We assemble data on the Pinatubo aerosol from space, air, and ground measurements, develop a composite picture, and assess the consistency and uncertainties of measurement and retrieval techniques. Satellite infrared spectroscopy, particle morphology, and evaporation temperature measurements agree with theoretical calculations in showing a dominant composition of H2SO4‐H2O mixture, with H2SO4 weight fraction of 65–80% for most stratospheric temperatures and humidities. Important exceptions are (1) volcanic ash, present at all heights initially and just above the tropopause until at least March 1992, and (2) much smaller H2SO4 fractions at the low temperatures of high‐latitude winters and the tropical tropopause. Laboratory spectroscopy and calculations yield wavelength‐ and temperature‐dependent refractive indices for the H2SO4‐H2O droplets. These permit derivation of particle size information from measured optical depth spectra, for comparison to impactor and optical‐counter measurements. All three techniques paint a generally consistent picture of the evolution of Reff, the effective radius. In the first month after the eruption, although particle numbers increased greatly, Reff outside the tropical core was similar to preeruption values of ∼0.1 to 0.2 μm, because numbers of both small (r < 0.2 μm) and large (r > 0.6 μm) particles increased. In the next 3–6 months, extracore Reff increased to ∼0.5 μm, reflecting particle growth through condensation and coagulation. Most data show that Reff continued to increase for ∼1 year after the eruption. Reff values up to 0.6–0.8 μm or more are consistent with 0.38–1 μm optical depth spectra in middle to late 1992 and even later. However, in this period, values from in situ measurements are somewhat less. The difference might reflect in situ undersampling of the very few largest particles, insensitivity of optical depth spectra to the smallest particles, or the inability of flat spectra to place an upper limit on particle size. Optical depth spectra extending to wavelengths λ > 1 μm are required to better constrain Reff, especially for Reff > 0.4 μm. Extinction spectra computed from in situ size distributions are consistent with optical depth measurements; both show initial spectra with λmax ≤ 0.42 μm, thereafter increasing to 0.78 ≤ λmax ≤ 1 μm. Not until 1993 do spectra begin to show a clear return to the preemption signature of λmax ≤ 0.42 μm. The twin signatures of large Reff (>0.3 μm) and relatively flat extinction spectra (0.4–1 μm) are among the longest‐lived indicators of Pinatubo volcanic influence. They persist for years after the peaks in number, mass, surface area, and optical depth at all wavelengths ≤1 μm. This coupled evolution in particle size distribution and optical depth spectra helps explain the relationship between global maps of 0.5‐ and 1.0‐μm optical depth derived from the Advanced Very High Resolution Radiometer (AVHRR) and Stratospheric Aerosol and Gas Experiment (SAGE) satellite sensors. However, there are important differences between the AVHRR ...

[1] This paper presents a climatology of the stratospheric aerosol produced with our lookup table (LUT) technique using data from the Stratospheric Aerosol and Gas Experiment (SAGE II) and the Cryogenic Limb Array Etalon Spectrometer (CLAES) instruments. The LUT climatology spans the period from December 1984 to August 1999. It includes values and uncertainties of measured extinction and optical depth at four SAGE II wavelengths (0.385-1.02 mm) and supplements these with results from the CLAES 12.82 mm wavelength during the key period January 1992 through May 1993, when the large particle sizes from the Pinatubo volcanic injection made many SAGE II extinction and optical depth spectra wavelength independent. Also included are retrieved values of effective radius R eff , distribution width s g , surface area S, and volume V. Aerosol retrievals show notable increases in all these parameters after major volcanic eruptions, with increases in R eff lagging increases in the others. Postvolcanic increases in s g , indicative of broader size distributions, are consistent with sudden increases in numbers of both small and large particles that exceed increases in intermediate-size particles. After Pinatubo, retrieved R eff and s g took nearly 5 years to return to pre-eruption values, while slightly shorter recovery times were obtained for S and V. During low-aerosol-loading periods, size distributions narrow in going from the tropical core to higher latitudes at altitudes between 20 and 22 km. Seasonal variations in S and V are observed at high latitudes for several altitude bands, but are less obvious in R eff . With some exceptions, LUT retrievals agree well with most previous climatologies. For example, agreement is good between LUT retrieved surface area and results from balloon-borne measurements, where available. However, there are a few noteworthy discrepancies. For example, values of surface area from principal component analysis of SAGE II data are less than LUT retrievals during near-background periods (e.g., 1989 to mid-1991, and after 1996) and greater than LUT retrievals in the peak of the Pinatubo plume. The smaller LUT-derived surface areas during the Pinatubo peak result from the constraint provided by the CLAES 12.82 mm extinction measurements.

