M. Gil

Chemical Ozone Loss in the Arctic Winter 1994/95 as Determined by the Match Technique

The chemically induced ozone loss inside the Arctic vortex during the winter 1994/95 has been quantified by coordinated launches of over 1000 ozonesondes from 35 stations within the Match 94/95 campaign. Trajectory calculations, which allow diabatic heating or cooling, were used to trigger the balloon launches so that the ozone concentrations in a large number of air parcels are each measured twice a few days apart. The difference in ozone concentration is calculated for each pair and is interpreted as a change caused by chemistry. The data analysis has been carried out for January to March between 370 K and 600 K potential temperature. Ozone loss along these trajectories occurred exclusively during sunlit periods, and the periods of ozone loss coincided with, but slightly lagged, periods where stratospheric temperatures were low enough for polar stratospheric clouds to exist. Two clearly separated periods of ozone loss show up. Ozone loss rates first peaked in late January with a maximum value of 53 ppbv per day (1.6 % per day) at 475 K and faster losses higher up. Then, in mid-March ozone loss rates at 475 K reached 34 ppbv per day (1.3 % per day), faster losses were observed lower down and no ozone loss was found above 480 K during that period. The ozone loss in hypothetical air parcels with average diabetic descent rates has been integrated to give an accumulated loss through the winter. The most severe depletion of 2.0 ppmv (60 %) took place in air that was at 515 K on 1 January and at 450 K on 20 March. Vertical integration over the levels from 370 K to 600 K gives a column loss rate, which reached a maximum value of 2.7 Dobson Units per day in mid-March. The accumulated column loss between 1 January and 31 March was found to be 127 DU (∼36 %).

Ozone depletion in and below the Arctic vortex for 1997

The winter 1996/97 was quite unusual with late vortex formation and polar stratospheric cloud (PSC) development and subsequent record low temperatures in March. Ozone depletion in the Arctic vortex is determined using ozonesondes. The diabatic cooling is calculated with PV-theta mapped ozone mixing ratios and the large ozone depletions, especially at the center of the vortex where most PSC existence was predicted, enhances the diabatic cooling by up to 80%. The average vortex chemical ozone depletion from January 6 to April 6 is 33, 46, 46, 43, 35, 33, 32 and 21 % in air masses ending at 375, 400, 425, 450, 475, 500, 525, and 550 K (about 14–22 km). This depletion is corrected for transport of ozone across the vortex edge calculated with reverse domain-filling trajectories. 375 K is in fact below the vortex, but the calculation method is applicable at this level with small changes. The column integrated chemical ozone depletion amounts to about 92 DU (21%), which is comparable to the depletions observed during the previous four winters.

A Study of Ozone Laminae Using Diabatic Trajectories, Contour Advection and Photochemical Trajectory Model Simulations.

In this paper, we show that the rate of ozone loss in both polar and mid-latitudes, derived from ozonesonde and satellite data, has almost the same vertical distribution (although opposite sense) to that of ozone laminae abundance. Ozone laminae appear in the lower stratosphere soon after the polar vortex is established in autumn, increase in number throughout the winter and reach a maximum abundance in late winter or spring. We indicate a possible coupling between mid-winter, sudden stratospheric warmings (when the vortex is weakened or disrupted) and the abundance of ozone laminae using a 23-year record of ozonesonde data from the World Ozone Data Center in Canada combined with monthly-mean January polar temperatures at 30 hPa.Results are presented from an experiment conducted during the winter of 1994/95, in phase II of the Second European Stratospheric And Mid-latitude Experiment (SESAME), in which 93 ozone-enhanced laminae of polar origin observed by ozonesondes at different time and locations are linked by diabatic trajectories, enabling them to be probed twice or more. It is shown that, in general, ozone concentrations inside laminae fall progressively with time, mixing irreversibly with mid-latitude air on time-scales of a few weeks. A particular set of laminae which advected across Europe during mid February 1995 are examined in detail. These laminae were observed almost simultaneously at seven ozonesonde stations, providing information on their spatial scales. The development of these laminae has been modelled using the Contour Advection algorithm of Norton (1994), adding support to the concept that many laminae are extrusions of vortex air. Finally, a photochemical trajectory model is used to show that, if the air in the laminae is chemically activated, it will impact on mid-latitude ozone concentrations. An estimate is made of the potential number of ozone molecules lost each winter via this mechanism.

Aerosol closure study by lidar, Sun photometry, and airborne optical counters during DAMOCLES field campaign at El Arenosillo sounding station, Spain

We present a comparison of aerosol properties derived from in situ and remote sensing instruments during DAMOCLES campaign, aimed at investigating the equivalence between the instrumentation and methodologies employed by several Spanish groups to study atmospheric aerosols at a regional background site. The complete set of instruments available during this closure experiment allowed collecting a valuable high-resolution aerosol measurement data set. The data set was augmented with airborne in situ measurements carried out in order to characterize aerosol particles during the midday of 29 June 2006. This work is focused on aerosol measurements using different techniques of high-quality instruments (ground-based remote sensing and aircraft in situ) and their comparisons to characterize the aerosol vertical profiles. Our results indicate that the variability between the detected aerosol layers was negligible in terms of aerosol optical properties and size distributions. Relative differences in aerosol extinction coefficient profiles were less than 20% at 355 and 532 nm and less than 30% at 1064 nm, in the region with high aerosol concentration. Absolute differences in aerosol optical depth (AOD) were below 0.01 at 532 and 1064 nm and less than 0.02 at 355 nm, less than the uncertainties assumed in the AOD obtained from elastic lidar. Columnar values of the lidar ratio revealed some discrepancies with respect to the in situ aircraft measurements, caused fundamentally by the lack of information in the lowest part of the boundary layer.

