A21C-0160
The Impact of 21st Century Source Gas Changes on the Upper Stratosphere
It is expected that future changes in the concentrations of surface source gases, including N2O, CH4, CO2, and chlorofluorocarbons, will impact stratospheric composition and dynamics. In this study,we use the GSFC two-dimensional chemistry and transport model to investigate the impact of these source gases on the middle and upper stratosphere during the 21st century. Specifically, we ran several model simulations in which these source gases are varied one at a time in order to assess the impact of each source gas individually. These are then compared with a complete simulation in which all source gases are allowed to vary simulataneously. In this way we examine the relative impact of each source gas on future changes in stratospheric ozone, water vapor, temperature, and age of air. We also derive sensitivity factors of these quantities to the variations of each source gas, and investigate the effects from different IPCC scenarios for future greenhouse gas emissions. The relative contribution of the 11-year solar cycle in UV flux to future stratospheric change will also be examined.
A21C-0161
What would have happened to the ozone layer if chlorofluorocarbons (CFCs) had not been regulated?
Ozone depletion by chlorofluorocarbons (CFCs) was first proposed by Molina and Rowland in their 1974 Nature paper. Since that time, the scientific connection between ozone losses and CFCs and other ozone depleting substances (ODSs) has been firmly established with laboratory measurements, atmospheric observations, and modeling research. The nations of the world implemented the Montreal Protocol (and amendments) which stopped ODS production in 1992. In this presentation we use a fully coupled radiation- chemical-dynamical model to simulate a future world where ODSs were never regulated and ODS production grew at an annual rate of 3%. In this "world avoided" simulation, 17% of the globally average column ozone is destroyed by 2020, and 67% is destroyed by 2065 in comparison to 1980. Large ozone depletions in the polar region become year-round rather than just seasonal as is currently observed in the Antarctic ozone hole. Very large temperature decreases are observed in response to circulation changes and decreased shortwave radiation absorption by ozone. Ozone levels in the tropical lower stratosphere remain constant until about 2053 and then collapse to near zero by 2058 as a result of heterogeneous chemical processes (as currently observed in the Antarctic ozone hole). The tropical cooling that triggers the ozone collapse is caused by an increase of the tropical upwelling. In response to ozone changes, ultraviolet (UV) radiation increases, tripling the erythemal (sunburn) radiation in the northern summer mid-latitudes by 2065.
A21C-0162
Total Ozone Observations at Arosa (Switzerland) by Dobson and Brewer: Temperature and Ozone Slant Path Effect
Dobson and Brewer spectrophotometers are the main ground based instruments used to monitor the ozone layer. Early total ozone (TOZ) measurements were made primarily with Dobson instruments; however, there has been a trend over the last years to replace them by the newer, more advanced Brewer spectrophotometer. Given this transition, it is of utmost importance to assure the homogeneity of the data taken with these two distinct instruments types if total ozone (TOZ) changes over long time periods are to be diagnosed accurately. Previous studies have identified a seasonal bias of few percentage from Brewer and Dobson spectrophotometers measurements at mid-latitudes. At Arosa (Switzerland), two Dobson and three Brewers instruments have been co-located since 1998, producing a unique dataset of quasi-simultaneous observations valuable for the study of systematic differences between these measurements. The differences can be at least partially attributed to seasonal variability in the atmospheric temperature and the ozone slant path. The effective temperature sensitivity of the ozone cross section has been calculated using different reference spectra, at high and low resolution, weighting of the slit functions for each operational Brewer and for the primary standard Dobson spectrophotometers. If one takes into account the temperature dependence of the [Bass, 1985] ozone absorption spectra (current remote sensing standard) and the ozone slant path effect, the seasonal bias between Dobson and Brewer TOZ measurements is reduced from an amplitude of about 2% to less than 0.5%. The use of different ozone laboratory spectra yields different results in retrieved TOZ, because of the sensitivity of the retrieval algorithms and uncertainties in the experimental ozone cross section measurements.
A21C-0163
A Stratospheric Consensus Ozone Database for Long-Term Climate Simulations
There is increasing evidence that the stratosphere exerts control on tropospheric climate. For example, changes in the Southern Annular Mode (SAM) and Northern Annular Mode (NAM) are thought to be influenced by stratospheric ozone depletion in recent decades. General Circulation Models (GCM) that do not include chemistry must prescribe accurate stratospheric ozone distributions in order to capture these effects. Therefore, a new consensus ozone database has been created to provide the best possible input for climate models using many observational ozone datasets, including, but not limited to, SAGE, SBUV, HALOE, and ozonesondes. Five databases were originally created and compared before merging into a master database. Strengths and weaknesses of these original databases will be outlined. The master database includes several versions (tiers) that have increasing levels of interannual variations represented, from tier 1 which only includes interdecadal changes to tier 3 which includes the observed interannual changes to high fidelity. The availability of three tiers will allow modelers to select a dataset that best fits their simulation. Details of the database construction and its improvements over earlier databases will be discussed.
