Intense Cyclone Activity Research Articles

ПРОЯВЛЕНИЯ ТИПОВ ЭЛЬ-НИНЬО И ЛА-НИНЬЯ В ИНТЕНСИВНЫХ ЦИКЛОНАХ ЧЕРНОМОРСКО-СРЕДИЗЕМНОМОРСКОГО РЕГИОНА

The extreme phases of the El Niño – Southern oscillation (ENSO) are accompanied by dangerous and destructiveweather events that are difficult to predict. At the same time, El Niño and La Niña events that form it have ambiguous features, andconsidering the classification of these events into different types provides a better understanding of the patterns of their regional manifestations. The aim of the paper is to study the manifestations of classified types of ENSO events in intense cyclonic activity in the Black Sea–Mediterranean region. The analysis was carried out for cyclones identified with the use of the NCEP/NCAR reanalysisdata on the geopotential height of 1000 hPa for the period 1951-2017 and exceeding the 75th percentile in intensity (average depth).It is shown that responses to different ENSO types from September to April differ in sign for the Western Mediterranean, especiallyin winter months, and in intensity (significance) for the Eastern Mediterranean and the Black Sea region. More consistent responsesare observed in the inter-season. In the Western Mediterranean, the frequency of deep cyclones decreases for both types of La Niñain autumn and in January, especially for the central La Niña type. For El Niño types, the frequency of deep cyclones significantlyincreases mainly in spring, especially for the central El Niño type in the Eastern Mediterranean and for the eastern El Niño type in theBlack Sea region. Different responses to El Niño types occur in the Mediterranean region and the Black Sea region due to the shift ofstorm tracks of Scandinavian cyclones to the Black Sea region. The results obtained show the probability of monthly anomalies in thefrequency of deep cyclones of the cold half-year in the Black Sea–Mediterranean region taking into account the type of El Niño/LaNiña events, and contribute to the development of a seasonal regional forecast of weather and climatic anomalies associated withdeep cyclones, with a lead time corresponding to the evolution time of events.

Meteorological situations that generated exceptional discharges along the Danube River. (Case study- the situation of April 2006).

For Europe, the undisputed importance of the Danube can be rendered by some general data: Its hydrographic basin surface exceeds 817000 km2, i.e. about 10% of that of the continent, its length is 2857 km and its mean multiannual discharge is about 6500 m3/s, thus ranking second to Volga river. Romania is the country with the largest surface situated within Danube’s basin (97.4%), representing 29% of Danube’s hydrographic basin. The water resources of the Danube in Bazias section amount to 173 billion m3, 30 billion m3 of which are technically usable resources.Our analysis aimed at determining those complex meteorological situations at the European continent level that triggered exceptional discharges along the Danube river, resulting in severe flooding, causing in turn heavy damages, fatalities, population evacuations and considerable rehabilitation costs. A complex analysis was performed, of statistical-synoptic type and those complex meteorological situations were identified that determined the occurrence of such disasters. Discharges and levels of the Danube were used along the whole measuring period, data from the archive of the National Meteorological Administration, and data, map and image archives from Wetterzentrale (Kartenarchiv, NCEP, NCAR, AVN etc.). The complex meteorological situations at the level of the European continent that triggered exceptional discharges along the Danube correlate with intense cyclonic activity, of both the Icelandic and the Mediterranean cyclones, with the negative phase of the North-Atlantic Oscillation and with decreasing or minimum solar activity (according to data from NOAA's Space Environment Center). The most disastrous floods occurred in the spring of 2006. The paper is important for meteorologists, in their weather forecasting activity, for hydrologists, in their hydrological forecasting and for the institutions involvedin flood management.

Wind and wave extremes associated with tropical‐like cyclones in the Mediterranean basin

