Aerosol measurements from earth orbiting spacecraft

Since the fall of 1978, two Earth-orbiting spacecraft sensors, SAM II, for Stratospheric Aerosol Measurement II, and SAGE, for Stratospheric Aerosol and Gas Experiment have been monitoring the global stratospheric aerosol. These experiments use the Sun as a source to make Earth-limb extinction measurements during each spacecraft sunrise and sunset. This paper describes the global aerosol data base (climatology) that is evolving. Seasonal and hemispheric variations such as the springtime layer expansion with warming temperatures and the local wintertime polar stratospheric clouds (PSC's) will be described. The PSC's enhance extinction by up to two orders of magnitude and optical depths by as much as an order of magnitude over the background 1000 nm values of about 1.2 × 10^?4 km^?1 and 1.3 × 10^?3, respectively. The detection and tracking of a number of volcanoes whose effluents penetrated the tropopause are also described. The mass of new aerosol injected into the stratosphere from each volcano is estimated. The May 1980 eruption of Mount St. Helens, for example, produced about 0.32 × 10⁹ kg of new stratospheric aerosol enhancing the Northern Hemispheric aerosol by more than 100 percent.     

Aerosol observations for climate studies

The SAM II and SAGE satellite systems have provided to date more than 5 years and almost 3 years, respectively, of data on atmospheric aerosol profiles on a near-global scale. Studies with these unique data sets are developing a global aerosol climatology for the first time and have shown the existence and quantification of polar stratospheric clouds (PSC's) and tropical stratospheric cirrus. In addition, a tropospheric cirrus climatology is evolving. Since these two experiments were launched, a series of large volcanic eruptions have occurred which have greatly impacted the stratospheric aerosol loading. The aerosol layer produced by the eruption of El Chichon, for example, increased the 30 mb temperatures in the northern tropics by as much as 4°C for 6 months after the eruption. This paper will describe in detail, from a climate perspective, the evolving aerosol and cloud climatologies as a function of space and time, and show the stratospheric dynamics of volcanic injections and their enhancements on stratospheric optical depth and mass loading.     

Validation of SAGE II data inversions by the European correlative experiments

An European program of correlative experiments has been organized in order to validate SAGE II data during three periods of observation over Europe (November 1984, April 1985, October 1985). About ten groups from France, Belgium, Germany and Italy were participating. The correlative data are lidar aerosol profiles, soundings of ozone profiles, and balloon observations, including limb photographies, polarimetric measurements of the aerosol scattered light and nitrogen dioxide extinction measurements. Results of the comparisons between SAGE II inverted data and correlative data are presented. The analysis of the aerosol correlative observations with the SAGE II four aerosol channel data, in term of profile and size distribution is perfectly consistent and provide a good indirect validatioin. The NO₂ comparison shows a good agreement between SAGE II and correlative data.     

Assessment of the ozone and temperature variability during 1979–1993 with the chemistry-climate model SOCOL

The chemistry-climate model SOCOL has been applied for the study of ozone and temperature anomalies during 1979–1993. Temperature and ozone anomalies have been obtained for a set of model runs forced by all major stratospheric forcing mechanisms. Forcings have been prescribed separately and together to assess their individual influence on stratospheric ozone and temperature. The results of these simulations have been compared to available satellite data. The model captures well ozone depletion and cooling in the upper stratosphere due to increases in the abundance of greenhouse gases and ozone depleting substances in the atmosphere. In the lower stratosphere, the model reproduces the warming over tropical and middle latitudes caused by the El-Chichon and Pinatubo eruptions. However, the simulated ozone response is overestimated in comparison with SAGE data. The best agreement with observations has been obtained for the run with all forcings included. This emphasizes the importance of the volcanic and solar forcings for the correct reproduction of observed trends. Comparison of near-global total ozone anomalies confirms an overestimation of ozone depletion just after volcanic eruptions, while the overall agreement with the model is fairly good.     

An analysis of preliminary SAGE II data on ozone and NO2

Zonal mean mixing ratios of ozone and NO₂ measured by SAGE II on several days in March and April, 1985 are compared against zonal means for this time of year previously measured by SAGE I, SBUV, and LIMS. After allowing for calculated diurnal variations of these gases, agreement within 15% is found for ozone and 20% for NO₂. It is noted that the profile error bars given on the SAGE II data tapes need to be carefully interpreted and that the measured tropical variances suggest that these error bars are being somewhat overestimated. Planetary waves in both ozone and NO₂ in the middle stratosphere should be derivable from the SAGE II measurements.     

