Aircraft observations of rapid meridional transport from the tropical tropopause layer into the lowermost stratosphere: Implications for midlatitude ozone (original) (raw)
Related papers
Impact of stratospheric dynamics and chemistry on northern hemisphere midlatitude ozone loss
Journal of Geophysical Research, 1998
The importance of dynamics for stratospheric ozone distribution in the northern hemisphere is investigated by using multiannual simulations of the coupled dynamic-chemical general circulation model ECHAM3/CHEM. This model includes a parameterization for heterogeneous reactions on the surfaces of polar stratospheric clouds (PSCs) and on sulfate aerosols. A warm and a cold stratospheric winter are examined to estimate the range of chemical ozone loss in the model due to heterogeneous reactions on PSCs. Ozone depletion in the model mainly occurs inside the polar vortex. An additional ozone reduction due to heterogeneous reactions on PSCs is found outside the polar vortex. Secondary vortex formation and vortex contraction after an elongation lead to a transport of air masses with chemically reduced ozone values out of the vortex. Except for such events the edge of the modeled polar vortex acts as a barrier to transport. During the formation of secondary vortices no additional heterogeneous reactions occur therein. Other dynamic events, such as the elongation of the polar vortex and its displacement to lower latitudes, lead t,o an intense ozone depletion. A minor stratospheric warming in the model causes a total aleactivation of chlorine compounds and prevents further ozone depletion. In midlatitudes, the amplitude of short-term variations of total ozone is amplified by PSC heterogeneous chemical ozone reduction. 1. Introduction After the discovery of the Antarctic ozone hole [Farman et al., 1985], several studies addressed the question of the importance of distinct chemical and dynamic reasons for the observed ozone depletion [e.g., Crutzen and Arnold, 1986; Solomon, 1986] (see World Meteorological Organization (WMO) [1992] for more detailed discussion). From satellite measurements it was obvious that the ozone decrease over the last decades was not restricted to the southern hemisphere high latitudes but also occurs in the northern hemisphere and at midlatitudes of both hemispheres [Stolarski et al., 1991, 1992; Randel and Wu, 1995]. This finding led to an intense debate on the characteristics of the stratospheric polar vortex and related effects on stratospheric transport processes at its edge, i.e., whether the polar vortex acts as a "containment vessel" [Mcintyre, 1989; Schoeberl et al., 1989] or as a "flowing processor" [Tuck, 1989; Proffittet al., 1989]. A comprehensive discussion was given by Schoeberl et al. [1992], Randel [1993], and Wanben Paper number 98JD01830. 0148-0227 / 98 / 98 JD-01830509.00 et al. [1997]. Measurements revealed that near the edge of the vortex the meridional poleward transport in winter has been reduced, resulting in different compositions of the air inside and outside the polar vortex (e.g., for southern hemisphere conditions [Tuck, 1989; Margitan et al., 1989] and for northern hemisphere conditions [Proffitt et al., 1990]). However, model studies [Juckes and Mcintyre, 1987] and observational studies [e.g., Tuck, 1989] clearly showed that the polar vortex
Ozone and tracer transport variations in the summer northern hemisphere stratosphere
Journal of Geophysical Research: Atmospheres, 2001
Constituent observations from the Upper Atmosphere Research Satellite (UARS) in combination with estimates of the residual circulation are used to examine the transport and chemical budgets of HF, CH4 and 03 in the summer Northern Hemisphere. Budget calculations ofHF, CH4 and 03 show that the transport tendency due to the residual circulation increases in magnitude and is largely opposed by eddy motions through the summer months. Ozone budget analyses show that between 100 and 31 hPa, the magnitudes of the mean circulation and eddy transport tenns increase through the summer months, producing tendencies that are factors of 2 to 3 times larger than the observed ozone change in the stratosphere. Chemical loss dominates the observed ozone decrease only at the highest latitudes, poleward of about 70øN. A comparison of observations from the Total Ozone Mapping Spectrometer with UARS-calculated total ozone suggests that poleward of 50øN, between 35% and 55% of the seasonal ozone decline during the summer occurs at altitudes below 100 hPa. The overall uncertainties, associated primarily with calculations of the residual circulation and eddy transport, are relatively large, and thus prevent accurate and useful constraints on the ozone chemical rate in the lower stratosphere. ozone must be well understood before accurate assessments of Copyright 2001 by the American Geophysical Union. Paper number 2001JD900004. 0148-0227/01/2001 JD900004509.00 anthropogenic processes can be made. Therefore it was recognized that a concerted effort must be made to study and assess the accuracy of the ozone budget in this region of the atmosphere. The focus of this paper will be to further examine transport variations in the summer NH stratosphere and assess how well we can constrain the budget terms using available tracer and circulation fields. The summer hemisphere has generally been characterized as a region of weak meridional circulation [Brasseur and Solomon, 1986; Luo et al., 1997]. Because topographically forced largescale planetary waves cannot propagate through the prevailing easterly winds present in the summer hemisphere [Charhey and Drazin, 1961], eddy wave activity is relatively weak. Statistics from the National Centers for Environmental Prediction (NCEP) analysis show that amplitudes of wave 1-3 geopotential height are significantly weaker from June through September in the NH midlatitudes [Randel, 1987]. Previous observations of tracer variability in the summer stratosphere have been explained as either remnants of the springtime final warming or normal mode wave oscillations [Ehhalt et al., 1983; Hess and Holton, 1985]. The variations in ozone and other trace gases in the summer stratosphere have been studied using various approaches. Results from a two-dimensional (2-D) model indicate that poleward of 40øN from 15 to 30 km, the net ozone loss during summer is due to photochemical destruction. This is attributed to the increased effectiveness of the odd nitrogen catalytic cycle [Perliski et al., 1989; Gao et al., 1999]. At lower latitudes, production and destruction are balanced by transport, while at higher altitudes, ozone is in photochemical equilibrium. However, the recent analysis of Rosenlof [1999] suggests that the seasonal cycle in transport is an important contributor to the summertime ozone budget between 60 ø and 70øN in the lower stratosphere.
