A51D-0802 0800h
Simple Tropospheric Ozone Derivation From TOMS: Insight Into Tropical Latitudinal Distribution
The latitudinal total ozone distribution subtracted from the background tropospheric ozone column over the Pacific Ocean, a pollution-free region, (hereafter the Zonal Mean method) shows good agreement with the latitudinal stratospheric ozone distribution from the CCD. The latitudinal tropospheric ozone distribution from the CCD method, with a persistent maximum over the southern tropical Atlantic, is also seen in the latitudinal tropospheric ozone distribution from the Zonal Mean method. This approach suggests that the sophisticated CCD method can be replaced by the simple Zonal Mean method. However, several features are different from the distribution from satellite-derived products of fire counts, MOPITT CO, TOMS AI, ozone from GEOS-CHEM model, and the Scan Angle Method results in DJF and MAM periods. For investigation for this discrepancy in boreal winter and spring, we compare the latitudinal ozone distribution from the CCD and Zonal Mean method by using the SAGE measurements and the SHADOZ ozonesoundings based on the assumption of zonally invariant stratospheric ozone. In spite of the same negative N-S gradient for DJF, the N-S gradient in stratospheric ozone from the CCD and the Zonal Mean method is a 5 DU smaller than that from the TOMS-SAGE and the TOMS-ozonesonde methods. Because the relatively lower stratospheric ozone in the southern tropical Atlantic is subtracted from TOMS total ozone, the CCD and Zonal Mean method-derived tropospheric ozone present a peak over the southern tropics. On the other hand, the TOMS-SAGE and the TOMS-ozonesonde method products exhibit a maximum over the northern tropical Atlantic. In the MAM period, the latitudinal distribution in the TOMS-ozonesonde-derived tropospheric ozone shows a higher ozone amount over the northern tropical Atlantic than the southern Atlantic due to the negative N-S gradient in stratospheric ozone. Therefore, the latitudinal tropospheric ozone distribution depends on the latitudinal stratospheric ozone distribution even in the tropics.
A51D-0803 0800h
A long data record (1979-2003) of stratospheric ozone derived from TOMS Cloud Slicing: Comparison with SAGE and implications for ozone recovery
Abstract. It is generally recognized that Stratospheric Aerosols and Gas Experiment (SAGE) stratospheric ozone data have become a standard long-record reference field for comparison with other stratospheric ozone measurements. This study demonstrates that stratospheric column ozone (SCO) derived from total ozone mapping spectrometer (TOMS) Cloud Slicing may be used to supplement SAGE data as a stand-alone long-record reference field in the tropics extending to middle and high latitudes over the Pacific. Comparisons of SAGE II version 6.2 SCO and TOMS version 8 Cloud Slicing SCO for 1984-2003 exhibit remarkable agreement in monthly ensemble means to within 1-3 Dobson Units (DU) (i.e., 1-1.5 percent of SCO) despite being independently-calibrated measurements. An important component of our study is to incorporate these column ozone measurements to investigate long-term trends for the period 1979-2003. Our study includes Solar Backscatter Ultraviolet (SBUV) version 8 measurements of upper stratospheric column ozone (i.e., zero to 32 hPa column ozone) to characterize seasonal cycles and seasonal trends in this region, as well as the lower stratosphere and troposphere when combined with TOMS SCO and total column ozone. The trend analyses suggest that most ozone reduction in the atmosphere since 1979 in mid-to-high latitudes has occurred in the lower stratosphere below ~25 km. The delineation of upper and lower stratospheric column ozone indicates that trends in the upper stratosphere during the latter half of the 1979-2003 period have reduced to near zero globally, while trends in the lower stratosphere have become larger by ~5 DU per decade from the tropics extending to mid-latitudes in both hemispheres. For TCO, the trend analyses suggest moderate increases over the 25-year time record in the extra-tropics of both hemispheres of around 4-6 DU (Northern Hemisphere) and 6-8 DU (Southern Hemisphere).