Comparison of ground reflectance measurement with satellite derived atmospherically corrected reflectance: A case study over semi-arid landscape

Atmospheric corrections to satellite data are important for comparing multitemporal data sets over tropical regions with variable aerosol loading. In this study, we evaluated the potential of 6S radiative transfer model for atmospheric corrections of IRS-P6 AWiFS satellite data sets, in a semi-arid landscape. Ground measurements of surface reflectance representing different land use/land cover categories were conducted to relate IRS-P6 AWiFS top of atmospheric reflectance. The 6S radiative transfer model was calibrated for local conditions using ground measurements for aerosol optical depth, water vapor and ozone with a sun photometer. Surface reflectance retrieved from 6S code was compared with top of atmosphere (TOA) reflectance and ground based spectroradiometer measurements. Accurate parameterization of the 6S model using measurements of aerosol optical depth, water vapor and ozone plays an important role while comparing ground and satellite derived reflectance measurements.     

Towards validation of SCIAMACHY lunar occultation NO2 vertical profiles

Vertical profiles of stratospheric nitrogen dioxide (NO₂) have been retrieved from moderate resolution lunar occultation transmission spectra measured by Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) on board the European Environmental Satellite (ENVISAT). These measurements were taken over the high southern latitude of 50°–90° during the period of 2003–2005. To assess the accuracy of the retrieved NO₂ profiles, the SCIAMACHY nighttime NO₂ profiles were compared with NO₂ profiles retrieved from sunrise solar occultation spectra measured by the Halogen Occultation Experiment (HALOE) and the Stratospheric Aerosol and Gas Experiments II (SAGE II) using a photochemical correction model. The validation results show good agreement of SCIAMACHY lunar occultation NO₂ with scaled HALOE and SAGE II profiles. The relative mean differences (rmd) with scaled HALOE profiles are within −13% to +5% and standard deviations (rms) of the relative differences are within 3–19% between 25 and 38 km. The rmd and rms with scaled SAGE II NO₂ profiles are in the range of −9 to +7 and 10–17% respectively between 22 and 39 km.     

Satellite stratospheric aerosol measurement validation

The validity of the stratospheric aerosol measurements made by the satellite sensors SAM II and SAGE has been tested by comparing their results with each other and with results obtained by other techniques (lidar, dustsonde, filter, impactor). The latter type of comparison has required the development of special techniques that (1) convert the quantity measured by the correlative sensor (e.g. particle backscatter, number, or mass) to that measured by the satellite sensor (extinction), and (2) quantitatively estimate the uncertainty in the conversion process. The results of both types of comparisons show agreement within the measurement and conversion uncertainties. Moreover, the satellite uncertainty is small compared to aerosol natural variability (caused by seasonal changes, volcanoes, sudden warmings, vortex structure, etc.). Hence, we conclude that the satellite measurements are valid.     

Validation of aerosol measurements by the satellite sensors SAM II and SAGE

The satellite sensors SAM II and SAGE have been developing a global data base on stratospheric aerosols since they were launched in October 1978 and February 1979, respectively. The validity of this data base has been tested by numerous comparisons with other measurements made by lidars, balloon-borne particle counters, and aircraft-borne impactors and filters. Because the satellite sensors measure extinction and the correlative sensors measure other properties (e.g., backscatter, number, mass), special techniques are required to convert each measured property to other properties and to quantify conversion uncertainties and measurement uncertainties. Use of these techniques in two major comparative experiments shows that the SAM II and SAGE extinction measurements agree with each other and with values derived from dustsonde, lidar, and filter measurements. In addition, the comparative experiments have highlighted the uncertainties of each type of sensor and stimulated further efforts to reduce these uncertainties.     

Comparison of ozone data derived from SBUV and SAGE with emphasis on longitudinal variations

Stratospheric ozone observations by the SAGE and SBUV satellite instruments in March and April, 1979 have been analyzed. All SAGE profiles have been smoothed vertically over 8 km to provide some compatibility with the SBUV vertical resolution. Comparing the zonal mean ozone mixing ratios against smoothed LIMS profiles, it is inferred that SAGE is systematically overestimating ozone by approximately 20% at tropical latitudes at pressures lower than 5 mb and that SBUV is underestimating ozone by approximately 15% at 50–70° latitude at 10 mb. A comparison of the longitudinal variations of ozone by SBUV and SAGE is made and the detectability of planetary waves in ozone is emphasized. The uncorrelated portion of the SAGE variances are found to be approximately consistent with the SAGE noise model. Based on the correlated variances, the amplitudes of the smoothed SAGE planetary waves in ozone are found to be the same, on average, as in the SBUV experiment at mid-latitudes between 1 and 10 mb. Planetary wave detectability is illustrated during two several day periods at mid-latitudes and a persistent and theoretically-consistent relationship between ozone and temperature is noted. These examples, however, indicate that differences between ozone planetary wave amplitudes derived from the two sensors may occur when there is a strong vertical gradient in wave amplitude.     

