A43D-01 13:40h
Celebrating Twenty Years of SAGE II
October 5, 2004 marked the twenty-year anniversary of the launch of SAGE II, a remarkable occasion for atmospheric gas and aerosol profile measurements from low Earth orbit. SAGE II has produced the longest time series of near-global stratospheric ozone and aerosol data in existence. Its high vertical resolution of better than 1km, stability, nearly self-calibrating characteristic and, of course, robustness have provided the scientific community with an unparalleled data set for use in atmospheric and climate studies. The ozone record has become the standard for ozone profile trend determinations and for the development of a global ozone climatology. The aerosol record has been extremely important for characterizing volcanic impacts and their importance in developing climate models and studying the effects on ozone heterogeneous chemistry. In general, the SAGE II data have contributed significantly to the atmospheric and climate studies of variability, forcing, responses, consequences and predictions. This paper will present the fundamental principles of the occultation technique, its advantages and a comparison with other remote sensing techniques. Examples of the SAGE II aerosol, ozone and water vapor data will be presented along with their use in developing climatologies and trends, and in understanding their effects on heterogeneous chemistry, climate forcing and volcanic impact.
A43D-02 INVITED 14:00h
Incorporating Occultation Data in 3D Global Modeling Investigations
Occultation data has been instrumental in increasing our understanding of global dynamical and chemical processes of the atmosphere. The use of occultation data in the upper stratosphere and lower mesosphere has been key to understanding the coupling between these regions (e.g., high latitude, winter/spring, NOx transport from the mesosphere into the upper stratosphere). Occultation data has been fundamental in understanding the processes that control stratospheric ozone and water vapor distributions and trends. And recently, occultation data has been used to better characterize the chemical and dynamical properties of the upper troposphere / lower stratosphere (UTLS) region. This presentation will focus on how occultation data, specifically that from SAGE II, HALOE, POAM II, POAM III, ILAS, and ILAS II, has been used in the above-mentioned regions to evaluate 3D chemical transport models and more recently 3D chemistry climate models. Specific scientific studies using these models with occultation data will be shown. Needs for development of future occultation platforms will be highlighted.
A43D-03 14:20h
Chlorine Reservoir Partitioning in the Polar Stratosphere Revealed by ILAS and HALOE data
Partitioning of chlorine reservoirs in the polar stratosphere was analyzed by utilizing two occultation sensors, the Improved Limb Atmospheric Spectrometer (ILAS) and the HALogen Occultation Experiment (HALOE). The ILAS was on board the Advanced Earth Observing Satellite (ADEOS), and continued regular operation from November 1996 through June 1997. ILAS monitored profiles of O$_{3}$ and ozone-related species, such as aerosols (or PSCs), HNO$_{3}$, NO$_{2}$, N$_{2}$O, CH$_{4}$, and water vapor on a regular basis, 14 times daily at high latitudes in the both hemispheres. The newest retrieval algorithm (Version 6.0) of the ILAS successfully derives chlorine nitrate (ClONO$_{2}$) profiles in both hemispheres. The HALOE was launched on the Upper Atmosphere Research Satellite (UARS) spacecraft in September 1991, which measured vertical profiles of O$_{3}$, HCl, HF, CH$_{4}$, H$_{2}$O, NO, NO$_{2}$, aerosol extinction, and temperature. Combined analysis of HCl/HALOE and ClONO$_{2}$/ILAS helps to elucidate chlorine reservoir partitioning, ClONO$_{2}$/HCl over polar regions and inform estimates of ozone loss by chemical processes. Difference in the latitudinal coverage of the two sensors limits the period of simultaneous analysis to several months for both hemispheres. However, these months include recovery periods after ozone depletion in both hemispheres and an inter-hemispheric comparison is therefore possible. In February and March 1997, some of the ClONO$_{2}$ data showed significant enhancement of ClONO$_{2}$ that peaked at ~2 ppbv in the vortex on the 475-K isentropic surface, which indicates deactivation of active chlorines into ClONO$_{2}$. Low HCl values observed with HALOE during corresponding period in the vortex confirm deactivation of active chlorine to ClONO$_{2}$ rather than HCl. For the Southern Hemisphere, the mixing ratios of ClONO$_{2}$ on the 475-K surface were extremely low, while HCl is relatively high in the vortex. In the Arctic summer, after a temporary enhancement of ClONO$_{2}$ in late spring, the chlorine partitioning should gradually shift toward HCl from ClONO$_{2}$. When photochemical balance between ClO-ClONO$_{2}$ and HCl-Cl reactions is assumed, the [ClONO$_{2}$]/[HCl] ratio has a linear correlation to [O$_{3}$]$^{2}$/[CH$_{4}$] [Dessler et al., 1995]. In boreal summer (May and June), [ClONO$_{2}$]/[HCl] ratios derived by ILAS and HALOE show a good linearity to [O$_{3}$]$^{2}$/[CH$_{4}$] derived by ILAS measurements at altitudes from 14 to 24 km. The two major species of inactive chlorines are HCl and ClONO$_{2}$: the sum of the two species indicates total Cly approximately except for activated chlorines. The correlation of Cly ($\sim$ ClONO$_{2}$ + HCl) versus N$_{2}$O/ILAS is almost consistent with the correlation estimated by Woodbridge et al. [1995], though the derived Cly is slightly larger than the estimate of Woodbridge et al at higher altitudes. References Dessler et al., GRL, 22, 1721-1724, 1995. Woodbridge et al., GRL, 100, 3057-3064, 1995.
