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- Author or Editor: W.P. Chu x
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Abstract
The variability of stratospheric water vapor between 1996 and 2004 has been studied using multiyear measurements from the Stratospheric Aerosol and Gas Experiment II (SAGE II) version 6.2 dataset, the Halogen Occultation Experiment (HALOE) version 19 dataset, and the balloon-borne frost point hygrometer data record at Boulder, Colorado (40°N, 105°W). The features derived from SAGE II and HALOE for 20° latitudinal zones from 60°S to 60°N at various altitudes (16–34 km) show good quantitative agreement regarding the phases and magnitudes of annual, semiannual, and quasi-biennial oscillations (QBO). For the latitudinal zones 20°–40° and 40°–60°, the hemispheric asymmetry at 22 km with mainly QBO in the north and predominantly annual oscillations in the south has been revealed by both SAGE II and HALOE observations. Strong correlation exists between SAGE II and HALOE lower-stratospheric H2O anomalies over low latitudes and 100-hPa tropical zonal mean temperature anomalies. The correlation coefficients based on the 0°–20°S water vapor time series with H2O lagged by 2 months are 0.81 and 0.70 for HALOE and SAGE II, respectively. For 35°–45°N, SAGE II and HALOE show consistent trends generally varying from −0.05 to −0.02 ppmv yr−1 between 16 and 34 km. The corresponding analyses based on frost point measurements over Boulder show insignificant trends. These trends are not strongly dependent on the end points of the analysis and stand in contrast to the positive trends reported in previous studies that include data records prior to 1994. For the lower stratosphere, investigations of the entire balloon-borne dataset over Boulder indicate higher values of mixing ratios after 1992–93 compared to the period 1980–92. In contrast, SAGE II monthly zonal mean measurements for 35°–45°N show insignificant differences between the periods 1987–89 and 1996–2004.
Abstract
The variability of stratospheric water vapor between 1996 and 2004 has been studied using multiyear measurements from the Stratospheric Aerosol and Gas Experiment II (SAGE II) version 6.2 dataset, the Halogen Occultation Experiment (HALOE) version 19 dataset, and the balloon-borne frost point hygrometer data record at Boulder, Colorado (40°N, 105°W). The features derived from SAGE II and HALOE for 20° latitudinal zones from 60°S to 60°N at various altitudes (16–34 km) show good quantitative agreement regarding the phases and magnitudes of annual, semiannual, and quasi-biennial oscillations (QBO). For the latitudinal zones 20°–40° and 40°–60°, the hemispheric asymmetry at 22 km with mainly QBO in the north and predominantly annual oscillations in the south has been revealed by both SAGE II and HALOE observations. Strong correlation exists between SAGE II and HALOE lower-stratospheric H2O anomalies over low latitudes and 100-hPa tropical zonal mean temperature anomalies. The correlation coefficients based on the 0°–20°S water vapor time series with H2O lagged by 2 months are 0.81 and 0.70 for HALOE and SAGE II, respectively. For 35°–45°N, SAGE II and HALOE show consistent trends generally varying from −0.05 to −0.02 ppmv yr−1 between 16 and 34 km. The corresponding analyses based on frost point measurements over Boulder show insignificant trends. These trends are not strongly dependent on the end points of the analysis and stand in contrast to the positive trends reported in previous studies that include data records prior to 1994. For the lower stratosphere, investigations of the entire balloon-borne dataset over Boulder indicate higher values of mixing ratios after 1992–93 compared to the period 1980–92. In contrast, SAGE II monthly zonal mean measurements for 35°–45°N show insignificant differences between the periods 1987–89 and 1996–2004.
Abstract
The SAGE II satellite system was launched on 5 October 1984. It has seven radiometric channels and is beginning to provide water vapor, NO2, and O2 concentration profiles and aerosol extinction profiles at a minimum of three wavelengths. In preparation for the use of these data and assuming the aerosol size distribution is lognormal, a parametric study has been conducted of the effect of size distribution parameters and composition of stratospheric aerosols on the expected extinction in the aerosol and water vapor channels. Our calculated results show that aerosol characteristics can be retrieved from the SAGE II data set assuming stratospheric aerosols are distributed lognormally. A simple, fast and operational method of retrieving characteristics of stratospheric aerosols from the water vapor and three-wavelength aerosol extinction profiles is proposed. Some examples are given to show the practicality of the scheme. Possible sources of error for the retrieved values and the limitation of the proposed method are discussed. Our method may also prove applicable to the study of aerosol characteristics in other multispectral extinction measurements.
