Person:
González Alemán, Juan Jesús

First Name

Juan Jesús

Last Name

González Alemán

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Físicas

Department

Física de la Tierra y Astrofísica

Area

Física de la Tierra

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Now showing 1 - 10 of 14

Analysis of the October 2014 subtropical cyclone using the WRF and the HARMONIE-AROME numerical models: Assessment against observations
(Elsevier Science INC, 2021-10-01) Quitián Hernández, L.; Bolgiani, P.; Santos Muñoz, D.; Sastre Marugán, Mariano; Díaz Fernández, Javier; González Alemán, Juan Jesús; Farrán, J.I.; López, L.; Valero Rodríguez, Francisco; Martín, M.L.
Subtropical cyclones (STCs) are low-pressure systems characterized by having a thermal hybrid structure and sharing tropical and extratropical characteristics. These cyclones are widely studied due to their harmful impacts, in some cases, similar to those caused by hurricanes or tropical storms. From a numerical modeling point of view, they are considered a challenge on account of their rapid intensification. That is the reason why this paper analyzes the simulations of the STC that occurred in October 2014 near the Canary Islands through two highresolution numerical models: Weather Research and Forecasting (WRF) and HARMONIE-AROME. In this study, the simulations obtained with both models of this STC are analyzed versus different observational data. METAR data are used to validate some surface simulated variables throughout the STC life while soundings are chosen to study the tropospheric behavior. Finally, MSG-SEVIRI satellite brightness temperature is used to be compared to those brightness temperatures simulated by both models to give information of the cloud top spatial structure of this atmospheric system. The 2 m temperature, 2 m dew-point temperature, and 10 m wind speed variables do not show significant deviations when carrying out the validation of both models against the available METAR data. It is outstanding the good results found for the HARMONIE-AROME model when analyzing the temperature sounding for both analyzed dates. Additionally, regarding the wind speed sounding, better results are presented in general by the HARMONIE-AROME model, being the WRF model slightly better during the pre-STC stage. Moreover, the skillfulness of the HARMONIE-AROME model is highlighted when simulating the infrared brightness temperature and cloud distribution compared to the WRF model.
Cyclones with tropical characteristics over the northeastern Atlantic and Mediterranean sea: analysis in present climate and future projections
(Universidad Complutense de Madrid, 2019-02-13) González Alemán, Juan Jesús; Gaertner Ruiz-Valdepeñas, Miguel Ángel; Gallardo Andrés, Clemente
Cyclones with tropical characteristics are low pressure systems showing characteristics of both baroclinic (extratropical) and diabatic (tropical) cyclones. Thus, they are within the continuum between the theoretical conceptual extreme of cyclones. Examples of these hybrid cyclones are subtropical cyclones (STCs) forming in the North Atlantic and medicanes of tropical likecyclones in the Mediterranean Sea.The scientific and forecasting community has recently focus on them due to their recognitionas weather damaging systems. They are associated with uncertainties and their relationship with climate change is not very well understood yet. Especially in the northeastern Atlantic (ENA) there is little knowledge of them. Therefore, this thesis aims to add further insight into their characteristics on both present and future climate in Anthropogenic Climate Change (ACC) context, with an additional evaluation of the tools that can be used for studying them in both climates...
Classification and Synoptic Analysis of Subtropical Cyclones within the Northeastern Atlantic Ocean
(American Meteorological Society, 2015-04) González Alemán, Juan Jesús; Valero Rodríguez, Francisco; Martín León, Francisco; Evans, Jenni L.
Since more research is needed on subtropical cyclones (STCs) formed within the North Atlantic eastern basin, this survey analyzes them from a synoptic point of view, on a climatological basis, with the main aims of studying their common features, complementing other studies of these storms in the North Atlantic, and aiding the forecasting community. Fifteen cases of STCs were identified during the period 1979-2011 by applying a set of criteria from two databases. Composite analysis reveals that an extratropical depression acts as a precursor when it is isolated from the westerlies and then suffers a deepening when becoming subtropical instead of decaying through occlusion. This process is accompanied by an atmospheric circulation, within the North Atlantic, whose main feature is characterized by notable departures from the climatological pattern with a statistically significant anomalous high pressure to the north of the STCs. Three conceptual models of synoptic pattern of subtropical cyclogenesis are derived and show that these departures appeared because the westerly circulation moves poleward and/ or the flow has a great meridional component, with the possibility of a blocked flow pattern occurring. Moreover, the identified STCs predominantly formed in a highly sheared (>10 m s^-1) environment with low sea surface temperature values (<25 degrees C), which differs from the dominant features of STCs in the North Atlantic, especially within its western region. Finally, a recent (2010) STC, identified by the authors, is synoptically discussed in order to achieve a better interpretation of the general results.