Temporal development of ozone within the Arctic Vortex during the winter of 1991/92

In this study we address the question of temporal ozone trends on isentropic surfaces within the Arctic polar vortex during EASOE. We have combined ozone sonde data from twelve campaign stations distributed throughout the European sector of the Arctic. The development of ozone at the 425, 475, 550 and 700K levels is presented, using analysed fields of isentropic potential vorticity and isentropic back-trajectories to separate inner vortex air from air staying outside the vortex. Vertical N2O profiles measured in Kiruna have been used to obtain information on the vertical movement of the polar air mass. Elimination of effects due to diabatic descent leads to a weak, yet significant, chemically induced loss of ozone at 475 K. At 425 K we observe a negative trend in the ozone mixing ratio, but for this level it has not been possible to assess the influence of subsidence. Heterogeneous chemistry on aerosols of volcanic origin from the eruption of Mt. Pinatubo might have contributed to the negative ozone trends.

Ground-based stratospheric NO2 monitoring at Keflavik (Iceland) during EASOE

This report presents ground based measurements of nitrogen dioxide above Keflavik, Iceland, 64[degrees]N, between December 1991, and February 1992. Using visible spectrometry, the authors observed column densities below 1 [times] 10[sup 15] molecules/cm[sup 2] inside the polar vortex.

Polar Stratospheric Cloud Observations in the 2006/07 Arctic Winter by Using an Improved Micropulse Lidar

Abstract The potential of a new improved version of micropulse lidar (MPL-4) on polar stratospheric cloud (PSC) detection is evaluated in the Arctic over Ny-Alesund (79°N, 12°E), Norway. The campaign took place from January to February 2007 in the frame of the International Polar Year (IPY) activities. Collocated Alfred Wegener Institute (AWI) Koldewey Aerosol Raman Lidar (KARL) devoted to long-term Arctic PSC monitoring is used for validation purposes. PSC detection is based on lidar retrievals of both backscattering ratio R and volume depolarization ratio δV. Two episodes were unequivocally attributed to PSCs: 21–22 January and 5–6 February 2007, showing a good correlation between MPL-4 and KARL backscattering ratio datasets (mean correlation coefficient = 0.92 ± 0.03). PSC layered structures were characterized for four observational periods coincident with KARL measurements. Also, PSC type classification was determined depending on the retrieved R and δV values as compared with those obtained by KARL l...

NO2 profiles during the CRISTA-2 experiment (August 1997) at subtropical regions

A ground-based spectrometer using the DOAS technique measuring at zenith was deployed at Izana Observatory during the 2nd CRISTA flight, in August 1997. CRISTA was flown on the ASTROPAS free-flying platform during the Space Shuttle mission STS-85, and among other species measured NO2 profiles. The twilight measurements of NO2 profiles. The twilight measurements of NO2 total column over the station obtained by the ground-based spectrometer has been used to estimate the profile of this species in the subtropics for summer and to compare with the results of CRISTA during the overpassings. The results of both data sets, and the origin of the discrepancies are discussed in the paper.

Ozone and NO2 monitoring in Southern Spain: The 1994/95 winter record low

During the winter 1994/95, three episodes occurred at El Arenosillo (37N, 6.7W) when the total ozone dropped below the 2σ level, in the months of November 94, January and February 95. These episodes are analysed in detail with the help of ozone sounding and ECMWF backtrajectories. The NO2 column measurements have been used as additional tool to get more insight of the cause of the observed low ozone. Results show that the January episode is related to the elongation and unusual position of the Arctic vortex over Europe. Temperatures in the stratosphere were at their minimum annual values and the backtrajectories present a southward strong meridional component. In addition, measurements of NO2 show values typical of winter high latitude. The episode in February, on the other hand, was of different origin. Although the total amounts were similar, the trajectory analysis shows typical air masses over the station, resulting in an absence of the secondary ozone maximum.

Cuantificación de la destrucción química de ozono en la estratosfera ártica a partir de medidas "in situ".

Las medidas “in situ” de ozono en la estratosfera por métodos electroquímicos en sondas embarcadas en globos proporcionan un grado de resolución vertical imposible de alcanzar por cualquier otro método. La amenaza de una posible destrucción masiva de la capa de ozono por mecanismos similares a los quesuceden en la Antártida han impulsado la investigación basadaen campañas de investigación coordinadas desde la Unión Europea. Desde hace unos años existe una red de estaciones de sondeo con un programa conjunto establecido para estudiar el fenómeno. Entre ellas, el I>NTA opera la estación de Keflavik (640N, 230W). Los resultados de las observaciones tanto individuales como coordinadas en un proyecto general denominado “Match”, indican que el ozono se destruye en el ártico durante el invierno a un ritmo similar al que tiene lugar en la Antártida y que los mecanismos que conducen la destrucción son idénticos a los que tienen lugar en el hemisferio sur. Sin embargo, no se observan valores en el contenido total de ozono tan bajos como en la primavera antártica, debido a una mayoractividad de las ondas planetarias que potencian el transporte meridional de ozono hacia el norte y en última instancia limita temporalmente la vida del vórtice.