Extreme Extratropical Cyclones Research Articles

Development of a catalogue of damage in Portuguese forest associated with extreme extratropical cyclones

In European forests, extreme wind events associated with severe extratropical cyclones are considered the main abiotic agent of forest vulnerability, leading to high economic losses in forests due to damage caused by the uprooting of trees and trunk breaks. Despite the importance recognized to severe cyclones and associated extreme phenomena, the impact on forest stocks is not always properly reported, leading to underestimation in the perception of losses, with direct consequences on forest governance decisions. This is particularly true in countries where other agents traditionally have a high impact, such as the countries under the influence of the Mediterranean, where wildfire is a recurrent menace with devastating effects. This work characterizes the situation observed in Portugal and presents the methodology followed to obtain information about forest damages and the procedure to identify the extreme extratropical cyclones responsible for those damages. As an example, available information and the recording of damage occurring in the Portuguese forest in winter 2017–2018 are presented and discussed. The study shows how difficult and demanding it is to obtain past information about the damage. In addition, there is high uncertainty about the precise identification of the event that caused the damage, as field records often occur several days or even weeks after the storm. To reduce the constraints, it is proposed to use a model whose skeleton of information has been designed to obtain useful information from traditional registries. The proposed model is useful for the characterization of losses and to support national policies to reduce the impact of damage associated with extreme wind events. The design of the catalogue can be used for recording information at the stand scale level by stakeholders and ensure compatibility with international databases for updating information purposes.

Inter-population synchrony in adult survival and effects of climate and extreme weather in non-breeding areas of Atlantic puffins

Seabirds are undergoing drastic declines globally and spend the non-breeding season at sea, making it challenging to study the drivers of their survival. Harsh weather and changes in climate conditions can have large impacts on seabird population dynamics through increased mortality. The intensity and persistence of extreme events are forecasted to increase with global warming. As shared conditions can induce population synchrony, multi-population studies of key demographic parameters are imperative to explore the influence of climate change. We used long-term mark-recapture data and position data to determine non-breeding stop-over areas of 5 Atlantic puffin (Fratercula arctica) populations over a latitudinal gradient in the Northeast Atlantic (56°11’-70°23’N). We investigated synchrony in adult survival in relation to shared stop-over areas. We quantified effects of extreme extra-tropical cyclones (ETCs) specific to populations’ stop-over areas and the North Atlantic Oscillation on adult survival. Populations with overlapping stop-over areas exhibited temporal synchrony in survival rates. Winter ETCs negatively influenced survival in 1 population, which was the one most exposed to extreme weather, but did not directly influence adult survival in the other 4 populations. Synchrony among populations with shared stop-over areas highlights the importance of these areas for adult survival, a key life-history rate. However, extreme weather was not identified as a driving factor for the majority of study populations. This suggests other factors in these areas, likely related to bottom-up trophic interactions, as environmental drivers of synchrony in the survival of Atlantic puffins.

Pseudo-climate modelling study on projected changes in extreme extratropical cyclones, storm waves and surges under CMIP5 multi-model ensemble: Baltic Sea perspective

In order to estimate the possible parameters of future extreme extratropical cyclones (ETCs), a pseudo-climate modelling study of three historical storms originating from the Atlantic Ocean and one from the Black Sea area was performed using multi-model approach considering IPCC emission scenarios RCP4.5 and RCP8.5 for the twenty-first century. Applying Weather Research and Forecasting atmosphere model (WRF), Finite Volume Community Ocean model (FVCOM-SWAVE) and the Simulating WAves Nearshore (SWAN) model, the changes in initial conditions in atmospheric air temperature, sea surface temperature and relative humidity were considered on the basis of 14 CMIP5 general circulation models ensemble. According to the future scenario results, no notable changes are expected in minimum atmospheric pressure within the ETCs of the future; however, the low pressure area was slightly larger and the strong wind zone was extending further south with greater peak wind speeds in the future (year 2081–2100) simulations. This, in turn, yielded a small surge height increase at Parnu under RCP4.5 scenario; however, under RCP8.5 scenario the surge increase was up to 22–59 cm. Westerly approaching ETCs will bring more precipitation to the Baltic Sea area in the (warmer) future. In case of a southerly cyclone, the results were more mixed. An insignificant increase in wave heights during extreme storm conditions occurred. Although RCP8.5 future scenario is usually considered as unrealistic, the results of this study still suggest that the extreme ETCs may become more dangerous in the future, although probably not as certainly as tropical cyclones.