Diagnosis of the Ozone Budget in the Southern Hemisphere Lower Stratosphere
The ozone budget in the southern hemisphere (SH) springtime lower stratosphere is studied using the SLIMCAT 3D chemical transport model (CTM). The model was run with UKMO and ECMWF analyses and both produce O 3 structure and variability that is in reasonable agreement with the observations during APE-GAIA (Airborne Polar Experiment -Geophysica Aircraft in Antarctica) campaign. In particular, the model generally reproduces the location of vortex edge well. The O 3 budget, based on its continuity equation, shows that transport processes play an important role in the lower stratosphere, but the horizontal and vertical transport of O 3 tend to show a large cancellation at mid-latitudes. Consequently, the net ozone change is similar to the chemical loss. The transport and chemistry O 3 change are generally out-of-phase. For the chemical loss, ClO x and BrO x cycles dominate in the polar vortex, ClO x cycles are responsible for about 80% of ozone loss below 400K where vortex air mixes rapidly to mid-latitudes.
Transport of near-tropopause air into the lower midlatitude stratosphere
Quarterly Journal of the Royal Meteorological Society, 1998
During the last week of January 1992 ozonesonde observations over Europe revealed a layer of very low ozone concentrations in the stratosphere-below 100 parts per billion (lo9) by volume in the potential-temperature range 360-380 K. A coincident lidar observation revealed that the air was virtually free of volcanic aerosol, which filled the lower stratosphere at that time. The layer corresponded well with low potential vorticity (PV) in ECMWF analysis fields. Trajectory calculations confirmed a subtropical origin for the layer, and PV fields suggest that it was formed in a streamer of low-PV air drawn from the troposphere over North America as the subtropical jet stream turned northwards on 25 January. Ozone profiles on the equatorward flank of the subtropical jet stream contain similar mixing ratios to those seen in the layer over Europe in the same potential-temperature range. The mass of the layer at its maximum extent is estimated as 6 x lOI5 kg. Most of the air in the layer eventually returned to the subtropics after mixing with ambient midlatitude air.
A comparison of Northern and Southern Hemisphere cross-tropopause ozone flux
Geophysical Research Letters, 2003
The troposphere is the lowest layer of the atmosphere extending from the surface to an average midlatitude height of about 12 km. The tropopause separates the troposphere from the atmospheric layer immediately above called the stratosphere. Approximately 90% of atmospheric ozone is in the stratosphere. The remaining 10% is found primarily in the troposphere. The sources of ozone include pollution, chemistry) and transport from the stratosphere. Knowledge of how much tropospheric ozone results from each source is required to answer questions concerning the tropospheric composition, factors producing change in its composition, and interactions between upper tropospheric composition and climate. A novel method of calculating the downward ozone flux across the midlatitude (30"-60") tropopause shows the Northern Hemisphere (NH) ozone flux to be significantly larger (-24%) than that calculated in the Southern Hemisphere (SH) during the year 2000. This diagnostic method makes it possible to separate dynamical aspects of transport from the seasonal cycle of ozone in the lowermost stratosphere and explain the hemispheric difference in the ozone flux. The SH total horizontal area of exchange is equal to or slightly greater than the area of exchange in the NH throughout an annual cycle. The mean changes in potential vorticity of parcels near the tropopause are also similar or slightly greater in the SH, suggesting that NH and SH downward total mass transport to the troposphere are comparable. These results imply that the greater NH ozone flux is mostly due to the amount of ozone available for exchange rat her than net hemispheric dynamical differences near the tropopause level.