Abstract
The SAGE II satellite system was launched on 5 October 1984. It has seven radiometric channels and is beginning to provide water vapor, NO2, and O2 concentration profiles and aerosol extinction profiles at a minimum of three wavelengths. In preparation for the use of these data and assuming the aerosol size distribution is lognormal, a parametric study has been conducted of the effect of size distribution parameters and composition of stratospheric aerosols on the expected extinction in the aerosol and water vapor channels. Our calculated results show that aerosol characteristics can be retrieved from the SAGE II data set assuming stratospheric aerosols are distributed lognormally. A simple, fast and operational method of retrieving characteristics of stratospheric aerosols from the water vapor and three-wavelength aerosol extinction profiles is proposed. Some examples are given to show the practicality of the scheme. Possible sources of error for the retrieved values and the limitation of the proposed method are discussed. Our method may also prove applicable to the study of aerosol characteristics in other multispectral extinction measurements.
Abstract
Ozone data from the Stratospheric Aerosol and Gas Experiment (SAGE) have been used in conjunction with meteorological information to study the ozone transport near 55°N due to planetary waves during the late February 1979 stratospheric warming. The results indicate an intense poleward eddy ozone transport in the middle stratosphere between ∼24 and 38 km altitudes and an equatorward transport above an altitude of ∼38 km. It is found that this equatorward eddy ozone transport in the upper stratosphere was accompanied by a poleward eddy heat transport, as expected on the basis of the ozone photochemistry. The results also show an equatorward eddy ozone transport in the lower stratosphere (below ∼25 km), but it is secondary. The transport effect of wavenumber 2 can account for a major portion of the net eddy ozone flux during this late February 1979 warming.
The phase relationship between temperature, meridional velocity and ozone mixing ratio waves has also been examined. Overall, the results agree qualitatively with existing model analyses. In the lower stratosphere, the temperature and ozone waves are found to be nearly in-phase. They are approximately out-of-phase in the upper stratosphere. A transition region is shown in between. However, this transition region is thinner and centered at a slightly lower altitude than that predicted in the model analyses of Hartmann and Garcia, Kawahira and those reported by Gille et al. The reason for this difference is discussed.
Abstract
Ozone data from the Stratospheric Aerosol and Gas Experiment (SAGE) have been used in conjunction with meteorological information to study the ozone transport near 55°N due to planetary waves during the late February 1979 stratospheric warming. The results indicate an intense poleward eddy ozone transport in the middle stratosphere between ∼24 and 38 km altitudes and an equatorward transport above an altitude of ∼38 km. It is found that this equatorward eddy ozone transport in the upper stratosphere was accompanied by a poleward eddy heat transport, as expected on the basis of the ozone photochemistry. The results also show an equatorward eddy ozone transport in the lower stratosphere (below ∼25 km), but it is secondary. The transport effect of wavenumber 2 can account for a major portion of the net eddy ozone flux during this late February 1979 warming.
The phase relationship between temperature, meridional velocity and ozone mixing ratio waves has also been examined. Overall, the results agree qualitatively with existing model analyses. In the lower stratosphere, the temperature and ozone waves are found to be nearly in-phase. They are approximately out-of-phase in the upper stratosphere. A transition region is shown in between. However, this transition region is thinner and centered at a slightly lower altitude than that predicted in the model analyses of Hartmann and Garcia, Kawahira and those reported by Gille et al. The reason for this difference is discussed.
