Development Of Extratropical Cyclones Research Articles

Regional assessment of overwash processes in a retrograding sand barrier (Paraíba do Sul River Deltaic Complex, Rio de Janeiro, Brazil)

Storm events are the primary mechanisms for generating overwash along the shoreline. This process occurs when wave runup exceeds the elevation of sandy features, often forming washover deposits. In retrograding barriers, overwash is the main driver of landward migration. Extreme wave energy events can lead to rapid changes in the morphology of these environments. On urbanized coastlines, storm impacts can be catastrophic and result in high reconstruction costs. Understanding the characteristics of storm events and the local morphological characteristics of these sandy features is crucial for risk assessments, hazard mitigation, and coastal area adaptations in the scenario of increasing storm events. The main objective of this study is to analyze the role of overwash processes in the retrogradation of the Quissamã barrier, located in the southern sector of the Paraíba do Sul River Delta Complex (PSRDC), on the coast of Rio de Janeiro. Using data from the global Wave Watch III model, sea warnings issued by the Brazilian Navy, atmospheric pressure charts, and astronomical tides, we identified storm events and mapped the washover fans formed after specific storm events. The washover fans were identified using PlanetScope images. The identified storm events were characterized by waves from the SE-S directions with high peak periods, and mostly occurred during spring tides or transitioning to neap tides. Additionally, the atmospheric pattern for most events was associated with the migration of cold fronts from high to low latitudes, leading to the development of extratropical cyclones. The geometry of the barrier also proved to be an essential morphological pattern. Considering the relative sea level along part of the Brazilian coast has been decreasing over the last 5500 years, storm events and associated processes are crucial for the retrogradation of barriers, maintaining the retrogradational characteristics of this coastal barrier.

Impact of the Gulf Stream front on atmospheric rivers and Rossby wave train in the North Atlantic

The Gulf Stream (GS) ocean front exhibits intense ocean–atmosphere interaction in winter, which has a significant impact on the genesis and development of extratropical cyclones in the North Atlantic. The atmospheric rivers (ARs), closely related with the cyclones, transport substantial moisture from the North Atlantic towards the Western European coast. While the influence of the GS front on extratropical cyclones has been extensively studied, its effect on ARs remains unclear. In this study, two sets of ensemble experiments are conducted using a high-resolution global Community Atmosphere Model forced with or without the GS sea surface temperature front. Our findings reveal that the inclusion of the GS front leads to approximately 25% enhancement of water vapor transport and precipitation associated with ARs in the GS region, attributed to changes in both AR frequency and intensity. Furthermore, this leads to a more pronounced downstream response in Western Europe, characterized by up to 60% (40%) precipitation increases (reductions) around Spain (Norway) for the most extreme events (exceeding 90 mm/day). The influence of the GS front on ARs is mediated by both thermodynamic and dynamic factors. The thermodynamic aspect involves an overall increase of water vapor in both the GS region and Western Europe, promoting AR genesis. The dynamic aspect encompasses changes in storm tracks and Rossby wave train, contributing to downstream AR shift. Importantly, we find the co-occurrence of ARs and the GS front is crucial for inducing deep ascending motion and heating above the GS front, which perturbs the deep troposphere and triggers upper-level Rossby wave response. These findings provide a further understanding of the complex interaction between the oceanic front in the western boundary current regions and extratropical weather systems and the associated dynamics behind them.

How well do forecast models represent observed long‐lived Rossby wave packets during southern hemisphere summer?

AbstractRossby wave packets (RWPs), are atmospheric perturbations linked to the occurrence of extreme weather events such as heatwaves, extratropical cyclone development and other equally destructive phenomena. Under certain circumstances, these packets can last from several days to 2–3 weeks in the atmosphere. Therefore, forecast models should be able to correctly predict their formation and development to enhance extreme weather events prediction from 10 to 30 days in advance. In this study, we assess whether the NCEP and IAP‐CAS sub‐seasonal forecast models can predict the evolution of observed RWPs that last more than 8 days (long‐lived RWPs or LLRWPs) during southern hemisphere summer. Results show that the NCEP (IAP‐CAS) model forecasts LLRWPs that appear eastward (westward) from the observed LLRWPs. Both models forecasted LLRWPs that rapidly lose energy after the 6th–7th lead day of simulation, which could limit LLRWPs prediction to the synoptic time scale. Additionally, both models better forecast LLRWPs when the packets manifest in the eastern Pacific. Southern Annular mode (SAM) and El Niño Southern‐Oscillation (ENSO) do not seem to exert a large influence in the representation of LLRWPs. Nevertheless, during the best LLRWPs forecasts, the observed circulation anomalies signal the manifestation of negative SAM events. In contrast, both forecast models struggle at forecasting LLRWPs when a blocking situation develops to the South of Australia. Lastly, an inactive Madden Julian Oscillation (MJO) seems to favor the development of accurate LLRWPs forecasts, whereas during phases 3, 5 in the NCEP model and 3, 8 for IAP‐CAS, the models struggle at forecasting LLRWPs.