Effect of vapor condensation on ascending performance of stratospheric airship

This paper reports a numerical investigation on the effects of water vapor condensing inside the air bag of a stratospheric airship on its ascending performance. The kinetic and thermal model considering vapor condensation was established, based on which a computer program was written in Fortran. The simulation results show that the vapor condensation remarkably affects the kinetic and thermal characteristics of the stratospheric airship in the ascent process. During the ascent process below 11 km, a large amount of latent heat is released when the water vapor in the air inside the air bag of the stratospheric airship condenses, which results in the increase of the temperature and the reduction of the weight of the air in the air bag, causing the airship to speed up, the accelerated expansion of the helium, and the decrease of the helium temperature in the helium bag. When the flight altitude is higher than 11 km, the effect of vapor condensation on the kinetic and thermal characteristics of the stratospheric airship is negligible because vapor is virtually nonexistent in the air.     

The limb infrared monitor of the stratosphere (LIMS) experiment: Temperature and nitrogen dioxide results

The Limb Infrared Monitor of the Stratosphere (LIMS) is a 6 channel scanning radiometer which measures the infrared emission by the earth's limb. These measurements are inverted to yield distributions of temperature, ozone, water vapor, nitric acid and nitrogen dioxide. The instrumentation and its orbital performance are briefly described. Retrievals of temperature and nitrogen dioxide are presented, with a discussion of their precision. Comparisons to in-situ rocket and balloon measurements are used to assess their accuracy. Special mention is made of the temperature data supplied for the FGGE II-b data sets. Results for ozone, water vapor and nitric acid are presented in companion papers.     

The global distribution and variability of stratospheric constituents measured by LIMS

The purpose of the Nimbus 7 LIMS experiment was to sound the composition and structure of the upper atmosphere and provide data for study of photochemistry, radiation, and dynamics processes. Vertical profiles were measured of temperature and ozone (O₃) over the 10-km to 65-km range and water vapor (H₂O), nitrogen dioxide (NO₂), and nitric acid (HNO₃) over the 10-km to ～50-km range. Latitude coverage extended from 64°S to 84°N. Several general features of the atmosphere have emerged from data analyses thus far. Nitrogen dioxide exhibits rapid latitudinal variations in winter and shows hemispheric asymmetry with generally higher vertical column amount in the summer hemisphere. HNO₃ data show that this gas is highly variable with altitude, latitude, and season. Smallest mixing ratios occur in the tropics, and the largest values occur in the high latitude winter hemisphere. The results show that O₃, NO₂, and HNO₃ are strongly affected during a stratospheric warming. There is a persistently low water vapor mixing ratio in the tropical lower stratosphere (～2–3 ppmv), a poleward gradient at all times in the mission, and evidence of increasing mixing ratio with altitude at tropical and middle latitudes.     

Ozone variations observed during the International Ozone Rocket Sonde Intercomparison

The International Ozone Rocket Sonde Intercomparison (IORI) conducted at Wallops Island during October 1979 provided a unique opportunity to observe ozone variations in great detail from several observing systems. The measurement period lasted 15 days during which time ozone observations were taken by ground-based, balloon, rocket, and satellite instruments. These data provided a unique opportunity for diagnosing regional stratospheric variability over a 2 week period. Examination of NMC analyses indicated that during this period the stratospheric polar vortex moved southeastward bringing air from high latitudes to Wallops Island above 10 mb. A concurrent change was observed in the upper stratosphere ozone fields observed by Nimbus-7 SBUV and in the ozone vertical distribution measured by the rocket soundings. In this study the satellite and rocket measurements are compared. The agreement is good, certainly within the errors of the measurements.     

Analytical pyrolysis experiments of Titan aerosol analogues in preparation for the Cassini Huygens mission.