Abstract
Liday observations of the stratosphere aerosol vertical distribution from October 1971 to July 1976 over midlatitude North America are presented. The results show the sudden increase in the stratospheric aerosol content after the eruption of the Volc´n de Fuego and its subsequent decline. The data are presented in terms of lidar scattering ratio profiles, vertically integrated aerosol backscattering, and rawinsonde temperature profiles. In the months immediately following the volcanic eruption, the lidar-derived aerosol structure is correlated with rawinsonde temperature structure showing the stratospheric temperature minimum occurring near the aerosol layer peak. Analysis of the time dependence of the integrated aerosol backscattering and the tropopause altitude indicates an approximate 0.9 correlation between aerosol loading and tropopause pressure. In addition, the integrated aerosol backscattering also showed some correlation with the minimum stratospheric temperature, i.e., a warmer stratospheric minimum is associated with a relatively higher aerosol loading.
The lidar backscatter data also show that rapid decay of the stratospheric aerosol occurred over the late winter to early spring period and that the summer to fall interval was quite stable. For both winter to summer periods of 1975 and 1976 in approximate 40% decrease in the total integrated aerosol backscattering was observed, while from January 1975 to January 1976 a 65% decrease occurred. For the 19-month period from January 1975 to July 1976 the exponential l/e decay time for the integrated aerosol backscattering was 11.6 months.
Abstract
Liday observations of the stratosphere aerosol vertical distribution from October 1971 to July 1976 over midlatitude North America are presented. The results show the sudden increase in the stratospheric aerosol content after the eruption of the Volc´n de Fuego and its subsequent decline. The data are presented in terms of lidar scattering ratio profiles, vertically integrated aerosol backscattering, and rawinsonde temperature profiles. In the months immediately following the volcanic eruption, the lidar-derived aerosol structure is correlated with rawinsonde temperature structure showing the stratospheric temperature minimum occurring near the aerosol layer peak. Analysis of the time dependence of the integrated aerosol backscattering and the tropopause altitude indicates an approximate 0.9 correlation between aerosol loading and tropopause pressure. In addition, the integrated aerosol backscattering also showed some correlation with the minimum stratospheric temperature, i.e., a warmer stratospheric minimum is associated with a relatively higher aerosol loading.
The lidar backscatter data also show that rapid decay of the stratospheric aerosol occurred over the late winter to early spring period and that the summer to fall interval was quite stable. For both winter to summer periods of 1975 and 1976 in approximate 40% decrease in the total integrated aerosol backscattering was observed, while from January 1975 to January 1976 a 65% decrease occurred. For the 19-month period from January 1975 to July 1976 the exponential l/e decay time for the integrated aerosol backscattering was 11.6 months.
Abstract
Sightings of polar stratospheric clouds (PSC's) by the SAM II satellite system during the northern and southern winters of 1979 are reported. PSC's were observed in the Arctic stratosphere at altitudes between about 17 and 25 km during January 1979, with a single sighting in November 1978, and in the Antarctic stratosphere from June to October 1979 at altitudes from the tropopause up to about 23 km. The measured extinction coefficients at 1 μm wavelength were as much as two orders of magnitude greater than that of the background stratospheric aerosol. with peak extinctions up to 10−2 km−1. The PSC's were observed when stratospheric temperatures were very low with a high probability of observation when temperatures were colder than 190 K and a low probability when temperatures were warmer than 198 K. In the Antarctic, clouds were observed in more than 90% of the events in which the minimum temperature was 185 K or less, and were observed in fewer than 10% of the occasions when the temperature was greater than 196 K.
Abstract
Sightings of polar stratospheric clouds (PSC's) by the SAM II satellite system during the northern and southern winters of 1979 are reported. PSC's were observed in the Arctic stratosphere at altitudes between about 17 and 25 km during January 1979, with a single sighting in November 1978, and in the Antarctic stratosphere from June to October 1979 at altitudes from the tropopause up to about 23 km. The measured extinction coefficients at 1 μm wavelength were as much as two orders of magnitude greater than that of the background stratospheric aerosol. with peak extinctions up to 10−2 km−1. The PSC's were observed when stratospheric temperatures were very low with a high probability of observation when temperatures were colder than 190 K and a low probability when temperatures were warmer than 198 K. In the Antarctic, clouds were observed in more than 90% of the events in which the minimum temperature was 185 K or less, and were observed in fewer than 10% of the occasions when the temperature was greater than 196 K.