Reduced Sea Ice Enhances Intensification of Winter Storms over the Arctic Ocean

AbstractThe ideal environment for extratropical cyclone development includes strong vertical shear of horizontal wind and low static stability in the atmosphere. Arctic sea ice loss enhances the upward flux of energy to the lower atmosphere, reducing static stability. This suggests that Arctic sea ice loss may facilitate more intense storms over the Arctic Ocean. However, prior research into this possibility has yielded mixed results with uncertain cause and effect. This work has been limited either in scope (focusing on a few case studies) or resolution (focusing on seasonal averages). In this study, we extend this body of research by comparing the intensification rate and maximum intensity of individual cyclones to local sea ice anomalies. We find robust evidence that reduced sea ice in winter (December–March) strengthens Arctic cyclones by enhancing the surface turbulent heat fluxes and lessening static stability while also strengthening vertical shear of horizontal wind. We find weaker evidence for this connection in spring (April–June). In both seasons, lower sea ice concentration also enhances cyclone-associated precipitation. Although reduced sea ice also weakens static stability in September/October (when sea ice loss has been especially acute), this does not translate to stronger storms because of coincident weakening of wind shear. Sea ice anomalies also have little or no connection to cyclone-associated precipitation in these months. Therefore, future sea ice reductions (e.g., related to delayed autumn freeze-up) will likely enhance Arctic cyclone intensification in winter and spring, but this relationship is sensitive to simultaneous connections between sea ice and wind shear.Significance StatementSea ice is a barrier between the ocean and atmosphere, limiting the exchange of energy between them. As the amount of sea ice in the Arctic Ocean declines, the ocean can transfer more heat to the atmosphere above in fall and winter. It is theorized that this extra energy may help intensify storms that pass through the Arctic. We examine individual storms over the Arctic Ocean and what sea ice conditions they experience as they develop. We find that storms intensify more when sea ice is lower than normal in the winter season only. This relationship may contribute to stronger Arctic winter storms in the future, including heavier precipitation and stronger winds (which can enhance wave heights and coastal erosion).

On the Influence of Sea Surface Temperature Distributions on the Development of Extratropical Cyclones

AbstractThe sea surface temperature (SST) distribution can modulate the development of extratropical cyclones through sensible and latent heat fluxes. However, the direct and indirect effects of these surface fluxes, and thus the SST, are still not well understood. This study tackles this problem using idealized channel simulations of moist baroclinic development under the influence of surface fluxes. The model is initialized with a zonal wind field resembling the midlatitude jet and a different SST distribution for each experiment, where the absolute SST, the SST gradient, and the meridional position of the SST front are varied. The surface latent heat flux associated with the absolute SST plays a key role in enhancing the moist baroclinic development, while the sensible heat fluxes associated with the SST gradient play a minor role that can be detrimental for the development of the cyclone. The additional moisture provided by the latent heat fluxes originates from about 1000 km ahead of the cyclone a day prior to the time of the most rapid deepening. When the SST in this region is higher than 16°C, the additional latent heat is conducive for explosive cyclone development. For SSTs above 20°C, the cyclones feature characteristics of hybrid cyclones with latent heat release close to their core, maintaining their intensity for a longer period due to continuous and extensive moisture supply from the surface. A high absolute SST with a weak SST gradient, however, can lead to a delay of the deepening stage, because of unorganized convection at early stages reducing environmental baroclinicity.