A21C-0164
Absolute quality of the Ozone Monitoring Instrument ozone columns and ozone profiles
We will present an absolute quality assessment of the total ozone column and vertical ozone profile data products from the Ozone Monitoring Instrument (OMI) onboard the NASA EOS-Aura satellite obtained by validation. OMI is an imaging UV-visible spectrometer mapping global ozone on a daily basis. Total ozone data have been derived using two algorithms; OMI-TOMS based on the TOMS version 8 algorithm and OMI- DOAS using the hyperspectral features of OMI. Vertical ozone profiles are derived from OMI nadir observation by optimal estimation. Column ozone was validated against a network of Dobson and Brewer ground stations, with airborne data gathered during NASA AVE campaigns and through comparisons of both ozone data products yielding absolute differences in DU. Most discovered instrumental shortcomings and algorithmic errors have been corrected in the collection 3 level-1B and ozone data sets and are publicly available. OMI ozone profiles have been validated against ozone profiles from the Microwave Limb Sounder (MLS), also onboard NASA EOS-Aura, yielding absolute differences in VMR. The primary OMI mission goal of continuing the NASA TOMS ozone record is achievable with either total column ozone data product. Daily global OMI ozone column and ozone profile data are well suited for estimating tropospheric ozone columns. Performing ozone trend studies and air quality studies requires the essential information presented here.
A21C-0165
Researcher and Educator Long Term Collaboration with NOAA ESRL Regarding Atmospheric Ozone Changes at the South Pole Through the NSF PolarTREC Program
The NOAA/ESRL team at South Pole has been monitoring the development of the annual ozone hole over two decades using balloon-borne and ground-based instruments. Collaboration with educators has become an important aspect of NOAA/ESRL to educate the public about ozone loss and ozone hole formation. Researcher Bryan Johnson and educator Elke Bergholz worked together at South Pole in 1998/1999 as part of the NSF teacher outreach program called Teachers Experiencing Antarctica (TEA). It has been almost a decade when they collaborated again concerning the ozone changes at South Pole as part of the International Polar Year (IPY) and the PolarTREC (http://www.polartrec.com) teacher outreach program sponsored by NSF. The TEA and PolarTREC programs selected teachers to travel to polar locations to work with research scientists collecting data and running experiments at various Arctic and Antarctic field sites. While in the field, daily contact with classrooms and students around the globe was done through internet journals, answering emails from students, and webinars. This will be followed up with presentations to schools and the public relating Ms Bergholz's experience and new "hands-on" understanding of ozone measurements and ozone depletion over Antarctica, and discussing what changes in ozone we have seen at South Pole since the first outreach program nearly a decade ago.
A21C-0166
Model simulations of stratospheric ozone loss caused by enhanced mesospheric NOx during Arctic Winter 2003/2004
Satellite observations show that the enormous solar proton events (SPEs) in October--November 2003 had significant effects on the composition of the stratosphere and mesosphere in the polar regions. After the October--November 2003 SPEs and in early 2004, significant enhancements of NOx (= NO + NO2) in the upper stratosphere and lower mesosphere in the Northern Hemisphere were observed by several satellite instruments. Here we present global full chemistry calculations performed with the CLaMS model to study the impact of mesospheric NOx intrusions on Arctic polar ozone loss processes in the stratosphere. Several model simulations are preformed with different upper boundary conditions for NOx at 2000K potential temperature (~50km altitude). In our study we focus on the impact of the non-local production of NOx, which means the downward transport of enhanced NOx from the mesosphere to the stratosphere. The local production of NOx in the stratosphere is neglected. Our findings show that intrusions of mesospheric air into the stratosphere, transporting high burdens of NOx, affect the composition of the Arctic polar region down to about 400 K (17-18km). We compare our simulated NOx and O3 mixing ratios with satellite observations by ACE-FTS and MIPAS processed at IMK/IAA and derive an upper limit for the ozone loss caused by enhanced mesospheric NOx. Our findings show that in the Arctic polar vortex (equivalent lat. > 70° N) the accumulated column ozone loss between 350-2000K potential temperature (~14-50km altitude) caused by the SPEs in October--November 2003 in the stratosphere is up to 3.3DU with an upper limit of 5.5DU until end of November. Further, we found that about 10DU, but in any case lower than 18DU, accumulated ozone loss additionally occurred until end of March 2004 caused by the transport of mesospheric NOx-rich air in early 2004. The solar-proton-produced NOx above 55km due to the SPEs of October-November 2003 had a negligibly small impact on ozone loss processes through the end of November in the lower stratosphere (350-700K ~ 14-27km). The mesospheric NOx intrusions in early 2004 yielded a lower stratospheric ozone loss of about 3.5DU and clearly lower than 6.5DU through the end of March. Overall, the non-local production of NOx is an additional variability in the existing variations of the ozone loss observed in the Arctic.
