Encarna Serrano

Routes of Transport across the Antarctic Polar Vortex in the Southern Spring

AbstractTransport in the lower stratosphere over Antarctica has been studied in the past by means of several approaches, such as contour dynamics or Lyapunov exponents. This paper examines the problem by means of a new Lagrangian descriptor, which is referred to as the function M. The focus is on the southern spring of 2005, which allows for a comparison with previous analyses based on Lyapunov exponents. With the methodology based on the function M, a much sharper depiction of key Lagrangian features is achieved and routes of large-scale horizontal transport across the vortex edge are captured. These results highlight the importance of lobe dynamics as a transport mechanism across the Antarctic polar vortex.

Monthly Characterization of the Tropospheric Circulation over the Euro-Atlantic Area in Relation with the Timing of Stratospheric Final Warmings

Abstract In recent decades, there has been a growing interest in the study of a possible active role of the stratosphere on the tropospheric climate. However, most studies have focused on this connection in wintertime. This paper deals with the possible relationship between variations in the timing of stratospheric final warmings (SFWs, observed in springtime) and monthly averaged changes in the Euro-Atlantic climate. On the basis of the date on which the SFW occurs, two sets of years have been selected for the period of study (1958–2002): “early years” and “late years,” reflecting a very early or a very late breakup of the polar vortex. The statistical significance of the early-minus-late differences in the analyzed fields has been established by applying a nonparametric test based on a Monte Carlo–like technique. Using data from 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40), a dynamical study for March and April has shown important differences between both sets of years i...

Isentropic Transport within the Antarctic Polar-Night Vortex: Rossby Wave Breaking Evidence and Lagrangian Structures

AbstractThe trajectories in the lower stratosphere of isopycnic balloons released from Antarctica by Vorcore and Concordiasi field campaigns during the southern springs of 2005 and 2010 showed events of latitudinal transport inside the stratospheric polar vortex, both away from and toward the poleward flank of the polar-night jet. The present paper applies trajectory-based diagnostic techniques to examine mechanisms at work during such events. Reverse domain-filling calculations of potential vorticity (PV) fields from the ECMWF Interim Re-Analysis (ERA-Interim) dataset during the events show irreversible filamentation of the PV fields in the inner side of the polar-night jet, which is a signature of planetary (Rossby) wave breaking. Balloon motions during the events are fairly consistent with the PV filaments. Events of both large (~15° of arc length) and small (~5° of arc length) balloon displacements from the vortex edge are associated, respectively, with deep and shallow penetration into the core of th...

Winter 10-Day Coupled Patterns between Geopotential Height and Iberian Peninsula Rainfall Using the ECMWF Precipitation Reanalysis

Abstract Ten-day winter anomalous precipitation variability in the Iberian Peninsula (IP), related to the North Atlantic atmospheric general circulation, is analyzed using 24-h forecast ECMWF precipitation data over 1979–96. The three main modes that explain the 10-day winter precipitation variability are described using the empirical orthogonal function (EOF) analysis. Singular value decomposition (SVD) analysis between the anomalous geopotential height for different levels and the IP precipitation is used as a tool to establish the relation between the precipitation and the North Atlantic atmospheric general circulation, showing how the first three SVD modes collect practically all possible precipitation–atmosphere links in these timescales. These resultant SVD atmospheric patterns are related to other known teleconnection patterns, such as the Arctic Oscillation (AO), the North Atlantic Oscillation (NAO), the Scandinavian pattern (SCA), and the east Atlantic pattern (EA). At the same time, the main res...

Dynamical Forcing of Subseasonal Variability in the Tropical Brewer–Dobson Circulation

Upwelling across the tropical tropopause exhibits strong subseasonal variability superimposed on the wellknown annual cycle, and these variations directly affect temperature and tracers in the tropical lower stratosphere.Inthiswork,the dynamicalforcing oftropical upwellingonsubseasonaltime scalesisinvestigated using the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim) for 1979‐2011. Momentum balance diagnostics reveal that transience in lower-stratospheric upwelling is linked to the effects ofextratropical wave forcing, with centers ofaction in the extratropical winter stratosphere and in the subtropical upper troposphere of both hemispheres. The time-dependent forcing in these regions induces a remote coupled response in the zonal mean wind and the meridional circulation (with associated temperature changes), which drives upwelling variability in the tropical stratosphere. This behavior is observed in the reanalysis, consistent with theory. Dynamical patterns reflect distinctive forcing of the shallow versus deep branchesoftheBrewer‐Dobsoncirculation; theshallow branchismost stronglycorrelated withwave forcing in the subtropical upper troposphere and lower stratosphere, while the deep branch is mainly influenced by highlatitude planetary waves.

An improved direct method of rubber cracking analysis for estimating 24-hour ozone levels

Abstract None of the numerous referenced experiments carried out since the 1940s for the study of the characteristic ozone-induced cracking that occurs on the surface of rubber materials subjected to strain, are appropriate for the estimation of moderate to low ozone concentrations in air over 24-h periods. Given this situation, a methodology based on the image analysis technique has been developed, which allows daily ozone averages of less than 60 ppb to be differentiated. Given the simplicity and low cost of this technique, it is especially suitable for the control of the harmful presence of ozone over extensive woodland or areas of agricultural crops. The proposed method uses two formulations simultaneously on the basis of a single type of rubber, one with 0.5% of antiozonant and the other with 1%. The rubber samples used are shaped such that the stresses throughout them are not constant. The tests were performed inside a chamber in which different daily ozone evolutions, typical of those observed during the summer in rural areas of the central part of the Iberian peninsula, were simulated. The results obtained show a close relation between 24-h O 3 averages and the dimensional distribution of the cracks observed at different locations on the surface of the rubber samples. Also, in the case of typical daily unimodal ozone evolutions, there would appear to be a certain relationship between the maximum hourly concentration reached during the exposure period and certain crack characteristics.

Intra-seasonal variability of extreme boreal stratospheric polar vortex events and their precursors

The 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 Niña 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.