AbstractThe Mediterranean Sea is a basin with intense cyclonic activity. The multidimensional impact of such weather events on human life enhances the need and highlights the importance for further research. In this framework, there is a great interest for the development, evolution and impacts of tropical‐like cyclones in the basin (medicanes). Besides their scientifically appealing features, their extremity and presence in a populated region with intense coastal activities can lead to social, natural and financial implications. The purpose of this work is the characterization of the risk exposed areas by this type of cyclones alongside their intensity and recurrence interval in terms of wind and wave parameters. In order to consider more than the strict and direct effects of the medicane vicinity, the extremes have been studied in radii greater than the typical cyclonic one and during all stages of the cyclone lifecycle. A high‐resolution, wind‐wave coupled modelling system is employed for the simulation of documented medicanes during a 25‐year period. Results from both the atmospheric and wave model are processed while different extreme indices and extreme value methodologies are utilized for the quantification of their likelihood of occurrence. It is found that risk exposed areas are mainly located in central and Western Mediterranean with wind and wave characteristics to have similar spatial distributions. Higher frequency and extreme values are present in the south of France (Gulf of Lion). In addition to the scientific interest regarding the results of the present study, useful information can be extracted in different sectors such as transportation routes, offshore economic activities, civil protection, early warning systems and reinsurance.

Квазипериодическая изменчивость общей и интенсивной циклонической активности в Черноморском регионе в 1951-2017 гг

Квазипериодическая изменчивость общей и интенсивной циклонической активности в Черноморском регионе в 1951-2017 гг

Intense Cyclones in the Black Sea Region: Change, Variability, Predictability and Manifestations in the Storm Activity

Cyclonic activity in the midlatitudes is a form of general atmospheric circulation, and the most intense cyclones are the cause of hydrometeorological anomalies that lead to economic damage, casualties and human losses. This paper examines the features of variability of intense cyclonic activity in the Black Sea region and the examples of their regional manifestations in the storm types. Based on 6-hourly NCEP/NCAR reanalysis data on 1000 hPa geopotential height fields with 2° × 2° spatial resolution and using the methodology by M.Yu. Bardin, objective data were obtained for the identification and estimation of the frequency of deep cyclones (reaching 0.75 and 0.95 quantiles by intensity and depth—intense and extreme cyclones, respectively) for the Black Sea region during the period 1951–2017. Additionally, a specific methodology of more precise cyclone identification based on spherical spline interpolation was successfully applied, and then the two methodologies were compared. The key point of the study is the following: In the background of negative significant linear trends and interdecadal variability (period of about 35 years), typical scales of their interannual variability on the periods of about 2.5–3.5 and 6–8 years were identified. These periods coincide with the time scales of the North Atlantic Oscillation and El Nino–Southern Oscillation, providing an outlook for further study of the patterns of their connection. Besides, seasonal forecasts of frequency of intense cyclones in the Black Sea region were successfully modeled using an artificial neural network technique. Finally, the case studies of regional manifestations of deep cyclones in the types of storms in the northern Black Sea coast revealed substantial differences in the location of deep centers of cyclones and storm tracks associated with the large-scale pressure fields.

A Physically Based Climatology of the Occurrence and Intensification of Australian East Coast Lows

AbstractThe subtropical part of the eastern Australian seaboard experiences intense cyclonic activity. The severe damage caused by the intense storms in the region, known as east coast lows (ECLs), has motivated a number of recent studies. Cyclones in this region appear to be driven by a combination of different (barotropic and baroclinic) formation mechanisms, consistent with the view emerging in the last decades that cyclones span a continuous spectrum of dynamical structures, with the barotropically driven tropical cyclone and the baroclinically driven extratropical cyclone being only the extremes of such a spectrum. In this work we revisit the climatology of cyclone occurrence in the subtropical east coast of Australia as seen in a global reanalysis, systematically applying classification criteria based on the cyclone vertical structure and thermal core. Moreover, we investigate the underlying processes driving the cyclone rapid intensification by means of an atmospheric limited-area energetics analysis. We show that ECLs have different spatial patterns according to the cyclone thermal structure, with the fraction of hybrid cyclones being larger toward the tropics and closer to the coast. Moreover, we find that explosively deepening cyclones in this region are driven by a different combination of processes with respect to the global case, with barotropic processes in the surrounding environment having a more dominant role in the energetics of cyclone rapid intensification. The findings of this work contribute to understanding the physical processes underlying the formation and intensification of Australian east coast lows and the associated coastal damage and risk.