Journal of Geophysical Research, 2002
1] A high-resolution three-dimensional off-line chemical transport simulation has been performed with the SLIMCAT model to examine transport and mixing of ozone depleted air in the lower stratosphere on breakup of the polar vortex in spring/summer 2000. The model included ozone, N 2 O, and F11 tracers and used simplified chemistry parameterizations. The model was forced by T106 European Centre for Medium-Range Weather Forecasts analyses. The model results show that, by the end of June, above 420 K, much of the ozonedepleted air is transported from polar regions to the subtropics. In contrast, below 420 K, most of the ozone-depleted air remains poleward of approximately 55°N. It is suggested that the influence of the upper extension of the tropospheric subtropical jet provides a transport barrier at lower levels, while strong stirring on breakup of the polar vortex is important at upper levels. The mean meridional circulation modifies the distribution of ozone-depleted air by moving it up the subtropics and down in the extratropics. The model simulation is validated by comparing vertical profiles of ozone loss against ozonesonde measurements. The model results are consistent with many of the features present in the ozonesonde measurements. F11-N 2 O correlation plots are examined in the model and they show distinct canonical correlation curves for the polar vortex, midlatitudes, and the tropics. Comparison against balloon and aircraft measurements show that the model reproduces the separation between the vortex and midlatitude curves; however, the ratio of N 2 O to F11 lifetimes is somewhat too small in the model. It is shown that anomalies from the midlatitude canonical correlation curve can be used to identify remnants of polar vortex air which has mixed with midlatitude air. At the end of June there is excellent agreement in the position of air with anomalous F11-N 2 O tracer correlation and ozone-depleted air from the polar vortex. Transport of ozone-depleted air on the breakup of the stratospheric polar vortex in spring/summer 2000,
Ozone and potential vorticity at the subtropical tropopause break
Journal of Geophysical Research, 1996
Ozone measurements near 200 mbar from two flights between California and Tahiti are interpreted using maps of potential vorticity (PV) on isentropic surfaces. We focus on extremely abrupt changes in ozone mixing ratio observed at latitudes of 13øN and 23.5øN. Their proximity to strong PV gradients on the 350 K isentropic surface shows that they are associated with crossings of the subtropical tropopause. Small-scale anticorrelations between ozone and carbon dioxide near one of the two ozone transitions indicate tha,t some stratosphere-troposphere exchange does occur in this region. Ozone mixing ratios on the stratospheric side of the subtropical tropopause varied from 50 to 100 parts per billion by volume, a range that is more commonly associated with the midlatitude troposphere and is much less than seen on the stratospheric side of the midlatitude tropopause.
Journal of Geophysical Research, 2000
Low-ozone (< 20 ppbv) air masses were observed in the upper troposphere in northern midlatitudes over the eastern United States and the North Atlantic Ocean on several occasions in October 1997 during the NASA Subsonic Assessment, Ozone and Nitrogen Oxide Experiment (SONEX) mission. Three cases of low-ozone air masses were shown to have originated in the tropical Pacific marine boundary layer or lower troposphere and advected poleward along a warm conveyor belt during a synoptic-scale disturbance. The tropopause was elevated in the region with the low-ozone air mass. Stratospheric intrusions accompanied the disturbances. On the basis of storm track and stratospheric intrusion climatologies, such events appear to be more frequent from September through March than the rest of the year. Oceanography, University of Rhode Island, Narragansett. above normal 36.9% of the time, normal ozone 56.0% of the time, and below normal 7.1% of the time. When anticyclonic weather patterns with southerly flow existed, total ozone was below normal 28.5 % of the time, normal 66.8% of the time, and above normal 4.7% of the time. When only flow direction was considered, above-normal total ozone was observed 30.1% of the time for northerly flow, while below-normal ozone was found 26.5% of the time for southerly flow. The Subsonic Assessment, Ozone and Nitrogen Oxide Experiment (SONEX) mission provided an opportunity to obtain more information regarding the transport of lowozone air from the tropics to northern midlatitudes. The purpose of SONEX was to study the upper troposphere/lower stratosphere in and near the North Atlantic flight corridor to better understand this region of the atmosphere and how civilian air travel might be affecting the atmospheric chemistry [Singh et al., 1999]. Bases of operations included NASA Ames (Moffett Field), California (37.4øN, 122.1ø-W); Bangor, Maine (44.8øN, 68.8øW); Shannon, Ireland (52.7øN, 8.9øW); and Lajes, Terceira Island, Azores (38.8øN, 27.1øW). It took place from