Subtropical Cyclone Formation via Warm Seclusion Development: The Importance of Surface Fluxes
(American Geophysical Union, 2020-04-27) Quitián Hernández, L.; González Alemán, Juan Jesús; Santos Muñoz, D.; Fernández González, S.; Valero Rodríguez, Francisco; Martín, M.L.
Subtropical cyclones (STCs) are characterized by a thermal hybrid structure with tropical and extratropical features. STCs are considered a numerical modeling challenge because of their rapid intensification. A fundamental part of their strength is derived from diabatic processes associated with convection and heat fluxes from the ocean. This study evaluates the importance of surface turbulent heat fluxes during the transition of an extratropical precursor into a STC. This cyclone evolved embedded within a strong meridional flow, having a Shapiro‐Keyser structure and undergoing a warm seclusion process. To assess the importance of those heat fluxes, two Weather Research and Forecasting simulations were defined considering the presence and absence of those fluxes. Results of both simulations reveal a warm seclusion process, which weakened in absence of the heat fluxes. During the system genesis and in absence of heat fluxes, the wind and rainfall values were increased due to the remarkably intense area of frontogenesis to the northwest. Given these results and the lack of transition in the absence of heat fluxes, the frontal nature of the system was verified. Considering the heat fluxes, the obtained potential vorticity values diminished, reducing wind shear and intensifying convection in the system, which favored its transition into an STC. This study is groundbreaking in that no STC has been linked to a warm seclusion process in the Eastern North Atlantic. Additionally, simulated wind field shows an underestimation in comparison with Atmospheric Motion Vectors, used as observational data so as to give a weight to the wind analysis.
El voto de los jóvenes
(INJUVE. Instituto de la Juventud. Ministerio de Sanidad, Servicios Sociales e Igualdad, 2003) González Alemán, Juan Jesús; Salido Cortés, Olga
El artículo hace una descripción de las pautas de voto de los jóvenes en elecciones generales desde mediados de los años ochenta, en lo relativo tanto a su grado de participación como a sus orientaciones ideológicas básicas (izquierdismo, radicalismo, etc.), dentro del marco general de un comportamiento electoral caracterizado por la estabilidad y la aversión al riesgo. En la última parte, el artículo trata de desentrañar las razones del voto juvenil, con especial atención a los componentes ideológicos y/o racionales del mismo.
Wind kinetic energy climatology and effective resolution for the ERA5 reanalysis
(Springer Nature, 2022-01-29) Bolgiani, Pedro; Calvo Sancho, C.; Díaz Fernández, Javier; Quitián Hernández, Lara; Santos Muñoz, D.; Farrán, J. I.; González Alemán, Juan Jesús; Valero Rodríguez, Francisco; Martín, M. L.; Sastre Marugán, Mariano
ERA5 represents the state of the art for atmospheric reanalyses and is widely used in meteorological and climatological research. In this work, this dataset is evaluated using the wind kinetic energy spectrum. Seasonal climatologies are generated for 30 degrees latitudinal bands in the Northern Hemisphere (periodic domain) and over the North Atlantic area (limited-area domain). The spectra are also assessed to determine the effective resolution of the reanalysis. The results present notable differences between the latitudinal domains, indicating that ERA5 is properly capturing the synoptic conditions. The seasonal variability is adequate too, being winter the most energetic, and summer the least energetic season. The limited area domain results introduce a larger energy density and range. Despite the good results for the synoptic scales, the reanalysis' spectra are not able to properly reproduce the dissipation rates at mesoscale. This is a source of uncertainties which needs to be taken into account when using the dataset. Finally, a cyclone tropical transition is presented as a case study. The spectrum generated shows a clear difference in energy density at every wavelength, as expected for a highly-energetic status of the atmosphere.
Major role of marine heatwave and anthropogenic climate change on a giant hail event in Spain
(American Geophysical Union, 2024-03-22) Martín, M.L.; Calvo-Sancho, Carlos; Taszarek, M.; González Alemán, Juan Jesús; Montoro-Mendoza, Ana; Díaz Fernández, Javier; Bolgiani, Pedro Mariano; Sastre Marugán, Mariano; Martín, Yago
A severe hailstorm that occurred in Spain on 30 August 2022, caused material and human damage, including one fatality due to giant hailstones up to 12 cm in diameter. By applying a pseudo‐global warming approach, here we evaluate how a simultaneous marine heatwave (and anthropogenic climate change) affected a unique environment conductive to such giant hailstones. The main results show that the supercell development was influenced by an unprecedented amount of convective available energy, with significant contributions from thermodynamic factors. Numerical simulations where the marine heatwave is not present show a notable reduction in the hail‐favorable environments, related mainly to modifications in thermodynamic environment. Our simulations also indicate that the environment in a preindustrial‐like climate would be less favorable for convective hazards and thus the hailstorm event would likely not have been as severe as the observed one, being possible to perform a novel attribution of such kind.