A21C-0167
Antarctic Ozone Hole: Self-Recovery in Late Spring
It is well accepted that the mixing with the air from middle latitudes leads to the recovery of the Antarctic ozone hole in the late spring after the vortex breaking. However, no models have successfully simulated the ozone recovery using this mechanism. Model usually fills up the ozone hole much slower than observations. Using the TOMS data of daily ozone column density, a budget analysis of two boxes, one from 60° S to the south pole and the other from 30° S to 60° S, shows that the mixing with the air from the middle latitudes alone cannot makes the ozone hole fully recovered, even if all the available extra ozone in the middle latitudes had been used to fill the hole. Therefore, increasing the mixing between the polar region and the middle latitudes cannot improve the model simulations of the recovery of the ozone hole. The time evolution of the total amount of ozone in those two boxes demonstrates that an extra ozone source is helping to fill the hole, especially in the early stage of the recovery. Based on the current knowledge of the ozone chemistry and transport in the stratosphere, the source of the extra ozone is very likely the one that is sequestered during the growing phase of the ozone hole. This means a significant part of the ozone, which is supposedly depleted during the growing phase of the ozone hole has actually not been destroyed photochemically, but is transformed into, e.g. a complex to avoid being detected as ozone. Once the physical and chemical conditions are changed after the vortex breaking the hidden ozone comes back into its normal gaseous form to fill the ozone hole. This conjecture would not only solve the ozone budget problem in the recovery phase of the Antarctic ozone hole and the problem of overestimation by the models of its dilution effects in the southern stratosphere but also reconcile the apparent contradiction between the observed rates of ozone depletion during the growing phase of the ozone hole and a recent lab measurement of the cross section of ClOOCl photolysis (Pope, et al., J. Phys. Chem. A 111, 4322, 2007), which is one of the key parameters of the current ozone hole theory.
A21C-0168
Systematic Pressure and Temperature Differences between Vaisala RS80 and RS92 Radiosonde-Systems
National meteorological centers are replacing the widely used Vaisala
RS80 radiosonde with the newer RS90 or RS92. Such change-overs often
introduce erroneous steps into long-term atmospheric temperature
records. We show that twin-flight campaigns with RS80 and RS92 sondes
on the same balloon, and the transition from RS80 to RS92 in
operational radio-soundings over Germany, consistently indicate higher
temperature readings from RS92 sondes in the stratosphere. In our
presentation we summarize these main differences between RS80 and RS92.
Significant differences are found in the stratosphere, above the
100~hPa level. The accuracy of our temperature results is of the order
of 0.1 to 0.5~K, and at this level we were not able to find significant
differences in the troposphere, although there are indications for
slightly higher daytime temperatures from RS92 sondes. During day-time
and near 50~hPa, RS92s report +0.3 ± 0.2~K higher temperature than
RS80s, increasing to +0.7 ± 0.4~K near 10~hPa (2σ
uncertainties). At night, the difference is smaller, +0.1 ± 0.1~K
near 50~hPa to +0.35 ± 0.2~K near 10~hPa. The mean day-to-night
difference (12-00~UT) is also larger for RS92s, by 0.1± 0.06~K
near 70~hPa, and by 0.76± 0.16~K near 10~hPa.
The main
contribution to this stratospheric day-time difference comes from an
over-correction of the radiation error in the Vaisala RS80 data
processing. The night-time difference at stratospheric levels (and
part of the day-time difference) is due to a low bias of the RS80
pressure measurement, typically by -0.4~hPa near 10~hPa. This shifts
temperature readings to lower pressure/ higher altitude. For
stratospheric levels, it results in lower temperatures from RS80
sondes (due to the vertical temperature increase).
Generally, RS92s give better temperature repeatabiliy, ±0.25~K
(2σ) near 50~hPa, and much more precise pressure, ±0.2~hPa
near 50~hPa, compared to RS80 systems, ±0.5~K, or ±1.5~hPa.
Geopotential heights from RS92s are also much more precise, ±100~m
near 10~hPa compared to only ±1000~m for RS80s. A major advantage
of the RS92 is the on-board GPS receiver. It gives more precise
altitude information (±10~m), than previously available in the
stratosphere. Geopotential heights from RS92s are in very good
agreement with the on-board GPS altitudes, typically within ± 100
near 10~hPa (and better below), with some changes between production
charges.
Our results indicate that long-term records of stratospheric
temperature should be corrected for the transition from Vaisala RS80
to the newer and better RS92 radiosonde system. In our presentation we show the
main differences and give estimates for an appropriate correction.
Reference Steinbrecht, W. et al., 2008, Pressure and Temperature
Differences between Vaisala RS80 and RS92 Radiosonde-Systems, J.
Atmos. Ocean. Tech., 25, 909--927, doi:
10.1175/2007JTECHA999.1
http://ams.allenpress.com/perlserv/?request=get-
abstract&doi=10.1175%2F2007JTECHA999.1
class="ab'>
A21C-0169
The Different ENSO Teleconnections and Their Effects on the Stratospheric Polar Vortex
Reanalysis data are used to study the El-Niño Southern Oscillation (ENSO) signal in the troposphere and
stratosphere
during the late fall to mid-winter period. Warm ENSO events have extratropical tropospheric teleconnections
that increase the wave-1, and reduce the wave-2 amplitude, as compared to cold ENSO. The increase in
wave-1 overwhelms the decrease in wave-2, so the net effect is a weakened vortex. This modification in
tropospheric wave forcing is induced by a deepening of the wintertime Aleutian low via the Pacific-North
America Pattern (PNA). Model results are also used to verify that the PNA is the primary mechanism through
which ENSO modulates the vortex.