http://hyperion.gsfc.nasa.gov/Data_services/cloud_slice/index.html
A51D-0804 0800h
The Latitude Dependence of the Effect Of Pinatubo on Stratospheric Ozone
Statistical analyses of TOMS and SBUV total ozone data indicate that the eruption of Pinatubo in 1991 led to a significant decrease in ozone at northern midlatitudes with little or no effect at southern midlatitudes despite the fact that aerosols were observed in both hemispheres. We argue that this puzzling absence of a southern hemisphere effect may be an artifact of the statistical analysis which does not fully account for interannual variability in dynamics. We have run a 3D CTM simulation of the past 30 years of stratospheric photochemistry with variable forcing due to chlorine/bromine compounds, solar ultraviolet radiation, and volcanic aerosols. This integration used winds from a general circulation model, which has similar interannual variability to the atmosphere. When this CTM output was examined with a standard time-series analysis, we found an effect of Pinatubo in the southern hemisphere, but not in the northern hemisphere. We then reran the CTM without volcanic aerosols. The subtraction of the two simulations indicated, as expected, that Pinatubo affected both emispheres in the model. This means that the northern hemisphere effect was in the model but did not show up in the statistical analysis. We also had an on-line parameterized chemical ozone tracer with seasonally repeating production and loss over the simulation. We used this as a dynamical surrogate to remove interannual variability from the original model output The residual time series was then analyzed for the Pinatubo effect and we were able to find it in both hemispheres. We suggest that the combination of the two volcanoes, El Chichon and Pinatubo, with the solar cycle and interannual variability led to this problem of analysis in the northern hemisphere of our model. We furthermore suggest that a similar effect may mask the response to Pinatubo in the southern hemisphere of the data. An analysis of the atmosphere's southern hemisphere with a good dynamical surrogate may solve the mystery of the missing southern hemisphere effect of Pintubo on ozone.
A51D-0805 0800h
The Contribution of Dynamic Interannual Variability to Ozone Trends
At middle latitudes the total column ozone and the lower stratospheric ozone mixing ratio exhibit natural variability. Models and statistical analyses of observations such as SAGE ozone profiles and TOMS column measurements show that seasonal cycle, solar cycle, and interannual dynamical variability and dynamical phenomena such as the quasi-biennial oscillation all contribute to ozone variability. These must be accounted for when deriving ozone trends. Systematic or random changes in the atmospheric circulation may also contribute to ozone trends. It is presently unclear how much of the lower stratospheric ozone trend derived from observations is due to changes in the chemical composition of the stratosphere and how much is due to changes in the atmospheric circulation. We are attempting to resolve this issue by comparing a twenty-five year three-dimensional simulation of ozone with fixed source gas boundary conditions with an identical simulation with time dependent source gas boundary conditions. Both simulations are driven with output from a general circulation model that produces realistic interannual variability in dynamical forcing. The model trend in ozone due to changes in composition is determined from the difference in these simulations. We compare these trends with trends determined from observations and model output using the same statistical analysis techniques. Initial results emphasize the complications to attribution of observed ozone trends to dynamical and photochemical effects that are due to interrelationships between trends in transport, temperature, and photochemical effects. It may not be possible to describe the ozone trend as a superposition of dynamical and photochemical contributions.
A51D-0806 0800h
Change In Ozone Trends At Southern High Latitudes
Long-term variations of total ozone columns at 60-70oS in spring have been investigated using both ground-based and satellite measurements. Strong positive correlation is shown between year-to-year variations of ozone and temperature in September and October. Based on this relationship, the effect of year-to-year vortex dynamical variations have been filtered out. This results in ozone time series which show increasing springtime ozone losses over the Antarctic until the mid-1990s. After that time, the ozone losses have leveled off. The analysis confirms that this change is consistent for all the measurement techniques and it is statistically significant at the 95% confidence level.