A43D-04 14:30h
On the Distribution of Ozone in Stratospheric Anticyclones
Thirteen years (1991-2004) of satellite occultation ozone data are combined with a climatology of stratospheric anticyclones and polar vortices to quantify the climatological ozone differences between air mass types. Ozone data from the Stratospheric Aerosol and Gas Experiment (SAGE) II, the Halogen Occultation Experiment (HALOE), the Polar Ozone and Aerosol Measurement (POAM) II and III missions, and the Improved Limb Atmospheric Spectrometer (ILAS) sensor are used in this study. Daily ozone measurements in the 400-1600 K altitude range are categorized as being either 1) in an anticyclone, 2) in a polar vortex, or 3) in neither (hereafter referred to as ``ambient"). Monthly mean ozone is then calculated in each air mass category from data combined over all years. This study focuses on ozone differences between anticyclones and the ambient environment. A composite annual cycle of ozone in ambient regions is compared to ozone in anticyclones as a function of altitude and latitude. Ozone differences result from both anomalous transport and photochemistry in the vicinity of stratospheric anticyclones. The relative importance of transport versus chemistry is inferred from the long-term ozone anomalies observed here. In summer, ozone gradients between different air mass types are small. In other seasons, results indicate three distinct vertical regimes at high latitudes. Below $\approx$600 K, anticyclones coincide with regions where ozone is reduced by 10-50% during the winter. Between 600 and 900 K from fall to mid-winter, anticyclones are associated with $\approx$10% more ozone than ambient air masses. Positive ozone anomalies are also observed in low latitude anticyclones within this vertical layer; however, they are half the size of their high latitude counterparts and peak several months later. Above 900 K the abundance of ozone in anticyclones is $\approx$10% less than in the surrounding air. This upper stratospheric regime results from the formation of ``low-ozone pockets" (LOPs) in stratospheric anticyclones. All LOPs that formed between November 1991 and November 2003 and were observed by a satellite used in this study (108 pockets) are documented here in the most comprehensive catalog of LOPs to date.
A43D-05 INVITED 14:40h
Trend detection in atmospheric data: Ozone Recovery
The levels of ozone-depleting substances in the atmosphere have begun to decrease, suggesting that early signs of ozone recovery in the stratosphere should soon be observed. Detecting changes in environmental parameters can be difficult, however, requiring that observing systems are designed appropriately and that statistical approaches incorporate what we currently understand about the measurements. Before monitoring even begins, the observing system can be designed to assure that parameters most responsive to environmental change are measured with adequate spatial resolution, temporal sampling, and instrument accuracy. This foresight in designing the observing system is particularly important because atmospheric responses to various forcings often show complicated patterns of change, which vary by altitude and region as well as with time. Ozone, for example, has experienced the greatest depletion in the upper and lower stratosphere as well as over the polar regions, particularly in the springtime. Exploring signatures of recovery as a function of altitude, latitude, and season can help determine whether observed changes are due to decreases in ozone- depleting substances, are part of natural variability, or are related to changes in stratospheric transport and composition due to climate change. Adequate temporal and spatial coverage combined with high accuracy can aid in attributing the observed changes and in assessing whether apparent trends or changes in trends provide clear and compelling evidence of ozone recovery.
