macroscopic features of industrial deposits are reported in detail. Extensive characterization studies such as elemental analysis, scanning electron microscopy, energy dispersive spectrometry, thermal behavior were conducted and size distribution of catalyst particles in deposits was measured. Computational fluid dynamics method was used to obtain the gas flow field around the vortex finder. The role of gas flow to the buildup of deposits was discussed. The results will provide comprehensive understanding of deposit formation and insight into the process and operation improvement.

The Beneficiation of Fine Coal by a Combination of Three-Product Cyclone and Fine Screen

ABSTRACTA novel classified gravity system, comprised of a three-product cyclone and a fine high-frequency screen, was developed and tested for recovery of fine coal. The three-product cyclone is characterized by the primary cylinder and a secondary cyclone. The effects of major parameters of the secondary cyclone, such as vortex finder diameter, vortex finder length, and spigot diameter, were investigated by single-factor experiments. Regression models of the yield and ash content of clean coal were developed with statistical design of experiments and showed good correlations of experimental results. The regression models indicated that the spigot diameter had the largest impact on the yield and ash content of clean coal. It also indicated that spigot diameter and vortex finder diameter jointly affect performances of the three-product cyclone. The cylinder played a significant role in desliming of the feed, giving the secondary cyclone a better gravity-separation condition. Ash reductions of +0.150 mm fractions were all above 70%, which showed that the cyclone had significant effects on fine coal separation in the classified gravity system.

Behavior of Alkali Metals and Ash in a Low-Temperature Circulating Fluidized Bed (LTCFB) Gasifier

A low-temperature circulating fluidized bed system (LTCFB) gasifier allows for pyrolysis and gasification to occur at low temperatures, thereby improving the retention of alkali and other inorganic elements within the system and minimizing the amount of ash species in the product gas. In addition, the low reactor temperature ensures that high-alkali biomass fuels can be used without risk of bed defluidization. This paper presents the first investigation of the fate of alkali metals and ash in low-temperature gasifiers. Measurements on bed material and product gas dust samples were made on a 100 kW and a 6 MW LTCFB gasifier. Of the total fuel ash entering the system, the largest fraction (40–50%) was retained in the secondary cyclone bottoms, while a lower amount (8–10%) was released as dust in the exit gas. Most of the alkali and alkaline earth metals were retained in the solid ash, along with Si and a minor fraction of Cl. Most Cl and S were released in gaseous form, with chlorine partly as methyl chlori...

Secondary Cyclogenesis along an Occluded Front Leading to Damaging Wind Gusts: Windstorm Kyrill, January 2007

Abstract Windstorm Kyrill affected large parts of Europe in January 2007 and caused widespread havoc and loss of life. In this study the formation of a secondary cyclone, Kyrill II, along the occluded front of the mature cyclone Kyrill and the occurrence of severe wind gusts as Kyrill II passed over Germany are investigated with the help of high-resolution regional climate model simulations. Kyrill underwent an explosive cyclogenesis south of Greenland as the storm crossed poleward of an intense upper-level jet stream. Later in its life cycle secondary cyclogenesis occurred just west of the British Isles. The formation of Kyrill II along the occluded front was associated (i) with frontolytic strain and (ii) with strong diabatic heating in combination with a developing upper-level shortwave trough. Sensitivity studies with reduced latent heat release feature a similar development but a weaker secondary cyclone, revealing the importance of diabatic processes during the formation of Kyrill II. Kyrill II moved farther toward Europe and its development was favored by a split jet structure aloft, which maintained the cyclone’s exceptionally deep core pressure (below 965 hPa) for at least 36 h. The occurrence of hurricane-force winds related to the strong cold front over north and central Germany is analyzed using convection-permitting simulations. The lower troposphere exhibits conditional instability, a turbulent flow, and evaporative cooling. Simulation at high spatiotemporal resolution suggests that the downward mixing of high momentum (the wind speed at 875 hPa widely exceeded 45 m s−1) accounts for widespread severe surface wind gusts, which is in agreement with observed widespread losses.