A51D-0807 0800h
Lower Stratosphere and Column Ozone Measurements from SAGE and HALOE
Both the Stratospheric Aerosol and Gas Experiment (SAGE) II (1984-present) and Halogen Occultation Experiment (HALOE) (1991-present) use solar occultation technique to measure ozone, aerosol extinctions and other trace gases. The SAGE-II ozone (V6.1) data have been shown to be of excellent quality, with accuracy of $\sim$10% or better, down to tropopause (Wang et al., 2002). The HALOE (v18) ozone data also show good agreements with ozonesonde. The differences are within 10% down to 100 hPa at tropical/subtropical regions and to 200 hPa at extratropical latitudes (Bhatt et al., 1999). In this study ozone profiles and stratospheric columns from the latest SAGE-II (v6.2) and HALOE (V19) retrievals will be further evaluated and compared by applying the PV mapping technique. Attempt will be made to combine both datasets and to derive tropospheric column ozone by the residual method (e.g. Chandra et al., 2003). This information will be beneficial to future/new satellite measurements such as AURA. The SAGE-III (2002-present) is a new generation of occultation instrument. It uses an 800 element Charged Couple Device (CCD) linear array to provide continuous spectral coverage from 280 to 1040 nm, and an additional photodiode at 1550 nm to extend aerosol information at longer wavelength. Since the SAGE-III has much higher spectral resolution (1-2 nm) than its predecessors, the retrieved ozone is less sensitive to enhanced aerosol or cloud. In other word it could provide more information for tropospheric ozone. The SAGE-III ozone quality especially in the lower stratosphere and troposphere will also be examined in this study. References Bhatt, P. P., E. E. Remsberg, L. L. Gordley, J. M. McInerney, V. G. Brackett, and J. M. Russell, An evaluation of the quality of Halogen Occultation Experiment ozone profiles in the lower stratosphere, J. Geophys. Res., 104, D8, 9,261-9,275, 1999. Chandra, S., J. R. Ziemke, and R. V. Martin, Tropospheric ozone at tropical and middle latitudes derived from TOMS/MLS residual: Comparison with a global model, J. Geophys. Res., 108(D9), 4291, doi:10.1029/2002JD002912, 2003. Wang H.J., D. M. Cunnold, L. W. Thomason, J. M. Zawodny, and G. E. Bodeker, Assessment of SAGE version 6.1 ozone data quality, J. Geophys. Res., 107(D23), 4691, doi:10.1029/2002JD002418, 2002
A51D-0808 0800h
Comparisons of Interannual Variability in Ozone as seen by SAGE II, HALOE, and Ozonesondes.
SAGE II and ozonesondes are the two primary source of information on trends in the vertical distribution of ozone in the mid and lower stratosphere (12-30 km). Ozone sonde data have been used to validate SAGE II ozone data, as well as all other satellite profile measurements of ozone below 30 km, and will be used to validate future profile measurements. Thus the sonde data will inevitably form a bridge between the occultation data and future ozone profile measurements from Aura and NPOESS. Previous work evaluating SAGE II data focused on comparison of nearly coincident profiles, and has shown that SAGE II and sonde data agree within 10% down to the tropopause; however there is a large spread in the differences between SAGE II and sondes in the lowermost stratosphere where ozone is most variable [Wang et al., 2002]. Our focus here is on comparison of the interannual variability shown by SAGE II, HALOE, and ozonesonde data in different regions of the northern mid-latitudes. Consequently, we rely on comparisons of monthly mean time series rather than limiting the results to coincidences. Monthly means form the basis for most trends analyses of ozone. We show here that SAGE II, HALOE, and the sondes are in good agreement in terms of interannual variability in the lowermost stratosphere, even though there are often very large differences in nearly coincident measurements. We use the satellite data to extend our analysis of the factors contributing to interannual variability in ozone. We find that unusually low values of ozone in the mid-latitude lower stratosphere are sometimes associated with so-called "ozone mini-hole" events. We use the occultation data to define the vertical distribution of ozone in these events, and use backward trajectories to determine their origin. Wang, H. J., D. M. Cunnold, L. W. Thomason, J. M Zawodny, and G. E. Bodeker, Assessment of SAGE version 6.1 ozone data quality, J. Geophys. Res, 107 (D23) 4691, 2002.
A51D-0809 0800h
Two-Dimensional Assimilation of the Solar Occultation Satellite Data from SAGE II and HALOE Together with SBUV Data to Study Long-term Ozone Trends
The Solar occultation data from SAGE II and HALOE have excellent vertical resolution but poor geographical coverage for a single day. In contrast, SBUV data has good geographical coverage but relatively poor vertical resolution. The methodology of two-dimensional chemistry-transport model-driven data assimilation allows us to combine these different instrument observations in a single mathematical framework to evaluate atmospheric ozone changes for several decades (1979-2003) and sets the stage for the future smooth connection to the SAGE II and HALOE data when these instruments stop functioning. The SUNY-SPb two-dimensional transport-chemistry model has been used to assimilate atmospheric composition data from different satellite instruments. The associated errors of the satellite observations are objectively calculated based on estimation theory. SBUV versus SAGE II and HALOE versus SAGE II results are compared for their overlap periods (1985-1989 and 1992-2003) based on the assimilation model calculation. Differences between global ozone trends derived from data only and from model assimilated ones are discussed. The differences between ozone trends in the Northern and Southern Hemispheres are discussed based on the difference in the air exchange between polar and mid-latitudes in the two hemispheres. Assimilated satellite data are used to study the role of solar activity variations, atmospheric dynamics, and aerosol effects for long-term ozone variability in different stratospheric altitude ranges.