This paper describes the life cycle of the background (nonvolcanic) stratospheric sulfate aerosol. The authors assume the particles are formed by homogeneous nucleation near the tropical tropopause and are carried aloft into the stratosphere. The particles remain in the Tropics for most of their life, and during this period of time a size distribution is developed by a combination of coagulation, growth by heteromolecular condensation, and mixing with air parcels containing preexisting sulfate particles. The aerosol eventually migrates to higher latitudes and descends across isentropic surfaces to the lower stratosphere. The aerosol is removed from the stratosphere primarily at mid-and high latitudes through various processes, mainly by isentropic transport across the tropopause from the stratosphere into the troposphere.

[1] This paper presents the methods used to produce a global climatology of the stratospheric aerosol using data from two satellite instruments: the Stratospheric Aerosol and Gas Experiment (SAGE II) and the Cryogenic Limb Array Etalon Spectrometer (CLAES). The climatology, which spans from December 1984 to August 1999, includes values and uncertainties of measured extinction and optical depth and of retrieved particle effective radius R eff , distribution width s g , surface area S, and volume V. As a basis for aerosol retrievals, a multiwavelength look-up table (LUT) algorithm was developed that matches the satellite-measured extinction ratios to precomputed ratios that are based on a range of unimodal lognormal size distributions. For cases in which the LUT does not find an acceptable match between measured and precomputed extinction spectra, a different technique called the parameter search technique is utilized. The combination of these two techniques and data from both satellites allows us to retrieve values of R eff , s g , S, and V over a wider range of conditions and from a wider range of wavelengths than used by other methods. This greater wavelength range helps constrain retrieved results, especially in postvolcanic conditions when particle sizes are greatly increased and SAGE II extinction spectra become essentially independent of wavelength. Our method includes an altitude-and time-dependent procedure that uses bimodal size distributions from in situ measurements to estimate bias and uncertainty introduced by assuming a unimodal functional form. Correcting for this bias reduces uncertainty in retrievals of R eff , S, and V by about 7%, 5%, and 1% (averaged over all altitude bands), leaving remaining uncertainties from the unimodal assumption of about ±18%, ±20%, and ±21%, respectively. Additional uncertainties, resulting from measurement error and spatiotemporal variability, are evaluated by propagating input uncertainties through the retrieval algorithm. In an accompanying paper we report on a climatology of R eff , S, and V and consider uncertainties in our retrieved values of these parameters. In this paper we examine the sensitivity of our retrievals to refractive index and measurement wavelength. We find, for example, that changing refractive index from a value for the stratospheric temperature of 215 K to that for 300 K can increase retrieved R eff by $7.5%, owing largely to effects at the CLAES 12.82 mm wavelength. When only SAGE II wavelengths are used, corresponding changes in R eff are much smaller.

We have designed and built a miniature near-IR tunable diode laser (TDL) spectrometer for measuring in situ the water vapor mixing ratio either in the Martian atmosphere or thermally evolved from Martian soil or ice samples. The laser hygrometer uses a thermoelectrically cooled single-mode distributed-feedback TDL at 1.87 microm to scan over a selected vibration-rotation line of both H2O and CO2 near 5327.3 cm(-1). A working prototype that weighs only 230 g has been built and used to generate spectra whose analysis demonstrates precision sensitivities as fine as 1 part in 10(6) by volume in 1 s or 0.1 part in 10(6) in 10 s at Martian pressures and temperatures. Absolute uncertainties of approximately 5% are calculated.