Waves and Swells in High Wind and Extreme Fetches, Measurements in the Southern Ocean

The generation and evolution of ocean waves by wind is one of the most complex phenomena in geophysics, and is of great practical significance. Predictive capabilities of respective wave models, however, are impaired by lack of field in situ observations, particularly in extreme Metocean conditions. The paper outlines and highlights important gaps in understanding the Metocean processes and suggests a major observational program in the Southern Ocean. This large, but poorly investigated part of the World Ocean is home to extreme weather around the year. The observational network would include distributed system of buoys (drifting and stationary) and autonomous surface vehicles (ASV), intended for measurements of waves and air-sea fluxes in the Southern Ocean. It would help to resolve the issues of limiting fetches, extreme Extra-Tropical cyclones, swell propagation and attenuation, wave-current interactions, and address the topics of wave-induced dispersal of floating objects, wave-ice interactions in the Marginal Ice Zone, Metocean climatology and its connection with the global climate.

Significantly increased extreme precipitation expected in Europe and North America from extratropical cyclones

For the Northern Hemisphere extratropics, changes in the mid-latitude storm tracks are key to understanding the impacts of climate warming, but projections of their future location in current climate models are affected by large uncertainty. Here, we show that in spite of this uncertainty in the atmospheric circulation response to warming, by analysing the behaviour of the storms (or extratropical cyclones) themselves, projections of change in the number of the most intensely precipitating extratropical cyclones are substantial and consistent across models. In particular, we show large increases in the frequency of extreme extratropical cyclones (those above the present day 99th percentile of precipitation intensity) by the end of the century. In both Europe and North America, these intensely precipitating extratropical cyclones are projected to more than triple in number by the end of the century unless greenhouse gas emissions are mitigated. Such changes in extratropical cyclone behaviour may have major impacts on society given intensely precipitating extratropical cyclones are responsible for many large-scale flooding events, and associated severe economic losses, in these regions.

Rapid wave modeling of severe historical extratropical cyclones off the Northeastern United States

Storms play a significant role in coastal zone hydrodynamics, morphodynamics and flooding. The US Northeast is influenced by both extratropical (e.g. nor'easters) and tropical cyclones, which produce extreme winds, storm surges and waves, and as a result erosion and coastal damage. In this study, simulations of 100 of the most severe historical extratropical cyclones in this region were used to evaluate a new, rapid numerical wave model that is a candidate model for ensemble forecasting and hazard assessment. The main tool used was a coupled hydrodynamic-wave model, forced by wind and pressure from preexisting meteorological reanalysis datasets. The coupled models were the Stevens institute Estuarine and Coastal Ocean hydrodynamic Model (sECOM) and the Mellor et al. (2008) (hereafter MDO) wave model, and includes several important physical interactions (e.g. wave setup). Wave model results were compared to offshore buoy observational data from 1980 to 2012, and a sensitivity analysis was used to evaluate important model parameters. Results show that the wave model is very accurate for wave height (Hs), with an average RMSE of 0.92 m and skill ranging from 0.7 to 0.9. Results were less accurate for average wave period (Tavg), with an average RMSE of 1.97 s and skill ranging from 0.5 to 0.7. However, a comparison with a more widely used existing rapid wave model shows a substantial improvement over those Tavg results. Large waves approach the coast in Massachusetts Bay during extratropical cyclones, leading to important wave impacts including setup, and modeled storm surge is shown to have good accuracy and no bias at Boston. These results demonstrate the strengths and weaknesses of the model for rapid simulations of waves under history's most extreme extratropical cyclones, and the evaluation results and sensitivity analysis are used to suggest its appropriate uses and possible avenues of improvement.