A51D-0810 0800h
Assimilation of solar occultation ozone data
Assimilation of ozone data from solar occultation instruments into a global ozone model at NASA's Global Modeling and Assimilation Office (GMAO) is presented. Solar occultation data have higher vertical resolution and better accuracy than ozone data from nadir-viewing operational instruments like the Solar Backscatter UltraViolet/2 SBUV/2 instrument, especially in the lower stratosphere. However, the sparsity of solar occultation measurements presents challenges in the assimilation process. Nevertheless, our earlier work showed that assimilation of Polar Ozone and Aerosol Measurement (POAM) III data improved the representation of Antarctic ozone profiles in wintertime significantly. We present results of new multi-year assimilation experiments that combine ozone observations from Stratospheric Aerosol and Gas Experiment (SAGE) II and POAM III instruments with SBUV/2 data within GMAO's ozone assimilation system. We found improvements in the representation of lower stratospheric and polar ozone following the addition of the occultation data. We discuss the implications for studies of temporal ozone changes and for possible applications to real-time analyses and forecasting of weather and pollution.
A51D-0811 0800h
SAGE I, II, and III Data Available From the Atmospheric Sciences Data Center
The Atmospheric Sciences Data Center (ASDC) at NASA Langley Research Center archives data from Stratospheric Aerosol and Gas Experiment (SAGE) I, II, and III. These data span approximately 25 years and can be used to study long term trends such as the effects of volcanic eruptions and changes in ozone levels. The SAGE I, II, and III projects cover the time span February 1979 through the present and provide vertical distributions of nitrogen dioxide, ozone, water vapor and aerosols. The SAGE I and II projects use Sun Photometers to collect these measurements. The SAGE I instrument had four spectral channels centered at wavelengths of 1000, 600, 450, and 385 nanometers for nearly global measurements of aerosol extinction profiles and ozone and nitrogen dioxide concentration profiles. SAGE II data contain profiles of aerosol extinction at 1020, 525, 453, and 385 nanometers(nm) and number density profiles of ozone, nitrogen dioxide, and molecular density, water vapor mixing ratio, and aerosol surface area and effective radius at a vertical resolution of 0.5km. It also includes retrieved molecular density from 40-75km on a 0.5km grid. The ASDC continues to receive and archive the SAGE II data. SAGE III, which was launched as part of the NASA Earth Observing System program on December 10, 2001, obtains profile measurements of aerosol extinction at eight wavelengths, nitrogen trioxide, chlorine dioxide, clouds, temperature and pressure in the mesosphere, stratosphere, and upper troposphere with a vertical resolution of 0.5 - 1 km resolution. SAGE III collects measurements during both solar and lunar occultation events. Solar event species are aerosol, water vapor, nitrogen dioxide, ozone, temperature and pressure. Cloud measurements are also collected during solar events. Lunar event species are chlorine dioxide, nitrogen dioxide, nitrogen trioxide, and ozone. These measurements are collected using a grating spectrometer. In addition to the SAGE data, the NASA Langley ASDC archives data from two other solar occultation instruments that expands the coverage area to the polar regions. The Polar Ozone and Aerosol Measurement (POAM) II instrument measures the vertical distribution of atmospheric ozone, nitrogen dioxide, and aerosol extinction and covers the time span October 1993 through November 1996. The Stratospheric Aerosol Measurement (SAM) II project measures vertical distribution of stratospheric aerosols in the polar regions of both hemispheres and covers the time span October 1978 through December 1993. These data along with documentation and read software are available from the NASA Langley ASDC at http://eosweb.larc.nasa.gov.
