Approved for Public release; distribution is unlimited / An explosive cyclogenesis event that occurred in the eastern Pacific Ocean on 14-17 December 1987 is investigated using the National Meteorological Center (NMC) final analyses and Geostationary Operational Environmental Satellite (GOES) digital imagery. Forecasts for this cyclone by the Navy Operational Global Atmospheric Prediction System (NOGAPS 3.0) and NMC Nested Grid Mesh (NGM) forecasts initialized at 12 UTC 14 December are also evaluated. Quasi-Lagrangian budgets of mass and vorticity are computed to determine the factors responsible for the development of this intense cyclone. The initial surface development occurs within a strong baroclinic zone southeast of a significant short-wave trough aloft. Rapid intensification is accompanied by large cyclonic vorticity advection in the upper troposphere as the surface cyclone moves under the divergent quadrant of a 250mb jet streak. A key element in this development is the superposition between the pre-existing surface low and upper level short-wave trough in a favorable weak static stability environment. These observations support earlier studies that upper level forcing acts as a critical catalyst in initiating eastern ocean explosive development. / http://archive.org/details/casestudyofexplo00curt / Lieutenant Commander, United States Navy

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This work deals with climatology of mediterranean cyclones. In first chapter short description of the Mediterranean area is given, second chapter depicts climate properties of Mediterranean focussed on air temperature, sea surface temperature and precipitations. Third chapter characterises Mediterranean cyclones, briefly brings some facts about their dividing and possibilities of their cyclogenesis in the Mediterranean area. In the last chapter the influence of cyclones at least partly originating in Mediterranean on the weather in the Czech Republic is studied.

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O papel dos fluxos de superfície de calor sensível e latente (FCSL) em dois ciclones extratropicais com desenvolvimento distinto na costa do sul do Brasil foi avaliado a partir de simulações numéricas utilizando o modelo de área limitada WRF versão 2.2. Em um dos ciclones, a circulação se originou em baixos níveis e propagou-se para a média troposfera (ciclone 1). No outro ciclone (ciclone 2) a circulação originou-se em níveis médios e propagou-se até a superfície. Foram realizadas simulações numéricas com e sem FCSL para cada um dos ciclones. A trajetória do ciclone 1 foi fortemente alterada na ausência de FCSL, exibindo deslocamento incorreto (para nordeste) e menor tempo de vida. Este comportamento esteve associado às mudanças no padrão de advecção de temperatura em baixos níveis e à diminuição da convergência de massa induzida pelo calor sensível, na ausência de FCSL. No experimento sem FCSL, ocorre também desacoplamento entre o ciclone em superfície e a onda em níveis médios e altos, com consequente enfraquecimento do sistema. O aumento da estabilidade estática e o mecanismo de convergência de Ekman são responsáveis por menor convergência nas regiões frontais na ausência de FCSL. A relação de fase entre os campos de altura geopotencial e temperatura em baixos níveis e o perfil vertical de aquecimento diabático também mostram condições mais favoráveis ao desenvolvimento do ciclone na presença dos FCSL. O ciclone 2 não teve a trajetória alterada entre as duas simulações. A advecção de temperatura e a convergência em baixos níveis devido ao calor sensível foram semelhantes, explicando a similaridade na trajetória nos experimentos com e sem FCSL. A convergência de Ekman diferenciou-se entre as duas simulações, especialmente no final do ciclo de vida do ciclone, mostrando que este processo também altera a intensidade de ciclones fracos. A influência dos FCSL mostrou-se dependente do mecanismo dominante de formação dos ciclones. O ciclone 1, com forçante dinâmica menos intensa, sofreu grandes variações em trajetória e tempo de vida na ausência de FCSL. Já o ciclone 2, sob forçante dinâmica mais definida e intensa, mostrou-se menos dependente dos processos de superfície para o seu deslocamento. Os mecanismos de aprofundamento foram mais intensos no ciclone 1. / The role of latent and sensible heat fluxes (LSHF) between ocean and atmosphere during the development of two extratropical cyclones over the southwestern Atlantic Ocean is analyzed using the WRF (Weather Range and Forecast) Mesoscale Model, version 2.2. In cyclone 1, the circulation has originated in low levels and propagated to the middle troposphere; the cyclone 2s circulation has originated in middle levels propagating towards the surface during its life cycle. The trajectory of cyclone 1 was strongly influenced by the surface heat fluxes, showing an incorrect displacement and a shorter lifetime in the absence of these fluxes. This behavior is associated with changes in low level temperature advection and the reduction of low level mass convergence is induced by sensible heat fluxes from surface. In the absence of LSHF there is also a decoupling of the surface low and the upper level wave, causing the weakening of the system. Without surface fluxes, the higher static stability and the weaker Ekman convergence mechanism are responsible for less convergence in the frontal regions of the cyclone. The lagging of the geopotential wave and the temperature wave in low levels, and the diabatic heating profile in the troposphere also show more favorable conditions to the cyclone deepening in the presence of surface fluxes. The trajectory of cyclone 2 showed no significant modification in the absence of LSHF. The temperature advection field is similar and the low level convergence related to sensible heat fluxes didn´t has an impact on the displacement of this system. The Ekman convergence had smaller magnitude in the no-LSHF simulation, especially in the final stages of the cyclone life cycle, indicating that this mechanism can be important also for the deepening of weak systems and not only for explosive systems, as considered in previous studies. This work shows that the role of the LSHF seems to be dependent on the cyclone development main mechanisms. In cyclone 1, where the dynamic forcings are less intense, the absence of surface fluxes had a great impact on the trajectory, intensity and duration of the system. In cyclone 2, with more intense dynamic forcings, the displacement was less influenced by surface processes. The deepening mechanisms had greater impact on the cyclone 1.