Abstract. Volcanic sulfate aerosols in the stratosphere produce significant long-term solar and infrared radiative perturbations in the Earth's atmosphere and at the surface, which cause a response of the climate system. Here we study the fundamental process of the development of this volcanic radiative forcing, focusing on the eruption of Mount Pinatubo in the Philippines on June 15, 1991. We develop a spectral-, space-, and time-dependent set of aerosol parameters for 2 years after the Pinatubo eruption using a combination of SAGE II aerosol extinctions and UARS-retrieved effective radii, supported by SAM II, AVHRR, lidar and balloon observations. Using these data, we calculate the aerosol radiative forcing with the ECHAM4 general circulation model (GCM) for cases with climatological and observed sea surface temperature (SST), as well as with and without climate response. We find that the aerosol radiative forcing is not sensitive to the climate variations caused by SST or the atmospheric response to the aerosols, except in regions with varying dense cloudiness. The solar forcing in the near infrared contributes substantially to the total stratospheric heating. A complete formulation of radiative forcing should include not only changes of net fluxes at the tropopause but also the vertical distribution of atmospheric heating rates and the change of downward thermal and net solar radiative fluxes at the surface. These forcing and aerosol data are available for GCM experiments with any spatial and spectral resolution.

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[1] This study examines various climatological features related to multiple tropopause events (MT events). The analysis is based on the lapse rate definition of the tropopause and is performed on a radiosonde data subset taken from the Integrated Global Radiosonde Archive database. The global statistics of MT events are analyzed, taking into consideration both their seasonal and geographical variations. Our results are in moderate qualitative agreement with those of earlier studies. They reinforce the analytical findings of other researchers, but at the same time highlight important differences in both the number and position of the maximum occurrence of MT events. We found a latitudinal band of multiple tropopause occurrence in the Northern Hemisphere and three centers in the Southern Hemisphere, which coincided with identified zones of maximum cyclogenesis. The climatological features of pressure, temperature, and vertical separation of MT events revealed the complexity of these phenomena, which behave very differently according to latitude and season.

[1] After the Mount Pinatubo volcanic eruption on 15 June 1991 the Stratospheric Aerosol and Gas Experiment (SAGE) II instrument made extensive aerosol extinction retrievals using the limb-viewing technique. In regions of high-aerosol loading, SAGE II was not able to make measurements, resulting in large information gaps both in latitudinal and in longitudinal coverage as well as in the vertical. Here we examine the possibility of filling the vertical gaps using lidar data. We compare every coincident backscattering measurement (at a wavelength of 0.694 mm) from two lidars, at Mauna Loa, Hawaii (19.5°N, 155.6°W), and at Hampton Virginia (37.1°N, 76.3°W), for the 2-year period after the Pinatubo eruption with the SAGE II version 6.0 extinctions at 0.525 and 1.02 mm wavelengths. This is the most comprehensive comparison ever of lidar data with satellite data for the Pinatubo period. We convert backscattering to extinction at the above wavelengths. At altitudes and times with coincident coverage, the SAGE II extinction measurements agree well with the lidar data but less so during the first six months after the eruption, due to the heterogeneity of the aerosol cloud. This shows that lidar data can be combined with satellite data to give an improved stratospheric aerosol data set.

We present statistics for the occurrence of multiple tropopauses for the entire globe, derived from the meteorological sounding data contained in the Integrated Global Radiosonde Archive (IGRA). The IGRA is the most comprehensive and largest radiosonde data set compiled to date, with more than 1500 stations and data starting from 1938. Statistics were derived from (a) the IGRA tropopause reports (reported tropopauses) and (b) tropopauses calculated from the sounding profiles reported in the IGRA (calculated tropopauses). This work constitutes a necessary precursor to conducting better research on the phenomena of multiple tropopauses and promotes understanding of the global structure of these events. Among other things, we calculated global counts and the latitudinal distribution of percentages of tropopauses with respect to the number of soundings, percentages of second and third tropopauses with respect to the first tropopause, and mean values of pressure and temperature of multiple tropopauses.

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[1] As a critical quality control step toward producing a stratospheric data assimilation system for volcanic aerosols, we conducted a comparison between Stratosphere Aerosol and Gas Experiment (SAGE) II aerosol extinction profiles and aerosol backscatter measured by five lidars, both in the tropics and midlatitudes, for the two-year period following the 1991 Mt. Pinatubo eruption. The period we studied is the most challenging for the SAGE II retrieval because the aerosol cloud caused so much extinction of the solar signal that in the tropics few retrievals were possible in the core of the cloud. We compared extinction at two wavelengths at the same time that we tested two sets of conversions coefficients. We used both Thomason and Jäger's extinction-to-backscatter conversion coefficients for converting lidar backscatter profiles at 0.532 mm or 0.694 mm wavelengths to the SAGE II extinction wavelengths of 0.525 mm and 1.020 mm or the nearby ones of 0.532 mm and 1.064 mm respectively. The lidars were located at Mauna Loa, Hawaii (19.5°N, 155.6°W), Camagüey, Cuba (21.4°N, 77.9°W), Hefei, China (31.9°N, 117.2°W), Hampton Virginia (37.1°N, 76.3°W), and Haute Provence, France (43.9°N, 5.7°W). For the six months following the eruption the aerosol cloud was much more heterogeneous than later. Using two alternative approaches, we evaluated the aerosol extinction variability of the tropical core of the Pinatubo stratospheric aerosol cloud at the timescale of 1-2 days, and found it was quite large. Aerosol variability played the major role in producing the observed differences between SAGE II and the lidars. There was in general a good agreement between SAGE II extinction measurements and lidar derived extinction, and we conclude that all five lidar sets we compared can be used in a future data assimilation of stratospheric aerosols. This is the most comprehensive comparison yet of lidar data with satellite data for the Pinatubo period.

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