Projected Significant Increase in the Number of Extreme Extratropical Cyclones in the Southern Hemisphere

Extratropical cyclones are responsible for much of the extreme weather in the midlatitudes; thus, how these cyclones may change under increasing greenhouse gas forcing is of much general interest. Previous studies have suggested a poleward shift in the location of these cyclones, but how the intensity may change remains uncertain, especially in terms of maximum wind speed. In this study, projected changes in extreme cyclones in the Southern Hemisphere, based on 26 models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5), are presented. Multiple definitions of extreme cyclones have been examined, including intensity exceeding constant thresholds of sea level pressure perturbations, 850-hPa vorticity, and 850-hPa winds, as well as variable thresholds corresponding to a top-5 or top-1 cyclone per winter month in these three parameters and the near-surface winds. Results presented show that CMIP5 models project a significant increase in the frequency of extreme cyclones in all four seasons regardless of the definition, with over 88% of the models projecting an increase. Spatial patterns of increase are also consistent, with the largest increase projected between 45° and 60°S, extending from the South Atlantic across the south Indian Ocean into the Pacific. The projected increases in cyclone statistics are consistent with those in Eulerian statistics, such as sea level pressure (SLP) variance. However, while the projected increase in SLP variance can be linked to increase in the mean available potential energy (MAPE), the increases in cyclone statistics are not well correlated with those in MAPE.

Spatio-temporal modelling of extreme storms

A flexible spatio-temporal model is implemented to analyse extreme extra-tropical cyclones objectively identified over the Atlantic and Europe in 6-hourly re-analyses from 1979-2009. Spatial variation in the extremal properties of the cyclones is captured using a 150 cell spatial regularisation, latitude as a covariate, and spatial random effects. The North Atlantic Oscillation (NAO) is also used as a covariate and is found to have a significant effect on intensifying extremal storm behaviour, especially over Northern Europe and the Iberian peninsula. Estimates of lower bounds on minimum sea-level pressure are typically 10-50 hPa below the minimum values observed for historical storms with largest differences occurring when the NAO index is positive.

Medium-Range Ensemble Sensitivity Analysis of Two Extreme Pacific Extratropical Cyclones

Abstract In this study, ensemble sensitivity analysis has been applied to examine the evolution of two extreme extratropical cyclones over the Pacific. Sensitivity using, as forecast metrics, forecast cyclone minimum pressure and location, as well as principal components (PCs) of the leading EOFs in forecast SLP variations near the cyclone center, has been computed for medium-range forecasts of up to 7.5 days. Results presented here show that coherent sensitivity patterns can be tracked from the forecast validation time back in time to at least day −6, with the sensitivity signal exhibiting downstream development characteristics in most cases. Comparing the different forecast metrics, sensitivity patterns derived from the PCs of the leading EOFs in forecast SLP variations are apparently more coherent than those derived from cyclone parameters. To test whether the linear sensitivity analyses provide quantitatively accurate guidance under the highly nonlinear evolution of the atmospheric flow, perturbed initial condition experiments have been conducted using initial condition perturbations derived based on ensemble sensitivity. Results of this study suggest that in the medium range, perturbations derived from cyclone parameters are quite effective in modifying the evolution of the cyclones out to 5.5 days, but are largely ineffective for 7.5-day forecasts. On the other hand, perturbations derived based on the PCs of the leading EOFs are still quite effective in modifying forecast cyclone location out to 7.5 days. These results suggest that EOF-based sensitivities perform better than cyclone parameter-based sensitivities in the medium range.

Fred Sanders' Roles in the Transformation of Synoptic Meteorology, the Study of Rapid Cyclogenesis, the Prediction of Marine Cyclones, and the Forecast of New York City's “Big Snow” of December 1947

Abstract Fred Sanders' career extended over 55 yr, touching upon many of the revolutionary transformations in the field of meteorology during that period. In this paper, his contributions to the transformation of synoptic meteorology, his research into the nature of explosive cyclogenesis, and related advances in the ability to predict these storms are reviewed. In addition to this review, the current status of forecasting oceanic cyclones 4.5 days in advance is presented, illustrating the progress that has been made and the challenges that persist, especially for forecasting those extreme extratropical cyclones that are marked by surface wind speeds exceeding hurricane force. Last, Fred Sanders' participation in a forecast for the historic 1947 snowstorm (that produced snowfall amounts in the New York City area that set records at that time) is reviewed along with an attempt to use today's operational global model to simulate this storm using data that were available at the time. The study reveals the predictive limitations involved with this case based on the scarcity of upper-air data in 1947, while confirming Fred Sanders' forecasting skills when dealing with these types of major storm events, even as a young aviation forecaster at New York's LaGuardia Airport.