Person: De La Cámara Illescas, Álvaro
Loading...
First Name
Álvaro
Last Name
De La Cámara Illescas
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física de la Tierra y Astrofísica
Area
Física de la Tierra
Identifiers
5 results
Search Results
Now showing 1 - 5 of 5
Item Can we improve the realism of gravity wave parameterizations by imposing sources at all altitudes in the atmosphere?(Journal of Advances in Modeling Earth Systems, 2022) Ribstein, Bruno; Millet, Christophe; Lott, François; De La Cámara Illescas, ÁlvaroA multiwave non-orographic gravity waves (GWs) scheme is adapted to represent waves of small intrinsic phase speed, inertial waves, and wave emission from all altitudes. This last change removes the launching altitude parameter, an arbitrary parameter systematically used in GW schemes. In offline calculations using reanalysis fields, these changes impose larger amplitude, saturated waves everywhere in the middle atmosphere, which produces more realistic GW vertical spectra than in previous configurations. The same scheme, tested online in the Laboratoire de Météorologie Dynamique Zoom (LMDz) general circulation model, performs at least as well as the operational non-orographic GW scheme. Some modest benefits are seen, for instance, in the equatorial tilt with altitude of the winter jets in the middle atmosphere. Although the scheme includes the effects of inertial waves, which are detected in the mesosphere by different observational platforms, the configuration that gives a reasonable climatology in LMDz hinders their vertical propagation and limits their presence at mesospheric altitudes.Item Quantifying stratospheric biases and identifying their potential sources in subseasonal forecast systems(Weather and Climate Dynamics, 2022) Lawrence, Zachary D.; Ábalos Álvarez, Marta; Ayarzagüena Porras, Blanca; Barriopedro Cepero, David; Calvo Fernández, Natalia; De La Cámara Illescas, Álvaro; Rachel W.-Y. WuThe stratosphere can be a source of predictability for surface weather on timescales of several weeks to months. However, the potential predictive skill gained from stratospheric variability can be limited by biases in the representation of stratospheric processes and the coupling of the stratosphere with surface climate in forecast systems. This study provides a first systematic identification of model biases in the stratosphere across a wide range of subseasonal forecast systems. It is found that many of the forecast systems considered exhibit warm global mean temperature biases from the lower to middle stratosphere, too strong/cold wintertime polar vortices, and too cold extratropical upper troposphere/lower stratosphere regions. Furthermore, tropical stratospheric anomalies associated with the Quasi-Biennial Oscillation tend to decay toward each system's climatology with lead time. In the Northern Hemisphere (NH), most systems do not capture the seasonal cycle of extreme vortex event probabilities, with an underestimation of sudden stratospheric warming events and an overestimation of strong vortex events in January. In the Southern Hemisphere (SH), springtime interannual variability of the polar vortex is generally underestimated, but the timing of the final breakdown of the polar vortex often happens too early in many of the prediction systems. These stratospheric biases tend to be considerably worse in systems with lower model lid heights. In both hemispheres, most systems with low-top atmospheric models also consistently underestimate the upward wave driving that affects the strength of the stratospheric polar vortex. We expect that the biases identified here will help guide model development for sub-seasonal to seasonal forecast systems, and further our understanding of the role of the stratosphere for predictive skill in the troposphere.Item Changes in stratospheric transport and mixing during sudden stratospheric warmings(Journal of Geophysical Research: Atmospheres, 2018) De La Cámara Illescas, Álvaro; Ábalos Álvarez, Marta; Hitchcock, P.The extreme disruptions of the wintertime stratospheric circulation during sudden stratospheric warmings (SSW) have large effects on tracer concentrations through alterations in transport. This study analyzes the changes in residual circulation and isentropic mixing associated with SSWs, by performing composites using reanalysis (European Centre for Medium-Range Weather Forecasts Re-Analysis Interim) and simulations of the Whole Atmosphere Community Climate Model. The advective Brewer-Dobson circulation accelerates around 15days prior to the wind reversal at 60 degrees N, 10hPa during the onset of SSWs. Soon afterward, it decelerates, leading to reduced advective transport into the vortex and descent over the pole, which persist for more than 2months below 30hPa. The isentropic mixing has a distinct signature in altitude: It is enhanced at the central date of the SSW in the