Abstract
We present a model of stratospheric aerosol optical properties (refractive index and relative size distribution) and their variability. The model's purposes are 1) providing flexible, efficient means for converting between different aerosol macroproperties (e.g., number or mass concentration, extinction or backscatter coefficient), and 2) quantifying the uncertainties in the conversion process. The latter purpose is achieved by including the results of a sensitivity analysis in the model output products.
The model has three layers, the boundaries of which are defined by tropopause height. Each layer includes a set of empirically based refractive indices and relative size distribution types. In contrast to previous models, this model allows for a range of sulfuric acid and ammonium sulfate refractive indices within the “inner stratospheric” layer (∼2 to 20 km above the tropopause, where the major peak in aerosol mixing ratio occurs). We show that nine different analytical types of size distribution previously recommended for this layer can be parameterized in terms of channel ratio—i.e., the relative size distribution indicator that has been extensively measured by dustsondes.
When so parameterized, all nine inner stratospheric function types give very similar results for the several conversion ratios of interest. This parameterization allows considerable saving of computer time while preserving the flexibility to handle certain types of size distribution change. We show that the inner stratospheric parameterization works because all nine inner stratospheric size distribution types are relatively narrow, and their optical integrals of interest are determined primarily by a size range that is well characterized by channel ratio.
Data from previous measurements made near the tropopause are used to demonstrate that, in that region, size distributions are broader than any of the inner stratospheric types, and that their optical integrals are strongly influenced by particles too large to be characterized by channel ratio. Hence, in the layer near the tropopause, conversion ratios can differ significantly from the inner stratospheric values; consequently, parameterization by channel ratios is not successful.
We develop methods for deriving vertical profiles of several conversion ratios and their uncertainties. We also demonstrate an application of the model: deriving profiles of number density and its uncertainty from satellite-measured profiles of extinction and its uncertainty. A companion paper applies the model to the task of validating satellite measurements of stratospheric aerosol extinction.
Abstract
We present a model of stratospheric aerosol optical properties (refractive index and relative size distribution) and their variability. The model's purposes are 1) providing flexible, efficient means for converting between different aerosol macroproperties (e.g., number or mass concentration, extinction or backscatter coefficient), and 2) quantifying the uncertainties in the conversion process. The latter purpose is achieved by including the results of a sensitivity analysis in the model output products.
The model has three layers, the boundaries of which are defined by tropopause height. Each layer includes a set of empirically based refractive indices and relative size distribution types. In contrast to previous models, this model allows for a range of sulfuric acid and ammonium sulfate refractive indices within the “inner stratospheric” layer (∼2 to 20 km above the tropopause, where the major peak in aerosol mixing ratio occurs). We show that nine different analytical types of size distribution previously recommended for this layer can be parameterized in terms of channel ratio—i.e., the relative size distribution indicator that has been extensively measured by dustsondes.
When so parameterized, all nine inner stratospheric function types give very similar results for the several conversion ratios of interest. This parameterization allows considerable saving of computer time while preserving the flexibility to handle certain types of size distribution change. We show that the inner stratospheric parameterization works because all nine inner stratospheric size distribution types are relatively narrow, and their optical integrals of interest are determined primarily by a size range that is well characterized by channel ratio.
Data from previous measurements made near the tropopause are used to demonstrate that, in that region, size distributions are broader than any of the inner stratospheric types, and that their optical integrals are strongly influenced by particles too large to be characterized by channel ratio. Hence, in the layer near the tropopause, conversion ratios can differ significantly from the inner stratospheric values; consequently, parameterization by channel ratios is not successful.
We develop methods for deriving vertical profiles of several conversion ratios and their uncertainties. We also demonstrate an application of the model: deriving profiles of number density and its uncertainty from satellite-measured profiles of extinction and its uncertainty. A companion paper applies the model to the task of validating satellite measurements of stratospheric aerosol extinction.
