Increased stratospheric ozone depletion due to mountain-induced atmospheric waves (original) (raw)
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Atmospheric Chemistry and Physics, 2004
The exceptional day-long observation of a polar stratospheric cloud (PSC) by two ground-based lidars at the Swedish research facility Esrange (67.9 • N, 21.1 • E) on 16 January 1997 is analyzed in terms of PSC dynamics and microphysics. Mesoscale meteorological modeling is utilized to resolve the time-space ambiguity of the lidar measurements. Microphysical properties of the PSC particles are retrieved by comparing the measured particle depolarization ratio and the PSC-averaged lidar ratio with theoretical optical data derived for different particle shapes. In the morning, nitric acid trihydrate (NAT) particles and then increasingly coexisting liquid ternary aerosol (LTA) were detected as outflow from a mountain wave-induced ice PSC upwind Esrange. The NAT PSC consisted of irregular-shaped particles with length-to-diameter ratios between 0.75 and 1.25, maximum dimensions from 0.7 to 0.9 µm, and a number density from 8 to 12 cm −3 and the coexisting LTA droplets had diameters from 0.7 to 0.9 µm, a refractive index of 1.39 and a number density from 7 to 11 cm −3. NAT activation was probably substantial (∼ 53%) which appears to be the effect of the high cooling rates (> 100 K/h) in the stratospheric mountain wave. The total amount of condensed HNO 3 was in the range of 57-90% of the HNO 3 gas reservoir. By early afternoon the mountain wave-induced ice PSC expanded above the lidar site. Its optical data indicate a decrease in minimum particle size from 4.3 to 1.9 µm with time, possibly due to a diminishing growth rate. Later on, following the cessation of particle nucleation upwind wave-processed LTA was observed only. Our study demonstrates that groundbased lidar measurements of PSCs can be comprehensively interpreted if combined with mesoscale meteorological data.
Airborne lidar observation of mountain-wave-induced polar stratospheric clouds during EASOE
Geophysical Research Letters, 1994
The airborne backscatter lidar Leandre was flown during the EASOE campaign on board the French ARAT-Fokker 27, to provide mesoscale observations of scattering layers in the stratosphere. The use of crosspolarization channels at the 532 nm laser emitted wavelength, allowed discrimination between the quasi-spherical particles of the Pinatubo aerosol and the non-spherical frozen particles of polar stratospheric clouds. Measurements taken on December 1 lth 1991 revealed mountain-wave-induced polar stratospheric clouds at 21 km altitude, extending over 300 km west and 300 km east from Kimna. The wavelength and amplitude of the perturbation imply local cooling ranging from 3øK to 10øK in the stratosphere, taking the temperature below the threshold of formation of polar stratospheric clouds.
Nonorographic generation of Arctic polar stratospheric clouds during December 1999
Journal of Geophysical Research, 2003
1] During December 1999, polar stratospheric clouds (PSCs) were observed in the absence of conditions conducive to generation by topographic gravity waves. The possibility is explored that PSCs can be generated by inertia gravity waves (IGW) radiating from breaking synoptic-scale Rossby waves on the polar front jet. The aerosol features on 7 and 12 December are selected for comparison with theory and with simulations using the University of Wisconsin Nonhydrostatic Modeling System (UWNMS). Consistent with Rossby adjustment theory, a common feature in the UWNMS simulations is radiation of IGW from the tropopause polar front jet, especially from sectors which are evolving rapidly in the Rossby wave breaking process. Packets of gravity wave energy radiate upward and poleward into the cold pool, while individual wave crests propagate poleward and downward, causing mesoscale variations in vertical motion and temperature. On 12 December the eastbound DC-8 lidar observations exhibited a fairly uniform field of six waves in aerosol enhancement in the 14-20 km layer, consistent with vertical displacement by a field of IGW propagating antiparallel to the flow, with characteristic horizontal and vertical wavelengths of 300and300 and 300and10 km. UWNMS simulations show emanation of a field of IGW upward and southwestward from a northward incursion of the polar front jet. The orientation and evolution of the aerosol features on 7 December are consistent with a single PSC induced by an IGW packet propagating from a breaking Rossby wave over western Russia toward the northeast into the coldest part of the base of the polar vortex, with characteristic period 9hours,verticalwavelength9 hours, vertical wavelength 9hours,verticalwavelength12 km, and horizontal wavelength 1000km.Lineartheoryshowsthatforbothofthesecases,IGWenergypropagatesupwardat1000 km. Linear theory shows that for both of these cases, IGW energy propagates upward at 1000km.Lineartheoryshowsthatforbothofthesecases,IGWenergypropagatesupwardat1 km/hour and horizontally at 100km/hour,withcharacteristictracespeed100 km/hour, with characteristic trace speed 100km/hour,withcharacteristictracespeed30 m/s. The spatial orientation of the PSC along IGW phase lines is contrasted with the nearly horizontal filamentary structures in the PSC, which are indicative of flow streamlines. It is suggested that vertical displacement is a crucial factor in determining whether a PSC will form and that most PSCs are relatable to specific synoptic and mesoscale motions.