A43D-06 15:00h
Lower Stratospheric Trends from a Comparison of ATMOS and ACE Measurements near 30\deg N Latitude
Long-term trends in the lower stratosphere have been derived from a comparison of volume mixing ratios measured from the solar occultation spectra recorded by the Atmospheric Chemistry Experiment (ACE) and a comparison of those results with measurements from the Atmospheric Trace MOlecule Spectroscopy Experiment (ATMOS) during Shuttle flights in May 1985 (Spacelab 3) and November 1994 (ATLAS 3). Trends are inferred from a comparisons at northern midlatitudes where sampling overlap occurs. Measured mixing ratios are referenced to those for N$_{2}$O, a conserved long-lived tracer to remove the contribution from atmospheric dynamics to the measured variations of the target molecules. Results are also compared with trends reported from other measurements and model predictions.
A43D-07 INVITED 15:10h
Smoke From a Distant Fire: Stratospheric Plumes in the SAM/SAGE/POAM and TOMS Era
In the boreal summer of 1998, the solar occultation instruments POAM III and SAGE II, along with the Earth-Probe TOMS, captured a remarkable phenomenon that until then had not been discovered: eruptive convective transport of forest fire smoke into the stratosphere. The effect on the stratosphere was a five-fold increase in zonal-average aerosol optical depth and a multi-month decay period. These same three instruments were the main players in characterizing yet another pyro-convective event in the boreal summer of 2001. On that occasion the aerosol layers attributable to the eruption reached to 18 km (potential temperature = 458 K), fully 9 km above the tropopause. Since then there have been more observations of stratospheric forest fire emissions, remotely and in situ, in other years and in the southern hemisphere as well. The discovery of extreme pyro-convection has shone a light on the strengths of high vertical resolution solar occultation instruments in their important monitoring of the stratosphere and the upper troposphere. It has also revealed unrealized potential in TOMS aerosol index archive, especially the newly released version 8 product. Moreover, the discovery of these so-called pyrocumulonimbus ("pyroCb" for short) has opened up avenues for new discoveries of past events in the 25-year TOMS and solar occultation record and a new interpretation of others. This report is a preliminary survey of the 1979-present satellite record of pyroCb events. We explore the invaluable quarter-century record of aerosol measurements made by SAM II, SAGE I-III, POAM II and III, and Nimbus-7 and Earth-Probe TOMS. In that time we find that the pyroCb effect on the lower stratosphere has been surprisingly substantial. We combine the TOMS aerosol index data, which can be used to unambiguously isolate dense upper troposphere-lower stratosphere smoke plumes, with aerosol extinction measurements from the solar occultation instruments in a way that clearly distinguishes the pyroCb events from volcanic eruptions. In so doing, we find that the pyroCb phenomenon had a repeated impact on the stratospheric aerosol burden in both boreal and austral hemispheres. We also show that the historical record contains reports of mystery clouds and volcanically-attributed aerosols that owe their existence to the pyroCb. In this era, more than 25 likely pyroCb eruptions can be identified. We will present the historical findings in both a temporal and spatial context, and highlight selected case studies.
A43D-08 15:30h
Trends in Non-Volcanic Stratospheric Aerosol Determined from 20 years of SAGE II Measurements
Junge's initial stratospheric aerosol measurements (1959-1960), at the end of a long volcanically quiescent period, and the long term stratospheric aerosol measurements beginning in the 1970s have been the basis for investigations of the trend of non-volcanic stratospheric aerosol. These investigations have been hampered by the difficulty of determining periods free of volcanic perturbations. Since 1959 there have been approximately 30 eruptions with volcanic explosivity indices of 4 or more. The longest records of stratospheric aerosol measurements, extending over 30 years, capture the three major aerosol-producing eruptions, Fuego, El Chichon and Pinatubo. The 20 year SAGE II record captures the decay of El Chichon aerosol, interrupted by the smaller tropical eruptions of Nevado del Ruiz, Nyamuragira, and Kelut, and the complete Pinatubo aerosol cycle. SAGE II measurements have not, in the past, been used to investigate trends since the data are limited by providing only two inter-volcanic periods between major eruptions, and only one cycle for a large eruption, Pinatubo. To circumvent this problem, and use the complete SAGE II record, we have developed a parametric exponential decay model to "devolcanize" the aerosol signal. The aerosol signal from the 5 major volcanic influences over the SAGE II record are each characterized by a 4 parameter model. The volcanic influence on the SAGE II measurements, captured by this 20 parameter model, is then subtracted from the 20 year record. The residual autocorrelated signal is then statistically investigated for trends. The modeling and trend investigation is done in 10 degree latitude bins (50N to 50S) and three altitude intervals (18-23, 24-29, 30-34 km). The results, which will be presented at the meeting, suggest that the global SAGE II data supplement nicely similar investigations of the four lidar, and one in situ, 30-year records of stratospheric aerosol. This work is being completed as part of the SPARC assessment of stratospheric aerosol.