During easterly Quasi-Biennial Oscillation (EQBO), warm ENSO does not show a PNA response in the
observational record. Consequently, the polar vortex does not show a strong response to the different
phases of ENSO under EQBO, nor to the different phases of QBO under WENSO. It is not clear whether the
lack of a PNA response to warm ENSO during EQBO is a real physical phenomenon or a feature of the
limited data record we have.
http://www.atmos.washington.edu/~cig4/publications.html
A21C-0170
Effect of stratospheric sudden warming and vortex intensification on the troposheric climate
The effect of stratospheric sudden warming (SSW) and vortex intensification (VI) on the tropopsheric climate is examined through composite analysis of the observational data. Specifically examined in the present study is the Eulerian meridional circulations associated with SSW and VI. It is found that prominent signal in the troposphere tends to appear associated with the occurrence of SSW and VI. The patterns created are very similar between SSW and VI except for the polarity. In the high latitude region, the pattern similar to the Arctic Oscillation (AO) is created before and after the occurrence of SSW and VI with changing polarities. In the tropics, convection tends to enhance in the SH (NH) tropics after the occurrence of SSW (VI). These signals are created through three prominent cells of the anomalous Eulerian meridional circulation that extends from polar cap to the tropical Southern Hemisphere.
A21C-0171
Stratospheric climate change as diagnosed from the CCMVal reference simulations
In collaboration with the National Centre for Atmospheric Science (NCAS) a new chemistry and aerosol package has been developed for the Met Office Unified Model. A high top version of the model is currently being used by the University of Cambridge and the Met Office to carry out the so called reference simulations defined by the CCMVal SPARC activity. These include reproducing the past, and predicting ozone recovery in the future. In this work we present the first results from these simulations, concentrating on ozone recovery and future stratospheric climate change.
A21C-0172
Transient Meridional Circulations in the Stratosphere Associated With Stratospheric Sudden Warming Events
Transient meridional circulations and the driven mass flux associated with stratospheric sudden warming events are examined on the basis of the residual velocity in the Transformed Eulerian Mean (TEM) equations. In order to estimate the residual velocity, we use "omega" vertical motion from the Met Office UK stratospheric assimilated data, along with the Japan Meteorological Agency global analysis data. During stratospheric sudden warming events, amplified planetary waves propagate vertically, provide westward momentum for the zonal mean flow, and cause a large deceleration of the westerly polar night jet. Such a deceleration then brings about the poleward residual mean meridional flow in the vicinity of the deceleration region; a warming occurs on the lower poleward flank of the region due to the induced downward flow, which gradually moves downward with time and drives transient downward mass flux from the stratosphere to the troposphere. The above time evolution can clearly depicted by both the data for recent sudden warming events. Estimated downward mass flux across the 100 hPa surface in the northern hemisphere is found to be larger due to the strengthened meridional circulation than that in undisturbed phases of the circulation by 30 to 50 %. Such increase of the mass flux might influence the tropospheric circulation after the warming events.
A21C-0173
A Simulation of Gravity Waves over Antarctica
A state-of-the-art forecast model, the Advanced Regional Prediction System (ARPS), is used to examine gravity wave generation, propagation, and effects on the stratospheric dynamics. Initialized with GEOS-5 data from NASA's Global Modeling and Assimilation Office, this regional model has been extended vertically up to 55 km and horizontally to cover nearly the entire hemisphere. With a 6-km (0.4 km) horizontal (vertical) resolution, 24-hour forecast runs yield realistic tropospheric circulation and gravity waves features. We illustrate the model performance and features of a strong gravity wave event during 15 July 2008 over Antarctica. Potential relationships between gravity waves and polar stratospheric clouds are investigated in connection with various satellite products.
A21C-0174
Longitudinal Variations in Stratospheric Ozone: Effects on "Downward Control"
The wave drag associated with the damping and breaking of vertically propagating planetary waves in the stratosphere has far-reaching consequences for the global circulation and climate. The planetary wave drag (PWD) exerts non-local control over the extratropical stratosphere that manifests as a wave-driven equator- to-pole meridional circulation, termed the Brewer-Dobson circulation (BDC). In the steady state, the BDC can exert "downward control," whereby the body force exerted by the PWD causes a mean meridional circulation and a simultaneous mass adjustment in the surface pressure. Thus any changes in the PWD in the stratosphere will produce a balanced response in the region below. The downward influence exerted by longitudinal variations in stratospheric ozone is examined using a mechanistic chemistry-dynamical model (CDM) of the extratropical atmosphere. The CDM is one-dimensional in height and self-consistently couples dynamics, radiative transfer, and the transport and photochemistry of ozone. The longitudinal variations in ozone induce a zonal-mean body force that affects the residual circulation via the PWD. Under steady-state conditions, for which the "downward control" principle applies, a WKB analysis yields an analytical expression that shows the direct connection between the residual vertical velocity and the transport and photochemistry of ozone. Because the one-dimensional model framework confines the waves to propagate solely in the vertical, a stratospheric reflecting surface is required for the planetary wave-induced ozone heating in the stratosphere to produce non-local changes in that are manifested in the troposphere. These results underscore the importance of longitudinal variations in ozone as a pathway for communicating, via the combined effects of "downward control" and planetary wave reflection, natural and human-caused changes in stratospheric ozone to changes in tropospheric climate.