A Possible Linkage between Dust Frequency and the Siberian High in March over Northeast Asia

Spring dust frequency in northeast Asia has been investigated using various approaches to understand the mechanisms of dust emission and transport. However, little attention has been paid to the linkage between dust activity and the Siberian High (SH), particularly when the SH pressure system is highly variable. In this study, we characterize the possible physical mechanisms of dust emission and transport associated with the Siberian High Intensity (SHI) and Siberian High Position Index (SHPI) in March using 18 years of ground-based observations and reanalysis data. We found that when the SHI was strong and the SH’s center was farther east (“Strong–East period”), surface and atmospheric temperatures were cooler than when the SHI was weak and the SH’s center was farther west (“Weak-West period”), due to anomalous anticyclonic pressure and strong easterlies. As a result, a reduction in the meridional temperature gradient in the lower atmosphere suppressed dust emission and transport, due to stagnant atmospheric conditions. This anomalous anticyclonic pressure in the Strong-East case seems to reduce the development of extratropical cyclones (ETC) in northeast Asia, leading to a less effective dust transport. A case study with composite analysis also showed a similar physical mechanism: stagnant air accompanying weakened westerlies in the Strong-East period suppressed dust transport to South Korea. Our findings reveal that the intensity and position of the SH can be utilized to identify spring transboundary air pollutants in northeast Asia.

Environmental control of tropical, subtropical, and extratropical cyclone development over the North Atlantic Ocean: Idealized numerical experiments

The North Atlantic Ocean in autumn is characterized by a variety of cyclone activity: tropical, subtropical, and extratropical cyclones are meridionally distributed from low to high latitudes, and cyclones are more active in the western part than in the eastern part. To examine to what degree the environmental fields explain the geographical distribution of the various cyclones, idealized numerical experiments are conducted using climatological environmental fields at different longitudes and latitudes. The experiments qualitatively reproduce the geographical distribution of development and types of cyclones, which enables an intercomparison of different types of cyclones on the basis of their structure, energy budget analysis, and sensitivity experiments. It is notable that subtropical cyclones can develop spontaneously in the climatological environment which does not have an upper‐tropospheric disturbance in the initial fields. While the simulated subtropical cyclones are sensitive to initial conditions, some of them have structures that are in good agreement with those of observed subtropical cyclones: a shallow warm‐core structure, concentrated convection near the cyclone centre embedded in synoptic‐scale cloud on the north and east sides, and a narrow mid‐tropospheric potential vorticity anomaly near the cyclone centre under a wide upper‐tropospheric anomaly on the west side. The subtropical cyclones exhibit characteristics intermediate between those of tropical cyclones and extratropical cyclones, notably multi‐scale structures with tropical characteristics on a small scale embedded in extratropical characteristics on a large scale.

On the relationship between atmospheric water vapour transport and extra-tropical cyclones development

In this study we seek to investigate the role of atmospheric water vapour on the intensification of extra-tropical cyclones over the North Atlantic Ocean and more specifically to investigate the linkage between atmospheric rivers' conditions leading to the explosive development of extra-tropical cyclones. Several WRF-ARW simulations for three recent extra-tropical storms that had major negative socio-economic impacts in the Iberian Peninsula and south-western Europe (Klaus, 2009; Gong, 2013 and Stephanie, 2014) are performed in which the water vapour content of the initial and boundary conditions are tuned. Analyses of the vertically integrated vapour transport show the dependence of the storms' development on atmospheric water vapour. In addition, results also show changes in the shape of the jet stream resulting in a reduction of the upper wind divergence, which in turn affects the intensification of the extra-tropical cyclones studied. This study suggests that atmospheric rivers tend to favour the conditions for explosive extra-tropical storms' development in the three case studies, as simulations performed without the existence of atmospheric rivers produce shallow mid-latitude cyclones, that is, cyclones that are not so intense as those on the reference simulations.

A Role of the Yellow and East China Seas in the Development of Extratropical Cyclones in Winter

Abstract To investigate whether the relatively warm Yellow and East China Seas play an active role in the deepening of extratropical cyclones over East Asia during winter, surface wind vectors downloaded from the Quick Scatterometer (QuikSCAT) website are used to compute the standard deviation of surface vorticity at ¼° resolution. In addition, a regional numerical atmospheric model is adopted to find atmospheric and/or oceanic conditions favorable for development of extratropical cyclones over the study area. These satellite-derived and modeled vorticity fields demonstrate that, on average, extratropical cyclone activity is moderate over the warm Yellow and East China Seas. This is because enhanced lower-level baroclinicity over these ocean areas is transferred as far as the shelf break of the East China Sea by strong northwesterly surface winds. Based on the numerical model results, the weak northwesterly surface wind condition is required for enhancing lower-level baroclinicity over the Yellow and East China Seas. This baroclinicity may contribute to enhancing cyclone development near Japan, with a simultaneous increase of lower-level baroclinicity over the Sea of Japan.