영동지역의 극한 대설에 대한 위성관측으로부터 구름 추적

본 연구에서는 겨울철 영동지역에서 2001 ~ 2012(12년) 동안 일신적설 50 cm 이상의 3개 극한 대설사례를 선정하여 위성에서 관측된 구름을 추적하여 공간적 특성을 분석하였다. 그리고 그 특성을 레이더 강수와 비교하였다. 이 연구에서 선정된 영동지역 극한 대설사례는 영동지역(영동 앞바다)에서 발생하여 발달하거나 동한만 부근에서 발생하여 영동지역으로 이동해 들어오는 독립되고 잘 발달된 그리고 크기가 작은 대류형 구름과 관련이 있다. 주강수 시기의 이 구름덩어리의 최저휘도온도는 -<TEX>$-40{\sim}-50^{\circ}C$</TEX>로 낮고, 휘도온도 <TEX>$-35^{\circ}C$</TEX> 혹은 <TEX>$-40^{\circ}C$</TEX> 이하의 구름 크기는 약 17,000 ~ 40,000 <TEX>$km^2$</TEX>로 중규모 대류복합체(<TEX>$-52^{\circ}C$</TEX> 이하 구름크기 50,000 <TEX>$km^2$</TEX>)보다 작은 크기이다. 이 때 레이더의 강수면적(0.5 mm/hr 이상)도 약 4,000 ~ 8,000 <TEX>$km^2$</TEX>로 작고 독립된 강수 형태를 보인다. 위성의 구름영역과 레이더 강수영역은 영동 앞바다에 비슷하게 위치하였으나 레이더 강수의 중심이 상대적으로 영동 해안에 인접해 위치하였다. 또한 구름이 발달하는 과정에서 구름의 극값과 강수의 극값이 일치하지 않는 경우도 나타났다. 그러나 모든 사례에서 주강수 시기에 구름은 영동 앞바다에 위치하였다. 따라서 구름덩어리의 위치가 극한 대설에 있어 무엇보다 중요한 요소인 것으로 판단된다. 수증기 영상은 건조구역(암역)의 가장자리 북쪽에서 구름덩어리가 발달함을 보여주었다. 따라서 위성관측의 구름영상과 지상 레이더에 의한 강수관측 값과 비교하여 보았을 때, 위에 선정된 극한 대설 사례는 부저기압 혹은 소용돌이의 발달과 관련되어 있는 것으로 생각된다. 영동지역 극한 대설에 대한 초단기 예보에 있어 초기에 동한만 혹은 영동지역에서 작고 발달된 대류형 구름을 탐지하고 추적하는 것이 중요하다. This study presents spatial characteristics of cloud using satellite image in the extreme heavy snowfall of the Yeongdong region. 3 extreme heavy snowfall events in the Yeongdong region during the recent 12 years (2001 ~ 2012) are selected for which the fresh snow cover exceed 50 cm/day. Spatial characteristics (minimum brightness temperature; Tmin, cloud size, center of cloud-cell) of cloud are analyzed by tracking main cloud-cell related with these events. These characteristics are compared with radar precipitation in the Yeongdong region to investigate relationship between cloud and precipitation. The results are summarized as follows, selected extreme heavy snowfall events are associated with the isolated, well-developed, and small-scale convective cloud which is developing over the Yeongdong region or moving from over East Korea Bay to the Yeongdong region. During the period of main precipitation, cloud-cell Tmin is low (<TEX>$-40{\sim}-50^{\circ}C$</TEX>) and cloud area is small (17,000 ~ 40,000 <TEX>$km^2$</TEX>). Precipitation area (<TEX>${\geq}$</TEX> 0.5 mm/hr) from radar also shows small and isolated shape (4,000 ~ 8,000 <TEX>$km^2$</TEX>). The locations of the cloud and precipitation are similar, but in there centers are located closely to the coast of the Yeongdong region. In all events the extreme heavy snowfall occur in the period a developed cloud-cell was moving into the coastal waters of the Yeongdong. However, it was found that developing stage of cloud and precipitation are not well matched each other in one of 3 events. Water vapor image shows that cloud-cell is developed on the northern edge of the dry(dark) region. Therefore, at the result analyzed from cloud and precipitation, selected extreme heavy snowfall events are associated with small-scale secondary cyclone or vortex, not explosive polar low. Detection and tracking small-scale cloud-cell in the real-time forecasting of the Yeongdong extreme heavy snowfall is important.