Sea Surface Cooling Induced by Extratropical Cyclones in the Subtropical North Pacific: Mechanism and Interannual Variability

AbstractThe influence of extratropical cyclones on the ocean is examined with a focus on the North Pacific subtropical front (STF), which is a zone of high sea surface temperature (SST) gradients located approximately 25–30°N. The STF becomes most pronounced and susceptible to frequent passages of cyclones in spring. Satellite observations reveal a significant decrease in SST concurrent with cyclone passage along the STF. The SST decreases for approximately 2 days and then gradually recovers over approximately 5 days. The magnitude of the cooling is approximately 0.4 °C. The ocean reanalysis data show a similar surface cooling with a deepening of the mixed layer. The cooling seems to reach the seasonal thermocline and persist there for more than a week. A cyclone over the STF is a subsynoptic cyclone accompanied by a larger synoptic high to the northwest of the low. The surface cooling is mainly attributable to the decrease in shortwave radiation due to the cloud band of the low and the increases in the latent heat and the ocean entrainment, which are associated with intensified northerly winds between the low‐ and high‐pressure systems. The STF varies in strength on interannual timescales in response to the western Pacific pattern, changing the baroclinicity of the overlying atmosphere and the activity of the cyclones. The intense cyclone activity weakens the seasonal SST warming in spring. It is suggested that the cyclones affect the variability of not only the mixed layer but also the seasonal thermocline.

Trends of intense cyclone activity in the Arctic from reanalyses data and regional climate models (Arctic-CORDEX)

The ability of state-of-the-art regional climate models (RCMs) to simulate the trends of intense cyclone activity in the Arctic is assessed based on an ensemble of 13 simulations from 11 models from the Arctic-CORDEX initiative. Some models employ large-scale spectral nudging techniques. Cyclone characteristics simulated by the ensemble in winter and summer are compared with the results from four reanalyses (ERA-Interim, NCEP-CFSR, NASA-MERRA2 and JMA-JRA55) in winter and summer for 1981-2010 period.

Tropical cyclone activity in global warming scenario

Research efforts focused on assessing the potential for changes in tropical cyclone activity in the greenhouse-warmed climate have progressed since the IPCC assessment in 1996. Vulnerability to tropical cyclones becoming more pronounced due to the fastest population growth in tropical coastal regions makes it practically important to explore possible changes in tropical cyclone activity due to global warming. This paper investigates the tropical cyclone activity over whole globe and also individually over six different ocean basins. The parameters like storm frequency, storm duration, maximum intensity attained and location of formation of storm have been examined over the past 30-year period from 1977 to 2006. Of all, the north Atlantic Ocean shows a significant increasing trend in storm frequency and storm days, especially for intense cyclones. Lifetime of intense tropical cyclones over south Indian Ocean has been increased. The intense cyclonic activity over north Atlantic, south-west Pacific, north and south Indian Ocean has been increased in recent 15 years as compared to previous 15 years, whereas in the east and west-north Pacific it is decreased, instead weak cyclone activity has been increased there. Examination of maximum intensity shows that cyclones are becoming more and more intense over the south Indian Ocean with the highest rate. The study of the change in the cyclogenesis events in the recent 15 years shows more increase in the north Atlantic. The Arabian Sea experiences increase in the cyclogenesis in general, whereas Bay of Bengal witnesses decrease in these events. Shrinking of cyclogenesis region occurs in the east-north Pacific and south-west Pacific, whereas expansion occurs in west-north Pacific. The change in cyclogenesis events and their spatial distribution in association with the meteorological parameters like sea surface temperature (SST), vertical wind shear has been studied for Indian Ocean. The increase in SST and decrease in wind shear correspond to increase in the cyclogenesis events and vice versa for north Indian Ocean; however, for south Indian Ocean, it is not one to one.

Spatio-temporal variability in macroalgal assemblages of American Samoa

Tribollet A.D., Schils T. and Vroom P.S. 2010. Spatio-temporal variability in macroalgal assemblages of American Samoa. Phycologia 49: 574–591. DOI: 10.2216/09-63.1Spatial and temporal variability of relative abundance of macroalgae at the genus and functional group levels was examined at 14 m depth across the six islands of American Samoa between 2004 and 2006. Diversity of common macroalgae was high with 54 taxa (50 genera and four algal functional groups) identified from sampled quadrats. The highest taxon richness (33) was found at the largest island, Tutuila. Crustose coralline algae, mixed turf algal assemblages, and the chlorophyte Halimeda were ubiquitous across all islands. Other algal genera or functional groups were, however, representative of specific areas. For instance, the chlorophyte Microdictyon was only found at Rose Atoll and Swains Island (the only low open-ocean atoll systems examined). Similarly, the siphonous green alga Rhipilia only occurred at Swains Island, where it was very abundant. Multivariate analyses revealed that macroalgal assemblages differed significantly among sites around a single island and among islands. All islands were significantly different from each other with Swains Islands having the most important dissimilarity with other islands. We hypothesize that Swains Island differs from the other islands because of its geographic isolation. Statistical analyses also highlighted significant differences in the relative abundance of macroalgae between years. The interaction between spatial and temporal variability was also significant, indicating that temporal changes in algal assemblages are island dependant, and spatial differences among islands are a function of the year in which surveys were conducted. Changes in algal assemblages between the 2004 and 2006 surveys were apparent for all islands except Swains Island and Tutuila, probably because of intense cyclone activity in the region during 2005 (Cyclone Olaf). This study contributes to the overall understanding of coral reef diversity and function in American Samoa and forms a baseline for future algal monitoring surveys.