A diagnosis of warm‐core and cold‐core extratropical cyclone development using the Zwack–Okossi equation

AbstractIn this study, the development of a warm‐core and cold‐core extratropical cyclone over North Atlantic is examined. The geostrophic relative vorticity tendency used to diagnose the development is calculated utilizing the so‐called extended form of the Zwack–Okossi development equation. In both cases, the cyclonic vorticity advection acted to develop the system, but warm‐air advection (diabatic heating) made the largest contribution to explosive development in the cold‐core (warm‐core) case. Further, a vertical cross section of the temperature advection in the warm‐core case reveals that the largest values of this contributor are located far and ahead of the cyclone center. Copyright © 2009 Royal Meteorological Society

Simulations of the Extratropical Transition of Tropical Cyclones: Phasing between the Upper-Level Trough and Tropical Cyclones

Abstract Whether the tropical cyclone remnants will become a significant extratropical cyclone during the reintensification stage of extratropical transition is a complex problem because of the uncertainty in the tropical cyclone, the midlatitude circulation, the subtropical anticyclone, and the nonlinear interactions among these systems. In a previous study, the authors simulated the impact of the strength of the midlatitude circulation trough without changing its phasing with the tropical cyclone. In this study, the impact of phasing is simulated by fixing the initial position and amplitude of the midlatitude trough and varying the initial position of the tropical cyclone. The peak intensity of the extratropical cyclone following the extratropical transition is strongly dependent on the phasing, which leads to different degrees of interaction with the midlatitude baroclinic zone. Many aspects of the simulated circulation, temperature, and precipitation fields appear quite realistic for the reintensifying and dissipating cases. Threshold values of various parameters in quadrants near and far from the tropical cyclone are extracted that discriminate well between reintensifiers and dissipators. The selection and distribution of threshold parameters are consistent with the Petterssen type-B conceptual model for extratropical cyclone development. Thus, these simulations suggest that phasing between the tropical cyclone and the midlatitude trough is a critical factor in predicting the reintensification stage of extratropical transition.

Analysis of Upper Pressure Patterns of Unusual Development of Extratropical Cyclone

Analysis of Upper Pressure Patterns of Unusual Development of Extratropical Cyclone

Simulations of the Extratropical Transition of Tropical Cyclones: Contributions by the Midlatitude Upper-Level Trough to Reintensification

Abstract The extratropical cyclone development processes during the reintensification stage of an extratropical transition from a tropical cyclone (TC) are described using numerical simulations. Three control simulations without a tropical cyclone present examine the extratropical cyclogenesis associated with upper-level troughs that are characterized as weak, moderate, and strong. When no tropical cyclone is included in the simulation, the minimum surface pressures attained with the weak, moderate, and strong troughs are 1003, 991, and 977 mb, respectively. In all three cases, the low tilts northwestward with height during intensification, and the rainfall pattern and eventual occlusion are representative of classic extratropical cyclone development. The interactions of a tropical cyclone with each of the three midlatitude circulation patterns are compared with the control simulations to illustrate the contributions to the extratropical transition of the tropical cyclone. In the three trough-with-TC case...

Extratropical Transition of Western North Pacific Tropical Cyclones: Midlatitude and Tropical Cyclone Contributions to Reintensification

Abstract This study of extratropical transition of western North Pacific tropical cyclones (TCs) addresses the reintensification stage during which the TC remnants develop as an extratropical cyclone. The hypothesis examined here is that reintensification depends on the interaction between the midlatitude circulation contributions from mid- and upper-level dynamic processes, low-level thermal processes from the decaying TC, and upper-level outflow characteristics from the decaying TC. Reintensification occurs when the combination of the dynamic and thermodynamic processes define a region that is favorable for extratropical cyclone development. The midlatitude circulation contribution to reintensification is characterized by comparing a control forecast made with an atmosphere-only version of the Coupled Ocean–Atmosphere Mesoscale Prediction System with a simulation in which the TC has been removed (NOTC). The midlatitude contribution is favorable if a significant extratropical cyclone forms in the NOTC si...

The Importance of the Horizontal Distribution of Heating during Extratropical Cyclone Development

Abstract Diagnostic and modeling results reveal that atmospheric heating typically acts to intensify extratropical cyclones. In addition, both the Petterssen–Sutcliffe and Zwack–Okossi development equations reveal that this relationship depends on the proportionality that exists between surface geostrophic vorticity tendency and the negative of the horizontal Laplacian of atmospheric heating. Because of this Laplacian relationship, the impact of a heating field with a given magnitude and vertical distribution depends on its horizontal distribution. This paper will show how horizontal heating distributions that differ by relatively small amounts over their entire extent can yield vorticity tendency responses that could contribute to either development or decay of an underlying cyclone.