midstratosphere (about 10hPa or 800K), and this signal is delayed and more persistent at lower altitudes. It is shown that sufficiently deep SSWs (particularly those related to Polar-night Jet Oscillation events) have a stronger response in the Brewer-Dobson circulation and mixing. In particular, both the polar downwelling and the tropical upwelling are anomalously weak in the lower stratosphere for 90days after the onset of Polar-night Jet Oscillation events. The redistribution of potential vorticity during the life cycle of SSWs is discussed due to its relevance for the stratospheric circulation. It is shown that the diffusive flux of potential vorticity, calculated in equivalent latitude coordinates, remains anomalously high in the lower stratosphere, a feature that is not seen in more conventional advective eddy fluxes across latitude circles.Item Analyzing ozone variations and uncertainties at high latitudes during sudden stratospheric warming events using MERRA-2(Atmospheric Chemistry and Physics, 2022) Shams, Shima Bahramvash; Walden, Von P.; Hannigan, James W.; Randel, William J.; Petropavlovskikh, Irina V.; Butler, Amy H.; De La Cámara Illescas, ÁlvaroStratospheric circulation is a critical part of the Arctic ozone cycle. Sudden stratospheric warming events (SSWs) manifest the strongest alteration of stratospheric dynamics. During SSWs, changes in planetary wave propagation vigorously influence zonal mean zonal wind, temperature, and tracer concentrations in the stratosphere over the high latitudes. In this study, we examine six persistent major SSWs from 2004 to 2020 using the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). Using the unique density of observations around the Greenland sector at high latitudes, we perform comprehensive comparisons of high-latitude observations with the MERRA-2 ozone dataset during the six major SSWs. Our results show that MERRA-2 captures the high variability of mid-stratospheric ozone fluctuations during SSWs over high latitudes. However, larger uncertainties are observed in the lower stratosphere and troposphere. The zonally averaged stratospheric ozone shows a dramatic increase of 9 %-29 % in total column ozone (TCO) near the time of each SSW, which lasts up to 2 months. This study shows that the average shape of the Arctic polar vortex before SSWs influences the geographical extent, timing, and magnitude of ozone changes. The SSWs exhibit a more significant impact on ozone over high northern latitudes when the average polar vortex is mostly elongated as seen in 2009 and 2018 compared to the events in which the polar vortex is displaced towards Europe. Strong correlation (R^(2) = 90 %) is observed between the magnitude of change in average equivalent potential voracity before and after SSWs and the associated averaged total column ozone changes over high latitudes. This paper investigates the different terms of the ozone continuity equation using MERRA-2 circulation, which emphasizes the key role of vertical advection in mid-stratospheric ozone during the SSWs and the magnified vertical advection in elongated vortex shape as seen in 2009 and 2018.Item Intra-seasonal variability of extreme boreal stratospheric polar vortex events and their precursors(Climate Dynamics, 2017) Díaz Durán, Adelaida; Serrano Mendoza, Encarnación; Ayarzagüena Porras, Blanca; Ábalos Álvarez, Marta; De La Cámara Illescas, ÁlvaroThe dynamical variability of the boreal stratospheric polar vortex has been usually analysed considering the extended winter as a whole or only focusing on December, January and February. Yet recent studies have found intra-seasonal differences in the boreal stratospheric dynamics. In this study, the intra-seasonal variability of anomalous wave activity preceding polar vortex extremes in the Northern Hemisphere is examined using ERA-Interim reanalysis data. Weak (WPV) and strong (SPV) polar vortex events are grouped into early, mid- or late winter sub-periods depending on the onset date. Overall, the strongest (weakest) wave-activity anomalies preceding polar vortex extremes are found in mid- (early) winter. Most of WPV (SPV) events in early winter occur under the influence of east (west) phase of the Quasi-Biennial Oscillation (QBO) and an enhancement (inhibition) of wavenumber-1 wave activity (WN1). Mid- and late winter WPV events are preceded by a strong vortex and an enhancement of WN1 and WN2, but the spatial structure of the anomalous wave activity and the phase of the QBO are different. Prior to mid-winter WPVs the enhancement of WN2 is related to the predominance of La Nia and linked to blockings over Siberia. Mid-winter SPV events show a negative phase of the Pacific-North America pattern that inhibits WN1 injected into the stratosphere. This study suggests that dynamical features preceding extreme polar vortex events in mid-winter should not be generalized to other winter sub-periods.