Comparative pyrolysis mass spectrometric data of Titan aerosol analogues, called "tholins", are presented. The Titan tholins were produced in the laboratory at Cornell by irradiation of simulated Titan atmospheres with high energy electrons in plasma discharge. Mass-spectrometry measurements were performed at FOM of the solid phase of various tholins by Curie-point pyrolysis Gas-Chromatography/Mass-Spectrometry (GCMS) and by temperature resolved in source Pyrolysis Mass-Spectrometry to reveal the composition and evolution temperature of the dissociation products. The results presented here are used to further define the ACP (Aerosol Collector Pyrolyser)-GCMS experiment and provide a basis for modelling of aerosol composition on Titan and for the interpretation of Titan atmosphere data from the Huygens probe in the future.     

Aerosols within the world climate research programme

Based on the findings of the meeting of JSC experts on “Aerosol and Climate” (Geneva, 27–31 October 1980) the general research strategy consisting of three phases will be presented. The three phases are: Phase I: Sensitivity tests with available models Phase II: Improvement of climate models and data bases Phase III: Development of advanced climate models with internal aerosol generation and regulation processes. COSPAR's role within this research strategy is outlined.     

Influence of solar 11-year variability on chemical composition of the stratosphere and mesosphere simulated with a chemistry-climate model

An understanding of observed global chemistry and climate changes caused by solar activity changes is a high priority in modern geosciences. Here, we discuss the influence of the ultraviolet spectral irradiance variability during solar cycle on chemical composition of the stratosphere and mesosphere with chemistry-climate model that fully describes the interactions between chemical and thermo-dynamical processes. We have performed several 20-year long steady-state runs and found a significant influence of solar irradiation on the chemical composition in the stratosphere and mesosphere. An enhanced photolysis during solar maximum results in destruction of methane, nitrous oxide and CFCs providing an increase in the chemical activity of the atmosphere with more pronounced effects in the mesosphere. In the mesosphere, an increase of HO_x caused by more intensive water vapor photolysis results in significant ozone depletion there. More intensive methane oxidation gives statistically significant rise to the stratospheric humidity. The influence of dynamical perturbations has been identified over high latitude areas. The response of OH is found to be in a good agreement with observation data. The response of the other species is hard to validate, because of the lack of theoretical and observational studies.     

Climatic influence of background and volcanic stratosphere aerosol models

A simple modelization of the earth atmosphere system including tropospheric and stratospheric aerosols has been derived and tested. Analytical expressions are obtained for the albedo variation due to a thin stratospheric aerosol layer. Also outlined are the physical procedures and the respective influence of the main parameters: aerosol optical thickness, single scattering albedo and asymmetry factor, and sublayer albedo. The method is applied to compute the variation of the zonal and planetary albedos due to a stratospheric layer of background H₂SO₄ particles and of volcanic ash.     

On the quasi-biennial oscillation in equatorial stratospheric temperatures and total ozone

The results of a cross-spectral analysis between monthly mean temperatures at 100 mb, 50 mb and 30 mb over the equator and the corresponding monthly mean BUV total ozone at different latitude zones are presented for the period 1970–1977. Significant squared coherences between total ozone and 50 mb equatorial temperatures at 26 months are only found between 5 degrees on each side of the equator, between 45 deg N and 55 deg N and at 45 deg S. At latitudes were the QBO in stratospheric temperature diminishes so does the QBO in total ozone (i.e. close to 35 deg N and 15 deg S). Over subtropical latitudes there is a tendency towards a more biennial oscillation in total ozone (not correlated with the equatorial QBO in stratospheric temperatures) and at 65 deg N and 65 deg S total ozone oscillates at periods greater than the equatorial QBO.     

中国不同地区剩余臭氧及臭氧探空订正因子

根据中国不同地点臭氧探空数据，研究气球炸点臭氧浓度定值（CMR）法、卫星（SBUV和MLS）纬向平均法确定的剩余臭氧Ω_res及其对订正因子C_ref的影响，同时检验臭氧垂直分布对C_ref的贡献.结果显示: CMR法对气球炸点高度依赖性明显，且易高估Ω_res使C_ref整体低于100%；卫星纬向平均Ω_res对气球炸点高度不敏感，但在中国东部的臭氧总量高值区或青藏高原及低纬度臭氧低值地区，Ω_res呈现近10DU以上低值，这是经向臭氧总量及其垂直分布差异在卫星遥感数据上的反映.地面到100hPa的对流层臭氧（Ω_tro），100~10hPa的平流层臭氧（Ω_str）以及10hPa以上的Ω_res对C_ref贡献平均分别为（16±3.4）%，（65±2.3）%，（19±3.3）%.表明基于C_ref评估或订正探空仪平流层臭氧测值时，需考虑对流层臭氧及确定Ω_res方法的影响.卫星纬向平均法，特别是近似实测的SBUV臭氧廓线的值适用于确定Ω_res.