Tropical cyclone losses in the USA and the impact of climate change — A trend analysis based on data from a new approach to adjusting storm losses

Economic losses caused by tropical cyclones have increased dramatically. Historical changes in losses are a result of meteorological factors (changes in the incidence of severe cyclones, whether due to natural climate variability or as a result of human activity) and socio-economic factors (increased prosperity and a greater tendency for people to settle in exposed areas). This paper aims to isolate the socio-economic effects and ascertain the potential impact of climate change on this trend. Storm losses for the period 1950–2005 have been adjusted to the value of capital stock in 2005 so that any remaining trend cannot be ascribed to socio-economic developments. For this, we introduce a new approach to adjusting losses based on the change in capital stock at risk. Storm losses are mainly determined by the intensity of the storm and the material assets, such as property and infrastructure, located in the region affected. We therefore adjust the losses to exclude increases in the capital stock of the affected region. No trend is found for the period 1950–2005 as a whole. In the period 1971–2005, since the beginning of a trend towards increased intense cyclone activity, losses excluding socio-economic effects show an annual increase of 4% per annum. This increase must therefore be at least due to the impact of natural climate variability but, more likely than not, also due to anthropogenic forcings.

Assimilation of GPS Radio Occultation Refractivity Data from CHAMP and SAC-C Missions over High Southern Latitudes with MM5 4DVAR

Abstract In this study, the GPS radio occultation (RO) data from the Challenging Minisatellite Payload (CHAMP) and Satellite de Aplicaciones Cientificas-C (SAC-C) missions are assimilated. An updated version of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) four-dimensional variational data assimilation system (4DVAR) is used to assess the impact of the GPS RO data on analyses and short-range forecasts over the Antarctic. The study was performed during the period of intense cyclonic activity in the Ross Sea, 9–19 December 2001. On average 66 GPS RO soundings were assimilated daily. For the assimilation over a single 12-h period, the impact of GPS RO data was only marginally positive or near neutral, and it varied markedly from one 12-h period to another. The large case-to-case variation was attributed to the low number of GPS RO soundings and a strong dependency of forecast impact on the location of the soundings relative to the rapidly developing cyclone. Despite the moderate general impact, noticeable reduction of temperature error in the upper troposphere and lower stratosphere was found, which demonstrates the value of GPS RO data in better characterizing the tropopause. Significant error reduction was also noted in geopotential height and wind fields in the stratosphere. Those improvements indicate that early detection of the upper-level precursors for storm development is a potential benefit of GPS RO data. When the assimilation period was extended to 48 h, a considerable positive impact of GPS RO data was found. All parameters that were investigated (i.e., temperature, pressure, and specific humidity) showed the positive impact throughout the entire model atmosphere for forecasts extending up to 5 days. The impact increased in proportion to the length of the assimilation period. Although the differences in the analyses as a result of GPS RO assimilation were relatively small initially, the subtle change and subsequent nonlinear growth led to noticeable forecast improvements at longer ranges. Consequently, the positive impact of GPS RO data was more evident in longer-range (e.g., greater than 2 days) forecasts. A correlation coefficient is introduced to quantify the linear relationship between the analysis errors without GPS RO assimilation and the analysis increments induced by GPS RO assimilation. This measure shows that the growth of GPS RO–induced modifications over time is related to the prominent error reduction observed in GPS RO experiments. The measure may also be useful for understanding how cycling analysis accumulates the positive impact of GPS RO data for an extended period of assimilation.