The Role of diabatic heating, torques and stabilities in forcing the radial- vertical circulation within cyclones part iii: case study of lee-side cyclones

Two phases of extratropical cyclone development identified in previous mass and angular momentum budget studies have been confirmed through the numerical simulations of the azimuthally-averaged mass-weighted radial motion within two leeside cyclones: a Mediterranean and an Alberta cyclone. In the Mediterranean cyclone, a moist baroclinic phase is identified with inward (outward) mass and storm angular momentum transport in the lower (higher) value isentropic layers. The mass and storm angular momentum are then transported diabatically from lower to higher value isentropic layers through latent heat release. In addition, storm angular momentum is transferred horizontally across the inclined isentropic surfaces by pressure stresses due to the paired negative and positive pressure torque in lower and higher value isentropic layers respectively. A dry-leeside baroclinic phase is identified in the early stage of the Alberta cyclone with inward (outward) transport of mass and angular momentum in the higher (lower) value isentropic layers. The redistribution of angular momentum is associated with the virtual transfer by torques. A transition from dry to moist phase is identified in the life cycle of the Alberta cyclone.

A Comparison of Extended and Quasigeostrophic Dynamics for a Case of Small–Rossby Number Extratropical Cyclone Development

Abstract This note compares the extended (EXT) and quasigeostrophic (QG) dynamics of a small–Rossby number extratropical cyclone using the Zwack–Okossi (ZO) equation. Applied to a cyclone that occurred on 8–9 November 1985 over the North Atlantic Ocean, results show that although differences exist, both the EXT and QG forms of the ZO equation provide very adequate estimates of the large-scale forcing processes associated with this case.

The dry intrusion perspective of extra‐tropical cyclone development

AbstractThe dry intrusion is a coherent region of air descending from near tropopause‐level. It often has a clear signature in satellite imagery, especially in the water vapour channel, where it is seen as a ‘dark zone’. Parts of dry intrusions are characterised by high potential vorticity and, upon approaching a low‐level baroclinic zone, rapid cyclogenesis may be expected to ensue. The leading edges of dry intrusions are defined by cold θw‐fronts (moisture fronts). In some places the dry intrusion undercuts rearward‐ascending warm air to give an ana‐cold front. In other places it overruns the warm air to produce an upper cold θw‐front in advance of the surface cold frontHere the dry intrusion is associated with the generation of potential instability and its eventual release as showers or thunderstorms. Identification of dry intrusions provides the forecaster with additional nowcasting evidence that is especially helpful when issuing severe weather warnings. The identification of water vapour dark zones associated with dry intrusions can also form the basis of methods for validating NWP models. Through their relationship to high potential vorticity, they can provide guidance for bogussing NWP models in situations of potentially severe weather. This article provides an introduction to the structure and behaviour of dry intrusions and their relationship to other aspects of extra‐tropical cyclones. Copyright © 2004 Royal Meteorological Society

A Composite Diagnosis of Synoptic-Scale Extratropical Cyclone Development over the United States

This paper presents a composite diagnosis of synoptic-scale forcing mechanisms associated with extratropical cyclone evolution. Drawn from 12 cyclone cases that occurred over the continental United States during the cool season months, the diagnosis provides a “climatology” of development mechanisms for difference categories of cyclone evolution ranging from cyclone weakening through three stages of cyclone intensification. Computational results were obtained using an “extended” form of the Zwack–Okossi equation applied to routine upper-air and surface data analyzed on a 230 km × 230 km grid. Results show that cyclonic vorticity advection, which maximizes in the upper troposphere, was the primary contributor to cyclone development regardless of the stage of development. A second consistent contributor to development was latent heat release. Horizontal temperature advection, often acknowledged as a development mechanism, was found to contribute to development only during more intense stages. During weakening and weaker development stages, temperature advection opposed development, as the warm-air advection invariably found at upper levels was dominated by cold air advection in the lower half of the sphere. In the more intense stages, development was moderated by dry-adiabatic cooling associated with the ascending vertical motions.

An Analytical Model Describing the Basic Structure and Development of Mature Extratropical Cyclones

Understanding the basic structure and development of extratropical cyclones is still quite important in modern meteorology. For this purpose a simple analytical model has been developed that is qualitative as well as quantitative and also reveals modern concepts like the frontal fracture and conveyor belts. The model solution can be derived from the quasigeostrophic equations of the two-layer model with a few additional assumptions.