http://eosweb.larc.nasa.gov
A51D-0812 0800h
A Unified Solar Occultation Data Base
The historical and ongoing archive of satellite-based solar and stellar occultation measurements is an international treasure. These data are valued particularly for their longevity, high vertical resolution, high accuracy and trend-quality nature. The Solar Occultation Satellite Science Team (SOSST), which is composed of a diverse community of scientists including representatives from all of the occultation instrument teams, is developing a single, unified data base of occultation data. The goal in developing such a data base is to more efficiently capitalize on the historical and continuing data from the occultation instruments, in part by increasing the use of SOSST data by climate modelers and the more general satellite community. The unified data base integrates measurements from all of the different occultation instruments, and includes ancillary meteorological data to facilitate scientific investigations. This presentation will describe the unified data base concept, and will outline a preliminary structure for the archive. To integrate applications of data from different instruments, cross-calibration of the data sets is required. Intercomparisons of the O3, NO2, H2O, and aerosol extinction profiles, utilizing the most recent retrieval versions from all instruments, will be summarized.
A51D-0813 0800h
Observed versus Modeled Arctic Ozone Loss during the 2002-2003 Winter
In the work presented here, results from the MOZART and SLIMCAT global three-dimensional chemical transport models(CTMs) are used to infer chemical ozone loss from Polar Ozone and Aerosol Measurement (POAM) III observations of stratospheric ozone during the 2002-2003 Arctic winter. Comparisons between observed ozone loss, loss inferred from model simulations, and theoretical estimates will be shown along with possible explanations for the differences. As the abundances of ozone-destroying chemicals decrease, accurately quantifying polar ozone loss is key to predicting the timing of ozone recovery. In spite of numerous investigations, numerical models routinely underestimate ozone loss in the lower polar stratosphere. Modeling discrepancies arise due to the inadequate representation of both chemical (i.e.dentrification, chlorine activation, and the sensitivity of ozone loss at high solar zenith angles) and dynamical (sub-grid scale mixing) processes. Comparisons between relevant chemical species and dynamical quantities will be used to understand the differences between observed and modeled ozone loss rates. Trajectory simulations will also be used to explore differences between ozone loss due to chemistry versus vertical and horizontal transport.
A51D-0814 0800h
Detection and Classification of Polar Stratospheric Clouds for the 2003/2004 Arctic and 2004 Antarctic Winters Using POAM III and HALOE Satellite Data
Measurements of aerosol extinction from the Polar Ozone and Aerosol Measurement (POAM) III and the Halogen Occultation Experiment (HALOE) satellite instruments during the 2003/2004 Arctic and the 2004 Antarctic winters are used to identify polar stratospheric clouds (PSCs). Techniques comparing the aerosol extinctions at multiple wavelengths are used to classify the clouds as either Type Ia or Type Ib. Type Ia are larger particles probably composed of nitric acid trihydrate (NAT), while Type Ib are smaller particles probably composed of super-cooled ternary solutions (STS). The characteristics of these PSCs are compared to results from previous years, and the appearance of Type Ia and Ib clouds are compared to results previously analyzed for the 1999/2000 Arctic winter. The capabilities of POAM III and HALOE to detect PSCs are compared. Recent results like these from solar occultation satellites can be used to validate the observations from instruments on newly launched satellites (e.g. Aura).
A51D-0815 0800h
Microphysical Modeling and POAM III Observations of Dehydration and Aerosol Extinction in the Antarctic Vortex
Stratospheric dehydration is examined for the Antarctic winter using the Integrated Microphysics and Aerosol Chemistry on Trajectories (IMPACT) model and data obtained by the Polar Ozone and Aerosol Measurement (POAM) III instrument. The model is applied to individual air parcels which are advected along 3-D trajectories using UKMO or NCEP global wind and temperature fields. Model results are compared to water vapor and aerosol extinction measurements obtained with the POAM instrument. The predicted water vapor mixing ratio value at the end of the winter season is consistent with POAM data, although modeled dehydration occurs more rapidly than is observed with POAM. Dehydration predictions in conjunction with modeled and observed aerosol extinctions allow several model parameters to be constrained. For example, measured aerosol extinctions provide useful limits on the NAT freezing parameters used in the model. In addition, a small temperature uncertainty is found to considerably affect model results.