A Case Study of Antarctic Katabatic Wind Interaction with Large-Scale Forcing*

Surface pressure decreases of up to 20 hPa occurred over much of the Antarctic continent during a 4-day midwinter period of 1988. The widespread change in the pressure field accompanied intense cyclonic activity to the north of the ice sheet. The equatorward mass transport across the Antarctic coastline resulted in a redistribution of atmospheric pressure that extended to the subtropics of the Southern Hemisphere. Most of the mass flux from Antarctica was the result of low-level processes and appears tied to the katabatic wind circulation. The observed surface pressure decrease over the continent reflects a perturbation of the mean meridional circulation between Antarctica and the subpolar latitudes by synoptic-scale processes. Zonally averaged circulations over Antarctica were examined using output from the European Centre for Medium-Range Weather Forecasts model. Results suggest that only a poorly defined return branch of the meridional circulation exists in the middle and upper troposphere. This southward-directed flow does not compensate for the northward mass transport provided by the katabatic wind outflow in the lower atmosphere. Isallobaric contours over the Antarctic ice sheet roughly match the area of the large-scale drainage catchment associated with katabatic wind transport through the Ross Sea sector. An intense extratropical cyclone was present in the circumpolar oceanic belt to the north of the continent. The horizontal pressure gradient associated with the cyclone prompted enhanced drainage off the high interior plateau. The resulting katabatic flow issued from the continent through a narrow corridor across the Ross Ice Shelf and out over the Southern Ocean.

Over-ocean atmospheric boundary layer dynamics under varying wind-wave development stage

Dynamic characteristics of the over-ocean atmospheric planetary boundary layer are obtained for a given geostrophic wind velocity and for varying wind-wave age, which depends on time and on varying near-water wind. Numerical experiments are done with use of a theoretical atmospheric boundary layer model and of a stochastic dependence of the non-dimensional sea surface roughness length on the wave age criterion. It is found that wind-wave development stage visibly influences the dynamic structure of the atmospheric boundary layer. So the wave age must be taken into account in analysing and modeling of atmospheric processes in the vicinity of frontal zones, in areas of intense cyclone activity etc. The discussed influence is important first of all in problems of synotic or of shorter time scales.

A composite diagnosis in sigma coordinates of the atmospheric energy balance during intense cyclonic activity

Following the recent trend for composite analysis of the energetics of cyclonic systems, a rapidly deepening Saharan depression is studied within this framework. This case refers to a cyclone which was the prevailing feature in the synoptic analyses over the Mediterranean for several days in mid March 1981. This system was marked with a range of interesting phenomena over the central and eastern Mediterranean, such as very strong surface winds, rising and transportation of desert dust to large distances, and coloured precipitation. The synoptic dynamics of the evolution of the system is briefly presented and a reasoning for its unusually rapid deepening is provided. The forms of energy considered here are kinetic energy, and sensible and latent heats. The diagnostic analysis of the budgets of these forms of energy has been carried out using the sigma coordinate system. Bearing in mind the explosive nature of the cyclogenesis studied here, the analysis is separated into two parts: one associated with the deepening phase of the cyclone and the other with its filling phase. The results are presented and discussed as time-height cross-sections of the energy contents; as time-averaged vertical distributions of budget components; and as vertically averaged budgets. The analysis revealed contrasting differences in the energy budgets in each phase of the development of the system.

A composite diagnosis in sigma coordinates of the atmospheric energy balance during intense cyclonic activity

AbstractFollowing the recent trend for composite analysis of the energetics of cyclonic systems, a rapidly deepening Saharan depression is studied within this framework. This case refers to a cyclone which was the prevailing feature in the synoptic analyses over the Mediterranean for several days in mid March 1981. This system was marked with a range of interesting phenomena over the central and eastern Mediterranean, such as very strong surface winds, rising and transportation of desert dust to large distances, and coloured precipitation. The synoptic dynamics of the evolution of the system is briefly presented and a reasoning for its unusually rapid deepening is provided.The forms of energy considered here are kinetic energy, and sensible and latent heats. The diagnostic analysis of the budgets of these forms of energy has been carried out using the sigma coordinate system. Bearing in mind the explosive nature of the cyclogenesis studied here, the analysis is separated into two parts: one associated with the deepening phase of the cyclone and the other with its filling phase. The results are presented and discussed as time‐height cross‐sections of the energy contents; as time‐averaged vertical distributions of budget components; and as vertically averaged budgets. The analysis revealed contrasting differences in the energy budgets in each phase of the development of the system.