A21C-0175
Predictability of Stratospheric Circulations in Northern Hemisphere Winters From 2001 to 2006
The predictability of stratospheric circulations in Northern Hemisphere winters from 2001 to 2006 is examined by the use of ensemble 1-month forecast data produced by the Japan Meteorological Agency. In the current study, we examine time variations of Root Mean Square Error (RMSE) and Anomaly Correlation (AC), a pattern correlation between forecast and analysis anomalies of 10-hPa height, along with the spread among ensemble forecast members of 10-hPa zonal-mean temperature. Stratospheric circulations in the winter season largely vary with stratospheric sudden warming (SSW) events which are caused by enhanced planetary waves propagating from the troposphere (e.g., Andrews et al. 1987); in such phases, the RMSE tends to be large. The predictable limit can be defined as the time when the RMSE value surpasses a climatological standard deviation of the analyzed height field. The resultant limit during SSW events ranges from 3 to 19 days according to the case, and the mean value is about 10 days. On the other hand, we can also define the predictability based on the time when the AC first reaches a critical value, say, 0.6. The result is similar to that on the basis of the RMSE. Moreover, it is found that such forecast errors are caused by poor predictability of both zonal mean and planetary-wave fields. Specifically examined is the predictability for warming peaks of SSWs based on the spread in terms of 10-hPa zonal-mean temperature averaged over latitudes north of 80°N. Most warming peaks are roughly predictable from one to two weeks in advance, while SSW events in Dec 2001 and in Jan 2006 have a long predictable period of more than 2 weeks. These results are consistent with the predictability estimated by the RMSE and AC.
A21C-0176
EC-Earth climate model overturning circulation analysis
The first numerical experiments have been analysed with new types of overturning stream functions for both the atmospheric and the oceanic components. These stream functions portray the flow in the meridional direction using a generalised vertical coordinate; examples are presented where temperature, humidity, salinity, density and geopotential height are used rather than the vertical height. These overturning stream capture the flows responsible for the meridional energy and freshwater transports more accurately than the ordinary Eulerian latitude-height stream functions. Here, they are used to study the inter-hemispheric energy and mass transports and the exchange between the tropics and the polar regions. In particular, the dynamics and the nature of the Hadley, Ferrel and Polar cells are illustrated in novel ways that illuminate constraints on the energy and mass transports arising from atmosphere-ocean coupling. The heat, moisture and salt are also traced by using the Lagrangian trajectory code TRACMASS in both the ocean and atmosphere. The preliminary results are shown in Lagrangian stream functions by using the different vertical coordinates as with the Eulerian stream functions. The Lagrangian trajectories have been started and terminated at chosen latitudes in order to trace the meridional Lagrangian transports, which can not be seen in the Eulerian projection. Thus, in this way it has been possible to quantify the cross-Equatrial transports. The dynamics of the heat, moisture and salt overturning circulation are hence better understood in our coupled ocean- atmosphere system by the use of these new analysis methods and can be applied to any OAGCM integration.
A21C-0177
Changes in the Stratospheric Brewer-Dobson Circulation: Causes and Impacts.
We examine the changes in the Brewer-Dobson circulation chemistry-climate model simulations of the past or future, and possible causes of these changes. All models show an increase in tropical upwelling and decrease in stratospheric mean age, both for the past and future. We use a series of Chemistry-Climate Model runs to quantify the impact of changes in tropical sea surface temperature, CO2, and polar ozone on the stratospheric circulation. All three factors cause changes in the mean age, but the relative impact of each factor depends on the time period analyzed: Over the past 30-40 years polar ozone depletion is the primary factor causing the decrease in mean age, whereas the continued increase in SSTs is the primary cause of the decrease in mean age over the next 50-60. We also examine the impact of these simulated changes on the stratospheric composition, and compare the simulated changes with observations.