The potential climatological and environmental importance of the stratospheric aerosol layer has prompted great interest in measuring the properties of this aerosol. In this paper we report on two recently deployed NASA satellite systems (SAM II and SAGE) that are monitoring the stratospheric aerosol. The satellite orbits are such that nearly global coverage is obtained. The instruments mounted in the spacecraft are sun photometers that measure solar intensity at specific wavelengths as it is moderated by atmospheric particulates and gases during each sunrise and sunset encountered by the satellites. The data obtained are “inverted” to yield vertical aerosol and gaseous (primarily ozone) extinction profiles with 1 km vertical resolution. Thus, latitudinal, longitudinal, and temporal variations in the aerosol layer can be evaluated. The satellite systems are being validated by a series of ground truth experiments using airborne and ground lidar, balloon-borne dustsondes, aircraft-mounted impactors, and other correlative sensors. We describe the SAM II and SAGE satellite systems, instrument characteristics, and mode of operation; outline the methodology of the experiments; and describe the ground truth experiments. We present preliminary results from these measurements.
The potential climatological and environmental importance of the stratospheric aerosol layer has prompted great interest in measuring the properties of this aerosol. In this paper we report on two recently deployed NASA satellite systems (SAM II and SAGE) that are monitoring the stratospheric aerosol. The satellite orbits are such that nearly global coverage is obtained. The instruments mounted in the spacecraft are sun photometers that measure solar intensity at specific wavelengths as it is moderated by atmospheric particulates and gases during each sunrise and sunset encountered by the satellites. The data obtained are “inverted” to yield vertical aerosol and gaseous (primarily ozone) extinction profiles with 1 km vertical resolution. Thus, latitudinal, longitudinal, and temporal variations in the aerosol layer can be evaluated. The satellite systems are being validated by a series of ground truth experiments using airborne and ground lidar, balloon-borne dustsondes, aircraft-mounted impactors, and other correlative sensors. We describe the SAM II and SAGE satellite systems, instrument characteristics, and mode of operation; outline the methodology of the experiments; and describe the ground truth experiments. We present preliminary results from these measurements.
Abstract
We show results from the first set of measurements conducted to validate extinction data from the satellite sensor SAM II. Dustsonde-measured number density profiles and lidar-measured backscattering profiles for two days are converted to extinction profiles using the optical modeling techniques described in the companion Paper I (Russell et al., 1981). At heights ∼2 km and more above the tropopause, the dustsonde data are used to restrict the range of model size distributions, thus reducing uncertainties in the conversion process. At all heights, measurement uncertainties for each sensor are evaluated, and these are combined with conversion uncertainties to yield the total uncertainty in derived data profiles.
The SAM II measured, dustsonde-inferred, and lidar-inferred extinction profiles for both days are shown to agree within their respective uncertainties at all heights above the tropopause. Near the tropopause, this agreement depends on the use of model size distributions with more relatively large particles (radius ≳0.6 μm) than are present in distributions used to model the main stratospheric aerosol peak. The presence of these relatively large particles is supported by measurements made elsewhere and is suggested by in situ size distribution measurements reported here. These relatively large particles near the tropopause are likely to have an important bearing on the radiative impact of the total stratospheric aerosol.
The agreement in this experiment supports the validity of the SAM II extinction data and the SAM II uncertainty estimates derived from an independent error analysis. Recommendations are given for reducing the uncertainties of future correlative experiments.
Abstract
We show results from the first set of measurements conducted to validate extinction data from the satellite sensor SAM II. Dustsonde-measured number density profiles and lidar-measured backscattering profiles for two days are converted to extinction profiles using the optical modeling techniques described in the companion Paper I (Russell et al., 1981). At heights ∼2 km and more above the tropopause, the dustsonde data are used to restrict the range of model size distributions, thus reducing uncertainties in the conversion process. At all heights, measurement uncertainties for each sensor are evaluated, and these are combined with conversion uncertainties to yield the total uncertainty in derived data profiles.
The SAM II measured, dustsonde-inferred, and lidar-inferred extinction profiles for both days are shown to agree within their respective uncertainties at all heights above the tropopause. Near the tropopause, this agreement depends on the use of model size distributions with more relatively large particles (radius ≳0.6 μm) than are present in distributions used to model the main stratospheric aerosol peak. The presence of these relatively large particles is supported by measurements made elsewhere and is suggested by in situ size distribution measurements reported here. These relatively large particles near the tropopause are likely to have an important bearing on the radiative impact of the total stratospheric aerosol.
The agreement in this experiment supports the validity of the SAM II extinction data and the SAM II uncertainty estimates derived from an independent error analysis. Recommendations are given for reducing the uncertainties of future correlative experiments.