Abrupt and persistent atmospheric circulation changes in the North Atlantic under La Niña conditions
(Elsevier, 2023-09-03) García-Burgos, Marina; Gómara Cardalliaguet, Íñigo; Rodríguez De Fonseca, María Belén; González Alemán, Juan Jesús; Zurita Gotor, Pablo; Ayarzagüena Porras, Blanca
Several recent studies have linked the exceptional North Atlantic and Eurasian atmospheric evolution during late February and March 2018 to the Sudden Stratospheric Warming (SSW) that took place a few weeks earlier. February 2018 was characterized by an abrupt transition from the positive to the negative phase of the North Atlantic Oscillation (NAO) and a subsequent persistence of the negative NAO for several weeks. This paper investigates the contribution of atmospheric and oceanic phenomena to both the 2018 event and a set of 19 identified analogues (including the former) for the period 1959-2022. Evidence is given that La Nin similar to a conditions in the tropical Pacific and upstream North Atlantic cyclones play an important role as a trigger for these events. Ensuing two-way tropospheric-strato-spheric coupling and eddy feedbacks provide extended-range persistence for negative NAO conditions. These results may help improve the prediction of such exceptional events.
On the atmospheric conditions leading to mountain lee waves in central Iberia under CMIP6 projections
(MDPI, 2024-01-20) Díaz Fernández, Javier; Calvo-Sancho, Carlos; Bolgiani, Pedro Mariano; González Alemán, Juan Jesús; Farrán, José Ignacio; Sastre Marugán, Mariano; Martín, M.L.
Mountain lee waves present significant hazards to aviation, often inducing turbulence and aircraft icing. The current study focuses on understanding the potential impact of global climate change on the precursor environments to mountain lee wave cloud episodes over central Iberia. We examine the suitability of several Global Climate Models (GCMs) from CMIP6 in predicting these environments using the ERA5 reanalysis as a benchmark for performance. The dataset is divided into two periods: historical data (2001–2014) and projections for the SSP5–8.5 future climate scenario (2015–2100). The variations and trends in precursor environments between historical data and future climate scenarios are exposed, with a particular focus on the expansion of the Azores High towards the Iberian Peninsula, resulting in increased zonal winds throughout the Iberian Peninsula in the future. However, the increase in zonal wind is insufficient to modify the wind pattern, so future mountain lee wave cloud events will not vary significantly. The relative humidity trends reveal no significant changes. Moreover, the risk of icing precursor environments connected with mountain lee wave clouds is expected to decrease in the future, due to rising temperatures. Our results highlight that the EC-EARTH3 GCM reveals the closest alignment with ERA5 data, and statistically significant differences between the historical and future climate scenario periods are presented, making ECEARTH3 a robust candidate for conducting future studies on the precursor environments to mountain lee wave cloud events.
Horizontal kinetic energy analysis of tropical transition simulations with the WRF and HARMONIE-AROME models
(Wiley, 2023-07-13) Calvo Sancho, Carlos; Bolgiani, Pedro Mariano; Subías, Álvaro; Sastre Marugán, Mariano; González Alemán, Juan Jesús; Martín, M.L.
Four tropical transition (TT) events in the North Atlantic basin are simulated with the Weather Research and Forecasting (WRF) and the HARMONIE-AROME (HAR) models to study the main features of the horizontal kinetic energy (HKE) spectra of these kinds of high-energetic atmospheric system. Though most of the times similar results are obtained with both models, HAR shows a more intense filtering and numerical dissipation, whereas WRF tends to represent overenergized spectra in the synoptic scale and especially at smaller wavelengths. Predictability is dissimilar for the four TTs studied due to the different spectral curve slope obtained for each case, ranging from unlimited to very poor predictability at synoptic scale. Additionally, an increased HKE is presented in the middle–upper troposphere spectra. A deep analysis of the different terms involved in the equation of the spectral energy budget is presented through a detailed study of one of these TTs. The role of all of them is studied, connecting the energy spectra and the meteorological processes involved. The energy budget terms related to the nonlinear spectral transfer, the three-dimensional divergence, and diabatic process tendencies are identified as the key ones, whereas the potential and kinetic conversion terms and the vertical flux HKE and pressure divergence terms play a secondary role on modulating the spectrum behaviour. The major energetic contributions are found at the synoptic scale, but results show that a two-dimensional energy cascade does not fully capture the whole spectrum of a TT. The role of convection, latent heat release, and moist convection outbursts is sketched and a link within different vertical levels is found. Results show that a high-energetic system, such as a TT, can effectively alter the atmospheric energy behaviour.