A21C-0178
Evidence for Recent Stratospheric Circulation Changes From Multiple Measurement Sources
Measured indicators of stratospheric circulation changes have been difficult to attain due to a lack of sufficient long-term stratospheric measurements. Several such datasets do exist however and each of them, such as stratospheric water vapor mixing ratios measured over Boulder, CO, suggest that changes have occurred in the stratosphere over the last 25 years. We show that the changes seen in the measured or measurement-based indicators of stratospheric circulation, including stratospheric water vapor measurements, a residual circulation calculation and age of air estimates, are consistent with each other. Collectively these datasets help to describe the two main features of recent stratospheric circulation changes: (1) a trend of increasing water vapor mixing ratios and age of air from 1980-2000, and (2) a large, persistent shift during the year 2000 towards increased mass flux in the lower stratosphere, decreased water vapor mixing ratios and decreased age of air. Global climate models have been unable to reproduce either the correct trend or the subsequent large shift in the stratospheric circulation. It is likely that these stratospheric changes are driven by changes in tropospheric wave activity that induces changes in both mean circulation and mixing between the tropics and extratropics. We will include a brief analysis of Eliassen- Palm flux divergence statistics calculated from the NCEP Reanalysis dataset as an indicator of wave driving of the stratosphere to begin to analyze the cause of the changes. We will also look for changes in measured stratospheric tracer-tracer correlations that can only occur due to circulation changes. These observed changes in the stratosphere provide a large constraint on global climate models and it is clearly important to more fully understand their causes.
A21C-0179
Thirty years of stratospheric mean age tracer measurements: no observable change in the stratospheric circulation
The increase of greenhouse gas abundances in the atmosphere is associated with an increased radiative forcing, leading to a warming of the troposphere and a cooling of the stratosphere. A secondary effect of increasing levels of greenhouse gases is a possible change in the stratospheric circulation with substantial feed-backs on ozone and on the climate system. Model calculations expect mean age values to decrease as a consequence of a stronger Brewer Dobson circulation. We present a data set of CO2 and SF6 measurements compiled from all balloon-borne observations available over the last 30 years in the mid latitudes of the Northern hemisphere. Consistent tropospheric reference time series have been compiled to derive mean age values dating back to the mid 1970ies. These data have been used to determine the long term evolution of mean age in the mid latitude stratosphere. Here we show that, in contrast to the model predictions, mean ages derived from stratospheric observations do not show a negative trend. Possible sources of uncertainties and the significance level to which the model predictions can be falsified are discussed.
A21C-0180
Looking for evidence of changes in stratospheric circulation using measurements of halocarbons and N20
The stratospheric lifetimes of the halocarbons and nitrous oxide are dominated by simple photolysis. For this class of trace gases measured by our airborne GC, local lifetimes span two orders of magnitude at any given altitude. Similarly, for each species the local photolytic lifetimes decrease by more than two orders of magnitude from the tropopause to 32 km. This range in lifetimes covers the dynamic time scales of stratospheric transport, and makes these halocarbons extremely sensitive to the altitude degree of freedom in the stratospheric transport. Tagging an irreducible air parcel (air particle) in terms of the maximum height encountered during its path to a final location takes advantage of this logarithmic decrease with altitude in the local photolytic lifetimes. In particular, maximum path height identifies the molecular species that will have undergone substantial loss as opposed to paths whose maximum height affords little loss. A measurement of these photolytic species at a given location in the stratosphere can then be used to calculate the distribution of maximum path heights corresponding to the distribution of irreducible air particles that make up the particular air parcel measured. Changes in the vertical profiles of these photolytic species and the path distributions generated from them are powerful tools for studying change in stratospheric dynamics with far more sensitivity to changes in the vertical path than to changes in the time scales of transport. This approach therefore complements the use of age of air to monitor changes in stratospheric circulation. We will focus on the time period before and after the observed changes in stratospheric water vapor in the year 2000.
A21C-0181
Lidar Measurements of Background Stratospheric Aerosol and Minor Volcanic Eruption Effects
Weekly lidar measurements of aerosol backscatter have been made at Mauna Loa Observatory, Hawaii and Boulder, Colorado. The measurements concentrate on the stratosphere and cover many years of background conditions. The period since 1996 is especially interesting since only minor injections of aerosol due to volcanic eruptions and forest fires have perturbed the background levels. These events are easily identified by a sharp peak above the background aerosol levels at altitudes just above the 16 to 17 km maximum level of the tropopause. The upper altitudes of the layer are unperturbed. Recent examples are the 2006 eruption of the African volcano Nyamuragira, the 2008 Alaskan eruptions. The background aerosols sources are not well quantified, but appear to have increased by 10% per year since 2000 as measured at the two locations. The (lidar) backscatter to total scatter ratio is sensitive to changes in the particle size distribution, but the increase cannot be explained without an increase in total aerosol mass.
A21C-0182
Upper Troposphere and Lower Stratosphere Water Vapor Measurements Using Optimized Raman Lidar and Balloon-borne Sensors
Upper tropospheric and lower stratospheric water vapor concentrations are important for reasons of atmospheric radiation and composition but the measurement challenge of quantifying concentrations at these altitudes is significant. Recent advances in Raman lidar technology now permit measurements of water vapor with high precision to well beyond the tropopause. Measurements demonstrating significant sensitivity to water vapor at altitudes of 20-24 km were acquired by the NASA/GSFC ALVICE Raman lidar both at the Table Mountain Facility of the Jet Propulsion Laboratories, Wrightwood, CA and at the Howard University Beltsville Campus in Beltsville, MD during 2007 and 2008. We show comparisons of these measurements with Crygenic Frostpoint Hygrometer. We also show the results of an empirical correction to Vaisala RS-92 radiosonde that permits useful measurements in the upper troposphere and lower stratosphere.