A51D-0816 0800h
Retrieval of Thermospheric Molecular Oxygen Profiles from Solar and Stellar Occultation Measurements.
We present two new data sets of thermospheric molecular oxygen (O2) density profiles retrieved from both solar and stellar occultation measurements. The solar occultation measurements are made by the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) instrument onboard the UARS satellite, and the stellar occultations are obtained from the SOLar STellar Irradiance Comparison Experiment (SOLSTICE) on the SORCE satellite. Both instruments are nominally solar experiments whose primary mission is to measure the magnitude and variability of the UV solar irradiance. However, a simple extension of either the operational solar measurements (in the case of SUSIM) or the daily stellar calibration sequence (in the case of SOLSTICE) provides an opportunity to remotely sense the Earth's upper atmosphere using occultation. By measuring the attenuation of sunlight or starlight in the O2 Schumann Runge continuum (140 - 170 nm), it is possible to retrieve density profiles of O2 in the thermosphere (120 - 250 km). Since October 1991, SUSIM has performed solar occultation measurements one day per week, measuring full-disk solar extinction as a function of tangent altitude at 141, 160 and 171 nm. Over 1500 occultation profiles are currently available for analysis, spanning a wide range of solar and geomagnetic activity. Two identical SOLSTICE instruments have been operating onboard the SORCE satellite since January 2003. In the first year of operation approximately 100 occultation events were obtained but since May 2004 these measurements have been made on a routine basis, approximately 10 times per week. Both data sets cover a wide range of latitudes in each hemisphere - up to 67.5 degrees for SOLSTICE and 75 degrees for SUSIM. Retrieval of O2 density profiles from the SUSIM and SOLSTICE transmission measurements is achieved using an optimal estimation inversion algorithm, similar to the operational algorithms used for the POAM II and III multi-wavelength solar occultation instruments. We present the retrievals obtained from these two data sets, and use them to study trends in the variation of O2 density as a function of latitude, season, local time, and solar and geomagnetic activity. The results of this parametric analysis will be compared systematically to the predictions of the MSIS-90 and NRLMSIS-00 thermospheric models.
A51D-0817 0800h
SAGE III Measurements of O3 and NO2 after a Major Solar Proton Event
Ozone and nitrogen dioxide measurements by the Stratospheric Aerosol and Gas Experiment (SAGE) III instrument showed the significant effects of a major solar proton event in October 2003. Coronal mass ejections (CME) in late October led to greatly increased particle fluxes entering the middle stratosphere. The earth's magnetic field deflects charged particles poleward and the effect of increased fluxes is most apparent in polar regions. The increase in charged particle fluxes led to increased gas ionization, resulting in enhanced odd nitrogen production. Enhanced NO2 abundances were measured by both SAGE III solar and lunar occultation in high Northern latitudes. The sunset solar measurements and nocturnal lunar measurements were clustered near 75 degrees north +/- 5 degrees between 2 and 6 November 2003 and provide a unique dataset to evaluate the diurnal cycle of NO2 abundances during an unusually strong proton event.
A51D-0818 0800h
Validation Summary and Scientific Results for ILAS-II Onboard the ADEOS-II Satellilte
The Improved Limb Atmospheric Spectrometer-II (ILAS-II) onboard the Advanced Earth Observing Satellite-II (ADEOS-II) was successfully launched on 14 December, 2002 from National Space Development Agency of Japan (NASDA)'s Tanegashima Space Center. ILAS-II is a solar-occultation atmospheric sensor which measures vertical profiles of O$_3$, HNO$_3$, NO$_2$, N$_2$O, CH$_4$, H$_2$O, ClONO$_2$, aerosol extinction coefficients etc. with four grating spectrometers. After the checkout period of the ILAS-II, ILAS-II started its routine operation since 2 April, 2003 until 24 October 2003 when ADEOS-II lost its function due to solar paddle failure. However, about 7 month of data were acquired by ILAS-II including whole period of Antarctic ozone hole in 2003 when ozone depletion was the largest in history. ILAS-II successfully measure vertical profiles of ozone, nitric acid, water, polar stratospheric clouds during this ozone hole period. Validations of the latest data retrieval algorithm of Version 1.4 have done for O$_3$, HNO$_3$, N$_2$O, CH$_4$, and aerosol extinction coefficients. By comparing ILAS-II Version 1.4 profiles with other correlative balloon-borne and satellite measurements, fairly good agreement was found. Using such validated ILAS-II Version 1.4 product, the characteristics of ozone depletion in the Antarctic winter-spring in 2003 was investigated. As a result, the record-high ozone depletion speed of -0.10 ppmv/day was found in September 2003 at around 18 km. Also, ILAS-II succeeded to capture small-scale periodic (around 10 days) ozone depletion at high latitudes where TOMS cannot measure. These results suggest that the existence of eccentric polar vortex and related low-temperature region in accordance with the availability of sun illumination play an important role in early spring ozone depletion.
