Abstract. In August 1998, severe forest fires occurred in many parts of Canada, especially in the Northwest Territories. In the week from August 5 to 11, more than 1000 different fires burned > 1 x 106 ha of boreal forest, the highest 1-week sum ever reported throughout the 1990s. In this study we can unambigously show for the

Lidar measurements at Garmisch-Partenkirchen (Germany) have almost continually delivered backscatter coefficients of stratospheric aerosol since 1976. The time series is dominated by signals from the particles injected into or formed in the stratosphere due to major volcanic eruptions, in particular those of El Chichon (Mexico, 1982) and Mt Pinatubo (Philippines, 1991). Here, we focus more on the long-lasting background period since the late 1990s and 2006, in view of processes maintaining a residual lower-stratospheric aerosol layer in absence of major eruptions, as well as the period of moderate volcanic impact afterwards. During the long background period the stratospheric backscatter coefficients reached a level even below that observed in the late 1970s. This suggests that the predicted potential influence of the strongly growing air traffic on the stratospheric aerosol loading is very low. Some correlation may be found with single strong forest-fire events, but the average influence of biomass burning seems to be quite limited. No positive trend in background aerosol can be resolved over a period as long as that observed by lidar at Mauna Loa. We conclude that the increase of our integrated backscatter coefficients starting in 2008 is mostly due to volcanic eruptions with explosivity index 4, penetrating strongly into the stratosphere. Most of them occurred in the mid-latitudes. A key observation for judging the role of eruptions just reaching the tropopause region was that of the plume from the Icelandic volcano Eyjafjallajökull above Garmisch-Partenkirchen (April 2010) due to the proximity of that source. The top altitude of the ash above the volcano was reported just as 9.3 km, but the lidar measurements revealed enhanced stratospheric aerosol up to 14.3 km. Our analysis suggests for two or three of the four measurement days the presence of a stratospheric contribution from Iceland related to quasi-horizontal transport, differing from the strong descent of the layers entering Central Europe at low altitudes. The backscatter coefficients within the first 2 km above the tropopause exceed the stratospheric background by a factor of four to five. In addition, Asian and Saharan dust layers were identified in the free troposphere, Asian dust most likely even in the stratosphere

[1] The six longest records of stratospheric aerosol (in situ measurements at Laramie, Wyoming, lidar records at: Garmisch-Partenkirchen, Germany; Hampton, Virginia; Mauna Loa, Hawaii; São José dos Campos, Brazil, and SAGE II measurements) were investigated for trend by (1) comparing measurements in the 3 volcanically quiescent periods since 1970 using standard analysis of variance techniques, and (2) analyzing residuals from a time/volcano dependent empirical model applied to entire data sets. A standard squared-error residual minimization technique was used to estimate optimum parameters for each measurement set, allowing for first order autocorrelation, which increases standard errors of trends but does not change magnitude. Analysis of variance over the 3 volcanically quiescent periods is controlled by the end points (pre-El Chichón and post-Pinatubo), and indicates either no change (Garmisch, Hampton, São José dos Campos, Laramie-0.15 mm) or a slight, statistically insignificant, decrease (Mauna Loa, Laramie-0.25 mm), À1 ± 0.5% yr À1 . The empirical model was applied to the same records plus 1020 nm SAGE II data separated into 33 latitude/altitude bins. No trend in stratospheric aerosol was apparent for 31 of 33 SAGE II data sets, 3 of 4 lidar records, and in situ measurements at 0.15 mm. For Hampton and Laramie-0.25 mm, the results suggest a weak negative trend, À2 ± 0.5% yr À1, while 2 SAGE II data sets (30-35 km, 30°and 40°N) suggest a positive trend of similar magnitude. Overall we conclude that no long-term change in background stratospheric aerosol has occurred over the period 1970-2004.

Size distributions of the stratospheric sulfuric acid aerosol derived from balloonborne particle counter measurements from Laramie, Wyoming, are used to calculate ratios of particle extinction, mass, and surface area to particle backscatter, and the wavelength dependences of particle backscatter and extinction. These ratios may then be used to infer particle extinction, mass, and area from midlatitude lidar data in the spectral range 355 nm to 1064 nm for the time period 1991 to 1999. The conversions are defined in four height intervals from the tropopause to 30 km with a time resolution of four months. Results of conversions from earlier studies are included to span the time period 1979 to 1999. The eruptions of El Chichón (1982) and Pinatubo (1991) strongly influence these conversions. Extended background levels are observed prior to El Chichón and since about 1997.

The spatial growth of individual contrails of commercial aircrafts in the time range from 1 min to 60 min behind the aircraft is investigated by means of a ground‐based scanning backscatter lidar. The growth in width varies between 18 m/min and 140 m/min, and the growth of the cross‐section between 3500 m²/min and 25000 m²/min. These values cover the findings of model calculations and former investigations. The vertical growth is often limited by boundaries of the humid layer at flight level, but values up to 18 m/min were observed. In a single case a vertical growth of 4.5 m/s during the early vortex regime was derived from video images.