A21C-0183
Interpretation of HALOE, ACE, and MIPAS Water Vapor and Methane Data in the Equatorial Upper Stratosphere
Water vapor and methane data measured by the Halogen Occultation Experiment (HALOE),the Atmospheric Chemistry Experiment (ACE), and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) are used to study time series of H2O+2*CH4 in the equatorial upper stratosphere. Recent studies [e.g. Nassar et. al., 2005] have shown that, generally, H2O+2*CH4 is a conserved quantity. However, multi-year time series of H2O+2*CH4 show unexpected time variations which occur even during periods of relative long- term stability in water vapor and methane entering the stratosphere. These variations are evident in time series for each dataset, are QBO and seasonal in nature, and peak near 2 mb with a magnitude of 2-3 % of the H2O+2*CH4 mixing ratio. The H2O+2*CH4 time variations are anti-correlated with the methane variations suggesting a connection to local transport. We address the potential causes of the variations in H2O+2*CH4 and rule out several possibilities such as QBO and seasonal (e.g. tape recorder) variations from the lower stratosphere and variations in water vapor from photodissociation. By using a common analysis approach to study water vapor and methane variations [e.g. Hansen and Robinson, 1989; Remsberg et. al., 1996], we calculate beta, also called the net chemical yield factor of water vapor from methane. Modeling studies of water vapor chemistry in the stratosphere [LeTexier et. al., 1988] found beta values >2 in the upper stratosphere and suggested that oxidation of molecular hydrogen must also be considered in the water vapor budget to explain these values. Using several approaches, we find beta values consistently >2 over the entire equatorial upper stratosphere using HALOE, ACE and MIPAS data. We then use this value of beta to calculate a time series which should better reflect the tropopause entry levels of water vapor and methane, and discuss the implications of this for the early 1990s increase in water vapor.
A21C-0184
An evaluation of proxies of polar stratospheric cloud presence based on CALIPSO observations
Due to the relative scarcity of polar stratospheric cloud (PSC) observations throughout either polar vortex, studies of the impact of PSCs on ozone chemistry are often based on proxies for PSC formation derived from models and/or other observations. The most common of these is to approximate the total volume of the vortex occupied by PSCs (VPSC) using the volume of the vortex (VNAT) in which the observed temperature is less than the nitric acid trihydrate (NAT) formation temperature (TNAT). The latter is computed from either assumed (climatological) or measured nitric acid and water vapor mixing ratios. The scope of CALIPSO observations of PSCs allows an unprecedented ability to obtain direct estimates of VPSC throughout the polar winter and spring. Herein, we compare VPSC estimated from CALIPSO data and VNAT computed using Microwave Limb Sounder (MLS) nitric acid and water vapor data. Our results show a highly non-linear relationship wherein VNAT significantly overestimates VPSC. We will discuss uncertainties in our findings and potential alternatives for TNAT as a proxy for PSC occurrence.
A21C-0185
A Reprocessed Standard NO2 Data Product from OMI
The OMI NO2 Team at NASA's Goddard Space Flight Center is producing a new version of the NO2 Standard Product. This new version incorporates algorithmic improvements and a modified set of data fields in the product files. The algorithm now features an improved surface reflectivity climatology, an improved time-dependent a priori profile climatology, a more careful treatment of clouds, and an improved calculation of air mass factors. Estimates of uncertainties have been tightened. Data fields have been made more intuitive, incorporating recommendations from current users, such as the inclusion of field-of-view corners. A separate field contains an estimate of the total NO2 column to the surface, which includes an estimate of the column below clouds. Some of the improvements have come out of validation studies of the previous Standard Product, while others address issues proposed by the user community. We will present comparisons of the new Standard Product to the previous release, and discuss the implications for validation. We will also discuss some limitations of the new product.
A21C-0186
Middle atmospheric Monitoring with SCIAMACHY limb observations
SCIAMACHY, the Scanning Imaging Absorption Spectrometer for Atmospheric CHartography (SCIAMACHY) orbits the Earth since March 2002 on board ESAs environmental satellite Envisat. SCIAMACHY is an 8-channel grating spectrograph covering the spectral range from 240 -- 2380 nm and performs atmospheric observations in nadir, solar/lunar occultation and limb-scatter geometry. Satellite observations of limb-scattered solar radiation in the UV/visible spectral range allow profile retrievals of several important minor constituents (e.g., O3, NO2, BrO, OClO) with good vertical resolution and near- global coverage on a daily basis. Furthermore, different types of atmospheric aerosols, e.g., tropospheric clouds, stratospheric background aerosols, PSCs, and NLCs/PMCs can be investigated with this technique. This presentation will (a) provide an overview of the data products successfully retrieved from SCIAMACHY limb-scatter observations at the University of Bremen, and (b) highlight the contributions of these limb observations to current scientific questions, such as long-term trends in stratospheric ozone, stratospheric bromine chemistry and the drivers for the variability of noctilucent clouds.