http://www-ilas2.nies.go.jp
A51D-0819 0800h
The Atmospheric Chemistry Experiment (ACE) on-board SCISAT-1
The Atmospheric Chemistry Experiment (ACE) is a Canadian scientific satellite mission to perform remote sensing measurements of the Earth's atmosphere. SCISAT-1, the satellite carrying the ACE payload, was successfully launched into low Earth orbit (650 km altitude, 74 degree inclination) on August 12, 2003. The primary instrument on-board SCISAT-1 is a high-resolution (0.02 cm-1) Fourier Transform Spectrometer (ACE-FTS) operating between 750 and 4100 cm-1. Two filtered imagers measure atmospheric extinction due to clouds and aerosols at 0.525 and 1.02 microns. The secondary instrument is a dual spectrograph called MAESTRO (Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) which extends the wavelength coverage to the 280-1000 nm spectral region. The satellite uses solar occultation to obtain altitude profiles of atmospheric trace gas species, temperature and pressure. The goals of the ACE mission are: (1) to measure and to understand the chemical and dynamical processes that control the distribution of ozone in the upper troposphere and stratosphere, with a particular emphasis on the Arctic region; (2) to explore the relationship between atmospheric chemistry and climate change; (3) to study the effects of biomass burning in the free troposphere; (4) to measure aerosol number density, size distribution and composition in order to reduce the uncertainties in their effects on the global energy balance. Initial results and validation comparisons from the ACE mission will be presented.
http://www.ace.uwaterloo.ca
A51D-0820 0800h
Comparative Studies of Aerosol Extinction Measurements Made by the SAGE II and SAGE III Satellite Experiments
SAGE II and SAGE III are two currently operating satellite systems designed to measure aerosol extinction coefficients and concentrations of trace gases in the atmosphere by using the techniques of solar and/or lunar occultation. Four of the nine aerosol channels used by SAGE III are centered at wavelengths very close to that of the four SAGE II aerosol channels. Since February 2002, there are occasions when measurement locations for both satellites are nearly coincident, thereby providing opportunities for a measurement comparison. In this paper, the coincidences are identified, and aerosol extinctions and optical depths measured by SAGE II and SAGE III at these coincidences are compared. It was found that in the main aerosol layer, between about 18 to 26 km, differences are less than about 30%. Larger differences are shown at altitudes near the tropopause and around 30 km. The contribution of measurement uncertainties to the observed differences is discussed.
A51D-0821 0800h
Thinning and Lowering of Tropical Cirrus During 1985--1999: Evidence for a Potential Cloud Negative Feedback Mechanism in Global Climate System
Using data from a single, high vertical resolution (1-km), self-calibrating satellite instrument--the Stratospheric Aerosol and Gas Experiment (SAGE) II, it is shown that the tropical high-altitude cloud layer is lowering during 1985-1999. In addition, the cirrus cloud layer above 12.5 km is thinning during the same period. This observed behavior of the tropical high cloud layer is further substantiated by the high-altitude cloud observations from the Internation Satellite Cloud Climatology Project (ISCCP) and by the 300-mb relative humidity measurements from the National Center for Environment Prediction (NCEP). The high cloud layer thinning and lowering coincides with a period of surface warming and increasing outgoing longwave radiation (OLR) reported recently in the literature. By allowing increased emissions of longwave radiation from top cloud layer to space, the thinning and lowering of the tropical high-altitude cirrus layer constitutes a potential negative cloud feedback mechanism in the global climate system, and is likely to be responsible for the observed increase in OLR in the Tropics during 1985--1999.
A51D-0822 0800h
Particle Size Distributions and Densities of Tropical Cirrus Clouds Observed by the ACE FTIR Instrument on the SciSat-1 Satellite.