Journal of Geophysical Research, 1999
Multispectral lidar measurements of polar stratospheric clouds (PSCs) from two winter campaigns in 1994/1995 and 1996/1997 at Sodankyl&, Finland, have been evaluated together with temperature data from local radiosondes to find optical parameters for a PSC classification of different particle types and their existence temperatures. Precise depolarization measurements show that both solid and liquid particles exist below the NAT (nitric acid trihydrate) temperature.
2020
Polar stratospheric clouds (PSCs) are a driver for ozone depletion in the lower polar stratosphere. They provide surface for heterogeneous reactions activating chlorine and bromine reservoir species during the polar night. The large-scale effects of PSCs are represented by means of parameterisations in current global chemistry-climate models, but one process is still a challenge: the representation of PSCs formed locally in conjunction with unresolved mountain waves. In this study, we investigate direct simulations of PSCs formed by mountain waves with the ICOsahedral Nonhydrostatic modelling framework (ICON) with its extension for Aerosols and Reactive Trace gases (ART) including local grid refinements (nesting) with two-way interaction. Here, the nesting is set up around the Antarctic Peninsula, which is a well-known hot spot for the generation of mountain waves in the Southern Hemisphere. We compare our model results with satellite measurements of PSCs from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and gravity wave observations of the Atmospheric Infrared Sounder (AIRS). For a mountain wave event from 19 to 29 July 2008 we find similar structures of PSCs as well as a fairly realistic development of the mountain wave between the satellite data and the ICON-ART simulations in the Antarctic Peninsula nest. We compare a global simulation without nesting with the nested configuration to show the benefits of adding the nesting. Although the mountain waves cannot be resolved explicitly at the global resolution used (about 160 km), their effect from the nested regions (about 80 and 40 km) on the global domain is represented. Thus, we show in this study that the ICON-ART model has the potential to bridge the gap between directly resolved mountainwave-induced PSCs and their representation and effect on chemistry at coarse global resolutions.
Polar Science, 2011
Solid polar stratospheric cloud (PSC) layers observed by lidar and a balloon-borne optical particle counter (OPC) on 17 December 1995 are reexamined in a comparative analysis framework. The typical radius of solid particles in the observed PSC is determined through the comparative analysis to have been approximately 2.3 mm. A backward trajectory analysis for the air mass in which the solid particles were observed shows that the air mass had experienced temperatures 2e3 K below the frost point of nitric acid tri-hydrate (NAT) during the 4 days preceding the observations. The back-trajectory analysis traces the air mass back to northern Greenland and Ellesmere Island on 16 December, one day before the observations. A microphysical box model is used to investigate possible mechanisms of formation for the observed solid particles. The results of this model suggest that the solid particles formed under mesoscale temperature fluctuations associated with mountain lee wave activity induced by the relatively high terrestrial elevations of northern Greenland and Ellesmere Island.
Journal of Aerosol Science, 2003
Observations of Polar Stratospheric Clouds (PSCs) were carried out with an airborne lidar on the stratospheric M55 Geophysica aircraft during a ight from Rovaniemi, Finland, on 9 January, 1997. The clouds were observed at the zenith, downwind from the Norwegian Alps: three PSCs, of somewhat di erent characteristics, were detected at heights between 23 and 28 km. In two of the clouds, di erent types of particles seem to coexist: echoes attributable to types I and II PSCs are found in di erent portions of the clouds. The formation of the PSCs is related to an orographic lee-wave, whose development was forecast by a mesoscale dynamical model used to plan the ight path. The largest observed PSC displays a complex structure, that appears to be in uenced by waves of di erent wavelengths. In particular, lidar and in situ data suggest the presence of a wave having a relatively short length (about 18 km) that overlaps on the main lee-wave. The short wavelength oscillation is thought to play a major role in the cloud development, determining the rapid formation and evaporation of particles and therefore the non-stationary character of the PSC.
Journal of Geophysical Research, 2003
1] Since 1994, Rayleigh lidar measurements of the Arctic middle atmosphere have been conducted at the Sondrestrom research facility near Kangerlussuaq, Greenland (67.0N,50.9W). The summer lidar observations typically cover the late June through August period. From these observations, 220 hours of noctilucent clouds (NLCs) have been detected by the lidar spanning 16 hours of local time. Organizing the cloud characteristics irrespective of local time reveals the most common cloud height as 82.5 km, the most common full-width-half-maximum (FWHM) as 0.7 km, and the most common peak volume backscatter coefficient as 20.0 Â 10 À11 m À1 sr À1 . The FWHM is noticeably thinner than determined by other lidar observations of NLCs in Norway and the South Pole. We found the mean backscatter strength to increase and the FWHM to decrease with decreasing cloud height. In addition, the cloud slopes with time are greater for the thicker weaker clouds at higher altitudes than the thinner stronger clouds at lower altitudes. Gravity-wave signatures are routinely observed in the cloud detections. Upon estimating stratospheric wave activity in the data, we observed stronger cloud backscatter during low gravity-wave activity and weak cloud backscatter during high gravity-wave activity. To help support these results, simulations from a microphysical cloud model were performed under summer mesospheric conditions with and without gravity-wave activity. Upon including short-period ($2-3 hours) gravity-wave activity, the model simulation reproduced the behavior observed in the ensemble cloud properties by producing a broader altitude distribution, weaker backscatter strength, and thinner clouds.