A21C-0187
Measurements of stratospheric ClO, HO2, BrO and O3 with a balloon-borne submillimeterwave heterodyne radiometer
ClO, HO2 and BrO are among the key trace gases in the photochemistry of stratospheric ozone. This paper reports the results of recent high altitude balloon flights of the Submillimeterwave Limb Sounder (SLS) instrument. The SLS is a heterodyne receiver that uses a superconductor-insulator-superconductor (SIS) tunnel junction mixer and tunable local oscillator to measure spectrally resolved atmospheric thermal emission in the 600 GHz to 700 GHz spectral region. Observed spectra and composition profiles of ClO, HO2, BrO, O3 and other gases were obtained from mid-latitude (34N) balloon flights in September of 2004, 2005 and 2007 and from a polar (67N) winter vortex flight in January, 2007. We compare these measured profiles with corresponding observations by satellite and other balloon-borne instruments. Observed diurnal variation of HO2 from mid-latitude flights and the ClO abundance observed in the winter polar vortex were analyzed using a photochemical model. We discuss implications for stratospheric O3 and polar chlorine chemistry.
A21C-0188
Sensitivity of Polar Stratospheric Ozone Loss to Uncertainties in Chemical Reaction Kinetics
Several recent observational and laboratory studies of processes involved in polar stratospheric ozone loss have prompted a reexamination of aspects of our understanding for this key indicator of global change. To a large extent, our confidence in understanding and projecting changes in polar and global ozone is based on our ability to simulate these processes in numerical models of chemistry and transport. The fidelity of the models is assessed in comparison with a wide range of observations. These models depend on laboratory- measured kinetic reaction rates and photolysis cross sections to simulate molecular interactions. The rates of all of these reactions are subject to uncertainty, some substantial. Given the complexity of the models, however, it is difficult to quantify uncertainties in many aspects of system. In this study we use trajectory box- model simulations for Antarctic and Arctic ozone to estimate the uncertainty in loss attributable to known reaction kinetic uncertainties. Following the method of earlier work, rates and uncertainties from the latest laboratory evaluations are applied in random combinations. We determine the key reactions and rates contributing the largest potential errors and compare the results with observations to evaluate which combinations are consistent with atmospheric data. Comparisons with ozone sonde and MLS data in the Antarctic and MATCH observations in the Arctic present a consistent picture of seasonal ozone loss and chlorine partitioning vis-a-vis the kinetic rates and their uncertainties. Implications for our theoretical and practical understanding of polar ozone loss will be assessed.
A21C-0189
Impact of Recent Laboratory Measurements of the ClOOCl Cross Section On Our Understanding of Polar Ozone Chemistry
The photolysis of ClOOCl is crucial in determining the rate of polar ozone loss due to the ClO+ClO cycle. Laboratory measurements of the ClOOCl cross section published in 2007 suggest that its photolysis rate is about a factor of six slower than the value used in most computer models. We show that the incorporation of these new cross sections into a photochemical model leads to poor agreement with values of ClO and ClOOCl measured during previous aircraft campaigns. The model under-estimates measured ClO and over- estimates measured ClOOCl by amounts much larger than the measurement uncertainties. These comparisons indicate that a model using the new cross section, and no other changes, provides a poor description of the chlorine photochemistry in the activated polar vortex. Such a simulation also results in much slower ozone loss rates than observed. Interestingly, a 3-D chemical transport model, WACCM, constrained to the slower photolysis rate produces chemical ozone loss rates greater than expected. We will present a summary of our understanding of polar ozone chemistry that builds on a workshop for the SPARC Initiative on the Role of Halogen Chemistry in Polar Stratospheric Ozone Depletion held during summer 2008 in Cambridge, England. We will also describe a new website that is designed to interface future laboratory determinations of the ClOOCl cross section with existing atmospheric measurements of ClO and ClOOCl.
A21C-0190
Laboratory Study of the UV Absorption Spectrum of the ClO Dimer (Cl2O2)
Catalytic ozone destruction cycles involving chlorine species play an important role in polar stratospheric ozone depletion. The UV photolysis of Cl2O2 (the ClO dimer) is a critical step in the ClO dimer catalytic cycle, which accounts for the majority of the observed polar ozone depletion. Consequently the determination of the ClO dimer UV spectrum has been the focus of a number of studies since the late 1980's. However, to this day, discrepancies exist among the published laboratory studies of the Cl2O2 spectrum. Here, we report a study of the UV absorption cross sections of the ClO dimer, in the gas-phase, in the wavelength region 200 - 450 nm at low temperatures (200 - 230 K) that was designed to resolve these discrepancies. Experiments were carried out in a thermostated Pyrex (or Quartz) reactor where Cl2O2 was formed from the self-reaction of the ClO radical, which was produced following the pulsed laser photolysis of various precursor mixtures (e.g. 351 nm photolysis of Cl2 and Cl2O mixtures), under static or flow conditions. UV spectra of the gas-phase species were acquired using diode array spectroscopy. The findings of the present study are compared with previously published results. The impact of the present work on calculated polar ozone depletion will also be discussed.