The FTIR spectrometer on the SciSat-1 satellite has been providing regular occultation measurements since the completion of its commissioning phase in late February 2004. During April and May of 2004, for tangent points occurring in the tropics, several occultations contained spectra that appear to exhibit extinction signals due to tropical cirrus clouds. The spectra of atmospheric aerosols and clouds have very broad bands with locations that shift with the particle size and shape. Moreover, they are usually obscured by gas phase absorptions that can become completely opaque for observations in the mid- to upper-troposphere. To overcome this interference, it has been customary to make measurements at selected wavelengths that are relatively free from gas phase interference. Conversely, the ACE FTIR instrument produced spectra that are broad band (800 to 4000 cm$^{-1}$) and high resolution (0.02 cm$^{-1}$). Thus they contain enough information for the simultaneous retrieval of the chemical compositions, phases and size distributions of cloud and aerosol particles, without additional information. We have developed techniques to make such standalone estimates by combining occultation measurements with of pure aerosol spectra and have tested them successfully on measurements made by the ATMOS instrument of the decay of the sulfate aerosol following the Pinatubo eruption. Using these retrieval methods, we have analysed the ACE FTIR observations of tropical cirrus clouds and determined the size distributions and vertical (number, area or volume) density profiles of the ice particles in the clouds. We will report the aerosol characteristics and discuss correlations between the retrieval results and the results of equilibrium thermodynamic calculations.
A51D-0823 0800h
Current Status of the SAGE III Water Vapor Measurements: Algorithm Development and Preliminary Intercomparisons
The Stratospheric Aerosol and Gas Experiment III (SAGE III) is part of NASA's Earth Observing System (EOS) program. The SAGE III instrument, onboard the METEOR 3M-1, was successfully launched on December 10, 2001. Since then SAGE III data products of aerosol, ozone, nitrogen dioxide and cloud occurrence have been archived and released. Monitoring the stratospheric water vapor is also one of the major goals of SAGE III mission. Water vapor measurements from SAGE III are accomplished through the absorption signals observed with 29 channels from 930 nm to 960 nm wavelength region. The retrieval of water vapor profiles has been complicated by a number of factors including the etaloning effects due to attenuator plate and the spectroscopic uncertainty of the ozone cross sections in the corresponding wavelength region. In this presentation, a review of SAGE III water vapor retrieval algorithm will be given. Errors due to the contributions of interfering species will be discussed. Several modification schemes added to the pre-launched algorithm will be shown to demonstrate the efforts to account for the noises caused by the etaloning efftects. Preliminary results will be shown that compare SAGE III retrieved water vapor profiles with the coincident measurements from balloon-borne frost-point hygrometers and several satellite instruments (SAGE II, HALOE, and POAM-III). The agreement is generally within 10% to 12% with no systematic biases for altitudes below 27 km. Agreement diverges rapidly above this altitude, with SAGE III having systematic wet biases of the order of 1 ppmv (or approximately 20%).
A51D-0824 0800h
Trends Inferred From Stratospheric Aerosol and Gas Experiment II Water Vapor Measurements
The Stratospheric Aerosol and Gas Experiment (SAGE) II instrument has collected vertical profiles of stratospheric ozone, nitrogen dioxide, water vapor, and aerosol extinction at four wavelengths with high resolution since the program's inception in October, 1984. The SAGE II processing team has made great strides in characterizing stratospheric water vapor by performing a wavelength-shift and increasing the channel-width by 10 percent from 1986-present for the latest version (v6.2). These advancements have significantly reduced an apparent bias (that existed in previous versions) except in the proximity of heavy aerosol levels. This new water vapor product has been validated through comparisons with ground-based and satellite data. With the ~20-year record of near-global, high vertical resolution (1 km) water vapor measurements, it is imperative to assess the quality of this data for use in trend studies. We present our validation efforts of SAGE II water vapor trends. Analysis techniques include calculating trends in the difference time series between de-seasonalized SAGE II v6.2 and Halogen Occultation Experiment (HALOE) v19 anomalies to assess potential drifts in the v6.2 water vapor channel during the UARS time frame (October 1991 to present), direct comparisons with trends inferred from HALOE and ground-based instruments, and theoretical tests to assess channel drifts between 1984 to 1991.